JP2008274855A - Internal combustion engine provided with decompression device and motorcycle equipped with the internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To downsize a starter motor, increase multipurpose properties of a decompression device, and miniaturize a valve motion cam and camshaft in an axial direction in an internal combustion engine provided with the decompression device opening engine valves during regular and reverse rotation of a crankshaft. <P>SOLUTION: The internal combustion engine E is provided with the starter motor and a decompression device D reducing compression pressure by opening an exhaust valve. The decompression device D is provided with: a regular rotation decompression cam 73 opening the exhaust valve during regular rotation of the crankshaft; and a reverse rotation decompression cam 93 opening the exhaust valve during reverse rotation of the crankshaft 17. Both decompression cams 73, 93 are arranged, clipping only one exhaust cam 34 in the axial direction of the camshaft 31 therebetween not to overlap the exhaust cam 34 in the axial direction, and drive one exhaust rocker arm 38. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an internal combustion engine having a decompression device that reduces the pressure in a combustion chamber by opening an engine valve and assists starting, and a motorcycle on which the internal combustion engine is mounted.

In an internal combustion engine including an engine valve that is opened and closed by a valve cam provided on a camshaft of a valve gear, and a decompression device, the decompression device opens the engine valve to reduce the compression pressure and facilitate startup What is made is known (for example, refer to Patent Document 1).
The decompression device is provided with a reverse decompression cam, and when the crankshaft rotating due to inertia when the internal combustion engine is stopped is rotated due to an increase in the compression pressure in the combustion chamber and then reversely rotated, the engine valve is driven by the reverse decompression cam. There is also known an internal combustion engine in which the starting pressure is reduced by reducing the compression pressure to quickly stop the crankshaft and the forward rotation torque of the crankshaft by a starter such as a starter motor is reduced. For example, see Patent Document 2).
Further, an internal combustion engine in which a forward rotation decompression cam and a reverse rotation decompression cam are provided on a camshaft of a valve operating device is also known. (For example, see Patent Document 3)
In addition, in a motorcycle equipped with an internal combustion engine equipped with a motor / generator that also serves as a starter motor, when the motorcycle is temporarily stopped, the operation of the internal combustion engine is temporarily stopped and then restarted. (For example, refer to Patent Document 4).
JP 2004-278410 A JP 2002-295218 A JP-A-5-257123 Japanese Patent Laid-Open No. 11-257123

By the way, when the internal combustion engine is started, such as when the internal combustion engine is restarted by an automatic stop / start control device or the like, a large load is applied to the starter motor, so that the starter motor or the motor / generator generator has been enlarged.
Further, in the case where the forward decompression cam is accommodated in a notch provided in the valve cam, the valve cam, and thus the camshaft, are axially arranged in order to prevent a reduction in the strength of the valve cam due to the notch. May increase in size.
A decompression device in which a forward rotation decompression cam and a reverse rotation decompression cam are arranged adjacent to different valve drive cams is difficult to apply to an internal combustion engine provided with an engine valve that is opened and closed by one valve drive cam.

  The present invention has been made in view of such circumstances, and the invention according to claims 1 to 5 is an internal combustion engine including a decompression device that opens an engine valve at the time of forward rotation and reverse rotation of a crankshaft. An object of the present invention is to reduce the size of the starting motor, to increase the versatility of the decompression device, and to reduce the size of the valve cam and the cam shaft in the axial direction. The invention described in claim 2 further aims to reduce the size of the cam follower that is driven by the decompression device and has a roller that contacts the valve cam. An object of the present invention is to secure a stable decompression operation by the decompression device by devising a method for supporting the decompression shaft for driving the forward decompression decompression member. In order to increase the degree, claim 5 further includes a motor / generator functioning also as a starter motor, and a motorcycle equipped with an internal combustion engine controlled by an automatic stop / start control device. The purpose is to reduce the size of the generator.

According to a first aspect of the present invention, a starter motor that rotates the crankshaft forward at the time of start-up, an engine valve that is driven to open and close by a valve operating device, and a decompression device that opens the engine valve to reduce the compression pressure are provided. An internal combustion engine, wherein the valve operating device is driven by a camshaft that is driven to rotate in synchronization with the rotation of the crankshaft, and a cam follower that is driven by a valve operating cam provided on the camshaft to open and close the engine valve. An internal combustion engine comprising:
The decompression device includes a forward rotation decompression member that opens the engine valve when the crankshaft rotates in the forward direction, and a reverse rotation decompression member that opens the engine valve when the crankshaft rotates in the reverse direction. The decompression member and the reverse decompression member are provided on the cam shaft, and sandwich only one valve cam in the axial direction of the cam shaft and do not overlap the valve cam in the axial direction. And an internal combustion engine that drives one of the cam followers.
A second aspect of the present invention is the internal combustion engine according to the first aspect, wherein the cam follower includes a roller that contacts the valve cam and a pair of support portions that support the roller, and the forward rotation decompression unit The member and the reverse decompression member are in contact with the forward rotation decompression contact portion and the reverse rotation decompression contact portion respectively provided on the pair of support portions.
A third aspect of the present invention is the internal combustion engine according to the first or second aspect, wherein the decompression device resists the resilient force of a control spring that sets an operating region in which the decompression operation of the forward-revolution decompression member is performed. The decompression shaft is driven by a drive member that moves, and the decompression shaft is rotatably supported by the camshaft so as to have a free end, and is provided at the free end. The forward rotation decompression member moves to a decompression position that is driven by the decompression shaft to open the engine valve and a decompression release position that does not open the engine valve, and the forward rotation decompression member has the free end portion The engine valve is opened in a state where the cam follower is pressed against the camshaft by the cam follower in contact with the forward rotation decompression member so as not to move.
A fourth aspect of the present invention is the internal combustion engine according to the first or second aspect, wherein the decompression device includes a first supported portion at a position overlapping the valve cam in the axial direction, and the axial direction. A decompression shaft rotatably supported by the camshaft at a second supported portion on a side opposite to the first supported portion across the forward rotation decompression member, and the forward rotation decompression member is And a decompression position that is driven by the decompression shaft to open the engine valve and a decompression release position that does not open the engine valve.
A fifth aspect of the present invention is a motorcycle equipped with the internal combustion engine according to any one of the first to fourth aspects, wherein the starting motor is constituted by a motor / generator that also serves as an electric motor, The engine is stopped and restarted according to the running state by the automatic stop / start control device.

According to the first aspect of the present invention, since the starting operation force is reduced by the decompression device, the starting motor can be reduced in size. Further, the forward-revolution decompression member and the reverse-revolution decompression member provided on the camshaft are arranged at positions where only one valve drive cam that drives a cam follower that opens and closes an engine valve opened by the decompression member is sandwiched in the axial direction. Moreover, since the one cam follower driven by the valve operating cam is driven, the decompression device of the present invention is also applied to an internal combustion engine having one cam follower that drives an engine valve that is opened to perform a decompression operation, for example. Can be used, and the versatility of the decompression device including the forward decompression decompression member and the reverse decompression decompression member can be enhanced. Furthermore, since the forward rotation decompression member and the reverse rotation decompression member do not overlap with the valve cam in the axial direction, it is not necessary to provide a notch in the cam surface for accommodating the decompression member in the valve cam. In addition to ensuring the required strength of the valve cam, the width of the valve cam in the axial direction can be reduced, and the valve cam and thus the cam shaft can be reduced in the axial direction.
According to the second aspect of the present invention, the forward rotation decompression member and the reverse rotation decompression member do not come into contact with the roller that comes into contact with the valve operating cam, so that the size of the roller is prevented from increasing. In addition, since the forward rotation decompression member and the reverse rotation decompression member are distributed and arranged on both sides of the roller, both decompression members can be disposed close to the cam follower, and the configuration of a valve operating device such as a cam follower A member can be arranged compactly. In addition, since the forward rotation decompression contact portion and the reverse rotation decompression contact portion are provided by using a pair of support portions for supporting the roller, it contributes to downsizing of the cam follower.
According to the third aspect of the present invention, the free end portion provided with the forward rotation decompression member in the decompression shaft is pressed against the camshaft when the engine valve is opened by the forward rotation decompression member. When setting the elastic force of the control spring to a small value and shifting the operating range where the decompression operation is performed to the low speed side of the engine rotation speed, etc. While reducing the diameter by reducing the diameter of the shaft, fluctuations in the forward rotation decompression member when contacting the cam follower are prevented, and a stable decompression operation is obtained. Furthermore, since the decompression shaft is cantilevered by the cam shaft, the decompression shaft can be easily assembled to the cam shaft.
According to the fourth aspect of the present invention, since the decompression shaft is supported by the camshaft at the first and second supported portions that are positioned so as to sandwich the forward rotation decompression member in the axial direction, the strength of the decompression shaft is kept low. In addition, the diameter of the decompression shaft can be reduced, and the size and weight can be reduced.
According to the fifth aspect of the present invention, since the starting operation force is reduced by the decompression device, in the motorcycle equipped with the internal combustion engine controlled by the automatic stop starting device, the electric motor / generator also serving as the starting motor is reduced in size. Can be

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
1-7 is a figure explaining 1st Embodiment of this invention.
Referring to FIGS. 1 and 2, an internal combustion engine E to which the present invention is applied is an air-cooled single-cylinder four-stroke internal combustion engine mounted on a motorcycle (see FIG. 1) as a vehicle. The motorcycle includes an internal combustion engine E, a centrifugal start clutch C1 that controls transmission and interruption of power of the crankshaft 17 to the primary reduction mechanism R1, and a constantly meshing gear transmission M as a transmission. A transmission clutch C2 including a friction clutch that transmits and cuts off the power of the crankshaft 17 transmitted to the transmission M via the primary reduction mechanism R1, and the power from the transmission M. And a chain type transmission mechanism R2 as a secondary speed reduction mechanism. The starting clutch C1, the clutch C, the transmission M, and the transmission mechanism R2 constitute a power transmission device that transmits the power generated by the internal combustion engine E to the rear wheels 10 as drive wheels.

  The motorcycle includes a vehicle body including a vehicle body frame and a vehicle body cover that covers the vehicle body frame, an internal combustion engine E supported by the vehicle body frame, and the power transmission device. The body frame includes a head pipe 1 as a front end portion thereof, one main frame 2 extending obliquely downward from the head pipe 1 toward the rear, and a pair of left and right extending obliquely upward from the rear portion of the main frame 2 to the rear. The rear frame 3 is provided. A front fork 4 having a front wheel 9 pivotally supported at the lower end and a handle 5 attached to the upper end is supported on the head pipe 1 so as to be steerable. A pivot shaft 6a provided on a pivot plate 6 attached to the rear portion of the main frame 2 supports the rear wheel 10 at the rear end and is supported by the left rear frame via a rear cushion (not shown). The swing arm 7 is supported to be swingable.

  In this embodiment, the front, rear, left, and right coincide with the front, rear, left, and right of the motorcycle, and the axial direction is the direction of the rotation center line La of the cam shaft 31 described later unless otherwise specified. It is assumed that the radial direction is centered on the rotation center line La. When one of the left and right is one in the axial direction, the other of the left and right is the other in the axial direction.

  Referring also to FIG. 3, the internal combustion engine E mounted on the vehicle body in a horizontal arrangement in which the rotation center line of the crankshaft 17 is oriented in the vehicle width direction is a cylinder 11 having a cylinder axis Lc extending forward in a substantially horizontal direction. And an engine body including a cylinder head 12 coupled to one end of the cylinder 11 in the cylinder axial direction and a crankcase 14 coupled to the other end of the cylinder 11 in the cylinder axial direction.

  2 to 4, the piston 15 slidably fitted to the cylinder 11 is rotatably supported by the crankcase 14 via a pair of main bearings 25 and 26 via a connecting rod 16. Connected to the crankshaft 17. The cylinder head 12 includes an engine valve that opens and closes the combustion chamber 18 facing the piston 15 in the cylinder axial direction, the intake port 19 and the exhaust port 20 that open to the combustion chamber 18, and the intake port 19 and the exhaust port 20, respectively. And an ignition valve 23 for burning the air-fuel mixture in the combustion chamber 18 are provided.

  A valve operating device 30 that opens and closes the intake valve 21 and the exhaust valve 22 is disposed in the valve operating chamber formed by the cylinder head 12 and the head cover 13 coupled to the cylinder head 12 by a bolt 24 penetrating the cam shaft 31. Is done. The valve operating device 30 includes a cam shaft 31 that is rotatably supported by the cylinder head 12 via a pair of bearings 35 and 36, and an intake cam that is provided on the cam shaft 31 as a valve operating cam. 33 and the exhaust cam 34 respectively driven by an intake rocker arm 37 and an exhaust rocker arm 38 as cam followers, and a valve spring 39 that constantly biases the intake valve 21 and the exhaust valve 22 in the valve closing direction.

The cam shaft 31 includes a shaft main body 32, an intake cam 33 formed integrally with the shaft main body 32, and an exhaust cam 34 press-fitted into the shaft main body 32. The shaft body 32 has a journal portion 32c, which is a portion supported by the bearing 35, at a shaft end portion 32a of the cam shaft 31, and a journal portion 32d, which is a portion supported by the bearing 36 via an intermediate member 96 described later. At the shaft end 32b of the cam shaft 31.
The exhaust cam 34 (see also FIG. 6) includes a base circle 34a that closes the exhaust valve 22, a cam peak 34b that opens the exhaust valve 22, a base circle 34a, and a cam peak 34b. And a cam surface 34c formed on the entire circumference of the exhaust cam 34 and in contact with a roller 38a to be described later. Similarly, the intake cam 33 has a base surface 33a that closes the intake valve 21, a cam peak portion 33b that opens the intake valve 21, and a cam surface on which a roller 37a, which will be described later, makes rolling contact. 33c.

  The camshaft 31 having a rotation center line La parallel to the rotation center line of the crankshaft 17 is ½ in synchronization with the rotation by the power of the crankshaft 17 transmitted via the valve gear transmission mechanism 40. Driven at a rotational speed. The transmission mechanism 40 spans between a drive sprocket 40a as a drive rotator provided on the crankshaft 17, a driven sprocket 40b as a driven rotator provided on the shaft end 32a of the camshaft 31, and both sprockets 40a and 40b. And a chain 40c as an endless transmission band. A decompression shaft 72 described later passes through a driven sprocket 40b coupled to the shaft end portion 32a by a pair of bolts 41 in the axial direction.

Each of the rocker arms 37 and 38 is swingably supported by a rocker shaft 42 held by the cylinder head 12. The intake rocker arm 37 includes a roller 37a as a contact portion that contacts the intake cam 33, and a position-adjustable adjustment screw 37b as a valve pressing portion that presses the intake valve 21. The exhaust rocker arm 38 includes a roller 38 a as a contact portion that contacts the exhaust cam 34, and a position-adjustable adjustment screw 38 b as a valve pressing portion that presses the exhaust valve 22. Each roller 37a, 38a is rotatably supported by a pair of support portions 37c, 37d; 38c, 38d of the respective rocker arms 37, 38 via needle bearings 37f, 38f.
With this valve operating device 30, the intake cam 33 opens and closes the intake valve 21 via the intake rocker arm 37, and the exhaust cam 34 opens and closes the exhaust valve 22 via the exhaust rocker arm 38 at a predetermined opening / closing timing and lift amount, respectively.

  Then, the air sucked through an intake device (not shown) having an intake pipe connected to the side wall 12i of the cylinder head 12 with the inlet port 19 opening is supplied from a fuel injection valve (not shown). The fuel is mixed with the formed fuel to form an air-fuel mixture, which is sucked into the combustion chamber 18 through the intake port 19 through the intake valve 21 opened in the intake stroke. The air-fuel mixture is compressed during the compression stroke in which the piston 15 rises, and is ignited and burned by the spark plug 23 at the end of the compression stroke, and the piston 15 driven by the pressure of the combustion gas in the expansion stroke in which the piston 15 descends The crankshaft 17 is driven to rotate. The combustion gas passes through the exhaust valve 22 opened in the exhaust stroke in which the piston 15 rises, passes through the exhaust port 20 from the combustion chamber 18 as exhaust gas, and then the side wall 12e of the cylinder head 12 where the outlet of the exhaust port 20 opens. Is discharged to the outside of the internal combustion engine E through an exhaust device (not shown) having an exhaust pipe connected to the exhaust gas.

  Referring to FIG. 2, a drive sprocket 40 a and a motor / generator G that also serves as a starter motor are sequentially provided at a shaft end 17 a that extends to the left of the main bearings 25 and 26 in the crankshaft 17. The electric generator / generator G includes a stator Ga fixed to the cover 27, and a rotor Gb surrounding the stator Ga and integrally coupled to the crankshaft 17.

  A connecting member 45 is rotatably provided on the crankshaft 17 at a shaft end 17b extending to the right of the main bearing 26 in the crankshaft 17. A primary drive gear 46 is provided at the left end portion of the connecting member 45, and the right end portion of the connecting member 45 constitutes a part of the clutch outer 50 of the starting clutch C1. The starting clutch C1 includes a clutch outer 50, a clutch inner 51 integrally coupled to the shaft end portion 17b, a swingable support supported by the clutch inner 51, and a centrifugal force generated according to the engine rotational speed. And a plurality of centrifugal weights 52 that can be connected to and separated from 50 and switch the starting clutch C1 between a connected state and a disconnected state. Each centrifugal weight 52 comes into contact with the clutch outer 50 when the engine rotational speed exceeds the idling rotational speed, and the starting clutch C1 is in a connected state, so that the power of the crankshaft 17 is transmitted to the primary drive gear 46. .

  A primary driven gear 47 that constitutes the primary reduction mechanism R1 together with the primary drive gear 46 is rotatably supported by the main shaft 56 of the transmission M. The primary driven gear 47 is coupled to a clutch outer 53 of the clutch C <b> 2 provided at the right shaft end portion of the main shaft 56. The clutch C2 includes a clutch outer 53, a clutch inner 54, and a number of clutch plates 55 that are operated by a clutch operating mechanism to be connected or disconnected. When the clutch plate 55 is frictionally joined by the spring force, the clutch C2 is in a connected state, and the power of the crankshaft 17 is transmitted to the clutch inner 54 that is integrally coupled to the main shaft 56 via the clutch outer 53, Further, it is transmitted to the transmission M. Further, when the frictional joining of the many clutch plates 55 is released, the clutch C2 is disconnected, the transmission of power from the clutch outer 53 to the clutch inner 54 is cut off, and the power of the crankshaft 17 is transmitted to the transmission. Not transmitted to M.

The transmission M includes a main shaft 56 provided with a main gear group 58 and a counter shaft 57 provided with a counter gear group 59, and has a gear ratio selected by a speed change operation mechanism (not shown) including a shift drum. Power is transmitted from the main shaft 56 to the counter shaft 57.
Therefore, the power of the crankshaft 17 is transmitted from the starting clutch C1 to the transmission M via the primary speed reduction mechanism R1 and the clutch C2, and the power after the shift is transmitted from the countershaft 57 via the transmission mechanism R2. The rear wheel 10 is driven to rotate by being transmitted to the wheel 10 (see FIG. 1).

  1 and 2, the internal combustion engine E includes a starter configured by a motor-generator G that also functions as a starter motor 60 and a kick starter mechanism 61 as a manual starter mechanism. The dual-purpose generator G (that is, the starting motor 60) and the decompression device D that reduces the starting operation force of the starting mechanism 61 are provided.

  2 and 4, the decompression device D includes a forward rotation decompression mechanism 70 for opening the exhaust valve 22 (see FIG. 3) when the crankshaft 17 is forwardly rotated, and an inertia immediately after the internal combustion engine E is stopped. When the piston 15 in the compression stroke driven by the crankshaft 17 rotating in the direction moves toward the bottom dead center before reaching the top dead center due to the compression pressure in the combustion chamber 18, the crankshaft 17 rotates in the reverse direction Further, a reverse decompression mechanism 90 for opening the exhaust valve 22 (see FIG. 3) and the exhaust valve 22 driven by the decompression mechanisms 70 and 90 to release the compression pressure in the combustion chamber 18 to the outside are included. And a valve mechanism.

4 to 6, the forward rotation decompression mechanism 70 that reduces the compression pressure when the internal combustion engine E is started is provided on the cam shaft 31 and rotates together with the cam shaft 31. The decompression mechanism 70 includes a forward rotation decompression body that is attached to the camshaft 31 so as to be relatively movable, and a control spring 78 that controls the operation of the forward rotation decompression body that occupies the decompression position and the decompression release position according to the engine rotational speed. Prepare.
Here, the decompression position refers to a position where each decompression cam 73, 93, which will be described later, presses the exhaust valve 22 during the compression stroke so as to reduce the compression pressure in the combustion chamber 18, that is, a position where the decompression operation is performed. The decompression release position is a position where the decompression cams 73 and 93 do not open the exhaust valve 22, that is, the decompression operation is not performed.

The forward decompression decompression body is supported by the camshaft 31 so as to be movable, and is driven by a centrifugal weight 71 as a drive member that moves against the elastic force of the control spring 78 according to the engine rotation speed, and the centrifugal weight 71 A decompression shaft 72 supported by the cam shaft 31 and a forward rotation decompression cam 73 as a forward rotation decompression member driven by the decompression shaft 72 are provided.
The control spring 78 sets an operation region in which the decompression operation of the decompression cam 73 is performed by its elastic force.

  The centrifugal weight 71 is supported by the camshaft 31 so as to be able to swing, and swings by the action of centrifugal force generated according to the engine rotation speed. The centrifugal weight 71 disposed on the opposite side of the camshaft 31 across the driven sprocket 40b in the axial direction swings with the rotation center line Ld of the decompression shaft 72 as the swing centerline. The centrifugal weight 71 occupies the low speed side stopper 74a and occupies the low speed side position when it is below a set rotational speed (hereinafter simply referred to as "set rotational speed") that is the engine rotational speed when cranking the internal combustion engine E. Occupies a high speed side position (indicated by a two-dot chain line in FIG. 5) that contacts the high speed side stopper 74b when the engine speed exceeds the set rotational speed. Each stopper 74a, 74b is provided on a stopper member 74 that is provided by being coupled to the driven sprocket 40b by a bolt 41.

Referring to FIG. 4, the decompression shaft 72 has a base end portion 72a penetrating the driven sprocket 40b and splined to the centrifugal weight 71, and rotates together with the centrifugal weight 71.
A decompression shaft 72 having a small-diameter portion 72c having a distal end portion 72b and a large-diameter portion 72d closer to the base end portion 72a than the distal end portion 72b in the axial direction extends from a through hole that is a circular hole provided in the cam shaft 31. A rotation center line Ld parallel to the rotation center line La is provided at a position that is slidably and rotatably accommodated in the accommodation hole 75 as the configured accommodation portion and is eccentric by a predetermined distance from the rotation center line La. . The decompression shaft 72 is supported in a cantilevered manner by one supporting portion 31e which is a part of the camshaft 31, at the only supported portion 72e provided in the large-diameter portion 72d located in the accommodation hole 75. Therefore, the distal end portion 72 b of the decompression shaft 72 is a free end portion, and a minute gap in the radial direction is formed between the housing hole 75 and the cam shaft 31. The size of the accommodation hole 75 is such that the large diameter portion 72d passes through when the decompression shaft 72 is inserted from the exhaust cam 34 side. The bearing portion 31e is provided between the journal portion 32c and the driven sprocket 40b in the axial direction at the shaft end portion 32a of the cam shaft 31.

  The decompression shaft 72 inserted into the accommodation hole 75 from the shaft end portion 32b side toward the shaft end portion 32a has a decompression cam 73 disposed between the intake cam 33 and the exhaust cam 34 in the axial direction. Abutting the cam 34 prevents movement in the axial direction. Specifically, when the decompression cam 73 is brought into contact with the side surface 34d of the exhaust cam 34 press-fitted into the shaft main body 32 on the side of the shaft end portion 32b, the decompression shaft 72 is prevented from moving to the right. Is retained. Further, the decompression cam 73 is brought into contact with a wall surface 76d of the space 76 described later on the shaft end portion 32a side, so that the decompression shaft 72 is prevented from moving to the left.

  Referring also to FIG. 6, the decompression cam 73 provided on the decompression shaft 72 is provided on the shaft main body 32 between the intake cam 33 and the exhaust cam 34 in the axial direction and opens outward in the radial direction. Is integrally formed with the distal end portion 72b of the decompression shaft 72 located in the space 76. The decompression cam 73 is disposed on the side of the intake cam 33 and the intake rocker arm 37 in the axial direction adjacent to the exhaust cam 34 in a state where the decompression cam 73 is in axial contact with the side surface 34d of the exhaust cam 34, and overlaps the exhaust cam 34 in the axial direction. Arranged so that there is no.

  The decompression cam 73 includes an operating portion 73b that performs decompression operation by pressing the exhaust valve 22 (see FIG. 3) via the exhaust rocker arm 38 when the decompression cam 73 occupies the decompression position, and a release portion that does not perform decompression operation. 73a. The operating portion 73b is in a state of slightly projecting radially outward from the cam surface 34c of the base circular portion 34a of the exhaust cam 34 during decompression operation, and abuts against a normal rotation decompression contact portion 67, which will be described later. 38 is driven to slightly open the exhaust valve 22, while the release portion 73a does not come into contact with the decompression contact portion 67.

  The decompression shaft 72 that is cantilevered by the cam shaft 31 is pressed radially inward by the decompression contact portion 67 when the operating portion 73b contacts the decompression contact portion 67, and the decompression shaft 72 is slightly The tip 72b is pressed against the camshaft 31. In this pressed state, the decompression cam 73 is prevented from moving due to the friction of the contact portion between the tip 72b and the cam shaft 31. Therefore, the decompression cam 73 opens the exhaust valve 22 in a state where the distal end portion 72 b is pressed against the camshaft 31 by the exhaust rocker arm 38 abutting against the decompression cam 73.

  Referring to FIGS. 4 and 7, the reverse decompression mechanism 90 that reduces the compression pressure when the crankshaft 17 rotates in the reverse direction is provided on the camshaft 31 and rotates together with the camshaft 31. The reverse decompression mechanism 90 includes a reverse decompression main body that is rotatably provided on the camshaft 31 and a camshaft 31 that is detachably provided on the cylinder head 12 and that rotates the reverse decompression main body when the crankshaft 17 rotates forward. And a stopper 97 for preventing being taken around.

  The reverse decompression main body includes a one-way clutch 91 as a control member that controls the operation of the reverse decompression main body that occupies the decompression position and the decompression release position according to the rotation direction of the crankshaft 17, and the one-way clutch 91. A reverse decompression cam 93 is provided as a reverse decompression member that is driven by the cam shaft 31 and supported by the cam shaft 31. The reverse decompression main body is disposed on the opposite side of the decompression cam 73 and the decompression shaft 72 across the exhaust cam 34 in the axial direction.

  The one-way clutch 91 includes a cylindrical outer member 91a, an inner member 91b configured by a cylindrical intermediate member 96 that is press-fitted and fixed to the shaft end portion 32b of the camshaft 31, a roller 91c, and a spring 91d. A clutch element. On the inner peripheral surface of the outer member 91a, three cam grooves 92 whose depth decreases in the reverse rotation direction R of the cam shaft 31 are provided at equal intervals in the circumferential direction. A roller 91c that contacts 91a and the inner member 91b, and a spring 91d that urges the roller 91c toward the shallower side of the cam groove 92 are housed.

  When the camshaft 31 rotates in the forward rotation direction N during the forward rotation of the crankshaft 17, the roller 91c moves deeper in the cam groove 92 against the elastic force of the spring 91d. And the outer member 91a become rotatable relative to each other. Further, when the camshaft 31 rotates in the reverse rotation direction R when the crankshaft 17 rotates in the reverse direction, the roller 91c moves shallower in the cam groove 92 and bites between the inner member 91b and the outer member 91a. Then, the inner member 91b and the outer member 91a that rotate integrally with the cam shaft 31 are in a restrained state in which relative rotation is impossible, and the cam shaft 31 and the outer member 91a rotate integrally.

  The cylindrical decompression cam 93 is integrally formed with the outer member 91a of the one-way clutch 91, and moves integrally with the outer member 91a. A decompression cam 93 that is slidably fitted to the outer periphery of the intermediate member 96 and is rotatably provided at the shaft end 32b is opposite to the intake cam 33 and the intake rocker arm 37 with respect to the exhaust cam 34 in the axial direction. It is disposed between the exhaust cam 34 and the bearing 36 adjacent to the exhaust cam 34. The decompression cam 93 is arranged so as not to overlap the exhaust cam 34 in the axial direction. Therefore, both decompression cams 73 and 93 are arranged with only one exhaust cam 34 interposed therebetween in the axial direction. Then, the movement of the decompression cam 93 to the right is blocked by the side surface of the bearing 36 via the spacer 94 abutting on the right side, and the movement of the decompression cam 93 to the left is a spacer abutting on the side surface 34e of the exhaust cam 34 It is blocked by the exhaust cam 34 through 95.

The decompression cam 93 includes an operation portion 93b that performs decompression operation by pressing the exhaust valve 22 (see FIG. 3) via the exhaust rocker arm 38 when the decompression cam 93 occupies the decompression position, and a release portion that does not perform decompression operation. 93a. The operating portion 93b is in a state of slightly projecting radially outward from the cam surface 34c at the base circle portion 34a during decompression operation, and abuts against a reverse decompression contact portion 69 described later to drive the exhaust rocker arm 38. While the exhaust valve 22 is slightly opened, the release portion 93a does not contact the decompression contact portion 69.
Therefore, both decompression cams 73 and 93 drive only one exhaust rocker arm 38 of the valve gear 30.

  When the camshaft 31 is rotated forward during the forward rotation of the crankshaft 17 and the one-way clutch 91 is disconnected, the engagement portion 91e provided on the outer member 91a contacts the stopper 97 and rotates forward. The accompanying rotation of the decompression cam 93 by the cam shaft 31 is prevented by the stopper 97, and the decompression cam 93 is brought into a stopped state in contact with the stopper 97. Further, when the camshaft 31 is reversely rotated and the one-way clutch 91 is in a connected state when the crankshaft 17 is reversely rotated, the camshaft 31 and the decompression cam 93 are integrally rotated reversely.

4, 6, and 7, the valve mechanism includes an exhaust valve 22 (see FIG. 3) as a decompression valve that allows the combustion chamber 18 to communicate with the outside to release the pressure in the combustion chamber 18, and each decompression cam 73. , 93 and an exhaust rocker arm 38 as a decompression cam follower that opens and closes the exhaust valve 22.
The exhaust rocker arm 38 is provided with a pair of decompression abutting portions 67 and 69 against which the decompression cams 73 and 93 abut. A pair of decompression abutting portions 67 and 69 each having a projecting portion projecting radially inward are integrally formed with a pair of support portions 38c and 38d constituting the bifurcated ends of the exhaust rocker arm 38, respectively. The Of the pair of decompression abutting portions 67, 69 arranged with the roller 38a interposed therebetween in the axial direction, the decompression abutting portion 67 corresponds to the decompression cam 73 in the axial direction and the intake rocker arm 37, the intake cam 33 and the roller 38a. The decompression contact portion 69 is disposed between the bearing 36 and the roller 38a in the axial direction corresponding to the decompression cam 93.

1 and 2, the kick start mechanism 61 includes a kick lever 61b having a kick pedal 61a operated by a driver, a kick shaft 61c coupled to the kick lever 61b, and one of the counter gear group 59. And a starting gear train including a pinion gear 61d meshing with the speed gear 59a. During the starting operation, the kick shaft 61c rotates with the first gear 59a in the main gear group 58 via the starting gear train and the first gear 59a rotatably supported by the counter shaft 57. The main shaft 56 is rotated by being transmitted to a first-speed gear 58a integrally provided with the main shaft 56. The rotation of the main shaft 56 is transmitted to the primary reduction mechanism R1 via the clutch C2 in the connected state, and further transmitted to the crankshaft 17 via the one-way clutch 62 provided on the crankshaft 17.
Here, the first speed gear 59a, the first speed gear 58a, the main shaft 56, the clutch C2, the primary reduction mechanism R1, and the one-way clutch 62 transmit the starting operation force of the starting mechanism 61 to the crankshaft 17. Configure the mechanism.

  The one-way clutch 62 having the same structure as the one-way clutch 91 includes an outer member 62a formed integrally with the connecting member 45, an inner member 62b splined to the clutch inner 51, an outer member 62a, and an inner member 62b. And a clutch element including a roller 62c and a spring 62d disposed therebetween. When the start mechanism 61 is operated during the start operation, the rotation of the kick shaft 61c causes the outer rotation via the pinion gear 61d, the first speed gear 59a, the first speed gear 58a, the main shaft 56, the clutch C2, and the primary reduction mechanism R1. The one-way clutch 62 is brought into a connected state by being transmitted to the member 62a. In this state, the rotation of the outer member 62a is transmitted to the inner member 62b via the clutch element, and further transmitted to the crankshaft 17 via the clutch inner 51, whereby the crankshaft 17 rotates. When the internal combustion engine E starts its own operation and leaves the cranking state, the one-way clutch 62 is disconnected and the crankshaft 17 is not transmitted from the inner member 62b to the outer member 62a.

  Referring to FIG. 1, the vehicle is provided with an automatic stop / start control device 100 that automatically stops and restarts the internal combustion engine E. The control device 100 stops the operation of the internal combustion engine E when the motorcycle temporarily stops at an intersection or the like according to the traveling state of the motorcycle such as when traveling or stopped by the vehicle speed sensor. By detecting the operation of the throttle grip, which is a driver's intention display for starting the motorcycle, the motor / generator G is caused to function as the starter motor 60 and the internal combustion engine E is restarted.

The operation of the decompression device D will be described with reference to FIGS.
When the internal combustion engine E is stopped, the centrifugal weight 71 occupies a low speed side position (indicated by a solid line in FIG. 5) that is urged by the control spring 78 and contacts the low speed side stopper 74a.
At the time of start-up such as restart by the automatic stop / start control device 100 (see FIG. 1), the internal combustion engine E is started by the motor / generator G or the start mechanism 61 and the crankshaft 17 is rotationally driven to rotate forward. During cranking, the camshaft 31 rotates forward together with the centrifugal weight 71. At this time, when the engine rotation speed is equal to or lower than the set rotation speed, the centrifugal force generated in the centrifugal weight 71 is small, the centrifugal weight 71 is biased by the control spring 78 and occupies the low speed side, and the decompression cam 73 is in the decompression position. Occupy.

  In this state, during the compression stroke of the internal combustion engine E, the operating portion 73b contacts the decompression contact portion 67 to drive the exhaust rocker arm 38, and the exhaust valve 22 driven by the swinging exhaust rocker arm 38 (see FIG. 3). The decompression operation is performed to open the valve with the lift amount for decompression. Thereby, the compression pressure in the combustion chamber 18 escapes to the outside during the compression stroke and is reduced.

  When the engine rotation speed exceeds the set rotation speed, the centrifugal force generated in the centrifugal weight 71 overcomes the elastic force of the control spring 78, and the centrifugal weight 71 rotates clockwise in FIG. As shown by the two-dot chain line, the rotation stops in contact with the high speed side stopper 74b and occupies the high speed side position. In the process until the centrifugal weight 71 moves from the low speed side position to the high speed side position, the decompression shaft 72 driven by the driving force of the centrifugal weight 71 and the driving force of the centrifugal weight 71 transmitted through the decompression shaft 72 The driven decompression cam 73 rotates integrally with the centrifugal weight 71, and the forward rotation decompression main body including the decompression cam 73 occupies the decompression release position indicated by a two-dot chain line in FIG. In this state, as indicated by a two-dot chain line in FIG. 6, the exhaust rocker arm 38 is not driven by the decompression cam 73 during the compression stroke, and therefore the exhaust valve 22 is not opened.

  The piston 15 in the compression stroke driven by the inertial rotating crankshaft 17 immediately after the stop at the end of the operation or immediately after the temporary stop such as idling stop by the automatic stop / start control device 100 causes the compression pressure in the combustion chamber 18 to When the crankshaft 17 moves backward before reaching the top dead center and the crankshaft 17 rotates in the reverse direction, the one-way clutch 91 is engaged and the decompression cam 93 rotates together with the camshaft 31 that rotates in the reverse direction. Then, the decompression cam 93 occupies the decompression position with the operating portion 93b abutting against the decompression abutting portion 69 of the exhaust rocker arm 38 (shown by a two-dot chain line in FIG. 7).

  In this state, during reverse rotation of the crankshaft 17 of the internal combustion engine E, the operating portion 93b contacts the decompression contact portion 69 to drive the exhaust rocker arm 38, and the exhaust valve 22 driven by the swinging exhaust rocker arm 38 is A decompression operation is performed to open the valve with a lift amount for decompression, and the compression pressure in the combustion chamber 18 escapes to the outside and is reduced.

  For this reason, the reverse rotation of the crankshaft 17 is quickly eliminated, and the crankshaft 17 is quickly stopped. In addition, when the crankshaft 17 rotates in the reverse direction, the one-way clutch 62 is in the connected state, but the crankshaft 17 is quickly stopped by the decompression operation of the decompression cam 93, so the reverse rotation of the crankshaft 17 causes the start operating force transmission mechanism to It is prevented from being transmitted.

Next, operations and effects of the embodiment configured as described above will be described.
The decompression device D includes a forward decompression cam 73 that opens the exhaust valve 22 when the crankshaft 17 rotates forward, and a reverse decompression cam 93 that opens the exhaust valve 22 when the crankshaft 17 rotates backward. The decompression cam 93 is disposed so as to sandwich only one exhaust cam 34 in the axial direction and does not overlap the exhaust cam 34 in the axial direction, and drives one exhaust rocker arm 38. Thereby, since the starting operation force is reduced by the decompression device D, the starting motor 60 can be reduced in size. Further, both decompression cams 73 and 93 provided on the camshaft 31 are positioned so as to sandwich only one exhaust cam 34 that drives the exhaust rocker arm 38 that opens and closes the exhaust valve 22 opened by the decompression cams 73 and 93 in the axial direction. Since one exhaust rocker arm 38 that is disposed and driven by the exhaust cam 34 is driven, there is one exhaust rocker arm that drives the exhaust valve that is opened to perform the decompression operation as in this embodiment. The decompression device D of the present invention can be used also for an internal combustion engine, and the versatility of the decompression device D including the forward rotation decompression cam 73 and the reverse rotation decompression cam 93 can be enhanced. Further, since both decompression cams 73 and 93 do not overlap with the exhaust cam 34 in the axial direction, it is not necessary to provide the exhaust cam 34 with notches in the cam surface in which the decompression cams 73 and 93 are accommodated. As a result, the width of the exhaust cam 34 in the axial direction can be reduced, and the exhaust cam 34 and thus the cam shaft 31 can be reduced in the axial direction.

  The exhaust rocker arm 38 has a roller 38a that contacts the exhaust cam 34 and a pair of support portions 38c and 38d that support the roller 38a. Both decompression cams 73 and 93 are provided on the pair of support portions 38c and 38d, respectively. Since the decompression cams 73 and 93 do not come into contact with the roller 38a that comes into contact with the exhaust cam 34 by making contact with the forward rotation decompression contact portion 67 and reverse rotation decompression contact portion 69, the roller 38a is axially moved. Is prevented from becoming large. Further, since the decompression cams 73 and 93 are arranged on both sides of the roller 38a in the axial direction, the decompression cams 73 and 93 can be arranged close to the exhaust rocker arm 38, and the intake rocker arm 37 and the exhaust The components of the valve gear 30 such as the rocker arm 38 can be arranged in a compact manner. In addition, since both decompression contact portions 67 and 69 are provided using a pair of support portions 38c and 38d for supporting the roller 38a, the exhaust rocker arm 38 can be reduced in size.

  The decompression device D includes a decompression shaft 72 driven by a centrifugal weight 71 that moves against the elastic force of a control spring 78 that sets an operation region in which a decompression operation of the forward rotation decompression cam 73 is performed. The forward rotation decompression cam 73 provided on the distal end portion 72b is supported by the cam shaft 31 in a cantilevered manner so as to have a free end portion 72b. The decompression cam 73 is moved to the decompression release position, and the decompression cam 73 opens the exhaust valve 22 in a state where the distal end 72b is pressed against the camshaft 31 by the exhaust rocker arm 38 abutting against the decompression cam 73 at the decompression abutment portion 67. As a result, the distal end portion 72b provided with the decompression cam 73 on the decompression shaft 72 is pressed against the cam shaft 31 when the exhaust valve 22 is opened by the decompression cam 73, so that it does not move. Therefore, while increasing the degree of freedom of setting the decompression operation by the decompression cam 73, such as when the operating region where the decompression operation is performed is shifted to the low speed side of the engine rotation speed by setting the elastic force of the control spring 78 small, Further, while reducing the weight by reducing the diameter of the decompression shaft 72, the deformation of the decompression cam 73 when contacting the exhaust rocker arm 38 is prevented, and a stable decompression operation is obtained. Furthermore, since the decompression shaft 72 is cantilevered by the cam shaft 31, the assembly of the decompression shaft 72 to the cam shaft 31 is facilitated.

  In the motorcycle equipped with the internal combustion engine E, the starting motor 60 is constituted by a motor / generator G that also serves as an electric motor, and the internal combustion engine E is stopped and restarted by the automatic stop / start control device 100 according to the running state. As a result, since the starting operation force is reduced by the decompression device D, the motor / generator G that also serves as the starting motor 60 is miniaturized in the motorcycle equipped with the internal combustion engine E controlled by the automatic stop / start control device 100. can do.

  Next, a second embodiment of the present invention will be described with reference to FIGS. The second embodiment is different from the first embodiment mainly in a part of the forward rotation decompression mechanism 70 of the decompression device D, and the others basically have the same configuration. Therefore, the description of the same part is omitted or simplified, and different points will be mainly described. In addition, about the member same as the member of 1st Embodiment, or a corresponding member, the same code | symbol was used as needed.

The intake cam 33 and the exhaust cam 34 are provided integrally with the shaft body 32 on the cam shaft 31.
The decompression shaft 82 formed integrally with the centrifugal weight 71 is configured by a hole which is a circular hole provided in a portion of the cam shaft 31 that overlaps the journal portion 32c, the intake cam 33 and the exhaust cam 34 in the axial direction. It is slidably and rotatably accommodated in an accommodation hole 85 as an accommodating portion. The decompression shaft 82 is located in the accommodation hole 85 and is separated from each other in the axial direction by a predetermined number of supported portions, here, in the two supported portions of the first and second supported portions 82m and 82n, The first and second support portions 31m and 31n, which are the predetermined number of support portions constituted by a part of the cam shaft 31, are slidably and rotatably supported.

  The first supported portion 82m and the first supported portion 31m are positioned so as to overlap the exhaust cam 34 in the axial direction. In this embodiment, the first supported portion 31m includes a part of the exhaust cam 34. The second supported portion 82n and the second supported portion 31n are provided between the journal portion 32c and the driven sprocket 40b in the axial direction at the shaft end portion 32a. The second supported portion 82n is located on the opposite side of the first supported portion 82m across the decompression cam 83 in the axial direction.

  The decompression shaft 82 inserted into the accommodation hole 85 from the shaft end portion 32a side of the cam shaft 31 toward the shaft end portion 32b is connected to the cam shaft 31 and the driven sprocket 40b by the cam shaft 31 and the bolt 41. The stop member 86 prevents movement in the axial direction. Specifically, when the housing hole 85 abuts against the closed end wall 85a in the axial direction, the movement of the decompression shaft 82 to the right is prevented, and the retaining member 86 moves to the left of the decompression shaft 82. Movement is prevented.

  The decompression cam 83 is provided integrally with the decompression shaft 82 so as to be positioned between the intake cam 33 and the exhaust cam 34 in the axial direction, and is disposed so as not to overlap the exhaust cam 34 in the axial direction. The

  The decompression cam 83 includes an operating portion 83b that performs decompression operation by pressing the exhaust valve 22 (see FIG. 3) through the exhaust rocker arm 38 when the decompression cam 83 occupies the decompression position, and a release portion that does not perform decompression operation. 83a. The decompression cam 83 has a maximum outer diameter equal to or smaller than the diameter of the accommodating hole 85 or equal to or smaller than the maximum outer diameter of the portion located in the accommodating hole 85 on the decompression shaft 82.

  For this reason, the operating portion 83b drives the exhaust rocker arm 38 by abutting against a reverse decompression abutting portion 68, which will be described later, while being positioned radially inward from the cam surface 34c of the base circle portion 34a during decompression operation. However, while the exhaust valve 22 is slightly opened, the release portion 93a does not contact the decompression contact portion 68. Therefore, the decompression cam 83 is disposed at a position where the entire decompression cam 83 does not protrude radially outward from the exhaust cam 34 including the base circle 34a.

  Further, as shown in FIG. 9, the forward rotation decompression abutment portion 68 formed integrally with one support portion 38c of the exhaust rocker arm 38 is larger than the decompression abutment portion 67 of the first embodiment in the radial direction. The abutment surface 68a projects radially inward, and is located radially inward from the cam surface 34c at the base circle 34a of the exhaust cam 34.

According to the second embodiment, the same operations and effects as the first embodiment are exhibited, and the following operations and effects are exhibited.
The decompression device D includes a first supported portion 82m in a position overlapping the exhaust cam 34 in the axial direction, and a second supported portion in a position opposite to the first supported portion 82m across the decompression cam 83 in the axial direction. 82n and a decompression shaft 82 rotatably supported by the camshaft 31, and the decompression cam 83 is driven by the decompression shaft 82 to move between the decompression position and the decompression release position. Since the cam shaft 31 is supported by the first and second supported portions 82m and 82n that sandwich the decompression cam 83 in the axial direction, the decompression shaft 82 of the decompression shaft 82 is supported by a plurality of support locations. The strength can be kept low, and the decompression shaft 82 can be made small in diameter, so that the size and weight can be reduced.

  Since the operating portion 83b of the decompression cam 83 abuts against the decompression abutting portion 68 radially inward of the base circle 34a of the exhaust cam 34, the decompression cam 83 can be reduced in size in the radial direction, and the decompression shaft 82 is further reduced. Can be disposed close to the rotation center line La of the cam shaft, the diameter of the shaft body 32 can be reduced, and the cam shaft 31 provided with the decompression shaft 82 can be reduced in weight. Further, the decompression cam 83 including the operating portion 83b is smaller than the diameter of the accommodation hole 85 or less than the largest outer diameter of the portion located in the accommodation hole 85 in the decompression shaft 82. The weight can be reduced, and the camshaft 31 can be further reduced in weight.

Hereinafter, an embodiment in which a part of the configuration of the above-described embodiment is changed will be described with respect to the changed configuration. The starter motor 60 may be a dedicated motor that does not function as a generator. The decompression member may be a member other than a cam, for example, a pin-like member driven by a decompression shaft.
The cam followers driven by the two decompression cams 73, 93; 83, 93 may be one alocker arm that opens and closes two exhaust valves.
In the second embodiment, for example, when the decompression cam 83 is formed of a member separate from the decompression shaft 82, the maximum outer diameter of the decompression cam 83 is within a range that does not protrude radially outward from the base circle 34a of the exhaust cam 34. It may be equal to or larger than the diameter of the accommodating hole 85 or larger than the maximum outer diameter of the portion located in the accommodating hole 85 on the decompression shaft 82.
The internal combustion engine may be a multi-cylinder internal combustion engine.

1 is a schematic right side view of a motorcycle on which an internal combustion engine to which the present invention is applied is mounted according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view taken along line 2-2 in FIG. 1. FIG. 2 is a schematic cross-sectional view of the internal combustion engine of FIG. 1 taken along a plane orthogonal to the rotation center line of the crankshaft. FIG. 3 is an enlarged view of the vicinity of a cylinder head in FIG. 2. It is a figure of the principal part by the 5 arrow view of FIG. FIG. 6 is a cross-sectional view of a main part taken along line 6-6 in FIG. 4, illustrating a decompression position and a decompression release position of a forward decompression decompression cam. FIG. 7 is a cross-sectional view of a main part taken along line 7-7 in FIG. FIG. 5 shows a second embodiment of the present invention and corresponds to FIG. 4. It is sectional drawing of the principal part in the 9-9 line | wire of FIG. 8, and is a figure corresponding to FIG.

Explanation of symbols

11 ... Cylinder, 12 ... Cylinder head, 17 ... Crankshaft, 18 ... Combustion chamber, 30 ... Valve drive, 31 ... Camshaft, 34 ... Exhaust cam, 38 ... Exhaust rocker arm, 40b ... Driven sprocket, 60 ... Starter motor, 61 ... Kick-type start mechanism, 70 ... Decompression mechanism, 72, 82 ... Decompression shaft, 73, 83 ... Decompression cam, 78 ... Control spring, 90 ... Decompression mechanism, 91 ... One-way clutch, 93 ... Decompression cam, 100 ... Automatic stop start Control device,
E: Internal combustion engine, G: Electric generator combined with motor.

Claims (5)

An internal combustion engine comprising: a starter motor that rotates a crankshaft at the time of startup; an engine valve that is driven to open and close by a valve operating device; and a decompression device that opens the engine valve to reduce a compression pressure. In an internal combustion engine, wherein the valve device includes a cam shaft that is rotationally driven in synchronization with the rotation of the crankshaft, and a cam follower that is driven by a valve cam provided on the cam shaft to open and close the engine valve.
The decompression device includes a forward rotation decompression member that opens the engine valve when the crankshaft rotates in the forward direction, and a reverse rotation decompression member that opens the engine valve when the crankshaft rotates in the reverse direction. The decompression member and the reverse decompression member are provided on the cam shaft, and sandwich only one valve cam in the axial direction of the cam shaft and do not overlap the valve cam in the axial direction. The internal combustion engine is arranged so as to drive one cam follower.   2. The internal combustion engine according to claim 1, wherein the cam follower includes a roller that contacts the valve cam and a pair of support portions that support the roller, and the forward rotation decompression member and the reverse rotation decompression member include: An internal combustion engine that abuts on the forward rotation decompression contact portion and the reverse rotation decompression contact portion provided on the pair of support portions, respectively.   3. The internal combustion engine according to claim 1, wherein the decompression device is driven by a drive member that moves against an elastic force of a control spring that sets an operation region in which a decompression operation of the forward decompression decompression member is performed. The decompression shaft is supported in a cantilevered manner so as to be rotatable on the camshaft so as to have a free end, and the forward rotation decompression member provided at the free end includes the decompression shaft. It is driven by a shaft to move to a decompression position where the engine valve is opened and a decompression release position where the engine valve is not opened. The forward rotation decompression member is in contact with the free rotation decompression member. An internal combustion engine, wherein the engine valve is opened in a state in which the cam follower is pressed against the camshaft by the cam follower so as not to move.   3. The internal combustion engine according to claim 1, wherein the decompression device sandwiches the first supported portion at a position overlapping the valve cam in the axial direction and the forward rotation decompression member in the axial direction. A decompression shaft rotatably supported by the camshaft at a second supported portion at a position opposite to the first supported portion; and the forward rotation decompression member is driven by the decompression shaft. An internal combustion engine which moves to a decompression position where the engine valve is opened and a decompression release position where the engine valve is not opened.   A motorcycle equipped with the internal combustion engine according to any one of claims 1 to 4, wherein the starter motor is constituted by a motor / generator that also serves as an electric motor, and the internal combustion engine is controlled by an automatic stop / start control device. A motorcycle characterized by being stopped and restarted according to a running state.

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