JPH0260843B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a decompression device for an internal combustion engine, particularly a four-stroke internal combustion engine.

[Conventional technology]

In this type of internal combustion engine, when the engine is stopped, the crankshaft generally rotates due to inertia, and after stopping due to resistance due to the compression pressure in the combustion chamber,
At the above compression pressure, it rotates slightly and stops.

Therefore, the next time the engine is restarted, it will start from the compression stroke of the piston, which requires a fairly large starting force. The starting operation is particularly difficult when starting manually using a hard starter or the like, or when starting an engine with a large displacement.

In order to reduce the starting force, a mechanism was conventionally known in which the compression pressure in the combustion chamber was reduced by manually opening the valve slightly (see, for example, Japanese Utility Model Publication No. 7695/1983). However, the above-mentioned valve opening operation must be performed manually at the same time as the starting operation, which is very cumbersome to operate.

Therefore, a valve closing prevention member consisting of a sleeve with a spherical heavy stud or a sickle-shaped heavy stud is provided on the camshaft near the valve drive cam or on the gear on the camshaft.
When the engine is rotating at low speeds, the above-mentioned blocking member is placed in contact with the tapepet by a spring to prevent the valve from being completely closed, and when the engine is rotating at high speeds, the above-mentioned blocking member is automatically closed by the tappet due to centrifugal force. It is known that the valve is retracted from the contact position with the valve to perform normal valve opening/closing operations (see, for example, Japanese Utility Model Application No. 55-36977 and Japanese Utility Model Publication No. 127806/1983).

[Problem to be solved by the invention]

However, with the above-mentioned engine that prevents the valve from closing completely when the engine rotates at low speed, the valve opens not only when starting, but also when idling, allowing unburned gas to be discharged from the combustion chamber. There is a problem.

The present invention was proposed in view of the above problems, and it is possible to automatically open the valve to reduce the starting force as described above, and there is less risk of unburned gas being discharged. The purpose is to provide a decompression device.

[Means to solve the problem]

In order to achieve the above object, a decompression device according to the present invention has the following configuration.

In other words, a pressure reducing cam is rotatably installed on the camshaft near the valve train cam to slightly open the exhaust valve or intake valve to reduce the pressure in the combustion chamber. A one-way clutch is interposed between the camshaft and the pressure-reducing cam, which engages only when the compression stroke begins and the crankshaft reverses due to the compression pressure in the combustion chamber, and the camshaft rotates in conjunction with this. Features.

[Effect]

With the above configuration, when the engine is stopped and the camshaft is reversed through the crankshaft due to the compression pressure in the combustion chamber during the compression stroke, the pressure reducing cam rotates through the one-way clutch, and the valve opens slightly. This reduces the compression pressure within the combustion chamber. As a result, even if the operation is restarted from the compression stroke at the next restart, the compression pressure in the combustion chamber is reduced.
This allows for easy starting.

〔Example〕

Hereinafter, the present invention will be specifically described based on embodiments shown in the drawings. In the figure, 1 is the crankshaft,
2 is the camshaft of the valve drive cams 3 and 4, which is connected to the crankshaft 1 through a chain etc. not shown in the figure.
It rotates in the same direction as with a reduction ratio of 1/2. 5 is a piston.

On the camshaft 2, a pressure reducing cam 6 is rotatably fitted and held adjacent to the side surface of the valve drive cam 3 for the exhaust valve, and there is a gap between the pressure reducing cam 6 and the camshaft 2. A directional clutch 7 is interposed.

The one-way clutch 7 rotates the pressure reducing cam 6 in the same direction only when the camshaft 2 is reversed due to the reversal of the crankshaft 1 when the engine is stopped as described above. The exhaust valve 9 is slightly opened via the rocker arm 8 by the rotation of the pressure reducing cam 6.

The one-way clutch 7 is a roller 7 in the case of the figure.
a and spring 7b, but it is not limited to this.

In the above configuration, during operation of the engine, the crankshaft 1 rotates in the clockwise direction in FIG. 1, and the camshaft 2 also rotates in the clockwise direction as indicated by the arrow in the figure. At this time, the one-way clutch 7 is not operated and the lower cam surface 6a of the pressure reducing cam 6 is stopped against the response surface 8a of the rocker arm 8 as shown in FIG.

If you stop the engine in this state, the crankshaft 1
continues to rotate due to inertia, and once it stops at the compression stroke of the piston 5 (for example, the position shown by the solid line in Figure 1), the compression pressure causes the piston 5 to return to, for example, the position shown by the chain line in the figure, and the crankshaft 1 is reversed. and stop. Accordingly, the camshaft 2 is also reversed in the counterclockwise direction, and the one-way clutch 7 is operated at this time to cause the pressure reducing cam 6 to rotate along with the camshaft 2 to the state shown in FIG. Then, the operating cam surface 6b of the pressure reducing cam 6, which is formed to have a slightly larger diameter than the lower cam surface of the valve train cam 3 that positions the exhaust valve 9 in the closed state, pushes up the response surface 8a of the rocker arm 8 and closes the exhaust valve. Open 9 slightly. As a result, the compressed pressure within the combustion chamber 10 escapes to the exhaust passage 11 and is reduced in pressure.

When the engine is restarted in this state, piston 5
is in the middle of the compression stroke as mentioned above, so that stroke will be completed first, but at that time the compression pressure mentioned above will be reduced, so there will be less resistance when starting with a hard starter etc. and it will start easily. It is possible.

If the operating cam surface 6b of the pressure reducing cam 6 and the responsive surface 8a of the rocker arm 8 are made to have a slightly longer surface as shown in the figure, the camshaft 2 will rotate in the normal clockwise direction at the time of startup, and the one-way clutch 7 will rotate. is cut, so the pressure reducing cam 6 is frictionally driven by the camshaft 2 and rotates in the same direction as the camshaft 2, but the left end of the operating cam surface 6b in the figure is
Since the valve remains open until it leaves the response surface 8a, compression pressure is not applied immediately. Further, as shown in the illustrated example, if an auxiliary spring 7b is provided that pushes the roller 7a of the one-way clutch 7, even if the camshaft 2 starts to rotate clockwise in the normal view, the one-way clutch 7 will be pushed in the engaging direction for a short time. The exhaust valve 9 can be kept open at least until the end of the first compression stroke.

Next, when the exhaust stroke begins, the valve operating cam 3 acts on the rocker arm 8 as shown in FIG. 4 to properly open the exhaust valve 9. At this time, the pressure reducing cam 6 is driven by friction on the camshaft 2 and rotates together with the valve drive cam 3.
As shown in FIG. 5, the large protrusion 6c hits the response surface 8a of the rocker arm 8 and does not rotate any further. When the exhaust valve 9 is closed, it is pushed back by the rocker arm 8 into the state shown by the solid line in FIG. 1, and remains in this position during operation thereafter.

In the embodiment, the exhaust valve 9 is opened by the pressure reducing cam 6, but the intake valve 12 may be opened. In addition to the illustrated overhead camshaft internal combustion engine, the present invention can also be applied to overhead valve or side valve internal combustion engines.

〔Effect of the invention〕

As explained above, the decompression device of the present invention has
With the above configuration, when the crankshaft 1 is reversed by the compression pressure in the combustion chamber 10 during the compression stroke due to the inertia rotation of the crankshaft 1 when the engine is stopped, and the camshaft 2 is rotated in conjunction with this, the camshaft 2 is reversed. The pressure reducing cam 6 rotates in the same direction as the camshaft 2 via the directional clutch 7, thereby making it possible to slightly open the valve 9 and automatically reduce the compression pressure in the combustion chamber. This makes it possible to reduce the starting force when restarting. There is a risk that unburned gas may leak when the valve 9 is opened.
This occurs only during one compression stroke when the engine is stopped or restarted, and does not leak during the engine's low-speed rotation during idling, unlike in the conventional case, so it is possible to prevent unburned gas from leaking. can be reduced to

Further, the decompression device of the present invention has the advantage that it can be constructed extremely simply by simply adding a pressure reducing cam and a one-way clutch to existing engine components.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional front view of an internal combustion engine equipped with the decompression device of the present invention, Fig. 2 is a sectional view taken along the line of Fig. 1, and Figs. 3, 4, and 5 show the operating states of the pressure reducing cam. FIG. 1 is a crankshaft, 2 is a camshaft, 3 and 4 are valve operating cams, 5 is a piston, 6 is a pressure reducing cam, 7 is a one-way clutch, 8 and 13 are rocker arms, and 9 and 12 are intake and exhaust valves.

Claims (1)

[Claims] 1. A pressure reducing cam is rotatably installed on the camshaft near the valve drive cam to slightly open the exhaust valve or intake valve to reduce the pressure in the combustion chamber. A one-way clutch is interposed between the camshaft and the pressure-reducing cam, which engages only when the crankshaft is reversed by the compression pressure in the combustion chamber during the compression stroke, and the camshaft is accordingly reversed. A decompression device for internal combustion engines.