JP2006090241A - Four-cycle engine for motorcycle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a four-cycle engine for a motorcycle, capable of reducing the size of the four-cycle engine, simplifying the structure, improving lubricating performance and improving support rigidity of a support shaft of an auxiliary driven gear. <P>SOLUTION: A cam chain chamber 101 storing a cam chain 98 is provided in one side face of a cylinder assembly 42, and an auxiliary drive gear 107 is provided outside in the axial direction of a cam drive sprocket 96 arranged in a crank shaft 52 so as to be adjacent to the cam drive sprocket 96. In the vicinity of the auxiliary drive gear 107, a rear end of a chain guide rail 141 for guiding running in the bottom chord side of the cam chain 98 is fixed. The auxiliary driven gear 108 engaged with the auxiliary drive gear 107 is arranged so as to overlap the chain guide rail 141 in side view. An engagement point 157 of the auxiliary drive gear 107 and the auxiliary driven gear 108 are arranged in the vicinity of a sliding face 158 of the cam chain 98 and the chain guide rail 141 in side view. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a four-cycle engine for a motorcycle.

As shown in Patent Document 1, in a four-cycle engine of a motorcycle, a cam drive sprocket of a crankshaft supported in the crankcase and a cam driven sprocket of a camshaft supported in the cylinder assembly are provided. A cam chain is wound around the cam chain, and a cam chain chamber for accommodating the cam chain is provided on one side of the cylinder assembly. A chain guide rail for guiding the travel of the chain line on the tension side of the cam chain, and a chain tension rail and a chain tensioner for tensioning the chain line on the loose side of the cam chain are provided in the cam chain chamber.
JP 2004-124998 A

  By the way, auxiliary machines such as an oil pump and a generator driven by the crankshaft are arranged in the vicinity of the crankshaft. These auxiliary machines and their driving gears are connected to the above-mentioned cam chain and chain guide rail. Therefore, the compactness of the entire engine tends to be impaired.

  The present invention has been made in order to solve the above-described problems, and is a motorcycle capable of achieving compactness, simplification of the structure, improvement of lubricity, and improvement of support rigidity of a support shaft of an auxiliary machine driven gear. An object of the present invention is to provide a four-cycle engine.

  In order to achieve the above object, a motorcycle four-cycle engine according to the present invention is installed with a cylinder assembly tilted substantially horizontally forward on the front of the crankcase, and the crankshaft is supported in the vehicle width direction inside the crankcase. A cam chain is wound between the cam drive sprocket provided on the crankshaft and the cam driven sprocket of the camshaft that is pivotally supported inside the cylinder assembly, and the cam chain chamber that houses this camchain is attached to one side of the cylinder assembly. Auxiliary machine drive gear is provided adjacent to the cam drive sprocket in the axial direction, and the rear end of the chain guide rail that guides the travel of the lower string side of the cam chain is fixed in the vicinity, and the auxiliary drive gear meshes with the auxiliary machine drive gear. Place the machine driven gear so that it overlaps the chain guide rail in side view. The engagement point of the auxiliary driven gear an auxiliary drive gear in a side view, characterized in that arranged on the sliding surface near the cam chain and the chain guide rails.

  Further, the four-cycle engine of the motorcycle according to the present invention is provided with a gear cover member that is mounted on the outer surface side of the crankcase and defines an accessory drive gear chamber between the crankcase and the accessory drive. The cam drive sprocket, the accessory drive gear, and the accessory driven gear are accommodated in the gear chamber, and the gear cover member is formed with a recess recessed toward the accessory drive gear chamber, and is driven to rotate by the crankshaft in the recess. A rotating accessory was provided.

  Further, the four-cycle engine of the motorcycle according to the present invention has a substantially U-shaped chain guide rail holding portion for restricting the movement of the rear end portion of the chain guide rail in the vertical direction and the rear side on the outer surface of the crankcase. At the same time, a protrusion is provided on the inner surface of the gear cover member so as to protrude toward the outer surface of the chain guide rail holding portion and restrict the movement of the rear end portion of the chain guide rail toward the outer surface.

  In the four-cycle engine of the motorcycle according to the present invention, an oil strainer chamber located below the accessory drive gear chamber is provided between the crankcase and the gear cover member, and the oil strainer chamber is provided in the cam chain chamber. The oil strainer chamber, the cam chain chamber, and the accessory drive gear chamber are separated from and adjacent to the crank chamber inside the crankcase, and the lower portion of the accessory drive gear chamber communicates with the crank chamber. The crank chamber and the oil strainer chamber were communicated below the communicating portion.

  In the four-cycle engine of the motorcycle according to the present invention, a boss portion that fastens and fixes the stationary side member of the rotary accessory is formed on the gear cover member, and the boss portion is provided on the side of the accessory drive gear chamber of the gear cover member. And a bearing portion for supporting the gear cover member side end portion of the gear shaft of the accessory driven gear is formed on the surface of the gear cover member on the accessory drive gear chamber side. The protruding height of the part was made substantially the same.

  Further, the four-cycle engine of the motorcycle according to the present invention is arranged such that the position of the mating surface of the crankcase and the gear cover member overlaps the concave portion of the gear cover member in plan view, and the cam chain of the mating surface and the cylinder assembly. A crankcase fastening portion for fastening the cylinder block to the crankcase was provided between the chamber and the chamber.

  The motorcycle four-cycle engine according to the present invention has a layout in which the accessory drive gear and the accessory driven gear mesh with each other through the chain guide rail, and at the same time the accessory is placed in the range between the crankshaft and the camshaft. The engine can be made compact by reducing the longitudinal length and vertical length of the engine closer to the cylinder axis.

  In addition, by forming a recess recessed in the accessory drive gear chamber side in the gear cover member that defines the accessory drive gear chamber, and housing the rotation side member of the rotary accessory in this recess, the width dimension of the engine Can contribute to compactness.

  In addition, the movement of the chain guide rail rear end is restricted by a substantially U-shaped chain guide rail holding part formed on the outer side of the crankcase and a protrusion formed on the inner side of the gear cover member, thus simplifying the structure. In addition, it is possible to reduce the size in the width direction of the engine by reducing the distance between adjacent accessory drive gears.

  The following is an embodiment of the present invention.

  FIG. 1 is a left side perspective view showing a scooter type motorcycle to which a four-cycle engine according to the present invention is applied.

  The body frame 2 of the motorcycle 1 is made of steel pipe, and a down pipe 4 extends rearward and downward from a head pipe 3 located at the frontal portion, and a pair of left and right rear pipes 5 extends rearward and obliquely upward from the vicinity of the rear end thereof. A step frame 6 is formed at a portion where the pipe 4 enters the lower part, and an engine bracket 7 is provided in the vicinity of the joint between the down pipe 4 and the rear pipe 5.

  A front fork 10 that supports a front wheel 9 is pivotally supported on the head pipe 3 together with a handle bar 11, a headlamp 12, a front fender 13, and the like, while being pivotally supported by the engine bracket 7 via a link 15. The rear wheel 17 is supported on the rear part of the power unit 16, and the shock absorber 18 is connected between the rear part of the power unit 16 and the rear part of the rear pipe 5.

  The power unit 16 swings up and down around a pivot shaft 19 installed at the rear end of the link 15 together with the rear wheel 17 to act as a swing arm of the rear wheel 17, and the power unit 16 and the rear wheel 17 are swung by a shock absorber 18. Buffered and restored. An air intake device (discharge pump) 21 is installed at the front upper part of the power unit 16, and an air cleaner 22 is installed at the rear upper part.

  A bottomed box-shaped container-like article storage box 24 that opens upward is installed above the rear pipe 5, and a seating seat 25 is placed so as to close the opening. The seating seat 25 can be opened and closed by lifting the rear end about the hinge portion 26 at the front end, so that articles can be taken in and out of the article storage box 24.

  A fuel tank 27 is installed behind the article storage box 24, and a refueling portion 28 passes through a tray portion 29 extending rearward from the upper edge of the article storage box 24 and faces upward. The fuel tank 27 has a shape that wraps around right after the article storage box 24.

  The front and rear portions of the vehicle body frame 2 are covered with a synthetic resin front frame cover 31 and a rear frame cover 32, respectively, to adjust the vehicle body appearance, and a tail lamp 33 is provided at the rear end of the rear frame cover 32. A rear fender 34 is provided above the rear wheel 17. A synthetic resin step board 35 is formed on the top of the step frame 6. The front frame cover 31, the rear frame cover 32, and the step board 35 are continuously connected.

  2 is a left side view of the power unit 16, FIG. 3 is a plan view of the power unit 16, FIG. 4 is a cross-sectional view of the power unit 16 taken along line IV-IV in FIG. 2, and FIG. 6 and 6 are developed cross-sectional views along the line VI-VI in FIG. This power unit 16 has a general layout for a scooter type motorcycle in which a four-cycle engine 37 and a transmission unit 38 are integrated.

  The four-cycle engine 37 is a forced air-cooling type, and a single-cylinder cylinder assembly 42 is installed on the front surface of the crankcase 41 so as to be inclined forward substantially horizontally. As shown in FIGS. 4 and 6, the crankcase 41 is a left-right split type in which the left case half 43 and the right case half 44 are combined, and the left case half 43 is integrally connected with a transmission case body 45 extending rearward. The transmission case body 45 is closed by a transmission case cover 46 to form a transmission case 47. The transmission case 47, a belt-type transmission 48 accommodated in the transmission case 47, and a deceleration transmission mechanism 49 are provided. A transmission unit 38 is configured.

  A crankshaft 52 extending in the vehicle width direction is supported by bearings 53 and 54 in a crank chamber 51 (see FIG. 6) inside the crankcase 41, and both ends thereof project to the left and right of the crankcase 41. The left end of the crankshaft 52 is The transmission case 47 extends inside. On the other hand, a driven shaft 56, an intermediate shaft 57, and a rear wheel shaft 58 are supported in order from the front at the rear portion of the transmission case 47, and the rear wheel shaft 58 protrudes from the right side surface of the transmission case 47 so that the rear wheel 17 rotates integrally therewith. It is attached.

  Inside the speed change case 47, a drive pulley 61 is mounted on the crankshaft 52, and a driven pulley 62 is mounted on the driven shaft 56, and a V-belt 63 is stretched between the pulleys 61 and 62, and on the left side of the driven pulley 62. A centrifugal clutch 64 is provided. The pulleys 61 and 62, the V belt 63, and the centrifugal clutch 64 constitute a belt type transmission 48.

  A primary drive gear 66 is provided near the right end of the driven shaft 56, a primary driven gear 67 and a secondary drive gear 68 are provided on the intermediate shaft, and a secondary driven gear 69 is provided on the rear wheel shaft 58. .. -69 are separated in a liquid-tight manner by a mission cover 70 mounted on the rear portion of the transmission case main body 45 and immersed in oil to constitute a deceleration transmission mechanism 49.

  The rotation of the crankshaft 52 is transmitted to the driven shaft 56 through the drive pulley 61, the V belt 63, the driven pulley 62, and the centrifugal clutch 64, and the rotation of the driven shaft 56 is decelerated in two stages by the speed reduction mission mechanism 49. And transmitted to the rear wheel 17. The effective diameter of the drive pulley 61 is increased by the action of the internal weight roller 71 as the centrifugal force increases. On the contrary, the effective diameter of the driven pulley 62 is reduced, so that the rotation of the crankshaft 52 is automatically changed steplessly ( And is transmitted to the driven shaft 56.

  A kick starter shaft 73 is installed between the crank shaft 52 and the driven shaft 56, a kick starter lever 74 is provided at the outer end thereof, and a kick starter mechanism 75 is provided at an intermediate portion of the kick starter shaft 73. Yes. A member 76 shown in FIG. 3 is a starter motor.

  On the other hand, the cylinder assembly 42 is assembled from a cylinder block 85, a cylinder head 86, and a head cover 87. A piston 89 inserted into a cylinder bore 88 inside the cylinder block 85 is connected to a crank pin 91 of the crankshaft 52 by a connecting rod 90. The reciprocating motion of the piston 89 in the cylinder bore 88 is converted into the rotational motion of the crankshaft 52 and becomes the output of the 4-cycle engine 37.

  A combustion chamber 93 that is aligned with the cylinder bore 88 is formed in the cylinder head 86 and a spark plug 94 is attached from the outside. A cam shaft 95 is supported in the vehicle width direction inside the cylinder head 86, and is attached to the crank shaft 52. A cam chain 98 is wound between a cam drive sprocket 96 provided and a cam driven sprocket 97 provided on the cam shaft 95.

  The rotation of the crankshaft 52 is decelerated to 1/2 and transmitted to the camshaft 95. The intake cam 99 and the exhaust cam 100 formed on the camshaft 95 are connected to an intake valve and an exhaust valve (not shown) via a rocker arm (not shown). ) At a predetermined timing. The cam chain 98 is accommodated in a cam chain chamber 101 provided on, for example, the right side surface of the cylinder assembly 42 (85, 86, 87).

  As shown in FIGS. 4 and 6, a gear cover member 104 is liquid-tightly mounted on the right side surface of the crankcase 41 (right case half body 44), and the auxiliary machine is driven between the crankcase 41 (crank chamber 51). A gear chamber 105 is defined. The auxiliary machine drive gear chamber 105 communicates with the cam chain chamber 101. In the auxiliary machine drive gear chamber 105, the cam drive sprocket 96 of the crankshaft 52 and an auxiliary machine drive provided adjacent to the outside (right side) in the axial direction thereof. A gear 107 and an accessory driven gear 108 that meshes with the accessory drive gear 107 are accommodated.

  The auxiliary machine drive gear 107 and the auxiliary machine driven gear 108 are gears that drive an oil pump 110 that is an auxiliary machine. The oil pump 110 is fixed to the right side surface of the right case half 44 and is crankshaft in a side view (see FIG. 5). 52 is located obliquely below the front. The gear shaft 111 of the oil pump 110 protrudes to the right, and the accessory driven gear 108 is mounted, and the right end portion of the gear shaft 111 is formed on the surface (left side surface) of the gear cover member 104 on the accessory driving gear chamber 105 side. A cylindrical bearing 112 is rotatably supported by the shaft. With this configuration, the gear shaft 111 can be supported at both ends by the oil pump 110 and the bearing portion 112 to increase the support rigidity of the gear shaft 111.

  An oil strainer chamber 115 is provided below the accessory drive gear chamber 105, and an oil strainer 116 is installed therein. The oil strainer chamber 115 is also defined between the crankcase 41 and the gear cover member 104, but is isolated from the cam chain chamber 101 and the accessory drive gear chamber 105. The oil strainer chamber 115, the cam chain chamber 101, and the accessory drive gear chamber 105 are adjacent to and isolated from the crank chamber 51, and the lower portion of the accessory drive gear chamber 105 is connected to the crank chamber by a communication portion 118 (see FIG. 6). 51, the crank chamber 51 and the oil strainer chamber 115 communicate with each other below the communication portion 118 through a communication portion 119 (see FIG. 5).

  The rotation of the crankshaft 52 is decelerated by the accessory drive gear 107 and the accessory driven gear 108 to drive the oil pump 110, whereby the oil stored at the bottom of the crank chamber 51 is pumped from the suction passage 121 of the oil pump 110. Then, the oil is discharged into the discharge passage 122 and oil is pressure-fed to each lubricating portion of the four-cycle engine 37. The oil is filtered by the oil strainer 116 before being sucked into the oil pump 110. A drain plug 123 for removing oil is provided at the lower part of the suction passage 121.

  As shown in FIG. 6, the gear cover member 104 is formed with a recess 127 that is recessed toward the accessory drive gear chamber 105, and a rotary accessory that is driven to rotate by the crankshaft 52, such as a generator 128, is formed in the recess 127. is set up. A stator 129, which is a fixed side member of the generator 128, is fastened and fixed to a boss portion 130 formed in a plurality of recesses 127 by bolts 131, and a right end portion of the crankshaft 52 passes through the center of the recess 127, thereby rotating the rotation side member of the generator 128. The rotor 132 is provided at the right end portion of the crankshaft 52 so as to rotate integrally. Then, the rotation of the crankshaft 52 causes the rotor 132 to go around the stator 129 to generate power.

  A plurality of stator 129 fastening bosses 130 formed in the recesses 127 of the gear cover member 104 also protrude from the surface (left side surface) of the gear cover member 104 on the auxiliary machine drive gear chamber 105 side, and are formed on this surface. The protruding height of the bearing 112 for supporting the gear shaft 111 of the oil pump 110 and the protruding height of the boss 130 are set to be substantially the same. As a result, the length of the boss portion 130 and the bolt 131 can be extended without taking up space, thereby improving the fastening strength of the stator 129 and improving the manufacturability of the gear cover member 104.

  The position of the mating surface 135 between the crankcase 41 and the gear cover member 104 is arranged so as to overlap the concave portion 127 of the gear cover member 104 in the width direction in a plan view (see FIG. 6), and the mating surface 135 and the cam of the cylinder assembly 42 are arranged. A crankcase fastening portion 136 for fastening the cylinder block 85 to the crankcase 41 is provided between the chain chamber 101 and the chain chamber 101.

  By the way, as shown in FIG. 5, in the cam chain chamber 101, there are a chain guide rail 141 for guiding the travel of the chain line on the tension side (lower chord side) of the cam chain 98, and the loose side (upper chord side) of the cam chain 98. A sled-like chain tension rail 142 and a chain tensioner 143 for tensioning the chain line are provided.

  The rear end of the chain guide rail 141 is inserted and held from the front in a substantially U-shaped chain guide rail holding portion 145 formed on the right side surface of the crankcase 41, thereby restricting the movement in the vertical direction and the rear direction. Further, the movement in the outer surface direction (right direction) is restricted by a protrusion 146 formed on the inner surface of the gear cover member 104 and protruding toward the outer surface (right side surface) of the chain guide rail holding portion 145.

  On the other hand, the holding projection 147 formed on the front side of the chain guide rail 141 is fitted into a recess 148 formed on the mating surface of the cylinder block 85 and the cylinder head 86, whereby front, rear, left and right of the front portion of the chain guide rail 141 are obtained. The movement in the vertical direction is restricted, and the contact portion 149 formed on the lower surface of the intermediate portion of the chain guide rail 141 is in contact with the bottom surface of the cam chain chamber 101, whereby the downward deflection of the intermediate portion of the chain guide rail 141 is restricted. Has been.

  The front end of the chain tension rail 142 is rotatably supported by a pivot shaft 151 provided in the vicinity of the front end of the cylinder block 85, and the chain tensioner 143 is installed in a tensioner housing 152 formed on the upper surface of the intermediate portion of the cylinder block 85. The presser 153 of the chain tensioner 143 presses the pressing seat 154 formed at the intermediate portion of the chain tension rail 142, whereby the tension of the cam chain 98 is properly maintained.

  Here, the chain guide rail holding portion 145 for fixing the rear end of the chain guide rail 141 is disposed in the vicinity of the accessory drive gear 107. The auxiliary machine driven gear 108 is arranged so as to overlap the chain guide rail 141 in a side view, and the meshing point 157 between the auxiliary machine drive gear 107 and the auxiliary machine driven gear 108 in the side view is a sliding between the cam chain 98 and the chain guide rail 141. The height near the surface 158 is set.

  A cooling fan 161 is fixed to the rotor 132 of the generator 128 that is fixed to the right end of the crankshaft 52 so as to rotate together. The cylinder assembly 42 and the right side of the crankcase 41 are covered with a cooling cowling 162 made of synthetic resin. . The cooling cowling 162 is formed with a cooling air suction port 163 that opens to the right side of the cooling fan 161 and a cooling air discharge port that is opened below the cylinder assembly 42. When the cooling fan 161 rotates together with the rotation of the crankshaft 52, the outside air is sucked as cooling air from the cooling air suction port 163, and this cooling air is forcedly cooled by the cylinder assembly 42 and then discharged from the cooling air discharge port. The cycle engine 37 is forcibly air-cooled.

  The four-cycle engine 37 configured as described above has a layout in which the accessory drive gear 107 and the accessory driven gear 108 mesh with each other through the chain guide rail 141 in a side view, so that the oil pump 110 as an accessory is connected to the crankshaft 52. The four-cycle engine 37 can be made compact by shortening the front-rear length and the vertical length of the four-cycle engine 37 by being within the range between the cam shafts 95 and simultaneously approaching the cylinder shaft.

  In addition, the gear cover member 104 that defines the accessory drive gear chamber 105 is formed with a recess 127 that is recessed toward the accessory drive gear chamber 105, and the generator 128 that is a rotary accessory is accommodated in the recess 127. It was also possible to contribute to the downsizing of the four-cycle engine 37 in the width direction.

  Further, the movement of the rear end portion of the chain guide rail 141 is restricted by a substantially U-shaped chain guide rail holding portion 145 formed on the right side surface of the crankcase 41 and a protrusion 146 formed on the inner surface of the gear cover member 104. Therefore, the holding structure of the rear end portion of the chain guide rail 141 is simplified, and the distance between the accessory drive gears 107 and 108 adjacent to the chain guide rail 141 is reduced to increase the width direction dimension of the four-cycle engine 37. Can be made compact.

  Further, an oil strainer chamber 115 is provided below the accessory drive gear chamber 105 and between the crankcase 41 and the gear cover member 104, and the oil strainer chamber 115 is isolated from the cam chain chamber 101 and the accessory drive gear chamber 105. The oil strainer chamber 115, the cam chain chamber 101, and the accessory drive gear chamber 105 are adjacent to and separated from the crank chamber 51 inside the crankcase 41, and the lower portion of the accessory drive gear chamber 105 is communicated with the crank chamber 51. Since the crank chamber 51 and the oil strainer chamber 115 are communicated with each other via the communication portion 119 below the communication portion 118, air bubbles are prevented from being mixed into the oil sucked by the oil pump 110, and lubricity is improved. The size of the cycle engine 37 is reduced by reducing the size in the cylinder axis direction. It can contribute to.

  Further, the position of the mating surface 135 between the crankcase 41 and the gear cover member 104 is arranged so as to overlap the concave portion 127 of the gear cover member 104 in plan view, and the cylinder block 85 is interposed between the mating surface 135 and the cam chain chamber 101. Since the crankcase fastening portion 136 is provided, the amount of overhang of the crankcase fastening portion 136 can be reduced, and this also contributes to the compactness of the four-cycle engine 37.

1 is a left side perspective view showing a scooter type motorcycle to which a four-cycle engine according to the present invention is applied. FIG. The left view of a power unit. The top view of a power unit. FIG. 4 is a cross-sectional view of the power unit along the line IV-IV in FIG. 2. The figure which shows one Embodiment of this invention with the longitudinal cross-section in alignment with the VV line | wire of FIG. The expanded sectional view which follows the VI-VI line of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Motorcycle 2 Body frame 37 4-cycle engine 41 Crankcase 42 Cylinder assembly 51 Crank chamber 52 Crankshaft 95 Camshaft 96 Cam drive sprocket 97 Cam driven sprocket 98 Cam chain 101 Cam chain chamber 104 Gear cover member 105 Auxiliary drive gear chamber 107 Auxiliary machine drive gear 108 Auxiliary machine driven gear 111 Gear shaft 112 Bearing section 115 Oil strainer chamber 116 Oil strainer 118, 119 Communication section 127 Recessed section 128 Generator 130 as an example of a rotary auxiliary machine driven to rotate by the crankshaft Boss section 135 Crank case And the gear cover member mating surface 136 Fastening portion 141 Chain guide rail 145 Chain guide rail holding portion 146 Protruding portion 157 Auxiliary drive gear and auxiliary gear Sliding surface of the engagement point 158 cam chain and the chain guide rails Bungiya

Claims (6)

A cylinder assembly is installed on the front of the crankcase with the cylinder tilted almost horizontally forward. The crankshaft is supported in the vehicle width direction inside the crankcase, and the cam drive sprocket provided on the crankshaft and the camshaft that is supported inside the cylinder assembly. A cam chain is wound between the cam driven sprocket and a cam chain chamber that houses the cam chain is provided on one side of the cylinder assembly, and an accessory drive gear is provided adjacent to the axially outer side of the cam drive sprocket. The rear end of the chain guide rail that guides the travel of the lower string side of the cam chain is fixed in the vicinity, and the accessory driven gear that meshes with the accessory drive gear is arranged so as to overlap the chain guide rail in side view, and in side view With the cam chain, set the meshing point of the auxiliary drive gear and auxiliary driven gear. 4-cycle engine of the motorcycle, characterized in that arranged on the sliding surface near the over down guide rail. A gear cover member is provided on the outer surface side of the crankcase to define an accessory drive gear chamber between the crankcase and the cam drive sprocket, the accessory drive gear, and the auxiliary drive gear chamber. 2. The motorcycle according to claim 1, wherein a machine driven gear is accommodated, and a concave portion recessed in the accessory drive gear chamber side is formed in the gear cover member, and a rotary auxiliary device driven to rotate by a crankshaft is provided in the concave portion. 4 cycle engine. A substantially U-shaped chain guide rail holding portion for restricting the vertical and rearward movement of the rear end portion of the chain guide rail is formed on the outer surface of the crankcase, and the chain guide is formed on the inner surface of the gear cover member. The four-cycle engine for a motorcycle according to claim 2, further comprising a protrusion that protrudes toward the outer surface of the rail holding portion and restricts movement of the rear end portion of the chain guide rail toward the outer surface. An oil strainer chamber located below the accessory drive gear chamber is provided between the crankcase and the gear cover member, and the oil strainer chamber is isolated from the cam chain chamber and the accessory drive gear chamber. The cam chain chamber and the accessory drive gear chamber are adjacent to and separated from the crank chamber inside the crankcase, and the lower portion of the accessory drive gear chamber is connected to the crank chamber. The crank chamber and the oil strainer chamber are located below the communication portion. A four-cycle engine for a motorcycle according to claim 2 or 3, wherein A boss portion for fastening and fixing the stationary side member of the rotary accessory is formed on the gear cover member, and the boss portion protrudes from the surface of the gear cover member on the side of the accessory drive gear chamber. The bearing side which supports the gear cover member side edge part of the gear shaft of the said auxiliary machine driven gear is formed in the chamber side surface, The protrusion height of this bearing part and the protrusion height of the said boss | hub part are made substantially the same. The motorcycle 4-cycle engine described. A crank for fastening the cylinder block to the crankcase between the mating surface and the cam chain chamber of the cylinder assembly is arranged so that the position of the mating surface of the crankcase and the gear cover member overlaps the concave portion of the gear cover member in plan view. The four-cycle engine for a motorcycle according to claim 2, further comprising a case fastening portion.

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