JPH06248910A - Valve system cam shaft provided with decompression device for engine - Google Patents

Abstract

PURPOSE:To ensure decomp. operation and decomp. releasing operation even when this valve system cam shaft is used in an engine of such specification as a gap between a centrifugal weight and an exhaust valve-cam is dimensionally increased, by rotationally interlocking a decomp. pin with the centrifugal weight so as to perform decomp. operation and decomp. releasing operation. CONSTITUTION:A shaft part 1, cam parts 2, 25, and a cam gear part 3 are integrally formed by synthetic resin into a valve system-cam shaft body 23. A centrifugal weight 8 is accomodated in a recessed part 6 provided on the end face 5 on the opposite side to the cam parts of the cam bear part 3. A decomp. pin 42 is rotationally passed through the cam gear part 3 in parallel with the shaft part 1, and its base end is connected to the centrifugal weight 8. When the centrifugal weight 8 is in decomp. position 36, a decomp. surface 39 abuts against the underside of an exhaust valve--tappet 31, and when the centrifugal weight 8 is in decomp. releasing position 38, the decomp. pin 42 is rotationally interlocked with the centrifugal weight 8 so that a decomp. releasing surface 40 faces to the underside of the exhaust valve-tappet 31.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine valve camshaft with a decompression device, and more particularly to a synthetic resin integrated valve camshaft body incorporating a decompression device.

[0002]

2. Description of the Related Art As a conventional valve camshaft for an engine, there is one shown in FIG. This prior art 1 is a so-called synthetic resin integrated valve camshaft, which is made of synthetic resin to form a shaft portion 101.
The cam portions 102 and 125 and the cam gear portion 103 are integrally formed. On the other hand, there is a conventional valve camshaft with a decompression device shown in FIG. This prior art 2
Of the both end surfaces 104 and 105 of the cam gear 103,
A concave portion 106 is formed on the cam portion side end surface 104, and a decompression centrifugal weight 108 pivotally supported by a pivot shaft 107 in the concave portion 106 and a swing end portion 10 of the centrifugal weight 108.
9 and the decompression spring 1 installed between the spring locking portion 110
11 and 11 are accommodated.

The valve camshaft main body 123 of the valve camshaft with decompression device shown in FIG. 5 includes a metal shaft portion 101 integrally formed with cam portions 102 and 125 and a metal cam gear portion 103. The cam gear portion 103 is formed separately, and the cam gear portion 103 is fitted and fixed to the shaft portion 101.

[0004]

Prior to the present invention, the inventor of the present invention has shown that the cam gear portion 103 of the valve housing cam shaft of the synthetic resin integrated type of the prior art 1 shown in FIG. In the same way, we considered incorporating a decompression device. That is, the cam portion side end surface 1 of the cam gear portion 103 shown in FIG.
04 is provided with a recessed portion 106 shown in FIG.
It was considered to accommodate 08 and the decompression spring 111. However, in the case of the synthetic resin integrated valve camshaft shown in FIG.
Due to a problem in molding, the recessed portion 10 is formed in the end surface 104 on the cam portion side.
6 cannot be formed.

That is, in the case of molding the synthetic resin integrated valve camshaft shown in FIG. 4, the cam portion side end surface 104 of the cam gear portion 103 and the shaft portion 101 and the cam portion 10 on the side thereof.
Cam part side forming mold 150 for molding 2.125, anti-cam part side forming face for molding the cam part side end face 105 opposite to the cam part side end face 104 and the shaft part 101 on the side thereof. 151, a tooth portion forming mold 152 for forming the tooth portion 119 of the cam gear portion 103 is used.

Then, the non-cam portion side forming die 151 and the tooth portion forming die 152 are provided with the shaft portion 1 as indicated by arrows 153 and 154.
01, it is possible to perform die cutting in a direction parallel to 01.
Due to the bulging of 02, it is not possible to perform die cutting in a direction parallel to the shaft portion 101. Therefore, the cam part side forming die 150 is divided into two halves, and each of the halves 155.
155 needs to be die-cut in the radial direction of the shaft portion 101 as indicated by arrows 156 and 157. Therefore, the cam gear unit 1
The cam portion side end surface 104 of No. 03 has a shaft portion 10 as shown in FIG.
It is not possible to form the recessed portion 106 that is recessed in the direction parallel to 1.

Therefore, first, as shown in FIG.
As a first prototype, a prototype in which a centrifugal weight 108 and a decompression spring were attached to the cam portion side end surface 104 of the cam gear portion 103 of the valve housing cam shaft of the synthetic resin integrated type shown in FIG. However, in this case, the centrifugal weight 108 and the decompression spring largely project laterally from the cam portion side end surface 104, so that they may interfere with the side surface of the counterweight 121 of the crankshaft 120. For this reason, it is necessary to form the thickness-reduced portion 158 on the side surface of the counterweight 121, and to correct the imbalance of the crankshaft 120 due to this thickness-reduction, it is also necessary to scrape the thickness of the crankpin 122 side. As a result, it has been found that the work of correcting the crankshaft 120 is required and the manufacturing process of the engine becomes complicated.

Next, as shown in FIG. 6 (B), as a second prototype, the cam gear 103 is uniformly thin so that the centrifugal weight 108 and the decompression spring do not interfere with the side surface of the counterweight 121. I made a prototype. In this way, although the work of correcting the crankshaft 120 is unnecessary, the strength of the tooth portion 119 of the cam gear portion 103 is reduced as the width thereof is shortened. Therefore, it has been found that such a product cannot be used in an engine of a specification in which a heavy load is applied to the tooth portion 119.

Next, as shown in FIG. 7, as a trial manufacture example 3, a recessed portion 106 is formed on the end surface 105 of the cam gear portion 103 on the side opposite to the cam portion, and a centrifugal weight 108 is formed in the recessed portion 106.
A prototype in which the decompression spring 111 was housed was manufactured. In this way, the centrifugal weight 108 and the decompression spring 111 do not project laterally from the cam portion side end surface 104 of the cam gear portion 103, and the width of the tooth portion 119 can be maintained long, so that all the above problems are solved. We were able to.

By the way, in the preceding prototype 3, the decompression device of the prior art 2 shown in FIG. 5 is used as it is.
That is, as shown in FIG. 7 (A), a diagonal decompression pin insertion hole 141 is opened in the shaft portion 101, and the decompression pin 142 is slidably inserted therein, and as shown in FIG. When 108 is in decompression position 136,
The base end portion 143 of the decompression pin 142 contacts the decompression surface 139 of the centrifugal weight 108, and as shown in FIG. 7A, the tip end portion 145 of the decompression pin 142 has the cam surface 1 near its side.
By a predetermined size 149 more than 48, the exhaust valve tappet 131 is lifted up to be decompressed.
As shown in FIG. 7B, when the centrifugal weight 108 is in the decompression releasing posture 138, the base end portion 1 of the decompression pin 142 is shown.
43 contacts the decompression releasing surface 140 of the centrifugal weight 108,
The tip end 145 of the decompression pin 142 shown in FIG. 7 (A) disappears and the decompression is released.

When such a decompression device is used in the preceding prototype 3, the following new problem arises. That is, since the centrifugal weight 108 is arranged closer to the end surface 105 on the side opposite to the cam portion, the distance between the centrifugal weight 108 and the exhaust valve cam portion 102 increases, and the decompression pin 142 needs to be lengthened accordingly. Shaft center 147 of shaft 101
It is necessary to reduce the inclination angle θ of the decompression pin 142 with respect to. Particularly when used in an engine with a large displacement, the exhaust valve cam portion 102 needs to be arranged away from the cam gear portion 103 as the bore diameter of the cylinder increases, so that the centrifugal weight 108 and the exhaust valve cam are disposed. The distance from the portion 102 is further increased, and it is necessary to further increase the length of the decompression pin 142.
It is necessary to further reduce the inclination angle θ of 2.

Therefore, if the length of the decompression pin 142 becomes too long, the sliding resistance of the decompression pin 142 in the decompression pin insertion hole 141 increases, and there is a risk that the decompression operation and decompression release operation cannot be performed reliably. Further, since the inclination angle θ of the decompression pin 142 becomes too small, the swing end portion 10 of the centrifugal weight 108 is reduced.
9 is pushed up in the direction of the arrow 134, and this is the recess 1
There is also a possibility that the centrifugal weight 108 may jump out of the vehicle 06 and ride on the end surface 105 on the side opposite to the cam portion, and the centrifugal weight 108 may become inoperable.

An object of the present invention is to prevent a centrifugal weight or a decompression spring from protruding laterally from an end surface of a cam gear portion on the cam portion side when a centrifugal decompression device is incorporated into a resin-integrated valve camshaft body. Another object of the present invention is to provide a device that can maintain the strength of the teeth of the cam gear portion high and that can reliably perform decompression operation and decompression cancellation operation even when used in an engine with a large displacement.

[0014]

According to the present invention, as shown in FIG. 1A, a valve is formed by integrally forming a shaft portion 1, a cam portion 2, 25 and a cam gear portion 3 with a synthetic resin. The cam shaft body 23 is used.

Of the both end surfaces 4 and 5 of the cam gear portion 3, the end surface 5 on the side opposite to the cam portion side end surface 5 is
A concave portion 6 is formed which is recessed in a direction parallel to the shaft portion 1. A decompression centrifugal weight 8 pivotally supported by a pivot shaft 7 in the concave portion 6 and a swing of the centrifugal weight 8 are provided. Moving end 9 and spring locking portion 1
The decompression spring 11 installed between 0 and 0 was accommodated.

Then, the swinging posture of the centrifugal weight 8 is changed to the decompression posture 36 (FIG. 1) based on the tension 33 of the decompression spring 11.
(See (B)) and the decompression releasing posture 38 based on the centrifugal force.
(See FIG. 1 (D)), and the rotatable decompression pin 42 is passed through the cam gear 3 in the vicinity of the shaft portion 1 in a direction parallel to the shaft portion 1 and bent at the base end portion of the decompression pin 42. An engaging portion 27 that is parallel to the decompression pin 42 is provided via the portion 26, and this engaging portion 27 is engaged with the swing end portion 9 of the centrifugal weight 8, and the decompression surface 39 and the decompression surface 39 are provided on the peripheral side surface of the distal end portion of the decompression pin 42. The release surface 40 was formed.

As a result, as shown in FIG. 1B, when the centrifugal weight 8 is in the decompression posture 36, the decompression surface 39 has the exhaust valve tappet as shown in FIG. 1C. When the centrifugal weight 8 is in contact with the lower surface of the valve 31 and is in the decompression releasing posture 38 as illustrated in FIG. 1D, the decompression releasing surface 40 is in the exhaust valve as illustrated in FIG. The decompression pin 42 is rotationally interlocked with the centrifugal weight 8 so as to face the lower surface of the tappet 31 for use.

[0018]

As shown in FIGS. 1A and 1B, the centrifugal weight 8 and the decompression spring 11 are connected to the end surface 5 of the cam gear portion 3 on the side opposite to the cam portion.
Since they are accommodated in the recessed portion 6 formed in the above, there is no room for these to laterally project from the cam portion side end surface 4. Therefore, as illustrated in FIG. 3, there is no room for these to interfere with the side surface of the counterweight 21 of the crankshaft 20, and there is no need to correct the crankshaft 20 such as removing the side surface of the counterweight 21. Does not complicate the manufacturing process.

As illustrated in FIGS. 1A and 1B,
Since the centrifugal weight 8 and the decompression spring 11 are housed in the recessed portion 6 formed in the end surface 5 of the cam gear portion 3 opposite to the cam portion 3, the width of the tooth portion 19 of the cam gear portion 3 can be kept wide and its strength is high. Can be maintained. Therefore, it can be used for an engine of a specification in which a heavy load is applied to the tooth portion 19.

As illustrated in FIG. 1A, the recessed portion 6
Is formed in the end surface 5 on the side opposite to the cam portion in a direction parallel to the shaft portion 1, so that it can be used for the die-cutting work of the counter-cam portion side forming die 151 (see FIG. 4) performed in the direction parallel to the shaft portion 1. The recessed portion 6 can be easily formed without any hindrance.

As illustrated in FIG. 1, since the decompression and decompression are performed by interlocking the decompression pin 42 with the centrifugal weight 8 in rotation, the distance between the centrifugal weight 8 and the exhaust valve cam 2 is increased. Even when used in an engine, the decompression operation and the decompression cancellation operation can be reliably performed. Further, the swinging end portion 9 of the centrifugal weight 8 does not ride on the end surface 5 on the side opposite to the cam portion due to the push-up of the decompression pin 42.

[0022]

Embodiments of the present invention will be described with reference to the drawings.
1A and 1B are views for explaining a valve operating camshaft with a decompression device for an engine according to an embodiment of the present invention, FIG. 1A is a longitudinal side view, and FIG. 1B is a view for explaining a decompression posture of a centrifugal weight. ,
1C is a diagram illustrating the relationship between the decompression surface and the exhaust valve tappet in the state of FIG. 1B, FIG. 1D is a diagram illustrating the decompression releasing posture of the centrifugal weight, and FIG. 1] is a view for explaining the relationship between the decompression release surface and the exhaust valve tappet in the state of FIG. 1 (D). 2A and 2B are views for explaining the cam gear portion of the valve operating camshaft main body of FIG. 1, FIG. 2A is a perspective view of the spring locking portion, and FIG. 2B is a view in the direction II of FIG. 1A. FIG. 2C is a sectional view taken along the line CC of FIG.
FIG. 2D is an enlarged cross-sectional view taken along the line DD of FIG. Figure 3
FIG. 2 is a cross-sectional plan view of an engine incorporating the valve operating cam shaft with the decompression pin device of FIG. 1.

The engine shown in FIG. 3 is a forced air-cooled, vertical single-cylinder overhead valve gasoline engine.
A cylinder (not shown) and a cylinder head (not shown) are sequentially provided on the upper side of 0 (front side of the drawing), and a cooling fan (not shown) is attached to the front side of the crankcase 30. On the front side of the cooling fan, a manual recoil starter (not shown)
Is attached. In the crankcase 30, the crankshaft 20 and the valve camshaft main body 23 are installed in parallel with each other, and the crank gear 24 of the crankshaft 20 and the cam gear portion 3 of the valve camshaft main body 23 are meshed with each other. Therefore, the valve operating cam shaft main body 23 is rotationally interlocked. Figure 1
As shown in (A), an exhaust valve tappet 31 and an intake valve tappet 32 are mounted on the exhaust valve cam portion 2 and the intake valve cam portion 25 of the valve camshaft main body 23 on the upper side thereof. The intake / exhaust valve (not shown) is opened by pushing up the tappets 31/32 by the cams 2/25.

The structure of the valve operating camshaft body 23 is as follows. As shown in FIG. 1A, the valve operating cam shaft main body 23 is of a synthetic resin integrated type, and the shaft portion 1, the cam portions 2 and 25, and the cam gear portion 3 are integrally formed of phenol resin. In the valve operating cam shaft body 23, a cam gear portion 3, an exhaust valve cam portion 2, and an intake valve cam portion 25 are sequentially arranged from the left side to the right side of the shaft portion 1.

A decompression device is incorporated in the valve camshaft body 23 as follows. That is, FIG.
As shown in (A), of the opposite end surfaces 4 and 5 of the cam gear portion 3, on the end surface 5 opposite to the end portion 4 on the side opposite to the cam portion,
An annular recessed portion 6 is formed which is recessed in a direction parallel to the shaft portion 1. As shown in FIG.
The decompression centrifugal weight 8 pivotally supported by the decompression spring 8 and the decompression spring 11 installed between the rocking end 9 of the centrifugal weight 8 and the spring locking portion 10 are accommodated, and the tension 33 of the decompression spring 11 is accommodated. The centrifugal weight 8 is biased in the centripetal direction. The centrifugal weight 8 is formed in a C shape.

When no centrifugal force is generated in the centrifugal weight 8,
Alternatively, when the centrifugal force generated in the centrifugal weight 8 is small,
The centrifugal weight 8 is, as shown in FIG.
The tension 33 of 1 maintains the decompression posture 36. Further, when a large centrifugal force is generated in the centrifugal weight 8, the centrifugal weight 8 swings against the tension 33 of the decompression spring 11, and maintains the decompression releasing posture 38 as shown in FIG. . An engaging recess 35 is formed on the swinging end 9 of the centrifugal weight 8.

As shown in FIG. 1A, in the vicinity of the shaft portion 1, a rotatable decompression pin 42 is passed through the cam gear portion 3 in a direction parallel to the shaft portion 1, and a bent portion is formed at a base end portion of the decompression pin 42. An engaging portion 27 parallel to the decompression pin 42 is provided via 26, and the engaging portion 27 is engaged with the engaging recessed portion 35 of the swing end portion 9 of the centrifugal weight 8 so that the tip end portion of the decompression pin 42 is used for the exhaust valve. It is located near the cam portion 2. The cam surface 48 near the tip of the decompression pin 42 is a portion that comes into contact with the exhaust valve tappet 31 when the piston head (not shown) comes close to the top dead center of the compression process.

A decompression surface 39 and a decompression releasing surface 40 are formed on the peripheral side surface of the tip portion of the decompression pin 42.
As the decompression surface 39, the arc surface portion of the peripheral side surface of the round bar-shaped decompression pin 42 is used as it is, and the decompression release surface 40 is used.
Uses a flat surface obtained by cutting off a part of the peripheral side surface of the decompression pin 42 as it is. And FIG. 1 (B)
As shown in FIG. 1C, when the centrifugal weight 8 is in the decompression posture 36, the decompression surface 39 contacts the lower surface of the exhaust valve tappet 31 as shown in FIG. As shown in FIG. 1, when the centrifugal weight 8 is in the decompression release posture 38,
As shown in (E), the decompression pin 42 is rotationally interlocked with the centrifugal weight 8 so that the decompression releasing surface 40 faces the lower surface of the exhaust valve tappet 31.

The operation of this decompression device is as follows. That is, when the crankshaft 20 (see FIG. 3) is rotated by the recoil starter to start the engine,
The valve operating cam shaft body 23 is interlocked with the rotation, and the decompression device also starts to rotate integrally. At the initial stage of this rotation, since the rotation speed is still low, the centrifugal force generated in the centrifugal weight 8 is small, and the centrifugal force shown in FIG.
As shown in FIG.
Thus, the decompression posture 36 is maintained. In this case,
As shown in (C), since the decompression surface 39 is in contact with the lower surface of the exhaust valve tappet 31, when the piston head comes to the top dead center side of the compression process, this decompression surface 39 is exhausted. The exhaust valve tappet 31 is pushed up by contacting the lower surface of the exhaust tappet 31. Therefore, the exhaust valve opens and the pressure is released from the combustion chamber, so that the piston head easily crosses the compression top dead center, so that the engine starting operation by the recoil starter can be performed with a small force.

When the engine speed is increased, the rotation speed of the crankshaft 20 (see FIG. 3) is increased, and the rotation speed of the valve operating camshaft main body 23 is increased to a predetermined rotation speed. The centrifugal force is increased, the centrifugal weight 8 swings, and the decompression releasing posture 38 shown in FIG. In this case, as shown in FIG. 1 (E), since the decompression releasing surface 40 faces the lower surface of the exhaust valve tappet 31, the exhaust valve tappet 41 is interlocked according to the cam surface of the exhaust valve cam portion 2. The exhaust valve is normally opened and the engine starts.

The structure of the spring locking portion 10 of this decompression device is as follows. That is, as shown in FIGS. 2 (A) and 2 (D), a protrusion 13 in which the spring engaging portion 10 is raised from the inner bottom surface 12 of the recessed portion in a direction parallel to the shaft portion 1, and the protrusion 1
3 and a headed pin 14 which is inserted through 3. A step is provided on the tip end surface of the protrusion, and the stepped portion 15 of the tip end surface of the protrusion is
The head 16 of the headed pin 14 is received by, and a spring end engaging gap 18 is provided between the step-down portion 17 of the tip end surface of the protrusion and the head 16 of the headed pin 14, and the end of the decompression spring 11 is provided there. 50 is locked. Therefore, the end portion 50 does not move. In addition, the projection 13 is formed on the bottom surface 1 of the recessed portion.
Since it is raised from 2 in a direction parallel to the shaft portion 1, the non-cam portion side forming mold 151 (see FIG. 4) is formed in a direction parallel to the shaft portion 1.
It does not hinder the die cutting work. Also, FIG.
As shown in (D), the headed pin 14 has a pin portion penetrating the cam gear portion 3, and a caulking portion 57 is formed at the tip end thereof to prevent the pin from coming off.

The structure of the pivot portion of the centrifugal weight 8 of this decompression device is as follows. That is, as shown in FIG. 2 (C), the pivot 7 having a head and a step is used, and the small diameter portion 51 of the pivot 7 is passed through the cam gear portion 3 and a caulking portion 53 is formed at the tip thereof. To prevent it from slipping out. Then, the base end portion of the centrifugal weight 8 is pivotally supported by the large diameter portion 52 of the pivot shaft 7 in an externally fitted shape. The crimp portion 53 is seated on a washer 54 embedded in the cam gear portion 3.

Further, as shown in FIG. 2 (B), the end surface 4 of the cam gear portion 3 on the cam portion side extends from the seated portion of the caulking portion 57 of the headed pin 14 and the periphery thereof to the tooth portion 19, and the pivot shaft. 7, the washer 54, which is the seating portion of the caulking portion 53, and the periphery thereof to the tooth portion 19, respectively
5 ・ 56 are formed, and as shown in FIG. 2 (C) ・ (D),
The caulking portions 53 and 57 are prevented from protruding laterally from the cam portion side end surface 4. Further, as shown in FIG. 2 (B), the step drop surfaces 55, 56 are formed in the die cutting directions 156, 157 so that the die halves 155, 155 shown in FIG. It is shaped according to.

Further, as shown in FIG. 2B, the step-down surfaces 55 and 56 are formed so as to avoid a portion 58 of the tooth portion 19 of the cam gear portion 3 which meshes with the crank gear 24 when the exhaust valve is opened. However, the tooth width of this portion 58 is prevented from becoming thin. When the exhaust valve is opened, the spring force of the valve spring (not shown) against the opening of the exhaust valve (not shown) and the expansion pressure in the combustion chamber (not shown) may affect the exhaust valve, push rod (not shown), This is because a rotational reaction force is transmitted to the cam gear portion 3 via the exhaust valve tappet 31, the exhaust valve cam portion 2, and the shaft portion 1 in this order, and the load on this portion 58 increases. In addition, the arrow 6 in FIG.
Reference numeral 0 indicates the rotation direction of the crank gear 24, and arrow 61 indicates the rotation direction of the cam gear portion 3.

This valve camshaft main body 23 is resin-molded by using the cam portion side forming die 150, the anti-cam portion side forming die 151, and the tooth portion forming die 152, as in the prior art 1 shown in FIG. To do.

The contents of the embodiments of the present invention are as described above, but the present invention is not limited to the above embodiments. For example, in the above embodiment, a manual recoil starter was used as the starting assist device, but a starting motor may be used instead of this.

[Brief description of drawings]

1A and 1B are views for explaining a valve operating camshaft of an engine with a decompression device according to an embodiment of the present invention, FIG. 1A is a longitudinal side view, and FIG. 1B is a decompression posture of a centrifugal weight. Figure,
1C is a diagram illustrating the relationship between the decompression surface and the exhaust valve tappet in the state of FIG. 1B, FIG. 1D is a diagram illustrating the decompression releasing posture of the centrifugal weight, and FIG. 1] is a view for explaining the relationship between the decompression release surface and the exhaust valve tappet in the state of FIG. 1 (D).

2A and 2B are views for explaining a cam gear portion of the valve operating camshaft main body of FIG. 1, FIG. 2A is a perspective view of a spring locking portion, and FIG. 2B is a II direction arrow of FIG. 1A. 2C is a sectional view taken along the line CC of FIG. 2B, and FIG. 2D is an enlarged view taken along the line DD of FIG. 2B.

3 is a cross-sectional plan view of an engine incorporating the valve operating camshaft with the decompression device of FIG. 1. FIG.

FIG. 4 is a diagram illustrating a valve operating cam shaft according to prior art 1,
FIG. 4A is a vertical side view, and FIG. 4B is B of FIG. 4A.
FIG.

5A and 5B are views for explaining a valve operating camshaft with a decompression device according to prior art 2, FIG. 5A being a vertical side view and FIG. 5B.
FIG. 6 is a sectional view taken along line BB of FIG.

6A and 6B are explanatory views of a preceding trial manufacture example, FIG. 6A is a plan view of the preceding trial manufacture example 1, and FIG. 6B is a plan view of the preceding trial manufacture example 2.

7A and 7B are explanatory views of a preceding prototype example 3, FIG. 7A is a vertical side view, and FIG. 7B is a view in the direction of arrow B in FIG. 7A.

[Explanation of symbols]

1 ... Shaft part, 2 ... (for exhaust valve) cam part, 3 ... Cam gear part,
4 ... Cam portion side end surface, 5 ... Non-cam portion side end surface, 6 ... Recessed portion,
Reference numeral 7 ... Axis, 8 ... Centrifugal weight, 9 ... Swing end portion of 8, 10 ... Spring locking portion, 11 ... Decompression spring, 23 ... Valve camshaft body,
25 ... (for intake valve) cam part, 26 ... bent part, 27 ...
Engagement part, 31 ... Exhaust valve tappet, 33 ... 11 tension,
36 ... Decompression posture, 38 ... Decompression release posture, 39 ...
Decompression surface, 40 ... Decompression release surface, 42 ... Decompression pin.

Claims (1)

[Claims] 1. A shaft (1) and a cam (2). (2) made of synthetic resin.
5) and the cam gear portion (3) are integrally formed as a valve camshaft main body (23). Among the both end surfaces (4) and (5) of the cam gear portion (3), the cam portion side end surface (4) ) Is formed on the end surface (5) on the side opposite to the cam portion, which is recessed in a direction parallel to the shaft portion (1).
In (6), a centrifugal weight (8) for decompression pivotally supported by a pivot (7), a swing end (9) of this centrifugal weight (8), and a spring locking portion (10). The decompression spring (11) installed between the two is accommodated, and the swinging posture of the centrifugal weight (8) is adjusted by the tension of the decompression spring (11).
The decompression posture (36) based on (33) and the decompression releasing posture (38) based on centrifugal force are freely switchable, and the shaft part
In the vicinity of (1), a rotatable decompression pin (42) is passed through the cam gear part (3) in a direction parallel to the shaft part (1), and a bending part (26) is provided at the base end of the decompression pin (42). Is provided with an engaging portion (27) parallel to the decompression pin (42).
By engaging (27) with the swinging end (9) of the centrifugal weight (8) and forming a decompression surface (39) and a decompression releasing surface (40) on the peripheral side surface of the tip of the decompression pin (42). When the centrifugal weight (8) is in the decompression posture (36), the decompression surface (39) contacts the lower surface of the exhaust valve tappet (31), and the centrifugal weight (8) is in the decompression releasing posture (38). In some cases, the decompression pin (42) is configured to rotate and interlock with the centrifugal weight (8) so that the decompression release surface (40) faces the lower surface of the exhaust valve tappet (31). Valve camshaft with decompression device.