JPS6027761Y2 - Pressure reducing device for starting four-stroke engines - Google Patents

Description

[Detailed description of the invention] This invention forcibly opens the exhaust valve to ignite combustion when cranking for starting a four-stroke engine is performed manually using a kick pedal, starter lobe, etc. The present invention relates to an improvement in a starting pressure reducing device that reduces the pressure in a room and enables easy cranking.

Conventionally, as such a device, for example,
As shown in Publication No. 8, the cam of the pressure-reducing camshaft is engaged with a rocker arm that can open the exhaust valve, so that the exhaust valve can be forcibly opened at any time, and the pressure-reducing cam can be opened at an appropriate time during cranking. A structure has been proposed in which the shaft is automatically returned to allow the exhaust valve to close, but in that case, the pressure reducing cam shaft is disposed above the rocker arm, and the rocker arm is attached to the upper surface of the rocker arm. Since the exhaust valve is forcibly opened by pushing down with a cam that engages with the rocker arm, the pressure reducing camshaft can be installed relatively freely without being obstructed by the exhaust valve or bushing rod on the lower side of the rocker arm. While this has the advantage of being able to be selected, it has the disadvantage that the overall length of the engine is increased due to the special installation of the decompression camshaft.

In addition, in order to eliminate such drawbacks, for example,
As shown in Japanese Patent No. 33244, it has also been proposed that a pressure reducing camshaft is disposed below the rocker arm, and the exhaust valve is forcibly opened by pushing up the rocker arm with a cam that engages the lower surface of the rocker arm. However, with this method, it is difficult to melt the pressure reducing camshaft located below the rocker arm from the shaft support of the rocker arm without interfering with the bushing rod and exhaust valve, which are also below the rocker arm. Disadvantages: The effective length of the arm for the rotational moment exerted by the pressure reduction camshaft on the rocker arm is not long enough, and as a result, a relatively large amount of force is required to operate the pressure reduction camshaft, and the cam surface of the camshaft is prone to wear. There is.

In order to solve this problem, if the rocker arm itself is made longer, the inertial mass of the rocker arm increases accordingly, which is disadvantageous in achieving high engine output.

The present invention has been proposed in view of the above, and aims to propose a compact pressure reducing device for starting a four-cycle engine that can take advantage of the advantages of each of the conventional devices and eliminate all of their disadvantages. Its features are that a rocker arm is disposed above the exhaust valve provided in the engine body, one end of which can press against the exhaust valve to open it, and the middle part of the rocker arm is pivoted to the engine body. In a four-cycle engine, the rocker arm is rotatably supported through the engine, and the other end of the rocker arm is linked to an arm drive member such as a valve drive camshaft that is connected to the engine crankshaft and can forcibly rotate the rocker arm. , the rocker arm is arranged at an angle with respect to the axis of the pivot shaft so as to widen a gap between the rocker arm and the side wall of the engine body adjacent to the arm toward the exhaust valve, and the rocker arm has a lower side surface of the exhaust valve side arm portion of the rocker arm. is rotatably supported by the side wall, and is rotatably supported by the side wall, and has a pressure-receiving protrusion protruding from its upper surface that rotates the rocker arm in the direction in which the exhaust valve opens when it receives a downward pressing force. The inner end surface of the pressure-reducing camshaft is located at an operating position in which, by rotation of the shaft, it engages with the upper surface of the pressure-receiving protrusion to open the exhaust valve to an intermediate opening degree. a cam such as an eccentric pin that can be moved between the exhaust valve and a non-operating position that allows the exhaust valve to close, and a return spring that biases the cam to the non-operating position is connected to the pressure reducing camshaft;
The cam is locked to the upper surface of the pressure receiving protrusion in the operating position against the biasing force of the return spring, and the locking is such that when the rocker arm is forcibly rotated, the upper surface of the pressure receiving protrusion is attached to the cam. The reason is that it is made to automatically unravel as it melts further.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the main parts of a four-cycle single-cylinder engine, and this engine consists of a cylinder block cb that houses a piston P therein, and an upper end of the cylinder block cb. The cylinder head ch has an intake hole 1p that opens into the combustion chamber A and an intake valve Iv that opens and closes the exhaust IEv. An exhaust valve Ep is provided, and a valve operating mechanism 0 for controlling the opening and closing of these valves Iv and Ev is configured as follows in a mechanism chamber vh formed between a cylinder head ch and a side wall of a head cover joined to its upper end. Ru.

That is, the valve train Vo includes a valve train camshaft 1 as a rocker arm drive member disposed at the center of both valves Iv and Ev;
Two rocker arms 2 connect the suction and exhaust cams 11 and 1e on the camshaft 1 and the suction and exhaust valves Ev and Ev.
L2e and intake and exhaust valves 1v.

The camshaft 1 is composed of valve springs 31% and 3e that respectively spring Ev in the closing direction, and the camshaft 1 is driven at a reduction ratio of 1/2 from the crankshaft (not shown) of the engine.

In addition, the symbols 4t and 4e are the respective pivots of the rocker arm 2L2e,
5it5e is a valve seat corresponding to the intake and exhaust valves Iv and Ev.

The valve operating mechanism Vo controls the opening and closing of the intake and exhaust valves Iv and Ev at the timing shown by lines I and II in FIG. 6, and its function is the same as that of the conventional one.

As clearly shown in FIG. 2, the rocker arm 2e for the exhaust valve Ev is arranged at an angle with respect to the axis of the pivot shaft 4e so as to widen the gap between the arm 2e and the head cover side wall W adjacent to the rocker arm 2e.

The rocker arm 2e has an intermediate portion rotatably supported by the cylinder head ch via a pivot 4e, and has a tappet adjustment bolt 13 at one end on the exhaust valve Ev side that presses against the upper end of the valve rod of the exhaust valve Ev. is screwed onto the exhaust cam 1e, and the other end is formed into an arcuate abutting surface against the cam surface of the exhaust cam 1e.

A pressure-receiving protrusion 6 that protrudes toward the side wall W of the head cover Hc is integrally formed on the lower side surface of the exhaust valve side arm portion 14 of the rocker arm 2e at an intermediate position between the pivot shaft 4e and the tappet adjustment bolt 13. On the side thereof, a pressure reducing camshaft 7 is rotatably supported by the side wall W substantially parallel to the pivot shaft 4e of the rocker arm 2e.

This pressure reducing camshaft 7 has an eccentric pin 7a as a cam at its inner end, whose side face faces the upper surface of the pressure receiving protrusion 6, and its outer end protrudes from the outer surface of the head cover Hc. An operating lever 8 is fixed to.

A pair of stoppers 9 and 10 are provided spaced apart on the head cover Hc with the operating lever 8 in between, one of which 9 is a retraction limit stop that restricts the non-operating position of the operating lever 8, and the other 10 is in the same operating position. It is an operation limit stopper that regulates the
A return spring 11 made of a torsion coil spring is connected to the operating lever 8 and urges it toward the backward limit stopper 9 .

Next, the relationship between the eccentric pin 7a of the pressure reducing camshaft 7 and the pressure receiving protrusion 6 of the rocker arm 2e will be explained with reference to FIGS. 4 and 5. FIG. This shows the non-operating state of the camshaft 7. In this state, the apex Q of the eccentric pin 7a (the point farthest from the center O of the decompression camshaft 7 on the circumferential surface of the eccentric pin 7a) is It is far away from the pressure receiving protrusion 6 on the right side,
Even when the exhaust valve Ev is closed and the pressure-receiving protrusion 6 is at the upper limit position, the eccentric pin 7a faces the upper surface of the pressure-receiving protrusion 6 with a constant gap 1 therebetween.

This is to prevent the eccentric pin 7a from interfering with the swinging of the rocker arm 2e during engine operation.

FIG. 5 shows the operating state of the pressure reducing camshaft 7 when the operating lever 8 has been rotated to the contact position with the operating limit stopper 10. In this state, the eccentric pin 7a is engaged with the upper surface of the pressure receiving protrusion 6. Then, the apex Q occupies a position slightly to the left past the contact point R with the pressure receiving protrusion 6, thereby pushing down the pressure receiving protrusion 6 by a certain amount m from the upper limit position to the position shown in FIG. The exhaust valve Ev is opened half way.

In this case, due to the elastic force of the valve spring 3e, the eccentric pin 7
A relatively large frictional force is generated on the contact surface between the pressure-receiving protrusion 6 and the pressure-receiving protrusion 6, and the frictional force resists the force of the return spring 11 of the operating lever 8 and locks the pressure-reducing camshaft 7 to the actuating device. , the above return spring 11 is designed.

If the apex Q of the eccentric pin 7a is placed past the contact point R with the pressure-receiving protrusion 6 as described above, the eccentric pin 7a The pressure-receiving protrusion 6 is pushed down slightly to increase the frictional force at the contact area, so that the pressure-reducing camshaft 7 can be more securely locked in the operating position, and the contact Providing unevenness such as serrations on the surface is also effective for locking.

Now, when starting the engine, first the operating lever 8 is rotated against the force of the return spring 11 until it comes into contact with the operating limit stopper 10, and then the lever 8 is released.

At this time, if the exhaust valve Ev is in the closed state, the pressure receiving protrusion 6 is at the upper limit position, so the eccentric pin 7a pushes it down to open the exhaust valve Ev halfway as described above, and the eccentric pin 7a It is locked in the operating position by the frictional force with the piece 6.

Therefore, when the engine is cranked by operating the kick pedal or starter lobe, the compressed gas in the combustion chamber A is initially discharged to the exhaust element LEp.
The starting torque is small and the rotation of the engine crankshaft can be easily accelerated.

When the engine reaches the exhaust stroke, the exhaust cam 1ef
As soon as the exhaust valve Ev is opened via the lock arm 2e and the rocker arm 2e is separated from the eccentric pin 7a, the pressure-reducing camshaft 7 is released and deactivated by the force of the return spring 11 of the operating lever 8. automatically rotates into position.

Thus, the engine starts through a regular stroke due to the inertial rotation of the crankshaft.

In addition, when the engine is stopped with the exhaust valve Ev open, the pressure-receiving protrusion 6 has already been sufficiently lowered by the action of the exhaust cam 1e, so the pressure-reducing camshaft 7 can be rotated to the operating position. At this time, the eccentric pin 7a and the pressure-receiving protrusion 6 cannot be engaged with each other, which means that the pressure-reducing camshaft 7 does not need to be operated.

Therefore, in this case, the engine can be cranked easily while the operating lever 8 remains in the non-operating position.

As shown in FIG. 6, the effective operating range S of the pressure-reducing camshaft 7 extends over all the four strokes of the engine except for the open section of the exhaust valve Ev, so no inconvenience occurs.

In particular, the engine's normal starting torque shows a peak value at the end of the compression stroke, as shown by the line ■, but the
As shown by the line (3), the above peak value can be significantly lowered by the operation, and the pressure reduction effect is remarkable.

As described above, according to the present invention, a rocker arm 2e whose one end can press against the exhaust valve Ev to open it is disposed above the exhaust valve Ev provided in the engine body, and the rocker arm 2e is The intermediate portion is rotatably supported on the engine body via a pivot 4e, and further includes a rocker arm 2e.
In a four-cycle engine in which the other end is linked to an arm driving member such as a valve drive camshaft 1 that is connected to the engine crankshaft and can forcibly rotate the rocker arm 2e, the rocker arm 2e is adjacent to the arm 2e. The rocker arm 2e is arranged to be inclined with respect to the axis of the pivot shaft 4e so as to widen the gap with the side wall W of the engine body toward the exhaust valve Ev. A pressure-receiving protrusion 6 is provided on the upper surface of the rocker arm 2e to rotate the rocker arm 2e in the opening direction of the exhaust valve Ev when it receives a downward pressing force, and is rotatably supported by the side wall W. The inner end surface of the pressure reducing cam shaft 7 is
The rotation of the pressure-receiving protrusion 6 engages the upper surface of the pressure-receiving protrusion 6 to open the exhaust valve Ev to an intermediate opening degree, and the operating position separates from the upper surface of the pressure-receiving protrusion 6 to allow the exhaust valve Ev to close. A cam such as an eccentric pin 7a that can move between a non-operating position and a non-operating position is provided, and a return spring 11 that biases the cam toward the non-operating position is connected to the pressure reducing camshaft 7, and the cam is configured to: In the operating position, the upper surface of the pressure receiving protrusion resists the biasing force of the return spring 11, and the locking is performed by the rocker arm 2.
When the upper surface of the pressure-receiving protrusion 6 separates from the cam during the forced rotation of the pressure-receiving protrusion 6, the pressure-reducing camshaft 7 is automatically released. Since it is pushed down via the pressure receiving protrusion 6 protruding from the side surface, the rocker arm 2e does not protrude below, and therefore the pressure reducing camshaft 7 interferes with the exhaust valve Ev, etc. below the rocker arm 2e. The rocker arm can be spaced apart from the rocker arm pivot 4e without any trouble, and the effective length of the arm for the rotational moment exerted on the rocker arm 2e by the decompression camshaft 7 can be made sufficiently long without making the rocker arm 2e itself particularly long. As a result, the operating force of the pressure reducing camshaft 7 can be reduced, and the wear of the sliding portion between the cam 7a and the upper surface of the pressure receiving protrusion 6 can be reduced. Furthermore, the inertial mass of the rocker arm 2e can be reduced, and the engine This is advantageous in achieving high output.

Furthermore, although the decompression camshaft 7 has a structure that pushes down the rocker arm 2e as described above, it hardly protrudes above the rocker arm 2e, so the entire height of the engine is reduced compared to that of an engine without a starting pressure reducing device. It can be kept as low as that.

Furthermore, although the pressure-receiving protrusion 6 is made to protrude from the side surface of the rocker arm 2e toward the side wall W of the engine body, the pressure-receiving protrusion 6 does not fit into the gap between the rocker arm 2e and the side wall W that widens due to the inclination of the rocker arm 2e. Since the side wall W can be easily arranged together with the cam, there is no need to specially bulge the side wall W to the side opposite to the pressure receiving protrusion 6 and the cam 7a, that is, to the outside so as to escape the pressure receiving protrusion 6 and the cam 7a. Coupled with the fact that the pressure reducing camshaft 7 hardly protrudes above the rocker arm 2e, this can significantly contribute to making the head of the engine body more compact.

[Brief explanation of the drawing]

The drawings show an example of the present invention applied to a four-stroke single-cylinder engine. Figure 1 is a vertical cross-sectional view of the main parts of the engine, and Figure 2 is a partial view of the engine shown in Figure 1 with the head cover cut away. Plane sectional view, Figure 3 is a side view of Figure 2, 4th and 5th
The figure is an explanatory diagram of the relationship between the pressure reducing camshaft and the pressure receiving protrusion of the non-exhaust valve side rocker arm. Figure 4 shows the relationship in the non-operating state of the pressure reducing camshaft, and Figure 5 shows the relationship in the operating state. , 6th
The figure is a diagram showing various characteristics of the above-mentioned engine relative to the crank angle. Lines I and II indicate the opening timing of the intake and exhaust valves, and line ■
Line 2 indicates the normal starting torque of the engine, and line ■ indicates the starting torque when the pressure reducing camshaft is operated. Ev...Exhaust valve, Ep...Exhaust hole, V
o...Valve mechanism, W...Side wall, 1...
...Valve drive camshaft as arm drive member, 2e...
...Middle Tsuka Arm, 4e...Axis, 6...
...Pressure receiving protrusion, 7...Reducing camshaft, 7a...
... Eccentric pin as a cam, 4 ... Exhaust valve side arm. 11...Return spring,

Claims (1)

[Scope of utility model registration request] A rocker arm 2e above the exhaust valve Ev provided in the engine body, one end of which can press against the exhaust valve Ev to open it.
At the same time, the middle part of the rocker arm 2e is rotatably supported on the engine body via a pivot 4e, and the other end of the rocker arm 2e is connected to the crankshaft of the engine and the rocker arm 2e is forcibly rotated. In a four-cycle engine that is linked to an arm driving member such as a movable valve drive camshaft 1, the rocker arm 2e is configured to widen the gap between the rocker arm 2e and the side wall W of the engine body adjacent to the arm 2e toward the exhaust valve Ev. The exhaust valve side arm portion 14 of the rocker arm 2e has a lower side surface that projects toward the side wall W and receives a downward pressing force from its upper surface. Exhaust valve Ev
A pressure-receiving protrusion 6 that rotates the rocker arm 2e in the opening direction is provided protrudingly on the inner end surface of a pressure-reducing cam shaft 7 that is rotatably supported by the side wall W. An operating position in which the pressure receiving protrusion 6 is engaged with the upper surface of the protrusion 6 to open the exhaust valve Ev to an intermediate opening degree, and an inoperative position in which the pressure receiving protrusion 6 is melted from the upper surface and the exhaust valve Ev is closed. A return spring 11 is connected to the pressure reducing cam shaft 7 to bias the cam toward the non-operating position. Return spring 11
The upper surface of the pressure-receiving protrusion 6 is locked against the urging force of the pressure-receiving protrusion 6, and the lock is automatically released when the upper surface of the pressure-receiving protrusion 6 melts from the cam when the rocker arm 2e is forcibly rotated. A pressure reducing device for starting a four-stroke engine.