JP2003013719A - Decompression device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decompression device capable of reducing the number of part items and facilitating an assembly. SOLUTION: This decompression device has a cam surface operated by the rotation of the camshaft of a valve gear mechanism and retractable relative to the peripheral surface of an intake valve side cam so as to slightly open an intake valve at the time of starting of an internal combustion engine. The device comprises a shaft part extending in the longitudinal direction of the camshaft and having a tip part with the cam surface positioned at the peripheral edge part of the intake valve side cam, a weight part disposed around the camshaft and swung about the shaft part by a centrifugal force caused by the rotation of the camshaft, and a clamp energizing the shaft part so that the cam surface of the shaft part is positioned at a projected position projected from the peripheral surface of the intake valve side cam and holding the shaft part on the camshaft. The shaft part is rotated by the swing of the weight part to recessedly move the cam surface from the peripheral surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a decompression device provided in an internal combustion engine that is started by a recoil starter, and more specifically, in order to facilitate starting by the recoil starter, an intake valve is Decompression device for slightly opening.

2. Description of the Related Art An internal combustion engine started by a recoil starter may be provided with a decompression device in order to reduce a rope pulling force. Pulling the recoil starter rope rotates the crankshaft of the internal combustion engine, which causes the piston to move towards top dead center and, in the absence of the decompression device, the air-fuel mixture in the combustion chamber. The compression resistance increases as it is compressed.
At the time of starting the internal combustion engine, if there is a decompression device, the intake valve is slightly opened and the compression resistance is weakened, whereby starting can be performed with a small force.

A conventional decompression device is disclosed in, for example, Japanese Utility Model Publication No. 53-20593. This decompression device includes a gear provided coaxially with a cam shaft of a valve mechanism, a weight pivotally supported by the gear by a pin so as to swing along a side surface thereof, and an elastic force applied to the weight. And a release pin having a cam surface that is held between a clamp claw formed on the weight and that is projected and retracted with respect to the peripheral surface of the intake valve side cam of the valve mechanism.

[0003]

DISCLOSURE OF THE INVENTION The decompression device is
It has pins, weights, torsion springs, and release pins, has a large number of parts, and is complicated to assemble. Therefore,
An object of the present invention is to provide a decompression device having a small number of parts and easy to assemble.

[0004]

The above object of the present invention is to operate by the rotation of the cam shaft of the valve mechanism and to slightly open the intake valve during the starting operation of the internal combustion engine so that the peripheral surface of the intake valve side cam is opened. A decompression device having a cam surface protruding and retracting with respect to, a shaft portion extending in the longitudinal direction of the cam shaft and having a tip portion having the cam surface positioned at a peripheral portion of the intake valve side cam; A weight portion arranged around the cam shaft and swinging about the shaft portion by a centrifugal force generated by rotation of the cam shaft, and the cam surface of the shaft portion protruding from the peripheral surface of the intake valve side cam. And a fastener for holding the shaft portion with respect to the cam shaft, and swinging the weight portion by centrifugal force after the internal combustion engine is started. The shaft rotates,
This can be achieved by a decompression device characterized in that the cam surface is retracted from the peripheral surface.

To assemble the decompression device according to the present invention to the internal combustion engine, the shaft portion is arranged in the longitudinal direction of the cam shaft, and the tip end portion having the cam surface is the peripheral edge portion of the intake valve side cam. Positioned on the
All that is required is to hold the shaft against the camshaft.

The decompression device according to the present invention operates as follows. In the stopped state of the internal combustion engine, the cam surface is urged by the fastener, and thus is in the protruding position. When the recoil starter of the internal combustion engine is pulled, a crankshaft (not shown) rotates, which causes the camshaft to start rotating. When the internal combustion engine is started, that is, while the rotation speed of the cam shaft is slow, the cam surface is in the protruding position, the tappet of the valve mechanism is pushed up to slightly open the intake valve, and the combustion chamber is halved. Put in a compressed state. Therefore, the recoil starter can be pulled with a small force. When the rotation speed of the cam shaft increases, the weight portion swings due to a centrifugal force that is larger than the urging force of the fastener, and the shaft portion also rotates accordingly, and the cam surface rotates around the circumference of the cam. Evacuate automatically from the surface.

According to the decompression device of the present invention, the number of parts is small, and the assembly is completed only by holding the shaft portion with respect to the cam shaft by the fastener, so that the assembly is easy. And it is also advantageous in terms of cost.

[0008]

DETAILED DESCRIPTION OF THE INVENTION Referring to the accompanying drawings,
An embodiment of the decompression device according to the present invention will be described. FIG. 1 is a vertical cross-sectional view of an OHC type 4-cycle engine including a decompression device according to an embodiment of the present invention, and particularly shows a valve mechanism and a cylinder portion. Also,
FIG. 2 is a cross-sectional view taken along the line II-II shown in FIG. Of these, FIG. 2A shows the protruding position of the cam surface provided on the shaft portion of the swinging member, and FIG. 2B shows the retracted position.

Referring to FIG. 1, an OH as an internal combustion engine
The structure of the C-type four-cycle engine 2 will be briefly described. The four-cycle engine 2 has a piston 6 that moves up and down in a cylinder 4, and when the piston 6 moves up, air in the combustion chamber 8 is increased. The fuel mixture is compressed. The four-cycle engine 2 has a valve operating chamber 10 in the upper part, and a valve operating mechanism 12 is provided inside the valve operating chamber 10. The valve mechanism 12 includes a cam shaft 14 that is rotationally driven by the engine 2 via a transmission unit 40 that uses a timing belt, and an intake valve side cam 16 and an exhaust valve side cam that are rotated by the cam shaft 14. 18, an intake valve-side cam 16 and an exhaust valve-side cam 18, respectively, are oscillated and an intake valve (only the upper end of the valve stem is shown for simplification of the drawing) 15 and an exhaust valve (not shown). It has an intake valve side rocker arm 20 and an exhaust valve side rocker arm 22 that open and close.

The engine 2 has a dencomp device 30 according to the present embodiment inside the valve operating chamber 10.
The dencomp device 30 is operated by the rotation of the cam shaft 14 of the valve mechanism 12 and is attached to the peripheral surface 16a of the intake valve side cam 16 so as to slightly open the intake valve when the engine 2 is started. It has a cam surface 32a that projects in and out (see FIG. 2). More specifically, the dencomp device 30 includes a decompression body 34 provided adjacent to the intake valve side cam 16 and coaxial with the cam shaft 14, and a swing member 36 supported by the decompression body 34.
And a holding member 38 as a fastener for attaching the swinging member 36 to the cam shaft 14 and the decompression body 34.

FIG. 3 is a perspective view showing the entire swing member 36. As can be seen from FIGS. 1 and 3, the swinging member 36 extends in the longitudinal direction of the cam shaft 14 and has a tip portion having the cam surface 32 a at the peripheral portion of the intake valve side cam 16. A shaft portion 32 that is positioned and a weight portion 35 that is arranged around the cam shaft 14 and that is swung about the shaft portion 32 as a pivot by a centrifugal force generated by the rotation of the cam shaft 14 are integrally provided. . The weight portion 35
Has a substantially C-shape that surrounds the cam shaft 14.

On the side surface of the decompression body 34 opposite to the intake valve side cam 16, a concave portion for receiving the weight portion 35 of the rocking member 36 so as to be rockable in the radial direction of the decompression body 34. 34a is formed.
The inner peripheral surface of the concave portion 34a constitutes a swing restricting means for restricting the swinging range of the weight portion 35 outward in the radial direction.
The weight portion 35 swings radially outward until it comes into contact with the inner peripheral surface of the recess 34a, and further swinging is restricted by the inner peripheral surface. When the weight portion 35 is located at a position where further swinging is restricted by the inner peripheral surface, the cam surface 32a is retracted from the peripheral surface 16a of the intake valve side cam 16 to a retracted position D (FIG. 2). (B)). Since the weight portion 35 is restricted from swinging outward in the radial direction by a predetermined amount or more by the inner peripheral surface, the cam surface 32a is maintained at the retracted position D during the operation of the engine 2. A through hole 34b extending in the longitudinal direction of the cam shaft 14 is formed in the decompression body 34, and the shaft portion 32 of the swinging member 36 has the intake valve side cam through the through hole 34b. It extends to the periphery of 16. In addition, a concave portion 16b that receives a tip end portion of the shaft portion 32 is provided in the peripheral portion of the intake valve side cam 16.
Are formed.

FIG. 4 is a sectional view taken along the line IV-IV shown in FIG. Of these, FIG. 4A shows the swing member 3
6, the shaft portion 32 and the holding member 38 when the cam surface 32a provided on the shaft portion 32 is in the protruding position (U).
4 (b) shows the positional relationship with the rocking member 36.
The cam surface 32a provided on the shaft portion 32 of the
4 shows the positional relationship between the shaft portion 32 and the holding member 38 in the state of FIG. Details of the sandwiching member 38 will be described with reference to FIG. The holding member 38 is the swing member 36.
The protruding position U where the cam surface 32a of the shaft portion 32 protrudes from the peripheral surface 16a of the intake valve side cam 16 (see FIG. 2).
The shaft portion 32 is biased so as to be positioned at (a) and the shaft portion 32 is positioned and held with respect to the cam shaft 14.

The holding member 38 extends in a direction crossing the shaft portion 32 and the cam shaft 14 of the swing member 36, and holds the shaft portion 32 and the cam shaft 14. More specifically, the holding member 38 has a substantially U-shape that is laterally oriented, and is specifically a hairpin snap pin made of a spring steel wire.

As can be seen with reference to FIGS. 1 and 3,
Of the pair of holding portions of the holding member 38 that extends straight in the lateral direction with respect to the longitudinal direction, the cam shaft 14 includes:
A hole 14a is formed as an insertion portion into which the cam shaft side holding portion 38a can be inserted. The hole 14a is a through hole that extends straight in the radial direction of the cam shaft 14. Also,
As can be seen from FIG. 2, the shaft portion 32 of the swinging member 36 is provided with a groove portion 32b that extends laterally with respect to the longitudinal direction and that receives the shaft portion side holding portion 38b of the holding member 38. Has been formed. The width dimension of the groove portion 32b is substantially equal to the width dimension of the shaft portion side holding portion 38b. Figure 2
As can be seen from FIG. 3 and FIG. 3, the bottom surface of the groove portion 32b forms an engagement surface 32c that engages with the holding member 38,
It is substantially flat.

The holding member 38 has a curved portion 38c which is curved at the base end, and the cam shaft side holding portion 38a and the shaft portion side holding portion 38b extend from the bending portion 38c. The cam shaft side holding portion 38a extends straightly as a whole. Further, the shaft-side holding portion 38b has a curved shape along the peripheral surface of the decompression body 34, and the tip end portion thereof moves away from the camshaft-side holding portion 38a so as to be separated therefrom. It is bent.

As described above, and as shown in FIG. 4, the engaging surface 32c of the shaft portion 32 that engages with the holding member 38 is substantially flat, and the engaging surface 32c is It is biased by the shaft-side holding portion 38b of the holding portion. As a result, the cam surface 32a formed at the tip of the shaft portion 32 is positioned at the protruding position U protruding from the peripheral surface 16a of the intake valve side cam 16 so that the shaft portion 32 can be positioned at the protruding position U. Positioning in the rotational direction with respect to the cam shaft 14 is performed. This position is shown in FIG. Further, the positional relationship between the holding member 38 and the swinging member 36 will be described with reference to FIG.
Are arranged so as to swing in a direction away from the curved portion 38c of the holding member 38.

Assembly of the dencomp device 30 according to the present embodiment is performed as follows. Decompression body 3
4 is attached to the cam shaft 14 adjacent to the intake valve side cam 16. The shaft portion 32 of the swing member 36 is inserted into the through hole 34b of the decompression body 34, and the recess 1 formed in the peripheral portion of the intake valve side cam 16 is formed.
The tip portion of the shaft portion 32 is inserted into 6b. The holding member 38 is moved laterally with respect to the longitudinal direction of the cam shaft 14 to move the shaft portion 32 into the cam shaft 14.
Hold against. More specifically, the cam shaft side holding portion 38a of the holding member 38 is inserted into the hole 14a formed in the cam shaft 14 and the decompression body 34, and the shaft portion side holding portion 38b is inserted. The assembly is completed by fitting the groove portions 32b formed in the shaft portion 32 and sandwiching them. Thereby, the shaft portion 32
Is positioned with respect to the longitudinal direction of the cam shaft 14,
And fixed.

Next, the dencomp device 30 according to the present embodiment operates as follows. In the stopped state before the engine 2 is started, the groove portion 3 of the shaft portion 32 is
The flat bottom surface 32c of 2b is biased by the holding member 38 to be positioned at the initial position shown in FIG. 4 (a). At this position, the cam surface 32a provided at the tip of the shaft portion 32 is located at the protruding position U protruding from the peripheral surface 16a of the intake valve side cam 16 as shown in FIG. is there.

When an operator pulls the recoil starter of the engine 2, a crank shaft (not shown) rotates,
The cam shaft 14 starts to rotate via the transmission means 40. When the engine 2 is started, that is, while the rotation speed of the cam shaft 14 is low, the cam surface 32a is kept in the position shown in FIG.
At the protruding position U shown in (a), the intake valve side rocker arm 20 is pushed up to slightly open the intake valve 15 to bring the inside of the combustion chamber 8 into a semi-compressed state. Therefore, the recoil starter can be pulled with a small force.

When the rotation speed of the cam shaft 14 increases,
As shown in FIG. 4B, the weight portion 35 swings due to centrifugal force. As a result, the shaft portion 32 rotates, and the bottom surface 32c of the groove portion 32b rotates in the direction R toward the curved portion 38c of the holding member 38. As a result, the shaft-side holding portion 38b is moved to the curved portion 3
Since the part far from 8c is pushed, the pair of holding parts 3
8a, 38b can be easily and surely spread. When the weight portion 35 comes into contact with the inner peripheral surface of the concave portion 34a of the decompression body 34 after swinging by a predetermined angle θ, and the rotation speed of the cam shaft 14 further increases,
No more rocking. At this time, the shaft portion 32 also rotates, and the cam surface 32a retracts from the peripheral surface 16a of the intake valve side cam 16. This state is shown in FIG. During operation of the engine 2, the cam surface 32a is held at the retracted position D.

When the engine 2 is stopped, the rotation speed of the cam shaft 14 becomes slower, and thereby the centrifugal force acting on the weight portion 35 becomes smaller, and the swinging member 3 becomes smaller.
FIG. 6A is a view from the position shown in FIG. 4B due to the urging force of the holding member 38 with respect to the engagement surface 32c.
Return to the position shown in. Accordingly, the cam surface 32a
2A from the retracted position D shown in FIG. 2B.
Return to the protruding position U shown in.

Dencomp device 30 according to the present embodiment
According to the above, by the sandwiching member 38 extending in the direction crossing the shaft portion 32 and the cam shaft 14, the shaft portion 32 is provided.
Since the cam shaft 14 is sandwiched and the swing member 36 is held with respect to the cam shaft 14, the assembling is easy. Further, the cam shaft 14 has
A hole 14a into which the cam shaft side holding portion 38a of the holding member 38 can be inserted is formed, and the shaft portion 32 is formed with a groove portion 32b that receives the shaft portion side holding portion 38b. Therefore, the swing member 36 can be positioned and fixed to the cam shaft 14 in the longitudinal direction.

Further, the engaging surface 32c of the shaft portion 32 which engages with the holding member 38 is substantially flat, and the engaging surface 32c is elastically pressed by the fastener 38. Therefore, the shaft portion 32 has a simple structure.
Can be positioned in the direction of rotation. Furthermore, since the engagement surface 32c of the shaft portion 32 rotates in the direction R toward the curved portion 38c of the U-shaped holding member 38 that is the fastener, of the shaft side holding portion 38b.
Since it is configured to push a portion far from the curved portion 38c, the U-shaped holding member 38 can be pressed with a smaller force.
Can be surely spread.

The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention. It goes without saying that it is one. For example, although the holding member 38 is used as the fastener in the present invention, in the fastener, the cam surface 32a of the shaft portion 32 projects from the peripheral surface 16a of the intake valve side cam 16. Any means for urging the shaft portion 32 toward the protruding position U and holding the shaft portion 32 with respect to the cam shaft 14 may be used. Therefore, for example, it may be configured by one elastic member that extends laterally with respect to the shaft portion 32 and biases the shaft portion 32 with respect to the cam shaft 14.

Further, the holding member 38 has the shaft portion 32.
It may be any holding member that holds the camshaft 14 and does not have to be U-shaped. Further, in the illustrated embodiment, the engaging surface 32c of the shaft portion 32 of the rocking member 36 with which the holding member 38 engages is formed in the groove portion 32b. In order to position the shaft portion 32 in the longitudinal direction, it is desirable that the groove portion 32b is formed, but the groove portion 32b is not essential, and only by forming the peripheral surface of the shaft portion 32 flat. Good.

According to the present invention, it is possible to provide a decompression device having a small number of parts and easy to assemble.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an OHC type four-cycle engine as an internal combustion engine including a decompression device according to an embodiment of the present invention, and particularly shows a valve mechanism and a cylinder portion.

FIG. 2 is a sectional view taken along the line II-II shown in FIG. Of these, FIG. 2A shows the protruding position of the cam surface provided on the shaft portion of the swinging member, and FIG. 2B shows the retracted position.

FIG. 3 is a perspective view showing an entire swing member.

4 is a cross-sectional view taken along the line IV-IV shown in FIG.
4A shows the positional relationship between the shaft portion and the sandwiching member when the cam surface provided on the shaft portion of the swinging member is in the protruding position, and FIG. 4B shows the swinging movement. 7 shows the positional relationship between the shaft portion and the sandwiching member when the cam surface provided on the shaft portion of the member is in the retracted position.

[Explanation of symbols]

2 Internal combustion engine 12 Valve mechanism 14 Cam shaft 14a Insertion part (hole) 15 Intake valve (upper end of valve stem) 16 Intake valve side cam 16a circumference 32 shaft 32a cam surface 32b groove 32c engagement surface 30 Dencomp equipment 35 Weight part 38 Fasteners (clamping member / elastic member) 38a One clamping part (camshaft side clamping part) 38b The other holding portion (shaft side holding portion) 38c curved part U protruding position R-axis rotation direction

Continued front page    F-term (reference) 3G016 AA19 BA27 BA34 BA36 BA40                       CA04 CA06 CA08 CA10 DA01                       GA01                 3G018 AB05 AB16 BA04 BA06 BA07                       CA08 DA03 DA04 DA32 FA06                       FA17 GA14

Claims (5)

[Claims] 1. The intake valve side cam (1) is operated by the rotation of a cam shaft (14) of a valve mechanism (12) so that the intake valve (15) is slightly opened when the internal combustion engine (2) is started.
Cam surface (32
a) in which the front end portion extending in the longitudinal direction of the cam shaft (14) and having the cam surface (32a) is the intake valve side cam (1).
6) The shaft portion (32) positioned at the peripheral edge portion and the shaft portion (32) swinging around the cam shaft (14) by the centrifugal force generated by the rotation of the cam shaft (14). The moving weight portion (35) and the cam surface (32a) of the shaft portion (32) are located at a protruding position (U) protruding from the peripheral surface (16a) of the intake valve side cam (16). A fastener (38) for urging the shaft portion (32) against the cam shaft (14).
The shaft portion (32) is rotated by the swinging of the weight portion (35) by the centrifugal force after the internal combustion engine (2) is started, and the cam surface (32a) is retracted from the peripheral surface (16a). A decompression device characterized in that. 2. The clamp which extends in a direction traversing the shaft portion (32) and the cam shaft (14) and elastically clamps the shaft portion (32) and the cam shaft (14). Decompression device according to claim 1, characterized in that it is a member (38). 3. The cam shaft (14) has an insertion portion (14a) extending laterally with respect to the longitudinal direction, into which one holding portion (38a) of the holding member (38) can be inserted. ,
Further, the shaft portion (32) has the other holding portion (38) of the holding member (38) extending laterally with respect to the longitudinal direction.
Decompression device according to claim 2, characterized in that a groove (32b) is formed for receiving b). 4. The engagement surface (32c) of the shaft portion (32) which engages with the holding member (38) is substantially flat.
In the rotational direction of the shaft portion (32), the engagement surface (32c) is elastically pressed by the fastener (38) so that the cam surface (32a) is located at the protruding position (U). 3. Positioning is performed.
Or the decompression device according to any one of 3 above. 5. The fastener comprises a substantially U-shaped elastic member (38) for holding the shaft portion (32) with respect to the cam shaft (14), and at the protruding position (U). The engaging surface (32c) of the shank (32) engaging the U-shaped elastic member (38) is substantially flat, the engaging surface (32c) being defined by the fastener (38). The shaft portion (32) is elastically pressed, and the weight portion (35) is swung by a centrifugal force.
Has the engagement surface (32c) of the U-shaped elastic member (3
The decompression device according to any one of claims 1 to 4, wherein the decompression device rotates in a direction (R) toward the curved portion (38c) of 8).