JPH0544408A - Camshaft of four stroke engine - Google Patents

Abstract

PURPOSE:To offer a camshaft for a four stroke engine that can simplify masking at the time of surface treatment of a cam part, and, at the same time, can surely prevent sticking of a surface finishing agent to a sprocket flange press fitting part. CONSTITUTION:In this camshaft 9 of a four stroke engine, a cam part 17 and a sprocket flange press fitting part 35 are separated making both sides of a cam part 17 as press fitting parts 33, 34 of bearings and the outside of a bearing press fitting part 33 on one side as a sprocket flange press fitting part 35. Since the sprocket flange press fitting part 55 is mounted away from the cam part 17 by constituting this camshaft like this, at the time of performing surface treatment on the cam part 17, a surface finishing agent does not stick to the sprocket flange press fitting part 55 even the masking of the part other than the cam part 17 is simplistically performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camshaft for a four-stroke engine in which a cam portion is surface-treated to improve wear resistance.

[0002]

2. Description of the Related Art When manufacturing a camshaft for a four-stroke engine, the cam portion may be surface-treated in order to improve wear resistance. In this surface treatment, a surface treatment agent such as a solid coating lubricant is applied to the cam portion by spraying or the like and dried to form a lubricating coating.

By the way, in a short-length camshaft used for a single cylinder engine or a V-type engine, there is an assembly type in which a sprocket flange for fixing a cam sprocket or a bearing such as a bearing or a bush is press-fitted. In such a camshaft, a cam portion is provided at an intermediate position, a sprocket flange is press-fitted on one side of the cam portion, and bearings are press-fitted at both ends of the camshaft.

When the above-mentioned surface treatment is applied to the cam portion, the sprocket flange press-fitting portion and the bearing press-fitting portion are masked and the surface treatment agent is applied only to the cam portion.

[0005]

However, when the cam portion and the sprocket flange press-fitting portion are adjacent to each other as in the conventional camshaft, the sprocket flange press-fitting portion must be masked with a masking tape, etc. The surface treatment agent may adhere to the sprocket flange press-fitted portion to form a lubricating film, and after the sprocket flange is press-fitted, the crankshaft drive torque applied to the sprocket gear may cause the sprocket flange to slip on the camshaft and cause the engine valve timing to be misaligned. There is.

However, the strict masking of the sprocket flange press-fitted portion of the camshaft requires a lot of time and cost.

The present invention has been made in order to solve this problem. It is possible to simplify the masking during the surface treatment of the cam portion, and at the same time reliably prevent the surface treatment agent from adhering to the sprocket flange press-fitted portion. An object is to provide a camshaft for a four-stroke engine.

[0008]

In order to achieve the above object, a camshaft of a four-stroke engine according to the present invention has a cam portion surface-treated so that a bearing or bush for bearings and a cam sprocket can be fixed. In a camshaft of an assembly type 4-stroke engine in which a sprocket flange etc. is press-fitted, both sides of the cam part provided in the middle part of the camshaft are bearing press-fitting parts, and the outside of one side bearing press-fitting part is the sprocket flange press-fitting part. The cam portion and the sprocket flange press-fitting portion are separated from each other.

[0009]

With this structure, since the sprocket flange press-fitting portion is arranged away from the cam portion, even if the masking for the cam portion surface treatment is simply performed, the surface treatment agent is applied to the sprocket flange press-fitting portion. There is no risk of adhesion. Therefore, the masking work time is significantly reduced.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a single cylinder OHC for a motorcycle equipped with a camshaft of a four-stroke engine according to the present invention.
FIG. 2 is a vertical sectional view of a cylinder portion of the engine, and FIG.
FIG. 2 is a sectional view taken along line II-II of FIG.

In the crankcase 2 of this engine 1,
A cylinder block 3 and a cylinder head 4 are mounted, a piston 6 slidable in a cylinder 5 formed in the cylinder block 3, and a crankshaft 7 rotatably supported in a crankcase 2. Are connected by a connecting rod 8, and the reciprocating motion of the piston 6 is converted into the rotational motion of the crankshaft 7 and becomes the output of the engine 1.

A camshaft 9 parallel to the crankshaft 7 has bearings 11, 12 in the cylinder head 4.
A cam chain 16 is rotatably supported by a cam sprocket 14 fixed to a sprocket flange 13 rotatably integrated with the camshaft 9 and a crank sprocket 15 rotatably integrated with the crankshaft 7. Be passed over. And camshaft 9
Are driven at half the rotation speed of the crankshaft 7.

An intake cam 18 and an exhaust cam 19 are integrally or integrally formed with a cam portion 17 provided at an intermediate portion of the cam shaft 9, and the intake cam 18 and the exhaust cam 19 are formed by the rocker shafts 21 and 22. The rocker arms 23 and 24, which are swingable around the sliding surfaces 23a,
24a is faced. The other ends of the rocker arms 23 and 24 are tappets 23b and 24b, which are in contact with the heads of the intake valve 25 and the exhaust valve 26, respectively.

The intake valve 25 and the exhaust valve 26 are
The intake port 28 and the exhaust port 29 communicating with the combustion chamber 27 are opened and closed, and are always spring-biased in the valve closing direction by the valve springs 31 and 32.

When the camshaft 9 is driven by the crankshaft 7 to rotate, the intake cam 18 and the exhaust cam 19 press the sliding surfaces 23a, 24a of the rocker arms 23, 24 at a predetermined timing, and the rocker arms 23, 2
4 tappets 23b, 23b are valve springs 31,
The intake valve 25 and the exhaust valve 26 are opened to the side of the combustion chamber 27 against the spring force of 32, the intake port 28 and the exhaust port 29 are communicated with the combustion chamber 27, and the gas in the cylinder 5 is exchanged.

FIG. 3 is a front view of the camshaft 9 showing an embodiment of the present invention.

The camshaft 9 has a bearing press-fitting portion 3 into which bearings 11 and 12 are press-fitted on both sides of a cam portion 17.
3, 34 are provided, and the sprocket flange press-fitting portion 35 into which the sprocket flange 13 for fixing the cam sprocket 14 is press-fitted is provided outside the bearing press-fitting portion on one side (33 in this embodiment). Therefore, the cam portion 17
And the sprocket flange press-fitting portion 35 are separated from each other.

Since a strong driving torque from the crankshaft 7 is applied to the sprocket flange 13, the fit between the sprocket flange 13 and the sprocket flange press-fitting portion 35 is set to be tight so as to prevent slippage after press fitting. The tightening margin is 0.0 in this embodiment.
It is set to 50 to 0.072 mm.

On the other hand, since the driving torque of the crankshaft 7 is not applied to the bearings 11 and 12, the fitting between the bearings 11 and 12 and the bearing press-fitting portions 33 and 34 is the same as the sprocket flange 13 and the sprocket flange press-fitting portion 35. Can be made looser than the fit, and the tightening margin is 0.001 to 0.0 in this embodiment.
It is set to 20 mm.

The cam portion 17 of the cam shaft 9 as described above.
As a surface treatment for improving wear resistance, for example, a surface treatment agent such as a solid film lubricant containing fluorine resin as a base and mixed with molybdenum disulfide, graphite or the like is sprayed with a spray 36 or the like as shown in FIG. When applying, since the sprocket flange press-fitting portion 35 and the cam portion 17 are separated from each other, it is not necessary to strictly mask the portions other than the cam portion 17 using masking tape or the like. For example, a cap-shaped masking cover 37, It is also possible to use a simple one by wearing 38 from the left and right of the camshaft 9.

Since this masking method is slightly inferior in masking property to the case where a masking tape or the like is used, the bearing press-fitting portions 33, 34 are located near the center 33a, 34a.
There is a case where the surface treatment agent permeates and adheres to the surface to form a lubricating film, but the drive torque of the crankshaft 7 is present between the bearing press-fitting portions 33 and 34 and the bearings 11 and 12 press-fitted therein. There is no risk of slippage because it does not hang. Thus, the masking work is greatly simplified and the work time is shortened.

The sprocket flange press-fitting portion 35
Is located at the back of the masking cover 37, the surface treatment agent does not adhere to the sprocket flange 13, and the sprocket flange 13 press-fitted therein has no risk of slipping even if it receives a strong driving torque from the crankshaft 7. Therefore, the valve timing of the engine 1 is kept accurate.

[0024]

As described above, in the camshaft of the four-stroke engine according to the present invention, the cam portion is surface-treated, and the bearing or bush for the bearing and the sprocket flange for fixing the cam sprocket are press-fitted. In the camshaft of the assembling type four-stroke engine, both sides of the cam portion provided in the intermediate portion of the camshaft are bearing press-fitting portions, and the outside of the bearing press-fitting portion on one side is a sprocket flange press-fitting portion, and the cam portion and the sprocket are The flange press-fitted portion is separated.

Therefore, since the sprocket flange press-fitting portion is arranged apart from the cam portion, even when the portion other than the cam portion is simply masked when the cam portion is subjected to the surface treatment, the sprocket flange press-fitting portion is provided. There is no risk of surface treatment agent sticking. Therefore, the masking work time is significantly reduced.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a cylinder portion of an engine including a camshaft of a four-stroke engine according to the present invention.

FIG. 2 is a sectional view taken along line II-II in FIG.

FIG. 3 is a front view of a camshaft showing an embodiment of the present invention.

FIG. 4 is a view showing a masking state at the time of cam surface treatment.

[Explanation of symbols]

 1 Engine 9 Camshaft 11, 12 Bearing 13 Sprocket Flange 14 Cam Sprocket 17 Cam Part 18 Intake Cam 19 Exhaust Cam 33, 34 Bearing Press-fitting Part 35 Sprocket Flange Press-fitting Part

Claims (1)

[Claims] 1. A camshaft of an assembly type four-stroke engine in which a cam portion is surface-treated, and a bearing or bush for a bearing, a sprocket flange for fixing a cam sprocket, and the like are press-fitted, and an intermediate portion of the camshaft. The cam portion of the four-stroke engine is characterized in that the cam portion and the sprocket flange press-fitting portion are separated from each other by using both sides of the cam portion as a bearing press-fitting portion and one side of the bearing press-fitting portion as a sprocket flange press-fitting portion. shaft.