JPH0734834A - Decompressing device of engine - Google Patents

Abstract

PURPOSE:To provide a decompression device of an engine where the structure is simple, the production cost is low, the working is smooth, and the structure is miniaturized and can be fitted to a cam shaft without increasing the size of the cam shaft. CONSTITUTION:In an engine having a cam shaft 5 where a gear 1 for driving a cam shaft or a sprocket and a cam 4 to control the opening/closing of an intake valve and an exhaust valve through a tuppet 3 are coaxially arranged, a moving body which is provided with an arm 8a abutted on the tuppet 3 and can be moved in the axial direction on the cam shaft, a return spring 9 to provide the energizing force in the axial direction with the moving body, and a ball 6 which is formed between the gear and the moving body, stored in the clearance which is reduced toward the outer circumference, and can be rolled in the radial direction are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine decompression device for reducing the compression pressure during cranking.

[0002]

2. Description of the Related Art In a conventional example of an engine decompression device,
The compression pressure is reduced when cranking the engine manually or automatically. However, the device itself is mounted near the cam on the cam shaft where there is not enough space, and the structure of the cam shaft itself is considerably restricted from the viewpoints of productivity, durability, production cost, etc. It has been difficult to obtain a decompression device that meets various conditions, and ingenuity has been repeated. As an example, there is a device described in Japanese Utility Model Laid-Open No. 1-118112 shown in FIGS. 6 and 7.

FIG. 6 is a vertical sectional view of a decompression device according to the present invention, and FIG. 7 is a horizontal sectional view of a main part in FIG. 6. The structure will be described with reference to these drawings. Reference numeral 101 is a cam shaft, and journal portions 101a at both ends thereof (only one side is shown)
Are supported on the crankcase via a main bearing (not shown). A sleeve 102 is fitted into the cam shaft 101 so as to be movable in the axial direction, and the outer diameter of the sleeve 102 is a base circle 1 of a cam 103 provided on the cam shaft 101.
It is formed slightly larger than the outer diameter of 03a.

Reference numeral 104 denotes the sleeve 1 when the compression pressure is reduced.
Reference numeral 02 is a tappet which is in sliding contact with the intake or exhaust valve (neither of which is shown) opened and closed via a push rod and a rocker arm. Furthermore, the cam side end surface of the sleeve 102 fitted in the cam shaft 101 and the cam 10
A return spring 105 for urging the sleeve 102 in a direction in which the sleeve 102 is always separated from the cam 103 is interposed between the return spring 105 and the No. 3. The other end surface of the sleeve 102 is formed with a taper guide surface 102a that expands in the radial direction, and a flange 107 is fixed to the cam shaft 101 through a pin 106, and the guide surface 107a of the flange 107 and the guide surface 107a. The tapered guide surfaces 102a are arranged so as to face each other.

Further, the guide surface 1 of the flange 107
07a and the taper guide surface 102a of the sleeve 102
A guide hole 101b passing through the shaft center and penetrating at a right angle to the axis is formed in the cam shaft 101 between and. A weight 109 is fixed to one end of the guide hole 101b, and a stopper 110 is provided to the other end of the guide pin 10b.
8 is inserted so that it can move back and forth. In addition, the guide pin 108
Between the stopper 110 and the outer peripheral surface of the cam shaft 101,
A return spring 111 for the weight is provided which constantly biases the weight 109 in the axial direction of the cam shaft 101.

When the engine is stopped, the return spring 111 draws the weight 109 toward the axial direction of the cam shaft 101 and slides the sleeve 102 toward the cam 103 against the urging force of the return spring 105. It has a necessary and sufficient spring constant.

Next, the operation of the conventional example having the above structure will be described. When the engine is stopped, the weight 109 receives the urging force of the return spring 111 and is pulled toward the axial center of the cam shaft 101, and the weight 109 is tapered.
The sleeve 102 is slidably brought into contact with the cam shaft 10
It is moved in the direction of the first cam 103 against the biasing force of the return spring 105. In this state, the tappet 104 rides on the outer peripheral portion of the sleeve 102 having an outer diameter slightly larger than the base circle 103a of the cam 103, and the valve is always in a half-open state.

When the cranking is performed manually or by a starter motor, the compression pressure is reduced because the valve is in the half-opened state as described above, and in the case of manual cranking, not only the burden on the operator is reduced, The strength design of the recoil starter becomes easy. When a starter motor is used, the load on the starter motor is reduced, and the capacity can be reduced and the shape can be reduced.

When the engine starts and the number of revolutions thereof gradually increases, the centrifugal force acting on the weight 109 gradually increases, and the weight 109 resists the biasing force of the return spring 111 for the weight. Try to move in the radial direction. Weight 10
As 9 moves outward while slidingly contacting the taper guide surface 102 a, the sleeve 102 receives the biasing force of the return spring 105 and slides on the cam shaft in the direction away from the cam 103. By the movement of the sleeve 102 on the cam shaft, the end surface on the cam side is separated from the tappet 104, and the decompression action is automatically released.

Since the weight 109 linearly moves in the radial direction, a large centrifugal force can be obtained and the response is good. Further, since the sleeve 102 slides on the cam shaft 101 in the axial direction, the sleeve 102 is not easily affected by the viscosity of the lubricating oil and the operation is smooth. Since the cam shaft 101 is simply provided with the guide hole 101b through which the guide pin 108 to which the weight 109 is fixed is inserted, the processing is easy. Further, since the sleeve 102 and the flange 107 are also simple in shape, they can be easily manufactured.

[0011]

However, the above-mentioned prior invention has the following problems. That is, the cam 10
3 and a drive gear (not shown) are integrally formed
Since the decompression device is attached to the camcorder 1 later, the camshaft 101 becomes larger by the amount of the decompression device and the weight 1
In order to return 09, it is necessary to return the sleeve return spring 105 while compressing it by the urging force of the weight return spring 111, and the weight 109 has a guide pin 108 fixed thereto. Therefore, even if the weight 109 is a sphere as shown in the figure, it cannot move as a rolling element such as a ball used for a ball bearing, and the apparatus as a whole is complicated and the production cost becomes high.

An object of the present invention is to provide an engine decompression device which has a simple structure, a low production cost, a smooth operation, and a small size which can be assembled to the cam shaft without enlarging the cam shaft. is there.

[0013]

In the decompression device for an engine of the present invention, a gear 1 or a sprocket for driving a cam shaft and a cam 4 for controlling opening / closing of an intake / exhaust valve via a tappet 3 are coaxially arranged. In an engine having the camshaft 5 described above, a movable body 8 having an arm that abuts against the tappet and movable in the axial direction on the camshaft, and a return spring 9 that applies an axial biasing force to the movable body. It is characterized in that it has a ball 6 which is formed between the gear and the movable body and which is housed in a gap which is close to the outer periphery as it reaches the outer periphery and is rollable in the radial direction.

[0014]

Next, the operation of the above configuration will be described with reference to the same reference numerals. During cranking when starting the engine, the moving body 8 is pressed against the side surface of the gear 1 by the urging force of the return spring 9 to roll and hold the ball 6 in the axial direction of the cam shaft 5, and at the same time, the moving body 8 Part of the tappet 3 is brought into contact with the sliding contact surface of the tappet 3 to push up the tappet 3,
The intake / exhaust valve is forcibly and half-opened from the valve seat to reduce the compression pressure during cranking and enable easy operation. When the engine is started, the centrifugal force acting on the ball 6 increases as the rotation increases, and exceeds the urging force of the return spring 9. For this reason, the ball 6 rolls in the accommodated gap toward the outer side in the radial direction, moves the moving body 8, and disengages from the tappet 3 a part of the moving body that was in contact with the sliding contact surface of the tappet 3. Let The tappet 3 is pushed down by the biasing force of the spring on the valve side, the tappet 3 and the cam 4 maintain a normal contact state, and the decompression function is automatically released.

[0015]

1 is a vertical sectional view of an engine decompression device according to a first embodiment of the present invention. The configuration will be described with reference to the drawings. In FIG. 1, 1 is a gear, 2 is a drive shaft, 3 is a tappet, 4 is a cam, 5 is a cam shaft, 6 is a ball, 7 is a tapered surface of a moving body, 8 is a moving body, and 9 is a return for a moving body. A spring, 10 are holes formed in the cam, 11 is a protrusion provided on the arm 8a of the moving body 8, and 100 is the decompression device of the first embodiment.

A gear 1 or a sprocket to which power is transmitted from a crankshaft gear (not shown) is formed integrally with the drive shaft 2 by cold forging. The cam 4, which operates the intake and exhaust valves via the tappet 3, is a member separate from the drive shaft 2 and is driven by a fixing means such as press fitting or spline coupling after completion of axial positioning with respect to the drive shaft 2. It is fixed to the shaft 2 so that it cannot rotate. It should be noted that a hole 10 penetrating the cam 4 in parallel with the axis of the cam 4 is provided at a location symmetrical to the highest convex portion of the cam lift.
Alternatively, a groove is provided.

A movable body 8 is mounted on the drive shaft 2 between an integrally formed gear 1 and a cam 4 which is a separate member. The moving body 8
Has a funnel-shaped space portion having a tapered inner surface 7 at the portion in contact with the cam-side side surface of the gear 1 so that the clearance becomes narrower from the fitting portion to the outer peripheral portion. An arm 8a is formed so as to penetrate through the hole 10 formed in the hole 4, and a projection 11 is provided at the tip of the arm 8a. The projection 11 is formed so that the position of the projecting end thereof is slightly outside the outer peripheral surface of the basic circle of the cam 4. A return spring 9 that constantly biases the moving body 8 from the cam 4 toward the gear 1 is provided outside the body of the moving body 8.

The gear-side funnel-shaped portion of the moving body 8 and the gear 1
Inside the gap formed by the side surface on the cam side and becoming narrower toward the outer peripheral portion, when the engine is operating, it rolls radially outward due to the action of centrifugal force and resists the biasing force of the return spring 9. A ball 6 for moving the moving body 8 to the cam side is stored.

Next, the operation of the first embodiment having the above construction will be described. When the engine is stopped, the moving body 8
Is in a state of being pressed from the cam 4 toward the side surface of the gear 1 by the urging force of the return spring 9, so that the arm 8a of the moving body 8 is drawn into the inside of the hole 10 formed in the cam 4 and formed at the tip. The protruding end of the projection 11 is brought into contact with the sliding contact surface of the tappet 3 with the cam 4 to push up the tappet 3. Therefore, when cranking manually or with a starter motor, the valve does not come into close contact with the valve seat even when the valve is closed, and the valve is held in a half-opened state, and the compression pressure is reduced by gas leakage from the valve seat. To do. Therefore, the manual cranking reduces the labor of the operator, and the load applied when the recoil starter or the starter motor is used is reduced, and the size and the capacity can be reduced.

When the engine is started and the number of revolutions increases, the centrifugal force acting on the balls 6 housed in the gap formed between the side surface of the gear 1 and the funnel-shaped end of the moving body 8. Is gradually increased, and the urging force of the return spring 9 that presses the moving body 8 against the side surface of the gear 1 is overcome. As a result, the balls 6 roll outward in the radial direction by the centrifugal force in the accommodated gap, and move the moving body 8 to the cam 4 side while resisting the urging force of the return spring 9. The arm 8a of the above is removed from the hole 10 formed in the cam, and the projection 11 at the tip end is disengaged from the sliding contact surface of the tappet 3 which is in contact therewith. The tappet 3 is pushed down from the valve side, the sliding contact surface and the outer peripheral surface of the cam 4 continue to maintain the contact state, and the decompression function is automatically released.

When the engine is stopped, the balls 6 roll radially inward in the funnel-shaped space as the centrifugal force decreases, and the moving body 8 moves toward the gear 1 by the urging force of the return spring 9. When the arm 8a moves, the projection 11 at the tip of the arm 8a comes into contact with the tappet 3 and automatically returns to the half-opened decompression state of the valve seat, and can immediately respond to the cranking at the next start.

2 and 3 are a longitudinal sectional view, a perspective view of a main portion and a partial transverse sectional view of a decompression device for an engine according to a second embodiment. The gear 21 is formed integrally with the drive shaft 22 for cold forging, the cam 24 is a separate member, and after the axial positioning with respect to the drive shaft 22 is completed, the drive shaft is fixed by press fitting or spline coupling. It is fixed to 22 so as not to rotate. A ball rolling surface 27 is formed on the side surface of the gear 21 opposite to the cam 24 by an inclination from the outer peripheral portion toward the axial center portion, and the ball 26 inserted in the rolling surface 27 is a flat plate portion of the moving body 28. Held by

A hole 30 is bored in the gear 21 in parallel with the axis, an arm 28a of the moving body 28 penetrates the hole 30, and a projection 31 at its tip abuts on a sliding contact surface of the tappet 23 with the cam 24. Pushing up on the tappet 23. In the second embodiment, the moving body 28 can be easily assembled by inserting the arm 28a having the projection 31 into the larger one of the key holes 30a formed in the gear 21 and then moving the smaller one. Becomes Except for the points described here, the configuration, operation, and effect are almost the same as those in the first embodiment.

FIG. 4 shows a longitudinal sectional view of an engine decompression device according to the third embodiment, and FIG. 5 shows an exploded perspective view of essential parts in FIG. In the cam shaft 35, the gear 31 is integrally formed with the drive shaft 32, and the cam 34 is attached to the drive shaft separately from the drive shaft by mechanical fixing means. The protrusion 41, to which the protrusion arm 41a that contacts the sliding contact surface of the tappet 33 is adhered, is formed separately from the moving body 38, and the arm portion 4 is formed.
1a penetrates the T groove 40 formed in the cam, and the fork part 41b constitutes the decompression device in a state of straddling the drive shaft 32.

The tip of the protruding arm 41a is the tappet 33.
Of the return spring 39 due to rolling of the balls 36 radially outward due to centrifugal force.
The movement and the movement of the moving body 38 and the projection body 41 against the urging force of the arm 41a cause the projection at the tip of the arm 41a to separate from the tappet and automatically release the decompression.
Is the same as.

[0026]

The engine decompression device according to the present invention has the following effects. It is possible to obtain a decompression device having a simple structure, low production cost, smooth operation, small size, and capable of being assembled to the cam shaft without increasing the size of the cam shaft. By mounting this decompression device, a manual cranking engine can reduce the labor of the operator and suppress the design strength of the recoil starter to a low level. If the engine is cranked by the starter motor, the load on the starter motor can be reduced, and the size and capacity of the starter motor can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view (a) and an exploded perspective view of essential parts of a decompression device for an engine according to a first embodiment of the present invention (b).

FIG. 2 is a schematic longitudinal sectional view (a) and an exploded perspective view (b) of essential parts of a decompression device for an engine according to a second embodiment of the present invention.

3 is a partial cross-sectional view taken along the arrow III in FIG.

FIG. 4 is a schematic vertical sectional view of a decompression device for an engine according to a third embodiment of the present invention.

5 is an exploded perspective view of a main part in FIG.

FIG. 6 is a vertical cross-sectional view of a conventional engine decompression device.

FIG. 7 is a cross-sectional view of the main part in FIG.

[Explanation of symbols]

1 ... Gear, 2 ... Drive shaft, 3 ... Tappet, 4 ... Cam, 5 ...
Cam shaft, 6 ... Ball, 7 ... Tapered surface, 8 ... Moving body, 9 ...
Return spring, 10 ... Hole, 111 ... Decompression device.

Claims (1)

[Claims] 1. A camshaft (5) in which a gear (1) or sprocket for driving a camshaft and a cam (4) for controlling opening and closing of an intake / exhaust valve via a tappet (3) are coaxially arranged. In the engine having, a movable body (8) having an arm that abuts against the tappet and movable in the axial direction on the cam shaft, and a return spring (9) that applies an axial biasing force to the movable body. And a ball (6) which is formed between the gear and the moving body and which is housed in a gap that is close to the outer circumference and is rollable in the radial direction. A decompression device for an engine, wherein the valve is controlled to be in a half-open state, and when the engine starts, the intake / exhaust valve is automatically released from the half-open state as the engine speed increases.