Title of Invention	AN INTERNAL COMBUSTION ENGINE WITH IMPROVED CRANK CHAIN
Abstract	To improve thermal efficiency in an internal combustion ,engine by reducing a distance between a crank portion and a piston, increasing the speed of behavior of the piston at a position near a top dead center to reduce thermal energy loss, and preventing generation of knocking. [Means for Resolution] In an internal combustion engine including: a connecting rod 2 that connects a crankpin 1a and a piston P1 having first and second connecting rods 21, 22, and a guide piston P2 disposed at a connecting portion between the first and second connecting rods 21,22, deformed portions P2c1, 1d2, which are removed portions or cut out portions, are formed on a lower end portion of a guide piston P2 and a balancer weight portion 1d of a crankshaft 1 in order to reduce the whole length of the connecting rod 2, whereby a bottom dead center of the guide piston P2 is set to the lower position.

Title of Invention

AN INTERNAL COMBUSTION ENGINE WITH IMPROVED CRANK CHAIN

Abstract

To improve thermal efficiency in an internal combustion ,engine by reducing a distance between a crank portion and a piston, increasing the speed of behavior of the piston at a position near a top dead center to reduce thermal energy loss, and preventing generation of knocking. [Means for Resolution] In an internal combustion engine including: a connecting rod 2 that connects a crankpin 1a and a piston P1 having first and second connecting rods 21, 22, and a guide piston P2 disposed at a connecting portion between the first and second connecting rods 21,22, deformed portions P2c1, 1d2, which are removed portions or cut out portions, are formed on a lower end portion of a guide piston P2 and a balancer weight portion 1d of a crankshaft 1 in order to reduce the whole length of the connecting rod 2, whereby a bottom dead center of the guide piston P2 is set to the lower position.

Full Text	[Designation of Document] Specification [Title of the Invention] INTERNAL COMBUSTION ENGINE [Technical Field] [0001] The present invention relates to an improved structure for achieving improvement of thermal efficiency and prevention of knocking in an internal combustion engine and, more specifically, to a structure focused on an improvement of a crank chain in the internal combustion engine. [Background Art] [0002] A crank chain in which efficiency of a crank movement is improved by reducing friction due to a side pressure applied to a piston from an inner wall of a cylinder bore in the crank movement of the crank chain in an internal combustion engine is known in the related art, and a structure in which a detailed remedial measure is taken such that the side pressure to the inner wall of the cylinder bore applied to the piston is reduced by employing a two-piece connecting rod including first and second connecting rods and a guide member at a joint portion thereof and bringing a rolling member provided at the guide member into rolling contact with the inner wall of the cylinder bore to reduce the side pressure applied to the inner wall of the cylinder bore, which is applied in turn to the piston is known. (For example, see Patent Documents 1 and 2). [Patent Document 1] Microfilm in Japanese Utility Model Application No. 60-63357 (JP-UM-A-61-179341) (pp.1, Fig. 1) [Patent Document 2] JP-A-8-303254 (pp.4-5, Fig. 1) [Disclosure of the Invention] [Problems that the Invention is to Solve] [0003] Both of crank chains in engines in Patent Documents 1 and 2 each are provided with a two-piece connecting rod 02 having first and second connecting rods 021, 022, and the first connecting rod 021 which is connected at one end 021a thereof to a crankpin Ola of a crankshaft 01 is connected at the other end 021b thereof to a sliding member 0P2 provided with a rolling member 0P21 such as a roller bearing or a wheel to be guided by an inner wall of a cylinder bore 020a in contact thereto, and the second connecting rod 022 which is connected at one end 022a thereof to the sliding member 0P2 is mounted to and holds a piston (slide runner) 0P1 at the other end 022b thereof, whereby a structure provided with the connecting rod 02 as a single member including the first connecting rod 021 and the second connecting rod 022 connected to each other via the sliding member 0P2 is achieved. [0004] The crank chain is adapted to reduce friction by receiving a side pressure applied to the inner wall of the cylinder bore 020a due to the operation of the first connecting rod 021 at the time of a crank movement by the sliding member 0P2 provided with the rolling member 0P21 such as the smoothly rotating roller bearing or the wheel and reducing the side pressure to the inner wall of the cylinder bore 020a received by the piston 0P1 mounted to the second connecting rod 022, so that energy loss due to the friction or the like during the crank movement is reduced by enabling smoothening of reciprocal sliding movement between the piston 0P1 and the inner wall of the cylinder bore 020a, whereby improvement of efficiency of the engine is achieved. [0005] The crank chains are each provided with the two-piece piston connecting rod including the first and second connecting rods as described above, and structurally, a distance between a crank web portion and the piston is relatively long, and hence the first connecting rod is relatively long. [0006] Regarding a behavior of the piston in the crank chain, the structure in which the connecting rod (con-rod) for connecting the crankpin and piston is long is not suitable for increasing the speed of the piston, in particular, of the behavior of the piston near a top dead center. [0007] Delay of the piston behavior leads to thermal energy loss by an amount corresponding to an excessive time due to the delay of the piston behavior, and in particular, in a quick combustion engine which requires a quick piston behavior, the engine structure in which the length of the piston connecting rod is long as described above can hardly be employed. [0008] Therefore, a crank chain in which the quick piston behavior near the top dead center of the piston is achieved during the crank movement is required. [Means for Solving the Problems] [0009] In order to solve the above-described problems, the present invention relates to a provision of an internal combustion engine focusing on an improvement of a crank chain. The invention according to Claim 1 is an internal combustion engine including a crankshaft having disk-shaped flywheels on both sides of a crankpin, and a connecting rod connected at a large end portion at one end thereof to the crankpin of the crankshaft and at a small end portion at the other end thereof to a piston which slides in a cylinder bore via a piston pin, characterized in that the disk-shaped flywheels are cut out at part of an outer peripheral portion thereof on a side opposite from the crankpin so that the crankshaft is located in proximity of the piston pin. [0010] In the internal combustion engine according to Claim 1, the invention according to Claim 2 is characterized in that plugs with a high specific gravity are provided on the flywheels on the side opposite from the crankpin. [0011] In the internal combustion engine according to Claim 1 or Claim 2, the invention according to Claim 3 is characterized in that an axial line passing through a center of the cylinder bore is arranged at a position shifted toward one side with respect to an axial line passing through a rotation center of the crankshaft, and a skirt portion of the piston which is guided by an inner wall of the cylinder bore in contact with the inner wall of the cylinder bore is formed largely on the one side. [0012] The invention according to Claim 4 is an internal combustion engine including a crankshaft having disk-shaped flywheels on both sides of a crankpin, and a connecting rod connected at a large end portion at one end thereof to the crankpin of the crankshaft and at a small end portion at the other end thereof to a piston which slides in a cylinder bore via a piston pin, characterized in that a distance between the disk-shaped flywheels on both sides of the crankpin is larger than the width of the piston pin, and both ends of the piston pin are positioned on side surfaces of the disk-shaped flywheels. [0013] In the internal combustion engine according to Claim 4, the invention according to Claim 5 is characterized in that the disk-shaped flywheels are formed to be wider on a side opposite from the crankpin in comparison with a crankpin side. [Advantage of the Invention] [0014] The invention according to Claim 1 is configured in such a manner that, in the internal combustion engine described above, the disk-shaped flywheels are cut out at the part of the outer peripheral portion thereof on the side opposite from the crankpin so that the crankshaft is located in proximity of the piston pin. Therefore, the length of the connecting rod can be reduced to increase the speed of the piston at a position near a top dead center, and heat released through the cylinder wall surface due to increase in piston speed can be minimized to effectively prevent lowering of a combustion pressure. [0015] In the invention according to Claim 1, the invention according to Claim 2 is configured in such a manner that the plugs with a high specific gravity are provided on the flywheels on the side opposite from the crankpin. Therefore, the inertia mass can be secured sufficiently even when the weight of the portion opposite from the crankpin is increased in comparison with the weight of the piston on the crankpin side and the connecting rod and the cutout on the outer peripheral portion of the flywheel on the side opposite from the crankpin is increased, and the piston speed at the position near the top dead center of the piston can further be increased by reducing the length of the connecting rod in comparison with a crank radius owing to the cutout of the flywheel on the side opposite from the crankpin, whereby a cooling loss to the cylinder wall surface is reduced, thereby improving a thermal efficiency. [0016] In the invention according to Claim 1 or Claim 2, the invention according to Claim 3 is configured in such a manner that the axial line passing through the center of the cylinder bore is arranged at the position shifted toward one side with respect to the axial line passing through the rotation center of the crankshaft, and the skirt portion of the piston which is guided by the inner wall of the cylinder bore in contact with the inner wall of the cylinder bore is formed largely on the one side. Therefore, the skirt portion on the side opposite from the offset side can be downsized by the offset, and hence the piston pin portion can be provided at a position closer to the crankshaft. [0017] In the internal combustion engine described above, the invention according to Claim 4 is configured in such a manner that the distance between the disk-shaped flywheels on both sides of the crankpin is larger than the width of the piston pin, and both ends of the piston pin are positioned on the side surfaces of the disk-shaped flywheels. Therefore, the length of the connecting rod can be reduced so that the piston speed at the position near the top dead center is increased, whereby the thermal energy released through the wall surface of the combustion chamber can be minimized to prevent lowering of the combustion pressure effectively. [0018] In the invention according to Claim 4, the invention according to Claim 5 is configured in such a manner that the disk-shaped flywheels are formed to be wider on the side opposite from the crankpin in comparison with the crankpin side. Therefore, the inertia mass of the flywheels can be secured while downsizing the crankpin portion, whereby the crankshaft can be downsized. [Best Mode for Carrying Out the Invention] [0019] An embodiment of the present invention shown in Fig. 1 to Fig. 7 will be described below. [0020] Figs. 1 and 2 show cross-sections of a principal structure of an internal combustion engine E according to a first embodiment, in which a structure of the internal combustion engine E including a crankcase 10, a cylinder block 20 to be connected to an upper portion in the drawing of the crankcase 10, a cylinder head 30 to be connected to the upper portion in the drawing of the cylinder block 20, and a head cover 40 for covering an upper portion of the cylinder head 30 is shown. [0021] As shown in Fig. 1, the crankcase 10 includes left and right half cases 10a, 10b, and case covers 10c, lOd for covering openings of the left and right half cases 10a, 10b, and a crankshaft 1 is rotatably supported in the crankcase 10 via a bearing. The bearing support of the crankshaft 1 in the crankcase 10 is achieved by support of the crankshaft 1 by two main bearings 11, 12 on the left and right half cases 10a, 10b at both sides of a crank portion and a bearing 13 at a right shaft end of the crankshaft 1 on the right case cover lOd of the right half case 10b. [0022] The support by the main bearings 11, 12 at both sides of the crank portion of the crankshaft on the left and right half cases 10a, 10b is such that the main bearing 11 on the left side is a radial ball bearing and the main bearing 12 on the right side is a roll bearing. The support by the bearing 13 on the case cover lOd of the right half case 10b on the right shaft end of the crankshaft 1 is achieved by a relatively small ball bearing which is fitted to an inner wall boss portion 10d2 on an outer wall structure lOdl of the case cover lOd. [0023] The cylinder block 20 is provided with a cylinder bore 20a which penetrates therethrough in the vertical direction in the drawing and, as shown in Fig. 2, the cylinder bore 20a is removed 20a2 in an arcuate shape in such a manner that a lower end 20al of a wall forming a left side in the drawing is cut out obliquely upward from a right side because it is close to the crank portion described later to form a short lower-side-forming wall 20a3. A piston PI performs a reciprocal sliding movement in the cylinder bore 20a as well known, and a guide piston P2 described later performs a reciprocal sliding movement. The cylinder block 20 is formed with a through space 20b (see Fig. 1) for allowing passage of a timing chain Tc for transmitting the rotation of the crankshaft 1 to a camshaft 30g via a sprocket le on the shaft 1. [0024] The cylinder head 30 is provided with a combustion chamber 30a defined by a recess on a lower portion thereof and an upper portion of the cylinder bore 20a, and an ignition plug, not shown, an opening 30b for air intake and exhaust, an air intake and exhaust valve 30c and so on are provided in the combustion chamber 30a, An intake and exhaust channel 30d and a mounting hole 30e for a valve stem are disposed in the cylinder head 30, and a valve mechanism including a cam 30f, a camshaft 30g, a rocker arm 30h, and so on is arranged upwardly thereof. The exposed upper portion thereof is covered by the head cover 40. [0025] As described above, the crankshaft 1 is rotatably supported by the bearing on the crankcase 10, and the relation between the crankshaft 1 and the cylinder bore 20a is such that a center axis X of the cylinder bore 20a is offset D to the right side in the drawing with respect to a rotation center 0 of the crankshaft 1 as will be understood from a side view of the engine shown in Fig. 2, whereby the side pressure from the piston PI or the guide piston P2 applied to an inner wall 20a4 of the cylinder bore is alleviated in relation to the connecting rod 2. [0026] The crankshaft 1 is provided with a single crankpin la and a pair of crank arm portions lb, lb on both sides of the crankpin la are provided with crank web portions lc, lc that continue to the arm portions lb, lb, respectively. The crank arm portions lb, lb and the crank web portions lc, lc integrated into substantially circular shape in side view in Fig. 2, and form flywheels F, F which are inertia mass members presenting substantially a disk shape having crank arm portions lb, lb on the crankpin la side which corresponds to the lower portion of the substantially circular shape, and crank web portions lc, lc on the side opposite from the crankpin la which corresponds to the upper portion in the drawing, [0027] The disk-shaped flywheels F, F are provided with balancer weight portions Id, Id of semi-circular like shape formed by increasing the thickness of the crank web portions lc, lc on the side opposite from the crankpin la, that is, on the side of the web portions, and the balancer weight portions Id, Id are formed to have characteristic outlines describe later. Accordingly, the balancer weight portions Id, Id of the crankshaft 1, which is offset D from the center line X of the cylinder bore 20a, on the side opposite from the crankpin can be provided at a position closer to the guide pin P2 having a deformed portion, describe later, which performs a reciprocal sliding movement in the cylinder bore 20a on the lower side, or to the deformed lower-side-forming wall 20a2, described above, of the cylinder bore 20a. [0028] In other words, the balancer weight portions Id, Id located on the disk-shaped flywheels F, F on the opposite side of the crankpin la are, as shown in Fig. 2, formed into a semi-circular like shape in side view defined by an outline including a pair of outline portions ldl, ldl positioned so as to lay along arcuate portions ld3 of the outlines of the disk-shaped flywheels F, F, and an outline portion ld2 with part of the arcuate portion ld3 interposed between the pair of outline portions ldl, ldl removed along a curve, whereby the balancer weight portions Id, Id can be provided at positions closer to the guide piston P2 provided with the deformed portion and the deformed lower-side-forming wall 20a2 of the cylinder bore 2 0a described above by an amount corresponding to the removed (cut out) portion. [0029] A connecting rod 2 is connected to the single crankpin la of the crankshaft 1, and the connecting rod 2 has a two-piece structure including a first connecting rod 21 and a second connecting rod 22. The first connecting rod 21 is rotatably connected to the crankpin la at one end, that is, at an end portion 21a which practically constitutes a large end portion of the connecting rod 2, and is rotatably connected to the above-described guide piston P2 at the other end 21b via a pin portion P2a which passes through a center portion of a main body, formed of sliding arms P2c, P2c extending on the left and right sides of the guide piston P2 in Fig. 2. [0030] The second connecting rod 22 of the connecting rod 2 is connected to and hence holds the above-describe piston PI which is supported so as to be capable of pivotal movement via a piston pin Pla and performs reciprocal sliding movement in the cylinder bore 20a at the other end 22b, that is, at the end portion 22b which practically constitutes a small end portion of the connecting rod 2, and the one end 22a is rotatably connected to the pin portion P2a of the guide piston P2 . The second connecting rod 22 characteristically has a relatively short structure. [0031] The guide piston P2 which performs the reciprocal sliding movement on a lower side in the cylinder bore 20a connects the first and second connecting rods 21, 22 as the two-piece connecting rod with respect to each other via the pin portion P2a by rotatably connecting and supporting the other end 21b of the first connecting rod 21 and the one end 22a of the second connecting rod 22 with the pin portion P2a of a guide piston P2a, whereby the connected body of the both connecting rods 21, 22, that is, the single connecting rod 2 is formed. [0032] The pin portion P2a of the guide piston P2 extends so as to pass through the center portion of the main body including the sliding arms P2c, P2c of the guide piston P2 extending in the lateral direction, that is, extends so as to be orthogonal to the extending direction of the sliding arms P2c, P2c and in parallel with the crankshaft 1, and both pin ends P2b, P2b (see Fig. 1) are fixed to the main body portion of the guide piston P2 so as not to rotate. The one end 22a of the second connecting rod 22 is rotatably connected and supported at the center portion of the pin portion P2a in the longitudinal direction as described above, and the other end 21b of the first connecting rod 21 is rotatably connected and supported as described above so as to sandwich the one end 22a of the second connecting rod 22 with its bifurcated branched end 21bl from both sides. [0033] The sliding arms P2c, P2c that form the main body of the guide piston P2 and extend in the left and right sides so as to pass across the cylinder bore 20a in Fig. 2, that is, the sliding arms P2c, P2c extending in the direction orthogonal to the crankshaft 1 are provided with sliding surfaces P2d, P2d which come into sliding contact with the inner wall of the cylinder bore 20a at the distal ends thereof, and the sliding surfaces P2d, P2d are provided with arcuate surfaces that extend along the inner wall of the cylinder bore 20a which is rather wide in the vertical and lateral direction. [0034] The guide piston P2 also has a structure which allows positioning of the crankshaft 1 at a position closer to the crank portion, that is, positioning of the crankshaft 1 at a position closer to the crank portion in the state in which the center line X of the cylinder bore 20a is offset toward the right side in the drawing by the amount D with respect to the rotation center axis 0 of the crankshaft 1, and the guide piston P2 is provided with the deformed portions on the sliding arms P2c, P2c and the sliding surfaces P2d, P2d, described later therefor. [0035] In other words, more specifically, the deformed portions on the sliding arms P2c, P2c and the sliding surfaces P2d, P2d that define the main body of the guide piston P2 respectively are portions formed into the deformed portions processed to have complementary shape that avoids contact therebetween at the positions closest to each other in the crank movement in order to achieve reduction in distance between the guide piston P2 and the balancer weight portions Id, Id of the flywheels F, F that are crank portions of the crankshaft 1 whose center line of the cylinder bore is offset D in cooperation with the deformed portions of the balancer weight portions Id, Id having the characteristic outlines, that is, in cooperation with the deformed portion having the outline ld2 with the portion of the arcuate portion ld3 linearly removed. [0036] Therefore, the arm P2c on the right side in Fig. 2 of the sliding arms P2c, P2c is not deformed specifically, and only the lower portion, that is, the side which is provided at a position closer to the crank portion, of the left arm P2c is removed P2cl so as to be cut off P2cl obliquely upwardly from the right side to the left side, and the sliding surfaces P2d, P2d of distal ends of the pair of sliding arms P2c, P2c are slightly large in the vertical and lateral directions as described above and include arcuate surfaces extending along the inner wall of the cylinder bore 20a. However, the sliding surface P2d on the left side in Fig. 2 has a smaller width in comparison with the sliding surface P2d on the right side in the vertical direction with cutting a lower skirt portion thereof. [0037] The removal structure of the sliding arm P2c and the sliding surface P2d of the guide piston P2 enables closer positional relation between the guide piston P2 and the lower end 20al of the cylinder bore with respect to the balancer weight portions Id, Id in cooperation with the arcuate shaped removal of the lower end 20al of the cylinder bore and the lower-side-forming wall 20a2, and the deformed portions having the characteristic outlines of the balancer weight portions Id, Id of the crankshaft 1 whose center line X of the cylinder bore 20a is offset D, whereby the shorter structure of the first connecting rod 21 is achieved, and in corporation with the short structure of the second connecting rod 22, the close structure between the balancer weight portions Id, Id of the flywheels F, F and the piston PI is achieved. [0038] The outline of the structure of the engine E and the structure of the crank chain is as described above. Here, advantage in structure of the crank chain in this embodiment will be described briefly in conjunction with the operation thereof. [0039] As will be understood from Fig. 1 and Fig. 2, the guide piston P2 and the balancer weight portions Id, Id of the disk-shaped flywheels F, F on both sides of the crankpin la of the crankshaft 1 of this embodiment enable reduction in distance therebetween in cooperation with the complementary deformed portion in the crank movement, and the length of the first connecting rod 21 is reduced. Since the second connecting rod 22 is formed to have a length as short as possible, the short connecting rod 2 which is short as a whole is obtained, thereby achieving the structure in which the distance between the balancer weight portions Id, Id of the disk-shaped flywheels F, F of the crankshaft 1 with respect to the piston PI is reduced. [0040] In conclusion, the reduction in length of the first connecting rod 21 enables achievement of high speed and acceleration of the reciprocal sliding movement of the guide piston P2 in the cylinder bore 20a during the crank movement, and the increased high speed and acceleration of the guide piston P2 enable high speed and acceleration of reciprocal sliding movement of the piston PI, whereby the speed of the behavior of the piston PI is increased to efficiently promote conversion from the thermal energy into the practice, more specifically, to a kinetic energy of the piston PI, thereby improving the efficiency of recovery of the combustion energy to improve the thermal efficiency and preventing occurrence of knocking by preventing excessive heating of a wall portion of a combustion chamber by the thermal energy. [0041] As a second embodiment of the present invention, a mode shown in Figs. 3 and 4 is conceivable. The internal combustion engine E in this embodiment is common to the engine E in the first embodiment described above in most part of the structure (the corresponding structures are represented by the same reference numerals) . However, the crankshaft 1 and the structures related thereto are different in structure. [0042] The crankshaft 1 is provided with the single crankpin la, and the crankpin la is provided with the first and second connecting rods 21, 22 as in the case of the first embodiment described above and the piston PI is mounted thereto via the guide piston P2 . Since the structures of these members as a whole and the structures of the piston PI and the guide piston P2 themselves are not specifically different from the first embodiment described above, description about the structures of these members are omitted. [0043] The crankshaft 1 is provided with the single crankpin la, and the pair of crank arm portions lb, lb and the crank web portions lc, lc continuing to the arm portions lb, lb on both sides of the crankpin la are formed integrally to form the flywheels F, F which are the substantially integral inertia mass members each presenting a circular shape in side view shown in a perspective view in Fig. 4. [0044] Therefore, the crank arm portions lb, lb are formed on the crankpin la side of the disk-shaped flywheels F, F and the crank web portions lc, lc are formed thereon on the side apart from the crankpin la on the opposite side. The crank web portions lc, lc are substantially the balancer weight portions Id, Id. The balancer weight portions Id, Id of the disk-shaped flywheels F, F are formed by increasing the thickness of the crank web portions lc, lc of the flywheels F, F, and formed into a shape similar to a half moon as shown in Fig. 8. [0045] As will be understood from Fig. 3, the disk-shaped flywheels F, F are provided with opposing surfaces Fl, Fl facing inwardly thereof which constitutes a pair formed on both sides of the crankpin la. A distance Dl between the opposing surfaces Fl, Fl is relatively narrow on the crankpin la side, and a distance D2 between these surfaces increase on the side opposite from the crankpin la, that is, on the side where the balancer weight portions Id, Id are formed. Therefore, although the flywheels F, F formed into a disk shape have a substantially circular shape in side view, they have shaped shifted from each other with shoulders in the direction of the thickness. [0046] The larger distance D2 between the surfaces Fl, Fl of the disk-shaped flywheels F, F opposed to each other in pair on the side opposite from the crankpin la is larger than the length L of the pin portion P2a having the extending length over the substantially entire lateral width of the guide piston P2, whereby the opposed surfaces Fl, Fl of the pair of disk-shaped flywheels F, F can receive the guide piston P2 moved downward to the bottom dead center or near the bottom dead center (a state shown in Fig, 3) in the crank movement within the larger surface distance D2 with a predetermined clearance. [0047] In practice, the reception of the guide piston P2 between the pair of opposed surfaces Fl, Fl of the flywheels allows entry of the guide piston P2 to a position between the inner surfaces of the balancer weight portions Id, Id of the flywheels F, F shown in Fig. 3 along both side surface portions P2e, P2e of the guide piston P2 in the lateral direction, that is, along the both pin ends P2b, P2b of the pin portion P2a of the guide piston P2. [0048] Therefore, outer peripheral ends IdO, IdO of the balancer weight portions Id, Id enter while rotating along the side surface portions P2e, P2e of the guide piston when the guide piston P2 is moved downward to the bottom dead center or near the bottom dead center in the rotation of the crank movement and, in this process, reach to a position nearest to the lower end 20al of the cylinder wall in the cylinder bore 20a. [0049] The structure of the ends of the opposed surfaces Fl, Fl, that is, the outer peripheral ends IdO, IdO of the balancer weight portions Id, Id that allows entry of the guide piston P2 along the side surface portions P2e, P2e in the width direction thereof on the basis of the wide structure between the opposed surfaces Fl, Fl of the pair of disk-shaped flywheels F, F on the side opposite from the crankpin la achieves positioning of the guide piston P2 closer to the crank portion without necessity of specific deformation of the guide piston P2 and the balancer weight portions Id, Id of the flywheels F, F, and consequently, achieves positioning of the piston PI closer to the crank portion, thereby realizing reduction in length of the connecting rod 21. [0050] Since the embodiments of the invention are configured as described above, the following effects and advantages are achieved. [0051] As the effects and advantages common to the first and second embodiments, the crankpin la and the piston PI are connected by the short connecting rod 21, and hence the speed of behavior of the piston PI near the top dead center of the piston PI can be increased. By increasing the behavior of the piston PI, conversion from the thermal energy to the practice is quickly achieved, which reduces energy loss correspondingly. Since the excessive heating of the wall portion of the combustion chamber of the thermal energy is constrained, generation of knocking is effectively prevented. Therefore, an optimal engine structure is provided in the application to the quick combustion engine. [0052] In the first embodiment, the balancer weight portions Id, Id of the flywheels F, F and the guide piston P2 are respectively provided with the deformed portions that are formed into complementary shapes to allow reduction of the distance therebetween in the crank movement. Therefore, the structure in which the length of the connecting rod 21 is reduced can be employed, whereby the speed and the acceleration of the piston PI can be increased to achieve quick conversion from the thermal energy into the practice. Consequently, reduction of the heat loss is achieved, and the excessive heating of the wall portion of the combustion chamber due to the thermal energy is constrained, whereby generation of knocking is effectively prevented. [0053] In the second embodiment, since the pair of disk-shaped flywheels F, F provided on both sides of the crankpin la oppose to each other in such a manner that the opposed surfaces Fl, Fl corresponding to the balancer weight portions Id, Id on the side opposite from the crankpin la at the large distance D2, the guide piston P2 which is moved to the bottom dead center in the crank movement is received between the opposed surfaces Fl, Fl with the clearance, the bottom dead center of the guide piston P2 can be set to a lower position correspondingly. [0054] As a consequence, the positioning of the piston PI closer to the crank portion is enabled, and the length of the connecting rod 21 can be reduced without providing specific deformation on the guide piston P2 and the balancer weight portions Id, Id of the flywheels F, F. [0055] Subsequently/ referring to Fig. 5 to Fig. 7, a third embodiment will be described. The internal combustion engine E in the third embodiment is significantly different in crank chain from the first and second embodiments and has a slight modification in a crankcase 50 and a cylinder block 60, but a cylinder head 70 is not modified. [0056] In other words, the axial length of the cylinder block 60 is reduced, the distance between a mating surface with respect to the crankcase 50 and a mating surface with respect to the cylinder head 70 is reduced, and the shape near the mating surface with respect to the crankcase 50 is modified. The crank chain in this embodiment is not provided with the guide piston, which is different from the first and second embodiments. [0057] A piston 80 which performs reciprocal sliding movement in a bore 60a of the cylinder block 60 is provided with a piston pin 83 laid across a pair of pin supporting arms 82, 82 projecting from a back surface of a piston crown portion 81 opposing to the combustion chamber. [0058] On the other hand, a crankshaft 90 rotatably supported at a journal portion 91 by main bearings 51, 52 on the crankcase 50 has an opposing pair of crank web portions 92, 92 of a specific shape. [0059] In other words, a counter weight portion 92w on the side opposite from the crankpin with respect to a rotation center of the crank web portion 92 is cut out on a circular outer peripheral portion of the crank web portion 92 having a largest diameter so that an outer peripheral edge 92wa is provided at a position closer to the center axis, and a crank arm portion 92a on the side of the crankpin has a shape projecting radially from the center portion. [0060] The crank web portion 92 has a symmetrical shape with respect to a straight line connecting a rotation center of the crankshaft 90 and a center of a crankpin 93. The opposed crank arm portions 92a, 92a are connected by the crankpin 93. [0061] Then, the counter weight portion 92w of the crank web portion 92 having the symmetrical shape has plugs 95, 95 of flat column shape embedded at symmetric positions. The plugs 95 are formed of tungsten or the like having a high specific gravity. [0062] A large end portion of a connecting rod 85 is supported by the crankpin 93 connecting the crank arm portions 92a, 92a so as to be capable of rotating about an axis thereof, and a small end portion is supported by the piston pin 83 laid across the pair of pin supporting arms 82, 82 of the piston 80 so as to be capable of rotating about an axis thereof, so that the crankshaft 90 and the piston 80 are connected by the connecting rod 85. [0063] In this crank chain, since the plugs 95 having the high specific gravity are embedded into the counter weight portion 92W of the crank web portion 92 on the opposite side of the crankpin, even thought the outer peripheral edge 92wa of the crank web portion 92 on the opposite side from the crankpin is moved largely toward the center axis, a sufficient counter weight (inertia mass) can be secured by the plugs 95, and since the crank web portion 92 does not interfere with the piston 80 even when the outer peripheral edge 92wa is moved largely toward the center axis, the length of the connecting rod 85 can be reduced. [0064] A ratio X (=L/r) of the length L of the connecting rod 85 (the length from the center of the crankpin to the center of the piston) with respect to a crank radius r (the distance from the rotation center of the crankshaft to the center of the crankpin) is 2. 0 or less, which is significantly small value in comparison with the normal value X = about 3.5. In other words, when the same crank radius r is employed, the length L of the connecting rod 85 can be reduced significantly with respect to the normal length, and hence the piston 80 can be provided at a position closer to the crank web portion 92, so that downsizing of the internal combustion engine E is achieved. [0065] As described above, since the ratio X is small value, the piston speed near the top dead center of the piston can further be increased, whereby the cooling loss to a cylinder wall surface is reduced, thereby improving heat efficiency. The inertia mass of the crank web portion 92 can also be secured sufficiently, so that reduction of vibrations is also achieved. [Brief Description of the Drawings] [0066] [Fig. 1] Fig 1 is a front cross-sectional view of an internal combustion engine showing a structure of a principal portion of a crank chain in the present invention. [Fig. 2] Fig. 2 is a side cross-sectional view of the internal combustion engine showing the structure of the principal portion of the crank chain in the present invention. [Fig. 3] Fig. 3 is a front cross-sectional view of the internal combustion engine showing the principal structure of the crank chain according to another embodiment of the present invention. [Fig. 4] Fig. 4 is a perspective view showing a balancer weight portion of a flywheel in Fig. 3. [Fig. 5] Fig. 5 is a front cross-sectional view of the internal combustion engine showing the structure of the principal portion of the crank chain according to still another third embodiment of the present invention in a state in which a piston is at a position near a top dead center. [Fig. 6] Fig. 6 is a side cross-sectional view of Fig. 5. [Fig. 7] Fig. 7 is a side cross-sectional view of the same when the piston is at the position near the top dead center. [Fig. 8] Fig. 8 is a drawing showing a crank chain in the related art. [Fig. 9] Fig. 9 is a drawing showing another example of the crank chain in the related art. [Description of Reference Numerals and Signs] [0067] 1. . .crankshaft, la...crankpin, lb...crank arm portion, lc...crank web portion, Id...balancer weight portion, 2. . .connecting rod, 21...first connecting rod, 21a...one end, 21b...the other end, 22...second connecting rod, 22a...one end, 22b...the other end, 10...crank case, 20...cylinder block, 20a... cylinder bore, 30...cylinder head, F...flywheel, Fl...opposed surface, PI. ..piston, P2...guide piston, P2a...pin portion, P2b...pin end, P2c...sliding arm, P2d...sliding surface, 50...crank case, 60...cylinder block, 70...cylinder head, 80...piston, 82...pin supporting arm, 83...piston pin, 85...connecting rod, 90...crankshaft, 92...crank web portion, 93...crankpin, 95...plug [Designation of Document] Claims [Claim 1] An internal combustion engine comprising: a crankshaft having disk-shaped flywheels on both sides of a crankpin; and a connecting rod connected at a large end portion at one end thereof to the crankpin of the crankshaft and at a small end portion at the other end thereof to a piston which slides in a cylinder bore via a piston pin, characterized in that the disk-shaped flywheels are cut out at part of an outer peripheral portion thereof on a side opposite from the crankpin so that the crankshaft is located in proximity of the piston pin. [Claim 2] The internal combustion engine according to Claim 1, characterized in that plugs with a high specific gravity are provided on the flywheels on the side opposite from the crankpin. [Claim 3] The internal combustion engine according to Claim 1 or Claim 2, characterized in that an axial line passing through a center of the cylinder bore is arranged at a position shifted toward one side with respect to an axial line passing through a rotation center of the crankshaft, and a skirt portion of the piston which is guided by an inner wall of the cylinder bore in contact with the inner wall of the cylinder bore is formed largely on the one side. [Claim 4] An internal combustion engine comprising: a crankshaft having disk-shaped flywheels on both sides of a crankpin; and a connecting rod connected at a large end portion at one end thereof to the crankpin of the crankshaft and at a small end portion at the other end thereof to a piston which slides in a cylinder bore via a piston pin, characterized in that a distance between the disk-shaped flywheels on both sides of the crankpin is larger than the width of the piston pin, and both ends of the piston pin are positioned on side surfaces of the disk-shaped flywheels. [Claim 5] The internal combustion engine according to Claim 4, characterized in that the disk-shaped flywheels are formed to be wider on a side opposite from the crankpin in comparison with a crankpin side.

Full Text

[Designation of Document] Specification
[Title of the Invention] INTERNAL COMBUSTION ENGINE
[Technical Field]
[0001]
The present invention relates to an improved structure for achieving improvement of thermal efficiency and prevention of knocking in an internal combustion engine and, more specifically, to a structure focused on an improvement of a crank chain in the internal combustion engine. [Background Art]
[0002]
A crank chain in which efficiency of a crank movement is improved by reducing friction due to a side pressure applied to a piston from an inner wall of a cylinder bore in the crank movement of the crank chain in an internal combustion engine is known in the related art, and a structure in which a detailed remedial measure is taken such that the side pressure to the inner wall of the cylinder bore applied to the piston is reduced by employing a two-piece connecting rod including first and second connecting rods and a guide member at a joint portion thereof and bringing a rolling member provided at the guide member into rolling contact with the inner wall of the cylinder bore to reduce the side pressure applied to the inner wall of the cylinder bore, which is applied in turn to the piston is known. (For example, see Patent Documents 1 and 2).

[Patent Document 1] Microfilm in Japanese Utility Model Application No. 60-63357 (JP-UM-A-61-179341) (pp.1, Fig. 1)
[Patent Document 2] JP-A-8-303254 (pp.4-5, Fig. 1) [Disclosure of the Invention] [Problems that the Invention is to Solve]
[0003]
Both of crank chains in engines in Patent Documents 1 and 2 each are provided with a two-piece connecting rod 02 having first and second connecting rods 021, 022, and the first connecting rod 021 which is connected at one end 021a thereof to a crankpin Ola of a crankshaft 01 is connected at the other end 021b thereof to a sliding member 0P2 provided with a rolling member 0P21 such as a roller bearing or a wheel to be guided by an inner wall of a cylinder bore 020a in contact thereto, and the second connecting rod 022 which is connected at one end 022a thereof to the sliding member 0P2 is mounted to and holds a piston (slide runner) 0P1 at the other end 022b thereof, whereby a structure provided with the connecting rod 02 as a single member including the first connecting rod 021 and the second connecting rod 022 connected to each other via the sliding member 0P2 is achieved.
[0004]
The crank chain is adapted to reduce friction by receiving a side pressure applied to the inner wall of the cylinder bore 020a due to the operation of the first connecting

rod 021 at the time of a crank movement by the sliding member 0P2 provided with the rolling member 0P21 such as the smoothly rotating roller bearing or the wheel and reducing the side pressure to the inner wall of the cylinder bore 020a received by the piston 0P1 mounted to the second connecting rod 022, so that energy loss due to the friction or the like during the crank movement is reduced by enabling smoothening of reciprocal sliding movement between the piston 0P1 and the inner wall of the cylinder bore 020a, whereby improvement of efficiency of the engine is achieved.
[0005]
The crank chains are each provided with the two-piece piston connecting rod including the first and second connecting rods as described above, and structurally, a distance between a crank web portion and the piston is relatively long, and hence the first connecting rod is relatively long.
[0006]
Regarding a behavior of the piston in the crank chain, the structure in which the connecting rod (con-rod) for connecting the crankpin and piston is long is not suitable for increasing the speed of the piston, in particular, of the behavior of the piston near a top dead center.
[0007]
Delay of the piston behavior leads to thermal energy loss by an amount corresponding to an excessive time due to the delay

of the piston behavior, and in particular, in a quick combustion engine which requires a quick piston behavior, the engine structure in which the length of the piston connecting rod is long as described above can hardly be employed.
[0008]
Therefore, a crank chain in which the quick piston behavior near the top dead center of the piston is achieved during the crank movement is required. [Means for Solving the Problems]
[0009]
In order to solve the above-described problems, the present invention relates to a provision of an internal combustion engine focusing on an improvement of a crank chain. The invention according to Claim 1 is an internal combustion engine including a crankshaft having disk-shaped flywheels on both sides of a crankpin, and a connecting rod connected at a large end portion at one end thereof to the crankpin of the crankshaft and at a small end portion at the other end thereof to a piston which slides in a cylinder bore via a piston pin, characterized in that the disk-shaped flywheels are cut out at part of an outer peripheral portion thereof on a side opposite from the crankpin so that the crankshaft is located in proximity of the piston pin.
[0010]
In the internal combustion engine according to Claim 1,

the invention according to Claim 2 is characterized in that plugs with a high specific gravity are provided on the flywheels on the side opposite from the crankpin.
[0011]
In the internal combustion engine according to Claim 1 or Claim 2, the invention according to Claim 3 is characterized in that an axial line passing through a center of the cylinder bore is arranged at a position shifted toward one side with respect to an axial line passing through a rotation center of the crankshaft, and a skirt portion of the piston which is guided by an inner wall of the cylinder bore in contact with the inner wall of the cylinder bore is formed largely on the one side.
[0012]
The invention according to Claim 4 is an internal combustion engine including a crankshaft having disk-shaped flywheels on both sides of a crankpin, and a connecting rod connected at a large end portion at one end thereof to the crankpin of the crankshaft and at a small end portion at the other end thereof to a piston which slides in a cylinder bore via a piston pin, characterized in that a distance between the disk-shaped flywheels on both sides of the crankpin is larger than the width of the piston pin, and both ends of the piston pin are positioned on side surfaces of the disk-shaped flywheels.

[0013]
In the internal combustion engine according to Claim 4, the invention according to Claim 5 is characterized in that the disk-shaped flywheels are formed to be wider on a side opposite from the crankpin in comparison with a crankpin side. [Advantage of the Invention]
[0014]
The invention according to Claim 1 is configured in such a manner that, in the internal combustion engine described above, the disk-shaped flywheels are cut out at the part of the outer peripheral portion thereof on the side opposite from the crankpin so that the crankshaft is located in proximity of the piston pin. Therefore, the length of the connecting rod can be reduced to increase the speed of the piston at a position near a top dead center, and heat released through the cylinder wall surface due to increase in piston speed can be minimized to effectively prevent lowering of a combustion pressure.
[0015]
In the invention according to Claim 1, the invention according to Claim 2 is configured in such a manner that the plugs with a high specific gravity are provided on the flywheels on the side opposite from the crankpin. Therefore, the inertia mass can be secured sufficiently even when the weight of the portion opposite from the crankpin is increased in comparison

with the weight of the piston on the crankpin side and the connecting rod and the cutout on the outer peripheral portion of the flywheel on the side opposite from the crankpin is increased, and the piston speed at the position near the top dead center of the piston can further be increased by reducing the length of the connecting rod in comparison with a crank radius owing to the cutout of the flywheel on the side opposite from the crankpin, whereby a cooling loss to the cylinder wall surface is reduced, thereby improving a thermal efficiency.
[0016]
In the invention according to Claim 1 or Claim 2, the invention according to Claim 3 is configured in such a manner that the axial line passing through the center of the cylinder bore is arranged at the position shifted toward one side with respect to the axial line passing through the rotation center of the crankshaft, and the skirt portion of the piston which is guided by the inner wall of the cylinder bore in contact with the inner wall of the cylinder bore is formed largely on the one side. Therefore, the skirt portion on the side opposite from the offset side can be downsized by the offset, and hence the piston pin portion can be provided at a position closer to the crankshaft.
[0017]
In the internal combustion engine described above, the invention according to Claim 4 is configured in such a manner

that the distance between the disk-shaped flywheels on both sides of the crankpin is larger than the width of the piston pin, and both ends of the piston pin are positioned on the side surfaces of the disk-shaped flywheels. Therefore, the length of the connecting rod can be reduced so that the piston speed at the position near the top dead center is increased, whereby the thermal energy released through the wall surface of the combustion chamber can be minimized to prevent lowering of the combustion pressure effectively.
[0018]
In the invention according to Claim 4, the invention according to Claim 5 is configured in such a manner that the disk-shaped flywheels are formed to be wider on the side opposite from the crankpin in comparison with the crankpin side. Therefore, the inertia mass of the flywheels can be secured while downsizing the crankpin portion, whereby the crankshaft can be downsized. [Best Mode for Carrying Out the Invention]
[0019]
An embodiment of the present invention shown in Fig. 1 to Fig. 7 will be described below.
[0020]
Figs. 1 and 2 show cross-sections of a principal structure of an internal combustion engine E according to a first embodiment, in which a structure of the internal

combustion engine E including a crankcase 10, a cylinder block 20 to be connected to an upper portion in the drawing of the crankcase 10, a cylinder head 30 to be connected to the upper portion in the drawing of the cylinder block 20, and a head cover 40 for covering an upper portion of the cylinder head 30 is shown.
[0021]
As shown in Fig. 1, the crankcase 10 includes left and right half cases 10a, 10b, and case covers 10c, lOd for covering openings of the left and right half cases 10a, 10b, and a crankshaft 1 is rotatably supported in the crankcase 10 via a bearing. The bearing support of the crankshaft 1 in the crankcase 10 is achieved by support of the crankshaft 1 by two main bearings 11, 12 on the left and right half cases 10a, 10b at both sides of a crank portion and a bearing 13 at a right shaft end of the crankshaft 1 on the right case cover lOd of the right half case 10b.
[0022]
The support by the main bearings 11, 12 at both sides of the crank portion of the crankshaft on the left and right half cases 10a, 10b is such that the main bearing 11 on the left side is a radial ball bearing and the main bearing 12 on the right side is a roll bearing. The support by the bearing 13 on the case cover lOd of the right half case 10b on the right shaft end of the crankshaft 1 is achieved by a relatively small

ball bearing which is fitted to an inner wall boss portion 10d2 on an outer wall structure lOdl of the case cover lOd.
[0023]
The cylinder block 20 is provided with a cylinder bore 20a which penetrates therethrough in the vertical direction in the drawing and, as shown in Fig. 2, the cylinder bore 20a is removed 20a2 in an arcuate shape in such a manner that a lower end 20al of a wall forming a left side in the drawing is cut out obliquely upward from a right side because it is close to the crank portion described later to form a short lower-side-forming wall 20a3. A piston PI performs a reciprocal sliding movement in the cylinder bore 20a as well known, and a guide piston P2 described later performs a reciprocal sliding movement. The cylinder block 20 is formed with a through space 20b (see Fig. 1) for allowing passage of a timing chain Tc for transmitting the rotation of the crankshaft 1 to a camshaft 30g via a sprocket le on the shaft 1.
[0024]
The cylinder head 30 is provided with a combustion chamber 30a defined by a recess on a lower portion thereof and an upper portion of the cylinder bore 20a, and an ignition plug, not shown, an opening 30b for air intake and exhaust, an air intake and exhaust valve 30c and so on are provided in the combustion chamber 30a, An intake and exhaust channel 30d and

a mounting hole 30e for a valve stem are disposed in the cylinder head 30, and a valve mechanism including a cam 30f, a camshaft 30g, a rocker arm 30h, and so on is arranged upwardly thereof. The exposed upper portion thereof is covered by the head cover 40.
[0025]
As described above, the crankshaft 1 is rotatably supported by the bearing on the crankcase 10, and the relation between the crankshaft 1 and the cylinder bore 20a is such that a center axis X of the cylinder bore 20a is offset D to the right side in the drawing with respect to a rotation center 0 of the crankshaft 1 as will be understood from a side view of the engine shown in Fig. 2, whereby the side pressure from the piston PI or the guide piston P2 applied to an inner wall 20a4 of the cylinder bore is alleviated in relation to the connecting rod 2.
[0026]
The crankshaft 1 is provided with a single crankpin la and a pair of crank arm portions lb, lb on both sides of the crankpin la are provided with crank web portions lc, lc that continue to the arm portions lb, lb, respectively. The crank arm portions lb, lb and the crank web portions lc, lc integrated into substantially circular shape in side view in Fig. 2, and form flywheels F, F which are inertia mass members presenting substantially a disk shape having crank arm portions lb, lb

on the crankpin la side which corresponds to the lower portion of the substantially circular shape, and crank web portions lc, lc on the side opposite from the crankpin la which corresponds to the upper portion in the drawing,
[0027]
The disk-shaped flywheels F, F are provided with balancer weight portions Id, Id of semi-circular like shape formed by increasing the thickness of the crank web portions lc, lc on the side opposite from the crankpin la, that is, on the side of the web portions, and the balancer weight portions Id, Id are formed to have characteristic outlines describe later. Accordingly, the balancer weight portions Id, Id of the crankshaft 1, which is offset D from the center line X of the cylinder bore 20a, on the side opposite from the crankpin can be provided at a position closer to the guide pin P2 having a deformed portion, describe later, which performs a reciprocal sliding movement in the cylinder bore 20a on the lower side, or to the deformed lower-side-forming wall 20a2, described above, of the cylinder bore 20a.
[0028]
In other words, the balancer weight portions Id, Id located on the disk-shaped flywheels F, F on the opposite side of the crankpin la are, as shown in Fig. 2, formed into a semi-circular like shape in side view defined by an outline including a pair of outline portions ldl, ldl positioned so

as to lay along arcuate portions ld3 of the outlines of the disk-shaped flywheels F, F, and an outline portion ld2 with part of the arcuate portion ld3 interposed between the pair of outline portions ldl, ldl removed along a curve, whereby the balancer weight portions Id, Id can be provided at positions closer to the guide piston P2 provided with the deformed portion and the deformed lower-side-forming wall 20a2 of the cylinder bore 2 0a described above by an amount corresponding to the removed (cut out) portion.
[0029]
A connecting rod 2 is connected to the single crankpin la of the crankshaft 1, and the connecting rod 2 has a two-piece structure including a first connecting rod 21 and a second connecting rod 22. The first connecting rod 21 is rotatably connected to the crankpin la at one end, that is, at an end portion 21a which practically constitutes a large end portion of the connecting rod 2, and is rotatably connected to the above-described guide piston P2 at the other end 21b via a pin portion P2a which passes through a center portion of a main body, formed of sliding arms P2c, P2c extending on the left and right sides of the guide piston P2 in Fig. 2.
[0030]
The second connecting rod 22 of the connecting rod 2 is connected to and hence holds the above-describe piston PI which is supported so as to be capable of pivotal movement via a piston

pin Pla and performs reciprocal sliding movement in the cylinder bore 20a at the other end 22b, that is, at the end portion 22b which practically constitutes a small end portion of the connecting rod 2, and the one end 22a is rotatably connected to the pin portion P2a of the guide piston P2 . The second connecting rod 22 characteristically has a relatively short structure.
[0031]
The guide piston P2 which performs the reciprocal sliding movement on a lower side in the cylinder bore 20a connects the first and second connecting rods 21, 22 as the two-piece connecting rod with respect to each other via the pin portion P2a by rotatably connecting and supporting the other end 21b of the first connecting rod 21 and the one end 22a of the second connecting rod 22 with the pin portion P2a of a guide piston P2a, whereby the connected body of the both connecting rods 21, 22, that is, the single connecting rod 2 is formed.
[0032]
The pin portion P2a of the guide piston P2 extends so as to pass through the center portion of the main body including the sliding arms P2c, P2c of the guide piston P2 extending in the lateral direction, that is, extends so as to be orthogonal to the extending direction of the sliding arms P2c, P2c and in parallel with the crankshaft 1, and both pin ends P2b, P2b (see Fig. 1) are fixed to the main body portion of the guide

piston P2 so as not to rotate. The one end 22a of the second connecting rod 22 is rotatably connected and supported at the center portion of the pin portion P2a in the longitudinal direction as described above, and the other end 21b of the first connecting rod 21 is rotatably connected and supported as described above so as to sandwich the one end 22a of the second connecting rod 22 with its bifurcated branched end 21bl from both sides.
[0033]
The sliding arms P2c, P2c that form the main body of the guide piston P2 and extend in the left and right sides so as to pass across the cylinder bore 20a in Fig. 2, that is, the sliding arms P2c, P2c extending in the direction orthogonal to the crankshaft 1 are provided with sliding surfaces P2d, P2d which come into sliding contact with the inner wall of the cylinder bore 20a at the distal ends thereof, and the sliding surfaces P2d, P2d are provided with arcuate surfaces that extend along the inner wall of the cylinder bore 20a which is rather wide in the vertical and lateral direction.
[0034]
The guide piston P2 also has a structure which allows positioning of the crankshaft 1 at a position closer to the crank portion, that is, positioning of the crankshaft 1 at a position closer to the crank portion in the state in which the center line X of the cylinder bore 20a is offset toward the

right side in the drawing by the amount D with respect to the rotation center axis 0 of the crankshaft 1, and the guide piston P2 is provided with the deformed portions on the sliding arms P2c, P2c and the sliding surfaces P2d, P2d, described later therefor.
[0035]
In other words, more specifically, the deformed portions on the sliding arms P2c, P2c and the sliding surfaces P2d, P2d that define the main body of the guide piston P2 respectively are portions formed into the deformed portions processed to have complementary shape that avoids contact therebetween at the positions closest to each other in the crank movement in order to achieve reduction in distance between the guide piston P2 and the balancer weight portions Id, Id of the flywheels F, F that are crank portions of the crankshaft 1 whose center line of the cylinder bore is offset D in cooperation with the deformed portions of the balancer weight portions Id, Id having the characteristic outlines, that is, in cooperation with the deformed portion having the outline ld2 with the portion of the arcuate portion ld3 linearly removed.
[0036]
Therefore, the arm P2c on the right side in Fig. 2 of the sliding arms P2c, P2c is not deformed specifically, and only the lower portion, that is, the side which is provided at a position closer to the crank portion, of the left arm P2c

is removed P2cl so as to be cut off P2cl obliquely upwardly from the right side to the left side, and the sliding surfaces P2d, P2d of distal ends of the pair of sliding arms P2c, P2c are slightly large in the vertical and lateral directions as described above and include arcuate surfaces extending along the inner wall of the cylinder bore 20a. However, the sliding surface P2d on the left side in Fig. 2 has a smaller width in comparison with the sliding surface P2d on the right side in the vertical direction with cutting a lower skirt portion thereof.
[0037]
The removal structure of the sliding arm P2c and the sliding surface P2d of the guide piston P2 enables closer positional relation between the guide piston P2 and the lower end 20al of the cylinder bore with respect to the balancer weight portions Id, Id in cooperation with the arcuate shaped removal of the lower end 20al of the cylinder bore and the lower-side-forming wall 20a2, and the deformed portions having the characteristic outlines of the balancer weight portions Id, Id of the crankshaft 1 whose center line X of the cylinder bore 20a is offset D, whereby the shorter structure of the first connecting rod 21 is achieved, and in corporation with the short structure of the second connecting rod 22, the close structure between the balancer weight portions Id, Id of the flywheels F, F and the piston PI is achieved.

[0038]
The outline of the structure of the engine E and the structure of the crank chain is as described above.
Here, advantage in structure of the crank chain in this embodiment will be described briefly in conjunction with the operation thereof.
[0039]
As will be understood from Fig. 1 and Fig. 2, the guide piston P2 and the balancer weight portions Id, Id of the disk-shaped flywheels F, F on both sides of the crankpin la of the crankshaft 1 of this embodiment enable reduction in distance therebetween in cooperation with the complementary deformed portion in the crank movement, and the length of the first connecting rod 21 is reduced. Since the second connecting rod 22 is formed to have a length as short as possible, the short connecting rod 2 which is short as a whole is obtained, thereby achieving the structure in which the distance between the balancer weight portions Id, Id of the disk-shaped flywheels F, F of the crankshaft 1 with respect to the piston PI is reduced.
[0040]
In conclusion, the reduction in length of the first connecting rod 21 enables achievement of high speed and acceleration of the reciprocal sliding movement of the guide piston P2 in the cylinder bore 20a during the crank movement,

and the increased high speed and acceleration of the guide piston P2 enable high speed and acceleration of reciprocal sliding movement of the piston PI, whereby the speed of the behavior of the piston PI is increased to efficiently promote conversion from the thermal energy into the practice, more specifically, to a kinetic energy of the piston PI, thereby improving the efficiency of recovery of the combustion energy to improve the thermal efficiency and preventing occurrence of knocking by preventing excessive heating of a wall portion of a combustion chamber by the thermal energy.
[0041]
As a second embodiment of the present invention, a mode shown in Figs. 3 and 4 is conceivable.
The internal combustion engine E in this embodiment is common to the engine E in the first embodiment described above in most part of the structure (the corresponding structures are represented by the same reference numerals) . However, the crankshaft 1 and the structures related thereto are different in structure.
[0042]
The crankshaft 1 is provided with the single crankpin la, and the crankpin la is provided with the first and second connecting rods 21, 22 as in the case of the first embodiment described above and the piston PI is mounted thereto via the guide piston P2 . Since the structures of these members as a

whole and the structures of the piston PI and the guide piston P2 themselves are not specifically different from the first embodiment described above, description about the structures of these members are omitted.
[0043]
The crankshaft 1 is provided with the single crankpin la, and the pair of crank arm portions lb, lb and the crank web portions lc, lc continuing to the arm portions lb, lb on both sides of the crankpin la are formed integrally to form the flywheels F, F which are the substantially integral inertia mass members each presenting a circular shape in side view shown in a perspective view in Fig. 4.
[0044]
Therefore, the crank arm portions lb, lb are formed on the crankpin la side of the disk-shaped flywheels F, F and the crank web portions lc, lc are formed thereon on the side apart from the crankpin la on the opposite side. The crank web portions lc, lc are substantially the balancer weight portions Id, Id. The balancer weight portions Id, Id of the disk-shaped flywheels F, F are formed by increasing the thickness of the crank web portions lc, lc of the flywheels F, F, and formed into a shape similar to a half moon as shown in Fig. 8.
[0045]
As will be understood from Fig. 3, the disk-shaped flywheels F, F are provided with opposing surfaces Fl, Fl facing

inwardly thereof which constitutes a pair formed on both sides of the crankpin la. A distance Dl between the opposing surfaces Fl, Fl is relatively narrow on the crankpin la side, and a distance D2 between these surfaces increase on the side opposite from the crankpin la, that is, on the side where the balancer weight portions Id, Id are formed. Therefore, although the flywheels F, F formed into a disk shape have a substantially circular shape in side view, they have shaped shifted from each other with shoulders in the direction of the thickness.
[0046]
The larger distance D2 between the surfaces Fl, Fl of the disk-shaped flywheels F, F opposed to each other in pair on the side opposite from the crankpin la is larger than the length L of the pin portion P2a having the extending length over the substantially entire lateral width of the guide piston P2, whereby the opposed surfaces Fl, Fl of the pair of disk-shaped flywheels F, F can receive the guide piston P2 moved downward to the bottom dead center or near the bottom dead center (a state shown in Fig, 3) in the crank movement within the larger surface distance D2 with a predetermined clearance.
[0047]
In practice, the reception of the guide piston P2 between the pair of opposed surfaces Fl, Fl of the flywheels allows entry of the guide piston P2 to a position between the inner

surfaces of the balancer weight portions Id, Id of the flywheels F, F shown in Fig. 3 along both side surface portions P2e, P2e of the guide piston P2 in the lateral direction, that is, along the both pin ends P2b, P2b of the pin portion P2a of the guide piston P2.
[0048]
Therefore, outer peripheral ends IdO, IdO of the balancer weight portions Id, Id enter while rotating along the side surface portions P2e, P2e of the guide piston when the guide piston P2 is moved downward to the bottom dead center or near the bottom dead center in the rotation of the crank movement and, in this process, reach to a position nearest to the lower end 20al of the cylinder wall in the cylinder bore 20a.
[0049]
The structure of the ends of the opposed surfaces Fl, Fl, that is, the outer peripheral ends IdO, IdO of the balancer weight portions Id, Id that allows entry of the guide piston P2 along the side surface portions P2e, P2e in the width direction thereof on the basis of the wide structure between the opposed surfaces Fl, Fl of the pair of disk-shaped flywheels F, F on the side opposite from the crankpin la achieves positioning of the guide piston P2 closer to the crank portion without necessity of specific deformation of the guide piston P2 and the balancer weight portions Id, Id of the flywheels F, F, and consequently, achieves positioning of the piston PI

closer to the crank portion, thereby realizing reduction in length of the connecting rod 21.
[0050]
Since the embodiments of the invention are configured as described above, the following effects and advantages are achieved.
[0051]
As the effects and advantages common to the first and second embodiments, the crankpin la and the piston PI are connected by the short connecting rod 21, and hence the speed of behavior of the piston PI near the top dead center of the piston PI can be increased. By increasing the behavior of the piston PI, conversion from the thermal energy to the practice is quickly achieved, which reduces energy loss correspondingly. Since the excessive heating of the wall portion of the combustion chamber of the thermal energy is constrained, generation of knocking is effectively prevented. Therefore, an optimal engine structure is provided in the application to the quick combustion engine.
[0052]
In the first embodiment, the balancer weight portions Id, Id of the flywheels F, F and the guide piston P2 are respectively provided with the deformed portions that are formed into complementary shapes to allow reduction of the distance therebetween in the crank movement. Therefore, the

structure in which the length of the connecting rod 21 is reduced can be employed, whereby the speed and the acceleration of the piston PI can be increased to achieve quick conversion from the thermal energy into the practice. Consequently, reduction of the heat loss is achieved, and the excessive heating of the wall portion of the combustion chamber due to the thermal energy is constrained, whereby generation of knocking is effectively prevented.
[0053]
In the second embodiment, since the pair of disk-shaped flywheels F, F provided on both sides of the crankpin la oppose to each other in such a manner that the opposed surfaces Fl, Fl corresponding to the balancer weight portions Id, Id on the side opposite from the crankpin la at the large distance D2, the guide piston P2 which is moved to the bottom dead center in the crank movement is received between the opposed surfaces Fl, Fl with the clearance, the bottom dead center of the guide piston P2 can be set to a lower position correspondingly.
[0054]
As a consequence, the positioning of the piston PI closer to the crank portion is enabled, and the length of the connecting rod 21 can be reduced without providing specific deformation on the guide piston P2 and the balancer weight portions Id, Id of the flywheels F, F.
[0055]

Subsequently/ referring to Fig. 5 to Fig. 7, a third embodiment will be described.
The internal combustion engine E in the third embodiment is significantly different in crank chain from the first and second embodiments and has a slight modification in a crankcase 50 and a cylinder block 60, but a cylinder head 70 is not modified.
[0056]
In other words, the axial length of the cylinder block 60 is reduced, the distance between a mating surface with respect to the crankcase 50 and a mating surface with respect to the cylinder head 70 is reduced, and the shape near the mating surface with respect to the crankcase 50 is modified.
The crank chain in this embodiment is not provided with the guide piston, which is different from the first and second embodiments.
[0057]
A piston 80 which performs reciprocal sliding movement in a bore 60a of the cylinder block 60 is provided with a piston pin 83 laid across a pair of pin supporting arms 82, 82 projecting from a back surface of a piston crown portion 81 opposing to the combustion chamber.
[0058]
On the other hand, a crankshaft 90 rotatably supported at a journal portion 91 by main bearings 51, 52 on the crankcase

50 has an opposing pair of crank web portions 92, 92 of a specific shape.
[0059]
In other words, a counter weight portion 92w on the side opposite from the crankpin with respect to a rotation center of the crank web portion 92 is cut out on a circular outer peripheral portion of the crank web portion 92 having a largest diameter so that an outer peripheral edge 92wa is provided at a position closer to the center axis, and a crank arm portion 92a on the side of the crankpin has a shape projecting radially from the center portion.
[0060]
The crank web portion 92 has a symmetrical shape with respect to a straight line connecting a rotation center of the crankshaft 90 and a center of a crankpin 93.
The opposed crank arm portions 92a, 92a are connected by the crankpin 93.
[0061]
Then, the counter weight portion 92w of the crank web portion 92 having the symmetrical shape has plugs 95, 95 of flat column shape embedded at symmetric positions.
The plugs 95 are formed of tungsten or the like having a high specific gravity.
[0062]
A large end portion of a connecting rod 85 is supported

by the crankpin 93 connecting the crank arm portions 92a, 92a so as to be capable of rotating about an axis thereof, and a small end portion is supported by the piston pin 83 laid across the pair of pin supporting arms 82, 82 of the piston 80 so as to be capable of rotating about an axis thereof, so that the crankshaft 90 and the piston 80 are connected by the connecting rod 85.
[0063]
In this crank chain, since the plugs 95 having the high specific gravity are embedded into the counter weight portion 92W of the crank web portion 92 on the opposite side of the crankpin, even thought the outer peripheral edge 92wa of the crank web portion 92 on the opposite side from the crankpin is moved largely toward the center axis, a sufficient counter weight (inertia mass) can be secured by the plugs 95, and since the crank web portion 92 does not interfere with the piston 80 even when the outer peripheral edge 92wa is moved largely toward the center axis, the length of the connecting rod 85 can be reduced.
[0064]
A ratio X (=L/r) of the length L of the connecting rod 85 (the length from the center of the crankpin to the center of the piston) with respect to a crank radius r (the distance from the rotation center of the crankshaft to the center of the crankpin) is 2. 0 or less, which is significantly small value

in comparison with the normal value X = about 3.5.
In other words, when the same crank radius r is employed,
the length L of the connecting rod 85 can be reduced significantly with respect to the normal length, and hence the piston 80 can be provided at a position closer to the crank web portion 92, so that downsizing of the internal combustion engine E is achieved. [0065]
As described above, since the ratio X is small value, the piston speed near the top dead center of the piston can further be increased, whereby the cooling loss to a cylinder wall surface is reduced, thereby improving heat efficiency.
The inertia mass of the crank web portion 92 can also be secured sufficiently, so that reduction of vibrations is also achieved. [Brief Description of the Drawings]
[0066]
[Fig. 1] Fig 1 is a front cross-sectional view of an internal combustion engine showing a structure of a principal portion of a crank chain in the present invention.
[Fig. 2] Fig. 2 is a side cross-sectional view of the internal combustion engine showing the structure of the principal portion of the crank chain in the present invention.
[Fig. 3] Fig. 3 is a front cross-sectional view of the internal combustion engine showing the principal structure of

the crank chain according to another embodiment of the present invention.
[Fig. 4] Fig. 4 is a perspective view showing a balancer weight portion of a flywheel in Fig. 3.
[Fig. 5] Fig. 5 is a front cross-sectional view of the internal combustion engine showing the structure of the principal portion of the crank chain according to still another third embodiment of the present invention in a state in which a piston is at a position near a top dead center.
[Fig. 6] Fig. 6 is a side cross-sectional view of Fig. 5.
[Fig. 7] Fig. 7 is a side cross-sectional view of the same when the piston is at the position near the top dead center.
[Fig. 8] Fig. 8 is a drawing showing a crank chain in the related art.
[Fig. 9] Fig. 9 is a drawing showing another example of the crank chain in the related art. [Description of Reference Numerals and Signs]
[0067]
1. . .crankshaft, la...crankpin, lb...crank arm portion, lc...crank web portion, Id...balancer weight portion,
2. . .connecting rod, 21...first connecting rod, 21a...one end, 21b...the other end, 22...second connecting rod, 22a...one end, 22b...the other end, 10...crank case, 20...cylinder block, 20a... cylinder bore, 30...cylinder

head, F...flywheel, Fl...opposed surface, PI. ..piston, P2...guide piston, P2a...pin portion, P2b...pin end, P2c...sliding arm, P2d...sliding surface, 50...crank case, 60...cylinder block, 70...cylinder head, 80...piston, 82...pin supporting arm, 83...piston pin, 85...connecting rod, 90...crankshaft, 92...crank web portion, 93...crankpin, 95...plug

[Designation of Document] Claims [Claim 1]
An internal combustion engine comprising: a crankshaft having disk-shaped flywheels on both sides of a crankpin; and a connecting rod connected at a large end portion at one end thereof to the crankpin of the crankshaft and at a small end portion at the other end thereof to a piston which slides in a cylinder bore via a piston pin, characterized in that the disk-shaped flywheels are cut out at part of an outer peripheral portion thereof on a side opposite from the crankpin so that the crankshaft is located in proximity of the piston pin. [Claim 2]
The internal combustion engine according to Claim 1, characterized in that plugs with a high specific gravity are provided on the flywheels on the side opposite from the crankpin. [Claim 3]
The internal combustion engine according to Claim 1 or Claim 2, characterized in that an axial line passing through a center of the cylinder bore is arranged at a position shifted toward one side with respect to an axial line passing through a rotation center of the crankshaft, and a skirt portion of the piston which is guided by an inner wall of the cylinder bore in contact with the inner wall of the cylinder bore is formed largely on the one side.

[Claim 4]
An internal combustion engine comprising: a crankshaft having disk-shaped flywheels on both sides of a crankpin; and a connecting rod connected at a large end portion at one end thereof to the crankpin of the crankshaft and at a small end portion at the other end thereof to a piston which slides in a cylinder bore via a piston pin, characterized in that a distance between the disk-shaped flywheels on both sides of the crankpin is larger than the width of the piston pin, and both ends of the piston pin are positioned on side surfaces of the disk-shaped flywheels. [Claim 5]
The internal combustion engine according to Claim 4, characterized in that the disk-shaped flywheels are formed to be wider on a side opposite from the crankpin in comparison with a crankpin side.

Documents:

0550-che-2006 abstract duplicate.pdf

0550-che-2006 claims duplicate.pdf

0550-che-2006 description (complete) duplicate.pdf

0550-che-2006 drawings duplicate.pdf

550-che-2006-abstract.image.jpg

550-che-2006-abstract.pdf

550-che-2006-claims.pdf

550-che-2006-correspondnece-others.pdf

550-che-2006-description(complete).pdf

550-che-2006-drawings.pdf

550-che-2006-form 1.pdf

550-che-2006-form 3.pdf

550-che-2006-form 5.pdf

550-che-2006-priority document.pdf

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Patent Number

230653

Indian Patent Application Number

550/CHE/2006

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

27-Feb-2009

Date of Filing

27-Mar-2006

Name of Patentee

HONDA MOTOR CO., LTD

Applicant Address

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

Inventors:

#	Inventor's Name	Inventor's Address
1	SUZUKI, MASATOSHI	C/o HONDA R&D CO., LTD., 4-1, CHUO 1-CHOME, WAKO-SHI, SAITAMA 351-0193,
2	IIJIMA, SATOSHI	C/o HONDA R & D CO., LTD., 4-1, CHUO 1-CHOME, WAKO-SHI, SAITAMA 351-0193,
3	MAEHARA, HAYATO	C/o HONDA R & D CO., LTD., 4-1, CHUO 1-CHOME, WAKO-SHI, SAITAMA 351-0193,

PCT International Classification Number

F02B 75/32

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2005-099999	2005-03-30	Japan
2	2005-320172	2005-11-02	Japan