JP2798625B2 - Camshaft bearing mechanism for cylinder head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camshaft bearing mechanism for a cylinder head (hereinafter simply referred to as a bearing mechanism). More specifically, the present invention relates to a bearing mechanism for rotatably supporting a journal portion of a camshaft, which is mounted on an upper surface of a cylinder head of an overhead camshaft type engine, among motorcycles, four-wheeled vehicles, and general-purpose engines.

[0002]

2. Description of the Related Art FIG. 7 illustrates a conventional cylinder head 51 incorporated in a four-valve engine (having four intake / exhaust valves per cylinder) for a motorcycle. As shown, on the upper surface of the cylinder head 51 in the overhead camshaft type engine,
As shown by hatching, a bearing portion 53 is formed in a semi-cylindrical shape to be fitted with the camshaft 52 (see also FIG. 8). On the other hand, although not shown, a semi-cylindrical recess corresponding to the bearing 53 is also formed on the cylinder head cover incorporated on the upper surface of the cylinder head.

[0003] Together, the two form a cylindrical tunnel through which the camshaft is inserted.

A sprocket wheel 54 is mounted on an end of the camshaft 52, and the camshaft 52 is rotated by a chain (not shown) that meshes with the sprocket wheel 54.

FIG. 1 illustrates a double overhead camshaft type engine, in which one camshaft is provided on each of an intake side and an exhaust side. However, in FIG. The camshaft 52 is shown only on the side. 52a is a cam, 5
2b is a journal supported by the bearing 53.

In the drawing, reference numeral 55 denotes a boss for fitting a head bolt (not shown) for connecting the cylinder head 51 to a cylinder block (not shown) connected to a lower portion of the cylinder head 51. (The intake side is not shown below the camshaft), 56 is a cam chain tunnel for rotating the cam chain, and 57 is a valve lifter to which an intake / exhaust valve is attached.
Since the engine uses a rocker arm (not shown), the positions of the camshaft 52 and the valve lifter 57 in the plan view are shifted. The hatched portion in the figure is the bearing 53 that rotatably supports the journal of the camshaft 52. As shown, the bearing 53 is formed between the cam chain tunnel 56 and the valve lifter 57 located closest to the cam chain tunnel 56, and between the valve lifters 57 of the respective cylinders. The boss 55 closest to the cam chain tunnel 56 is formed on the cylinder side of the bearing 53 located closest to the cam chain tunnel 56.

The above-mentioned cylinder head 51 is referred to as a first prior art for convenience. FIG. 9 shows another example of a conventional cylinder head. In the cylinder head 61, a bearing portion 62 indicated by hatching is formed only between valve lifters 63 of each cylinder. As a result, the cam chain tunnel 64
The bearing 62 closest to the cam chain tunnel is located farther from the cam chain tunnel 64 than in the first prior art. This cylinder head 61 is referred to as a second prior art for convenience.

In FIGS. 7 to 9, the front of the mounted vehicle is indicated by an arrow F as an example.

As a prior art, Japanese Utility Model Application Laid-Open No. 57-205 has been proposed.
A bearing device disclosed in Japanese Patent Publication No. 04-2004 is known.

[0010]

In the case of the second prior art, since the cam chain tunnel and the bearing are separated from each other, the bearing is separated from the sprocket wheel of the camshaft. As a result, the downward bending force of the drive chain must be cantilevered. Therefore, it is necessary to take measures such as increasing the shaft diameter in order to improve the strength of the camshaft. Moreover, the profile of the cam is usually designed as a simple linear mass system considering only the load received from the valve, but when the load conditions described above are applied, a considerably complicated design method is used. It will be necessary.

In the case of the first prior art, since the bearing is close to the sprocket wheel, there is nothing like the second prior art, but first, the thickness of the bearing closest to the cam chain tunnel is reduced. Since the width of the cylinder head is increased and the space above the boss portion for the head bolt cannot be effectively used, the width of the cylinder head also increases accordingly.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and the present invention utilizes a valve lifter of a cylinder head to provide a bearing which is close to a sprocket wheel of a camshaft and which is closest to a cam chain tunnel. It is an object of the present invention to provide a bearing mechanism capable of shortening the width of a cylinder head by moving the position of the section toward the cylinder.

[0013]

The bearing mechanism according to the first aspect of the present invention has a cam chain tunnel for rotating a cam chain and a head bolt for connecting a cylinder head and a cylinder block. Boss portion and a valve lifter to which an intake / exhaust valve is mounted are arranged in that order, a bearing mechanism for receiving a camshaft in a cylinder head of an overhead camshaft type engine, wherein the camshaft bearing portion is The valve lifter is formed between the boss portion adjacent to the cam chain tunnel and the valve lifter.

[0014] The camshaft bearing portion may include the cam.
The valve lifter closest to the chain tunnel and the valve
Also formed between the valve lifter adjacent to the brifter
It is preferred that

The term "overhead camshaft type" as used in the claims means both a single overhead camshaft and a double overhead camshaft.

[0016]

According to the bearing mechanism of the present invention, only the boss for the head bolt is interposed between the bearing portion closest to the cam chain tunnel and the cam chain tunnel. The bearing for the journal unit is in close proximity. Therefore, the support for the downward bending force by the drive chain does not have a long cantilever shape as in the second related art. As a result, it is possible to maintain a high strength and to adopt a cam profile which is more suitable for actual use conditions and more advantageous in performance by a conventional design method.

Further, since the bearing closest to the cam chain tunnel is formed closer to the cylinder than the boss for the head bolt as described above, the bearing and the guide wall for the valve lifter can be used in common. As shown in the comparative diagram, the width of the engine can be reduced by the thickness of the bearing. It corresponds to the dimension indicated by D in FIG. If the sprocket wheel of the camshaft is a bolt-on type, the width of the engine can be further reduced by disposing the bolt in the space above the boss for the head bolt. As a result, in the case of a motorcycle, the width of the vehicle body including the width of the fuel tank can be reduced, so that the riding position becomes slim and the degree of freedom in shaping the vehicle body increases.

[0018]

Next, an embodiment of a camshaft bearing according to the present invention will be described with reference to the drawings.

FIG. 1 is a partially cutaway perspective view showing an example of a cylinder head to which the bearing mechanism of the present invention is applied, FIG. 2 is a sectional view of a main part of an engine body incorporating the cylinder head of FIG. 1, and FIG. 1 is a plan view of the cylinder head of FIG. 1, FIG. 4 is a sectional view taken along line AA of FIG. 3, and FIG. 5 is a partial plan view of the cylinder head showing another example of the cylinder head to which the bearing mechanism of the present invention is applied. FIG. 6A is a plan view showing the degree of reduction in the width of the cylinder head of FIG. 1, and FIG. 6B is a plan view showing a comparative example.

1 and FIGS. 3 to 6, the front of the mounted vehicle is indicated by an arrow F as an example.

FIG. 1 exemplifies a partial cross section of a four-valve engine (having four intake / exhaust valves per cylinder) for a motorcycle. FIG. 1 shows a state in which only one of the two camshafts 2 is mounted thereon for easy understanding of the shape of each part of the cylinder head 1.
2a is a cam, and 2b is a journal. 2 and 3, a flange 2c is formed at one end of the camshaft 2, and a sprocket wheel 3 is mounted on the flange 2c with a plurality of bolts 4. I have.

Reference numeral 5 denotes a cam chain tunnel, in which a sprocket wheel 3 is accommodated, and a cam chain (not shown) for meshing with the sprocket wheel and driving the sprocket wheel to rotate therein is rotated. Reference numeral 6 denotes a hole for mounting an ignition plug (hereinafter, referred to as a plug hole), and reference numeral 7 denotes a cylindrical valve lifter for mounting an intake valve. Although the valve lifter 7 is of course formed for the exhaust valve, the cam 2 of the camshaft 2 is shown in the drawing.
It does not appear just below a.

Reference numeral 8 denotes a bearing portion which is recessed in a semi-cylindrical shape to support the journal portion 2b of the camshaft 2 (see also FIG. 4). Reference numeral 9 denotes a boss formed in the cam chain tunnel. A head bolt for connecting a cylinder block (not shown) is screwed to a lower portion of the cylinder head 1. The position of the upper end face of the boss 9 is below the lower end of the sprocket wheel 3 as is clear from FIG. Therefore, even in the case of the illustrated bolt-on type sprocket wheel 3, the bolt head can be positioned exactly above the boss portion 9 (FIG. 3).
As a result, the position of the sprocket wheel 3 can be made closer to the bearing portion 8 and, as described above, the cylinder head width in the axial direction of the camshaft 2 can be reduced as shown in FIG. it can.

As shown by hatching in the plan view of the cylinder head 1 in FIG. 3, the bearing 8 is provided between the intake valve lifters 7a (below the camshaft 2 and not shown in the drawing) of each cylinder and exhaust gas. It is formed between each of the valve lifters 7a. In addition, it is formed between the cam chain tunnel 5 and the valve lifter 7 b closest to the cam chain tunnel 5. That is, the bearing 8 is provided substantially around the valve lifter 7b closest to the cam chain tunnel 5. Therefore, it can be said that such influence is cut off from the cam located on the valve lifter 7b which is most susceptible to the bending force by the cam chain.

Although not shown, a cylinder head cover is connected to the upper surface of the cylinder head 1. And the cylinder head cover is also attached to the cylinder head cover.
A bearing portion recessed in a semi-cylindrical shape is formed at a position corresponding to the bearing portion 8.

In the above embodiment, a bolt-on type sprocket wheel is taken as an example. However, the bearing mechanism of the present invention can be applied to a camshaft having a press-fit type sprocket wheel press-fitted into a camshaft. it can.

Further, in the above embodiment, the cam chain tunnel is formed at the end of the cylinder head.
Although a so-called side cam chain type engine is taken as an example, it is needless to say that the present invention can be applied to a center cam chain type engine as shown in FIG. A cam chain tunnel 12 is formed at the center of the cylinder head 11 for the center cam chain type engine, and a cam shaft (not shown) to which a sprocket wheel is fixed is installed at the center. A boss 13 is formed on both sides of the cam chain tunnel 12, and a bearing 15 is formed substantially around a valve lifter 14 closest to the cam chain tunnel 12.

[0028]

According to the present invention, since the support for the downward bending force by the drive chain does not become a long cantilever shape, the strength is maintained and the actual use condition is satisfied.
It is possible to adopt a cam profile that is more advantageous in performance.

Further, since the width of the cylinder head can be reduced, the width of the engine can be reduced. In the case of a motorcycle, the width of the vehicle body including the width of the fuel tank can be reduced. Slim, and the degree of freedom in shaping the vehicle body increases.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an example of a cylinder head to which a bearing mechanism of the present invention is applied.

FIG. 2 is a sectional view of a main part of an engine body in which the cylinder head of FIG. 1 is incorporated.

FIG. 3 is a plan view of the cylinder head of FIG. 1;

FIG. 4 is a sectional view taken along line AA of FIG. 3;

FIG. 5 is a partial plan view showing another example of the cylinder head to which the bearing mechanism of the present invention is applied.

6A is a plan view showing a degree of reduction in the width of the cylinder head in FIG. 1, and FIG. 6B is a plan view showing a comparative example.

FIG. 7 is a plan view showing an example of a cylinder head to which a conventional bearing mechanism is applied.

FIG. 8 is a sectional view taken along line BB of FIG. 7;

FIG. 9 is a plan view showing another example of a cylinder head to which a conventional bearing mechanism is applied.

[Explanation of symbols]

 1, 11 ... Cylinder head 2 ... Cam shaft 2a ... Cam 2b ... Journal part 3 ... Sprocket wheel 5, 12 ... Cam chain tunnel 7, 14 ... Valve lifter 8, 15 ... Bearing parts

Claims (2)

(57) [Claims] 1. A cam chain tunnel for rotating a cam chain, a boss for fitting a head bolt for connecting a cylinder head to a cylinder block, and a valve lifter to which an intake / exhaust valve is mounted. Are arranged in that order, a camshaft bearing mechanism in a cylinder head of an overhead camshaft type engine, wherein a camshaft bearing portion is formed between the boss portion and the valve lifter close to the cam chain tunnel. Bearing mechanism of the cylinder head. 2. The camshaft bearing according to claim 2 , wherein
The valve lifter closest to the chain tunnel and the valve
Also formed between the valve lifter adjacent to the brifter
The camshaft bearing mechanism for a cylinder head according to claim 1, wherein: