JPH11200819A - Cam shaft for valve system of ohc engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce weight of a cam shaft for a valve system, an engine noise and vibration, while securing strength of a cam driving member. SOLUTION: This cam shaft 1 for a valve system arranged in an engine main body head part of an OHC engine, and connected to a crank shaft arranged in an engine main body lower part via a time control transmission system to drive an intake valve and an exhaust valve of the OHC engine is formed with a synthetic resin, and is integrally formed by injection molding with a metal sprocket 2 arranged in the head part side of the engine main body and composing the time control transmission system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive mechanism for intake and exhaust valves in an OHC engine, and more particularly to a valve operating camshaft for driving intake and exhaust valves.

[0002]

2. Description of the Related Art A general-purpose OHC engine used for mowing or spraying agricultural chemicals is provided with a camshaft (valve-operating cam) for driving an intake valve and an exhaust valve at a head of the engine body, and provided at a lower portion of the engine body. Connected to the crankshaft via a timing transmission system. In this case, the timing transmission system is a mechanism for synchronously driving the crankshaft and the valve operating camshaft at a predetermined timing, and for example, a mechanism in which sprockets respectively attached to the crankshaft and the camshaft are connected by a chain. No.
In addition, as the timing transmission system, there are also those using a timing pulley and a timing belt, those using a gear, and the like, which are appropriately selected according to the design conditions of the engine.

Conventionally, as shown in FIG. 9, an intake / exhaust independent cam (FIG. 9 (a)) provided independently for intake and exhaust, and one cam for this valve operating camshaft. There is a suction / discharge type cam (FIG. 9B) that operates the suction and exhaust valves. In this case, as shown in FIG. 9A, the independent suction / discharge type cam is formed by forming a cam ridge 72 on a metal camshaft 71 formed of cast iron, cast steel, an iron-based sintered material, or the like. It is formed. A metal sprocket 73 serving as a cam driving member is provided on the camshaft 71.
Is fixed by press-fitting, screwing, key connection, or the like, and disposed on the head of the engine body.

[0004] On the other hand, in the cam of the dual-purpose type, a metal cam 75 having a support pin hole 74 in the center is formed of cast iron or the like, and the cam 75 is pressed into a metal sprocket 76, screwed, or used as a key. It is used after being fixed. In recent years, in such a suction-discharge shared cam, Japanese Patent Application Laid-Open No.
A cam and a sprocket integrally formed of a sintered metal or a synthetic resin, such as a camshaft for a valve train disclosed in Japanese Patent No. 7416, have also been proposed.

[0005]

However, if such a valve operating camshaft is formed entirely of metal, the weight of the camshaft increases, and the engine weight increases, and the center of gravity of the engine moves away from the crankshaft. There is a problem. Also, there is a problem that the cam operation noise becomes loud and contributes to engine noise and vibration.

On the other hand, if the valve operating camshaft is formed of a synthetic resin, the above-mentioned problems are small. However, in the conventional system in which the cam driving member such as a sprocket is integrally formed, the strength of the cam driving member is reduced. And the durability is inferior to those made of metal. In addition, when a synthetic resin sprocket or the like is used, there is a disadvantage that it is difficult to add another device such as a decompression mechanism to the sprocket.

An object of the present invention is to reduce the weight of a valve operating camshaft and reduce engine noise and vibration while ensuring the strength of a cam driving member.

[0008]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

That is, the valve operating camshaft of the OHC engine according to the present invention is disposed at the head of the engine main body of the OHC engine, and is connected to a crankshaft disposed at a lower portion of the engine main body via a timing transmission system. A valve operating camshaft for driving intake and exhaust valves of the OHC engine, wherein the valve operating cam is formed of synthetic resin, and is disposed on the head side of the engine body to constitute a timing transmission system. It is characterized in that it is formed integrally with a cam drive member made of steel. In this case, preferably, the valve operating cam is integrally formed with a cam driving member such as a sprocket by injection molding.

[0010] This makes it possible to reduce the weight of the valve operating cam while maintaining the strength of the cam driving member, which is the power input portion. Further, noise and vibration due to the cam operation can be reduced as compared with a conventional metal cam. Further, since the sprocket is made of metal, not only the strength of the power input portion can be ensured, but also an auxiliary mechanism such as a decompression mechanism can be provided on the sprocket side.

That is, the cam drive member projects from the base circle so as to increase the diameter of the base circle of the valve operating cam when the engine is started, and opens at least one of the intake and exhaust valves in the compression stroke of the engine. After the engine is driven, a decompression mechanism that retreats from the base circle by centrifugal force can be provided.

Note that a sprocket wheel for a chain, a timing pulley, a gear, or the like can be used as the cam driving member.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view showing a configuration of an OHC engine using a valve operating camshaft according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along line AA of FIG. is there.

The engine 10 shown in FIG. 1 is a general-purpose air-cooled engine, and has a structure in which a cylinder 11, a crankshaft 15, and the like are arranged in an engine body 41 including a cylinder case 12 and a head cover 44 covering the cylinder case 12. Has become. A cam 1 (hereinafter, abbreviated as cam 1) for driving the intake and exhaust valves of the engine 10 is provided on the head (upper portion in FIG. 1) of the engine body 41. In the present invention, the cam 1 is formed of a synthetic resin such as polyacetal, polyamide, or polycarbonate, and is formed by injection molding with a metal sprocket 2 as a cam driving member.

The cylinder 11 of the engine 10 is provided with a cylinder bore 11a, in which a piston 13 is reciprocally mounted. Cylinder case 1
2, a crankcase 14 is formed integrally with the cylinder case 12, and a crankshaft 15 is rotatably attached thereto. Also, the crankshaft 15
Is connected to the piston 13 by a connecting rod 16, and the reciprocating motion of the piston 13 drives the crankshaft 15 to rotate. A flywheel 17 is attached to an end of the crankshaft 15 for smooth rotation. The crankcase 14 is provided with a bearing 28 for rotatably supporting the crankshaft 15 and an oil seal 29 for sealing leakage of lubricating oil in the crankcase 14.

An intake port 18 is formed in the upper part of the cylinder 11, and an intake valve (intake valve) 19 is provided to open and close the intake port 18. An exhaust port 42 (see FIG. 6) is formed on the back side of the intake port 18 in FIG. 1, and an exhaust valve (exhaust valve) for opening and closing the exhaust port 42 is provided.
43 (see FIG. 6). Further, as shown in FIG. 2, a carburetor (carburetor) 21 for supplying a mixture of fuel and air into the cylinder bore through the suction port 18 is attached to the cylinder case 12. Further, a muffler 22 for silencing exhaust gas and discharging the exhaust gas to the outside is attached to the exhaust port 42 side. A spark plug 20 is located near the suction port 18.
Is provided, and the air-fuel mixture supplied into the cylinder bore via the suction port 18 is ignited at a predetermined timing.

An intake valve 1 is provided above the cylinder case 12.
9 and a cam 1 for opening and closing the exhaust valve 43 are rotatably provided. The cam 1 is a so-called one-cam type valve-operating cam that drives a suction and exhaust valve by one cam, and is formed integrally with a metal sprocket 2. Then, with the crankshaft 15 as the drive side, the timing transmission system sets the crankshaft
It is driven at the number of rotations. In this embodiment, a chain and a sprocket are used as a timing transmission system, and the sprocket 2 is driven by a chain 33 bridged between the sprocket 31 and the sprocket 31 attached to the crankshaft 15. It has become so.

FIG. 3 shows a cam 1 according to an embodiment of the present invention.
FIG. 4 is a left side view of the cam 1 of FIG. As shown in FIGS. 3 and 4, the cam 1 includes a cam body 1c having a base circular portion 1a and a cam surface 1b, and a flange portion 1d formed on the right side of the sprocket 2 in FIG. Have been. The cam 1 is formed of a synthetic resin as described above, and is integrally formed with the sprocket 2 by injection molding. In this case, the sprocket 2 is provided with a spline groove 2a at the center thereof, and the cam 1 and the sprocket 2 are prevented from rotating by the synthetic resin entering the spline groove. Also, sprocket 2
Is further provided with a resin communication hole 2b, so that the cam 1 and the sprocket 2 are also prevented from rotating when the synthetic resin goes around there. Although only one resin communication hole 2b is provided in FIG. 3, a plurality of resin communication holes 2b may be provided, and the number thereof is not limited.

The cam 1 is formed such that the sprocket 2 is sandwiched between the cam body 1c and the flange 1d. Accordingly, the sprocket 2 is integrated with the cam 1 in such a manner that the sprocket 2 is prevented from coming off in the axial direction. That is, the cam 1 is prevented from rotating by the spline groove 2a and the resin communication hole 2b, and the cam body 1c and the flange 1
The sprocket 2 is retained in the axial direction by d.
It is integrated with.

Further, a shaft hole 1e is formed in the center of the cam 1. In this shaft hole 1e, as shown in FIG.
Fixed shaft 23 press-fitted and fixed to cylinder case 12
Is inserted. Thereby, the cam 1 and the sprocket 2 integrated therewith are rotatably supported in the cylinder case 12.

As described above, since the cam 1 according to the present invention is formed of a synthetic resin, it is possible to reduce the weight of the cam 1 and to reduce noise and vibration caused by the cam operation as compared with a conventional metal cam. Can be reduced. Further, since the sprocket 2, which is a portion to which the power for driving the cam is input, is made of metal, the strength of the member can be increased as compared with the case where the cam and the cam driving member are all made of synthetic resin. Performance can be improved.

On the other hand, a decompression mechanism 51 as shown in FIG. 3 is provided on the surface of the sprocket 2 opposite to the cam 1. 5 to 8 are explanatory diagrams showing the configuration and operation of the decompression mechanism 51. FIGS. 5 and 6 show states when the engine is stopped and started, and FIGS. 7 and 8 show states when the engine is driven. ing. The decompression mechanism 51 is a device for reducing the burden on the operator when the engine is started,
When the piston 13 is in the compression stroke, the intake valve 19 is slightly opened to release the pressure in the cylinder bore, and the force required to rotate the crankshaft 15 is reduced. In the present invention, since the sprocket 2 is made of metal, such a decompression mechanism 51 can be provided on the sprocket 2 side.

The decompression mechanism 51 operates a decompression pin 53 having a D-shaped cross section by a release lever 52 as shown in FIGS. When the engine is stopped and started, the decompression pin 53 protrudes from the base circle portion 1a to open the intake valve 19, and after the engine is started, the engine speed is increased and the release lever 52 is operated by using the centrifugal force together with the normal operation. It is configured to return to valve operation.

Here, the release lever 52 is a plate-shaped member that is swingably mounted around an anchor pin 54 fixed to the sprocket 2, and has a notch 52a formed at the tip end thereof. . One end of the release lever 52 has a flange portion 1 d of the cam 1.
Is attached to the return spring 55 fixed thereto. On the other hand, the sprocket 2 is provided with a decompression pin 53 which is attached to the sprocket 2 from the right side to the left side in the drawing so as to reach the base circle portion 1a of the cam 1. The decompression pin 53 includes a sprocket 2
A pin lever 56 is mounted on the right side in the drawing, and the pin lever 56 is rotatable about the decompression pin 53. In addition, an interlocking pin 57 is provided at the tip end of the pin lever 56, and the interlocking pin 57 is engaged with the notch 52 a of the release lever 52. Therefore, when the release lever 52 swings right and left in the figure, the pin lever 56 rotates around the decompression pin 53, and the decompression pin 53 having a D-shaped cross section also rotates.

When the engine 10 is stopped, the release lever 52 is pulled leftward in the figure by a return spring 55. At this time, the pin lever 56 also receives the force in the direction of the arrow together with the release lever 52 and is held at the position shown in FIG. Thus, the decompression pin 53 is in a state as shown in FIG. 6, and a part thereof protrudes from the base circle portion 1a of the cam 1.

In this case, rocker arms 26 and 27 swinging around rocker shafts 25a and 25b come into contact with the base circle portion 1a and the cam surface 1b of the cam 1 so as to open and close the suction and exhaust valves. Has become. That is, the rocker arms 26 and 27 are connected to the intake valve 19 and the exhaust valve 43, respectively.
The opening and closing operations of the intake valve 19 and the exhaust valve 43 are appropriately shifted from each other by the movement of the cam 1. For this reason, when a part of the decompression pin 53 protrudes from the base circle portion 1a of the cam 1, the rocker arm 26 is pushed by the decompression pin 53 as shown in FIG.
9 moves downward, and the suction port 18 communicates with the inside of the cylinder bore. Therefore, even when the base circle portion 1a is in contact with the rocker arms 26 and 27 (compression stroke), the intake valve 19 can be opened to release the pressure in the cylinder bore, and the force required to rotate the crankshaft 15 can be obtained. Can be reduced.

On the other hand, when the engine starts and the sprocket 2 rotates to increase the rotation speed, a centrifugal force acts on the release lever 52. Therefore, the release lever 52 is swung toward the outer periphery of the sprocket 2, and rotates around the anchor pin 54 against the urging force of the return spring 55. In addition, the pin lever 56 also rotates together with the release lever 52, and becomes a state as shown in FIG. At this time, the decompression pin 53 is in a state as shown in FIG. 8, the D-cut surface of the decompression pin 53 faces the base circle portion 1a, and the decompression pin 53 is housed in the base circle portion 1a. Therefore, the cam 1 comes into contact with the rocker arm 26 as it is, and a normal valve opening / closing operation is performed.

Although the invention made by the present invention has been specifically described based on the embodiments, the present invention is not limited to the above embodiments and can be variously modified without departing from the gist thereof. Needless to say, there is.

For example, in the above-described embodiment, the timing transmission system is constituted by a sprocket and a chain. However, the timing transmission system may be constituted by a timing pulley and a timing belt, and may be constituted by a plurality of gears. You may. Further, in the above-described example, the return spring 55 is configured using a tension spring, but may be configured using a torsion spring or a leaf spring.

In addition, lubricating oil may be stored in the crankcase 14 and sprayed on the chain 33 by an impeller having a pusher fin.
In this case, the impeller is provided separately from the crankshaft 15 so that the splasher fin contacts the lubricating oil. Then, the gear teeth formed on a part of the impeller mesh with the gears attached to the crankshaft 15 to rotate the impeller, and the lubricating oil is splashed up by the splasher fins.

[0032]

According to the invention disclosed in the present invention,
The effect obtained by the representative one will be briefly described as follows.

(1) The valve-operating cam is formed of a synthetic resin and is formed integrally with a metal sprocket (cam driving member), thereby reducing the weight of the cam while maintaining the strength of the power input portion. Becomes possible. Further, noise and vibration due to the cam operation can be reduced as compared with a conventional metal cam.

(2) Since the sprocket is made of metal, not only the strength of the power input portion can be ensured, but also an auxiliary mechanism such as a decompression mechanism can be provided on the sprocket side.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration of an OHC engine using a valve operating camshaft according to an embodiment of the present invention.

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

FIG. 3 is a cross-sectional view showing a configuration of a valve cam according to an embodiment of the present invention.

FIG. 4 is a left side view of the valve cam shown in FIG. 3;

FIG. 5 is an explanatory diagram showing the configuration and operation of the decompression mechanism, and shows a state when the engine is stopped and when the engine is started.

FIG. 6 is an explanatory diagram showing the configuration and operation of the decompression mechanism, and shows a state when the engine is stopped and when the engine is started.

FIG. 7 is an explanatory diagram showing the configuration and operation of the decompression mechanism, and shows a state when the engine is driven.

FIG. 8 is an explanatory diagram showing the configuration and operation of the decompression mechanism, and shows a state when the engine is driven.

9A and 9B are explanatory diagrams showing the configuration of a conventional valve operating camshaft, wherein FIG. 9A shows a configuration of a suction-discharge independent cam, and FIG. 9B shows a configuration of a dual-discharge cam.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Valve cam 1a Base circle portion 1b Cam surface 1c Cam body 1d Flange portion 1e Shaft hole 2 Sprocket (cam drive member) 2a Spline groove 2b Resin communication hole 10 Engine 11 Cylinder 11a Cylinder bore 12 Cylinder case 13 Piston 14 Crank case 15 Crankshaft 16 Connecting rod 18 Intake port 19 Intake valve 23 Fixed shaft 25a Rocker shaft 25b Rocker shaft 26 Rocker arm 27 Rocker arm 31 Sprocket 33 Chain 41 Engine body 42 Exhaust port 43 Exhaust valve 44 Head cover 51 Decompression mechanism 52 Release lever 52a Notch pin 53 Decompression pin 54 Anchor pin 55 Return spring 56 Pin lever 57 Interlocking pin

Claims (3)

[Claims] An OHC engine is provided at the head of an engine body thereof and is connected to a crankshaft provided at a lower portion of the engine body via a timing transmission system to drive intake and exhaust valves of the OHC engine. A valve operating camshaft, wherein the valve operating cam is formed of a synthetic resin, and is formed integrally with a metal cam driving member disposed on the head side of the engine body and constituting the timing transmission system. A valve camshaft for an OHC engine. 2. The valve operating camshaft of an OHC engine according to claim 1, wherein the cam drive member is provided with a base circle from above the base circle so as to increase the diameter of the base circle of the valve operating cam when the engine is started. A valve operating cam for an OHC engine, comprising a decompression mechanism that protrudes and opens at least one of the intake and exhaust valves during a compression stroke of the engine and that retracts from a base circle by centrifugal force after driving the engine. shaft. 3. The camshaft for an OHC engine according to claim 1, wherein said cam drive member is a sprocket wheel for a chain.