JP6706388B2 - Internal combustion engine - Google Patents

Description

The present invention relates to a decompression device for an internal combustion engine.

Patent Document 1 discloses a decompression device for an internal combustion engine. The decompression device includes a decompression cam having a small-diameter partial cylindrical surface having an axis parallel to the rotation axis of the camshaft. The decompression cam causes a part of the partial cylindrical surface to project from the virtual cylindrical surface coaxial with the cam shaft at a rotational speed lower than a preset value. The slipper of the exhaust side rocker arm contacts the protruding decompression cam and opens the exhaust valve. By opening the exhaust valve during the compression stroke in the low rotation range, the drive resistance of the piston is reduced and the vibration of the internal combustion engine is suppressed.

Japanese Unexamined Patent Publication No. 2014-129794

The collision noise between the decompression cam and the exhaust side rocker arm is reduced when the piston does not go over the compression top dead center and the cam shaft reverses. In addition to reducing such collision noise, it is required to reduce collision noise between the decompression cam and the exhaust side rocker arm and exhaust valve seating noise during normal rotation of the camshaft.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an internal combustion engine that can further reduce the collision sound between the decompression cam and the exhaust side rocker arm and the seating sound of the exhaust valve.

According to the first aspect of the present invention, a base surface having a shape of a partial cylindrical surface coaxial with a rotation axis of a camshaft, and a base surface provided in the camshaft continuously with the base surface in a rotation direction, Of the exhaust side rocker arm, which is provided on the exhaust side rocker arm and lifts outwardly in the radial direction to regulate the lift amount of the exhaust valve, and maintains contact with the base surface and the lift surface. A cam follower that causes rocking, and a decompression cam that projects a curved projecting surface having a generatrix parallel to the rotation axis of the cam shaft from a virtual cylindrical surface that is coaxial with the cam shaft at a preset rotational speed, and A convex decompression follower surface of a convex curved surface which is provided on the exhaust side rocker arm outside the virtual cylindrical surface, faces the virtual cylindrical surface at a position closest to the virtual cylindrical surface, and contacts the curved protruding surface, A concave decompression follower surface that is provided upstream of the convex decompression follower surface in the normal direction of the camshaft, is formed into a concave curved surface having a generatrix parallel to the rotation axis of the camshaft, and contacts the curved projection surface; An internal combustion engine including is provided.

According to the second side surface, in addition to the configuration of the first side surface, the upstream end of the concave decompression follower surface is provided at a position farther from the rotation axis of the cam shaft than the curved protruding surface.

According to the third aspect, in addition to the configuration of the first or second aspect, the concave decompression follower surface moves away from the rotation axis of the camshaft as it moves away from the convex decompression follower surface.

According to the fourth aspect, in addition to the configuration of any one of the first to third aspects, the internal combustion engine is formed between the convex decompression follower surface and the concave decompression follower surface, and is more than the curved projecting surface. An auxiliary concave decompression follower surface composed of a concave curved surface having a small curvature is further provided.

According to the fifth aspect, in addition to the configuration of the fourth aspect, the auxiliary concave decompression follower surface is formed of a part of a cylindrical surface having a larger curvature than the concave decompression follower surface.

According to the sixth aspect, in addition to the configuration of any one of the first to fifth aspects, the internal combustion engine is provided downstream of the convex decompression follower surface in the forward rotation direction of the camshaft, and A second concave decompression follower surface formed on a concave curved surface having a generatrix parallel to the rotation axis and contacting the curved protruding surface is further provided.

According to the seventh aspect, the base surface having a shape of a partial cylindrical surface coaxial with the rotation axis of the camshaft, and the base surface, which is continuous with the base surface in the rotation direction, are provided on the camshaft and have a diameter larger than that of the base surface. The lift surface that bulges outward in the direction to define the lift amount of the exhaust valve, and the rocker arm on the exhaust side, which is kept in contact with the base surface and the lift surface to swing the rocker arm on the exhaust side. A cam follower to cause, a decompression cam for projecting a curved projecting surface having a generatrix parallel to the rotation axis of the cam shaft from a virtual cylindrical surface coaxial with the cam shaft at a preset rotational speed, and the virtual cylindrical surface. Of the convex decompression follower surface that is provided on the exhaust side rocker arm on the outside of the camshaft, faces the virtual cylindrical surface at the position closest to the virtual cylindrical surface, and contacts the curved protruding surface, and in the forward direction of the camshaft. An internal combustion engine is provided, which is provided downstream of the convex decompression follower surface and has a concave decompression follower surface formed in a concave curved surface having a generatrix parallel to the rotation axis of the camshaft and contacting the curved projection surface. It

According to the eighth aspect, in addition to the configuration of the seventh aspect, the downstream end of the concave decompression follower surface is provided at a position farther from the rotation axis of the cam shaft than the curved protruding surface.

According to the ninth aspect, in addition to the configuration of the seventh or eighth aspect, the concave decompression follower surface moves away from the rotation axis of the camshaft as it moves away from the convex decompression follower surface.

According to the tenth aspect, in addition to the configuration according to any one of the seventh to ninth aspects, the internal combustion engine is formed between the convex decompression follower surface and the concave decompression follower surface, and more than the curved protruding surface. An auxiliary concave decompression follower surface composed of a concave curved surface having a small curvature is further provided.

According to the eleventh aspect, in addition to the configuration of the tenth aspect, the auxiliary concave decompression follower surface is formed of a part of a cylindrical surface having a larger curvature than the concave decompression follower surface.

According to the twelfth aspect, in addition to the configuration according to any one of the first to eleventh aspects, the internal combustion engine is coupled to the crankshaft to generate power in accordance with the rotation of the crankshaft and to supply the supplied power. Accordingly, an AC generator for driving the crankshaft around its rotation axis is further provided.

According to the thirteenth aspect, the base surface having a shape of a partial cylindrical surface coaxial with the rotation axis of the camshaft, and the base surface, which is continuous with the base surface in the rotation direction, are provided on the camshaft and have a diameter larger than that of the base surface. The lift surface that bulges outward in the direction to define the lift amount of the exhaust valve, and the rocker arm on the exhaust side, which is kept in contact with the base surface and the lift surface to swing the rocker arm on the exhaust side. A cam follower to cause, a decompression cam for projecting a curved projecting surface having a generatrix parallel to the rotation axis of the cam shaft from a virtual cylindrical surface coaxial with the cam shaft at a preset rotational speed, and the virtual cylindrical surface. Provided on the exhaust side rocker arm on the outside of, and a convex decompression follower surface of a convex curved surface facing the virtual cylindrical surface and contacting the curved protruding surface, the curved protruding surface from the virtual cylindrical surface. The most projecting top surface and upstream of the top surface in the normal rotation direction of the camshaft are formed into a concave curved surface having a generatrix parallel to the rotation axis of the camshaft to form the convex decompression follower surface. An internal combustion engine having a cushioning surface in contact is provided.

According to the fourteenth side surface, in addition to the configuration of the thirteenth side surface, the curved projecting surface is provided downstream of the top surface in the forward direction of rotation of the camshaft, and is a bus line parallel to the rotation axis of the camshaft. It further has a 2nd buffer surface formed in the concave curved surface which has.

According to the fifteenth aspect, a base surface having a shape of a partial cylindrical surface coaxial with the rotation axis of the camshaft, and a cam surface that is continuous with the base surface in the rotation direction and is provided on the camshaft have a diameter larger than that of the base surface. The lift surface that bulges outward in the direction to define the lift amount of the exhaust valve, and the rocker arm on the exhaust side, which is kept in contact with the base surface and the lift surface to swing the rocker arm on the exhaust side. A cam follower to cause, a decompression cam for projecting a curved projecting surface having a generatrix parallel to the rotation axis of the cam shaft from a virtual cylindrical surface coaxial with the cam shaft at a preset rotational speed, and the virtual cylindrical surface. Provided on the exhaust side rocker arm on the outside of, and a convex decompression follower surface of a convex curved surface facing the virtual cylindrical surface and contacting the curved protruding surface, the curved protruding surface from the virtual cylindrical surface. The most projecting top surface and a downstream surface of the top surface in the forward direction of the camshaft are formed into a concave curved surface having a generatrix parallel to the rotation axis of the camshaft to form a convex decompression follower surface. An internal combustion engine having a cushioning surface in contact is provided.

According to the first aspect, the curved protruding surface of the decompression cam projects in the centrifugal direction of the cam shaft in the low rotation speed range lower than the set rotation speed. During the normal rotation of the camshaft, the curved protruding surface of the decompression cam successively contacts the concave decompression follower surface and the convex decompression follower surface of the exhaust side rocker arm. Since the concave decompression follower surface is formed as a concave curved surface, the curved protruding surface of the decompression cam can slide in the tangential direction with respect to the concave curved surface at the start of contact. Therefore, the collision noise between the decompression cam and the exhaust side rocker arm can be suppressed.

According to the second aspect, when the contact is started, the curved protruding surface of the decompression cam comes into contact with the concave curved surface. The collision noise between the decompression cam and the exhaust side rocker arm can be suppressed.

According to the third aspect, even if the curved projection surface of the decompression cam is slightly displaced due to dimensional tolerance or assembly error, the curved projection surface of the decompression cam slides tangentially to the concave curved surface at the start of contact. You can Therefore, the collision noise between the decompression cam and the exhaust side rocker arm can be suppressed.

According to the fourth aspect, since the concave decompression follower surface, the auxiliary concave decompression follower surface, and the convex decompression follower surface are continuous, the curved projection surface of the decompression cam can smoothly follow the concave decompression follower surface to the convex decompression follower surface. it can. The collision noise between the decompression cam and the exhaust side rocker arm can be suppressed.

According to the fifth aspect, the curved projection surface of the decompression cam can smoothly follow the concave decompression follower surface to the convex decompression follower surface according to the change in the curvature. The collision noise between the decompression cam and the exhaust side rocker arm can be suppressed.

According to the sixth aspect, the curved protruding surface of the decompression cam contacts the convex decompression follower surface and then the second concave decompression follower surface during the normal rotation of the camshaft. Since the second concave decompression follower surface is formed as a concave curved surface, the lift amount of the exhaust valve gently changes when the decompression cam separates from the second concave decompression follower surface. As a result, the seating noise of the exhaust valve is reduced. Moreover, during the reverse rotation of the camshaft, the curved protruding surface of the decompression cam successively contacts the second concave decompression follower surface and the convex decompression follower surface. Since the second concave decompression follower surface is formed as a concave curved surface, the curved protruding surface of the decompression cam can slide tangentially to the concave curved surface at the start of contact. Therefore, when the piston does not go over the compression top dead center and the cam shaft reverses, the collision noise between the decompression cam and the exhaust side rocker arm can be suppressed.

According to the seventh aspect, during the normal rotation of the camshaft, the curved protruding surface of the decompression cam contacts the convex decompression follower surface and then the concave decompression follower surface. Since the concave decompression follower surface is formed as a concave curved surface, the lift amount of the exhaust valve gradually changes when the decompression cam separates from the concave decompression follower. As a result, the seating noise of the exhaust valve is reduced. Moreover, during the reverse rotation of the camshaft, the curved protruding surfaces of the decompression cam successively contact the concave decompression follower surface and the convex decompression follower surface. Since the concave decompression follower surface is formed as a concave curved surface, the curved protruding surface of the decompression cam can slide in the tangential direction with respect to the concave curved surface at the start of contact. Therefore, when the piston does not go over the compression top dead center and the cam shaft reverses, the collision noise between the decompression cam and the exhaust side rocker arm can be suppressed.

According to the eighth aspect, the curved projection surface of the decompression cam is a concave curved surface and separates from the rocker arm in response to the rotation of the camshaft. When seated, the lift amount of the exhaust valve surely changes gently. In this way, the seating noise of the exhaust valve can be reduced.

According to the ninth aspect, even if the curved protruding surface of the decompression cam is slightly displaced due to dimensional tolerance, assembly error, or the like, the lift amount of the exhaust valve changes gently when seated. In this way, the seating noise of the exhaust valve can be reduced.

According to the tenth aspect, since the convex decompression follower surface, the auxiliary concave decompression follower surface, and the concave decompression follower surface are continuous, the curved projection surface of the decompression cam can smoothly follow the convex decompression follower surface to the concave decompression follower surface. it can. The collision noise between the decompression cam and the exhaust side rocker arm can be suppressed.

According to the eleventh aspect, the curved projection surface of the decompression cam can smoothly follow the concave decompression follower surface from the convex decompression follower surface according to the change in the curvature. The collision noise between the decompression cam and the exhaust side rocker arm can be suppressed.

According to the twelfth aspect, such an alternator can establish the idling state of the internal combustion engine. When idling, the alternator can realize the reciprocating motion of the piston without passing through the combustion stroke. Fuel consumption is suppressed and exhaust noise of the internal combustion engine is reduced.

According to the thirteenth aspect, the curved projecting surface of the decompression cam projects in the centrifugal direction of the camshaft in the low rotation speed range lower than the set rotation speed. During the normal rotation of the camshaft, the curved protruding surfaces of the decompression cam successively contact the convex decompression follower surface of the exhaust side rocker arm at the buffer surface and the top surface. Since the buffer surface of the decompression cam is formed as a concave curved surface, the convex decompression follower surface can slide in the tangential direction with respect to the concave curved surface of the decompression cam at the start of contact. Therefore, the collision noise between the decompression cam and the exhaust side rocker arm can be suppressed.

According to the fourteenth aspect, during the normal rotation of the camshaft, the curved protruding surface of the decompression cam contacts the convex decompression follower surface with the second buffer surface following the top surface. Since the second buffer surface is formed as a concave curved surface, the lift amount of the exhaust valve changes gently when the convex decompression follower surface separates from the second buffer surface. As a result, the seating noise of the exhaust valve is reduced. Moreover, during the reverse rotation of the cam shaft, the curved protruding surface of the decompression cam successively contacts the second buffer surface and the top surface. Since the second buffer surface is formed as a concave curved surface, the convex decompression follower surface can slide in the tangential direction with respect to the second buffer surface at the start of contact. Therefore, when the piston does not go over the compression top dead center and the cam shaft reverses, the collision noise between the decompression cam and the exhaust side rocker arm can be suppressed.

According to the fifteenth aspect, the curved projecting surface of the decompression cam projects in the centrifugal direction of the camshaft in the low rotation speed range lower than the set rotation speed. During the normal rotation of the camshaft, the curved protruding surfaces of the decompression cam successively contact the top surface and the cushioning surface. Since the buffer surface is formed as a concave curved surface, the lift amount of the exhaust valve changes gently when the convex decompressor surface separates from the buffer surface. As a result, the seating noise of the exhaust valve is reduced. Moreover, during the reverse rotation of the camshaft, the curved protruding surface of the decompression cam successively contacts the buffer surface and the top surface. Since the buffer surface is formed as a concave curved surface, the convex decompress follower surface can slide in the tangential direction with respect to the buffer surface at the start of contact. Therefore, when the piston does not go over the compression top dead center and the cam shaft reverses, the collision noise between the decompression cam and the exhaust side rocker arm can be suppressed.

FIG. 1 is a side view schematically showing a scooter type motorcycle according to an embodiment of a saddle type vehicle. (First embodiment) FIG. 2 is a horizontal sectional view taken along line 2-2 of FIG. (First embodiment) FIG. 3 is an enlarged vertical sectional view of the cylinder head taken along line 3-3 of FIG. (First embodiment) FIG. 4 is a sectional view taken along line 4-4 of FIG. (First embodiment) FIG. 5 is an enlarged vertical sectional view of a part of FIG. (First embodiment) FIG. 6 is an enlarged vertical sectional view of a part of FIG. (First embodiment) FIG. 7 corresponds to FIG. 5 and is a vertical cross-sectional view showing the position of the decompression cam when the cam pin is displaced from the first position to the second position in the decompression device according to the first embodiment. (First embodiment) FIG. 8 corresponds to FIG. 6 and is an enlarged vertical sectional view schematically showing the configuration of the decompression device according to the second embodiment. (Second embodiment) FIG. 9 is an enlarged vertical sectional view corresponding to FIG. 6 and schematically showing the configuration of the decompression device according to the third embodiment. (Third Embodiment)

49... AC generator (AC generator starter)
89... Exhaust valve 95... Cam shaft 97b... Exhaust side rocker arm 101... Cam follower 108a... Base surface 108b... Lifting surface 109... Roller 112... Decompression cam 122... Virtual cylindrical surface 129... Curved protrusion Surface (partial cylindrical surface)
133... Convex decompression follower surface 134... Recessed decompression follower surface 134a... Upstream end 135... (Second) concave decompression follower surface 135a... Downstream end 136... Auxiliary concave decompression follower surface 137... (Second) auxiliary concave decompression follower surface 143... Convex decompression follower surface 144... Decompression cam 145... Curved projection surface 146... Top surface 147... Buffer surface 148... (Second) buffer surface 151... Decompression device Xc... Rotation axis line (of camshaft)

An embodiment of the present invention will be described below with reference to the accompanying drawings. In the following description, the front-rear direction, the up-down direction, and the left-right direction are the directions viewed by an occupant on the motorcycle.

First embodiment

FIG. 1 schematically shows a scooter type motorcycle according to an embodiment of a saddle type vehicle. The motorcycle 11 includes a vehicle body frame 12 and a vehicle body cover 13. The vehicle body frame 12 includes a head pipe 14 at a front end thereof, a main frame 15 connected to the head pipe 14 at a front end thereof, a cross pipe 16 connected to a rear portion of the main frame 15 and extending in the vehicle width direction, and the cross pipe 16 And a pair of left and right rear frames 17 having front ends connected to both ends and extending in the vehicle front-rear direction. A front fork 18 that supports the front wheels WF rotatably around a horizontal axis and a rod-shaped steering handle 19 are steerably supported by the head pipe 14.

The vehicle body cover 13 is attached to the vehicle body frame 12. An occupant seat 21 is mounted on the vehicle body cover 13 above the rear frame 17. The vehicle body cover 13 includes a front cover 22 that covers the head pipe 14 from the front, a leg shield 23 that is continuous from the front cover 22, and a lower end of the leg shield 23 that is continuous between the passenger seat 21 and the front wheels WF. And a step floor 24 arranged above.

A unit swing type drive unit 25 is arranged in a space below the rear frame 17. The drive unit 25 is connected to a bracket 26 connected to the front end of the rear frame 17 via a link 27 so as to be swingable in the vertical direction. A rear wheel WR is supported at the rear end of the drive unit 25 so as to be rotatable around a horizontal axis. A rear cushion unit 28 is arranged between the rear frame 17 and the drive unit 25 at a position apart from the link 27 and the bracket 26. The drive unit 25 includes an air-cooled single-cylinder internal combustion engine 29, and a transmission device 31 that is connected to the internal combustion engine 29 and the rear wheels WR and transmits the output of the internal combustion engine 29 to the rear wheels WR. The transmission case 31a of the transmission 31 is coupled to the engine body 29a of the internal combustion engine 29.

The engine body 29a of the internal combustion engine 29 includes a crankcase 33 that supports the crankshaft 32 rotatably around a rotation axis, a cylinder block 34 that is connected to the crankcase 33, and a cylinder head 35 that is connected to the cylinder block 34. , A head cover 36 coupled to the cylinder head 35. An intake device 37 and an exhaust device 38 are connected to the cylinder head 35. The intake device 37 includes an air cleaner 39 supported by the transmission case 31 a, and a throttle body 41 arranged between the air cleaner 39 and the cylinder head 35. A fuel injection valve 42 is attached to the upper side wall of the cylinder head 35. The exhaust device 38 includes an exhaust pipe 43 that extends rearward from a lower side wall of the cylinder head 35 and below the engine body 29a, and an exhaust muffler that is connected to a downstream end of the exhaust pipe 43 and is connected to the crankcase 33 (illustrated in the drawing). )) and.

As shown in FIG. 2, a cylinder bore 44 is defined in the cylinder block 34. A piston 45 is slidably fitted into the cylinder bore 44 along the cylinder axis C. The cylinder axis C inclines slightly upward. The crankshaft 32 is connected to the piston 45. The rotation axis Xis of the crankshaft 32 is oriented in the vehicle width direction.

A combustion chamber 46 is defined in the cylinder head 35. The combustion chamber 46 continues from the cylinder bore 44. The piston 45 faces the cylinder head 35 and separates the combustion chamber 46 from the cylinder head 35. The air-fuel mixture is introduced into the combustion chamber 46 via the intake device 37. The exhaust gas in the combustion chamber 46 is discharged through the exhaust device 38.

The crankcase 33 is divided into a first case half 33a and a second case half 33b. The first case half body 33a and the second case half body 33b cooperate to define the crank chamber 47. The crank of the crankshaft 32 is housed in the crank chamber 47. The first case half 33a has a bearing 48a that rotatably supports the crankshaft 32, while the second case half 33b has a bearing 48b that rotatably supports the crankshaft 32.

An alternator starter 49 is connected to the crankcase 33. The alternator starter 49 includes an outer rotor 51 fixed to the crankshaft 32 protruding through the first case half 33a of the crankcase 33 and protruding from the first case half 33a, and a crankshaft surrounded by the outer rotor 51. 32 and an inner stator 52 arranged around 32. The inner stator 52 is fixed to a support plate 53 fastened to the first case half 33a. An electromagnetic coil 52a is wound around the inner stator 52. A magnet 51a is fixed to the outer rotor 51. When the outer rotor 51 rotates relative to the inner stator 52, electric power is generated by the electromagnetic coil 52a. On the other hand, when a current flows through the electromagnetic coil 52a, a magnetic force is generated in the electromagnetic coil 52a, causing the outer rotor 51 to rotate. At this time, the AC generator starter 49 functions as a motor. The alternator starter 49 can rotate the crankshaft 32 without using a gear or the like.

A control circuit (ECU) is connected to the AC generator starter 49. The control circuit controls the supply of electric power to the electromagnetic coil 52a. The driving force of the alternator starter 49 may be used, for example, as a starter to rotate the crankshaft 32 when the internal combustion engine 29 is started, and is used to smoothly restart the motorcycle 11 during idle stop. Good. Here, the control circuit has, for example, an idle stop determination unit, an idle stop control unit, and a motor idle drive processing unit.

The idle stop determination unit has a function of determining whether or not to perform idle stop control when the vehicle is temporarily stopped during traveling. The throttle opening calculated by the throttle opening calculation unit and the traveling speed of the vehicle calculated by the vehicle speed calculation unit are input to the idle stop determination unit during traveling. The idle stop determination unit outputs an idle stop control instruction signal to the idle stop control unit when the throttle opening and the traveling speed are equal to or less than a predetermined value. An instruction signal is supplied from the idle stop SW determination unit to the idle stop determination unit. When it is confirmed that the idle stop switch is ON by the instruction signal, the idle stop determination unit prompts execution of idle stop control.

The idle stop control unit performs idle stop control based on the instruction signal from the idle stop determination unit. The idle stop control unit stops the operation of the fuel injection valve 42 and the operation of the spark plug. This interrupts the combustion operation of the internal combustion engine 29. When the motorcycle 11 restarts after being temporarily stopped, the idle stop control unit drives the crankshaft 32 in the reverse direction based on the rotation angle of the crankshaft 32, and performs control for ensuring the normal rotation drive of the crankshaft 32.

The motor idle drive processing unit maintains the engine rotation speed at a predetermined rotation speed while the motorcycle 11 is stopped while the combustion operation of the internal combustion engine 29 is stopped by the idle stop determination unit and the idle stop control unit. Perform motor idle control. The motor idle drive processing unit stops the motor idle control when the accelerator request is not detected after the elapse of a predetermined time. When the accelerator request is detected before the elapse of a predetermined time, the crankshaft 32 is rotationally driven by the AC generator starter 49 to start the motorcycle 11. When the motorcycle 11 starts, the combustion stroke of the internal combustion engine 29 is restarted.

A cylindrical generator cover 54 surrounding the AC generator starter 49 is coupled to the first case half body 33a. An air inlet 54a is defined at the open end of the generator cover 54. A radiator 55 is arranged at the air inlet 54a. A cooling fan 56 is coupled to the outer surface of the outer rotor 51. The cooling fan 56 rotates according to the rotation of the crankshaft 32, and the cooling air flows through the radiator 55.

The transmission device 31 is housed in the transmission case 31a, and electronically controlled V-belt type continuously variable transmission (hereinafter referred to as "transmission") 57 that continuously changes the rotational power transmitted from the crankshaft 32, and a transmission. A reduction gear mechanism 59, which is housed in the case 31a and reduces the rotational power of the transmission 57 and transmits it to the axle 58 of the rear wheel WR, is provided. The rear wheel WR is arranged between the transmission case 31 a and the support arm 61. The support arm 61 continuously extends from the crankcase 33 toward the rear of the vehicle. The exhaust muffler described above is attached to the support arm 61. The axle 58 of the rear wheel WR is supported on both sides by the transmission case 31a and the support arm 61 so as to be rotatable around its axis.

The transmission case 31 a includes a case main body 62 that is continuous from the second case half body 33 b of the crankcase 33, a case cover 64 that is fastened to the case main body 62, and defines a transmission chamber 63 between the case main body 62 and the case main body 62. A gear cover 66 is fastened to the case main body 62 and defines a gear chamber 65 between the case main body 62 and the case main body 62. The transmission 57 is accommodated in the transmission chamber 63. A reduction gear mechanism 59 is housed in the gear chamber 65. The case main body 62 and the case cover 64 cooperate to form a mission case.

The transmission 57 is arranged in the transmission chamber 63, and is arranged in the drive pulley device 67 attached to the crankshaft 32 as a drive shaft, and in the transmission chamber 63, and from the transmission chamber 63 to the gear chamber 65. And a driven pulley device 69 attached to the driven shaft 68 protruding. In the drive pulley device 67, between the fixed sheave 73 fixed to the crankshaft 32 and the movable sheave 74 supported by the crankshaft 32 so as to be movable in the axial direction of the crankshaft 32 while facing the fixed sheave 73. The V belt 71 is wrapped around. Similarly, in the driven pulley device 69, the V-belt 71 is provided between the fixed sheave 78 that is coaxially mounted on the driven shaft 68 and the movable sheave 79 that is coaxially mounted on the driven shaft 68 while facing the fixed sheave 78. Is wrapped around. By the action of the actuator unit 72, the belt winding diameter of the drive pulley device 67 is electronically controlled in a variable manner. The belt winding diameter of the driven pulley device 69 changes according to the change of the belt winding diameter of the drive pulley device 67.

In the drive pulley device 67, the movable sheave 74 is arranged between the second case half body 33 b of the crankcase 33 and the fixed sheave 73. The movable sheave 74 has a movable sheave boss 74 a that receives the crankshaft 32. The movable sheave boss 74 a extends from the sheave body that receives the V-belt 71 toward the second case half body 33 b of the crankcase 24. The transmission 57 includes a first shift mechanism 75a including a centrifugal weight and a cam plate, and a second shift mechanism 75b including the actuator unit 72 described above. Axial movement of the movable sheave 74 is realized according to the functions of the first shift mechanism 75a and the second shift mechanism 75b, and the winding radius of the V belt 71 changes.

The driven pulley device 69 has a cylindrical shape that is coaxial with the driven shaft 68, has an inner cylinder 76 that is coaxially attached to the driven shaft 68, and has a cylindrical shape that is coaxial with the driven shaft 68. And an outer cylinder 77 to be mounted. The inner cylinder 76 is supported by the driven shaft 68 so as to be relatively rotatable. The outer cylinder 77 is supported by the inner cylinder 76 so as to be relatively rotatable and axially relatively displaceable. The fixed sheave 78 is coaxially fixed to the inner cylinder 76. The inner cylinder 76 and the fixed sheave 78 are integrally formed from a material such as aluminum which is lighter than steel. The movable sheave 79 is coaxially fixed to the outer cylinder 77. The outer cylinder 77 and the movable sheave 79 are integrally formed from a material such as aluminum which is lighter than steel. The movable sheave 79 moves toward or away from the fixed sheave 78 according to the relative axial displacement of the outer cylinder 77 and the inner cylinder 76.

A centrifugal clutch 81 is attached to the driven shaft 68. The centrifugal clutch 81 includes a clutch plate 81a fixed to the inner cylinder 76. A helical spring 82 is arranged between the clutch plate 81a and the movable sheave 79. The helical spring 82 exerts an elastic force that presses the movable sheave 79 toward the fixed sheave 78. When the winding radius of the V-belt 71 is increased by the drive pulley device 67, the movable sheave 79 moves away from the fixed sheave 78 in the driven pulley device 69 against the elastic force of the coiled spring 82, and the winding radius of the V-belt 71 decreases. ..

The centrifugal clutch 81 includes an outer plate 81b fixed to the driven shaft 68. The outer plate 81b faces the clutch plate 81a. When the clutch plate 81a rotates, centrifugal force acts to couple the outer plate 81b to the clutch plate 81a. In this way, the rotation of the driven pulley device 69 is transmitted to the driven shaft 68. When the engine speed exceeds the set speed, the centrifugal clutch 81 establishes a power transmission state.

The reduction gear mechanism 59 is arranged between the drive gear 83 fixed to the driven shaft 68 protruding into the gear chamber 65, the final gear 84 fixed to the axle 58 of the rear wheel WR, and the drive gear 83 and the final gear 84. Idle gears 85a and 85b. The idle gears 85a and 85b are fixed to a common intermediate shaft 86. The drive gear 83 meshes with the idle gear 85a, and the final gear 84 meshes with the idle gear 85b. Thus, the rotation of the driven shaft 68 is decelerated and transmitted to the axle 58 of the rear wheel WR.

As shown in FIG. 3, the internal combustion engine 29 has a valve mechanism 87. The valve mechanism 87 includes an intake valve 88, which is axially displaceably supported by the cylinder head 35 by a valve shaft 88b extending from the valve body 88a while disposing a valve body 88a in the combustion chamber 46, and a combustion chamber 46. The exhaust valve 89 is disposed on the cylinder head 35 so as to be displaceable in the axial direction by a valve shaft 89b extending from the valve body 89a while disposing the valve body 89a. The valve body 88a of the intake valve 88 is seated on the valve seat 92a that is embedded in the cylinder head 35 at the opening of the intake port 91a connected to the combustion chamber 46 and defines the intake port. The valve body 89a of the exhaust valve 89 is seated on the valve seat 92b that is embedded in the cylinder head 35 at the opening of the exhaust port 91b connected to the combustion chamber 46 and defines the exhaust port.

The valve shafts 88b and 89b are supported by the cylinder head 35 so as to be slidable in the axial direction. The valve shafts 88b and 89b have one end (outer end) which penetrates the cylinder head 35 and is arranged outside the combustion chamber 46. A flange 93 is fixed to the outer ends of the valve shafts 88b and 89b. A helical spring 94, which is an elastic member, is sandwiched between the flange 93 and the outer surface of the cylinder head 35. The helical spring 94 exerts an elastic force in an extension direction in which the flange 93 is moved away from the outer surface of the cylinder head 35. The valve elements 88a and 89a are seated on the valve seats 92a and 92b based on the elastic force of the helical spring 94.

The valve mechanism 87 has a cam shaft 95 rotatably supported by the cylinder head 35 about an axis Xc parallel to the rotation axis Xis of the crankshaft 32, and an axis Xk parallel to the rotation axis Xis of the crankshaft 32. And a pair of rocker shafts 96 supported by the cylinder head 35, and an intake side rocker arm 97a and an exhaust side rocker arm 97b which are rockably supported by the rocker shaft 96 around the axis Xk. Each of the rocker arms 97a and 97b extends from the rocker shaft 96 in the centrifugal direction and has a first operating point 98 at its distal end, and a distal end extending from the rocker shaft 96 in the centrifugal direction opposite to the first arm 99. And a second arm 102 having a cam follower 101. The rocker arms 97a and 97b contact the outer ends of the intake valve 88 and the exhaust valve 89 at the operating point 98 of the first arm 99, respectively. The rocker arms 97a and 97b come into contact with the cam shaft 95 by the cam follower 101, respectively. Details of the camshaft 95 and the rocker arms 97a and 97b will be described later.

As shown in FIG. 4, the valve mechanism 87 includes a timing chain 103. The timing chain 103 is wound around a crank sprocket (not shown) fixed to the crankshaft 32 and a cam sprocket 104 fixed to the camshaft 95. The timing chain 103 transmits the rotation of the crankshaft 32 to the camshaft 95. The camshaft 95 rotates in synchronization with the rotation of the crankshaft 32.

The internal combustion engine 29 includes a spark plug 105. The spark plug 105 is supported by the cylinder head 35. The spark plug 105 penetrates the cylinder head 35 and exposes the electrode 105a at the tip into the combustion chamber 46. The spark plug 105 ignites the air-fuel mixture in the combustion chamber 46 with a spark generated at the electrode 105a according to the supplied electric signal.

The cam shaft 95 is rotatably supported by the cylinder head 35 via a pair of bearings 106. A ball bearing is used for the bearing 106, for example. A first cam 107 for the intake side rocker arm 97a and a second cam 108 for the exhaust side rocker arm 97b are formed on the cam shaft 95 between the bearings 106. The first cam 107 and the second cam 108 are displaced from each other in the axial direction of the cam shaft 95.

Referring also to FIG. 5, the cam follower 101 includes a roller 109 which is rotatably supported by the second arm 102 around a rotation axis parallel to the axis Xc of the cam shaft 95. The outer peripheral surface of the roller 109 contacts the first cam 107 and the second cam 108, respectively. The roller 109 can rotate in response to the rotation of the first cam 107 and the second cam 108. The roller 109 follows the profiles of the first cam 107 and the second cam 108 while rotating. The opening and closing of the intake valve 88 and the exhaust valve 89 are controlled by the roller 109 moving toward and away from the axis Xc of the camshaft 95.

The first cam 107 is provided on the camshaft 95 continuously with the base surface 107a in the rotational direction and the base surface 107a having the shape of a partial cylindrical surface coaxial with the axis line Xc of the camshaft 95, and is more than the base surface 107a. And a lift surface 107b that bulges outward in the radial direction and defines the lift amount of the intake valve 88. The cam follower 101 of the intake side rocker arm 97a maintains the contact with the base surface 107a and the lift surface 107b to cause the intake side rocker arm 97a to swing.

The second cam 108 is provided on the camshaft 95 continuously with the base surface 108a in the rotational direction and on a base surface 108a having a shape of a partial cylindrical surface coaxial with the axis Xc of the camshaft 95, and is more than the base surface 108a. And a lift surface 108b that bulges outward in the radial direction and defines the lift amount of the exhaust valve 89. The cam follower 101 of the exhaust side rocker arm 97b maintains the contact with the base surface 108a and the lift surface 108b to cause the exhaust side rocker arm 97b to swing.

As shown in FIGS. 4 and 5, the valve mechanism 97 includes the decompression device 111 according to the first embodiment. The decompression device 111 is attached to the camshaft 95, the decompression follower 113 defined by the exhaust side rocker arm 97b so that the decompression cam 112 can come into contact with the decompression cam 112, and the decompression device 111 is attached to the camshaft 95 so that the decompression device can operate in the operating position and the non-operating position. And a drive arm 114 that drives the decompression cam 112 between them.

The decompression cam 112 and the drive arm 114 are supported by a step surface 115 formed on the cam shaft 95 between the second cam 108 and the bearing 106. The step surface 115 is partitioned between a large-diameter shaft 116a that defines the second cam 108 and a small-diameter shaft 116b that is continuous with the large-diameter shaft 116a and has a smaller diameter than the large-diameter shaft 116a and that is received by the bearing 106. Faced to bearing 106. The step surface 115 is connected to the edges of the base surface 108a and the lift surface 108b of the second cam 108 at right angles to the axis Xc of the cam shaft 95.

The decompression cam 112 includes a shaft body 117 having an axis parallel to the axis line Xc of the cam shaft 95. The shaft body 117 is formed on the cam shaft 95 and is rotatably received around a shaft center (=rotation axis Xd) in a through hole 118 that defines a cylindrical space coaxial with the shaft body 115. In this way, the decompression cam 112 is rotatably supported by the cam shaft 95 about the rotation axis Xd.

The decompression cam 112 includes a cam body 119 coaxial with the shaft 117. In the cam body 119, a cylindrical surface 121 that is coaxial with the shaft body 117 and continuous around the axis of the shaft body 117 is defined. The cylindrical surface 121 is arranged coaxially with the axis line Xc of the cam shaft 95, and is arranged at a position displaced from the virtual cylindrical surface 122 facing the decompression follower 113 in the axial direction of the cam shaft 95. Here, the virtual cylindrical surface 122 is a cylindrical surface coaxial with the cylindrical surface 121 and continuous from the cylindrical surface 121 in the axial direction.

The decompression cam 112 has a cam groove 124 that receives the cam pin 123. The cam pin 123 is composed of a cylindrical body having an axis parallel to the axis Xc of the cam shaft 95. The cam groove 124 is formed on the end surface of the cam body 119 and linearly extends from the cylindrical surface 121 toward the axis. When the cam pin 123 moves in the circumferential direction around the axis Xc of the cam shaft 95, the decompression cam 112 changes its posture around its axis between an operating position and a non-operating position.

The drive arm 114 is supported by the cam shaft 95 so as to be swingable around a swing shaft 125. The swing shaft 125 has an axis parallel to the axis Xc of the cam shaft 95. The swing shaft 125 is pressed into the step surface 115 by, for example, press fitting. A spacer 126 is mounted on the swing shaft 125 between the step surface 115 and the drive arm 114. The size of the spacer 126 in the axial direction of the camshaft 95 corresponds to the size of the virtual cylindrical surface 122. In this way, the virtual cylindrical surface 122 is arranged between the drive arm 114 and the step surface 115.

The swing shaft 125 is arranged at least in the circumferential direction of the cam shaft 95 at a position distant from the rotation axis Xd of the decompression cam 112. It is desired that the swing shaft 125 be separated from the decompression cam 112 as much as possible. Here, the rotation axis Xd of the swing shaft 125 and the decompression cam 112 is arranged on one diameter line on both sides of the axis Xc.

The cam pin 123 is fixed to the tip of the drive arm 114. The cam pin 123 moves between a first position that establishes the operating position of the decompression cam 112 and a second position that establishes the non-operating position of the decompression cam 112. A torsion spring 127 is attached to the spacer 126. One end of the torsion spring 127 is hooked on the drive arm 114. The other end of the torsion spring 127 is hooked on the small diameter shaft 116b. The torsion spring 127 exerts an elastic force that drives the cam pin 123 toward the first position.

The drive arm 114 is curved between the swing shaft 125 and the cam pin 123, bypassing the small diameter shaft 116b. A centrifugal weight 128 is attached to the drive arm 114 between the swing shaft 125 and the cam pin 123. The centrifugal weight 128 exerts a centrifugal force that moves the cam pin 123 from the first position to the second position against the elastic force of the torsion spring 127 when the rotation of the cam shaft 95 reaches a preset rotation number.

The cam body 119 of the decompression cam 112 is disposed in a space inside the virtual cylindrical surface 122, and has a partial cylindrical surface 129 coaxial with the shaft body 117 and continuing from the cylindrical surface 121, and bus lines at both ends of the partial cylindrical surface 129. And a connecting plane 131. The decompression cam 112 projects a part of the partial cylindrical surface 129 from the virtual cylindrical surface 122 to the outside in the operating position. The partial cylindrical surface 129 corresponds to a curved projecting surface having a generatrix parallel to the axis Xc of the camshaft 95.

As shown in FIG. 6, the decompression follower 113 is provided on the exhaust side rocker arm 97 b outside the virtual cylindrical surface 122 and faces the virtual cylindrical surface 122 at a position closest to the virtual cylindrical surface 122 and is partially cylindrical surface 129. To the convex decompression follower surface 133 which is a convex curved surface that contacts with the convex decompression follower surface 133 in the forward direction of the camshaft 95, and which has a generatrix parallel to the axis Xc of the camshaft 95. A first concave decompression follower surface 134 that is formed and contacts the partial cylindrical surface 129 and a convex decompression follower surface 133 that is provided downstream of the convex decompression follower surface 133 in the forward direction of the camshaft 95 and that has a generatrix parallel to the axis Xc of the camshaft 95. And a second concave decompression follower surface 135 that is in contact with the partial cylindrical surface 129. In the decompression follower 113, a first auxiliary concave decompression follower surface 136 composed of a concave curved surface having a curvature smaller than that of the partial cylindrical surface 129 is formed between the convex decompression follower surface 133 and the first concave decompression follower surface 134. .. Similarly, between the convex decompress follower surface 133 and the second concave decompress follower surface 135, a second auxiliary concave decompress follower surface 137 composed of a concave curved surface having a curvature smaller than that of the partial cylindrical surface 129 is formed.

The upstream end 134a of the first concave decompression follower surface 134 is arranged at a position distant from the axis Xc of the camshaft 95 in the radial direction as compared with the partial cylindrical surface 129. The downstream end 135a of the second concave decompression follower surface 135 is arranged at a position farther from the axis Xc of the cam shaft 95 than the partial cylindrical surface 129 in the radial direction. The first concave decompression follower surface 134 moves away from the axis line Xc of the camshaft 95 as it moves away from the convex decompression follower surface 133 in the circumferential direction of the virtual cylindrical surface 122. The second concave decompression follower surface 135 moves away from the axis Xc of the camshaft 95 as it moves away from the convex decompression follower surface 133 in the circumferential direction of the virtual cylindrical surface 122. The first concave decompression follower surface 134 is formed by a part of a cylindrical surface having a curvature smaller than that of the partial cylindrical surface 129. The second concave decompression follower surface 135 is formed by a part of the cylindrical surface having a curvature smaller than that of the partial cylindrical surface 129. The first auxiliary concave decompression follower surface 136 is formed by a part of a cylindrical surface having a curvature smaller than that of the partial cylindrical surface 129. The second auxiliary concave decompression follower surface 137 is formed of a part of a cylindrical surface having a curvature smaller than that of the partial cylindrical surface 129. The first auxiliary concave decompression follower surface 136 is formed of a part of a cylindrical surface having a larger curvature than the first concave decompression follower surface 134. The second auxiliary concave decompression follower surface 137 is formed of a part of a cylindrical surface having a larger curvature than the second concave decompression follower surface 135. The first auxiliary concave decompression follower surface 136 and the second auxiliary concave decompression follower surface 137 may be formed of a part of a cylindrical surface having a curvature smaller than that of the convex decompression follower surface 133, and have a curvature larger than that of the convex decompression follower surface 133. It may be formed of a part of the cylindrical surface.

Here, the convex decompression follower surface 133 is farther from the axis line Xc of the camshaft 95 than the outer peripheral surface of the roller 109. Since the cylindrical surface 121 and the virtual cylindrical surface 122 have the same diameter, the convex decompression follower surface 133 is maintained at a constant distance from the virtual cylindrical surface 122. As shown in FIG. 7, when the flat surface 131 continuous with the partial cylindrical surface 129 is arranged inside the virtual cylindrical surface 122 in the non-operating position of the decompression cam 112, the contact between the decompression cam 112 and the decompression follower 113 is avoided. It

Next, the operation of the decompression device 111 will be described. In the internal combustion engine 29, the intake stroke, the compression stroke, the combustion stroke, and the exhaust stroke are sequentially repeated. In the intake stroke, the intake valve 88 opens. The piston 45 descends due to the inertial force of the crankshaft 32. The air-fuel mixture is introduced into the combustion chamber 46. Fuel is injected from the fuel injection valve 42 by the throttle body 41 into the air introduced from the intake device 37. In the compression stroke, the piston 45 rises due to the inertial force of the crankshaft 32. The intake valve 88 and the exhaust valve 89 are maintained in the closed state. The air-fuel mixture is compressed in the combustion chamber 46. In the combustion stroke, the air-fuel mixture is ignited in the combustion chamber 46. The intake valve 88 and the exhaust valve 89 are maintained in the closed state. The explosion in the combustion chamber 46 causes the piston 45 to descend. The driving force is transmitted to the crankshaft 32. In the exhaust stroke, the exhaust valve 89 opens. The inertia force of the crankshaft 32 raises the piston 45. The exhaust gas after combustion is escaped to the exhaust pipe 43. The intake stroke is performed again in response to the subsequent lowering of the piston 45. When the internal combustion engine 29 is started, the driving force is transmitted from the AC generator starter 49 to the crankshaft 32. The alternator starter 49 generates a driving force according to electric power supplied from, for example, a battery (not shown).

The valve mechanism 87 operates in conjunction with the rotation of the crankshaft 32. The opening/closing of the intake valve 88 is controlled by swinging the intake rocker arm 97a. The rocker arm 97a swings in response to the contact between the roller 109 and the first cam 107. The rocker arm 97a maintains the closed state of the intake valve 88 while the roller 109 contacts the base surface 107a of the first cam 107. When the roller 109 follows the lift surface 107b, the intake valve 88 opens. The opening/closing of the exhaust valve 89 is controlled by the rocking of the exhaust side rocker arm 97b. The rocker arm 97b swings in response to the contact between the roller 109 and the second cam 108. The rocker arm 97b keeps the exhaust valve 89 closed while the roller 109 contacts the base surface 108a of the second cam 108. When the roller 109 follows the lift surface 108b, the exhaust valve 89 opens.

When the engine speed of the internal combustion engine 29 is lower than a predetermined speed, the centrifugal weight 128 does not generate a sufficient centrifugal force in the decompression device 111 according to the rotation of the camshaft 95. Therefore, the drive arm 114 maintains the cam pin 123 in the first position according to the elastic force of the torsion spring 127. The decompression cam 112 is in the operating position. The partial cylindrical surface 129 projects from the virtual cylindrical surface including the virtual cylindrical surface 122. In response to the rotation of the camshaft 95, the partial cylindrical surface 129 causes the first concave decompression follower surface 134 of the decompression follower 113, the first auxiliary concave decompression follower surface 136, the convex decompression follower surface 133, the second auxiliary concave decompression follower surface 137, and the second auxiliary concave decompression follower surface 137. The two concave decompression follower surfaces 135 are successively contacted. Thus, the exhaust valve 89 opens during the compression stroke. The pressure in the combustion chamber 46 is released. The drive resistance of the piston 45 is reduced, and the vibration of the internal combustion engine is suppressed.

When the engine speed of the internal combustion engine 29 reaches or exceeds a predetermined engine speed, in the decompression device 111, a sufficient centrifugal force is generated in the centrifugal weight 128 according to the rotation of the camshaft 95. Therefore, the drive arm 114 drives the cam pin 123 from the first position to the second position against the elastic force of the torsion spring 127. The attitude of the decompression cam 112 changes to the non-operating position. The decompression cam 112 fits inside a virtual cylindrical surface including the virtual cylindrical surface 122. The contact between the decompression follower 113 and the decompression cam 112 during the rotation of the camshaft 95 is avoided. The exhaust valve 89 is kept closed during the compression stroke. The driving force of the piston 45 due to the explosion is maximized. The internal combustion engine 29 efficiently produces power.

According to the present embodiment, the partial cylindrical surface 129 of the decompression cam 112 projects in the centrifugal direction of the cam shaft 95 in the low rotation speed range below the set rotation speed. During the normal rotation of the cam shaft 95, the partial cylindrical surface 129 of the decompression cam 112 successively contacts the first concave decompression follower surface 134 and the convex decompression follower surface 133 of the exhaust side rocker arm 97b. Since the first concave decompression follower surface 134 is formed as a concave curved surface, the partial cylindrical surface 129 of the decompression cam 112 can slide tangentially to the concave curved surface at the start of contact. Therefore, the collision noise between the decompression cam 112 and the exhaust side rocker arm 97b can be suppressed.

The upstream end 134a of the first concave decompression follower surface 134 is arranged at a position farther from the axis Xc of the cam shaft 95 than the partial cylindrical surface 129 of the rocker arm 97b. At the start of contact, the partial cylindrical surface 129 of the decompression cam 112 surely contacts the concave curved surface of the first concave decompression follower surface 134. The collision noise between the decompression cam 112 and the exhaust side rocker arm 97b can be suppressed.

The first concave decompression follower surface 134 according to the present embodiment moves away from the axis Xc of the camshaft 95 as it moves away from the convex decompression follower surface 133. Therefore, even if the partial cylindrical surface 129 of the decompression cam 112 is slightly displaced due to dimensional tolerance or assembly error, the partial cylindrical surface 129 of the decompression cam 112 is tangential to the first concave decompression follower surface 134 at the start of contact. You can slide to. Therefore, the collision noise between the decompression cam 112 and the exhaust side rocker arm 97b can be suppressed.

In addition, in the decompression follower 113, between the convex decompression follower surface 133 and the first concave decompression follower surface 134, a first auxiliary concave decompression follower constituted by a concave curved surface having a curvature smaller than that of the partial cylindrical surface 129 of the decompression cam 112. A surface 136 is formed. Since the first concave decompression follower surface 134, the first auxiliary concave decompression follower surface 136, and the convex decompression follower surface 133 are continuous, the partial cylindrical surface 129 of the decompression cam 112 changes from the first concave decompression follower surface 134 to the convex decompression follower surface 133. It can follow smoothly. The collision noise between the decompression cam 112 and the exhaust side rocker arm 97b can be suppressed.

The first auxiliary concave decompression follower surface 136 is formed of a part of a cylindrical surface having a curvature larger than that of the first concave decompression follower surface 134. As a result, the partial cylindrical surface 129 of the decompression cam 112 smoothly follows the first concave decompression follower surface 134 to the convex decompression follower surface 133 according to the change in the curvature. The collision noise between the decompression cam 112 and the exhaust side rocker arm 97b can be suppressed.

Furthermore, during normal rotation of the cam shaft 95, the partial cylindrical surface 129 of the decompression cam 112 contacts the convex decompression follower surface 133 and then the second concave decompression follower surface 135. Since the second concave decompression follower surface 135 is formed into a concave curved surface, the lift amount of the exhaust valve 89 changes gently when the decompression cam 112 separates from the second concave decompression follower surface 135. As a result, the seating sound of the exhaust valve 89 is reduced. Moreover, when the piston 45 does not go over the compression top dead center and the camshaft 95 reverses, the partial cylindrical surface 129 of the decompression cam 112 contacts the second concave decompression follower surface 135 and the convex decompression follower surface 133 one after another. Since the second concave decompression follower surface 135 is formed as a concave curved surface, the partial cylindrical surface 129 of the decompression cam 112 can slide tangentially to the concave curved surface at the start of contact. Therefore, when the piston 45 does not go over the compression top dead center and the cam shaft 95 reverses, the collision noise between the decompression cam 112 and the exhaust side rocker arm 97b can be suppressed.

The downstream end 135 a of the second concave decompression follower surface 135 is located farther from the axis Xc of the camshaft 95 than the partial cylindrical surface 129 of the decompression cam 112. In response to the rotation of the cam shaft 95, the partial cylindrical surface 129 of the decompression cam 112 is a concave curved surface and separates from the rocker arm 97b. When seated, the lift amount of the exhaust valve 89 changes gently. In this way, the seating sound of the exhaust valve 89 can be reduced.

The second concave decompression follower surface 135 according to the present embodiment moves away from the axis Xc of the camshaft 95 as it moves away from the convex decompression follower surface 133. Therefore, even if the partial cylindrical surface 129 of the decompression cam 112 is slightly displaced due to dimensional tolerance, assembly error, etc., the lift amount of the exhaust valve 89 for seating changes gently. In this way, the seating sound of the exhaust valve 89 can be reduced.

In the decompression follower 113, between the convex decompression follower surface 133 and the second concave decompression follower surface 135, a second auxiliary concave decompression follower surface 137 constituted by a concave curved surface having a curvature smaller than that of the partial cylindrical surface 129 of the decompression cam 112 is provided. It is formed. Since the convex decompression follower surface 133, the second auxiliary concave decompression follower surface 137, and the second concave decompression follower surface 135 are continuous, the partial cylindrical surface 129 of the decompression cam 112 changes from the convex decompression follower surface 133 to the second concave decompression follower surface 135. It can follow smoothly. The collision noise between the decompression cam 112 and the exhaust side rocker arm 97b can be suppressed.

The second auxiliary concave decompression follower surface 137 is formed of a part of a cylindrical surface having a curvature larger than that of the second concave decompression follower surface 135. As a result, the partial cylindrical surface 129 of the decompression cam 112 can smoothly follow the convex decompression follower surface 133 to the second concave decompression follower surface 135 according to the change in curvature. The collision noise between the decompression cam 112 and the exhaust side rocker arm 97b can be suppressed.

In this embodiment, the internal combustion engine 29 employs motor idling control. In the motor idling control, fuel is not injected from the fuel injection valve 42 into the air introduced from the intake device 37 into the combustion chamber 46 when the accelerator is off (the accelerator is not operated). To maintain idling, the driving force is transmitted from the AC generator starter 49 to the crankshaft 32. The alternator starter 49 generates a driving force according to electric power supplied from, for example, a battery (not shown). When idling, the alternator starter 49 can realize the reciprocating motion of the piston 45 without passing through the combustion stroke. Fuel consumption is suppressed and exhaust noise of the internal combustion engine 29 is reduced.

Second embodiment

FIG. 8 schematically shows the configuration of the decompression device 141 according to the second embodiment. In the decompression device 141, the decompression follower 142 includes the first concave decompression follower surface 134, the first auxiliary concave decompression follower surface 136, the convex decompression follower surface 133, the second auxiliary concave decompression follower surface 137, and the second concave decompression follower surface. Instead of 135, it has a convex decompression follower surface 143 with a single convex curved surface. On the other hand, the curved projecting surface 145 of the decompression cam 144 is provided upstream of the top surface 146 that most projects from the virtual cylindrical surface 122 and the top surface 146 in the normal direction of the camshaft 95, and the axis line Xc of the camshaft 95. A first cushioning surface 147 formed into a concave curved surface having a generatrix parallel to and a generatrix provided downstream of the top surface 146 in the normal direction of the camshaft 95 and parallel to the axis Xc of the camshaft 95. And a second buffer surface 148 formed into a concave curved surface. Other configurations are the same as those in the above-described embodiment.

Here, the convex decompression follower surface 143 of the decompression follower 142 is formed of a part of a cylindrical surface that is coaxial with the rotation axis of the roller 109 and has a smaller diameter than the roller 109. Therefore, the convex decompression follower surface 143 faces the virtual cylindrical surface 122 at the set interval. On the other hand, the top surface 146 of the decompression cam 144 is configured as a part of a cylindrical surface having the same diameter as the partial cylindrical surface 129. The first cushioning surface 147 and the second cushioning surface 148 of the decompression cam 144 are each configured by a partial cylindrical surface having a curvature smaller than that of the convex decompression follower surface 143. The upstream end 147a of the first buffer surface 147 is located closer to the axis Xc of the camshaft 95 than the convex decompression follower surface 143 when the decompression cam 144 is in the operating position. The downstream end 148a of the second buffer surface 148 is arranged at a position closer to the axis line Xc of the cam shaft 95 than the convex decompression follower surface 143 when the decompression cam 144 is in the operating position.

During the normal rotation of the camshaft 95, the curved protruding surface 145 of the decompression cam 144 successively contacts the convex decompression follower surface 143 of the exhaust side rocker arm 97b at the first buffer surface 147 and the top surface 146. Since the first buffer surface 147 of the decompression cam 144 is formed as a concave curved surface, the convex decompression follower surface 143 can slide in the tangential direction with respect to the first buffer surface 147 of the decompression cam 144 at the start of contact. Therefore, the collision noise between the decompression cam 144 and the exhaust side rocker arm 97b can be suppressed.

During the normal rotation of the cam shaft 95, the curved protruding surface 145 of the decompression cam 144 contacts the convex decompression follower surface 143 at the second buffer surface 148 following the top surface 146. Since the second cushioning surface 148 is formed as a concave curved surface, the lift amount of the exhaust valve 89 changes gently when the convex decompression follower surface 143 separates from the second cushioning surface 148. As a result, the seating sound of the exhaust valve 89 is reduced. Moreover, during the reverse rotation of the camshaft 95, the curved protruding surface 145 of the decompression cam 144 contacts the second buffer surface 148 and the top surface 146 one after another. Since the second buffer surface 148 is formed as a concave curved surface, the convex decompression follower surface 143 can slide in the tangential direction with respect to the second buffer surface 148 at the start of contact. Therefore, when the piston 45 does not go over the compression top dead center and the cam shaft 95 reverses, the collision noise between the decompression cam 144 and the exhaust side rocker arm 97b can be suppressed.

Third embodiment

FIG. 9 schematically shows the configuration of the decompression device 151 according to the third embodiment. In the decompression device 151, the cam follower 101 also serves as the decompression follower 142. That is, the roller 109 of the cam follower 101 functions as the convex decompression follower surface 143 of the above-mentioned convex curved surface over the entire circumference of the cylindrical surface. The rollers 109 are opposed to the virtual cylindrical surface 122 at set intervals. The top surface 146 of the decompression cam 144 is configured as a part of a cylindrical surface having the same diameter as the partial cylindrical surface 129. The first cushioning surface 147 and the second cushioning surface 148 of the decompression cam 144 are each configured by a partial cylindrical surface having a smaller curvature than the cylindrical surface of the roller 109. The upstream end 147a of the first buffer surface 147 is arranged at a position closer to the axis Xc of the cam shaft 95 than the roller 109 when the decompression cam 144 is in the operating position. The downstream end 148a of the second buffer surface 148 is arranged at a position closer to the axis Xc of the cam shaft 95 than the roller 109 when the decompression cam 144 is located at the operating position. Other configurations are similar to those of the second embodiment described above.

During the forward rotation of the camshaft 95, the curved protruding surface 145 of the decompression cam 144 successively contacts the roller 109 of the exhaust side rocker arm 97b at the first buffer surface 147 and the top surface 146. Since the first cushioning surface 147 of the decompression cam 144 is formed as a concave curved surface, the roller 109 can slide in the tangential direction with respect to the first cushioning surface 147 of the decompression cam 144 at the start of contact. Therefore, the collision noise between the decompression cam 144 and the exhaust side rocker arm 97b can be suppressed.

During the normal rotation of the cam shaft 95, the curved protruding surface 145 of the decompression cam 144 contacts the roller 109 at the second buffer surface 148 following the top surface 146. Since the second buffer surface 148 is formed as a concave curved surface, when the roller 109 separates from the second buffer surface 148, the lift amount of the exhaust valve 89 changes gently. As a result, the seating sound of the exhaust valve 89 is reduced. Moreover, during the reverse rotation of the camshaft 95, the curved protruding surface 145 of the decompression cam 144 contacts the second buffer surface 148 and the top surface 146 one after another. Since the second cushioning surface 148 is formed as a concave curved surface, the roller 109 can slide in the tangential direction with respect to the second cushioning surface 148 at the start of contact. Therefore, when the piston 45 does not go over the compression top dead center and the cam shaft 95 reverses, the collision noise between the decompression cam 144 and the exhaust side rocker arm 97b can be suppressed.

Claims (15)

A base surface (108a) having a shape of a partial cylindrical surface coaxial with the rotation axis (Xc) of the camshaft (95);
The camshaft (95) is provided continuously with the base surface (108a) in the rotation direction, and rises radially outward from the base surface (108a) to define the lift amount of the exhaust valve (89). A lift surface (108b),
A cam follower (101) provided on the exhaust side rocker arm (97b) and maintaining contact with the base surface (108a) and the lift surface (108b) to cause the exhaust side rocker arm (97b) to swing. When,
A curved projecting surface (129) having a generatrix parallel to the rotation axis (Xc) of the camshaft (95) from an imaginary cylindrical surface (122) coaxial with the camshaft (95) at a rotational speed lower than a preset value. Decompression cam (112) for projecting the
The curved protrusion (122) is provided on the exhaust side rocker arm (97b) outside the virtual cylindrical surface (122) and faces the virtual cylindrical surface (122) at a position closest to the virtual cylindrical surface (122). 129) and a convex decompression follower surface (133) having a convex curved surface,
It is provided upstream of the convex decompression follower surface (133) in the normal rotation direction of the camshaft (95), and is formed into a concave curved surface having a generatrix parallel to the rotation axis (Xc) of the camshaft (95). Internal combustion engine comprising a concave decompression follower surface (134) that contacts the curved protruding surface (129). The internal combustion engine according to claim 1, wherein the upstream end (134a) of the concave decompression follower surface (134) is farther from the rotation axis (Xc) of the camshaft (95) than the curved protruding surface (129). An internal combustion engine, which is provided at a different position. The internal combustion engine according to claim 1 or 2, wherein the concave decompression follower surface (134) moves away from the rotation axis (Xc) of the camshaft (95) as it moves away from the convex decompression follower surface (133). Internal combustion engine. The internal combustion engine according to any one of claims 1 to 3, which is formed between the convex decompression follower surface (133) and the concave decompression follower surface (134), and is formed more than the curved protruding surface (129). The internal combustion engine further comprising an auxiliary concave decompression follower surface (136) composed of a concave curved surface having a small curvature. The internal combustion engine according to claim 4, wherein the auxiliary concave decompression follower surface (136) is formed by a part of a cylindrical surface having a larger curvature than the concave decompression follower surface (134). organ. The internal combustion engine according to any one of claims 1 to 5, wherein the camshaft (95) is provided downstream of the convex decompression follower surface (133) in a normal rotation direction of the camshaft (95). The internal combustion engine further comprising a second concave decompression follower surface (135) formed on a concave curved surface having a generatrix parallel to the rotation axis (Xc) and contacting the curved protruding surface (129). A base surface (108a) having a shape of a partial cylindrical surface coaxial with the rotation axis (Xc) of the camshaft (95);
The camshaft (95) is provided continuously with the base surface (108a) in the rotation direction, and rises radially outward from the base surface (108a) to define the lift amount of the exhaust valve (89). A lift surface (108b),
A cam follower (101) provided on the exhaust side rocker arm (97b) and maintaining contact with the base surface (108a) and the lift surface (108b) to cause the exhaust side rocker arm (97b) to swing. When,
A curved projecting surface (129) having a generatrix parallel to the rotation axis (Xc) of the camshaft (95) from an imaginary cylindrical surface (122) coaxial with the camshaft (95) at a rotational speed lower than a preset value. Decompression cam (112) for projecting the
The curved protrusion (122) is provided on the exhaust side rocker arm (97b) outside the virtual cylindrical surface (122) and faces the virtual cylindrical surface (122) at a position closest to the virtual cylindrical surface (122). 129) and a convex decompression follower surface (133),
It is provided on the downstream side of the convex decompression follower surface (133) in the normal direction of rotation of the camshaft (95) and is formed into a concave curved surface having a generatrix parallel to the rotation axis (Xc) of the camshaft (95). Internal combustion engine comprising a concave decompression follower surface (135) that contacts the curved protruding surface (129). The internal combustion engine according to claim 7, wherein the downstream end (135a) of the concave decompression follower surface (135) is farther from the rotation axis (Xc) of the camshaft (95) than the curved protruding surface (129). An internal combustion engine, which is provided at a different position. The internal combustion engine according to claim 7 or 8, wherein the concave decompression follower surface (135) moves away from the rotation axis (Xc) of the camshaft (95) as it moves away from the convex decompression follower surface (133). Internal combustion engine. The internal combustion engine according to any one of claims 7 to 9, which is formed between the convex decompression follower surface (133) and the concave decompression follower surface (135), and is formed more than the curved projecting surface (129). The internal combustion engine further comprising an auxiliary concave decompression follower surface (137) formed of a concave curved surface having a small curvature. Internal combustion engine according to claim 10, characterized in that the auxiliary concave decompression follower surface (137) is formed by part of a cylindrical surface having a greater curvature than the concave decompression follower surface (135). organ. The internal combustion engine according to any one of claims 1 to 11, wherein the internal combustion engine is coupled to a crankshaft (32) to generate electric power according to rotation of the crankshaft (32), and to supply electric power according to supplied electric power. The internal combustion engine further comprising an AC generator (49) for driving the crankshaft (32) around its rotation axis (Xis). A base surface (108a) having a shape of a partial cylindrical surface coaxial with the rotation axis (Xc) of the camshaft (95);
The camshaft (95) is provided continuously with the base surface (108a) in the rotation direction, and rises radially outward from the base surface (108a) to define the lift amount of the exhaust valve (89). A lift surface (108b),
A cam follower (101) provided on the exhaust side rocker arm (97b) and maintaining contact with the base surface (108a) and the lift surface (108b) to cause the exhaust side rocker arm (97b) to swing. When,
A curved projecting surface (145) having a generatrix parallel to the rotation axis (Xc) of the camshaft (95) from a virtual cylindrical surface (122) coaxial with the camshaft (95) at a rotational speed lower than a preset value. Decompression cam (144) for projecting the
A convex decompression follower of a convex curved surface, which is provided on the exhaust side rocker arm (97b) outside the virtual cylindrical surface (122) and faces the virtual cylindrical surface (122) and contacts the curved protruding surface (145). A surface (143),
The curved protruding surface (145) is provided upstream of the top surface (146) that most projects from the virtual cylindrical surface (122) and in the normal direction of the camshaft (95). A buffer surface (147) formed in a concave curved surface having a generatrix parallel to the rotation axis (Xc) of the camshaft (95) and contacting the convex decompression follower surface (143). Internal combustion engine. The internal combustion engine according to claim 13, wherein the curved protruding surface (145) is provided downstream of the top surface (146) in the forward direction of rotation of the camshaft (95), and the curved protruding surface (145) of the camshaft (95) is provided. The internal combustion engine further comprising a second buffer surface (148) formed on a concave curved surface having a generatrix parallel to the rotation axis (Xc). A base surface (108a) having a shape of a partial cylindrical surface coaxial with the rotation axis (Xc) of the camshaft (95);
The camshaft (95) is provided continuously with the base surface (108a) in the rotation direction, and rises radially outward from the base surface (108a) to define the lift amount of the exhaust valve (89). A lift surface (108b),
A cam follower (101) provided on the exhaust side rocker arm (97b) and maintaining contact with the base surface (108a) and the lift surface (108b) to cause the exhaust side rocker arm (97b) to swing. When,
A curved projecting surface (145) having a generatrix parallel to the rotation axis (Xc) of the camshaft (95) from a virtual cylindrical surface (122) coaxial with the camshaft (95) at a rotational speed lower than a preset value. Decompression cam (144) for projecting the
A convex decompression follower of a convex curved surface, which is provided on the exhaust side rocker arm (97b) outside the virtual cylindrical surface (122) and faces the virtual cylindrical surface (122) and contacts the curved protruding surface (145). A surface (143),
The curved projecting surface (145) is provided on the top surface (146) that most projects from the virtual cylindrical surface (122) and downstream of the top surface (146) in the forward direction of the camshaft (95). A buffer surface (148) formed in a concave curved surface having a generatrix parallel to the rotation axis (Xc) of the camshaft (95) and contacting the convex decompression follower surface (143). Internal combustion engine.

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