JP2014129794A - Decompression device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decompression device of an internal combustion engine which reduces a contact sound between a cam follower and an exhaust cam and a contact sound between an exhaust valve and a valve seat which are generated due to the reverse rotation of a crank shaft when a piston cannot get over a compression top dead point at the stop of the internal combustion engine.SOLUTION: The decompression device comprise: a circular base round part (33a) and a cam mountain part (33b); the exhaust cam (33); a decompression weight (65); and a notched retreating part (55) which is connected to the decompression weight (65), turns in the same direction as the forward direction of a cam shaft (31), and is recessed to a protruded part (54) protruding from the base round part (33a) and the base round part (33a). The decompression device also comprises a decompression cam (51) for switching the exhaust valve (18) by the abutment of the protruded part (54) on a cam follower (42c), and in the decompression cam (51), a notch (56) notched shallower than the retreating part (55) is continuously formed at the front side of the retreating part (55) in the forward direction of the cam shaft (31).

Description

  The present invention relates to a decompression device for an internal combustion engine that opens the exhaust valve in a compression stroke at the start of the internal combustion engine, thereby reducing the compression pressure in the cylinder by the piston and facilitating the start of the internal combustion engine.

  The following is known as a conventional decompression device for an internal combustion engine. A camshaft rotatably supported by a cylinder head of an internal combustion engine, an arc-shaped base circle centered on the axis of the camshaft, and a base circle so as to protrude outward from the base circle An exhaust cam having a cam peak portion connected thereto is integrally provided, and the cam peak portion of the exhaust cam opens the exhaust valve via the cam follower as the exhaust cam rotates. On the side surface of the cam, a decompression weight that is urged by a spring in a direction approaching the camshaft side and opens from the camshaft by the centrifugal force and in the same direction as the normal rotation direction of the camshaft is rotatable. A decompression cam rotatably supported on a side surface of the exhaust cam is connected to the decompression weight.

  The shape of the decompression cam 71 in the conventional decompression device as viewed in the camshaft axial direction is shown in FIG. An arcuate projecting portion 72 centering on the rotation center C of the decompression cam 71 and a retracting portion 73 cut out of a part thereof are formed. When the decompression weight is closed, the projecting portion 72 of the decompression cam 71 is formed. Projecting from the base circle of the exhaust cam and the decompression weight is opened against the urging force of the spring by centrifugal force, the retracting part 73 is rotated to a position facing the cam follower side of the rocker arm, and the decompression cam It is designed to immerse radially inward from the base circle.

  In this decompression device, when the rotational speed of the camshaft is lower than a predetermined rotational speed, such as at the start of driving of the internal combustion engine, that is, when centrifugal force that drives the decompression weight in the opening direction does not act on the decompression weight 71, Decompression state in which the protrusion 72 protrudes from the base circle of the exhaust valve, the decompression cam 71 pushes up the cam follower in the compression stroke of the internal combustion engine, the rocker arm opens the exhaust valve, and the compression pressure in the cylinder is reduced It becomes.

  Further, when the engine speed of the internal combustion engine increases and the camshaft rotation speed becomes higher than the predetermined rotation speed, that is, the centrifugal force that drives the decompression weight in the opening direction acts on the decompression weight and becomes larger than the inferring force of the spring. The decompression weight is driven in the opening direction, the decompression cam is rotated by the decompression weight, and the retracting portion 73 formed on the decompression cam 71 faces the cam follower side of the rocker arm, and the retracting portion 73 of the decompression cam 71 is exhausted. The decompression cam 71 enters the decompression release state in which the exhaust valve is closed without pushing up the cam follower by immersing inward in the radial direction from the base circle portion of the cam.

JP 2010-1789 A

  In the above-described internal combustion engine decompression device, when the internal combustion engine is stopped, if the crankshaft reverses without the piston overcoming the compression top dead center, the camshaft also rotates in reverse. When the internal combustion engine is stopped, the decompression cam 71 is in a decompressed state in which the projecting portion 72 of the decompression cam 71 projects from the base circle of the exhaust valve, and the cam follower is pressed against the decompression cam. When the exhaust cam is reversed as the camshaft is reversed, the decompression cam 71 is rotated in the reverse direction around the rotation axis of the camshaft as the exhaust cam is rotated, and the decompression cam is dragged by the cam follower, that is, The decompression cam 71 is rotated in a direction in which the decompression cam is released, and the decompression weight may be driven in an opening direction outward from the axial center line of the camshaft as the decompression cam rotates.

  Further, the reverse rotation of the camshaft advances, and when the cam follower reaches the bending portion 74 where the retracting portion 73 of the decompression cam 71 and the arcuate portion are continuous, and over the bending portion 74, the decompression cam 71 rotates and retreats. 73 is in a decompression release state facing the cam follower side of the rocker arm, and the cam follower vigorously contacts the base circle part of the exhaust cam, so the contact sound when the cam follower contacts the base circle part, There was a possibility that a contact sound would be generated by closing the exhaust valve that was open and contacting the valve seat. Such a contact sound is generated when the internal combustion engine is stopped, so that the contact sound tends to be more conspicuous, and reduction of the contact sound has been desired.

  In order to achieve the above object, the invention according to claim 1 is directed to a camshaft rotatably supported by a cylinder head, an arc-shaped base circle centered on an axis of the camshaft, and the base circle. And an exhaust cam that opens and closes an exhaust valve via a rocker arm at the cam nose, and a cam nose that is connected to the base circle so as to protrude outward in the radial direction from the portion; A decompression weight that is pivotably supported on the side surface of the camshaft, and is connected to the decompression weight so as to rotate in the same direction as the normal rotation direction of the camshaft and protrudes from the base circle portion. A decompression part that opens and closes the exhaust valve by abutting the cam follower of the rocker arm. In the decompression device for an internal combustion engine provided with a cam, the decompression cam has a notch portion that is notched at a depth shallower than the withdrawal portion on the front side of the withdrawal portion in the forward rotation direction of the camshaft. A decompression device for an internal combustion engine, which is provided in series.

  According to a second aspect of the present invention, a bending point where the notch and the protruding portion are connected is a first bending portion, and a bending point where the notch and the retracting portion are connected is a second bending portion. In addition, the second bent portion is configured to protrude from the base circle portion, and the protrusion amount of the second bent portion from the base circle portion is determined by the protrusion of the protrusion portion of the decompression cam from the base circle portion. The decompression device for an internal combustion engine according to claim 1, wherein the decompression device is smaller than the amount.

  The invention according to claim 3 is characterized in that the width of the notch in the direction along the rotation direction of the decompression cam is narrower than the width of the protrusion in the direction along the rotation direction of the decompression cam. A decompression device for an internal combustion engine according to claim 1 or 2.

  The invention according to claim 4 is characterized in that the width of the notch portion in the direction along the rotation direction of the decompression cam is narrower than the width of the retracting portion in the direction along the rotation direction of the decompression cam. A decompression device for an internal combustion engine according to claim 3.

  According to a fifth aspect of the present invention, the decompression weight is rotatably supported on a side surface of the exhaust cam via a decompression pin having an axis parallel to the camshaft, and the forward rotation direction of the camshaft is caused by centrifugal force. The decompression device for an internal combustion engine according to any one of claims 1 to 4, wherein the decompression device operates in the same direction as the engine.

  According to a sixth aspect of the present invention, when a bending point where the notch and the protruding portion are connected is a first bending portion, and a bending point where the notch and the retracting portion are connected is a second bending portion. In addition, an angle formed by a straight line passing through the central axis of the decompression cam and the first bent portion and a bottom surface portion of the notch is a straight line passing through the central axis of the decompression cam and the second bent portion, 6. The decompression device for an internal combustion engine according to claim 5, wherein the angle is larger than an angle formed with a bottom surface portion of the retracting portion.

  According to the decompression device for an internal combustion engine according to claim 1, the notch portion that is notched at a depth shallower than the retracting portion is connected to the front side of the retracting portion in the normal rotation direction of the cam shaft of the decompression cam. Therefore, even if the camshaft is reversed, the notch moves to a position facing the outside of the base circle before the retracting part of the decompression cam. Even if the piston cannot get over the compression top dead center, the camshaft is reversed, the cam follower of the rocker arm is dragged, and the decompression cam is reversed, the cam follower moves from the protruding portion of the decompression cam through the notch. And reach the evacuation unit. Therefore, the amount of movement that the cam follower moves to the base circle side can be regulated by the notch cut at a shallow depth, and the cam follower immediately reaches the base circle from the lift state of the cam follower by the decompression cam. Therefore, it is possible to effectively reduce the contact sound when the cam follower contacts the base circle.

  According to the decompression device for an internal combustion engine according to claim 2, in addition to the effect of the decompression device for an internal combustion engine according to claim 1, the following effects are produced. In the decompression device for an internal combustion engine according to claim 2, the second bent portion of the decompression cam is configured to protrude from the base circle portion, and the protruding amount of the second bent portion is larger than the protruding amount of the first bent portion. When the contact point between the cam follower and the decompression cam shifts from the first bent portion to the second bent portion of the decompression cam, the lift amount of the cam follower when the cam follower is in contact with the second bent portion is The amount of lift is smaller than when the first follower is in contact with the first bent portion, and the cam follower passes through the second bent portion from the first bent portion when the cam follower contacts the decompression cam. It is possible to reduce the contact noise caused by the cam follower coming into contact with the base circle portion of the exhaust cam.

  Furthermore, since the lift amount of the exhaust valve when the cam follower is in contact with the second bent portion is smaller than the lift amount of the exhaust valve when it is in contact with the first bend, the exhaust valve is a valve seat valve. The momentum of contact with the seat surface can be reduced, and the contact noise of the exhaust valve contacting the valve seat surface can be reduced.

  According to the decompression device for an internal combustion engine according to claim 3, in addition to the effect of the decompression device for the internal combustion engine according to claim 1 or 2, the notch portion of the decompression cam in the direction along the rotation direction of the decompression cam. Since the width of the camshaft is formed to be narrower than the width of the protrusion in the direction along the rotation direction of the decompression cam, the protrusion of the decompression cam projects from the base circle of the exhaust cam during normal rotation of the camshaft. The decompressed area can be sufficiently widened and secured.

  According to the decompression device for an internal combustion engine according to claim 4, in addition to the effect of the decompression device for the internal combustion engine according to claim 3, the width of the notch in the direction along the rotation direction of the decompression cam is Since it is formed to be narrower than the width of the retracting portion in the direction along the rotation direction, the region of the decompression release state by the retracting portion can be sufficiently widened and secured during normal rotation of the camshaft.

  The decompression device for an internal combustion engine according to claim 5 has the following effects in addition to the effects of the decompression device for an internal combustion engine according to claims 1 to 4. The decompression weight of the decompression device for an internal combustion engine according to claim 5 is rotatably supported on the side surface of the exhaust cam via a decompression pin having a central axis parallel to the camshaft, and is rotated in the forward direction of the camshaft by centrifugal force. When the cam shaft rotates in the same direction as the cam follower, the force to drive the decompression weight in the opening direction tends to increase when the cam follower reaches the retracting portion from the protruding portion of the decompression cam. Sound and operation sound with decompression way tend to be loud. Therefore, the decompression apparatus having the decompression weight according to the fifth aspect can be suitably used.

  According to the decompression device for an internal combustion engine according to claim 6, in addition to the effect of the decompression device for an internal combustion engine according to claim 5, the following effect is achieved. In the conventional decompression device, when the cam follower moves directly from the projecting portion of the decompression cam to the retracting portion during the reverse rotation of the camshaft, a straight line passing through the bent portion where the projecting portion and the retracting portion are continuous, and the rotation center axis of the decompression cam, Since the angle formed with the bottom surface is small, when the cam follower of the rocker arm gets over the bent part, the force that tries to operate the decompression weight increases, so when the cam follower gets over the bent part, the decompression weight Was easily actuated in the direction of opening, and the operating sound was loud. However, according to the decompression device for an internal combustion engine according to claim 6, the angle formed by the straight line connecting the rotation center axis of the decompression cam and the first bent portion and the bottom surface portion of the notch portion is the bent portion of the conventional decompressor device. Is larger than the angle formed between the straight line passing through the rotation center axis of the decompression cam and the bottom surface of the retracting portion, so that the force to actuate the decompression weight in the direction of opening the decompression weight when the cam follower gets over the first bent portion. It is possible to reduce the operating noise of the decompression weight.

1 is a left side view of a motorcycle equipped with a power unit according to an embodiment of the present invention. It is a cross-sectional view of the whole power unit. It is a longitudinal cross-sectional view of a part of the internal combustion engine. It is sectional drawing of the valve operating mechanism and decompression apparatus of a decompression state. It is sectional drawing of the valve operating mechanism and decompression apparatus of a decompression cancellation | release state. It is a perspective view of a decompression cam. It is the VII-VII arrow line view of FIG. 6, Comprising: It is the figure which showed the cross-sectional shape of the decompression cam. It is a principal part side view of the decompression apparatus which is a decompression state. It is a principal part side view of a decompression device in the state where the 1st bent part of a decompression cam is contacting the decompression cam contact part of a rocker arm. It is a principal part side view of a decompression device in the state where the 2nd bent part of a decompression cam is contacting the decompression cam contact part of a rocker arm. It is a principal part side view of the decompression apparatus of a decompression cancellation | release state. It is a principal part side view of a decompression device at the time of camshaft reverse rotation start. FIG. 2 is an enlarged cross-sectional view of a main part around an exhaust valve of an internal combustion engine in a decompressed state. It is the figure which showed the rocker arm lift amount in the time passage at the time of camshaft reverse rotation. It is the figure which showed the cross-sectional shape of the decompression cam of the conventional decompression apparatus.

  Hereinafter, an embodiment according to the present invention will be described with reference to FIGS.

  The internal combustion engine E according to the present embodiment is a single-cylinder four-stroke internal combustion engine that forms the front part of a power unit P that is mounted on a motorcycle such as a scooter. The scooter type motorcycle 1 on which the power unit P is mounted. Is shown in FIG. In this specification, the forward direction of the motorcycle 1 is the front, and the front, rear, left and right are defined with reference to the posture facing the front.

  The body frame F of the motorcycle 1 extends rearward horizontally after the down tube 81 extends obliquely downward from the head pipe 80. A cross member 82 oriented in the horizontal direction is fixed to the rear end portion 81a of the down tube 81, and ends of a pair of rear frame pipes 83 are fixed to the left and right of the cross member 82. The pipe 83 extends obliquely upward and then extends horizontally toward the rear.

  A front fork 84 is pivotally supported on the head pipe 80, and a front wheel FW is pivotally supported at the lower end thereof. A front fender 91 is provided above the front wheel FW. Is provided. A storage device 86 and a fuel tank 87 are supported by the rear frame pipe 83, and a seat 88 is disposed above the storage device 86 and the fuel tank 87.

  A bracket 89 is provided at the front ends of the left and right rear frame pipes 83, and the power unit P is swingably connected to the bracket 89 via a link mechanism 90. A rear wheel RW disposed on the right side of the rear portion of the power unit P is pivotally supported by the power unit P.

  FIG. 2 shows a cross-sectional view of the entire power unit P. The power unit P is hung rearward from the front internal combustion engine E to form a belt continuously variable transmission T, and a rear wheel RW is provided to a speed reduction mechanism R provided at the rear thereof.

  The internal combustion engine E employs a four-stroke / one-cylinder SOHC type valve system. A crankshaft 9 is pivotally supported by a left / right crankcase 2 through a main bearing 13 in a horizontal direction. The cylinder block 3 is provided forward from the left and right crankcases 2 in a substantially horizontal forward leaning posture, and the cylinder head 4 and the head cover 5 are sequentially stacked on the cylinder block 3 and fastened together. Left and right side surfaces, a right crankcase cover 6a and a left crankcase cover 6b are attached.

  The cylinder block 3 is formed with a cylinder bore 7 penetrating in a substantially horizontal direction, and a piston 8 is fitted into the cylinder bore 7. A crankpin 10 of the crankshaft 9 is connected to the piston 8 via a connecting rod 11. Yes.

  The cylinder head 4 is provided with a combustion chamber 12. Combustion energy in the combustion chamber 12 of the internal combustion engine E is converted into kinetic energy of the piston 8, and the piston 8 is reciprocated, and the crankshaft 9 is connected via the connecting rod 11. Is driven to rotate.

  As shown in FIG. 3, the cylinder head 4 is formed with an intake port 15 having an intake port 15 a that opens to the combustion chamber 12 and an exhaust port 16 having an exhaust port 16 a that opens to the combustion chamber 12. An intake valve 17 and an exhaust valve 18 each comprising a poppet valve and an ignition plug 19 facing the center of the combustion chamber 12 are provided to open and close the opening 15a and the exhaust port 16a, respectively (see FIG. 2). In the internal combustion engine E of the present embodiment in which the crankshaft 9 is mounted horizontally on the motorcycle 1, the intake port 15a is positioned on the upper side and the exhaust port 16a is positioned on the lower side.

  Further, an intake valve seat 15b is fitted over the circumferential direction of the intake port 15a of the intake port 15, and a valve seat surface 15c on which the intake valve 17 is seated is formed on the combustion chamber side of the intake valve seat 15b. An exhaust valve seat 16b is fitted over the exhaust port 16 in the circumferential direction of the exhaust port 16, and a valve seat surface 16c on which the exhaust valve 18 is seated is formed on the combustion chamber side of the exhaust valve seat 16b.

  The intake valve 17 and the exhaust valve 18 as engine valves are composed of valve portions 17a and 18a and stem portions 17b and 18b. The stem portions 17b and 18b are slidable in the valve guide 20 press-fitted into the cylinder head 2. It is inserted and constantly urged in the valve closing direction by the resilient force of the valve spring 21. The intake valve 17 and the exhaust valve 18 are driven by a valve mechanism 30 to open and close the intake port 15 and the exhaust port 16 that open to the combustion chamber 12 in synchronization with the engine rotation.

  As shown in FIGS. 3 and 4, the valve operating mechanism 30 is accommodated in an upper part of the cylinder head 4 in a valve operating chamber 14 including the cylinder head 4 and the head cover 5. The valve mechanism 30 includes a camshaft 31 on which an intake cam 32 and an exhaust cam 33 are formed. The camshaft 31 is rotatably supported by bearings 35 and 36 by a cylinder head 2 and a camshaft holder 34. Accordingly, the intake cam 32 and the exhaust cam 33 rotate to open and close the intake valve 17 and the exhaust valve 18.

  As shown in FIG. 4, in the valve operating chamber 14, bearing portions 22, 22 extending from the cylinder head 2 to the left and right with the intake valve 17 and the exhaust valve 18 interposed therebetween are formed. A semicircular arc-shaped shaft support portion 22a is formed. Bearings 35 and 36, which are ball bearings, are sandwiched between the coaxial support portion 22a and the semi-arc-shaped shaft support portion 34a of the camshaft holders 34 and 34. The left and right bearings 35 and 36 direct the camshaft 31 in the left-right direction. It is supported rotatably. FIG. 4 shows the decompression device in the decompressed state, and FIG. 5 shows the decompression device in the decompressed state.

  The camshaft 31 is formed between the left and right bearings 35 and 36 and is formed with an intake cam 32 that is a valve operating cam that opens and closes the intake valve 17, and the exhaust valve 18 is adjacent to the right side of the intake cam 32. An exhaust cam 33 is formed as a valve cam for opening and closing the valve.

  As shown in FIG. 3, the intake cam 32 includes an arc-shaped base circle portion 32a centering on the axis of the camshaft 31, and a base circle portion 32a that protrudes radially outward from the base circle portion 32a. And a cam crest portion 32b connected to each other. Similarly, the exhaust cam 33 has an arc-shaped base circle 33a centered on the axis of the camshaft 31, and a cam peak connected to the base circle 33a so as to protrude radially outward from the base circle 33a. It has a portion 33b.

  As shown in FIG. 2, a chain chamber 23 is formed through the cylinder head 4, the cylinder block 3, and the crankcase 2 so as to penetrate in the front-rear direction, located further to the left of the left bearing portion 22 of the cylinder head 4. ing.

  A driven chain sprocket 37 is fitted in the chain chamber 23 to the left end 31a of the camshaft 31 protruding leftward from the left bearing 35, and a drive chain sprocket 24 is fitted to the crankshaft 9. . A timing chain 25 is bridged between the drive sprocket 24 and the driven chain sprocket 37, and the power of the crankshaft 9 is transmitted to the camshaft 31 through the timing chain 25 at a half rotational speed of the crankshaft 9. The camshaft 31 is rotated in accordance with the rotation timing of the crankshaft 9.

  As shown in FIG. 3, a pair of rocker arm shafts 40, 40 are installed on the camshaft holders 34, 34 in parallel with the camshaft 31, and the intake side rocker arm 41 and the exhaust side are provided on the rocker arm shafts 40, 40. Rocker arms 42 are pivotally supported adjacent to each other.

  In the intake side rocker arm 41, a roller support portion 41a which is divided into two branches extending inwardly supports a roller 43 as a cam follower in contact with the intake cam 32, and an end portion 41b extending outward. Is in contact with the upper end portion 17c of the stem portion 17b of the intake valve 17.

  The exhaust-side rocker arm 42 has a roller support portion 42a extending inwardly and divided into a bifurcated portion, and a roller 44 as a cam follower in contact with the exhaust cam 33 is rotatably supported. An outer end portion extending outward 42 b is in contact with the upper end portion 18 c of the stem portion 18 b of the exhaust valve 18.

  Further, as shown in FIGS. 3 and 4, of the two roller support portions 42 a of the exhaust rocker arm 42, one of the roller support portions 42 a has a decompression cam 51 when the decompression cam 51 is in a decompressed state. A decompression cam contact portion 42c that is in contact with the cam surface is formed to extend outward from the outer periphery of the roller 44 in the exhaust cam direction. In the present embodiment, the amount of protrusion that the decompression cam contact portion 42c protrudes from the outer peripheral surface of the roller 44 is 0.35 mm.

  Since the intake valve 17 and the exhaust valve 18 are always urged in the closing direction by the valve spring 21, the roller 44 is always urged in the direction in contact with the intake cam 32 and the exhaust cam 33, and the intake cam 32 of the camshaft 31 is urged. As the exhaust cam 33 rotates, the intake-side rocker arm 41 and the exhaust-side rocker arm 42 are swung following the outer peripheral shape of the intake cam 32 and the outer peripheral shape of the exhaust cam 33, and the intake valve 17 and the exhaust valve 18 are predetermined. The door is opened and closed at the opening / closing timing and lift amount.

  Air sucked through an intake device having an intake pipe 26 attached to the side of the cylinder head 4 where the inlet of the intake port 15 opens is mixed and mixed with fuel supplied from a fuel supply device such as a carburetor. In the intake stroke, it is sucked into the combustion chamber 12 through the intake valve 17 opened through the intake port 15 and compressed in the state of the air-fuel mixture in the compression stroke in which the piston 8 moves up.

  The air-fuel mixture is ignited and burned by the spark plug 19 at the end of the compression stroke, and the piston 8 driven by the pressure of the combustion gas rotates the crankshaft 9 in the expansion stroke in which the piston 8 descends.

  The combustion gas passes through the exhaust valve 18 opened in the exhaust stroke in which the piston 8 ascends, passes through the exhaust port 16 from the combustion chamber 12 as exhaust gas, and then the side of the cylinder head 4 where the outlet of the exhaust port 16 opens. Is discharged to the outside of the internal combustion engine E through an exhaust pipe (not shown) attached to the engine.

  The internal combustion engine E includes a decompression device 50 that reduces the starting operation force by releasing the compression pressure in the combustion chamber 12 during the compression stroke at the time of starting. As shown in FIG. 4, the decompression device 50 is provided between the exhaust cam 33 and the bearing 36 of the valve mechanism 30 in the cylinder head 4.

  The decompression device 50 includes a decompression cam 51 that puts the exhaust valve 18 in a decompressed state, a decompression weight 65 that rotates the decompression cam 51 from the decompressed state to the decompressed release state by centrifugal force according to the rotational speed of the camshaft, and a decompression weight 65 Is provided with a torsion coil spring 67 that urges the cam shaft 31 toward the camshaft 31 in the closing direction.

  As shown in FIG. 6, the decompression cam 51 includes a large-diameter columnar columnar body 52 and a small-diameter support shaft 53 that is coaxial with the rotation center axis C of the columnar body 52. Further, as shown in FIG. 8, the support shaft 53 is rotatably supported on the right side surface of the base circle portion of the exhaust cam 33. Further, a concave portion 61 that is missing in a U-shape for inserting an operating pin 68 provided on a decompression weight 65 described later is formed on the right side portion of the cylindrical main body 52 of the decompression cam 51.

  FIG. 7 is a view showing the vertical cross-sectional shape of the cylindrical main body 52 taken in the direction of arrows VII-VII in FIG. The cross-sectional shape of the cylindrical main body 52 is such that the projecting portion 54 formed in an arc shape centering on the rotation center axis C of the decompression cam 51 and the arc-shaped projecting portion 54 are cut out so as to be immersed in the projecting portion 54. A notch-like retracting portion 55 and a notch portion 56 that is notched to a depth shallower than the retracting portion 55 are connected to the front portion of the retracting portion 55 in the forward rotation direction of the camshaft 31. .

  The width of the notch 56 in the direction along the rotational direction of the decompression cam 51 is formed narrower than the width of the protrusion 54 and further narrower than the width of the retracting portion 55. A bending point where the projecting portion 54 of the decompression cam 51 and the cutout portion 56 are connected is referred to as a first bending portion 57, and a bending point where the cutout portion 56 and the retracting portion 55 are connected is referred to as a second bent portion 58. In FIG. 7, what is indicated by a broken line is an imaginary line obtained by extending the outline of the projecting portion 54 of the decompression cam 51, and the second bent portion 58 is located radially inward from the broken line.

As shown in FIG. 7, the decompression cam 51 has an angle θ ₁ formed by a straight line L ₁ passing through the rotation center axis C of the decompression cam 51 and the first bent portion 57 and a bottom surface portion 59 of the notch portion 56. Is formed to be larger than an angle θ ₂ formed by a straight line L ₂ passing through the central axis C of the decompression cam 51 and the second bent portion 58 and the bottom surface portion 60 of the retracting portion.

Further, the length R of the straight line L ₁ connecting the rotation center axis C of the decompression cam 51 and the first bent portion 57 is equal to the straight line L ₂ connecting the central axis C of the decompression cam 51 and the second bent portion 58. It is longer than the length r. Further, the distance h from the rotation center axis C of the decompression cam 51 to the bottom surface portion 60 of the notch 56 is longer than the distance H from the rotation center axis C of the decompression cam 51 to the bottom surface portion 59 of the retracting portion 55. It has become.

  As shown in FIG. 8, the decompression cam 51 is positioned on the right side surface of the base circular portion 33 a of the exhaust cam 33 by the support shaft 53 on the opposite side of the top portion of the cam crest 33 b with the rotation shaft of the exhaust cam 33 interposed therebetween. And is rotatably supported. Further, as shown in FIG. 9, the decompression cam 51 is configured such that when the decompression cam 51 is rotated and the projecting portion 54 faces the roller 44 of the rocker arm 42, the cam surface of the projecting portion 51 of the decompression cam 51 becomes the exhaust cam 33. The base cam 33 is supported by the exhaust cam 33 so as to protrude from the cam surface of the base circle 33a, and the amount of protrusion is set to 0.145 mm, for example.

  10, when the second bent portion 58 faces the roller 44 of the rocker arm 42, the second bent portion 51 of the decompression cam 51 protrudes from the cam surface of the base circular portion 33a of the exhaust cam 33, and The notch 56 is formed so that the protruding amount of the second bent portion 58 is smaller than the protruding amount of the first bent portion 57, that is, the protruding amount of the protruding portion 54. The protruding amount of the second bent portion 58 is, for example, It is set to 0.007 mm.

  Further, as shown in FIG. 11, when the retracting portion 55 faces the roller 44 of the rocker arm 42, the retracting portion 55 is immersed inward in the radial direction from the cam surface of the base circular portion 33 a of the exhaust cam 33. It has become.

  As shown in FIGS. 3 and 4, the decompression way 65 for rotating the decompression cam 51 and the right end surface of the exhaust cam 33 on the projecting portion 54 side are press-fitted into the base end portion 66 a and become parallel to the camshaft 31. Thus, it is rotatably supported via a decompression pin 66 protruding rightward.

  As shown in FIG. 8, the decompression weight 65 extends from the base end portion 65a supported by the decompression pin 66 so as to be swingable so that the thick arm 65b surrounds the decompression shaft 31, and the thin arm 65c further comprises the decompression shaft. 31, the distal end portion 65 d of the thin-walled arm 65 c is formed so as to extend past the decompression cam 51.

  An operating pin 68 protrudes from the side surface of the distal end portion 65d of the thin arm 65c toward the decompression cam. The operating pin 68 is fitted into a U-shaped recess 61 formed in the cylindrical main body 52 of the decompression cam 51.

  As shown in FIGS. 8 to 10, the distal end portion 65d of the decompression weight 65 moves as the decompression weight 66 swings around the decompression pin 66, and the operating pin 68 protruding from the distal end portion 65d is moved. Due to the movement, the decompression cam 51 is rotated around the support shaft 53 fitted into the side surface of the exhaust cam 33. Therefore, the protruding portion 54, the retracting portion 55, and the notch portion 56 of the cylindrical body portion 52 of the decompression cam 51 are in a predetermined positional relationship with the outer peripheral surface of the exhaust cam 33 depending on the swing amount of the decompression weight 65.

  As shown in FIG. 8, the torsion coil spring 67 is wound around the decompression pin 66 by being shifted rightward as shown in FIG. 4, and one end 67a of the torsion coil spring 67 is a cam. After being wound around the shaft 31, it is fixed to the side surface of the exhaust cam 33, and the other end portion 67b is locked in a hole 65d formed in the base end portion 65a of the decompression weight 65. The decompression weight 65 is always urged by a torsion coil spring 67 in a direction in which the inner peripheral surfaces of the thick arm 65 b and the thin arm 65 c of the decompression weight 65 are in contact with the camshaft 31.

  When the internal combustion engine E starts and the rotational speed of the camshaft 51 rotating in the forward rotation direction is equal to or lower than the predetermined rotational speed, the decompression device 50 is in a decompressed state as shown in FIG. The centrifugal force generated in the decompression weight 65 is smaller than the urging force of the torsion coil spring 67, the swing amount of the decompression weight 65 is small, and the protrusion 54 of the decompression cam 51 protrudes from the outer peripheral surface of the base circle 33a of the exhaust cam 33. Is in a state. If the protrusion 54 of the decompression cam 51 faces the rocker arm 42 decompression cam contact part 42c during the rotation of the exhaust cam 33, the decompression cam contact part 42c of the exhaust rocker arm 42 is pushed up by the protrusion 54 of the decompression cam 51, The upper end 18c of the exhaust valve 18 is pressed by the outer end 41b of the side rocker arm 41, and even if the internal combustion engine E is in the compression stroke, the exhaust valve 18 is opened and the decompressed state is reached to reduce the pressure. In this embodiment, the rotation of the decompression cam 51 in the decompression release state is defined as normal rotation, and the return to the decompression state is defined as reverse rotation.

  When the rotational speed of the internal combustion engine E increases to a predetermined rotational speed or higher, the centrifugal force generated in the decompression weight 65 becomes larger than the urging force of the coil spring 67, and the decompression weight 65 resists the ineffective force of the coil spring 67. 9 and 10, as the decompression weight 65 swings, the protruding portion 54, the first bent portion 57, the notched portion 56, and the second bent portion 58 are moved. The decompression cam 51 is rotated so as to face the decompression cam contact portion 42c in this order.

  Further, when the rotation speed of the internal combustion engine E increases and the decompression weight 65 swings further outward and the decompression cam 51 is rotated as shown in FIG. 11, the decompression cam contact portion 42c of the exhaust side rocker arm 42 is brought into contact with the decompression cam contact portion 42c. Since the notch portion 56 of the decompression cam 51 faces the facing portion, the retracting portion 55 is immersed radially inward from the cam surface of the base circular portion 33a of the exhaust cam 33, and the decompression cam stopper of the exhaust side rocker arm 42 is placed. The contact portion 42 c does not come into contact with the decompression cam 51, and the roller 44 of the exhaust side rocker arm 42 comes into contact with the outer peripheral surface of the exhaust cam 33, so that the exhaust side rocker arm 42 follows the shape of the outer peripheral surface of the exhaust cam 33. Thus, the decompression device 50 enters the decompression release state.

  When the internal combustion engine E is stopped and the rotation of the camshaft 31 is reduced, the centrifugal force generated in the decompression weight 65 is reduced, and the decompression weight 65 is swung back by the biasing force of the torsion coil spring 67. Then, the decompression device 50 returns to the decompressed state.

  By the way, when the internal combustion engine E stops, the piston 8 may not get over the compression top dead center, and the reverse rotation of the crankshaft 9 may occur. When the crankshaft 9 rotates in the reverse direction, the timing chain 25 also rotates in the reverse direction, and the camshaft 31 rotates in reverse. At this time, the rotational speed of the camshaft 31 is low, and the decompression device 50 is in the decompressed state. Therefore, the decompression cam contact portion 42c of the exhaust side rocker arm 42 is in pressure contact with the protruding portion 54 of the decompression cam 51, and the reverse rotation of the camshaft 31 At the same time, the decompression cam 51 may be dragged and rotated by the decompression cam abutting portion 42c, and the decompression weight 65 may be actuated outwardly in the direction in which decompression is released, that is, forward rotation.

  Here, in this embodiment, FIG. 14 shows changes in the rocker arm lift amount over time when the camshaft 31 rotates in the reverse direction and the decompression cam 51 is dragged by the decompression cam contact portion 42c. The rocker arm lift amount refers to the lift amount that the roller 44 of the rocker arm 42 is lifted from the outer peripheral surface of the base circle portion 33a of the exhaust cam 33, and the end portion 42b of the rocker arm 44 that is swung according to the rocker arm lift amount is the exhaust valve. 18 is pressed to determine the lift amount of the exhaust valve.

  First, since the camshaft 31 is at a rotation speed equal to or lower than a predetermined rotation at the early stage of reverse rotation of the camshaft 31, the decompression cam 51 is in a decompressed state, and the protruding portion 54 of the decompression cam 51 has a base circle portion 33a of the exhaust cam 33. It is in a state of projecting by 0.145 mm.

  Depending on at which phase of the exhaust cam the reverse rotation of the camshaft 31 is started, when the decompression cam 51 is at a position away from the decompression cam abutting portion 42c of the rocker arm 42 as shown in FIG. Even if is in a decompressed state, the protruding portion 54 does not contact the decompression cam contact portion 42c of the rocker arm 42, and the roller 44 of the rocker arm 42 is in contact with the base circle portion 33a of the exhaust cam 33. The amount is 0 mm and is indicated by point A in FIG.

  When the reverse rotation of the camshaft 31 proceeds, the decompression cam 51 supported on the side surface of the exhaust cam 33 gradually approaches the rocker arm 42, and the roller 44 of the rocker arm 42 moves to the base circle of the exhaust cam 33 as shown in FIG. The protruding portion 54 of the decompression cam 51 contacts the decompression cam contact portion 42c of the rocker arm 42 while being in contact with 33a. The rocker arm lift amount at this time is still 0 mm, and is indicated by a point B in FIG.

  Further, when the camshaft 31 is reversed, the exhaust cam 33 is reversed while the protruding portion 54 of the decompression cam 51 is in contact with the decompression cam contact portion 42c of the rocker arm 42, and accordingly, the rocker arm lift amount increases. Since the decompression cam 51 is in the decompressed state, in this embodiment, the projecting portion 54 projects 0.145 mm from the base circle portion 33a of the exhaust cam, and the decompression cam contact portion 42c of the rocker arm 42 projects 0.35 mm from the roller 44. Therefore, the rocker arm lift amount is 0.495 mm including both, and is indicated by a point C in FIG.

  When the reverse rotation of the camshaft 31 proceeds, the decompression cam is dragged and rotated by the pressure contact of the cam contact portion 42c, and the decompression cam contact portion 42c eventually contacts the first bent portion 57 as shown in FIG. Since the protruding amount of the first bent portion 57 from the base circle portion 33a is the same as the protruding amount of the protruding portion 54, the rocker arm lift amount at that time is the same as that when the protruding portion 54 is in contact with the cam contact portion 42c. It is 0.495 mm which is the same as the rocker arm lift amount, and is indicated by a point D in FIG.

  When the decompression cam contact portion 42c gets over the first bent portion protrusion, the decompression cam contact portion 42c comes into contact with the shallow notch portion 56, and the rocker arm lift amount gradually decreases. As shown in FIG. It comes into contact with 58. Since the protrusion amount of the second bent portion 58 of the present embodiment from the base circle portion 33a is 0.007 mm, the rocker arm lift amount at this time is 0.357 mm, which is indicated by a point E in FIG.

  When the camshaft further reverses, when the cam contact portion 42c gets over the second bent portion 58, the decompression cam 51 is further rotated in the reverse rotation direction by the decompression cam contact portion 42c, and as shown in FIG. Since the retracting portion 55 faces the decompression cam contact portion 42c, and the retracting portion 55 is immersed in the base circle portion 33a of the exhaust cam 33, the cam contact portion 42c is not in contact with the decompression cam 51. The roller 44 of the exhaust side rocker arm 41 is brought into contact with the base circle portion 33a of the exhaust cam, and the decompression device 50 is brought into the decompression release state, and the rocker arm lift amount becomes 0 mm, which is indicated by a point F in FIG.

  FIG. 15 shows a cross-sectional shape of a decompression cam 71 of a conventional decompression device 70 in which a notch is not provided in the decompression cam. The conventional decompression cam 71 is provided with a projecting portion 72 and a retracting portion 73, and a notch is not formed on the front side of the retracting portion 73 in the forward rotation direction of the camshaft 31, and the exhaust side rocker arm 41 is not formed. The decompression cam contact portion 42c does not pass through the second bent portion from the bent portion 74 where the projecting portion 72 and the retracting portion 73 are continuous, so that the roller 44 of the exhaust side rocker arm 41 can be connected to the base circle portion 33a of the exhaust cam 33. Since it contacts the surface, the lift amount of the rocker arm changes as shown by the broken line in FIG. That is, after passing from point A to point D, the point G is reached where the bent portion 74 is located while maintaining the rocker arm lift amount, and then the decompression cam 71 is further rotated in the reverse direction by the decompression cam contact portion 42c. Since the retracting portion 73 faces the decompression cam contact portion 42c and the retracting portion 73 is immersed in the base circle portion 33a of the exhaust cam 33, the cam contact portion 42c is not in contact with the decompression cam 71. Then, the roller 44 of the exhaust side rocker arm 41 is brought into contact with the base circle portion 33a of the exhaust cam and the decompression is released, and the rocker arm lift amount becomes 0 mm, and the state shown by the point F in FIG. In the conventional decompression device 70, the rocker arm lift amount changes from 0.495 mm to the lift amount of 0 mm immediately, so that the contact sound to the roller base circle and the contact sound when the exhaust valve is seated on the valve seat are likely to increase. .

  In the present embodiment, unlike the conventional decompression cam 70, the cam contact portion 42c that has passed over the first bent portion 57 does not immediately contact the decompression cam, but does not immediately contact the second bent portion 58. Therefore, the rocker arm lift amount is changed from 0.495 mm at the first bent portion 57 to 0.3 mm at the second bent portion 58 to 0 mm at the retracting portion 55, and from the lift state of the exhaust rocker arm 42 by the decompression cam 51. The roller 44 is prevented from reaching the base circle portion 33a immediately, and the contact sound when the roller 44 contacts the base circle portion 33a is reduced.

  Further, in this embodiment, as shown in FIG. 7, the angle θ1 formed by the straight line L1 passing through the central axis C of the decompression cam 51 and the first bent portion and the bottom surface portion 60 of the notch 56 is the decompression cam. Since the angle θ2 formed by the central axis C of 51, the straight line L2 passing through the second bent portion 58, and the bottom surface portion 59 of the retracting portion 55 is larger, the decompression cam contact portion 42c is moved over the first bent portion 57. The force for operating the decompression weight 65 in the opening direction can be reduced. Therefore, as shown in FIG. 14, the slope A connecting the point D and the point E becomes a gentler slope than the slope B connecting the point E and the point F, and the decompression weight swings rapidly in the opening direction. Thus, the operation sound of the decompression weight 65 can be reduced.

  Further, the ratio of the distance from the rocker arm swinging central axis to the decompression cam contact portion 42a and the distance from the rocker arm pivoting central axis to the upper end 18c of the exhaust valve 18 is about 1.37 times in this embodiment. Therefore, the exhaust valve lift amount is 1.37 times the rocker arm lift amount, and is 0. 0 when the decompression cam contact portion 42c is in contact with the protruding portion 54 and in the contact state with the first bent portion 57. 678 mm and 0.489 mm when in contact with the second bent portion 58. In the decompression device of the present embodiment, as shown in FIG. 13, the exhaust valve 18 in the opened state with the lift amount of the exhaust valve being 0.678 mm is not immediately seated on the exhaust side valve seat, but is 0.489 mm. Since the seating is performed after passing through the valve open state, the contact sound at the time of sitting is reduced.

  As described above, in the decompression device 50 according to the present embodiment, the decompression cam 51 has a depth shallower than the withdrawal portion 55 on the front side of the withdrawal portion 55 in the forward rotation direction of the camshaft 31, that is, in the forward rotation direction of the decompression cam 51. Since the notch portion 56 is continuously provided, even if the decompression cam contact portion 42c of the exhaust side rocker arm 41 gets over the second bent portion 58, the decompression cam contact portion 42c has a depth shallower than that of the retracting portion 55. After passing through the notch 56, it moves to the retracting part 55. Therefore, the amount of movement of the roller 44, which is the cam follower of the exhaust side rocker arm 42, to the base circle 33a side of the exhaust cam 33 can be regulated by the notch 56 cut out at a shallow depth, and the decompression cam 51 From the lifted state of the exhaust side rocker arm 42, the roller 44 can be prevented from reaching the base circle portion 33a immediately, and the contact sound when the roller 44 contacts the base circle portion 33a can be reduced.

  Further, the second bent portion 58 of the decompression cam 51 is configured to protrude from the base circle portion 33 a of the exhaust cam 33, and the amount of protrusion of the second bent portion 58 from the base circle portion 33 a is the amount of the protrusion 54 of the decompression cam 51. When the contact point between the decompression cam contact portion 42c of the exhaust side rocker arm 42 and the decompression cam 51 is intended from the first bent portion 57 of the decompression cam 51 to the second bent portion because it is smaller than the protruding amount from the base circle portion 33a. In addition, since a slight lift amount of the exhaust valve 18 can be ensured at the time of passing through the second bent portion, the contact sound of the exhaust valve 18 contacting the valve seat surface 16c of the exhaust valve seat 16b, the roller 44 Can be prevented from coming into contact with the base circle 33a.

  Further, since the width of the notch 56 in the direction along the rotation direction of the camshaft 31 is narrower than the width of the protrusion 54 in the direction along the rotation direction of the camshaft 31, the decompression cam contact portion 42c becomes the protrusion 54. The contact width can be ensured, and the area where the decompression device 50 is in the decompressed state can be sufficiently secured.

  Further, since the width of the cutout portion 56 in the direction along the rotation direction of the camshaft 31 is narrower than the width of the retraction portion 55 in the direction along the rotation direction of the camshaft 31, the decompression release state by the retraction portion 55 of the decompression cam 51 This area can be secured sufficiently.

  Furthermore, in the decompression device 50 of the present embodiment, the decompression weight 65 is rotatably supported on the camshaft 31 via a decompression pin 66 having an axis parallel to the camshaft 31, and the camshaft 31 has a centrifugal force. Since the decompression weight 65 that opens and operates in the same direction as the forward rotation direction of the camshaft 31 as in this embodiment, the decompression cam abuts when the camshaft 31 rotates in the reverse direction. When the portion 42c reaches the retracting portion 55 from the projecting portion 54 of the decompression cam 51, the force to drive the decompression weight 65 in the opening direction increases, so that the contact sound when the roller 44 contacts the base circle portion 33a The operating sound of decompression weight 65 tends to be loud. Therefore, when applied to the decompression device 50 having the decompression weight 65 as in the present embodiment, the contact sound when the roller 44 contacts the base circle portion 33a and the operation sound of the decompression weight 65 are reduced. More effective.

Further, in the conventional decompression device, as shown in FIG. 15, when the decompression cam contact portion 42 a of the cam follower 42 moves directly from the projection 72 of the decompression cam 71 to the retracting portion 73 when the camshaft 31 is reversely rotated, a straight line passing through the rotational center axis line C of the bent portion 74 and the decompression cam 71 continuous 72 and the retracted portion 73, the angle theta ₃ is less made in the bottom surface portion 75 of the retracting unit 73, the decompression cam abutment portion 42a of the rocker arm 42 is When overcoming the bent portion 74, the force to actuate the decompression weight 65 in the opening direction increases, so that when the decompression cam contact portion 42a gets over the bent portion 74, the decompression weight 65 operates in the direction to forcefully open. It was easy to be done and the operation sound was loud. However, in the decompression device 50 of the present embodiment, the angle θ ₁ formed by the straight line L ₁ passing through the central axis C of the decompression cam 51 and the first bent portion 57 and the bottom surface portion 60 of the notch 56 is the conventional decompression cam. Since θ ₂ is larger than an angle θ ₂ formed by a straight line L ₂ passing through the central axis C of 51 and the second bent portion 58 and a bottom surface portion 59 of the retracting portion 55, θ ₂ is a bent portion 74 of the conventional decompression device. and a straight line passing through the rotational center axis C of the decompression cam 71, from substantially equal to the angle by theta ₃ made in the bottom surface portion 74 of the retracting unit 73, theta since ₁ is greater than the theta ₃ of a conventional decompression cam 71, the In the decompression device of the embodiment, it is possible to reduce the force to actuate the decompression weight in the direction of opening the decompression weight when the cam follower gets over the first bent portion, and it is possible to reduce the operation sound of the decompression weight.

E: Internal combustion engine, P: Power unit, C: Center axis, L ₁ ... Straight line, L ₂ ... Straight line, θ ₁ ... Angle, θ ₂ ... Angle 1 ... Motorcycle, 4 ... Cylinder head, 18 ... Exhaust valve, 31 ... Camshaft, 33 ... Exhaust cam, 33a ... Base circle, 33b ... Cam crest, 41 ... Cam follower, 42 ... Exhaust side rocker arm, 42c ... Decompression cam contact, 50 ... Decompression device, 51 ... Decompression cam, 54 ... Projection , 55 ... retracting part, 56 ... notch part, 57 ... first bent part, 58 ... second bent part, 59 ... first bottom part, 60 ... second bottom part, 60 ... recessed part, 65 ... decompression weight, 66 ... decompression pin.

Claims (6)

A camshaft (31) rotatably supported on the cylinder head (4);
An arc-shaped base circle portion (33a) centering on the axis of the camshaft (31), and the base circle portion (33a) connected to the base circle portion (33a) so as to protrude radially outward from the base circle portion (33a). An exhaust cam (33) that opens and closes the exhaust valve (18) through the rocker arm (42) at the cam peak (33b),
A decompression weight (65) that is rotatably supported on the side surface of the exhaust cam (33) and that operates by centrifugal force,
Connected to the decompression weight (65) and rotated in the same direction as the normal rotation direction of the camshaft (31), the protrusion (54) protruding from the base circle (33a) and the base circle ( 33a) is provided with a notch-shaped retracting part (55), and the protrusion (54) contacts the cam follower (42c) of the rocker arm (42) to open the exhaust valve (18). In the decompression device (50) of the internal combustion engine (E) provided with the decompression cam (51) to be
The decompression cam (51) has a notch portion cut out at a depth shallower than the retracting portion (55) on the front side of the retracting portion (55) in the forward rotation direction of the camshaft (31). (56) A decompression device for an internal combustion engine, characterized by being provided in series.   The bending point where the cutout part (56) and the protruding part (54) are connected is the first bending part (57), and the bending point where the cutout part (56) and the retracting part (55) are connected is the first bending part. When the second bent portion (58) is used, the second bent portion (58) is configured to protrude from the base circular portion (33a), and the base circular portion (33a) of the second bent portion (58) is formed. 2. The decompression device for an internal combustion engine according to claim 1, wherein a projecting amount from the base circle portion (33 a) of the projecting portion (54) in the decompression cam (51) is smaller. .   The width of the notch (56) in the direction along the rotation direction of the decompression cam (51) is smaller than the width of the protrusion (54) in the direction along the rotation direction of the decompression cam (51). The decompression device for an internal combustion engine according to claim 1 or 2, wherein the decompression device is used.   The width of the notch (56) in the direction along the rotation direction of the decompression cam (51) is smaller than the width of the retracting portion (55) in the direction along the rotation direction of the decompression cam (51). 4. A decompression device for an internal combustion engine according to claim 3, wherein   The decompression weight (65) is rotatably supported on the side surface of the exhaust cam (33) via a decompression pin (66) having an axis parallel to the camshaft (31), and the camshaft ( The decompression device for an internal combustion engine according to any one of claims 1 to 4, wherein the decompression operation is performed in the same direction as the forward rotation direction of (31). The bending point where the cutout part (56) and the protruding part (54) are connected is the first bending part (57), and the bending point where the cutout part (56) and the retracting part (55) are connected is the first bending part. When 2 bent parts (58)
An angle (θ ₁ ) formed by a straight line (L ₁ ) passing through the central axis (C) of the decompression cam (51) and the first bent part (57) and the bottom part (60) of the notch part (56). )But,
An angle (θ ₂ ) formed by a straight line (L ₂ ) passing through the central axis (C) of the decompression cam (51) and the second bent portion (58) and a bottom surface portion (59) of the retracting portion (55). The decompression device for an internal combustion engine according to claim 5, wherein the decompression device is larger than.

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