JPS63131810A - Decompression device for internal combustion engine - Google Patents

Abstract

PURPOSE:To achieve the improvement in startability, by forming the shape of a decompression cam so as to provide two kinds of tappet lifting amounts. CONSTITUTION:The rising piece 16 of a decompression cam 13 is engaged with the forked part of a decompression weight 4. On the circumferential part of the decompression cam 13, the first cam surface 18a which is located on the inside of the base circle of a valve open/close cam 12, the second and the third cam surfaces 18b, 18c which are projected outward from the base circle are formed. The third cam surface 18c is formed so as to be higher than the second cam surface 18b. Thus, the decompression amount at the initial stage of start can be increased, and then it can be decreased, so that the startability can be improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a method for reducing the compression pressure in a combustion chamber by slightly opening an exhaust valve or an intake valve when starting an internal combustion engine, thereby reducing the force required for starting. It relates to a decompression device.

[Conventional technology]

Generally, as shown in Japanese Utility Model Application No. 59-43603, in this type of device, when the engine is stopped or when the engine speed is still low at the beginning of startup, the decompression cam that engages with the decompression weight is moved by the decompression weight. It is held in a position slightly protruding from the base circle of the valve opening/closing cam, and the valve opening/closing tappet is pushed up slightly by the decompression cam every revolution during the compression stroke, opening the valve slightly and lightening the starting load. . When the engine speed increases to a predetermined speed and the centrifugal force of the decompression weight, which rotates integrally with the camshaft, exceeds the force of the return spring, the decompression weight swings against the return spring, causing the decompression weight to swing out against the return spring. The decompression cam that engages with the valve opening/closing cam is disposed inward of the base circle of the valve opening/closing cam. In this way,
The decompression cam no longer pushes up against the valve opening/closing tappet, and the valve closes completely during the compression stroke.

[Problem that the invention seeks to solve]

In this type of equipment, for example, if a coil starter and starter motor are used together, the compression pressure at startup should be sufficiently low in the case of a small-capacity starter motor, and then the decompression should be released immediately in a low rotational speed range due to startability etc. It is desirable, but if you release the decompression at too low a rotation speed,
There is a possibility that splatter may occur during manual starting using the recoil starter.

The present invention has been made in view of the above points, and has two stages of decompression at the time of startup, the amount of decompression is large at the beginning of startup, and the amount of decompression is reduced thereafter until it reaches a predetermined rotation speed. Even when a starter motor and a coil starter are used together, sufficient starting performance is achieved.

[Means for solving problems]

The configuration of the present invention to achieve the above-mentioned problems includes a decompression cam and a decompression weight that is rotatably biased in one direction by a return spring, and rotates integrally with the camshaft at the time of startup and engages with the decompression weight. The decompression cam is held by the decompression weight in a position that protrudes beyond the base circle of the valve opening/closing cam fixed to the camshaft, and during the compression stroke, the valve opening/closing tappet is slightly pushed up to slightly open the valve and reduce the starting load. When the rotational speed increases, the decompression weight, which rotates integrally with the camshaft, rotates against the return spring due to the action of centrifugal force, rotating the decompression cam that engages with the decompression weight, thereby opening and closing the valve using the decompression cam. In the decompression device for an internal combustion engine, the rotation angle of the decompression weight at the time of startup is set in two stages depending on the rotation speed, and the decompression cam interlocked with the rotation angle is of two types. It is characterized by having a cam shape that provides a tappet push-up amount of .

[Effect]

When the engine is stopped, or when the engine speed is still low at the beginning of engine startup, for example below 450 rpm (see Figure 9), the tappet of the decompression cam engages with the decompression weight, which is biased to rotate in one direction by the return spring. The cam surface with a large push-up amount is held at a position where it can come into contact with the lower surface of the tappet.

Therefore, when the camshaft makes one revolution, the tappet is pushed up by a predetermined height by the cam surface of the decompression cam in the compression stroke every revolution, and the valve opens slightly, reducing the starting load. In this case, the amount of decompression is large and the starting load is sufficiently reduced.

Then, the engine speed increases to some extent, for example 45.
When the speed reaches 0 to 11,000 rpm (see Figure 9), the decompression weight, which rotates integrally with the camshaft, rotates against the return spring, causing the decompression cam that engages with it to rotate, so that the decompression weight rotates further than the cam surface. The cam surface that pushes up the tappet with a small amount is held at a position where it can come into contact with the lower surface of the tappet.

Therefore, in this case as well, when the camshaft rotates once,
During each rotation, the tappet is pushed up by a predetermined height by the cam surface of the decompression cam during the compression stroke, and the valve opens slightly to reduce the starting load. In this case, the decompression amount is smaller than that at the initial stage of startup.

Then, the rotation speed increases further, for example, 10QQrp.
m or more (see Figure 9), the decompression weight further rotates against the return spring due to centrifugal force, causing the decompression cam to rotate inward from the base circle of the valve opening/closing cam. Alternatively, the flush cam surface is held in a position where it can come into contact with the lower surface of the tappet.

Therefore, the push-up action of the tappet by the decompression cam is eliminated, and the valve is completely closed during the compression stroke.

〔Example〕

Fig. 1 is a perspective view of the device of the present invention, Fig. 2 is a front view thereof, and Fig. 3 is a perspective view of the device of the present invention.
Figures 5 to 5 are explanatory diagrams of the same operation.

A first decompression weight 4 and a second decompression weight 5 are disposed in a recess 3 provided on one side of a cam gear 2 fixed to a camshaft 1. These two decomp weights 4.
5 are opposed to each other with the camshaft 1 interposed therebetween, and are rotatably attached to the side surfaces of the cam gear 2 through first and second pins 6.7 provided at opposite ends thereof. The ends of the two decompression weights 4 and 5 on the side of the bin 6.7 have a protrusion 9 provided at the end of the other decompression weight 4 in a recess 8 provided at the end of one decompression weight 5. They are inserted and engaged with each other.

Moreover, two tension coil springs 10.11 are stretched between these decompression weights 4.5, and these springs 10.11 have different spring constants, and in this example, the first tension coil spring 10 is The 45 Orpm release spring has a small spring constant, and the second tension coil spring 11 is a 1100 Orpm release spring with a large spring constant.

On the other hand, a decompression cam 1 is mounted on the camshaft 1 between the valve opening/closing cam 12 fixedly installed on the camshaft 1 and the decompression weight 4.5.
3 is arranged. This decompression cam 13 is rotatably attached to a flat part 14 formed on the circumferential surface of the cam shaft with a pin 15. This decompression cam 13 is provided with an upright piece 16 on its circumferential portion, and this upright piece 16 engages with a bifurcated portion 17 that protrudes in the camshaft 1 direction on the side surface of the tip end of the first decompression weight 4. Further, the upper surface of the peripheral portion of the decompression cam 13 forms a decompression cam surface, and includes a first cam surface 18a, a second cam surface 18b, and a third cam surface 18C. The first cam surface 18a is located inside the base circle 12a of the valve opening/closing cam 12, and the second cam surface 18b is adjacent to the first cam surface 18a and located outside of the base circle 12a of the valve opening/closing cam 12. The protruding third cam surface 18c is adjacent to the second cam surface 18b, protrudes further outward than the second cam surface 18b, and is formed one step higher than the second cam surface 18b.

The lower surface of the valve opening/closing tappet 19 is connected to the valve opening/closing cam 1.
2 and the decompression cam 13.

In the above structure, when the engine is stopped or when the engine speed is still low at the beginning of startup, in this example, 450 rpm
In the following, the force of the first tension coil spring 10 overcomes the centrifugal force of the first and second decompression weights 4.5, and the first and second decompression weights 4.5 are drawn toward the camshaft 1 side. Accordingly, the third cam surface 18c of the decompression cam 13 that is engaged with the first decompression weight 4 is held at a position where it can come into contact with the lower surface of the tappet 19.

Therefore, when the camshaft 1 makes one revolution, the tappet 19 moves to the third cam surface 1 of the decompression cam 13 in the compression stroke for every revolution.
8c, the valve is pushed up by a predetermined height, and the valve opens slightly, reducing the starting load.

In this case, the amount of decompression is large and the starting load is sufficiently reduced (see FIG. 9).

Then, the engine speed increases to a certain extent, and in this example it reaches 45.
At 0 to 11000 rpm, the first decompression weight 4
The centrifugal force of the second decompression weight 5 overcomes the force of the first tension coil spring 10, and the first pin 6 and the second pin 7
It swings outward around the center, and is held at a position where the drag force of the spring 10.11 and the centrifugal force are balanced.

At this time, the third cam surface 18c of the decompression cam 13 is pulled toward the cam gear 2 around the bin 15 by the first decompression weight 4, and the third cam surface 18C is separated from the lower surface of the tappet 19, and the second cam Only surface 18b is tappet 1
Place it on the bottom surface of 9.

Therefore, in this case as well, when the camshaft l rotates once,
The tappet 19 is decompressed during the compression stroke for each rotation.
is pushed up by a predetermined height by the second cam surface 18b of
The valve opens slightly, reducing the starting load. In this case, the amount of decompression is smaller than that at the initial stage of startup (see FIG. 9).

Then, the engine speed increases further to 11 in this example.
000 rpm or more, the first decompression weight 4 and the second decompression weight 5 are activated by the tension coil spring 10.1.
1 and further swings outward around the first pin 6 and second pin 7 due to the action of centrifugal force, and the peripheral wall surface 2 of the recess 3 of the cam gear 2
0 and is held in that state.

At this time, the second cam surface 18b of the decompression cam 13 is pulled toward the cam gear 2 around the pin 15 by the first decompression weight 4, the second cam surface 18b is separated from the lower surface of the tappet 19, and the first cam Only surface 18a is taped) 1
Place it on the bottom surface of 9.

Therefore, since the first cam surface 18a is located inward from the base circle 12a of the valve opening/closing cam 12, there is no pushing up action of the valve opening/closing tappet 19 by the decompression cam 13.
The valve closes completely during the compression stroke (see Figure 9).

As described above, in this example, two springs 10.11
By using these springs 1O111 and selecting appropriate spring constants, the first decompression weight 4 was made to swing in two stages, and the amount of decompression was configured in two stages, but the spring resistance varied depending on the mounting position. It is also possible to use two springs with different values to swing the first decompression weight 4 in two stages, similarly to the above example, and configure the decompression amount in two stages.

What is shown below is configured so that by selecting appropriate values for the swing loads of the two decompression weights, one of the decompression weights swings in two stages, and the amount of decompression becomes two stages. .

That is, as shown in FIGS. 6 to 8, two decompression weights 21 and 22 are rotated by first and second pins 23 and 24, respectively, in the recess 3 provided on one side of the cam gear 2, as in the above example. It can be installed freely. The ends of the two decompression weights 21 and 22 on the pin 23 and 24 sides are
Each is provided with projections 25, 26 and engages with one another. One tension coil spring 27 is stretched between these decompression weights 21 and 22.

In this example, the first decompression weight 21 is a weight with a large swing load that fully operates at 45 Qrpm, and the second decompression weight 22 is a weight with a small swing load that fully operates at 11,000 rpm.

The decompression cam 13 is the same as the above example, and the cam shaft l
The upright piece 16 of the decompression cam 13 is rotatably attached to the flat part 14 of the decompression cam 13 with a pin 15, and the upright piece 16 of the decompression cam 13 is attached to a bifurcated part 28 that protrudes in the direction of the camshaft 1 on the side surface of the tip of the first decompression way 21.
is engaged.

Therefore, when the engine is stopped or when the engine speed is still low at the beginning of engine startup, in this example, when the engine speed is 450 rpm or less, the first
The force of the tension coil spring 27 overcomes the centrifugal force of the second decompression weights 21.degree. 22, and the first and second decompression weights 21.degree. 22 are drawn toward the camshaft 1 side.
Accordingly, the third cam surface 18C of the decompression cam 13 that is engaged with the first decompression weight 21 is held at a position where it can come into contact with the lower surface of the tappet 19.

Therefore, as in the above example, the valve opens slightly during the compression stroke, reducing the starting load. In this case, the amount of decompression is large and the starting load is sufficiently reduced (see FIG. 9).

Then, the engine speed increases to a certain extent, and in this example it reaches 45.
When it becomes 0~l100Orp, the second decompression weight 2
2 swings outward around the second pin 24 due to the action of centrifugal force against the tension coil spring 27, and the concave portion 3 of the cam gear 2 swings outward.
It comes into contact with the peripheral wall surface 20 of and is held in that state. At this time, the protrusion 26 of the second decompression weight 22 pushes up the protrusion 25 of the first decompression weight 21, and the first decompression weight 21 is thereby rotated by a predetermined angle. At this time, the swing angle of the first decompression weight 21 is smaller than that of the second decompression weight 22, and the third cam surface 18c of the decompression cam 13 is controlled by the first decompression weight 21.
is pulled toward the cam gear 2 around the pin 15, and the third cam surface 18C is separated from the lower surface of the tappet 19, leaving only the second cam surface 18b disposed on the lower surface of the tappet 19.

Therefore, in this case as well, the valve opens slightly during the compression stroke, reducing the starting load, as in the above example.

In this case, as in the above example, the decompression amount is smaller than that at the initial stage of startup (see FIG. 9).

Then, the engine speed increases further to 11 in this example.
000 rpm or higher, the first decompression weight 21 resists the tension coil spring 27 and is rotated by centrifugal force.
It swings further outward around the pin 23, contacts the peripheral wall surface 20 of the recess 3 of the cam gear 2, and is held in that state. At this time, the respective protrusions 25 and 26 of the first decompression weight 21 and the second decompression weight 22 have some distance between them.

At this time, the second cam surface 18b of the decompression cam 13 is pulled toward the cam gear 2 around the pin 15 by the first decompression weight 21, and the second cam surface 18b is pulled toward the tappet 19.
Only the first cam surface 18a is separated from the lower surface of the tappet 19 and is disposed on the lower surface of the tappet 19.

Therefore, similarly to the above example, the decompression cam 13 does not push up the valve opening/closing tappet 19, and the valve is completely closed during the compression stroke.

〔Effect of the invention〕

As explained above, according to the present invention, the decompression at the time of starting is performed in two stages, the amount of decompression is large at the initial stage of starting, and the amount of decompression is reduced thereafter until it reaches a predetermined number of rotations. Even when a coil starter is used together, it exhibits sufficiently good starting performance.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention; FIG. 1 is a perspective view of the device of the present invention, FIG. 2 is a front view thereof, and FIGS. 3 to 5 are explanatory diagrams of the same operation.
6 to 8 are explanatory views of the operation of the apparatus of the present invention according to another embodiment, and FIG. 9 is a graph showing the relationship between the rotation speed and the compression pressure. 1 is the camshaft, 2 is the cam gear, 3 is the recess, 4 and 21 are the first
Decompression weight, 5, 22 is the second decompression weight,
6.23 is the first pin, 7.24 is the second pin, 8 is the recess,
9 is a protrusion, 10 is a first tension coil spring, 11 is a second tension coil spring, 12 is a valve opening/closing cam, 12a
is the base circle, 13 is the decompression cam, 15 is the pin, 16 is the upright piece, 17.28 is the bifurcated part, 18a is the first decompression cam surface, 18b is the second decompression cam surface, 18C is the third decompression cam surface, 18 is for valve opening/closing. Tappet, 20 is the peripheral wall surface,
25 and 26 are protrusions, and 27 is a tension coil spring.

Claims (4)

[Claims] (1) The decompression cam is equipped with a decompression cam and a decompression weight that is rotatably biased in one direction by a return spring, and the decompression cam, which rotates together with the camshaft and engages with the decompression weight during startup, is fixed to the camshaft by the decompression weight. The valve opening/closing tappet is held in a position that protrudes beyond the base circle of the valve opening/closing cam.During the compression stroke, the valve opening/closing tappet is slightly pushed up to open the valve slightly to reduce the starting load, and as the rotation speed increases, it becomes integrated with the camshaft. The rotating decompression weight rotates against a return spring due to the action of centrifugal force, and the decompression cam engaged with the decompression weight is rotated to eliminate the pushing up action of the valve opening/closing tappet by the decompression cam. In the decompression device, the rotation angle of the decompression weight at the time of startup is set in two stages depending on the rotation speed, and the decompression cam interlocked with this is set in two stages.
A decompression device for an internal combustion engine, characterized in that it has a cam shape that provides various tappet pushing amounts. (2) The first aspect of the present invention is characterized in that two return springs with different spring constants are used to give the decompression weight two rotation angles at the time of startup.
A decompression device for an internal combustion engine as described in . (3) Two return springs with different spring resistance depending on the mounting position are used to give the decompression weight two rotation angles at the time of starting. Internal combustion engine decompression device. (4) An internal combustion engine according to claim 1, characterized in that two decompression weights having different swing loads are connected by a return spring to give two rotation angles to the decompression weight at the time of starting. decompression device.