JPH09184410A - Decompression mechanism of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable enclosure of the mechanism for a driven timing gear as well as enabling the constitution of a decompression mechanism without exerting any particular machining on the base surface of a cam. SOLUTION: A hollow part 21 communicating with the base surface 10a of a cam 10 via a through hole 24 is formed on a driven timing gear 8, and a decompression lever 26, a decompression spring and a centrifugal lever 33 are stored in this hollow part and the decompression lever 26 swing between its operational position A having its operational piece 28 projected to the outside of the through hole 24 and stacked on the base surface 10a to form a minute lift part, and a non-operational position B where the operational piece 28 is retreated inside the through hole 24. In addition, the decompression spring energizes the decompression lever 26 to the operational position A side and the centrifugal lever 33 forces the decompression level 26 to swing to the non- operational position B when the gear 8 rotates by more than the preset rotational speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine in which a cam for opening and closing an engine valve is integrally connected to one end of a driven timing gear driven to be decelerated from a crankshaft.
The present invention relates to a decompression mechanism for appropriately lowering a compression pressure of a combustion chamber at the time of starting operation to reduce an operating load.

[0002]

2. Description of the Related Art A decompression mechanism of such an engine is disclosed in, for example, Japanese Patent Publication No. 6-6889.
Already known.

[0003]

In the conventional decompression mechanism, as disclosed in the above publication, a concave groove is provided on the base surface of the cam and the actuating portion of the decompression bar pivotally supported at the driven timing is provided. Since it is arranged so that it can appear in and out of the concave groove, there is a drawback in that the base surface of the cam needs to be subjected to troublesome groove processing, and the manufacturing cost is high.

The present invention has been made in view of the above circumstances, and provides a decompression mechanism for an engine which does not require machining on the cam surface and can be compactly stored in a driven timing gear. With the goal.

[0005]

To achieve the above object, in the decompression mechanism of the present invention, a cam for opening and closing an engine valve is integrally connected to one end of a driven timing gear that is decelerated from a crankshaft. In the installed engine, the driven timing gear has a hollow portion communicating with the base surface of the cam through the through hole, and the hollow portion has an operating piece bent toward the through hole. A decompressor capable of oscillating between an operating position in which the projecting member protrudes out of the through hole and overlaps the base surface of the cam to form a minute lift portion, and an inactive position in which the operating piece retreats into the through hole. A decompression spring that urges the decompressor toward the operating position and a centrifugal lever that senses a rotational speed of the driven timing gear equal to or higher than a predetermined value and swings the decompressor to the inoperative position are housed. This The features.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on embodiments of the present invention shown in the accompanying drawings.

First, in FIGS. 1 and 2, reference numeral 1 indicates an engine body of a four-cycle engine, which is sucked into a valve operating chamber 2 formed on one side thereof in association with rotation of a crankshaft 3.
A valve train 6 for opening and closing the exhaust valves 4 and 5 (engine valves) is provided.

The valve train 6 includes a drive timing gear 7 fixed to the crankshaft 3 and a driven timing gear 8 supported by the intermediate shaft 9 and driven from the drive timing gear 7 at a speed reduction ratio of ½. A cam 10 integrally provided at one end of the driven timing gear 8; a pair of cam followers 12 and 13 supported by a cam follower shaft 11 so as to be swung by the cam 10; and a rocker shaft 14. A pair of rocker arms 15 and 16 each having one end in contact with the valve heads of the intake and exhaust valves 4 and 5, and the cam followers 12, 13 at the other ends of the rocker arms 15 and 16, respectively.
A pair of push rods 17 and 18 for connecting
And the valve springs 19 and 20 for urging the intake and exhaust valves 4 and 5 in the valve closing direction, respectively, and the lift surface of the cam 10 is pushed through the cam followers 12 and 13 to the push rod 1.
When the intake valves 7 and 18 are pushed up, the intake and exhaust valves 4 and 5 are opened. When the base surface of the cam 10 faces the cam followers 12 and 13, the intake and exhaust valves 4 and 5 are closed by the urging forces of the valve springs 19 and 20. It has become.

3 to 5, the driven timing gear 8 has a hollow portion 21 whose end face opposite to the cam 10 is open, and the hollow portion 21 is provided with a decompression mechanism 22. The mechanism 22 will be described below.

A pair of bosses 23, 23 and a through hole 24 for communicating the hollow portion 21 with the base surface 10a of the cam 10 are provided in the inner end wall of the hollow portion 21 of the driven timing gear 8, and the bosses 23, 23 are provided. Supports both ends of the first pivot 25 that swingably supports the decompressor 26. The decompressor 26 is made of a steel plate, and has a long arm 26a and a short arm 26b bent at right angles to each other. The long arm 26a is arranged so as to extend so as to be orthogonal to the axes of the gear 8 and the cam 10, and an operating piece 28 bent toward the through hole 24 is provided at the tip thereof. Further, the long arm 26a is provided with a large-diameter hole 29 which penetrates the boss 30 of the gear 8 and the cam 10 supported by the intermediate shaft 9 and avoids interference with them. On the other hand, the short arm 26b is arranged so as to face the open surface of the hollow portion 21, opposite to the operating piece 28.

As shown in FIG. 5, the decompressor 26 projects the actuating piece 28 out of the through hole 24 and overlaps a part of the base surface 10a of the cam 10 to form a minute lift portion. It is possible to swing around the first pivot 25 between the operating position A and the non-operating position B in which the operating piece 28 is retracted into the through hole 24. The operating position A of the decompressor 26
In FIG. 4, the desired overlapping position of the operating piece 28 with respect to the base surface 10a is immediately after the lift surface along the rotational direction R of the cam 10, as shown in FIG.

Further, a second pivot 32, which is parallel to the axes of the gear 8 and the cam 10, is provided on the inner end wall of the hollow portion 21 so that the centrifugal lever 33 is swingably supported. The centrifugal lever 33 has an arcuate shape along the inner peripheral wall of the hollow portion 21, and a notch 34 with which the short arm 26b is engaged is formed at an intermediate portion thereof.

Thus, this centrifugal lever 33 has the second pivot 3
When the decompressor 26 is swung inward and outward in the radial direction around 2, the decompressor 26 is swung to the operating position A and the non-operating position B. That is, the decompression spring 35 that urges the decompression lever 26 toward the operating position A is connected. The decompression spring 35 is composed of a torsion coil spring and is attached to the second pivot 32.

In this way, the decompression mechanism 22 is housed in the hollow portion 21 of the driven timing gear 8.

A cover 36 that closes the open surface of the hollow portion 21 is fitted on the inner peripheral surface of the driven timing gear 8 to prevent the centrifugal lever 33 from being separated from the second pivot 32. The cover 33 is prevented from coming off by engaging an engaging hole 37 formed in the peripheral wall of the cover 36 with an elastic engaging claw 38 protruding from the inner end wall of the hollow portion 21.

Next, the operation of this embodiment will be described.

When the engine is not operating, the centrifugal lever 33 holds the decompressor 26 in the operating position A by the urging force of the decompression spring 35, so that the operating piece 28 overlaps a part of the base surface 10a of the cam 10 and is minute. Form a list.

Therefore, when the crankshaft 3 is cranked by manually operating the recoil type starter to start the engine, the base surface 10a of the cam 10 passes through the cam followers 12 and 13, and in the compression stroke of the engine,
The minute lift portion, that is, the operating piece 28 is the cam follower 12,
The push rods 17 and 18 are slightly pushed up via 13 to open the intake and exhaust valves 4 and 5 slightly,
Part of the compression pressure of the combustion chamber of the engine is released to the outside,
Since the increase in cranking load is alleviated, the starting operation can be performed lightly.

When the engine is started and the rotational speed of the driven timing gear 8 rises above a predetermined value, the centrifugal lever 3
3 swings around the second pivot 32 against the set load of the decompression spring 35 due to an increase in the centrifugal force acting on it, and swings the decompression lever 26 to the non-operating position B, so that the operating piece 28 of the cam 10 moves. Through hole 24 away from base surface 10a
Move in. Therefore, the cam 10 is adapted to properly open and close the exhaust valves 4 and 5 according to the original cam profile without being interfered with by the decompressor 26.

As described above, in the non-operating position B of the decompressor 26, the operating piece 28 is simply retracted into the through hole 24 to avoid the interference with the cam 10, so that the base of the cam 10 is prevented. The surface 10a does not need to be specially processed, so that the cam 10 can be easily formed, and the sliding contact between the cam 10 and the cam followers 12, 13 can be made smooth.

Moreover, since the decompression mechanism 22 is compactly housed in the driven timing gear 8, there is no problem that the valve operating device 6 is enlarged by the mechanism 22.

The present invention is not limited to the above embodiments, and various design changes can be made without departing from the scope of the invention. For example, only the cam follower 13 of the exhaust valve 5 system may be operated by the decompressor 26.

[0023]

As described above, the decompression mechanism of the present invention is
In an engine in which a cam for opening and closing an engine valve is integrally connected to one end of a driven timing gear that is decelerated from the crankshaft, the driven timing gear has a hollow portion that communicates with the base surface of the cam surface through a through hole. The hollow portion has an operating piece bent toward the through hole, and the operating piece projects outside the through hole and overlaps with the base surface of the cam to form a minute lift portion. A decompressor capable of swinging between the operating piece and a non-operating position where the operating piece retreats into the through hole; a decompressing spring biasing the decompressor toward the operating position; and a predetermined value of a driven timing gear. Since the centrifugal lever that senses the number of rotations and swings the decompressor to the inoperative position is housed, the decompression mechanism can be configured without any special processing on the cam. With reduced costs, during non-operation of the decompression lever can ensure smooth operation of the cam. In addition, the decompression mechanism can be built in the driven timing gear, and the valve operating device can be prevented from increasing in size.

[Brief description of the drawings]

FIG. 1 is a vertical sectional front view of an essential part of an engine showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along line 2-2 of FIG.

FIG. 3 is an enlarged view of a main part of FIG. 1;

FIG. 4 is a sectional view taken along line 4-4 in FIG. 3;

FIG. 5 is a sectional view taken along line 5-5 of FIG. 4;

[Explanation of symbols]

 A operating position B non-operating position 3 crankshaft 4, 5 intake / exhaust valve as an engine valve 8 driven timing gear 10 cam 10a base surface 21 hollow part 22 decompression mechanism 24 through hole 26 decompressor 28 actuating piece 33 centrifugal lever 35 decompression Spring

Claims (1)

[Claims] 1. An engine in which a cam (10) for opening and closing an engine valve (4, 5) is integrally connected to one end of a driven timing gear (8) that is driven to decelerate from a crankshaft (3), The driven timing gear (8) has a hollow portion (2) communicating with the base surface (10a) of the cam (10) through the through hole (24).
1) is formed, and the through hole (2) is formed in the hollow portion (21).
4) has an actuating piece (28) bent toward the cam, and the actuating piece (28) projects to the outside of the through hole (24) and the cam (10).
Of the through hole (2) and the operating position (A) where the minute lift portion is formed by overlapping with the base surface (10a) of the operating hole (2).
4) a decompressor (26) that can oscillate between a non-actuated position (B) that retreats into 4), and this decompressor (2)
6) The decompression spring (35) for urging the decompression spring (35) toward the operating position (A), and the decompression lever (26) by detecting the number of revolutions of the driven timing gear (8) at a predetermined value or more. A decompression mechanism for an engine, characterized in that it accommodates a centrifugal lever (33) that swings to B).