JPH0517104U - Camsyaft - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a camshaft capable of improving rigidity without causing an increase in weight. A camshaft is provided with a plurality of cams, and an offset portion for offsetting an upper portion of a cylinder head bolt with respect to an axis of the bolt.
In the camshaft 10, the offset portion 10a is formed into a shape that is nearly parallel to the direction of the maximum cam load σ _MAX that acts on the adjacent cam 11.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a camshaft of an internal combustion engine.

[0002]

[Problems to be solved by conventional techniques and devices]

 In the camshaft of an overhead cam mechanism that is rotatably supported by the cylinder head of an internal combustion engine and drives the intake and exhaust valves, this camshaft is located above the cylinder head bolt in relation to the cylinder head bolt that attaches the cylinder head to the cylinder block. It is known that the bolt is arranged so as to substantially overlap with the axis of the bolt.

In the camshaft having such an arrangement, the diameter of the upper portion of the bolt is reduced by reducing the diameter of the upper portion of the bolt so that the cylinder head bolt for attaching the cylinder head to the cylinder block can be easily attached and detached. An offset portion is provided that is offset with respect to the axis. Therefore, in the camshaft provided with the offset portion, it is necessary to increase the overall shaft diameter in order to secure the rigidity in the offset portion, which causes a problem that the weight of the entire camshaft increases.

The present invention has been made in view of the above points, and an object of the present invention is to provide a camshaft capable of improving the rigidity without increasing the weight.

[0005]

[Means and Actions for Solving the Problems]

 According to the present invention, in order to achieve the above object, a plurality of cams are attached to a camshaft provided with an offset portion for offsetting an upper portion of a cylinder head bolt with respect to an axis of the bolt. The parts are shaped to be nearly parallel to the direction of the maximum cam load that acts on the adjacent cams.

When the offset portion is formed into a shape that is nearly parallel to the direction of the maximum cam load that acts on the adjacent cams, the cam shaft has an increased section modulus in the direction of the maximum cam load, and the cam load that acts on the cams increases. The maximum bending stress due to is reduced. As a result, the camshaft is improved in rigidity without increasing the weight. That is, when showing such a relationship as a model, for example, in the shaft 1 shown in FIG. 8 in which both ends are supported and the load σ acts in the center, the maximum bending stress F _{MAX at} an arbitrary cross section IX-IX is , At the position of the point P, the bending moment at this time is M, and the section modulus at the section IX-IX is S _M , it is given by the following equation.

F _MAX = M / S _M (1) Here, the section modulus S _M is a value determined by the cross-sectional shape of the shaft 1, and the cross-section of the shaft 1 at the offset portion has the same shape and the same shape. Even the area varies depending on the angle formed by the offset portion and the load σ. For example, when the shaft diameter is 20 mm and the maximum distance from the outer circumference of the shaft to the offset portion is set to 5 mm, as shown in Fig. 9, when the offset portion 1a is orthogonal to the direction of the load σ, the section modulus S _M is 395.3. On the other hand, as shown in FIG. 10, when the offset portion 1a is parallel to the direction of the load σ, the section modulus S _M is 685.98.

Therefore, in the shaft 1, by forming the offset portion 1a into a shape nearly parallel to the load σ, the section modulus S _M is reduced and the maximum bending stress F _MAX acting on the offset portion 1a is reduced. Can be suppressed. This improves the rigidity of the shaft 1 without increasing the weight.

[0009]

【Example】

 Hereinafter, a first embodiment of the present invention will be described in detail with reference to FIGS. FIG. 1 shows a main part of the cam shaft 10. The cam shaft 10 is rotatably supported by a plurality of cam journals (not shown), and a plurality of cams 11 are attached to it. As shown in the figure, the camshaft 10 has an offset portion 10a that is adjacent to the cam 11 and that has a smaller diameter in a portion located above the cylinder head bolt 12 and is offset toward the axial center side with respect to the axis of the bolt 12. Is provided. As shown in FIG. 2, the offset portion 10a is formed in a shape substantially parallel to the long axis of the cam 11.

[0010] Here, if the cam shaft 10 is rotated at low speed, indicating a load sigma acting on the cam 11 schematically generally represented as shown in FIG. 3, the maximum value sigma _MAX at maximum lift point L _MAX Take Therefore, when the offset portion 10a of the cam shaft 10 is formed as described above, the cam 11 has the maximum cam load at the position of the point P ₁ shown in FIG. 2 corresponding to the maximum lift point L _MAX , and acts on the cam 11. The direction of the maximum cam load σ _MAX is substantially parallel to the direction of the offset portion 10a.

Therefore, in the camshaft 10, since the section modulus S _{M at the} offset portion 10 a increases, the maximum bending stress F _MAX becomes smaller according to the equation (1). Therefore, the camshaft 10 is reduced in weight by the amount corresponding to the offset portion 10a, and the rigidity is improved. . Here, if the offset portion 10a is formed in a shape nearly parallel to the long axis of the cam 11, the camshaft 10 is opposite to the axis C as shown in FIG. 4, contrary to FIG. It may be formed at the side position.

Next, a second embodiment of the present invention relating to the camshaft when rotating at a high speed will be described with reference to FIGS. 5 and 6. In the following description, the same components as those in the above embodiment are designated by the same reference numerals in the drawings, and detailed description thereof will be omitted. When the camshaft rotates at a high speed, the load σ acting on the cam is generally expressed as shown in FIG. 5, and the maximum value σ _MAX1 at the two points sandwiching the maximum lift point L _MAX of the cam is shown. , Σ _MAX2 . Therefore, if the camshaft is rotated at a high speed, as shown in FIG. 6, the largest of the cam load heavy sigma _MAX1 at the position of the point P ₂ and the point P ₃ is the cam 11, sigma _MAX2 acts.

[0013] Therefore, in the cam shaft 10 in this embodiment, the offset portion 10a adjacent the cam 11, the maximum cam load sigma _MAX1, sigma _MAX2 is nearly parallel to the direction of the respective acting, 6 Shape into shape. By molding the offset portion 10a in such a shape, the section modulus S _M of the offset portion 10a is increased and the maximum bending stress F _MAX can be reduced, as in the above-described embodiment. Therefore, the camshaft 10 can be reduced in weight and improved in rigidity. Of course, in FIG. 6, the offset portion 10a may be formed at a position opposite to the axis C.

A third embodiment of the present invention relating to a camshaft in consideration of both low speed rotation and high speed rotation will be described with reference to FIG. Normally, the engine is placed in various rotational states from low speed to high speed. Therefore, in the present embodiment, the shape of the offset portion 10a of the commonly used camshaft 10 is set as shown in FIG. 7 in the direction in which the maximum cam load σ _MAX acts at low speed and at the time of high speed rotation. maximum cam load sigma _MAX1, sigma _MAX2 is shaped into nearly parallel to the shape and direction of the respective acting.

As a result, in the camshaft 10 of the present embodiment, the increase in the section modulus S _M , and thus the decrease in the maximum bending stress F _MAX , is low compared to the cases of the above-described embodiments, but the maximum bending stress is low. By reducing F _MAX, the weight and rigidity of the camshaft 10 can be reduced. It is needless to say that the offset portion 10a may be formed at a position opposite to the axis C of the camshaft 10 as in the above-described embodiments.

[0016]

[Effect of the device]

 As is clear from the above description, according to the camshaft of the present invention, the rigidity can be improved without increasing the weight, and the offset portion can be easily molded, so that it has industrial utility value. Is large.

[Brief description of drawings]

FIG. 1 is a plan view showing a main part of a camshaft according to a first embodiment of the present invention.

2 is a cross-sectional view of an offset portion of the camshaft shown in FIG.

FIG. 3 is a load characteristic diagram showing an outline of a load acting on the cam when the camshaft of FIG. 1 rotates at a low speed.

FIG. 4 is a cross-sectional view showing a modified example in which the position of the offset portion is changed in the camshaft of FIG.

FIG. 5 is a load characteristic diagram showing a second embodiment of the present invention and showing an outline of a load acting on a cam at a high speed rotation.

FIG. 6 is a cross-sectional view showing the shape of an offset portion in a camshaft used during high speed rotation.

FIG. 7 shows a second embodiment of the present invention, and is a cross-sectional view of an offset portion of a camshaft in consideration of low speed rotation and high speed rotation of the camshaft.

FIG. 8 is an explanatory diagram for explaining a model relationship between the maximum bending stress, the bending moment, and the section modulus when a load is applied to an arbitrary shaft.

9 is a cross-sectional view taken along line IX-IX in FIG. 8, showing a case where the offset portion is orthogonal to the load direction.

FIG. 10 is a cross-sectional view of the shaft in the case where the offset portion is parallel to the load direction in FIG.

[Explanation of symbols]

10 camshaft 10a offset part 11 cam σ _MAX maximum cam load C camshaft axial center

Claims (1)

[Scope of utility model registration request] 1. A camshaft having a plurality of cams attached thereto, wherein the camshaft is provided with an offset portion for offsetting an upper portion of a cylinder head bolt with respect to an axis of the bolt, the offset portions acting on adjacent cams. A camshaft characterized by being formed into a shape that is substantially parallel to the direction of the maximum cam load.