EP1447530B1

EP1447530B1 - Decompressor for 4-stroke cycle internal combustion engines

Info

Publication number: EP1447530B1
Application number: EP02700715A
Authority: EP
Inventors: Atsushi Ogasawara; Seiji Onozawa; Kuniaki Ikui
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2001-03-26
Filing date: 2002-02-22
Publication date: 2008-12-24
Anticipated expiration: 2022-02-22
Also published as: KR20030041864A; IL152766A0; JP2002285812A; AR033203A1; KR100813746B1; MY135269A; JP4338333B2; BR0204676B1; CN1263943C; EP1447530A1; DE60230541D1; BR0204676A; TR200202556T1; TW515863B; ES2317988T3; WO2002077422A1; CN1460146A; EP1447530A4

Description

TECHNICAL FIELD

The present invention relates to a decompression device for promoting start of a 4 stroke cycle internal combustion engine using a starter motor.

BACKGROUND ART

A mechanical decompression device has been known (see Japanese Laid-Open Patent Publication No. Hei 11-107727 , Japanese Laid-Open Patent Publication No. 2000-199412 and Japanese Patent Publication No. 2890218 ). When an engine is started by a starter motor, the mechanical decompression device is operated to open an intake valve or an exhaust valve in case that rotational speed of a camshaft is lower than a predetermined value, and set to a non-operative state by centrifugal force of a weight in the decompression device in case that rotational speed of the camshaft exceeds the predetermined value.
An electrical decompression device has been also known (see Japanese Laid-Open Patent Publication No. Hei 11-324744 ). In case of engine start by a starter motor, the electrical decompression device is operated by excitation of an electromagnetic solenoid to promote rotation of a crankshaft of the engine, and after the crankshaft has reached a rotational speed at which the engine can start rotation by itself not relying on the starter motor, excitation of the electromagnetic solenoid is cancelled to cancel operation of the decompression device.
In the above-mentioned mechanical decompression device, since the decompression device is changed for operation and non-operation utilizing centrifugal force, a weight for producing centrifugal force is indispensable. Therefore, inertia of a valve moving cam system becomes large, a starter motor of large output becomes necessary and miniaturization of the starter motor was difficult.
In the above-mentioned electrical decompression device, since it is required to excite the electromagnetic solenoid only when operation of the decompression device is necessary, the decompression device can be miniaturized. However, an electronic judgment device for discriminating operation and non-operation of the decompression device is necessary, and it is difficult to apply this decompression device to a small-type 4 stroke cycle internal combustion engine having no electronic control apparatus. Further, even in case of an internal combustion engine having an electronic control apparatus, the electronic control apparatus becomes complicated.

DISCLOSURE OF INVENTION

The present invention relates to an improvement of a decompression device of a 4 stroke cycle internal combustion engine for overcoming the above-mentioned difficulties. The present invention provides a decompression device of a 4 stroke cycle internal combustion engine having intake and exhaust valves opened and closed by respective intake and exhaust cams made integral with a camshaft and a starter motor for starting the engine, comprising: a decompression cam fitted on the camshaft so as to rotate freely; a one-way clutch fitted on the camshaft which is adjacent to the decompression cam and capable of transmitting reverse rotation torque to the decompression cam only when the camshaft rotates in reverse; a torque limiter inserted between the decompression cam and the one-way clutch for canceling transmission of the reverse rotation torque larger than a predetermined torque; a first decompression cam stopper provided on a fixed portion engaging with an engaging section formed on the decompression cam for stopping rotation of the decompression cam in normal rotational direction; and a second decompression cam stopper provided on a fixed portion engaging with the engaging section for stopping rotation of the decompression cam in reverse rotational direction, a lift of a cam section of the decompression cam being higher than a base circle of the exhaust cam and lower than a maximum lift of a cam section of the exhaust cam, the exhaust valve being not opened by the decompression cam when the first decompression cam stopper engages with the engaging section.
According to the present invention, when the starter motor is rotated in reverse, reverse rotation torque is transmitted to the decompression cam from the camshaft rotating in reverse through the one-way clutch and the torque limiter to rotate the decompression cam in reverse, and the engaging section of the decompression cam engages with one of the decompression cam stoppers of the fixed portion to be stopped. In this stopped state, even if the camshaft rotates in reverse, a large reverse rotation force of the starter motor does not act on the camshaft, the decompression cam, the engaging section and the decompression cam stopper because the torque limiter exists.
If the starter motor is rotated normally from the above state that reverse rotation is stopped, the exhaust valve or the intake valve is opened by the decompression cam having a lift larger than the base circle of the exhaust cam or the intake cam, so that occurrence of a large normal rotation resistance torque to the crankshaft in compression stroke is avoided and the crankshaft can rotate with a large rotational acceleration.
Then, when the exhaust valve or the intake valve is opened largely by the cam nose of the exhaust cam or the intake cam, rotational resistance to the decompression cam which was acting to open the exhaust valve or the intake valve disappears and decompression cam rotates slightly together with the camshaft. Next, when action of the exhaust cam or the intake cam to open the exhaust valve or the intake valve is dissolved, the decompression cam is stopped. The decompression cam rotates in normal direction again when the exhaust valve or the intake valve is next opened by the cam nose. After this procedure has been repeated several times, the engaging section of the decompression cam engages with another decompression cam stopper of the engine main body and the decompression cam is stopped at a non-operative position. In this state, action of the decompression cam to open the exhaust valve or the intake valve is cancelled automatically and the engine can shift to the ordinary operation.
According to the present invention, since centrifugal force is not utilized, inertia of the valve moving system becomes small and miniaturization of the starter motor becomes possible. Since change from starting operation state to ordinary operation state is carried out mechanically not using electronic control, complication of control system of the internal combustion engine can be avoided and cost-down becomes possible.
The torque limiter may be formed so that torque transmitted through the torque limiter is smaller when the camshaft rotates in normal direction and larger when the camshaft rotates in reverse direction. When the camshaft is rotated in reverse to have the engaging section of the decompression cam engaged with one of the stopper of the fixed portion, the decompression cam can be rotated in reverse surely overcoming reverse rotation resistance given to the decompression cam by the exhaust valve and decompression preparation state can be set easily.
The torque limiter may comprise a touching member disposed on one of adjacent side surfaces of the one-way clutch and the decompression cam, a depression formed on another of the adjacent side surfaces and a spring for forcing the touching member against the depression, and the depression may be shaped so that transmitted torque is smaller when the camshaft rotates in normal direction and larger when the camshaft rotates in reverse direction. Or, the torque limiter may comprise a touching member disposed on one of adjacent circumferential surfaces of the one-way clutch and the decompression cam, a depression formed on another of the adjacent circumferential surfaces and a spring for forcing the touching member against the depression, and the depression may be shaped so that transmitted torque is smaller when the camshaft rotates in normal direction and larger when the camshaft rotates in reverse direction. By such constitutions, the torque limiter can be formed compact and simple, and miniaturization and lightening of the decompression device can be attempted.

BRIEF DESCRIPTION OF DRAWINGS

Fig 1 is a longitudinal sectional view of a 4 stroke cycle internal combustion engine having a decompression device according to an embodiment of the present invention.
Fig. 2 is a cross sectional view of the internal combustion engine.
Fig 3 is an enlarged cross sectional view of an essential part of the internal combustion engine.
Fig. 4 is a sectional view taken along the line IV-IV of Fig. 3.
Fig. 5 is a sectional view taken along the line V-V of Fig. 3.
Fig. 6(a) and Fig. 6(b) are a front view and a sectional view, respectively, of a egg-shaped depression formed on a decompression cam.
Fig. 7 is a view for explaining action of the above embodiment.
Fig. 8 is a view for explaining action of the above embodiment.
Fig. 9 is a view for explaining action of the above embodiment.
Fig. 10 is a view for explaining action of the above embodiment.
Fig. 11 is a view for showing relation among crank angle and valve lifts owing to an exhaust cam, an intake cam and a decompression cam.
Fig. 12 is an enlarged cross sectional view of an essential part of an internal combustion engine according to another embodiment of the present invention.
Fig. 13 is a sectional view taken along the line XIII-XIII of Fig. 12.
Fig. 14 is a sectional view taken along the line XIV-XIV of Fig. 12.
Fig. 15 is a stretched view of a part of an inner surface of a decompression cam.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described with reference to Figs. 1 to 11.
Figs. 1 and 2 show a single-cylinder OHC 4 stroke cycle internal combustion engine 1 for a motorcycle having a decompression device according to the present invention. The main body of the internal combustion engine 1 comprises a cylinder block 2, a cylinder head 3 provided on an upper end of the cylinder block 2 detachably and a crankcase (not shown) provided at a lower portion of the cylinder block 2. A piston 5 is fitted in a cylinder bore 4 of the cylinder block 2 so as to slide up and down. The piston 5 is connected to a crankshaft (not shown) through a connecting rod so that the crankshaft is driven to rotate when the piston reciprocates up and down.
The cylinder head 3 is formed with an intake passage 7 and an exhaust passage 8 communicating with a combustion chamber 8 at an upper position of the cylinder bore 4. An intake valve 9 and an exhaust valve 10 for opening and closing the intake passage 7 and the exhaust passage 8 are arranged in V-shape. The intake valve and the exhaust valve 10 are always forced to close by valve springs 12 inserted between the cylinder head 3 and retainers 11 integrally attached to tops of the intake valve 9 and the exhaust valve 10. On an upper stream side of the intake passage 7 are arranged a throttle valve and a carburetor.
At a central position of a space above the intake valve 9 and the exhaust valve 10, a camshaft 13 is pivotally supported by means of a pair of bearings 14. A driven sprocket 16 is integrally attached to an end of the camshaft 13 by bolts 15, and an endless chain 17 is laid over the driven sprocket 16 and a drive sprocket (not shown) fixed to the crankshaft (not shown). The camshaft 13 is driven so as to rotate with a rotational speed equal to half of that of the crankshaft.
At respective middle positions between the intake valve 9 and the camshaft 13 and between the exhaust valve 10 and the camshaft 13, rocker shafts 18 are supported by the cylinder head 3 in parallel with the camshaft 13. Each of the rocker shafts 18 has an intake rocker arm 19 or an exhaust rocker arm 20 pivoted so as to rock. Each rocker arm 18, 19 has an end with a tappet screw 21 fixed by a lock nut 22 and another bifurcated end. A roller support shaft 23 is fitted to the bifurcated end and an intake roller 25 or an exhaust roller 26 is pivotally supported on the roller support shaft 23 through a needle bearing 24.
The camshaft 13 is formed with an intake cam 27 and an exhaust cam 28 adapted to come into contact with the intake roller 25 and the exhaust roller 26 of the intake rocker arm 19 and the exhaust rocker arm 20, respectively.
As shown in Fig. 2, a one-way clutch 29 is positioned outside of the exhaust cam 28 and fitted on the camshaft 13. A decompression cam 38 is fitted on a small diameter cylindrical portion 30 of the one-way clutch 29 so as to rotate.
Fig. 3 is an enlarged view of the one-way clutch 29, the decompression cam 38 and portions neighboring them shown in Fig. 2. Fig. 4 is a IV-IV section of Fig. 3 and Fig. 5 is V-V section of Fig. 3. As shown in Fig. 4, a large diameter cylindrical portion 31 of the one-way clutch has three cam cuts 32 formed circumferentially at regular intervals. In each of the cam cuts 32 is fitted a cam roller 33 loosely, and a coil spring 34 is inserted between the cam cut 33 and the cam roller 33. When the camshaft 13 rotates in normal direction as shown by the arrow N, the one-way clutch 29 becomes disconnected state, and when the camshaft 13 rotates in reverse direction as shown by the arrow R, the one-way clutch 29 becomes connected state.
Further, the large diameter cylindrical portion 31 of the one-way clutch 29 has blind holes 35 each extending from an inner side surface toward the outer side. Between the adjacent cam cuts 32, each three blind holes 35 are arranged. In each blind hole 35 are put a coil spring 36 and a ball 37 as shown in Fig. 3. On an out side surface of the decompression cam 38 are formed twelve egg-shaped depression 39 at regular intervals circumferentially as shown in Fig. 5. The ball 37 pushed by the coil spring 36 toward the decompression cam 38 faces the egg-shaped depression 39 and fits in the depression 39 (Fig. 3). The blind hole 35, the coil spring 36 and the ball 37 of the one-way clutch 29 and the egg-shaped depression 39 of the decompression cam 38 constitute a torque limiter 40. Fig. 6(a) is a front view of the egg-shaped depression,39 and Fig. 6(b) is a sectional view thereof. The depression 39 comprises a steep slope portion 39a and a gentle slope portion 39b.
As shown in Fig. 5, the decompression cam 38 has an engaging projection 41 projecting in radial direction. As shown in Fig. 1, the cylinder head 3 is formed with a reverse rotation stopper 42 that engages with the engaging projection 41 to stop the decompression cam 38 when the decompression cam 38 rotates in reverse. The intake rocker arm 19 is formed with a normal rotation stopper 43 that engages with the engaging projection 41 to stop the decompression cam 38 when the decompression cam 38 rotates normally.
On an outer circumferential surface of the small diameter cylindrical portion 30 of the one-way clutch 29 are fitted a stopper ring 44 of plastics neighboring an inner side edge of the decompression cam 38. As shown in Fig. 2, an ignition plug 45 is screwed to the cylinder head penetrating it so that an electrode 46 of the ignition plug 45 is projected into the combustion chamber 6.
According to the embodiment constructed as stated above, in case that the single-cylinder OHC 4 stroke cycle internal combustion engine 1 is stopped, if the crankshaft (not shown) is rotated in reverse by means of the starter motor, the camshaft 13 also rotates in reverse counterclockwise.
When the camshaft 13 rotates in reverse counterclockwise in Fig. 4, the one-way clutch 29 also rotates counterclockwise together with the camshaft, and the ball 37 pushed put by spring force of the coil spring 36 fitted in the blind hole 35 of the one-way clutch 29 engages with the steep slope portion 39a of the egg-shaped depression 39 of the decompression cam 38 to produce large transmission torque in reverse rotational direction of the torque limiter 40. Thus, reverse rotation torque is transmitted from the one-way clutch 29 to the decompression cam 38 to rotate the decompression cam 38 in reverse. Even if the decompression cam 38 is given rotational resistance torque by the bifurcated end portion 20a of the exhaust rocker arm 20 touching the cam nose 38a of the decompression cam 38, the decompression cam 38 can rotate in reverse counterclockwise because reverse rotation torque transmitted to the decompression cam 38 from the one-way clutch 29 is large. Since the engaging projection 41 of the decompression cam 38 is stopped by the reverse rotation stopper 42 as shown in Fig. 1, the decompression cam 38 is stopped. In this state, the bifurcated end portion 20a of the exhaust rocker arm 20 touches the cam nose 38a of the decompression cam 38 and the exhaust valve 10 is slightly opened.
If the crankshaft is rotated normally by the starter motor from the state of Fig. 1, the camshaft 13 also rotates normally clockwise and the exhaust cam 28 also rotates in the same direction. However, since the bifurcated end portion 20a of the exhaust rocker arm 20 touches the cam nose 38a of the decompression cam 38 to give the decompression cam 38 rotational resistance torque and the one-way clutch 29 is disconnected from the camshaft 13 so as to shut torque transmission, the decompression cam 38 is held in the stopped state shown in Fig. 1. On the one hand, the exhaust cam and the intake cam rotate together with the camshaft 13.
When the cam nose 28a of the exhaust cam 28 touches the exhaust roller 26, the exhaust roller 26 begins to be pushed up. Then, as shown in Fig. 8, the exhaust roller 26 and the bifurcated end portion 20a of the exhaust rocker arm 20 are pushed up and the exhaust valve 10 is largely opened. At the same time, the rotational resistance torque acting on the decompression cam 38 disappears because the bifurcated end portion 20a of the exhaust rocker arm 20 is separated from the cam nose 38a of the decompression cam 38. And the decompression cam 38 is rotated by a very small accompanied rotation torque produced by friction between the camshaft 13 and the one-way clutch 29. Namely, the decompression cam 38 rotates accompanied by the camshaft 13. The decompression cam 38 rotates accompanied by the camshaft 13 only when the bifurcated end portion 20a of the exhaust rocker arm 20 is separated from the cam nose 38a of the decompression cam 38, namely by an angle corresponding to the cam angle of the exhaust cam 28. After that, the cam nose 28a of the exhaust cam 28 passes through the exhaust roller 26, the exhaust roller 26 and the bifurcated end portion 20a of the exhaust rocker arm 20 are lowered, the bifurcated end portion 20a of the exhaust rocker arm 20 touches the cam section 38a of the decompression cam 38, the decompression cam 38 is stopped by the rotational resistance torque and the crankshaft 13, the exhaust cam 28 and the intake cam 27 continue to rotate normally.
When the camshaft 13 has rotated further by about one revolution, the cam nose 28a of the exhaust cam 28 touches the exhaust roller 26 again to push up it and the bifurcated end portion 20a of the exhaust rocker arm 20 separates from the cam nose 38a of the decompression cam 38. At that time, the decompression cam 38 again rotates accompanied by the camshaft 13 by the cam angle of the exhaust cam 28. when the camshaft 13 has rotated by two or more revolutions, the bifurcated end portion 20a of the exhaust rocker arm 20 separates from the cam nose 38a of the decompression cam 38 to complete the decompression operation. At the same time as the ordinary operation is commenced, the engaging projection 41 of the decompression cam 38 is stopped by the normal rotation stopper 43 and the decompression cam 38 is held in non-operation state. The gentle slope portion 39b of the egg-shaped depression 39 of the decompression cam 38 is formed for mitigating shock when the decompression cam 38 is stopped by the normal rotation stopper 43.
Fig. 11 is a graph showing relation among cam lifts owing to the intake cam, the exhaust cam and the decompression cam and the crank angle. In Fig. 11, IN is the lift of the intake cam, EX is the lift of the exhaust cam and DC is the lift of the decompression cam. The exhaust valve opens influenced by either of lifts of the exhaust cam and the decompression cam which is larger. After the normal rotation is commenced, the exhaust valve is opened along the curve A-B-C-D-E-F-G-H-I-J. With respect to the decompression cam, the lift becomes zero when the above-mentioned accompanied rotation advances to some extent and the cam nose disengages from the bifurcated end portion of the exhaust rocker arm.
As mentioned above, in the embodiment shown in Figs. 1 to 11, the starting system is not provided with a weight having a large moment of inertia and the crankshaft is rotated with relatively small rotational speed by several revolutions. Therefore, starting of the engine is improved largely, output of the starter motor can be made small and miniaturization and lightening of the starter motor can be attempted.
Figs. 12 to 14 show another embodiment of the present invention. This embodiment is different from the above-mentioned embodiment only in shapes of the one-way clutch and the decompression cam. Otherwise, the both embodiments have the same constructions, therefore similar parts are affixed with the same symbols.
Fig. 12 is an enlarged view of an essential portion of the embodiment. As shown in Fig. 12, a one-way clutch 50 positioned longitudinally outside of the exhaust cam 28 is fitted on the camshaft 13, and a decompression cam 58 is fitted on an outer periphery 51 of the one-way clutch so as to rotate.
Fig. 13 is a XIII-XIII section of Fig. 12, and Fig. 14 is a XIV-XIV section of Fig. 12. As shown in Fig. 13, on an inner surface of an outer half portion of the one-way clutch 50 are formed three cam cuts 52 circumferentially at regular intervals. In each cam cut 52 is loosely fitted a cam roller 53 and a coil spring 54 is inserted between the cam cut 52 and the cam roller 53. When the cam shaft 13 rotates normally, the one-way clutch 50 becomes the disconnected state, and when the camshaft 13 rotates in reverse, the one-way clutch 50 becomes the connected state. This constitution is the same as that in the above-mentioned embodiment.
As shown in Figs. 12 and 14, on the outer periphery 51 of the one-way clutch 50 are formed twelve blind holes 55 at regular intervals opening radially outward. In each blind hole 55 are put a coil spring 56 and a ball 57. On an inner peripheral surface of the decompression cam 58 are formed twelve egg-shaped depressions 59 circumferentially at regular intervals. Fig. 15 is a stretched view of a part of the inner surface of the decompression cam. The depression 59 has a steep slope portion 59a and a gentle slope portion 59b similarly to the above-mentioned embodiment. The ball 57 pushed by the coil spring 59 against the decompression cam faces the egg-shaped depression 59 and engages with the depression 59. The blind holes 55, the coil springs 59 and the balls 57 of the one-way clutch 50 and the egg-shaped depressions 59 of the decompression cam 58 constitute a torque limiter 60.
The decompression cam 58 has a cam nose 58a and an engaging projection 61 similar to those of the above-mentioned embodiment. The engaging projection 61 is stopped by the reverse rotation stopper 42 of the cylinder head 3 when the decompression cam 58 rotates in reverse, and is stopped by the normal rotation stopper 43 of the intake rocker arm 19 when the decompression cam 58 rotates normally. In an annular depression formed on an outer peripheral surface of the one-way clutch 50 neighboring an edge of the decompression cam 58 is fitted a stopper ring 62 of plastics.
This embodiment shows that the torque limiter can be formed between an outer circumferential surface of the one-way clutch and an inner circumferential surface of the depression cam. When the camshaft rotates in reverse, the decompression cam also rotates in reverse. When the camshaft rotates normally and the bifurcated end portion 20a of the exhaust rocker arm separates from the cam nose 58a of the decompression cam, the depression cam rotates normally owing to the very small accompanied rotation torque produced between the camshaft and the one-way clutch and engagement of the torque limiter. This working and other working of not shown portion are the same as those in the above-mentioned embodiment, therefore further detailed explanation is omitted.

Claims

A decompression device of a 4 stroke cycle internal combustion engine having intake and exhaust valves opened and closed by respective intake and exhaust cams made integral with a camshaft and a starter motor for starting said engine, comprising:
a decompression cam fitted on said camshaft so as to rotate freely;

a one-way clutch fitted on said camshaft which is adjacent to said decompression cam and capable of transmitting reverse rotation torque to said decompression cam only when said camshaft rotates in reverse;

a torque limiter inserted between said decompression cam and said one-way clutch for canceling transmission of said reverse rotation torque larger than a predetermined torque;

a first decompression cam stopper provided on a fixed portion engaging with an engaging section formed on said decompression cam for stopping rotation of said decompression cam in normal rotational direction; and

a second decompression cam stopper provided on a fixed portion engaging with said engaging section for stopping rotation of said decompression cam in reverse rotational direction,

a lift of a cam section of said decompression cam being higher than a base circle of said exhaust cam and lower than a maximum lift of a cam section of said exhaust cam,

said exhaust valve being not opened by said decompression cam when said first decompression cam stopper engages with said engaging section.
A decompression device of a 4 stroke cycle internal combustion engine as claimed in claim 1, wherein torque transmitted through said torque limiter is smaller when the camshaft rotates in normal direction and larger when the camshaft rotates in reverse direction.
A decompression device of a 4 stroke cycle internal combustion engine as claimed in claim 1 or 2, wherein said torque limiter comprises a touching member disposed on one of adjacent side surfaces of said one-way clutch and said decompression cam, a depression formed on another of said adjacent side surfaces and a spring for forcing said touching member against said depression, and said depression is shaped so that transmitted torque is smaller when said camshaft rotates in normal direction and larger when said camshaft rotates in reverse direction.
A decompression device of a 4 stroke cycle internal combustion engine as claimed in claim 1 or 2, wherein said torque limiter comprises a touching member disposed on one of adjacent circumferential surfaces of said one-way clutch and said decompression cam, a depression formed on another of said adjacent circumferential surfaces and a spring for forcing said touching member against said depression, and said depression is shaped so that transmitted torque is smaller when said camshaft rotates in normal direction and larger when said camshaft rotates in reverse direction.
A decompression device of a 4 stroke cycle internal combustion engine having intake and exhaust valves opened and closed by respective intake and exhaust cams made integral with a camshaft and a starter motor for starting said engine, comprising:
a decompression cam fitted on said camshaft so as to rotate freely;

a one-way clutch fitted on said camshaft which is adjacent to said decompression cam and capable of transmitting reverse rotation torque to said decompression cam only when said camshaft rotates in reverse;

a torque limiter inserted between said decompression cam and said one-way clutch for canceling transmission of said reverse rotation torque larger than a predetermined torque;

a first decompression cam stopper provided on a fixed portion engaging with an engaging section formed on said decompression cam for stopping rotation of said decompression cam in normal rotational direction; and

a second decompression cam stopper provided on a fixed portion engaging with said engaging section for stopping rotation of said decompression cam in reverse rotational direction,

a lift of a cam section of said decompression cam being higher than a base circle of said intake cam and lower than a maximum lift of a cam section of said intake cam,

said intake valve being not opened by said decompression cam when said first decompression cam stopper engages with said engaging section.
A decompression device of a 4 stroke cycle internal combustion engine as claimed in claim 5, wherein torque transmitted through said torque limiter is smaller when the camshaft rotates in normal direction and larger when the camshaft rotates in reverse direction.
A decompression device of a 4 stroke cycle internal combustion engine as claimed in claim 5, wherein said torque limiter comprises a touching member disposed on one of adjacent side surfaces of said one-way clutch and said decompression cam, a depression formed on another of said adjacent side surfaces and a spring for forcing said touching member against said depression, and said depression is shaped so that transmitted torque is smaller when said camshaft rotates in normal direction and larger when said camshaft rotates in reverse direction.
A decompression device of a 4 stroke cycle internal combustion engine as claimed in claim 5, wherein said torque limiter comprises a touching member disposed on one of adjacent circumferential surfaces of said one-way clutch and said decompression cam, a depression formed on another of said adjacent circumferential surfaces and a spring for forcing said touching member against said depression, and said depression is shaped so that transmitted torque is smaller when said camshaft rotates in normal direction and larger when said camshaft rotates in reverse direction.