阅读说明：本技术 内燃机 (Internal combustion engine ) 是由 国石贤 岩崎崇生 阿藤绅司 平山周二 久我信二 于 2020-02-05 设计创作，主要内容包括：本发明提供一种内燃机,可以从起动时起可靠地实现减压的功能,而且可以降低减压功能的切换转速。内燃机(35)具备：减压配重(109),所述减压配重(109)与臂部件(108)结合,利用在重力的作用下绕摆动轴线(Xs)作用于第一方向(DR1)并根据绕凸轮轴(82)的旋转轴线(Xc)的旋转角位置而变化的第一转矩(Tf),朝向非动作位置对减压凸轮(106)施加驱动力；弹性部件(125),所述弹性部件(125)与臂部件(108)连结,具有绕摆动轴线(Xs)在第二方向(DR2)上生成第二转矩(Ts)的弹性,并朝向动作位置对减压凸轮(106)施加驱动力；以及起动电机(54),所述起动电机(54)与曲轴(61)连结,在起动之前将曲轴(61)定位于第二转矩超过第一转矩的旋转角位置。(The invention provides an internal combustion engine, which can reliably realize the decompression function from the starting time and can reduce the switching speed of the decompression function. An internal combustion engine (35) is provided with: a decompression weight (109) coupled to the arm member (108), the decompression weight (109) applying a driving force to the decompression cam (106) toward the non-operating position by a first torque (Tf) acting in a first direction (DR1) around a swing axis (Xs) by a gravity force and changing according to a rotational angle position around a rotational axis (Xc) of the camshaft (82); an elastic member (125) that is coupled to the arm member (108), has elasticity that generates a second torque (Ts) in a second direction (DR2) about the swing axis (Xs), and applies a driving force to the decompression cam (106) toward the operating position; and a starter motor (54), wherein the starter motor (54) is coupled to the crankshaft (61) and positions the crankshaft (61) at a rotational angle position at which the second torque exceeds the first torque before starting.)

1. An internal combustion engine is provided with:

a crankshaft (61);

a camshaft (82), the camshaft (82) being coupled to the crankshaft (61) and rotating at a reduction ratio of 2 to 1 with respect to the crankshaft (61);

a decompression cam (106) that displaces the decompression cam (106) between an operating position and a non-operating position, wherein the operating position is a position in which a curved protruding surface (116a) having a generatrix parallel to a rotation axis (Xc) of the camshaft (82) protrudes from a virtual cylindrical surface (118) that is coaxial with the camshaft (82) when the rotation speed is less than a predetermined rotation speed, and the non-operating position is a position in which the curved protruding surface (116a) is retracted from the virtual cylindrical surface (118);

a decompression sliding surface (126), which is provided on an exhaust side rocker arm (93b), and which is in contact with the curved protrusion surface (116a) when the camshaft (82) rotates;

an arm member (108), the arm member (108) being supported by the camshaft (82) so as to be swingable about a swing axis (Xs) extending parallel to a rotation axis (Xc) of the camshaft (82), and being coupled to the decompression cam (106) at a position away from the swing axis (Xs);

a decompression weight (109) coupled to the arm member (108), the decompression weight (109) applying a driving force to the decompression cam (106) toward the non-operating position by a first torque (Tf) acting in a first direction (DR1) around the swing axis (Xs) by gravity and changing according to a rotational angle position around a rotational axis (Xc) of the camshaft (82); and

an elastic member (125) that is coupled to the arm member (108), has elasticity that generates a second torque (Ts) in a second direction (DR2) opposite to the first direction (DR1) about the pivot axis (Xs), and applies a driving force to the decompression cam (106) toward the operating position,

the internal combustion engine is characterized in that,

the starter motor (54) is connected to the crankshaft (61), and positions the crankshaft (61) at a rotational angle position at which the second torque (Ts) exceeds the first torque (Tf) before starting.

2. The internal combustion engine of claim 1,

the starter motor (54) reverses the crankshaft (61) to a rotational angle range of the crankshaft (61) established in an expansion stroke when the crankshaft (61) is stopped.

3. The internal combustion engine of claim 2,

the starter motor (54) exerts a torque smaller than a torque reaching the top dead center of a compression stroke when the crankshaft (61) rotates in the reverse direction.

4. An internal combustion engine according to claim 3,

the starter motor (54) rotates the crankshaft (61) in reverse at a predetermined rotational angle.

5. The internal combustion engine of claim 4,

the inclination angle of the cylinder axis (C) with respect to the horizontal plane is set within the following range: positioning the crankshaft (61) at the rotational angle position at which the second torque (Ts) exceeds the first torque (Tf) when the crankshaft (61) reverses at the predetermined rotational angle.

6. An internal combustion engine is provided with:

a crankshaft (61);

a camshaft (82), the camshaft (82) being coupled to the crankshaft (61) and rotating at a reduction ratio of 2 to 1 with respect to the crankshaft (61);

a decompression cam (106) that displaces the decompression cam (106) between an operating position and a non-operating position, wherein the operating position is a position in which a curved protruding surface (116a) having a generatrix parallel to a rotation axis (Xc) of the camshaft (82) protrudes from a virtual cylindrical surface (118) that is coaxial with the camshaft (82) when the rotation speed is less than a predetermined rotation speed, and the non-operating position is a position in which the curved protruding surface (116a) is retracted from the virtual cylindrical surface (118);

a decompression sliding surface (126), which is provided on an exhaust side rocker arm (93b), and which is in contact with the curved protrusion surface (116a) when the camshaft (82) rotates;

an arm member (108), the arm member (108) being supported by the camshaft (82) so as to be swingable about a swing axis (Xs) extending parallel to a rotation axis (Xc) of the camshaft (82), and being coupled to the decompression cam (106) at a position away from the swing axis (Xs);

a decompression weight (109) coupled to the arm member (108), the decompression weight (109) applying a driving force to the decompression cam (106) toward the non-operating position by a first torque (Tf) acting in a first direction (DR1) around the swing axis (Xs) by gravity and changing according to a rotational angle position around a rotational axis (Xc) of the camshaft (82); and

an elastic member (125) that is coupled to the arm member (108), has elasticity that generates a second torque (Ts) in a second direction (DR2) opposite to the first direction (DR1) about the pivot axis (Xs), and applies a driving force to the decompression cam (106) toward the operating position,

the internal combustion engine is characterized in that,

the first torque (Tf) and the second torque (Ts) are set such that the first torque (Tf) exceeds the second torque (Ts) at least a portion of the decompression weight (109) located below the center of the camshaft (82) in the direction of gravity, and the first torque (Tf) is lower than the second torque (Ts) at other positions.

7. An internal combustion engine according to any one of claims 1 to 6,

when the crankshaft (61) is located at a position other than the rotational angle position when the crankshaft (61) is stopped, the decompression cam (106) is located at the non-operating position.

8. An internal combustion engine according to any one of claims 1 to 7,

the decompression cam (106) is held at the operating position until the rotational speed of the camshaft (82) exceeds a predetermined rotational speed as the crankshaft (61) rotates.

9. An internal combustion engine according to any one of claims 1 to 8,

when mounted on a vehicle (11), the rotation of the crankshaft (61) is stopped in response to the stop of the vehicle (11), and the engine is restarted in response to the operation of an accelerator (28).

Technical Field

The present invention relates to an internal combustion engine including a decompression device that opens an exhaust valve in a compression stroke.

Background

Patent document 1 discloses a decompression mechanism that opens an exhaust valve during a compression stroke of an internal combustion engine at the time of startup to reduce rotational resistance of a crankshaft due to compression operation of a piston. The decompression mechanism includes an arm member supported by the camshaft so as to be swingable about a swing axis extending parallel to the rotation axis of the camshaft, and coupled to the decompression cam at a position spaced apart from the swing axis. A decompression weight is coupled to the arm member, and the decompression weight applies a driving force to the decompression cam toward a non-operating position in accordance with a centrifugal force generated by rotation of the camshaft. A torsion spring that applies a driving force to the decompression cam toward the operating position is connected to the arm member.

Prior art documents

Patent document

Patent document 1: japanese laid-open patent publication (JP 2015) 224579

Disclosure of Invention

Problems to be solved by the invention

In patent document 1, the center of gravity of the decompression weight is distant from the rotation axis of the camshaft according to the shape of the decompression weight. As a result, the centrifugal force of the decompression weight increases. A greater elastic force can be applied to the torsion spring as the centrifugal force increases. Even if the crankshaft is located at any rotational angle position, the decompression cam can be maintained at the operating position by the torsion spring. At the time of startup, the deactivation of the pressure reducing function can be suppressed. If the switching rotational speed of the pressure reducing function is further reduced, the occurrence of knocking can be further suppressed.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an internal combustion engine capable of reliably realizing a decompression function from the time of startup and reducing the switching rotational speed of the decompression function.

Means for solving the problems

According to a first aspect of the present invention, an internal combustion engine includes: a crankshaft; a camshaft coupled to the crankshaft and rotating at a reduction ratio of 2 to 1 with respect to the crankshaft; a decompression cam that is displaced between an operating position and a non-operating position, the operating position being a position at which a curved protruding surface having a generatrix parallel to a rotation axis of the camshaft protrudes from a virtual cylindrical surface coaxial with the camshaft when the rotation speed is less than a preset rotation speed, the non-operating position being a position at which the curved protruding surface retreats from the virtual cylindrical surface; a decompression sliding surface provided to an exhaust-side rocker arm and coming into contact with the curved protrusion surface when the camshaft rotates; an arm member supported by the camshaft so as to be swingable about a swing axis extending parallel to a rotation axis of the camshaft, the arm member being coupled to the decompression cam at a position away from the swing axis; a decompression weight coupled to the arm member, the decompression weight applying a driving force to the decompression cam toward the non-operating position by a first torque acting in a first direction around the swing axis by a gravity and changing according to a rotational angle position around a rotational axis of the camshaft; and an elastic member that is coupled to the arm member, has elasticity that generates a second torque in a second direction opposite to the first direction about the pivot axis, and applies a driving force to the decompression cam toward the operating position, wherein the internal combustion engine is provided with a starter motor that is coupled to the crankshaft and positions the crankshaft at a rotation angle position where the second torque exceeds the first torque before starting.

According to a second aspect, in addition to the structure of the first aspect, the starter motor reverses the crankshaft to a rotational angle range of the crankshaft established in an expansion stroke when the crankshaft is stopped.

According to a third aspect, in addition to the configuration of the second aspect, the starter motor exerts a torque smaller than a torque reaching a top dead center of a compression stroke when the crankshaft rotates in a reverse direction.

According to a fourth aspect, in addition to the structure of the third aspect, the starter motor reverses the crankshaft at a predetermined rotation angle.

According to a fifth aspect, on the basis of the structure of the fourth aspect, the inclination angle of the cylinder axis with respect to the horizontal plane is set within the following range: positioning the crankshaft at the rotational angle position at which the second torque exceeds the first torque when the crankshaft is reversed at the predetermined rotational angle.

According to a sixth aspect of the present invention, an internal combustion engine includes: a crankshaft; a camshaft coupled to the crankshaft and rotating at a reduction ratio of 2 to 1 with respect to the crankshaft; a decompression cam that is displaced between an operating position and a non-operating position, the operating position being a position at which a curved protruding surface having a generatrix parallel to a rotation axis of the camshaft protrudes from a virtual cylindrical surface coaxial with the camshaft when the rotation speed is less than a preset rotation speed, the non-operating position being a position at which the curved protruding surface retreats from the virtual cylindrical surface; a decompression sliding surface provided to an exhaust-side rocker arm and coming into contact with the curved protrusion surface when the camshaft rotates; an arm member supported by the camshaft so as to be swingable about a swing axis extending parallel to a rotation axis of the camshaft, the arm member being coupled to the decompression cam at a position away from the swing axis; a decompression weight coupled to the arm member, the decompression weight applying a driving force to the decompression cam toward the non-operating position by a first torque acting in a first direction around the swing axis by a gravity and changing according to a rotational angle position around a rotational axis of the camshaft; and an elastic member that is coupled to the arm member, has elasticity that generates a second torque in a second direction opposite to the first direction about the pivot axis, and applies a driving force to the decompression cam toward the operating position, wherein the first torque and the second torque are set such that the first torque exceeds the second torque when the decompression weight is located at least in a portion below a center of the camshaft in a direction of gravity, and the first torque is lower than the second torque in other positions.

According to a seventh aspect of the present invention, in the configuration according to any one of the first to sixth aspects, when the crankshaft is located at a position other than the rotational angle position when the crankshaft is stopped, the decompression cam is located at the non-operating position.

According to an eighth aspect, in addition to the structure of the seventh aspect, the decompression cam is held at the operating position until the rotation speed of the camshaft exceeds a predetermined rotation speed with rotation of the crankshaft.

According to a ninth aspect of the present invention, in addition to the configuration of any one of the first to eighth aspects, when mounted on a vehicle, rotation of the crankshaft is stopped in response to a stop of the vehicle, and the engine is restarted in response to an operation of an accelerator.

Effects of the invention

According to the first aspect, the crankshaft is positioned at a specific rotational angle position by the starter motor. When a particular rotational angular position is established, the decompression weight generates a first torque that exceeds a second torque generated by the elastic member. A second torque exceeding the first torque causes the curved protrusion surface to protrude from the virtual cylindrical surface. Therefore, when the camshaft rotates, the curved convex surface of the decompression cam draws the decompression sliding surface of the exhaust side rocker arm. The exhaust valve is opened by the decompression cam. Even if the elastic force of the elastic member is reduced, the function of reducing the pressure can be realized by the action of the starter motor from the starting time. Therefore, the switching rotational speed of the pressure reducing function can be reduced. The generation of the tapping sound can be further suppressed.

According to the second aspect, since the piston is located at a position in the expansion stroke, the piston is pushed in a direction in which the pressure of the air compressed in the combustion chamber drops. Then, the combustion chamber goes through an exhaust stroke and an intake stroke, and therefore, the motion resistance with respect to the displacement of the piston is reduced. At start-up, potential energy may be imparted to the rotation of the crankshaft prior to the compression stroke. The operation of the internal combustion engine can be smoothly started.

According to the third aspect, at the time of reverse rotation of the crankshaft, the piston in the expansion stroke cannot pass the top dead center in the compression stroke in accordance with the movement resistance of the piston. Therefore, the piston stops before the top dead center of the compression stroke at the time of reverse rotation. Thus, the rotational angle position of the crankshaft at the time of startup is set. At start-up, potential energy may be imparted to the rotation of the crankshaft prior to the compression stroke. The operation of the internal combustion engine can be started smoothly, and the start can be started in a state where the phase of the camshaft is within a certain range.

According to the fourth aspect, the starter motor reverses the crankshaft by a predetermined rotation angle, and therefore, the control of the reverse rotation can be simplified as compared with the case where a reverse rotation angle is set for each rotation angle position of the crankshaft. However, since the piston is surely stopped before the top dead center of the compression stroke, the operation of the internal combustion engine can be smoothly started.

According to the fifth aspect, it is possible to secure the crankshaft at a specific rotational angular position at the time of reverse rotation of the crankshaft in accordance with the inclination angle of the cylinder axis. The decompression function can be reliably ensured at the time of reverse rotation of the crankshaft in accordance with the posture of the cylinder axis.

According to the sixth aspect, since the spring load of the elastic member can be reduced, the weight of the decompression weight can be suppressed accordingly. The reduced weight of the pressure reducing weight can contribute to the compactness of the pressure reducing mechanism.

According to the seventh aspect, when the crankshaft is located at a position other than the rotational angle position when the crankshaft is stopped, the elastic member may have a smaller elastic force as the decompression cam is located at the non-operating position. The elastic force of the elastic member can be sufficiently reduced. The switching rotational speed of the pressure reducing function can be reduced.

According to the eighth aspect, the decompression cam is held at the operating position until the centrifugal force accompanying rotation of the camshaft sufficiently increases. Therefore, the operation of the internal combustion engine can be smoothly started up from the start to the predetermined rotation speed.

According to the ninth aspect, the idle stop function can be implemented when the vehicle is stopped.

Drawings

Fig. 1 is a side view schematically showing an overall image of a motorcycle (saddle-ride type vehicle) according to an embodiment of the present invention.

Fig. 2 is a front view of the motorcycle.

Fig. 3 is a cross-sectional view of the internal combustion engine viewed in a cross-sectional plane including the cylinder axis, the rotation axis of the crankshaft, the axial center of the main shaft, and the axial center of the auxiliary shaft.

Fig. 4 is an enlarged sectional view taken along line 4-4 of fig. 3.

Fig. 5 is an enlarged vertical sectional view taken along line 5-5 of fig. 4.

Fig. 6 is an enlarged vertical sectional view taken along line 6-6 of fig. 5.

Fig. 7 is an enlarged vertical sectional view taken along line 7-7 of fig. 5.

Fig. 8 is an enlarged vertical cross-sectional view schematically showing the configuration of the decompression device when the cam pin of the decompression cam is located at the second position, corresponding to fig. 6.

Fig. 9 is a timing chart showing a relationship among torque required for reverse rotation of the crankshaft, first torque acting around the rocking shaft, and second torque in the combustion stroke of the internal combustion engine.

Fig. 10 is a timing chart showing a relationship between torque required for reverse rotation of the crankshaft, first torque acting around the rocking shaft, and second torque in the combustion stroke of the internal combustion engine.

Description of the reference numerals

11 … straddle type vehicle (motorcycle), 28 … accelerator, 35 … internal combustion engine, 54 … starter motor (ACG starter), 61 … crankshaft, 82 … camshaft, 93b … exhaust side rocker arm, 106 … decompression cam, 108 … arm component, 109 … decompression weight, 116a … curved convex surface, 118 … imaginary cylinder surface, 125 … elastic component (torsion spring), 126 … decompression sliding surface, C … cylinder axis, DR1 … first direction, DR2 … second direction, Tf … first torque, Ts … second torque, Xc … (camshaft) axis, Xs … (arm component) swing axis.

Detailed Description

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Here, the upper, lower, front, rear, left, and right of the vehicle body are defined based on the line of sight of the occupant seated in the motorcycle.

Fig. 1 schematically shows an overall image of a motorcycle as a saddle-ride type vehicle according to an embodiment of the present invention. The motorcycle 11 includes a frame 12 and a body cover 13 attached to the frame 12. The vehicle body cover 13 has a box cover 16 that covers the fuel tank 14 and is connected to a passenger seat 15 behind the fuel tank 14. Fuel is stored in the fuel tank 14. When the motorcycle 11 is driven, the occupant gets over the occupant seat 15.

The frame 12 has: a head pipe 17; a main frame 19 extending rearward and downward from the head pipe 17 and having a pivot frame 18 at a rear lower end; a lower frame 21 extending downward from the head pipe 17 at a position below the main frame 19; a left and right seat frame 22 extending rearward in the horizontal direction from the bent region 19a of the main frame 19; and a rear frame 23 extending rearward and upward from the pivot frame 18 below the seat frame 22 and combined with the seat frame 22 from below at a rear end. The rear frame 23 supports the seat frame 22 from below.

The head pipe 17 rotatably supports a front fork 24. The front wheel WF is rotatably supported by the front fork 24 around an axle 25. A steering handle 26 is coupled to an upper end of the front fork 24. As shown in fig. 2, the steering handle 26 extends horizontally in the vehicle width direction. Handles 27 are fixed to both ends of the steering handle 26. The driver grips the grips 27 with the left and right hands respectively when driving the motorcycle 11.

A right-hand grip 27 shown in fig. 2 is rotated around an axis and functions as an accelerator 28 that determines the opening degree of a throttle valve from a rotation angle. A brake lever 29 extending in parallel with the grip 27 is disposed in front of the right grip 27. A braking force is applied to the front wheel WF, for example, by operating the brake lever 29. The occupant can adjust the speed of the vehicle according to the operation of the handle 27 and the operation of the brake lever 29. A clutch lever 31 extending in parallel with the handle 27 is disposed in front of the left-end handle 27.

As shown in fig. 1, a swing arm 33 is connected to the body frame 12 at the rear of the vehicle so as to be swingable up and down about a pivot shaft 32. A rear wheel WR is rotatably supported around an axle 34 at a rear end of the rocker arm 33. An internal combustion engine 35 that generates a driving force transmitted to the rear wheel WR is mounted on the vehicle body frame 12 between the front wheel WF and the rear wheel WR. The power of the internal combustion engine 35 is transmitted to the rear wheel WR through the power transmission device 36.

The internal combustion engine 35 includes: a crankcase 37 disposed between the lower frame 21 and the main frame 19 and connected to the lower frame 21 and the main frame 19, respectively; a cylinder block 38 extending upward from the front side of the crankcase 37 and having a cylinder axis C that inclines forward; a cylinder head 39 coupled to an upper end of the cylinder block 38 and supporting a valve mechanism; and a cylinder head cover 40 coupled to an upper end of the cylinder head 39 and covering the valve mechanism 81 on the cylinder head 39. In the crankcase 37, power is generated around the rotation axis Rx.

An intake device 41 that supplies the mixture gas to the internal combustion engine 35 and an exhaust device 42 that discharges the exhaust gas of the internal combustion engine 35 toward the rear of the vehicle are connected to the internal combustion engine 35. The intake device 41 includes: a throttle body 43 that is coupled to the rear wall of the cylinder head 39 and adjusts the flow rate of air by the action of a throttle; and an air cleaner (not shown) connected to the throttle body 43 through a connection pipe to clean outside air supplied to the internal combustion engine 35. The throttle body 43 controls the opening of the throttle valve in accordance with the operation amount of the accelerator 28. A fuel injection device 44 that injects fuel facing the intake passage of the cylinder head 39 is inserted into the throttle body 43.

The exhaust device 42 includes an exhaust pipe 45 coupled to the front wall of the cylinder head 39 and extending rearward in the downward direction of the internal combustion engine 35. A catalyst 46 for purifying exhaust gas discharged from the internal combustion engine 35 is mounted on the exhaust pipe 45. A muffler (not shown) having a muffler function of the internal combustion engine 35 and discharging exhaust gas to the atmosphere behind the axle 34 is connected to the rear end of the exhaust pipe 45.

As shown in fig. 3, a cylinder 48 that guides the linear reciprocating motion of the piston 47 along a cylinder axis C is defined in the cylinder block 38. Here, a single cylinder 48 that houses a single piston 47 is formed in the cylinder block 38. A combustion chamber 49 is defined between the piston 47 and the cylinder head 39. An ignition plug 51 facing the combustion chamber 49 is mounted to the cylinder head 39. The spark plug 51 ignites the mixture gas in the combustion chamber 49 by a spark generated in the electrode based on the supplied electric signal.

The crankcase 37 is divided into a first case half body 37a and a second case half body 37 b. The first case half body 37a and the second case half body 37b face each other at inner surfaces. The first half case body 37a and the second half case body 37b are joined to each other at mating surfaces in a fluid-tight manner and cooperate to define the crank chamber 53. An ACG cover 55 that houses an ACG starter 54 and a sprocket cover 57 that houses a sprocket 56 between the first case half body 37a and the ACG starter are coupled to an outer surface of the first case half body 37 a. A clutch cover 59 for accommodating a friction clutch 58, which will be described later, between the second case half body 37b and the outer surface of the second case half body 37b is coupled.

The crankshaft 61 includes: journals 64a and 64b connected to ball bearings 62 and 63 fitted into the first half case 37a and the second half case 37b, respectively; and a crank 65 disposed between the journals 64a, 64b and housed in the crank chamber 53. The crank 65 has a crank arm 66 integrated with the journals 64a, 64b, and a crank pin 67 connecting the crank arms 66 to each other. The axes of the journals 64a, 64b coincide with the axis of rotation Rx. A large end of a connecting rod 68 extending from the piston 47 is rotatably connected to the crank pin 67. The connecting rod 68 converts the linear reciprocating motion of the piston 47 into the rotational motion of the crankshaft 61.

An ACG starter 54 is connected to one end of a crankshaft 61 projecting outward in one direction from the crankcase 37. The ACG starter 54 includes: a stator 71 fixed to an outer surface of the crankcase 37, and a rotor 72 coupled to one end of the crankshaft 61 projecting from the crankcase 37 so as not to rotate relative thereto. Stator 71 has a plurality of coils 71a arranged in the circumferential direction around crankshaft 61 and wound around the stator core. The rotor 72 includes a plurality of magnets 72a arranged in the circumferential direction along a ring-shaped track surrounding the stator 71. When crankshaft 61 rotates, magnet 72a is displaced relative to coil 71a, and ACG starter 54 generates electric power. In contrast, when a current flows through coil 71a, a magnetic field is generated by coil 71a, causing rotation of crankshaft 61.

The internal combustion engine 35 includes a dog clutch type transmission 73 combined with the crankshaft 61. The transmission 73 is housed in a transmission chamber 74 that is continuously partitioned from the crank chamber 53 in the crankcase 37. The transmission 73 includes a main shaft 75 and a counter shaft 76 having an axial center parallel to the axial center of the crankshaft 61. The main shaft 75 and the sub shaft 76 are rotatably supported by the crankcase 37 by rolling bearings.

A plurality of transmission gears 77 are supported on the main shaft 75 and the counter shaft 76. The transmission gear 77 is disposed between the rolling bearings and housed in the transmission chamber 74. The transmission gear 77 includes: a rotary gear 77a supported coaxially and relatively rotatably on the main shaft 75 or the counter shaft 76; a fixed gear 77b fixed to the main shaft 75 so as not to be relatively rotatable and meshing with the corresponding rotary gear 77 a; and a shift gear 77c supported by the main shaft 75 or the counter shaft 76 so as to be relatively non-rotatable and axially displaceable, and meshing with the corresponding rotary gear 77 a. The axial displacement of the rotating gear 77a and the fixed gear 77b is restricted. When the shift gear 77c is coupled to the rotary gear 77a by axial displacement, relative rotation of the rotary gear 77a and the main shaft 75 or the counter shaft 76 is restricted. When the shift gear 77c meshes with the fixed gear 77b of the other shaft, rotational power is transmitted between the main shaft 75 and the counter shaft 76. When the shift gear 77c is coupled to the rotary gear 77a meshing with the fixed gear 77b of the other shaft, rotational power is transmitted between the main shaft 75 and the counter shaft 76. In this way, the counter shaft 76 outputs the rotational force of the crankshaft 61 at an arbitrary reduction ratio via the transmission 73.

The main shaft 75 is connected to the crankshaft 61 outside the crankcase 37 via a primary speed reduction mechanism 78 housed between the crankcase 37 and the clutch cover 59. The primary speed reduction mechanism 78 includes a power transmission gear 78a and a driven gear 78b supported rotatably relative to the main shaft 75. The power transmission gear 78a is fixed to the other end of the crankshaft 61 that protrudes outward from the crankcase 37. The driven gear 78b meshes with the power transmission gear 78 a.

The friction clutch 58 housed between the crankcase 37 and the clutch cover 52 is coupled to the main shaft 75. The friction clutch 58 includes a clutch outer 58a and a clutch hub 58 b. The driven gear 78b of the primary speed reduction mechanism 78 is coupled to the clutch outer 58 a. In the friction clutch 58, connection and disconnection are switched between the clutch outer 58a and the clutch hub 58b in accordance with an operation of the clutch lever 31.

Sprocket 56 is fixed to countershaft 76. The power transmission device 36 includes a sprocket 56, a driven sprocket (not shown) fixed to the axle 34 of the rear wheel WR, and a winding chain 79 wound around the sprocket 56 and the driven sprocket. The sprocket 56 transmits the rotational force of the counter shaft 76 to the rear wheel WR via the winding chain 79.

The internal combustion engine 35 is equipped with a valve mechanism 81 that controls the flow of the mixture gas and the exhaust gas with respect to the combustion chamber 49. The valve mechanism 81 includes a camshaft 82 supported by the cylinder head 39 so as to be rotatable about an axis Xc parallel to the rotation axis Rx of the crankshaft 61. Sprockets 83a and 83b are fixed to the camshaft 82 and the crankshaft 61, respectively. A cam chain 84 is wound around the sprockets 83a and 83 b. The cam chain 84 transmits rotation of the crankshaft 61 to the camshaft 82. The camshaft 82 rotates at a reduction ratio of 2 to 1 with respect to the crankshaft 61.

As shown in fig. 4, the valve mechanism 81 includes: an intake valve 85 in which a valve head 85a is disposed in the combustion chamber 49 and which is supported by the cylinder head 39 so as to be axially displaceable by a valve stem 85b extending from the valve head 85 a; and an exhaust valve 86 in which a valve head 86a is disposed in the combustion chamber 49 and which is supported by the cylinder head 39 so as to be axially displaceable by a valve stem 86b extending from the valve head 86 a. A valve head 85a of the intake valve 85 is embedded in the cylinder head 39 at an opening of the intake port 87a, and is seated on a valve seat 88a that partitions the intake port with respect to the combustion chamber 49. An air passage of the throttle body 43 is connected to the intake port 87 a. A valve head 86a of the exhaust valve 86 is embedded in the cylinder head 39 at an opening of the exhaust port 87b, and is seated on a valve seat 88b that partitions the exhaust port with respect to the combustion chamber 49. An exhaust pipe 45 is connected to the exhaust port 87 b.

The valve stems 85b, 86b have one ends (outer ends) that project upward from the cylinder head 39 and are disposed outside the combustion chamber 49. A retainer 89 is fixed to the outer ends of the valve stems 85b and 86b by the action of a pin. A coil spring 91 is sandwiched in a compressed state between the retainer 89 and the outer surface of the cylinder head 39. The coil spring 91 exerts an elastic force in the extending direction in which the retainer 89 is away from the outer surface of the cylinder head 39. The valve heads 85a, 86a are seated on the valve seats 88a, 88b by the elastic force of the coil spring 91.

The valve mechanism 81 includes: a pair of rocker arms 92 supported by the cylinder head 39 and having an axial center Xk parallel to the rotation axis Rx of the crankshaft 61; and an intake side rocker arm 93a and an exhaust side rocker arm 93b supported by the rocker shaft 92 so as to be swingable about the axial center Xk. Each of the rocker arms 93a and 93b includes: a first arm 95 extending in the centrifugal direction from the rocker shaft 92 and having an operating point 94 at a leading end thereof; and a second arm 97 extending in a centrifugal direction from the rocker shaft 92 in a direction opposite to the first arm 95 and having a cam follower 96 at a front end. The rocker arms 93a, 93b contact the outer ends of the intake valve 85 and the exhaust valve 86, respectively, at an operating point 94 of the first arm 95. The rocker arms 93a, 93b are respectively in contact with the camshaft 82 via the cam followers 96. Details of the camshaft 82 and the rocker arms 93a, 93b are discussed later.

As shown in fig. 5, the cam shaft 82 is rotatably coupled to a pair of bearings 99 fixed to the cylinder head 39 by a pressing member 98. The bearing 99 is, for example, a ball bearing. A first cam lobe 101 for the intake side rocker arm 93a and a second cam lobe 102 for the exhaust side rocker arm 93b are formed on the camshaft 82 between the bearings 99. The first cam lobe 101 and the second cam lobe 102 are arranged to be offset in the axial direction of the camshaft 82.

As shown in fig. 4, the cam follower 96 includes a roller 103 supported by the second arm 97 so as to be rotatable about a rotation axis parallel to the axis Xc of the cam shaft 82. The outer circumferential surface of the roller 103 contacts the first cam lobe 101 and the second cam lobe 102, respectively. The roller 103 is rotatable upon receiving rotation of the first cam lobe 101 and the second cam lobe 102. The roller 103 follows the contours of the first cam lobe 101 and the second cam lobe 102 while rotating. Opening and closing of the intake valve 85 and the exhaust valve 86 are controlled by bringing the roller 103 closer to or away from the axis Xc of the camshaft 82.

The first cam lobe 101 includes: a basal surface 101a having a shape of a partial cylindrical surface coaxial with the axis Xc of the camshaft 82; and a lift surface 101b provided to the camshaft 82 continuously with the base surface 101a in the rotational direction, and bulging outward in the radial direction from the base surface 101a to define the lift amount of the intake valve 85. The roller 103 of the intake side rocker arm 93a maintains contact with the ground surface 101a and the lift surface 101b to cause the intake side rocker arm 93a to swing.

The second cam lobe 102 includes: a basal surface 102a having a shape of a partial cylindrical surface coaxial with the axis Xc of the camshaft 82; and a lift surface 102b provided to the camshaft 82 continuously with the base surface 102a in the rotational direction, and bulging outward in the radial direction from the base surface 102a to define the lift amount of the exhaust valve 86. The roller 103 of the exhaust side rocker arm 93b maintains contact with the floor surface 102a and the lift surface 102b to cause the exhaust side rocker arm 93b to swing.

As shown in fig. 6, the valve mechanism 81 includes a decompression device 105 that opens the exhaust valve 86 in the compression stroke so as to be less than a predetermined rotation speed (per minute). The pressure reducing device 105 includes: a decompression cam 106 assembled to the cam shaft 82 and displaced between an operating position and a non-operating position; a decompression follower 107 formed on the exhaust side rocker arm 93b and contacting the decompression cam 106 at a rotation speed (per minute) less than a predetermined value; an arm member 108 supported by the cam shaft 82 so as to be swingable about a swing axis Xs extending parallel to the axis Xc of the cam shaft 82, and connected to the decompression cam 106 at a position away from the swing axis Xs; and a decompression weight 109 coupled to the arm member 108 and configured to apply a driving force to the decompression cam 106 toward the non-operating position.

As shown in fig. 5, the decompression cam 106 and the arm member 108 are supported on a step surface 111 formed on the cam shaft 82 between the second cam lobe 102 and the bearing 99. The step surface 111 is divided between a large diameter shaft 112a that defines the second cam lobe 102 and a small diameter shaft 112b that is continuous with the large diameter shaft 112a, is smaller in diameter than the large diameter shaft 112a, and is housed in the bearing 99, and faces the bearing 99. The step surface 111 is connected to the base surface 102a of the second cam lobe 102 and the edge of the lift surface 102b orthogonally to the axis Xc of the camshaft 82.

The decompression cam 106 includes a shaft body 113 having an axial center parallel to the axis Xc of the camshaft 82. The shaft body 113 is rotatably housed around an axial center (i.e., a rotation axis Xd) in a shaft hole 114 formed in the camshaft 82 and defining a cylindrical space coaxial with the shaft body 113. Thus, the decompression cam 106 is rotatably supported by the cam shaft 82 about the rotation axis Xd.

The decompression cam 106 includes a cam main body 115 coaxial with the shaft body 113. As shown in fig. 7, the cam main body 115 is formed with: a partial cylindrical surface 116 formed coaxially with the rotation axis Xd of the decompression cam 106; and a notch 117 which is a plane parallel to the rotation axis Xd of the decompression cam 106 and connected to a generatrix at one end of the partial cylindrical surface 116. The partial cylindrical surface 116 protrudes at a predetermined height from an imaginary cylindrical surface 118 coaxial with the camshaft 82, and forms a curved protrusion surface 116a having a generatrix parallel to the rotation axis Xc of the camshaft 82. The lift amount of the exhaust valve 86 during the decompression operation is set according to the projection height of the curved projection surface 116 a. The notch 117 is disposed inside an imaginary partial cylindrical surface 119 that forms one cylinder continuously from the partial cylindrical surface 116. The decompression follower 107 comes into contact with the curved protrusion surface 116a when the cam shaft 82 rotates.

As shown in fig. 6, the decompression cam 106 has a cam groove 122 that houses a cam pin 121. The cam pin 121 is constituted by a cylindrical body having an axial center parallel to the axis Xc of the cam shaft 82. The cam groove 122 is formed in an end surface of the cam main body 115 and linearly extends from the partial cylindrical surface 116 toward the axial center. When the cam pin 121 moves in the circumferential direction around the rotation axis Xc of the cam shaft 82, the decompression cam 106 changes its posture around its axial center between the operating position and the non-operating position.

As shown in fig. 5, the arm member 108 is coupled to the cam shaft 82 via, for example, a swing shaft 123 that is press-fitted into the step surface 111. The swing shaft 123 supports the arm member 108 swingably about a swing axis Xs which is an axial center extending parallel to the rotation axis Xc of the cam shaft 82. A spacer 124 is attached to the swing shaft 123 between the step surface 111 and the arm member 108. The cam body 115 of the decompression cam 106 is disposed in a space between the arm member 108 and the step surface 111 by the action of the spacer 124.

As shown in fig. 6, the rocking shaft 123 is disposed at a position spaced apart from the rotation axis Xd of the decompression cam 106 at least in the circumferential direction of the cam shaft 82. It is desirable that the swing shaft 123 be as far away from the decompression cam 106 as possible. A cam pin 121 is fixed to the front end of the arm member 108. The cam pin 121 moves between a first position that establishes an operating position of the decompression cam 106 and a second position that establishes a non-operating position of the decompression cam 106.

As shown in fig. 5, a torsion spring 125 is mounted on the spacer 124. One end of torsion spring 125 is hung on arm member 108. The other end of the torsion spring 125 is hung on the small-diameter shaft 112 b. The torsion spring 125 exerts an elastic force that drives the cam pin 121 toward the first position.

The decompression weight 109 generates a torque in the first direction DR1 about the swing axis Xs by the action of centrifugal force generated in the rotation of the camshaft 82. The decompression cam 106 is driven toward the non-operating position. The torsion spring 125 has elasticity to generate a torque in the second direction DR2 opposite to the first direction DR1 about the swing axis Xs. The decompression cam 106 is driven toward the operating position. When the internal combustion engine 35 operates at a rotation speed less than a predetermined rotation speed (per minute), the torque of the torsion spring 125 exceeds the torque of the decompression weight 109, and the cam pin 121 is held at the first position. When the internal combustion engine 35 is operated at a predetermined rotational speed (per minute) or more, the torque of the decompression weight 109 exceeds the torque of the torsion spring 125, and the cam pin 121 moves to the second position.

As shown in fig. 7, the decompression follower 107 includes a decompression sliding surface 126 facing the virtual cylindrical surface 118. When the decompression cam 106 is located at the operating position, the decompression sliding surface 126 contacts the curved protrusion surface 116a on the outer side of the imaginary cylindrical surface 118 when the camshaft 82 rotates. When the decompression cam 106 is located at the non-operating position, the decompression slide face 126 forms a gap between it and the cutout 117 when the cam shaft 82 rotates.

Next, the operation of the pressure reducing device 105 will be described. During operation of the internal combustion engine 35, rotation of the crankshaft 61 is transmitted to the camshaft 82 at a reduction ratio of 2 to 1. As the camshaft 82 rotates, the cam follower 96 of the intake-side rocker arm 93a successively draws the basal surface 101a and the lift surface 101b of the first cam lobe 101. Therefore, the intake side rocker arm 93a swings in accordance with the cam profile of the first cam lobe 101, opening and closing the intake valve 85. Likewise, the cam follower 96 of the exhaust side rocker arm 93b successively delineates the basal surface 102a and the lift surface 102b of the second cam lobe 102. The exhaust rocker arm 93b swings in accordance with the cam profile of the second cam lobe 102 to open and close the exhaust valve 86. The opening and closing operation of the intake valve 85 and the opening and closing operation of the exhaust valve 86 are performed at timings corresponding to the intake stroke and the exhaust stroke of the internal combustion engine 35.

Here, in the case of less than a predetermined rotation speed (per minute), centrifugal force does not sufficiently act on the decompression weight 109, and the cam pin 121 is held at the first position by the action of the torsion spring 125. Therefore, the curved convex surface 116a of the decompression cam 106 protrudes outward from the virtual cylindrical surface 118. While the cam follower 96 of the exhaust side rocker arm 93b draws the basal surface 102a of the second cam lobe 102, the curved convex surface 116a of the decompression cam 106 draws the decompression sliding surface 126 of the exhaust side rocker arm 93 b. Causing the exhaust side rocker arm 93b to swing. The exhaust valve 86 is opened during the compression stroke. Thus, in the compression stroke, the movement resistance with respect to the displacement of the piston 47 decreases. The operation of the internal combustion engine 35 can be smoothly started.

As the rotational speed (per minute) increases, the centrifugal force acting on the decompression weight 109 increases. As a result, the cam pin 121 moves from the first position toward the second position against the elastic force of the torsion spring 125. The decompression cam 106 rotates about the rotation axis Xd. Since the curved protrusion surface 116a is formed by a partial cylindrical surface 116, the protrusion of the curved protrusion surface 116a is maintained until a predetermined rotational speed (per minute) is reached. The decompression lift curve is maintained.

When a predetermined rotation speed (per minute) is secured, the cam pin 121 reaches the second position by the action of the centrifugal force acting on the decompression weight 109 as shown in fig. 8. The cutout 117 of the decompression cam 106 faces the decompression slide face 126. Since the cutout 117 is located inward of the imaginary cylindrical surface 118, the decompression cam 106 is prevented from contacting the decompression sliding surface 126 while the cam follower 96 of the exhaust rocker arm 93b draws the base surface 102a of the second cam lobe 102. The decompression function of the exhaust valve 86 is disabled. During the compression stroke, the exhaust valve 86 maintains a closed state.

The motorcycle 11 of the present embodiment employs an idle stop system. In the idle stop system, when the stop of the front wheel WF and the rear wheel WR is detected in accordance with the operation of the brake lever 29, the operation of the internal combustion engine 35 is stopped. The linear reciprocating motion of the piston 47 is stopped. The rotation of the crankshaft 61 is stopped.

After the operation is stopped, the internal combustion engine 35 performs a swing back control. The ACG starter 54 drives the crankshaft 61 in the reverse direction in response to the supply of electric power. The crankshaft 61 is positioned about the rotation axis Rx in a rotation angle range established in the expansion stroke. In response to the reverse rotation, the air is compressed in the combustion chamber 49.

When the operation of the accelerator 28 is detected after the swing-back control is implemented, the internal combustion engine 35 is restarted. At the time of restart, since the piston 47 is located at a position in the expansion stroke, the piston 47 is pushed in a downward direction by the pressure of the air compressed in the combustion chamber 49. Then, the combustion chamber 49 undergoes the exhaust stroke and the intake stroke, and therefore the movement resistance with respect to the displacement of the piston 47 is reduced. At the time of restart, potential energy may be imparted to the rotation of the crankshaft 61 before the compression stroke. The operation of the internal combustion engine 35 can be smoothly started.

During the swing-back control, as shown in fig. 9, a torque Tc smaller than a torque TQ reaching the top dead center of the compression stroke (hereinafter referred to as "compression top dead center") is set in the ACG starter 54. Therefore, piston 47 cannot go beyond compression top dead center when crankshaft 61 is rotating in the reverse direction. The piston 47 stops just before the compression top dead center. The rotation angle of crankshaft 61 is about 5 ° to 15 ° in the normal rotation direction from the rotation angle position of compression top dead center (0 °). When the crankshaft 61 rotates in the reverse direction, the displacement of the piston 47 corresponding to the expansion stroke in the normal rotation compresses air in the combustion chamber 49, and therefore the torque TQ required for driving the crankshaft 61 at the compression top dead center is maximized.

The crankshaft 61 is reversely rotated at a predetermined rotation angle. Here, the rotation angle of the swing-back control is set to, for example, 510 °. The rotation angle of the swing-back control may be set to a value equal to a walking assist angle at which the piston 47 can reach the compression top dead center by the inertial force of the rotation at the time of starting. The ACG starter 54 reversely rotates the crankshaft 61 by a predetermined rotational angle, and therefore, control of reverse rotation is simplified as compared with a case where a reverse rotational angle is set for each rotational angle position of the crankshaft 61. However, since the piston 47 is surely stopped just before the compression top dead center, the operation of the internal combustion engine 35 can be smoothly started.

When the crankshaft 61 is stopped, the decompression weight 109 generates a first torque Tf acting in the first direction DR1 about the swing axis Xs by the action of gravity. The first torque Tf varies according to the rotational angle position about the rotational axis Xc of the camshaft 82. On the other hand, the torsion spring 125 generates a second torque Ts acting in the second direction DR2 about the swing axis Xs based on the elastic force thereof. The second torque Ts is determined according to the spring load of the torsion spring 125, and therefore, the second torque Ts is maintained constant.

When the rotation of the crankshaft 61 is stopped, as shown in fig. 10, the ACG starter 54 positions the crankshaft 61 at a rotational angle position, at which the second torque Ts exceeds the first torque Tf, about the rotation axis Rx before starting. The second torque Ts exceeding the first torque Tf causes the curved protrusion surface 116a to protrude from the virtual cylindrical surface 118. When the camshaft 82 rotates, the curved convex surface 116a of the decompression cam 106 draws the decompression sliding surface 126 of the exhaust side rocker arm 93 b. The exhaust valve 86 is opened by the action of the decompression cam 106. Even if the spring load (elastic force) of the torsion spring 125 is set small, the decompression function can be realized from the start by the action of the ACG starter 54. Therefore, the switching rotational speed (per minute) of the decompression function can be reduced as the spring load of the torsion spring 125 is reduced. The generation of the tapping sound can be further suppressed. On the other hand, when the crankshaft 61 is stopped at a rotational angle position at which the first torque Tf exceeds the second torque Ts, the curved protruding surface 116a recedes from the virtual cylindrical surface 118 by the action of gravity acting on the decompression weight 109.

In the decompression device 105, the exhaust valve 86 is opened at the determined timing in the compression stroke, and therefore, the rotational angle position of the decompression cam 106 is necessarily determined on the camshaft 82 about the axis Xc. Further, the swing shaft 123 is further away from the cam pin 121 coupled to the decompression cam 106, and the swing amount of the arm member 108 can be reduced when the decompression cam 106 rotates from the operating position to the non-operating position. Therefore, the position of the decompression weight 109 is determined about the axis Xc of the camshaft 82 with respect to the swing shaft 123. In this way, the variation of the first torque is determined according to the inclination angle of the cylinder axis C set with respect to the horizontal plane. The spring load of the torsion spring 125 can be appropriately set according to the inclination angle of the cylinder axis C.

In the present embodiment, when the ACG starter 54 rotates the crankshaft 61 in the reverse direction according to the backswing control, the crankshaft 61 is positioned at a rotation angle position where the second torque Ts exceeds the first torque Tf. That is, the inclination angle of the cylinder axis C with respect to the horizontal plane is set within the following range: when the crankshaft 61 is reversed at a predetermined rotation angle, the crankshaft 61 is positioned at a rotation angle position where the second torque Ts exceeds the first torque Tf. It is possible to secure the crankshaft 61 at a specific rotational angular position when the crankshaft 61 is reversely rotated according to the inclination angle of the cylinder axis C. It is possible to reliably ensure the decompression function when the crankshaft 61 is reversely rotated in accordance with the posture of the cylinder axis C.

In the torsion spring 125 of the present embodiment, when the crankshaft 61 is located at a position other than the rotational angle position determined in the backswing control while the crankshaft 61 is stopped, a spring load is set to such an extent that the decompression cam 106 is located at the non-operating position. The spring load of the torsion spring 125 is reduced compared to the spring load of such a degree that the pressure-reducing cam 106 is located at the action position at any rotational angle position. The torsion spring 125 has a small elastic force. The elastic force of the torsion spring 125 can be sufficiently reduced. The switching rotational speed of the pressure reducing function can be reduced.