Title of Invention	AN IMPROVED INTERNAL COMBUSTION ENGINE
Abstract	1. An improved internal combustion engine comprising a piston (14) that is slidably fitted in a cylinder (13) is connected to a crankshaft (20), characterized in that it has a first connecting rod (22) rotatably supported at one end by a piston pin (21) and provided with an intermediate pin (23) at the other end, a second connecting rod (24) rotatably supported at one end by the intermediate pin (23) and rotatably supported at the other end by a crankpin (25), and a link arm (26) rotatably supported at one end by the intermediate pin (23) and rotatably supported at the other end by a fixed portion (27), in that the first connecting rod (22) is disposed substantially along the axis (L2) of the cylinder (13), the second connecting rod (24) is disposed substantially orthogonal to the axis (L2) of the cylinder (13), and the fixed portion (27) rotatably supporting the other end of the link arm (26) is positioned downwardly of the crankshaft (20) when the piston (14) is positioned at the top dead center; the time of upward movement of said piston (14) is shorter than the time of downward movement thereof.

Title of Invention

AN IMPROVED INTERNAL COMBUSTION ENGINE

Abstract

1. An improved internal combustion engine comprising a piston (14) that is slidably fitted in a cylinder (13) is connected to a crankshaft (20), characterized in that it has a first connecting rod (22) rotatably supported at one end by a piston pin (21) and provided with an intermediate pin (23) at the other end, a second connecting rod (24) rotatably supported at one end by the intermediate pin (23) and rotatably supported at the other end by a crankpin (25), and a link arm (26) rotatably supported at one end by the intermediate pin (23) and rotatably supported at the other end by a fixed portion (27), in that the first connecting rod (22) is disposed substantially along the axis (L2) of the cylinder (13), the second connecting rod (24) is disposed substantially orthogonal to the axis (L2) of the cylinder (13), and the fixed portion (27) rotatably supporting the other end of the link arm (26) is positioned downwardly of the crankshaft (20) when the piston (14) is positioned at the top dead center; the time of upward movement of said piston (14) is shorter than the time of downward movement thereof.

Full Text	FORM 2 THE PATENTS ACT 1970 [39 OF 1970] THE PATENTS RULES, 2003 COMPLETE SPECIFICATION [See Section 10; rule 13] "AN IMPROVED INTERNAL COMBUSTION ENGINE" HONDA GIKEN KOGYO KABUSHIKI KAISHA, a corporation of Japan, having a place of business at 1-1 Minamiaoyama 2-chome, Minato-ku, Tokyo, JAPAN The following specification particularly describes the invention and the manner in which it is to be performed: The present invention is relates to an improved internal combustion engine. ITechnical Field of the Invention] The present invention relates to an internal combustion engine in which a piston that is slidably fitted in a cylinder is connected to a crankshaft via connecting means. [0002] [Description of the Related Art] An internal conLbustion engine in which an axis of a crankshaft is disposed on the axis of a cylinder, and a connecting rod for connecting a piston and the crankshaft is divided into a first connecting rod on the piston side rind a second connecting rod on the crankshaft side and rotatably supported by an intermediate pin, and the intermediate pin and the fixed portion are connected by a link arm is known from JP-A'-2000-55164 and JP-A-7-11971. [0003] The one disclosed in the aforementioned JP-A-2000-55164 is constructed in such a manner that the first connecting rod on the piston side positions on the axis' of the cylinder'when the piston is at the intermediate section between the top dead center and the bottom dead center, so that the side pressure 02- 6- 7;17:08 ;HONOA RS.D, AS A KA, P AT E N T Dept. R EM R F Y&S AG A R C i':/K) ;0484622945 # 7/ 49 between the piston and the cylinder is reduced and thus abrasion therebetween is reduced. The one disclosed in the aforementioned JP-A-7-11971 assumes a diesel internal combustion engines, in which the piston is positioned at the top dead center twice for a short time period in association with the rotation of the crankshaft, and pilot fuel injection is perfoinaied when it is at the top dead center for the first time, and main fuel injection is performed when it is at the top dead center for the second time. ^0005] - [Problems to be Solved by the Invention] In order to increase the degree of constant volume when burning the air-fuel mixture of the internal combustion engine to improve heat efficiency and to realize improvement of air intake efficiency and reduction of pumping loss, it is desired that the piston moves downward from the top dead center slowly in its expansion stroke. On the other hand, in order to promote mixing of the air-fuel mixture in the combustion chamber to shorten the burning time, and to reduce heat loss during compression, it is desired that the piston moves upward quickly in its compression stroke. However, since the axis of the crankshaft is disposed on the axis of the cylinder in the related art, both of the change of the crank angle between the expansion stroke and the intake stroke and the change of the crank angle between the compression stroke and the exhaust stoke are 180°, and thus it is difficult to satisfy the aforementioned two requirements. In addition, since the first and the second connecting rod for connecting the piston and the crankshaft are disposed on the axis of the cylinder almost in series in the related art, there arise a problem in that the dimension of the internal combustion engine in the direction of the axis of the cylinder may be increased. With such circumstances in view, it is an object of the present invention to increase the degree of constant volume of the air-fuel mixture of the internal combustion engine while it is burning to improve heat efficiency, and to decrease the dimension thereof in the direction of the axis of the cylinder. [Means for Solving the Problems] In order to achieve the aforementioned object, the invention proposes an improved internal combustion engine comprising a piston that is slidably fitted in a cylinder is connected to a crankshaft, characterized in that it has a first connecting rod rotatably supported at one end by a piston pin and provided with an intermediate pin at the other end, a second connecting rod rotatably supported at one end by the intermediate pin and rotatably supported at the other end by a crankpin, and a link arm rotatably supported at one end by the intermediate pin and rotatably supported at the other end by a fixed portion, in that the first connecting rod is disposed substantially along the axis of the cylinder, the second connecting rod is disposed substantially orthogonal to the axis of the cylinder, and the fixed portion rotatably supporting the other end of the link arm is positioned downwardly of the crankshaft when the piston is positioned at the top dead center; the time of upward movement of said piston is shorter than the time of downward movement thereof. In this arrangement, since the time of upward movement of the piston is shorter than the time of downward movement thereof owing to the connecting means that connects the piston to the crankshaft^ the amount of movement of the piston with respect to the amount of increase in crank angle (the amount of increase in volume of the combustion chamber) during expansion stroke is reduced, and thus the degree of constant volume of the air-fuel mixture while it is burning increases thereby improving heat efficiency of the internal combustion engine, in addition, since the intake stroke period is longer in comparison with 180 degCA of the normal internal coiubustion engine, the flowing velocity of intake air is lowered, thereby realizing improvement of intake efficiency, reduction of pumping loss, and downsizing in the diameter of the intake valve. In addition, since the compression stroke period is shorter in comparison with 180 degCA of the normal internal combustion engine, mixing of the air-fuel mixture in the combustion chamber may be promoted and thus the burning time is shortened, and heat loss during compression may be reduced. [0011] ^ In addition to the construction as stated in Claim 1, the .invention according to Claim 2 proposes an internal combustion engine characterized in that the connecting means comprises a first connecting rod rotatably supported at one end by a piston pin and provided with an intermediate pin at the other end, a second connecting rod rotatably supported at one end by the inteanaediate pin and rotatably supported at the other end by a crankpin, and a link arm rotatably supported at one end by the intermediate pin and rotatably supported at the other end by a fixed portion, in that the first connecting rod is disposed substantially along the axis of the cylinder, the second connecting rod is disposed substantially orthogonal to the axis of the cylinder, and the fixed portion rotatably supporting the other end of the link arm is positioned downwardly of the crankshaft when the piston is positioned at the top dead center. f^012] In this arrangement, since the second connecting rod is disposed orthogonal to the axis of the cylinder, the dimension of the internal combustion engine in the direction of the axis thereof may be reduced in comparison with those in the related art in which both of the first and the second connecting rod are disposed along the axis of the cylinder. Since the pivotal angle of the first connecting rod in an early phase of the expansion stroke is smaller, and in addition, the velocity of the downward movement of the piston is lower in an early phase of the expansion stroke in comparison with that in the normal internal combustion engine, friction loss between the piston and the cylinder may be reduced. In addition, since the first connecting rod can pivot only to one side with respect to the axis of the cylinder, occurrence of slapping sound of the piston may be reduced. In addition to the construction as otatod injClaliit 2> the invention (accordihg to—Gl-aim -3 proposes an internal combustion engine characterized in that the axis of the crankshaft is positioned upwardly of the straight line passing through the axis of the intermediate pin and being orthogonal to the axis of the cylinder when the piston is at the top dead center. [0014] In this arrangement/ since the axis of the crankshaft is positioned upwardly of the straight line passing through the axis of the intermediate pin and being orthogonal to the axis of the cylinder when the piston is at the top dead center, a tensile load is generated on the second connecting rod in an early phase of the expansion stroke in which the piston moves downward from the top dead center, whereby the second connecting rod is strengthwise advantageous, thereby enabling downsizing in diameter. [0015] The invention as stated m Claim 4 proposes an internal combustion engine wherein the piston slidably fitted in the cylinder is connected to the crankshaft via the connecting means for opening and closing the intake valve and an exhaust valve in response to reciprocation of the piston, characterized in that the connecting means is constructed in such a manner that the time of upward movement of the piston is shorter than the time of downward movement thereof, and the substantial area of the opening of the exhaust valve is made to be larger than the substantial area of the opening of the intake valve. In this arrangement, since the time of upward movement of the piston is shorter than the time of downward movement thereof due to the connecting means that connects the piston to the crankshaft, the amount, of movement of the piston with respect to the amount of increase in crank angle in the expansion stroke (the amount of increase in volume of the combustion chamber) is smaller, and thus the degree of constant volume of the air-fuel mixture at the time of combustion increases, thereby increasing heat efficiency of the internal combustion engine. In addition, since the intake stroke period of the internal combustion engine, which is longer than 180 degCA, flowing velocity of intake air may be lowered to realize improvement of the air intake efficiency, reduction of pumping loss, and downsizing in diameter of the intake valve. Further, since the compression stroke period of the internal combustion engine, which is shorter than 180 degCA, mixing of the air-fuel mixture in the combustion chamber may be promoted and thus the burning time is shortened, and heat loss during compression may be reduced. Still further, since the substantial area of the opening of the exhaust valve is made to be larger than the substantial area of opening of the intake valve, exhaust gas can be discharged from the combustion chamber smoothly to minimize exhaust loss even when the movement of the piston at the time of the initiation of the exhaust stroke is faster than the related art because the time of upward movement of the piston is set to be shorter than the time of downward movement of the piston. The invention i^is setf^rth in Claim 5 proposes an internal combustion engine wherein the piston slidably fitted in the cylinder is connected to the crankshaft via the connecting rod for opening and closing the intake valve and the exhaust valve in response to reciprocation of the piston, characterized in that the cylinder head in which the combustion chamber is partitioned is disposed between the piston and the crankshaft, and the substantial area of the opening of the exhaust valve is made to be larger than the substantial area of the opening of the intake valve. [0018] In this arrangement, since the cylinder head in which the combustion chamber is partitioned is disposed between the 02- piston and the crankshaft in the internal combustion engine, the amount of increase in volume of the combustion chamber with respect to the amount of increase in crank angle based on the top dead center of the piston may be reduced in comparison with the internal combustion engine in the related art in which the combustion chamber is disposed on the side of the piston opposite from the crankshaft, and thus the degree of constant volume of the air-fuel mixture during combustion can be increased, thereby increasing heat efficiency. In addition, since a tensile load is exerted on the connecting rod during expansion stroke, consideration of buckling is not necessaacy in comparison with the internal combustion engine of the related art on which a compression load is exerted, and thus the strength of the connecting rod is reduced for reducing the weight thereof. In addition, though the velocity of movement of the piston in the vicinity of the bottom dead center is faster than that of the internal combustion engine of the related art, since the substantial area of the opening of the exhaust valve is made to be larger than the substantial area of the opening of the intake valve, exhaust gas can be discharged from the combustion chamber smoothly to minimize exhaust loss. [Detailed Description of Preferred Embodiments] Referring now to examples of the present invention illustrated in attached drawings, embodiments of the present invention will be described. [Description of the^Drawings1 [Fig. 1] Fig, 1 is a vertical cross section of an internal combustion engine {in a state in which a piston is at the top dead center). [Fig. 23 Fig. 2 is a vertical cross section of the internal combustion engine (in a state in which the piston is at the bottom dead center). [Fig. 3] Fig. 3 is a cross sectional view taken along the line 3-3 in Fig. 1. [Fig. 4] Fig. 4 is a graph showing the relation of the stroke of the piston with respect to the crank angle of the internal combustion engine. [Fig. 5] Fig. 5 is a drawing of the modification of the first embodiment, corresponding to Fig. 3. [Fig. 6] Fig. 6 is a vertical cross sectional view of the internal combustion engine according to the second embodiment (in a state in which the piston is at the top dead center), [Fig. 7] Pig. 7 is a vertical cross sectional view of the internal combustion engine according to the third embodiment (in a state in which the piston is at the top dead center). [Fig. 8] Fig. 8 is a vertical cross sectional view of the internal combustion engine according to the fourth embodiment (in a state in which the piston is at the top dead center). [Fig. 9] Fig. 9 is a vertical cross sectional view of the internal combustion engine according to the fourth embodiment (in a state in which the piston is at the bottom dead center). [Fig. 10] Fig. 10 is an explanatory drawing illustrating the change of the position of the intermediate pin in the case where the second connecting rod is expanded at the top dead center. [Fig. 11] Fig. 11 is an explanatory drawing illustrating the change of the position of the intermediate pin in the case where the second connecting rod is expanded and the link arm is contracted at the top dead center. [Pig. 12} Fig. 12 is a vertical cross sectional view of the internal combustion engine according to the fifth embodiment (in a state in which the piston is at the top dead center). [Fig. 13] Fig. 13 is a vertical cross sectional view of the internal combustion engine according to the fourth embodiment (in a state in which the piston is at the bottom dead center). [Fig. 141 Fig. 14 is a drawing viewed in the direction of the line 14-14 in Fig. 12. [Fig. 15] Fig. 15 is an explanatory drawing illustrating the operation of the crank angle 0. [Fig. 16] Fig. 16 is a graph showing the relation between the crank anale 0 and the piston displacement x. [0020] Fig. 1 to Fig. 4 show the first embodiment of the present invention. Fig. 1 is a vertical cross section of an internal combustion engine (in a state in which a piston is at the top dead center), Fig. 2 is a vertical cross section of the internal combustion engine (in a state in which the piston is at the bottom dead center), and Fig. 3 is a drawing viewed in the direction 3-3 in Fig. 1, and Fig. 4 is a graph showing a relation of the stroke of the piston with respect to the crank angle-In this specification, the direction toward the top dead center and the direction toward the bottom dead center of the piston 14 of the internal combustion engine E are defined to be upward and downward respectively- [0021] As shown in Fig. 1, a four-cycle internal combustion engine E comprises a cylinder block 11 and a cylinder head 12, and the piston 14 is slidably fitted into a cylinder 13 provided in the cylinder block 11. The cylinder head 12 is provided with a combustion chamber 15 facing toward the upper surface of the piston 14, an intake port 16 continuing into the combustion chamber 15, a exhaust port 17 continuing into the combustion chamber 15, an intake valve 18 opening and closing an intake valve hole, and an exhaust valve 19 for opening and closing an exhaust valve hole. [0022] A crankshaft 20 is disposed in such a manner that the axis 111 lies on one side with respect to the axis L2 of the cylinder 13. One end of the second connecting rod 24 is supported by the other end of the first connecting rod 22, one end of which is rotatably supported by the piston pin 21 and extending downward, via an intermediate pin 23, and the other end of the second connecting rod 24 extending from the intermediate pin 23 toward one side is rotatably supported by a crankpin 25. A link arm 26 rotatably supported at one end by the intermediate pin 23 is rotatably supported at the other end by a fixed portion 27 positioned downwardly of the crankshaft 20 via a pivot pin 28. [0023] When the piston 14 is positioned at the top dead center, the axis L3 of the first connecting rod 22 {that is, a line segment connecting the axis L4 of the piston pin 21 and the axis L5 of the intermediate pin 23) coincides with the axis L2 of the cylinder 13, and the axis L6 of the second connecting rod 24 (that is, a line segment connecting the axis L5 of the intermediate pin 23 and the axis L7 of the crankpin 25) is almost orthogonal to the axis L3 of the first connecting rod 22. The axis L8 of the link arm 26 (that is, a line segment connecting the axis L5 of the intermediate pin 23 and the axis L9 of the pivot pin 28) inclines with respect to the axis L3 of the first connecting rod 22 so that the right side is lower as seen in the figure. [0024] The aforementioned first connecting rod 22, the second connecting rod 24, and the link arm 26 constitute connecting means 29 of the present invention. [0025] The rotational direction of the crankshaft 2 0 is set to the direction in which the crankpin 25 moves upward and then downward while the piston 14 moves downward from the top dead center to the bottom dead center. [0026] As is apparent from Fig. 3, the relation between the diameter Dl of the intake valve 18 and the diameter D2 of the exhaust valve 19 is the reverse of the internal combustion engine in the related art. Therefore, the substantial area of the opening of the exhaust valve 19 is made to be larger than the substantial area of the opening of the intake valve 18 by setting the diameter D2 of the exhaust valve 19 to be larger than the diameter Dl of the intake valve 18, that is, by setting the peripheral length of the exhaust valve 19 to be larger than the peripheral length of the intake valve 18. In this embodiment, the intake valve 18 and the exhaust valve 19 are disposed on a diameter line of the combustion chamber 15, and two ignition plugs 30, 31 are disposed so as to interpose the diameter line. [0027] In order to make the substantial area of the opening of the exhaust valve 19 larger than the substantial area of the opening of the intake valve 18, as shown in the modification in Fig. 5, two exhaust valves 19/ 19 may be disposed for one intake valve 19 for example, so that the sum of the peripheral lengths of two exhaust valves 19 becomes larger than the peripheral length of one intake valve 18. in this modification, the intake valve 18 is disposed on one side of the diameter line of the combustion chamber 15, two exhaust valves 19, 19 are disposed on the other side thereof, and the two ignition plugs 30, 31 are disposed on the diameter line- [0028] Fig. 2 shows a state in which the piston 14 is at the bottom dead center. When the piston 14 moves between the top dead center and the bottom dead center, the axis L5 of the intermediate pin 23 at the lower end of the first connecting rod 22 moves on the arc A having its center at the axis L9 of the pivot pin 28 while being tied down by the link arm 26. During the movement, the axis L5 of the intermediate pin 23 will never move to the right side of the axis L2 of the cylinder 13 in the figure. [0029] The crankshaft 20 rotates by 216° while the piston 14 moves from the top dead center to the bottom dead center, and the crankshaft 20 rotates by 144" while the piston 14 moves from the bottom dead center to the top dead center. In other words, in the internal combustion engine E of the present invention, the time period of the expansion stroke and the intake stroke (crank angle) are longer than the time period of the compression stroke and the exhaust stroke (crank angle). [0030] Fig. 4 shows a relation of the strokes of the piston with respect to the crank angles. The chain line represents a characteristic of the internal combustion engine in the related art in which the axis of the crankshaft is disposed on the axis of the cylinder and the piston pin and the crankpin are connected by a connecting rod. The aforementioned characteristic shown in a chain line is similar to the sine curve, in which the delayed side (the compression stroke and the exhaust stroke) and the advanced side (the expansion stroke and the intake stroke) are symmetrical with respect to the top dead center. In contrast to it, the characteristic of the present «nbodiment shown in a solid line is such that the delayed side and the advanced side are asymmetrical with respect to the top dead center since the time period of the expansion stroke and the intake stroke are longer than the time period of the compression stroke and the exhaust stroke as described above. [0031] According to the aforementioned characteristic^ the internal combustion engine E of this embodiment exercises the following effect in comparison with the internal combustion engine in the related art. [0032] (1) In order to improve heat efficiency of the internal combustion engine E, it is desirable that the degree of constant volume of the air-fuel mixture when being burned. In order to do so, the smaller the amount of increase in volume of the combustion chamber 15 is with respect to the amount of increase in crank angle when the piston 14 moves downward from the top dead center during the Expansion stroke, the more the degree of constant volume increases and thus heat efficiency improves. As is apparent from the portion showing the expansion stroke in the graph in Fig. 4, downward displacement of the piston 14 from the top dead center of the internal combustion engine E of this embodiment shown in a solid line is smaller than downward displacement ot the piston of the internal combustion engine in the related art shown in a chain line, and thus the degree of constant volume in the expansion stroke is increased, thereby improving heat efficiency. [0033] (2) AS is apparent from the portion showing the intake stroke of the graph in Fig. 4, since the intake stroke period of the internal combustion engine E of this embodiment shown in a solid line is 216 degCA, which is longer than 180 degCA of the related art, the flowing velocity of intake air may be lowered to realize improvement of the air intake efficiency, reduction of pumping loss, and downsizing in diameter of the intake valve 18. [0034] (3) As is apparent from the portion showing the compression stroke in the graph in Fig. 4, since the compression stroke period of the internal combustion engine E of this embodiment shown in a solid line is 144 degCA, which is shorter than 180 degCA of the related art, mixing of the air-fuel mixture in the combustion chamber 15 may be promoted and thus the burning time is shortened, and heat loss (cooling loss) during compression may be reduced. [0035] The internal combustion engine E of this embodiment may exercise the following effects owing to the construction of the connecting means 29. [0036] (4) Since the second connecting rod 24 is disposed so as to be orthogonal to the axis L2 of the cylinder 13, the dimension of the internal combustion engine E in the direction of the axis L2 of the cylinder 13 may be reduced in comparison with the case in which both of the first connecting rod 22 and the second connecting rod 24 are disposed along the axis L2 of the cylinder 13. [0037] (5) Since the pivotal angle of the first connecting rod 22 in a state in which the pressure in the combustion chamber 15 is especially high (that is, in an early phase of the expansion stroke) is significantly small in comparison with the normal internal combustion engine provided with a single connecting rod, and the velocity of the downward movement of the piston 14 in an early phase of the expansion stroke in which the pressure in the combustion chamber 15 is high is low, friction loss due to the side pressure of the piston 14 may be reduced. [0038] (6> Since the first connecting rod 22 pivots only to one side with respect to the axis L2 of the cylinder 13, slapping sound generated when the piston 14 hits against the cylinder 13 may be reduced- [0039] In general, in the internal combustion engine of the related art, the substantial area of the opening of the exhaust valve is set to be smaller than the substantial area of the opening of the intake valve. The first reason is that the marginal mach number of choking of exhaust gas is large due to high temperature thereof, and the second reason is that there is enough time for discharging exhaust gas because the movement of the piston is slower on the side of the bottom dead center than on the side of the top dead center. [0040] As is described in conjunction with Fig. 4/ the exhaust stroke period of the internal combustion engine E of the present embodiment is shorter than that of the related art, and thus the movement of the piston 14 in the vicinity of the bottom dead center becomes faster, which may result in increase in exhaust loss if nothing is done. Especially, though it is general that the exhaust valve is opened at the position before reaching the bottom dead center, if the timing for opening the exhaust valve for utilizing the expansion stroke effectively is delayed to the position in the vicinity of the bottom dead center, there is apprehension that smooth discharge of exhaust gas is impaired and thus exhaust loss may further be increased. However, since the substantial area of the opening of the exhaust valve 19 is set to be larger than the substantial area of the opening of the intake valvel 18 in the present embodiment, it is possible to enable smooth discharge of exhaust gas and minimize increase in exhaust loss while utilizing the expansion stroke effectively by setting the timing in opening the exhaust valve as close as possible to the bottom dead center. [0041] In the first embodiment, when the piston 14 is at the top dead center, the second connecting rod 24 extends along the direction orthogonal to the axis L2 of the cylinder 13, while in the second embodiment shown in Fig. 6, the axis L6 of the second connecting rod 24 extends upward slightly obliquely with respect to the direction orthogonal to the axis L2 of the cylinder 13. Further, in the third embodiment shown in Fig. 7, the axis L6 of the second connecting rod 24 extends downward slightly obliquely with respect to the direction orthogonal to the axis L2 of the cylinder 13. [0042] More specifically, in the second embodiment shown in Fig. 6, when the piston 14 is at the top dead center, S is positioned upwardly of Q where Q is the position of the axis L5 of the intermediate pin 23 located on the axis L2 of the cylinder 13, and S is the intersection between the axis L2 of the cylinder 13 and the line perpendicular thereto from the axis LI of the crankshaft 20. In contrast to it, in the second embodiment shown in Fig. 7, S is located downwardly of Q. [0043] Since the embodiment shown in Fig. 6 and Fig- 7 is such that the first connecting rod 22 and the second connecting rod 24 are disposed almost at a right angle when the piston 14 is at the top dead center, all the effects of the first embodiment can be achieved. However, in a narrow sense, because of the positional relation between S and Q, when the piston 14 is moved downward from the top dead center shown in the figure during the expansion stroke, a tensile load is exerted on the second connecting rod 24 in the second embodiment shown in Fig. 6, while a compressive load is exerted to the second connecting rod 24 only momentarily in the third embodiment shown in Fig. 7. Therefore, the second embodiment (See Fig. 6) in which no compressive load is exerted thereon is advantageous in view of strength of the second connecting rod 24, and thus employing the layout of the second embodiment may contribute to downsizing of the second connecting rod 24 in diameter and thus reduction of the weight thereof. [0044] Referring now to Fig. 8 to Fig. 11, the fourth embodiment of the present invention will be described. [0045] The construction in the fourth embodiment is similar to that of the second embodiment described in conjunction with Fig. 6, the axis LI of the crankshaft 20 and the axis L9 of the pivot pin 28 are positioned slightly higher than those in the second embodiment. When the piston 14 is at the top dead center, the second connecting rod 24 is disposed such that the side of the axis LI of the crankshaft 20 is higher than the axis L5 of the intermediate pin 23, and the link arm 26 is disposed such that the side of the axis L9 of the pivot pin 28 is lower than the axis L5 of the intermediate pin 23. [0046] According to the fourth embodiment, the following effects are exercised in addition to the effects of the first embodiment and the second embodiment. [0047] in other words, in an early phase of the expansion stroke wherein the piston 14 is at the top dead center, a load due to the explosion of the air-fuel mixture in the combustion chamber 15 is transmitted to the first connecting rod 22 via the pistonl4, and a downward explosion load F acts on the intermediate pin 23 at the lower end of the first connecting rod 22. The explosion load F is decomposed into a tensile load Fl that pulls the second connecting rod 24 in the lower left direction and a compression load F2 for compressing the link arm 26 in the lower right direction, the second connecting rod 24 is extended by ALl by the tensile load Fl, and the link arm 26 is compressed by AL2 by the compression load F2. Since an angle formed between the second connecting rod 24 and the horizontal line and an angle formed between the link arm 26 and the horizontal line are small, the tensile load Fl of the second connecting rod 24 and the compression load F2 of the link arm 26 with respect to the explosion load F are magnified. [0048] In Fig. 10, assuming that the second connecting rod 24 is expanded by ALl and the length of the link arm 26 is not changed, the position of the intermediate pin 23 at the lower end of the first connecting rod 22 is lowered by AL'. Actually, as shown in Fig, 11, since the second connecting rod 24 is expanded by ALl, and the link arm 26 is compressed by AL2, the position of the intermediate pin 23 at the lower end of the first connecting rod 22 is lowered by AL, which is further larger than the AL'. [0049] In this manner, when the position of the inteannediate pin 23 is lowered by AL in an early phase of the expansion stroke, the position of the piston 14 is also lowered by AL, and the volume of the combustion chamber 15 is increased, thereby decreasing compression ratio correspondingly. Since the magnitude of AL increases with increases in explosion load F, the rate of decrease in compression ratio increases with increases in load of the internal combustion engine E, As a consequent, knocking may be prevented by reducing compression ratio under high load conditions while enabling the operation of high heat efficiency with high compression ratio in a wide range of operation under partial load conditions for reducing the amount of consumption. in addition, such variable compression ration control can be realized only by changing the layout of the first connecting rod 22, the second connecting rod 24, and the link arm 26 without necessity of a special actuator or a controller, which realizes very low costs. [0050] Though the first connecting rod 22 itself is compressed by the explosion load F and thus the length thereof is compressed, thereby lowering the position of the piston 14 correspondingly and reducing the compression ratio thereof, reduction in compression ratio in association with the expansion and compression of the second connecting rod 24 and the link arm 26 is much larger than that. The reason is that the distance of downward travel of the piston 14 in association with contraction of the first connecting rod 22 disposed vertically is exactly the amount of contraction described above, but the distance of downward travel of the piston 14 in association with expansion and contraction of the second connecting rod 24 and the link arm 26 disposed substantially horizontally is the magnified amount of expansion and contraction. [0051] Fig. 12 to Fig. 16 show the fifth embodiment of the present invention, in which Fig. 12 is a vertical cross sectional view of the internal combustion engine (in a state in which the piston is at the top deaci center). Fig. 13 is a vertical cross sectional view of the internal combustion engine {in a state in which the piston is at the bottom dead center). Fig. 14 is a drawing viewed in the direction 14-14 in Fig. 12, Fig. 15 is an explanatory drawing of the action of the internal combustion engine, and Fig. 16 is a graph showing the relation between the crank angle 6 and the piston displacement x. [0052] As shown in Fig. 12 to Fig. 15, the outline of a power unit P for a motorcycle having an internal combustion engine E comprises a mission case 111, a cylinder head 112 tied on the front surface of the mission case 111, a cylinder block 113 tied on the front surface of the cylinder head 112, and a cover 114 tied on the front surface of the cylinder block 113. The piston 116 is slidably fitted in a cylinder 115 supported within the cylinder block 113, and a piston pin 117 is supported at the front end of legs 116a, 116a projecting integrally from the piston 116 toward the front. When the piston 116 is at the top dead center shown in Fig. 12, U-shaped notches 115a, 115a for avoiding interference with the piston pin 117 are formed on the front end of the cylinder 115. [0053] A crankshaft 119 supported on the mating surface between the cylinder head 112 and the mission case 111 is provided with a pair of crank pins 119a, 119a, and a pair of connecting rods 121, 121 supported by these crankpin 119a, 119a at the larger ends thereof via needle bearings 120, 120 are connected to both ends of the piston pin 117 through the openings 112a, 112a of the cylinder head 112 and an opening {not shown) of the cylinder block 113. [0054] A combustion chamber 122 is formed in the cylinder head 112 so as to be faced toward the top surface of the piston 116, and an intake port 123 extending upwardly from the combustion chamber 122 and the exhaust port 124 extending downwardly therefrom are opened and closed respectively by an intake valve 125 and an exhaust valve 126 disposed in the shape of a letter V- As is apparent from Fig. 14, the substantial area of the opening of the exhaust valve 126 is set to be larger than the substantial area of the opening of the intake valve 125. An ignition plug 108 is mounted in the combustion chamber 122 so as not to interfere with the intake valve 125 and the exhaust valve 126. [0055] An air intake rocker shaft 130 and an exhaust rocker shaft 131 are supported in the mission case ill, and an air intake rocker arm 132 pivotally supported by the air intake rocker shaft 130 abuts against an air intake cam 133 fixed on a cam shaft 128 and the stem end of the intake valve 125. An intermediate portion of a L-shaped driven exhaust rocker arm 134 is pivotally supported by an exhaust rocker shaft 131, and one end of the driven exhaust rocker arm 134 abuts against the stem end of the exhaust valve 126 and the other end thereof is connected to one end of a connecting rod 135. A driving exhaust rocker arm 136 being independent from the air intake rocker arm 132 is pivotally supported by the air intake rocker shaft 130, and the driving exhaust rocker arm 136 is abutted by an exhaust cam 137 fixed to a cam shaft 128 and connected to the other end of the connecting rod 135. [0056] Rotation of the camshaft 128 is transmitted to the intake valve 125 via an air intake cam 133 and the air intake rocker arm 132, and opens the intake valve 125 once per two turns of the crankshaft 119. Rotation of the camshaft 128 is transmitted to the exhaust valve 126 via the exhaust cam 137, the driving exhaust rocker arm 136, the connecting rod 135, and the driven exhaust rocker airm 134, and opens the exhaust valve 126 once per two turns of the crankshaft 119. [0057] The operation of the fifth embodiment will now be described. [0058] Fig. 15 is a schematic drawing of the internal combustion engine E of the present embodiment, which comprises the cylinder 115, the piston 116 slidably fitted to the cylinder 115, the cylinder head 112 connected to the cylinder 115, the combustion chamber 122 formed on the upper surface of the cylinder head 112 facing toward the piston 116, the crankshaft 119/ the connecting rods 121, 121 for connecting the piston 116 to the crankshaft 119. The cylinder head 112 is disposed *«if at the position interposed between the piston 116 and the crankshaft 119. [0059] Fig. 15(A) shows a sate in which the piston 116 is at the top dead center, and a crank angle 6 in this moment is 0°. Fig. 15(C) shows a state in which the piston 116 is at the bottom dead center, and a crank angle 0 in this moment is 180°, Pig. 15(B) shows a state in which the piston 116 is at the midpoint between the top dead center and the bottom dead center. The crank angle 6 at this moment is not 90°, but an angle Ob is larger than 90°. The reason is that the connecting rods 121, 121 are positioned on the cylinder axis L at the top dead center and the bottom dead center, while the connecting rods 121, 121 inclines by the angle with respect to the cylinder axis L at the aforementioned mid point. [0060] In Fig- 16, the relation between the crank angle 6 with respect to the top dead center of the internal combustion engine E and the displacement x of the piston 116 with respect to the top dead center is shown by a broken line. The stroke of the piston 116 between the top dead center and the bottom dead center is 60 mm in this case. As is described in Fig, 15(B), when the piston 116 is at the midpoint of the top dead center and the bottom dead center (when the displacement is at the position of -30 mm), the crank angle 8 becomes an angle 9b, which is larger than 90°. In contrast to it, in the cosine curve shown by a solid line, the crank angle 0 is 90° when the piston 116 is at the midpoint between the top dead center and the bottom dead center. [0061] In this manner, it is appreciated that the line (see the broken line) showing the relation of the displacement x of the piston 116 with respect to the crank angle 6 is positioned on the upper side of the cosine curve shown by a solid line in the internal combustion engine E of this embodiment. It means that the amount of increase in displacement x of the piston 116 with respect to the amount of increase in the crank angle 0 is smaller than the characteristic of the cosine curve when the piston moves downward from the top dead center in the expansion stroke. [0062] In order to increase heat efficiency of the internal combustion engine E, it is desirable to increase the degree of constant volume of the air-fuel mixture during combustion. In order to do so, when the piston 116 moves downward from the top dead center during the expansion stroke, the smaller the amount of increase in the volume of the combustion chamber 122 with respect to the amount of increase in crank angle 9 is, the more the degree of constant volume is increased, thereby increasing heat efficiency. As is clear from the portion Showing the expansion stroke, which is the range of 0° to 180" in crank angle 9, in the graph in Fig. 16, the displacement X of the piston 116 from the top dead center of the internal combustion engine E in the present embodiment shown by a broken line is smaller than the displacement x of the piston of the internal combustion engine in the related art shown by a chain line. Therefore, the degree of constant volume of the air-fuel mixture in the expansion stroke is increased, thereby increasing the heat efficiency- 10063] In the internal combustion engine E of the present embodiment, since the line (see the broken line) showing the relation of displacement x of the piston 116 with respect to the crank angle 8 is positioned on the upper side of the cosine curve shown in a solid line, when the piston moves upward from the bottom dead center during the exhaust stroke, the amount of increase in displacement x of the piston 116 with respect to the amount of increase in crank angle 6 is larger than the characteristic of the cosine curve, and thus the exhaust amount of exhaust gas per unit time period is larger than the case of the internal combustion engine in the related art. However, since the substantial area of the opening of the exhaust valve 126 is set to be larger than the substantial area of the opening of the intake valve 125, exhaust loss can be minimized by discharging exhaust gas smoothly from the combustion chamber 122. [0064] In the expansion stroke in which a largest load is exerted to the connecting rods 121, 121, since the piston 116 moves away from the crankshaft 119, a tensile load in the direction opposite from that of the internal combustion engine E of the related art acts on the connecting rods 121, 121. In this manner, exertion of a tensile load on the connecting rods 121, 121 makes them advantageous in strength in comparison with the case where a compression load is exerted thereon, whereby the connecting rods 121, 121 may be made thinner to reduce the weight. [0065] Since the connecting rods 121, 121 are divided into two pieces, and are connected to both ends of the crankshaft 119 in the axial direction through the both sides of the pxston 116, exertion of biased load on the piston 116 may be prevented and thus durability thereof against abrasion may be enhanced. In addition, since the leg portions 116a, 116a are projected from the piston 116 in the direction away from the crankshaft 119 and the piston pin 117 is provided at the extremities of the leg portions 116a, 116a, the entire lengths of the connecting rods 121, 121 become longer than the case of the internal combustion engine E in the related art. As a consequent, the pivotal angle of the connecting rods 121, 121 with respect to the cylinder axis L decreases, and thus side thrust exerted on the piston 116 decreases thereby enhancing durability thereof against abrasion. [0066] Though the embodiments of the present invention have been described in detail, various modifications in design may be made on the present invention without departing from the scope of the invention. [0067] For example, a four-cycle internal combustion engine E is exemplified in the embodiments, while the present invention may also be applied to a two-cycle internal combustion engine. [0068] [Effects of the Invention] As is described thus far, according to the invention as (set forjfch-irf'Claim 17 since the time of downward movement of the piston is shorter than the time of upward movement thereof owing to the connecting means that connects the piston to the crankshaft, the amount of movement of the piston with respect to the amount of increase in crank angle (the amount of increase in volume of the combustion chamber) during expansion stroke is reduced, and thus the degree of constant volume of the air-fuel mixture while it is burning increases thereby improving heat efficiency of the internal combustion engine, In addition, since the intake stroke period is longer in comparison with 180 degCA of the normal internal combustion engine, the flowing velocity of intake air is lowered, thereby realizing improvement of intake efficiency, reduction of pumping loss, and downsizing in the diameter of the intake valve. In addition, since the compression stroke period is shorter in comparison with 180 degCA of the normal internal combustion engine, mixing of the air-fuel mixture in the combustion chamber may be promoted and thus the burning time is shortened, and heat loss during compression may be reduced. [0069] According to the invention a6 set^forth in Claim 2, since the second connecting rod is disposed orthogonal to the axis of the cylinder, the dimension of the internal combustion engine in the direction of the axis thereof may be reduced in comparison with those in the related art in which both of the first and the second connecting rod are disposed along the axis of the cylinder. Since the pivotal angle of the first connecting rod in an early phase of the expansion stroke is smaller, and in addition, the velocity of the downward movement of the piston is lower in an early phase of the expansion stroke in comparison with that in the normal internal combustion engine, friction loss between the piston and the cylinder may be reduced. In addition, since the first connecting rod can pivot only to one side with respect to the axis of the cylinder, occurrence of slapping sound of the piston may be reduced. [0070] According to the invention as iet forth in Claim 3; since the axis of the crankshaft is positioned upwardly of the straight line passing through the axis of the intermediate pin and being orthogonal to the axis of the cylinder when the piston is at the top dead center, a tensile load is generated on the second connecting rod in an early phase of the expansion stroke in which the piston moves downward from the top dead center, whereby the second connecting rod is strengthwise advantageous, thereby enabling downsizing in diameter. [0071] According to the invention ^s set forth in Claim 4, since the time of upward movement of the piston is shorter than the time of downward movement thereof by the connecting means for connecting the piston to the crankshaft, the amount of movement of the piston with respect to the amount of increase in crank angle decreases in the expansion stroke {the amount of increase in volume of the combustion chamber) is smaller, and thus the degree of constant volume of the air-fuel mixture at the time of combustion increases, thereby increasing heat efficiency of the internal combustion engine. In addition, since the intake stroke period of the internal combustion engine, which is longer than 180 degCA, flowing velocity of intake air may be lowered to realize improvement of the air intake efficiency, reduction of pumping loss, and downsizing in diameter of the intake valve. Further, since the compression stroke period of the internal combustion engine, which is shorter than 180 degCA, mixing of the air-fuel mixture in the combustion chamber may be promoted and thus the burning time is shortened, and heat loss during compression may be reduced. Still further, since the substantial area of the opening of the exhaust valve is made to be larger than the substantial area of opening of the intake valve, exhaust gas can be discharged from the combustion chamber smoothly to minimize exhaust loss even when the movement of the piston at the time of the initiation of the exhaust stroke is faster than the related art because the time of upward movement of the piston is set to be shorter than the time of downward movement of the piston. [0072] According to the invention^assgt forth in Claims, since the cylinder head in which the combustion chamber is partitioned is disposed between the piston and the crankshaft in the internal combustion engine, the amount of increase in volume of the combustion chamber with respect to the amount of increase in crank angle based on the top dead center of the piston may be reduced in comparison with the internal combustion engine in the related art in which the combustion chamber is disposed on the side of the piston opposite from the crankshaft, and thus the degree of constant volume of the air-fuel mixture during combustion can be increased, thereby increasing heat efficiency. In addition, since a tensile load is exerted on the connecting rod during expansion stroke, consideration of buckling is not necessary in comparison with the internal combustion engine of the related art on which a compression load is exerted, and thus the strength of the connecting rod is reduced for reducing the weight thereof. In addition,,though the velocity of movement of the piston in the vicinity of the bottom dead center is faster than that of the internal combustion engine of the related art, since the substantial area of the opening of the exhaust valve is made to be larger than the substantial area of the opening of the intake valve, exhaust gas can be discharged from the combustion chamber smoothly to minimize exhaust loss. [Reference Numerals] 13 cylinder 14 piston 18 intake valve 19 exhaust valve 20 crankshaft 21 piston pin 22 first connecting rod 23 intermediate pin 24 second connecting rod 25 crankpin 26 link arm 27 fixed portion 29 connecting means 112 cylinder head 115 cylinder 116 piston 119 crankshaft 121 connecting rod 122 combustion chamber 125 intake valve 126 exhaust valve LI axis of the crankshaft L2 axis of the cylinder- L5 axis of the intermediate pin 40 We Claim: 1. An improved internal combustion engine comprising a piston (14) that is slidably fitted in a cylinder (13) is connected to a crankshaft (20), characterized in that it has a first connecting rod (22) rotatably supported at one end by a piston pin (21) and provided with an intermediate pin (23) at the other end, a second connecting rod (24) rotatably supported at one end by the intermediate pin (23) and rotatably supported at the other end by a crankpin (25), and a link arm (26) rotatably supported at one end by the intermediate pin (23) and rotatably supported at the other end by a fixed portion (27), in that the first connecting rod (22) is disposed substantially along the axis (L2) of the cylinder (13), the second connecting rod (24) is disposed substantially orthogonal to the axis (L2) of the cylinder (13), and the fixed portion (27) rotatably supporting the other end of the link arm (26) is positioned downwardly of the crankshaft (20) when the piston (14) is positioned at the top dead center; the time of upward movement of said piston (14) is shorter than the time of downward movement thereof. 2. An improved internal combustion engine as claimed in Claim 1, wherein the axis (LI) of the crankshaft (20) is positioned upwardly of the straight line passing through the axis (L5) of the intermediate pin (23) and being orthogonal to the axis (L2) of the cylinder (13) when the piston (14) is at the top dead center. 3. An improved internal combustion engine as claimed in claim 1, wherein a piston (14) slidably fitted in the cylinder (13) is connected to a crank shaft (20) via a connecting means (29).

Full Text

FORM 2
THE PATENTS ACT 1970 [39 OF 1970]
THE PATENTS RULES, 2003 COMPLETE SPECIFICATION
[See Section 10; rule 13]
"AN IMPROVED INTERNAL COMBUSTION ENGINE"
HONDA GIKEN KOGYO KABUSHIKI KAISHA, a corporation of Japan, having a place of business at 1-1 Minamiaoyama 2-chome, Minato-ku, Tokyo, JAPAN
The following specification particularly describes the invention and the manner in which it is to be performed:

The present invention is relates to an improved internal combustion engine. ITechnical Field of the Invention]
The present invention relates to an internal combustion
engine in which a piston that is slidably fitted in a cylinder
is connected to a crankshaft via connecting means.
[0002]
[Description of the Related Art]
An internal conLbustion engine in which an axis of a
crankshaft is disposed on the axis of a cylinder, and a
connecting rod for connecting a piston and the crankshaft is
divided into a first connecting rod on the piston side rind a
second connecting rod on the crankshaft side and rotatably
supported by an intermediate pin, and the intermediate pin and
the fixed portion are connected by a link arm is known from
JP-A'-2000-55164 and JP-A-7-11971.
[0003]
The one disclosed in the aforementioned JP-A-2000-55164
is constructed in such a manner that the first connecting rod
on the piston side positions on the axis' of the cylinder'when
the piston is at the intermediate section between the top dead
center and the bottom dead center, so that the side pressure

02- 6- 7;17:08 ;HONOA RS.D, AS A KA, P AT E N T Dept. R EM R F Y&S AG A R C i':/K) ;0484622945 # 7/ 49
between the piston and the cylinder is reduced and thus abrasion therebetween is reduced.

The one disclosed in the aforementioned JP-A-7-11971 assumes a diesel internal combustion engines, in which the piston is positioned at the top dead center twice for a short time period in association with the rotation of the crankshaft, and pilot fuel injection is perfoinaied when it is at the top dead center for the first time, and main fuel injection is performed when it is at the top dead center for the second time.
^0005] -
[Problems to be Solved by the Invention]
In order to increase the degree of constant volume when burning the air-fuel mixture of the internal combustion engine to improve heat efficiency and to realize improvement of air intake efficiency and reduction of pumping loss, it is desired that the piston moves downward from the top dead center slowly in its expansion stroke. On the other hand, in order to promote mixing of the air-fuel mixture in the combustion chamber to shorten the burning time, and to reduce heat loss during compression, it is desired that the piston moves upward quickly in its compression stroke.
However, since the axis of the crankshaft is disposed on the axis of the cylinder in the related art, both of the

change of the crank angle between the expansion stroke and the intake stroke and the change of the crank angle between the compression stroke and the exhaust stoke are 180°, and thus it is difficult to satisfy the aforementioned two requirements.
In addition, since the first and the second connecting rod for connecting the piston and the crankshaft are disposed on the axis of the cylinder almost in series in the related art, there arise a problem in that the dimension of the internal combustion engine in the direction of the axis of the cylinder may be increased.
With such circumstances in view, it is an object of the present invention to increase the degree of constant volume of the air-fuel mixture of the internal combustion engine while it is burning to improve heat efficiency, and to decrease the dimension thereof in the direction of the axis of the cylinder.
[Means for Solving the Problems]
In order to achieve the aforementioned object, the invention proposes an improved internal combustion engine comprising a piston that is slidably fitted in a cylinder is connected to a crankshaft, characterized in that it has a first connecting rod rotatably supported at one end by a piston pin and provided with an intermediate pin at the other end, a second connecting rod rotatably supported at one end by the intermediate pin and rotatably supported at the other end by a crankpin, and a link arm rotatably supported at one end by the intermediate pin and rotatably supported at the other end by a fixed portion, in that the first connecting rod is disposed substantially along the axis of the cylinder, the second connecting rod is disposed substantially orthogonal to the axis of the cylinder, and the fixed portion rotatably supporting the other end of the link arm is positioned downwardly of the crankshaft when the piston is positioned at the top dead center; the time of upward movement of said piston is shorter than the time of downward movement thereof.

In this arrangement, since the time of upward movement
of the piston is shorter than the time of downward movement
thereof owing to the connecting means that connects the piston
to the crankshaft^ the amount of movement of the piston with
respect to the amount of increase in crank angle (the amount
of increase in volume of the combustion chamber) during
expansion stroke is reduced, and thus the degree of constant
volume of the air-fuel mixture while it is burning increases
thereby improving heat efficiency of the internal combustion
engine, in addition, since the intake stroke period is longer
in comparison with 180 degCA of the normal internal coiubustion
engine, the flowing velocity of intake air is lowered, thereby
realizing improvement of intake efficiency, reduction of
pumping loss, and downsizing in the diameter of the intake valve.
In addition, since the compression stroke period is shorter
in comparison with 180 degCA of the normal internal combustion
engine, mixing of the air-fuel mixture in the combustion
chamber may be promoted and thus the burning time is shortened,
and heat loss during compression may be reduced.
[0011] ^
In addition to the construction as stated in Claim 1, the .invention according to Claim 2 proposes an internal combustion engine characterized in that the connecting means

comprises a first connecting rod rotatably supported at one end by a piston pin and provided with an intermediate pin at the other end, a second connecting rod rotatably supported at one end by the inteanaediate pin and rotatably supported at the other end by a crankpin, and a link arm rotatably supported at one end by the intermediate pin and rotatably supported at the other end by a fixed portion, in that the first connecting rod is disposed substantially along the axis of the cylinder, the second connecting rod is disposed substantially orthogonal to the axis of the cylinder, and the fixed portion rotatably supporting the other end of the link arm is positioned downwardly of the crankshaft when the piston is positioned at the top dead center.
f^012]
In this arrangement, since the second connecting rod is disposed orthogonal to the axis of the cylinder, the dimension of the internal combustion engine in the direction of the axis thereof may be reduced in comparison with those in the related art in which both of the first and the second connecting rod are disposed along the axis of the cylinder. Since the pivotal angle of the first connecting rod in an early phase of the expansion stroke is smaller, and in addition, the velocity of the downward movement of the piston is lower in an early phase of the expansion stroke in comparison with that in the normal internal combustion engine, friction loss between the piston

and the cylinder may be reduced. In addition, since the first connecting rod can pivot only to one side with respect to the axis of the cylinder, occurrence of slapping sound of the piston may be reduced.
In addition to the construction as otatod injClaliit 2> the invention (accordihg to—Gl-aim -3 proposes an internal combustion engine characterized in that the axis of the crankshaft is positioned upwardly of the straight line passing through the axis of the intermediate pin and being orthogonal to the axis of the cylinder when the piston is at the top dead center.
[0014]
In this arrangement/ since the axis of the crankshaft is positioned upwardly of the straight line passing through the axis of the intermediate pin and being orthogonal to the axis of the cylinder when the piston is at the top dead center, a tensile load is generated on the second connecting rod in an early phase of the expansion stroke in which the piston moves downward from the top dead center, whereby the second connecting rod is strengthwise advantageous, thereby enabling downsizing in diameter.
[0015]
The invention as stated m Claim 4 proposes an internal combustion engine wherein the piston slidably fitted in the

cylinder is connected to the crankshaft via the connecting means for opening and closing the intake valve and an exhaust valve in response to reciprocation of the piston, characterized in that the connecting means is constructed in such a manner that the time of upward movement of the piston is shorter than the time of downward movement thereof, and the substantial area of the opening of the exhaust valve is made to be larger than the substantial area of the opening of the intake valve.
In this arrangement, since the time of upward movement of the piston is shorter than the time of downward movement thereof due to the connecting means that connects the piston to the crankshaft, the amount, of movement of the piston with respect to the amount of increase in crank angle in the expansion stroke (the amount of increase in volume of the combustion chamber) is smaller, and thus the degree of constant volume of the air-fuel mixture at the time of combustion increases, thereby increasing heat efficiency of the internal combustion engine. In addition, since the intake stroke period of the internal combustion engine, which is longer than 180 degCA, flowing velocity of intake air may be lowered to realize improvement of the air intake efficiency, reduction of pumping loss, and downsizing in diameter of the intake valve. Further, since the compression stroke period of the internal combustion engine, which is shorter than 180 degCA, mixing of

the air-fuel mixture in the combustion chamber may be promoted and thus the burning time is shortened, and heat loss during compression may be reduced. Still further, since the substantial area of the opening of the exhaust valve is made to be larger than the substantial area of opening of the intake valve, exhaust gas can be discharged from the combustion chamber smoothly to minimize exhaust loss even when the movement of the piston at the time of the initiation of the exhaust stroke is faster than the related art because the time of upward movement of the piston is set to be shorter than the time of downward movement of the piston.
The invention i^is setf^rth in Claim 5 proposes an internal combustion engine wherein the piston slidably fitted in the cylinder is connected to the crankshaft via the connecting rod for opening and closing the intake valve and the exhaust valve in response to reciprocation of the piston, characterized in that the cylinder head in which the combustion chamber is partitioned is disposed between the piston and the crankshaft, and the substantial area of the opening of the exhaust valve is made to be larger than the substantial area of the opening of the intake valve.
[0018]
In this arrangement, since the cylinder head in which the combustion chamber is partitioned is disposed between the

02-
piston and the crankshaft in the internal combustion engine, the amount of increase in volume of the combustion chamber with respect to the amount of increase in crank angle based on the top dead center of the piston may be reduced in comparison with the internal combustion engine in the related art in which the combustion chamber is disposed on the side of the piston opposite from the crankshaft, and thus the degree of constant volume of the air-fuel mixture during combustion can be increased, thereby increasing heat efficiency. In addition, since a tensile load is exerted on the connecting rod during expansion stroke, consideration of buckling is not necessaacy in comparison with the internal combustion engine of the related art on which a compression load is exerted, and thus the strength of the connecting rod is reduced for reducing the weight thereof. In addition, though the velocity of movement of the piston in the vicinity of the bottom dead center is faster than that of the internal combustion engine of the related art, since the substantial area of the opening of the exhaust valve is made to be larger than the substantial area of the opening of the intake valve, exhaust gas can be discharged from the combustion chamber smoothly to minimize exhaust loss.
[Detailed Description of Preferred Embodiments] Referring now to examples of the present invention illustrated in attached drawings, embodiments of the present invention will be described.

[Description of the^Drawings1
[Fig. 1]
Fig, 1 is a vertical cross section of an internal combustion engine {in a state in which a piston is at the top dead center).
[Fig. 23 Fig. 2 is a vertical cross section of the internal combustion engine (in a state in which the piston is at the bottom dead center).
[Fig. 3]
Fig. 3 is a cross sectional view taken along the line 3-3 in Fig. 1.

[Fig. 4]
Fig. 4 is a graph showing the relation of the stroke of the piston with respect to the crank angle of the internal combustion engine.
[Fig. 5]
Fig. 5 is a drawing of the modification of the first embodiment, corresponding to Fig. 3.
[Fig. 6]
Fig. 6 is a vertical cross sectional view of the internal combustion engine according to the second embodiment (in a state in which the piston is at the top dead center),
[Fig. 7]
Pig. 7 is a vertical cross sectional view of the internal combustion engine according to the third embodiment (in a state in which the piston is at the top dead center).
[Fig. 8]
Fig. 8 is a vertical cross sectional view of the internal combustion engine according to the fourth embodiment (in a state in which the piston is at the top dead center).
[Fig. 9]
Fig. 9 is a vertical cross sectional view of the internal combustion engine according to the fourth embodiment (in a state in which the piston is at the bottom dead center).
[Fig. 10]
Fig. 10 is an explanatory drawing illustrating the change

of the position of the intermediate pin in the case where the second connecting rod is expanded at the top dead center.
[Fig. 11]
Fig. 11 is an explanatory drawing illustrating the change of the position of the intermediate pin in the case where the second connecting rod is expanded and the link arm is contracted at the top dead center.
[Pig. 12}
Fig. 12 is a vertical cross sectional view of the internal combustion engine according to the fifth embodiment (in a state in which the piston is at the top dead center).
[Fig. 13]
Fig. 13 is a vertical cross sectional view of the internal combustion engine according to the fourth embodiment (in a state in which the piston is at the bottom dead center).
[Fig. 141
Fig. 14 is a drawing viewed in the direction of the line 14-14 in Fig. 12.
[Fig. 15]
Fig. 15 is an explanatory drawing illustrating the
operation of the crank angle 0.
[Fig. 16]
Fig. 16 is a graph showing the relation between the crank anale 0 and the piston displacement x.

[0020]
Fig. 1 to Fig. 4 show the first embodiment of the present invention. Fig. 1 is a vertical cross section of an internal combustion engine (in a state in which a piston is at the top dead center), Fig. 2 is a vertical cross section of the internal combustion engine (in a state in which the piston is at the bottom dead center), and Fig. 3 is a drawing viewed in the direction 3-3 in Fig. 1, and Fig. 4 is a graph showing a relation of the stroke of the piston with respect to the crank angle-In this specification, the direction toward the top dead center and the direction toward the bottom dead center of the piston 14 of the internal combustion engine E are defined to be upward and downward respectively-
[0021]
As shown in Fig. 1, a four-cycle internal combustion engine E comprises a cylinder block 11 and a cylinder head 12, and the piston 14 is slidably fitted into a cylinder 13 provided in the cylinder block 11. The cylinder head 12 is provided with a combustion chamber 15 facing toward the upper surface of the piston 14, an intake port 16 continuing into the combustion chamber 15, a exhaust port 17 continuing into the combustion chamber 15, an intake valve 18 opening and closing an intake valve hole, and an exhaust valve 19 for opening and closing an exhaust valve hole.

[0022]
A crankshaft 20 is disposed in such a manner that the axis 111 lies on one side with respect to the axis L2 of the cylinder 13. One end of the second connecting rod 24 is supported by the other end of the first connecting rod 22, one end of which is rotatably supported by the piston pin 21 and extending downward, via an intermediate pin 23, and the other end of the second connecting rod 24 extending from the intermediate pin 23 toward one side is rotatably supported by a crankpin 25. A link arm 26 rotatably supported at one end by the intermediate pin 23 is rotatably supported at the other end by a fixed portion 27 positioned downwardly of the crankshaft 20 via a pivot pin 28.
[0023]
When the piston 14 is positioned at the top dead center, the axis L3 of the first connecting rod 22 {that is, a line segment connecting the axis L4 of the piston pin 21 and the axis L5 of the intermediate pin 23) coincides with the axis L2 of the cylinder 13, and the axis L6 of the second connecting rod 24 (that is, a line segment connecting the axis L5 of the intermediate pin 23 and the axis L7 of the crankpin 25) is almost orthogonal to the axis L3 of the first connecting rod 22. The axis L8 of the link arm 26 (that is, a line segment connecting the axis L5 of the intermediate pin 23 and the axis L9 of the pivot pin 28) inclines with respect to the axis L3 of the first

connecting rod 22 so that the right side is lower as seen in the figure.
[0024]
The aforementioned first connecting rod 22, the second connecting rod 24, and the link arm 26 constitute connecting means 29 of the present invention.
[0025]
The rotational direction of the crankshaft 2 0 is set to the direction in which the crankpin 25 moves upward and then downward while the piston 14 moves downward from the top dead center to the bottom dead center.
[0026]
As is apparent from Fig. 3, the relation between the diameter Dl of the intake valve 18 and the diameter D2 of the exhaust valve 19 is the reverse of the internal combustion engine in the related art. Therefore, the substantial area of the opening of the exhaust valve 19 is made to be larger than the substantial area of the opening of the intake valve
18 by setting the diameter D2 of the exhaust valve 19 to be larger than the diameter Dl of the intake valve 18, that is, by setting the peripheral length of the exhaust valve 19 to be larger than the peripheral length of the intake valve 18. In this embodiment, the intake valve 18 and the exhaust valve
19 are disposed on a diameter line of the combustion chamber 15, and two ignition plugs 30, 31 are disposed so as to interpose

the diameter line.
[0027]
In order to make the substantial area of the opening of the exhaust valve 19 larger than the substantial area of the opening of the intake valve 18, as shown in the modification in Fig. 5, two exhaust valves 19/ 19 may be disposed for one intake valve 19 for example, so that the sum of the peripheral lengths of two exhaust valves 19 becomes larger than the peripheral length of one intake valve 18. in this modification, the intake valve 18 is disposed on one side of the diameter line of the combustion chamber 15, two exhaust valves 19, 19 are disposed on the other side thereof, and the two ignition plugs 30, 31 are disposed on the diameter line-
[0028]
Fig. 2 shows a state in which the piston 14 is at the bottom dead center. When the piston 14 moves between the top dead center and the bottom dead center, the axis L5 of the intermediate pin 23 at the lower end of the first connecting rod 22 moves on the arc A having its center at the axis L9 of the pivot pin 28 while being tied down by the link arm 26. During the movement, the axis L5 of the intermediate pin 23 will never move to the right side of the axis L2 of the cylinder 13 in the figure.
[0029]
The crankshaft 20 rotates by 216° while the piston 14

moves from the top dead center to the bottom dead center, and
the crankshaft 20 rotates by 144" while the piston 14 moves from the bottom dead center to the top dead center. In other words, in the internal combustion engine E of the present invention, the time period of the expansion stroke and the intake stroke (crank angle) are longer than the time period of the compression stroke and the exhaust stroke (crank angle).
[0030]
Fig. 4 shows a relation of the strokes of the piston with respect to the crank angles. The chain line represents a characteristic of the internal combustion engine in the related art in which the axis of the crankshaft is disposed on the axis of the cylinder and the piston pin and the crankpin are connected by a connecting rod. The aforementioned characteristic shown in a chain line is similar to the sine curve, in which the delayed side (the compression stroke and the exhaust stroke) and the advanced side (the expansion stroke and the intake stroke) are symmetrical with respect to the top dead center. In contrast to it, the characteristic of the present «nbodiment shown in a solid line is such that the delayed side and the advanced side are asymmetrical with respect to the top dead center since the time period of the expansion stroke and the intake stroke are longer than the time period of the compression stroke and the exhaust stroke as described above.

[0031]
According to the aforementioned characteristic^ the internal combustion engine E of this embodiment exercises the following effect in comparison with the internal combustion engine in the related art.
[0032]
(1) In order to improve heat efficiency of the internal
combustion engine E, it is desirable that the degree of constant
volume of the air-fuel mixture when being burned. In order
to do so, the smaller the amount of increase in volume of the
combustion chamber 15 is with respect to the amount of increase
in crank angle when the piston 14 moves downward from the top
dead center during the Expansion stroke, the more the degree
of constant volume increases and thus heat efficiency improves.
As is apparent from the portion showing the expansion stroke
in the graph in Fig. 4, downward displacement of the piston
14 from the top dead center of the internal combustion engine
E of this embodiment shown in a solid line is smaller than
downward displacement ot the piston of the internal combustion
engine in the related art shown in a chain line, and thus the
degree of constant volume in the expansion stroke is increased,
thereby improving heat efficiency.
[0033]
(2) AS is apparent from the portion showing the intake
stroke of the graph in Fig. 4, since the intake stroke period

of the internal combustion engine E of this embodiment shown in a solid line is 216 degCA, which is longer than 180 degCA of the related art, the flowing velocity of intake air may be lowered to realize improvement of the air intake efficiency, reduction of pumping loss, and downsizing in diameter of the intake valve 18. [0034]
(3) As is apparent from the portion showing the
compression stroke in the graph in Fig. 4, since the compression
stroke period of the internal combustion engine E of this
embodiment shown in a solid line is 144 degCA, which is shorter
than 180 degCA of the related art, mixing of the air-fuel
mixture in the combustion chamber 15 may be promoted and thus
the burning time is shortened, and heat loss (cooling loss)
during compression may be reduced.
[0035]
The internal combustion engine E of this embodiment may exercise the following effects owing to the construction of the connecting means 29.
[0036]
(4) Since the second connecting rod 24 is disposed so
as to be orthogonal to the axis L2 of the cylinder 13, the
dimension of the internal combustion engine E in the direction
of the axis L2 of the cylinder 13 may be reduced in comparison
with the case in which both of the first connecting rod 22 and

the second connecting rod 24 are disposed along the axis L2 of the cylinder 13.
[0037]
(5) Since the pivotal angle of the first connecting rod 22 in a state in which the pressure in the combustion chamber 15 is especially high (that is, in an early phase of the expansion stroke) is significantly small in comparison with the normal internal combustion engine provided with a single connecting rod, and the velocity of the downward movement of the piston 14 in an early phase of the expansion stroke in which the pressure in the combustion chamber 15 is high is low, friction loss due to the side pressure of the piston 14 may be reduced.
[0038]
(6> Since the first connecting rod 22 pivots only to one side with respect to the axis L2 of the cylinder 13, slapping sound generated when the piston 14 hits against the cylinder 13 may be reduced-
[0039]
In general, in the internal combustion engine of the related art, the substantial area of the opening of the exhaust valve is set to be smaller than the substantial area of the opening of the intake valve. The first reason is that the marginal mach number of choking of exhaust gas is large due to high temperature thereof, and the second reason is that there

is enough time for discharging exhaust gas because the movement of the piston is slower on the side of the bottom dead center than on the side of the top dead center.
[0040]
As is described in conjunction with Fig. 4/ the exhaust stroke period of the internal combustion engine E of the present embodiment is shorter than that of the related art, and thus the movement of the piston 14 in the vicinity of the bottom dead center becomes faster, which may result in increase in exhaust loss if nothing is done. Especially, though it is general that the exhaust valve is opened at the position before reaching the bottom dead center, if the timing for opening the exhaust valve for utilizing the expansion stroke effectively is delayed to the position in the vicinity of the bottom dead center, there is apprehension that smooth discharge of exhaust gas is impaired and thus exhaust loss may further be increased. However, since the substantial area of the opening of the exhaust valve 19 is set to be larger than the substantial area of the opening of the intake valvel 18 in the present embodiment, it is possible to enable smooth discharge of exhaust gas and minimize increase in exhaust loss while utilizing the expansion stroke effectively by setting the timing in opening the exhaust valve as close as possible to the bottom dead center.
[0041]
In the first embodiment, when the piston 14 is at the

top dead center, the second connecting rod 24 extends along the direction orthogonal to the axis L2 of the cylinder 13, while in the second embodiment shown in Fig. 6, the axis L6 of the second connecting rod 24 extends upward slightly obliquely with respect to the direction orthogonal to the axis L2 of the cylinder 13. Further, in the third embodiment shown in Fig. 7, the axis L6 of the second connecting rod 24 extends downward slightly obliquely with respect to the direction orthogonal to the axis L2 of the cylinder 13.
[0042]
More specifically, in the second embodiment shown in Fig. 6, when the piston 14 is at the top dead center, S is positioned upwardly of Q where Q is the position of the axis L5 of the intermediate pin 23 located on the axis L2 of the cylinder 13, and S is the intersection between the axis L2 of the cylinder 13 and the line perpendicular thereto from the axis LI of the crankshaft 20. In contrast to it, in the second embodiment shown in Fig. 7, S is located downwardly of Q.
[0043]
Since the embodiment shown in Fig. 6 and Fig- 7 is such that the first connecting rod 22 and the second connecting rod 24 are disposed almost at a right angle when the piston 14 is at the top dead center, all the effects of the first embodiment can be achieved. However, in a narrow sense, because of the positional relation between S and Q, when the piston 14 is moved

downward from the top dead center shown in the figure during the expansion stroke, a tensile load is exerted on the second connecting rod 24 in the second embodiment shown in Fig. 6, while a compressive load is exerted to the second connecting rod 24 only momentarily in the third embodiment shown in Fig. 7. Therefore, the second embodiment (See Fig. 6) in which no compressive load is exerted thereon is advantageous in view of strength of the second connecting rod 24, and thus employing the layout of the second embodiment may contribute to downsizing of the second connecting rod 24 in diameter and thus reduction of the weight thereof.
[0044]
Referring now to Fig. 8 to Fig. 11, the fourth embodiment of the present invention will be described.
[0045]
The construction in the fourth embodiment is similar to that of the second embodiment described in conjunction with Fig. 6, the axis LI of the crankshaft 20 and the axis L9 of the pivot pin 28 are positioned slightly higher than those in the second embodiment. When the piston 14 is at the top dead center, the second connecting rod 24 is disposed such that the side of the axis LI of the crankshaft 20 is higher than the axis L5 of the intermediate pin 23, and the link arm 26 is disposed such that the side of the axis L9 of the pivot pin 28 is lower than the axis L5 of the intermediate pin 23.

[0046]
According to the fourth embodiment, the following effects are exercised in addition to the effects of the first embodiment and the second embodiment.
[0047]
in other words, in an early phase of the expansion stroke wherein the piston 14 is at the top dead center, a load due to the explosion of the air-fuel mixture in the combustion chamber 15 is transmitted to the first connecting rod 22 via the pistonl4, and a downward explosion load F acts on the intermediate pin 23 at the lower end of the first connecting rod 22. The explosion load F is decomposed into a tensile load Fl that pulls the second connecting rod 24 in the lower left direction and a compression load F2 for compressing the link arm 26 in the lower right direction, the second connecting rod 24 is extended by ALl by the tensile load Fl, and the link arm 26 is compressed by AL2 by the compression load F2. Since an angle formed between the second connecting rod 24 and the horizontal line and an angle formed between the link arm 26 and the horizontal line are small, the tensile load Fl of the second connecting rod 24 and the compression load F2 of the link arm 26 with respect to the explosion load F are magnified.
[0048]
In Fig. 10, assuming that the second connecting rod 24 is expanded by ALl and the length of the link arm 26 is not

changed, the position of the intermediate pin 23 at the lower
end of the first connecting rod 22 is lowered by AL'. Actually, as shown in Fig, 11, since the second connecting rod 24 is
expanded by ALl, and the link arm 26 is compressed by AL2, the position of the intermediate pin 23 at the lower end of the
first connecting rod 22 is lowered by AL, which is further larger than the AL'.
[0049]
In this manner, when the position of the inteannediate pin 23 is lowered by AL in an early phase of the expansion stroke, the position of the piston 14 is also lowered by AL, and the volume of the combustion chamber 15 is increased, thereby decreasing compression ratio correspondingly. Since the
magnitude of AL increases with increases in explosion load F, the rate of decrease in compression ratio increases with increases in load of the internal combustion engine E, As a consequent, knocking may be prevented by reducing compression ratio under high load conditions while enabling the operation of high heat efficiency with high compression ratio in a wide range of operation under partial load conditions for reducing the amount of consumption. in addition, such variable compression ration control can be realized only by changing the layout of the first connecting rod 22, the second connecting rod 24, and the link arm 26 without necessity of a special actuator or a controller, which realizes very low costs.

[0050]
Though the first connecting rod 22 itself is compressed by the explosion load F and thus the length thereof is compressed, thereby lowering the position of the piston 14 correspondingly and reducing the compression ratio thereof, reduction in compression ratio in association with the expansion and compression of the second connecting rod 24 and the link arm 26 is much larger than that. The reason is that the distance of downward travel of the piston 14 in association with contraction of the first connecting rod 22 disposed vertically is exactly the amount of contraction described above, but the distance of downward travel of the piston 14 in association with expansion and contraction of the second connecting rod 24 and the link arm 26 disposed substantially horizontally is the magnified amount of expansion and contraction.
[0051]
Fig. 12 to Fig. 16 show the fifth embodiment of the present invention, in which Fig. 12 is a vertical cross sectional view of the internal combustion engine (in a state in which the piston is at the top deaci center). Fig. 13 is a vertical cross sectional view of the internal combustion engine {in a state in which the piston is at the bottom dead center). Fig. 14 is a drawing viewed in the direction 14-14 in Fig. 12, Fig. 15 is an explanatory drawing of the action of the internal

combustion engine, and Fig. 16 is a graph showing the relation between the crank angle 6 and the piston displacement x.
[0052]
As shown in Fig. 12 to Fig. 15, the outline of a power unit P for a motorcycle having an internal combustion engine E comprises a mission case 111, a cylinder head 112 tied on the front surface of the mission case 111, a cylinder block 113 tied on the front surface of the cylinder head 112, and a cover 114 tied on the front surface of the cylinder block 113. The piston 116 is slidably fitted in a cylinder 115 supported within the cylinder block 113, and a piston pin 117 is supported at the front end of legs 116a, 116a projecting integrally from the piston 116 toward the front. When the piston 116 is at the top dead center shown in Fig. 12, U-shaped notches 115a, 115a for avoiding interference with the piston pin 117 are formed on the front end of the cylinder 115.
[0053]
A crankshaft 119 supported on the mating surface between the cylinder head 112 and the mission case 111 is provided with a pair of crank pins 119a, 119a, and a pair of connecting rods 121, 121 supported by these crankpin 119a, 119a at the larger ends thereof via needle bearings 120, 120 are connected to both ends of the piston pin 117 through the openings 112a, 112a of the cylinder head 112 and an opening {not shown) of the cylinder block 113.

[0054]
A combustion chamber 122 is formed in the cylinder head 112 so as to be faced toward the top surface of the piston 116, and an intake port 123 extending upwardly from the combustion chamber 122 and the exhaust port 124 extending downwardly therefrom are opened and closed respectively by an intake valve 125 and an exhaust valve 126 disposed in the shape of a letter V- As is apparent from Fig. 14, the substantial area of the opening of the exhaust valve 126 is set to be larger than the substantial area of the opening of the intake valve 125. An ignition plug 108 is mounted in the combustion chamber 122 so as not to interfere with the intake valve 125 and the exhaust valve 126.
[0055]
An air intake rocker shaft 130 and an exhaust rocker shaft 131 are supported in the mission case ill, and an air intake rocker arm 132 pivotally supported by the air intake rocker shaft 130 abuts against an air intake cam 133 fixed on a cam shaft 128 and the stem end of the intake valve 125. An intermediate portion of a L-shaped driven exhaust rocker arm 134 is pivotally supported by an exhaust rocker shaft 131, and one end of the driven exhaust rocker arm 134 abuts against the stem end of the exhaust valve 126 and the other end thereof is connected to one end of a connecting rod 135. A driving exhaust rocker arm 136 being independent from the air intake

rocker arm 132 is pivotally supported by the air intake rocker shaft 130, and the driving exhaust rocker arm 136 is abutted by an exhaust cam 137 fixed to a cam shaft 128 and connected to the other end of the connecting rod 135.
[0056]
Rotation of the camshaft 128 is transmitted to the intake valve 125 via an air intake cam 133 and the air intake rocker arm 132, and opens the intake valve 125 once per two turns of the crankshaft 119. Rotation of the camshaft 128 is transmitted to the exhaust valve 126 via the exhaust cam 137, the driving exhaust rocker arm 136, the connecting rod 135, and the driven exhaust rocker airm 134, and opens the exhaust valve 126 once per two turns of the crankshaft 119.
[0057]
The operation of the fifth embodiment will now be described.
[0058]
Fig. 15 is a schematic drawing of the internal combustion engine E of the present embodiment, which comprises the cylinder 115, the piston 116 slidably fitted to the cylinder 115, the cylinder head 112 connected to the cylinder 115, the combustion chamber 122 formed on the upper surface of the cylinder head 112 facing toward the piston 116, the crankshaft 119/ the connecting rods 121, 121 for connecting the piston 116 to the crankshaft 119. The cylinder head 112 is disposed

*«if

at the position interposed between the piston 116 and the crankshaft 119.
[0059]
Fig. 15(A) shows a sate in which the piston 116 is at
the top dead center, and a crank angle 6 in this moment is 0°. Fig. 15(C) shows a state in which the piston 116 is at the bottom
dead center, and a crank angle 0 in this moment is 180°, Pig. 15(B) shows a state in which the piston 116 is at the midpoint between the top dead center and the bottom dead center. The crank angle 6 at this moment is not 90°, but an angle Ob is larger than 90°. The reason is that the connecting rods 121, 121 are positioned on the cylinder axis L at the top dead center and the bottom dead center, while the connecting rods 121, 121
inclines by the angle with respect to the cylinder axis L at the aforementioned mid point.
[0060]
In Fig- 16, the relation between the crank angle 6 with respect to the top dead center of the internal combustion engine E and the displacement x of the piston 116 with respect to the top dead center is shown by a broken line. The stroke of the piston 116 between the top dead center and the bottom dead center is 60 mm in this case. As is described in Fig, 15(B), when the piston 116 is at the midpoint of the top dead center and the bottom dead center (when the displacement is at the position of -30 mm), the crank angle 8 becomes an angle 9b,

which is larger than 90°. In contrast to it, in the cosine curve shown by a solid line, the crank angle 0 is 90° when the piston 116 is at the midpoint between the top dead center and the bottom dead center.
[0061]
In this manner, it is appreciated that the line (see the broken line) showing the relation of the displacement x of the
piston 116 with respect to the crank angle 6 is positioned on the upper side of the cosine curve shown by a solid line in the internal combustion engine E of this embodiment. It means that the amount of increase in displacement x of the piston 116 with respect to the amount of increase in the crank angle 0 is smaller than the characteristic of the cosine curve when the piston moves downward from the top dead center in the expansion stroke.
[0062]
In order to increase heat efficiency of the internal combustion engine E, it is desirable to increase the degree of constant volume of the air-fuel mixture during combustion. In order to do so, when the piston 116 moves downward from the top dead center during the expansion stroke, the smaller the amount of increase in the volume of the combustion chamber 122 with respect to the amount of increase in crank angle 9 is, the more the degree of constant volume is increased, thereby increasing heat efficiency. As is clear from the portion

Showing the expansion stroke, which is the range of 0° to 180" in crank angle 9, in the graph in Fig. 16, the displacement X of the piston 116 from the top dead center of the internal combustion engine E in the present embodiment shown by a broken line is smaller than the displacement x of the piston of the internal combustion engine in the related art shown by a chain line. Therefore, the degree of constant volume of the air-fuel mixture in the expansion stroke is increased, thereby increasing the heat efficiency-
10063]
In the internal combustion engine E of the present embodiment, since the line (see the broken line) showing the relation of displacement x of the piston 116 with respect to
the crank angle 8 is positioned on the upper side of the cosine curve shown in a solid line, when the piston moves upward from the bottom dead center during the exhaust stroke, the amount of increase in displacement x of the piston 116 with respect
to the amount of increase in crank angle 6 is larger than the characteristic of the cosine curve, and thus the exhaust amount of exhaust gas per unit time period is larger than the case of the internal combustion engine in the related art. However, since the substantial area of the opening of the exhaust valve 126 is set to be larger than the substantial area of the opening of the intake valve 125, exhaust loss can be minimized by discharging exhaust gas smoothly from the combustion chamber

122.
[0064]
In the expansion stroke in which a largest load is exerted to the connecting rods 121, 121, since the piston 116 moves away from the crankshaft 119, a tensile load in the direction opposite from that of the internal combustion engine E of the related art acts on the connecting rods 121, 121. In this manner, exertion of a tensile load on the connecting rods 121, 121 makes them advantageous in strength in comparison with the case where a compression load is exerted thereon, whereby the connecting rods 121, 121 may be made thinner to reduce the weight.
[0065]
Since the connecting rods 121, 121 are divided into two pieces, and are connected to both ends of the crankshaft 119 in the axial direction through the both sides of the pxston 116, exertion of biased load on the piston 116 may be prevented and thus durability thereof against abrasion may be enhanced. In addition, since the leg portions 116a, 116a are projected from the piston 116 in the direction away from the crankshaft 119 and the piston pin 117 is provided at the extremities of the leg portions 116a, 116a, the entire lengths of the connecting rods 121, 121 become longer than the case of the internal combustion engine E in the related art. As a consequent, the pivotal angle of the connecting rods 121,

121 with respect to the cylinder axis L decreases, and thus side thrust exerted on the piston 116 decreases thereby enhancing durability thereof against abrasion.
[0066]
Though the embodiments of the present invention have been described in detail, various modifications in design may be made on the present invention without departing from the scope of the invention.
[0067]
For example, a four-cycle internal combustion engine E is exemplified in the embodiments, while the present invention may also be applied to a two-cycle internal combustion engine.
[0068]
[Effects of the Invention]
As is described thus far, according to the invention as (set forjfch-irf'Claim 17 since the time of downward movement of the piston is shorter than the time of upward movement thereof owing to the connecting means that connects the piston to the crankshaft, the amount of movement of the piston with respect to the amount of increase in crank angle (the amount of increase in volume of the combustion chamber) during expansion stroke is reduced, and thus the degree of constant volume of the air-fuel mixture while it is burning increases thereby improving heat efficiency of the internal combustion engine, In addition, since the intake stroke period is longer in

comparison with 180 degCA of the normal internal combustion engine, the flowing velocity of intake air is lowered, thereby realizing improvement of intake efficiency, reduction of pumping loss, and downsizing in the diameter of the intake valve. In addition, since the compression stroke period is shorter in comparison with 180 degCA of the normal internal combustion engine, mixing of the air-fuel mixture in the combustion chamber may be promoted and thus the burning time is shortened, and heat loss during compression may be reduced.
[0069]
According to the invention a6 set^forth in Claim 2, since the second connecting rod is disposed orthogonal to the axis of the cylinder, the dimension of the internal combustion engine in the direction of the axis thereof may be reduced in comparison with those in the related art in which both of the first and the second connecting rod are disposed along the axis of the cylinder. Since the pivotal angle of the first connecting rod in an early phase of the expansion stroke is smaller, and in addition, the velocity of the downward movement of the piston is lower in an early phase of the expansion stroke in comparison with that in the normal internal combustion engine, friction loss between the piston and the cylinder may be reduced. In addition, since the first connecting rod can pivot only to one side with respect to the axis of the cylinder, occurrence of slapping sound of the piston may be reduced.

[0070]
According to the invention as iet forth in Claim 3; since the axis of the crankshaft is positioned upwardly of the straight line passing through the axis of the intermediate pin and being orthogonal to the axis of the cylinder when the piston is at the top dead center, a tensile load is generated on the second connecting rod in an early phase of the expansion stroke in which the piston moves downward from the top dead center, whereby the second connecting rod is strengthwise advantageous, thereby enabling downsizing in diameter.
[0071]
According to the invention ^s set forth in Claim 4, since the time of upward movement of the piston is shorter than the time of downward movement thereof by the connecting means for connecting the piston to the crankshaft, the amount of movement of the piston with respect to the amount of increase in crank angle decreases in the expansion stroke {the amount of increase in volume of the combustion chamber) is smaller, and thus the degree of constant volume of the air-fuel mixture at the time of combustion increases, thereby increasing heat efficiency of the internal combustion engine. In addition, since the intake stroke period of the internal combustion engine, which is longer than 180 degCA, flowing velocity of intake air may be lowered to realize improvement of the air intake efficiency, reduction of pumping loss, and downsizing in diameter of the

intake valve. Further, since the compression stroke period of the internal combustion engine, which is shorter than 180 degCA, mixing of the air-fuel mixture in the combustion chamber may be promoted and thus the burning time is shortened, and heat loss during compression may be reduced. Still further, since the substantial area of the opening of the exhaust valve is made to be larger than the substantial area of opening of the intake valve, exhaust gas can be discharged from the combustion chamber smoothly to minimize exhaust loss even when the movement of the piston at the time of the initiation of the exhaust stroke is faster than the related art because the time of upward movement of the piston is set to be shorter than the time of downward movement of the piston.
[0072]
According to the invention^assgt forth in Claims, since the cylinder head in which the combustion chamber is partitioned is disposed between the piston and the crankshaft in the internal combustion engine, the amount of increase in volume of the combustion chamber with respect to the amount of increase in crank angle based on the top dead center of the piston may be reduced in comparison with the internal combustion engine in the related art in which the combustion chamber is disposed on the side of the piston opposite from the crankshaft, and thus the degree of constant volume of the air-fuel mixture during combustion can be increased, thereby

increasing heat efficiency. In addition, since a tensile load is exerted on the connecting rod during expansion stroke, consideration of buckling is not necessary in comparison with the internal combustion engine of the related art on which a compression load is exerted, and thus the strength of the connecting rod is reduced for reducing the weight thereof. In addition,,though the velocity of movement of the piston in the vicinity of the bottom dead center is faster than that of the internal combustion engine of the related art, since the substantial area of the opening of the exhaust valve is made to be larger than the substantial area of the opening of the intake valve, exhaust gas can be discharged from the combustion chamber smoothly to minimize exhaust loss.

[Reference Numerals]

13 cylinder
14 piston
18 intake valve
19 exhaust valve
20 crankshaft
21 piston pin
22 first connecting rod
23 intermediate pin
24 second connecting rod
25 crankpin
26 link arm
27 fixed portion
29 connecting means
112 cylinder head
115 cylinder
116 piston
119 crankshaft
121 connecting rod
122 combustion chamber
125 intake valve
126 exhaust valve
LI axis of the crankshaft
L2 axis of the cylinder-
L5 axis of the intermediate pin
40

We Claim:
1. An improved internal combustion engine comprising a piston (14) that is slidably fitted in a cylinder (13) is connected to a crankshaft (20), characterized in that it has a first connecting rod (22) rotatably supported at one end by a piston pin (21) and provided with an intermediate pin (23) at the other end, a second connecting rod (24) rotatably supported at one end by the intermediate pin (23) and rotatably supported at the other end by a crankpin (25), and a link arm (26) rotatably supported at one end by the intermediate pin (23) and rotatably supported at the other end by a fixed portion (27), in that the first connecting rod (22) is disposed substantially along the axis (L2) of the cylinder (13), the second connecting rod (24) is disposed substantially orthogonal to the axis (L2) of the cylinder (13), and the fixed portion (27) rotatably supporting the other end of the link arm (26) is positioned downwardly of the crankshaft (20) when the piston (14) is positioned at the top dead center; the time of upward movement of said piston (14) is shorter than the time of downward movement thereof.
2. An improved internal combustion engine as claimed in Claim 1, wherein the axis (LI) of the crankshaft (20) is positioned upwardly of the straight line passing through the axis (L5) of the intermediate pin (23) and being orthogonal to the axis (L2) of the cylinder (13) when the piston (14) is at the top dead center.
3. An improved internal combustion engine as claimed in claim 1, wherein a piston (14) slidably fitted in the cylinder (13) is connected to a crank shaft (20) via a connecting means (29).

Documents:

519-mum-2002-cancelled pages(28-10-2005).pdf

519-mum-2002-claims(granted)-(28-10-2005).doc

519-mum-2002-claims(granted)-(28-10-2005).pdf

519-mum-2002-correspondence(23-5-2006).pdf

519-mum-2002-correspondence(ipo)-(27-10-2005).pdf

519-mum-2002-drawing(28-10-2005).pdf

519-mum-2002-form 1(12-6-2002).pdf

519-mum-2002-form 1(28-10-2005).pdf

519-mum-2002-form 13(28-10-2005).pdf

519-mum-2002-form 19(8-6-2004).pdf

519-mum-2002-form 2(granted)-(28-10-2005).doc

519-mum-2002-form 2(granted)-(28-10-2005).pdf

519-mum-2002-form 3(12-6-2002).pdf

519-mum-2002-form 3(28-10-2005).pdf

519-mum-2002-form 3(7-4-2004).pdf

519-mum-2002-form 5(12-6-2002).pdf

519-mum-2002-power of authority(12-8-2002).pdf

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Patent Number

209889

Indian Patent Application Number

519/MUM/2002

PG Journal Number

38/2007

Publication Date

21-Sep-2007

Grant Date

10-Sep-2007

Date of Filing

12-Jun-2002

Name of Patentee

HONDA GIKEN KOGYO KABUSHIKI KAISHA

Applicant Address

1-1, MINAMIAOYAMA, 2-CHOME, MINATO-KU, TOKYO,

Inventors:

#	Inventor's Name	Inventor's Address
1	RYO KUBOTA	C/O KABUSHIKI KAISHA HONDA GIJUTSU KENKYUSHO, 4-1, CHUO 1-CHOME, WAKO -SHI, SAITAMA,
2	HIROYUKI TANAKA	C/O KABUSHIKI KAISHA HONDA GIJUTSU KENKYUSHO, 4-1, CHUO 1-CHOME, WAKO -SHI, SAITAMA,
3	SATOSHI IIJIMA	C/O KABUSHIKI KAISHA HONDA GIJUTSU KENKYUSHO, 4-1, CHUO 1-CHOME, WAKO -SHI, SAITAMA,
4	KAZUNORI KIKUCHI	C/O KABUSHIKI KAISHA HONDA GIJUTSU KENKYUSHO, 4-1, CHUO 1-CHOME, WAKO -SHI, SAITAMA,
5	MASATOSHI SUZUKI	C/O KABUSHIKI KAISHA HONDA GIJUTSU KENKYUSHO, 4-1, CHUO 1-CHOME, WAKO -SHI, SAITAMA,

PCT International Classification Number

F02B75/32

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2001-195293	2001-06-27	Japan
2	2005-106858	2002-04-09	Japan