Title of Invention

A SPARK IGNITION 4-STROKE ENGINE

Abstract

A spark ignition 4-stroke engine wherein a plurality of ignition plugs (49, 50) which are faced with one combustion chamber (45) being mounted in a cylinder head (39), an intake port (70) being disposed in said cylinder head (39) for making a swirl generate in said combustion chamber (45), characterized in that the intake port (70) is on the plane perpendicular to the axial line of the cylinder bore (44) and is formed in a shape which has the first path portion (70a) extending in a tangential direction to the guide cylinder (98) on the outer side of the guide cylinder (98) and the tapering second path portion (70b) contiguous to the first path portion (70a) and curved in such a manner as to wind part of the guide cylinder (98), and the valve head portion (74a) of the intake valve (74) and the valve seat (97) are covered with the opposing wall (39a) of the cylinder head (39) except the portion which overlaps with the first and second path portions (70a, 70b), wherein the calorific value of the ignition plugs (49, 50) mounted in the cylinder head (39) becomes higher while leaving said intake port (70) along the flow direction of the swirl in said combustion chamber (45).

Full Text

FORM 2 THE PATENTS ACT, 1970 [39 OF 1970] COMPLETE SPECIFICATION [See Section 10; Rule 13] "A SPARKING 4-STROKE 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 nature of the invention and the manner in which it is to be performed:- Original 678/MUM/2001 GRANTED - 8 MAY 2006 The present invention relates to a spark ignition 4-stroke engine. This invention relates to a spark ignition four¬cycle engine wherein a plurality of ignition plugs exposed to the same combustion chamber are attached to a cylinder head. [0002] . [Prior Art] Conventionally, a four-cycle engine of the type mentioned is already known from the official,gazette of Domestic Publication of PCT International Publication for Patent Application No. Hei 10-500750 and-. so forth. [0003] [Problem to be Solved by the Invention] In the conventional four-cycle engine described above, a plurality of ignition plugs are attached to a free space other than an intake valve and an exhaust, valve in order to achieve reduction of the fuel cost and augmentation of the character of exhaust gas. [0004] Meanwhile, also a configuration wherein an intake port is provided in a cylinder head in an arrangement wherein a swirl is produced in a combustion chamber.in order to augment the combustibility of air fuel mixture is conventionally known well. If a plurality of ignition plugs exposed to the same combustion chamber are attached to a cylinder head of an engine designed with an intention to produce such a swirl as just described, then the ignition plugs are liable to be cooled because air fuel mixture from the intake port contacts with the ignition plug immediately after it flows into the combustion chamber, and there is the possibility that failure in firing by smoking of the ignition plug may occur. [0005] The present invention has been made in such a situation as described above, and it is an object of the present invention to provide a spark ignition four-cycle engine which prevents occurrence of failure in firing by smoking of an ignition plug. [0006] [Means for Solving the Problem] In order to attain the object described above, according to the present invention as set forth in claim 1, a spark ignition four-cycle engine wherein a plurality of ignition plugs exposed to the same combustion chamber are attached to a cylinder head is characterized in that an intake port is provided in the cylinder head so that a swirl can be produced in the combustion chamber, and the plurality of ignition plugs which provide a heating value which increases away from the intake port along a flowing direction of the swirl in the combustion chamber are attached to the cylinder head. [0007] With such a configuration as described above, the heating value of the ignition plug with which air fuel mixture flowing into the combustion chamber from the intake port may immediately contact is set comparatively low, and even if the ignition plug is cooled by contact with the air fuel mixture, occurrence of smoking is prevented and occurrence of failure in ignition by smoking can be prevented. [0008] Further, the invention as set forth in claim 2 is characterized, in addition to the configuration of the invention given above as set forth in claim 1, in that the intake port which is opened in the combustion chamber above the ignition plug at which the heating value is lowest is provided in the cylinder head which is coupled to a cylinder block having a cylinder axial line extending substantially horizontally. With such a configuration as just described, even if fuel which runs along an inner face of a lower portion of the intake port without being atomized flows into, the combustion chamber; since the heating value of the ignition plug with which the fuel may possibly contact is lowest among the plurality of ignition plugs, occurrence of smoking is prevented, and occurrence of failure in firing by smoking can be prevented. According to the present invention, there is provided a spark ignition 4- stroke engine wherein a plurality of ignition plugs (49, 50) which are faced with one combustion chamber (45) being mounted in a cylinder head (39), an intake port (70) being disposed in said cylinder head (39) for making a swirl generate in said combustion chamber (45), characterized in that the intake port (70) is on the plane perpendicular to the axial line of the cylinder bore (44) and is formed in a shape which has the first path portion (70a) extending in a tangential direction to the guide cylinder (98) on the outer side of the guide cylinder (98) and the tapering second path portion (70b) contiguous to the first path portion (70a) and curved in such a manner as to wind part of the guide cylinder (98), and the valve head portion (74a) of the intake valve (74) and the valve seat (97) are covered with the opposing wall (39a) of the cylinder head (39) except the portion which overlaps with the first and second path portions (70a, 70b), wherein the calorific value of the ignition plugs (49, 50) mounted in the cylinder head (39) becomes higher while leaving said intake port (70) along the flow direction of the swirl in said combustion chamber (45). [Brief Description of the Drawings] [FIG. 1] FIG. 1 is a side elevational view of a motorcycle. [FIG. 2] FIG. 2 is a sectional view of a power unit taken along line 2-2 of FIG. 1. [FIG. 3] FIG. 3 is an enlarged view as viewed in a direction of an arrow mark taken along line 3-3 of FIG. 2. [FIG. 4] FIG. 4 is an enlarged view as viewed in a direction of an arrow mark taken along line 4-4 of FIG. 2. [FIG. 5] FIG. 5 is an enlarged view as viewed in a direction of an arrow mark taken along line 5-5 of FIG. 2. [FIG. 6] FIG. 6 is a view as viewed in a direction of an arrow mark 6 in FIG. 5. [FIG. 7] FIG. 7 is a projection drawing of an intake port on a plane perpendicular to an axial line of a cylinder bore. [FIG. 8] FIG. 8 is a sectional view taken along line 8-8 of FIG. 5. [0009] [Mode for Carrying Out the Invention] In the following, an embodiment of the present invention is described with reference to a working example of the present invention shown in the accompanying drawings. [0010] FIGS. 1 to 8 show a working example of the present invention, and FIG. 1 is a side elevational view of a motorcycle; FIG. 2 is a sectional view of a power unit taken along line 2-2 of FIG. 1; FIG. 3 is an enlarged view as viewed in a direction of an arrow mark taken along line 3-3 of FIG. 2; FIG. 4 is an enlarged view as viewed in a direction of an arrow mark taken along line 4-4 of FIG. 2; FIG. 5 is an enlarged view as viewed in a direction of an arrow mark taken along line 5-5 of FIG. 4; FIG. 6 is & view & icwed in a dilection of an arrow mark in FIG. 5; FIG. 7 is a projection drawing of an intake port on a plane perpendicular to an axial line of a cylinder bore; and FIG. 8 is a sectional view taken along line 8-8 of FIG. 5. [0011] Referring first to FIG. 1, a front fork 17 on which a front wheel WF is supported for rotation is supported for steering operation on a head pipe 16 provided at a front end of a body frame 15 of a motorcycle. A handle bar 18 is connected to the top end of the front fork 17, and a front fender 19 which covers over the front wheel WF is supported on the front fork 17.. A rear fork 20 on which a rear wheel WR is supported for rotation is supported for pivotal motion at an intermediate portion of the body frame 15, and a rear cushion 21 is provided between a rear portion of the body frame 15 and the rear fork 20. [0012] A power unit P composed of a spark ignition four¬cycle engine E of the water cooled type and a speed change gear M is supported at an intermediate portion of the body frame 15, and output power of the speed change gear M is transmitted to the rear wheel WR through an endless chain 22, [0013] An air cleaner 23 and a radiator 24 disposed above the engine E are supported on the body frame 15, and a fuel tank 25 disposed above the speed change gear M and an accommodation box 26 disposed above the fuel tank 25 into which electric parts can be accommodated are supported on the body frame 15. [0014] An exhaust pipe 27 which introduces exhaust gas from the engine E is connected to an exhaust muffler 28 disposed between the power unit P and the rear wheel WR. [0015] A front portion of the body frame 15, the engine E, the air cleaner 23 and the radiator 24 are covered with a leg shield 29 made of a synthetic resin and attached to the body frame 15. A rear portion of the body frame 15, the fuel tank 25 and the accommodation box 26 are covered with a rear cover 30 made of a synthetic resin and attached to the body frame 15, and a rear fender 31 which covers over a rear portion of the rear wheel WR is provided contiguously to the rear cover 30. A seat 32 which can open or close an upper end opening of the accommodation box 26 is provided on the rear cover 30, and a driver can be seated on the seat 32. [0016] A wind screen 33 having a light transmitting property is disposed forwardly of the driver seated on the seat 32. The wind screen 33 is attached to a handle cover 34 which covers the handle bar 18. [0017] Referring to FIGS. 2 to 5, an engine body 37 of the engine E includes a cylinder block 38 having a cylinder bore 44 in which a piston 43 is fitted for sliding movement, a cylinder head 39 coupled to the cylinder block 38 and cooperating with a top portion of the piston 43 to form a combustion chamber 45 therebetween, and a crankcase 40 coupled to the cylinder block 38 and supporting a crankshaft 47, which is connected to the piston 43 by a connecting rod 46, for rotation thereon. The cylinder block 38, cylinder head 39 and crankcase 40 are fastened together by a plurality of, for example, four, through bolts 41, .... The crankcase 40 is formed from a right crankcase half 40a and a left crankcase half 40b coupled to each other along a mating face provided by a plane which includes an operating axial line of the piston 43, and a crank chamber 42 is formed in the crankcase 40. Further, the engine body 37 is supported on the body frame 15 in a posture wherein the cylinder head 39 disposed directly rearwardly of the front wheel WF is disposed at a front portion and the axial line of the cylinder bore 44, that is, the cylinder axial line, extends substantially horizontally. [0018] The speed change gear M includes a main shaft 51 and a countershaft 52 supported on the crankcase 40 and having axial lines parallel to the crankshaft 47, and a plurality of gear trains 53 provided between the main shaft 51 and the countershaft 52 for allowing selective establishment. A shift drum 54 which rotates in order to selectively establish the gear trains 53 is supported for rotation on the crankcase 40. [0019] One end portion of the crankshaft 47 which projects from the right crankcase half 40a is connected to a driving gear 56 through a centrifugal clutch 55, and a driven gear 57 which meshes with the driving gear 56 is supported for relative rotation at one end of the main shaft 51 which projects from the right crankcase half 40a. The driven gear 57 is connected to a clutch outer 60 of a clutch 59 by a rubber damper 58. The clutch 59 is a multiple disk cluck which connects and disconnects a clutch inner 62 coupled to the main shaft 51 and the clutch outer 60 to and from each other. Selective establishment of the gear trains 53 is allowed in a condition wherein the clutch 59 is disconnected. The centrifugal clutch 55 and the clutch 59 are covered with a right cover 63 coupled to the right crankcase half 40a. [0020] A driving sprocket wheel 64 around which the chain 22 is wrapped is secured to an end portion of the countershaft 52 which projects from the left crankcase half 40b, and power is transmitted from the driving sprocket wheel 64 to the rear wheel WR through the chain 22. [0021] A rotor 66 of a dynamo 65 is secured to the other end portion of the crankshaft 47 which projects from the left crankcase half 40b, and a stator 67 of the dynamo 65 is secured to a left cover 68 which is coupled to the left crankcase half 40b in such a manner as to cover the dynamo 6 5. [0022] A jacket 48 for circulating cooling water is provided for the cylinder block 38 and the cylinder head 39 of the engine body 37 described above, and a pair of ignition plugs 49, 50 whose ignition timings are different from each other are mounted on the cylinder head 39 such that they are exposed to the combustion chamber 45. [0023] An intake port 70 for supplying air fuel mixture into the combustion chamber 45 is provided in the cylinder head 39 such that it is opened upwardly at an upper portion of the cylinder head 39, and an exhaust port 71 for discharging exhaust gas from the combustion chamber 45 is provided in the cylinder head 39 such that it is opened downwardly at a lower portion of the cylinder head 39. The air cleaner 23 is connected to the intake port 70 through a carburetor not shown, and the exhaust pipe 27 is connected to the exhaust port 71. [0024] An intake valve 74 for changing over between connection and disconnection between the intake port 70 and the combustion chamber 45 and an exhaust valve 75 for changing over between connection and disconnection between the exhaust port 71 and the combustion chamber 45 are disposed for opening and closing movement on the cylinder head 39. The intake valve 74 and the exhaust valve 75 are spring-biased in a valve closing direction. [0025] The intake valve 74 and the exhaust valve 75 are driven to open or close by a valve mechanism 76. The valve mechanism 76 is accommodated in a valve motion chamber 79 formed between the cylinder head 39 and a head cover 78 coupled to the cylinder head 39 by a plurality of bolts 77. [0026] The valve mechanism 76 includes a camshaft 80 supported for rotation on the cylinder head 39 such that it has an axial line parallel to the crankshaft 47 and having intake side and exhaust side cams 81, 82 provided thereon, intake side and exhaust side rocker shafts 83, 84 supported on the cylinder head 3 9 and having axial lines parallel to the camshaft 80, an intake side rocker arm 85 supported for rocking motion on the intake side rocker shaft 83 to follow the intake side cam 81 to drive the intake valve 74 to open or close, and an exhaust side rocker arm 86 supported for rocking motion on the exhaust side rocker shaft 84 to follow the exhaust side cam 82 to drive the exhaust valve 75 to open or close. [0027] Referring particularly to FIG. 2, a driving sprocket wheel 87 is secured to the crankshaft 47 between the left crankcase half 40b of the crankcase 40 and the dynamo 65, and a chain path 88 interconnecting the crank chamber 42 in the crankcase 40 and the valve motion chamber 79 at a portion corresponding to the driving sprocket wheel 87 is provided across the left crankcase half 40b, cylinder block 38 and cylinder head 39. '[0028] Meanwhile, a driven sprocket wheel 89 is secured to an end portion of the camshaft 80 at a portion corresponding to the chain path 88, and an endless chain 90 which can run in the chain path 88 extends between and along the driven sprocket wheel 89 and the driving sprocket wheel 87. [0029] The chain 90 is wrapped around an idle sprocket wheel 91 supported on the cylinder block 38 between the driving sprocket wheel 87 and the driven sprocket wheel 89, and tensile force is applied to the chain 90 between the idle sprocket wheel 91 and the driving sprocket wheel 87 from a tensioner 92 disposed on the left crankcase half 40b. [0030] A water pump 93 having a rotational axial line coaxial with the camshaft 80 of the valve mechanism 76 is attached to the cylinder head 39. A thermostat 95 is provided on a pump housing 94 of the water pump 93. The thermostat 95 operates so that, when the engine E is in a cold condition, cooling water of the jacket 48 is returned to the jacket 48 via the thermostat 95 and water pump 93, but in a condition after warming up of the engine E is completed, cooling water from the jacket 48 is returned to the jacket 48 via the radiator 24, thermostat 95 and water pump 93. [0031] Referring particularly to FIG. 5, a valve seat 97 in the form of a ring disposed at an inner end of the intake port 70 is securely mounted by force fitting or the like on the cylinder head 39 at a position displaced from the center of the combustion chamber 45. The intake valve 74 includes a valve head portion 74a which can be seated on a valve seat 97, and a stem 74b connecting coaxially and integrally to the valve head portion 74a. The stem 74b is fitted for sliding movement in a guide cylinder 98 provided coaxially with the valve seat 97 in the cylinder head 39. Besides, a valve spring 99 which exerts a spring force for seating the valve head portion 74a on the valve seat 97 is provided between an upper end portion of the stem 74b which projects from the guide cylinder 98 and the cylinder head 39, and the intake side rocker arm 85 of the valve mechanism 76 is connected for interlocking operation to an upper end of the stem 74b. [0032] An inner end of the exhaust port 71 is disposed such that the center of the combustion chamber 45 is positioned between the inner end of the exhaust port 71 and the inner end of the intake port 70 on a diametrical line of the combustion chamber 45, and the exhaust valve 75 positioned at the inner end of the exhaust port 71 and having a valve head portion 75a to be seated on a valve seat (not shown) securely mounted on the cylinder head 39 is supported for opening and closing movement in a guide cylinder (not shown) secured to the cylinder head 39 in a similar manner to the intake valve 74 is connected for interlocking operation to the exhaust side rocker arm 86 of the valve mechanism 76. [0033] Referring to FIG. 6, the intake port 70 is provided in the cylinder head 39 so that a swirl may be produced in the combustion chamber 45, and the pair of ignition plugs 49, 50 attached to the cylinder head 39 are set so that the heating value may become higher away from the intake port 70 along a flowing direction 101 of the swirl in the combustion chamber 45. In particular, the heating value of the ignition plug 49 located immediately on the downstream side of the intake port 70 along the flowing direction 101 is set lower than the heating value of the ignition plug 50 positioned farther away from the intake port 70 along the flowing direction 101, and in the present embodiment, the ignition plug 49 having a lower heating value is disposed on the upstream side of the exhaust port 71, that is, the exhaust valve 75, along the flowing direction 101, and the ignition plug 50 having a higher heating value is disposed on the downstream side of the exhaust port 71, that is, the exhaust valve 75, along the flowing direction 101. [0034] Besides, since the engine E is carried on the body frame 15 such that the axial line of the cylinder bore 44 thereof extends substantially horizontally and the intake port 70 is disposed at a side wall of an upper portion of the cylinder head 39, in the combustion chamber 45, the ignition plug 49 having a lower heating value is disposed immediately below the opening end of the intake port 70 to the combustion chamber 45, that is, the intake valve 74. [0035] By the way, the intake port 70 has such a shape that it produces a swirl in the combustion chamber 45, and is formed in such a shape on a projection drawing on a plane perpendicular to the axial line of the cylinder bore 44 that the intake port 70 has, as shown in FIG. 7, a first path portion 70a which extends in a tangential direction to the guide cylinder 98 on the outer side of the guide cylinder 98, and a tapering second path portion 70b contiguous to the first path portion 70a and curved in such a manner as to wind part of the guide cylinder 98. [0036] The first path portion 70a extends linearly in a tangential direction to the guide cylinder 98 perpendicularly to a straight line 102 which interconnects, for example, the center C1 of the combustion chamber 45 and the center C2 of the guide cylinder 98. The second path portion 70b is formed in such a curved shape that it winds part of the guide cylinder 98 without intersecting with the straight line 102 on the projection drawing mentioned above. [0037] Referring also to FIG. 8, on the cylinder head 39, an opposing wall 39a (indicated by slanting lines in FIG. 7) which covers the valve head portion 74a of the intake valve 74 and the valve seat 97 except a portion which overlaps with the first and second path portions 70a, 70b of the intake port 70 is provided in an opposing relationship to part of the valve head portion 74a and the valve seat 97. In particular, a portion of the valve seat 97 which is disposed in the form of a ring at the inner end of the intake port 70 functions as a substantial intake valve opening 103, and the intake valve opening 103 which is a region other than the portion of the valve seat 97 which is covered with the opposing wall 39a is opened when the intake valve 74 is opened. [0038] An inner side face of the intake port 70 at a portion corresponding to an inner side outer profile line which defines the second path portion 70b is formed from a vertical wall 39b (refer to FIG. 5) provided on the cylinder head 39 perpendicularly to the opposing wall 39a. [0039] Now, operation of the present embodiment is described. The intake port 70 on the projection drawing on the plane perpendicular to the axial line of the cylinder bore 44 is formed in a shape which has the first path portion 70a extending in a tangential direction to the guide cylinder 98 on the outer side of the guide cylinder 98 and the tapering second path portion 70b contiguous to the first path portion 70a and curved in such a manner as to wind part of the guide cylinder 98, and the valve head portion 74a of the intake valve 74 and the valve seat 97 are covered with the opposing wall 39a of the cylinder head 39 except the portion which overlaps with the first and second path portions 70a, 70b on the projection drawing. [0040] Accordingly, air fuel mixture having been introduced by the intake port 70 is taken into the combustion chamber 45 in such a manner that it winds part of the outer periphery of the stem 74b provided on the intake valve 74, but the air fuel mixture is not whirled in the intake port 70. Therefore, the air fuel mixture can be introduced into the combustion chamber 45 while preventing a drop of the flow rate, and a strong swirl can be formed in the combustion chamber 45. Besides, since the intake port 70 is required only to be shaped so as to pass air fuel mixture smoothly therethrough, the path resistance in the intake port 70 can be suppressed low. [0041] Further, since the cylinder head 39 which forms a wall at an end of the second path portion 70b on the projection drawing mentioned hereinabove is formed in a shape wherein it does not intersect with the straight line 102 which interconnects the center CI of the combustion chamber 45 and the center C2 of the guide cylinder 98, production of a flow of air fuel mixture which flows from the intake port 70 into the combustion chamber 45 in a direction opposite to that of a swirl flow produced in the combustion chamber 45 can be prevented with certainty. Consequently, the swirl in the combustion chamber 45 can be made further strong. [0042] Furthermore, since the inner side face of the intake port 70 at the portion corresponding to the inner side outer profile line of the second path portion 70b is formed from the vertical wall 39b provided on the cylinder head 39 perpendicularly to the opposing wall 39a, the intake port 70 can be inclined so that the intake range of air fuel mixture into the combustion chamber 45 is defined accurately and the angle with respect to the plane perpendicular to the cylinder axial line may be smaller, and consequently, the swirl flow in the combustion chamber 45 can be made further strong. [0043] By the way, while a plurality of, for example, a pair of ignition plugs 49, 50 are attached to the cylinder head 39 in such a manner as to be exposed to the combustion chamber 45 in a free space other than the intake valve 74 and the exhaust valve 75 in order to achieve reduction of the fuel cost and augmentation of the character of exhaust gas, the heating values of the ignition plugs 49, 50 are set different from each other, and the heating value of the ignition plug 49 which is positioned nearer to the intake port 70 along the flowing direction 101 of the swirl in the combustion chamber 45 is set lower than the heating value of the ignition plug 50 which is positioned farther from the intake port 70. [0044] In particular, while the heating value of the ignition plug 50 which is exposed to combustion gas of a comparatively high temperature by combustion of air fuel mixture which has become comparatively lean as a result of progress of evaporation and diffusion of the air fuel mixture in the combustion chamber 45 is set comparatively high, the heating value of the ignition plug 49 which may possibly be cooled by contact with comparatively rich air fuel mixture introduced into the combustion chamber 45 from the intake port 70 is set comparatively low. Consequently, occurrence of failure in ignition at the ignition plug 49 by smoking can be prevented. [0045] Further, since the engine body 37 is carried on the body frame 15 in a posture wherein the cylinder axial line extends substantially horizontally and the intake port 70 is provided in the cylinder head 39 in such a manner that it is opened in the combustion chamber 45 above the ignition plug 49 at which the heating value is lowest, even if fuel running along the inner face of a lower portion of the intake port 70 without being atomized flows into the combustion chamber 45, since the heating value of the ignition plug 49 with which the fuel may possibly contact is lowest between the ignition plugs 49, 50, occurrence of smoking by contact with the fuel which is not in an atomized state can be prevented, and occurrence of failure in firing by smoking at the ignition plug 49 can be prevented. [0046] While an embodiment of the present invention is described above, the present invention is not limited to the embodiment described above, and various design alterations can be made without departing from the spirit of the present invention as set forth in the claims. [0047] For example, while, in the embodiment described above, the intake port 70 provided in the cylinder head 39 is formed as a swirl port in order to produce a swirl in the combustion chamber 45, the present invention can be applied widely to any engine wherein an intake air flow is introduced into the combustion chamber 45 in a deviated state irrespective of the shape of the intake port, and the heating value of a plurality of ignition plugs should be set along a flow of intake air. [0048] [Effect of the Invention] As described above, according to the invention as set forth in claim 1, even if the ignition plug is cooled by contact with air fuel mixture having flowed into the combustion chamber from the intake port, occurrence of smoking is prevented and occurrence of failure in ignition by smoking can be prevented. [0049] Further, according to the invention as set forth in claim 2, even if fuel which runs along an inner face of a lower portion of the intake port without being atomized flows into the combustion chamber, occurrence of smoking at the ignition plug which may possibly contact with the fuel is prevented, and occurrence of failure in firing by smoking can be prevented. We Claim: 1. A spark ignition 4-stroke engine wherein a plurality of ignition plugs (49, 50) which are faced with one combustion chamber (45) being mounted in a cylinder head (39), an intake port (70) being disposed in said cylinder head (39) for making a swirl generate in said combustion chamber (45), characterized in that the intake port (70) is on the plane perpendicular to the axial line of the cylinder bore (44) and is formed in a shape which has the first path portion (70a) extending in a tangential direction to the guide cylinder (98) on the outer side of the guide cylinder (98) and the tapering second path portion (70b) contiguous to the first path portion (70a) and curved in such a manner as to wind part of the guide cylinder (98), and the valve head portion (74a) of the intake valve (74) and the valve seat (97) are covered with the opposing wall (39a) of the cylinder head (39) except the portion which overlaps with the first and second path portions (70a, 70b), wherein the calorific value of the ignition plugs (49, 50) mounted in the cylinder head (39) becomes higher while leaving said intake port (70) along the flow direction of the swirl in said combustion chamber (45). 2. A spark ignition 4-stroke as claimed in claim 1, wherein said cylinder head (39) joining to a cylinder block (38) with a generally horizontal cylinder axis, the intake port (70) that opens towards the combustion chamber (45) being disposed above the ignition plug (49) whose calorific value is the lowest in said cylinder head (39).

Documents:

678-mum-2001-abstract(24-10-2006).pdf

678-mum-2001-abstract(8-5-2006).pdf

678-mum-2001-abstract(granted)-(6-3-2007).pdf

678-mum-2001-affidavit(24-10-2006).pdf

678-mum-2001-cancelled pages(24-10-2006).pdf

678-mum-2001-claims(complete)-(17-7-2001).pdf

678-mum-2001-claims(granted)-(24-10-2006).doc

678-mum-2001-claims(granted)-(24-10-2006).pdf

678-mum-2001-claims(granted)-(6-3-2007).pdf

678-MUM-2001-CORRESPONDENCE(15-2-2010).pdf

678-mum-2001-correspondence(30-10-2006).pdf

678-mum-2001-correspondence(ipo)-(23-4-2007).pdf

678-mum-2001-correspondence(ipo)-(24-7-2006).pdf

678-mum-2001-description(complete)-(17-7-2001).pdf

678-mum-2001-description(granted)-(6-3-2007).pdf

678-mum-2001-drawing(complete)-(17-7-2001).pdf

678-mum-2001-drawing(granted)-(6-3-2007).pdf

678-mum-2001-drawings(24-10-2006).pdf

678-mum-2001-form 1(17-7-2001).pdf

678-mum-2001-form 1(24-10-2006).pdf

678-mum-2001-form 1(8-5-2006).pdf

678-mum-2001-form 18(14-6-2005).pdf

678-mum-2001-form 2(complete)-(17-7-2001).pdf

678-mum-2001-form 2(granted)-(24-10-2006).doc

678-mum-2001-form 2(granted)-(24-10-2006).pdf

678-mum-2001-form 2(granted)-(6-3-2007).pdf

678-mum-2001-form 2(title page)-(complete)-(17-7-2001).pdf

678-mum-2001-form 2(title page)-(granted)-(6-3-2007).pdf

678-mum-2001-form 3(17-7-2001).pdf

678-mum-2001-form 3(5-5-2006).pdf

678-mum-2001-form 4(26-4-2006).pdf

678-mum-2001-form 5(17-7-2001).pdf

678-mum-2001-mareked copy(8-5-2006).pdf

678-mum-2001-petition under rule 137(8-5-2006).pdf

678-mum-2001-petition under rule 138(8-5-2006).pdf

678-mum-2001-power of authority(30-10-2006).pdf

678-mum-2001-power of authority(31-10-2001).pdf

678-mum-2001-power of authority(8-5-2006).pdf

678-mum-2001-specification(amanded)-(24-10-2006).pdf

678-mum-2001-specification(amanded)-(8-5-2006).pdf

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