JP3859175B2 - Cam structure design method - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a cam structure design method , and more particularly to a cam structure design method capable of reducing wear while ensuring engine performance.
[0002]
[Prior art]
In a vehicle, an intake valve and an exhaust valve are operated via a rocker arm and a tappet of a valve mechanism by rotation of a cam provided on a cam shaft.
[0003]
As shown in FIG. 5, the cam 102 is formed integrally with the cam shaft 104, and a cam profile 108 is formed on the outer peripheral surface by a cam lift portion 106 protruding from the same cam base circle BC as the outer peripheral surface of the cam shaft 104. . The cam profile 108 is formed with a minimum curvature radius region S on the tip side. Further, as shown in FIG. 6, the minimum curvature radius portion S has a minimum curvature radius , but there is a minimum curvature radius angle θ1. Although not shown, the cam profile 108 is in direct contact with the contact surface of the follower of the rocker arm or tappet.
[0004]
In the cam 102 shown in FIG. 5, the relationship between the valve lift Y (lift curve) and the cam curvature radius ( RR ) is shown in FIG. Further, a second-order differential value d2Y / dθ2 obtained by second-order differentiation of the valve lift Y (lift curve) is as shown in FIG.
[0005]
Such cam structures are disclosed, for example, in Japanese Utility Model Publication Nos. 6-10090, 62-148735, 63-83403, and 2-95705. . The one described in Japanese Utility Model Publication No. 6-10090 is configured such that the seating speed at the buffer portion is not constant, but is raised at the middle portion, so that the shift of the seating timing accompanying the change in the engine rotational speed is not widened. This lowers the seating speed in the high speed rotation area where the deformation is large, and reduces the noise in the high speed rotation area without deteriorating the combustibility in the low speed rotation area. In Japanese Utility Model Publication No. 62-148735, a four-cycle internal combustion engine is provided with a valve that starts to open in the second half of the exhaust stroke and closes immediately before the intake stroke, and introduces air into the combustion chamber prior to the intake stroke. It is what you want to do. Japanese Utility Model Publication No. 63-83403 discloses a cam profile of a cam so that the valve speed characteristic in the buffer portion when the intake / exhaust valve is seated decreases at the initial and final stages of the buffer portion and increases at the intermediate portion. Is formed. Japanese Patent Application Laid-Open No. 2-95705 discloses an exhaust valve opening / closing function having an asymmetric profile in which the maximum valve lift position is biased to the valve opening side from the intermediate position during the valve opening period by a maximum of 20 degrees at the crank angle. It is possible to increase the exhaust gas pressure when opening the valve without changing the valve opening period and maximum valve lift, and this can further improve the efficiency of the turbocharger. It is what makes it possible.
[0006]
[Problems to be solved by the invention]
By the way, since the contact surface pressure acts on the cam profile of the cam and the contact surface of the follower, wear occurs.
[0007]
In order to suppress this wear within an allowable range, first, the height of the cam lift portion is changed, second, the width (working angle) of the cam lift portion is changed, third, the area of the cam lift portion is changed, fourth First, various measures such as asymmetric valve lift and fifth, change of the cam base circle may be taken.
[0008]
However, the smaller the radius of curvature of the minimum radius of curvature, the greater the contact surface pressure per unit area between the cam profile and the contact surface of the driven body, and thus the greater the wear. Therefore, the minimum curvature radius of the minimum curvature radius portion must be greater than the allowable range.
[0009]
However, in the prior art, not only the minimum curvature radius portion is changed, but the entire valve lift Y (lift curve) is changed. For this reason, the overall change of the valve lift Y (lift curve) has an inconvenience that it affects the engine performance and causes a decrease in the engine performance.
[0010]
In addition, the change of the cam base circle requires a change in the layout of the entire cylinder head, which increases the number of manufacturing steps and is disadvantageous in terms of cost.
[0011]
[Means for Solving the Problems]
Accordingly, in order to eliminate the above-described disadvantages, the present invention provides a method for designing a cam structure of a cam provided on a cam shaft so as to operate a valve mechanism of an engine. In order to reduce the contact surface pressure per unit area with the surface, a positive change value having a maximum amplitude at the minimum curvature radius angle is added to the second-order differential value of the valve lift at the minimum curvature radius portion of the cam profile. In addition, a negative change value that is approximately half the amplitude of the positive change value and approximately half the action angle of the positive change value is added before and after the positive change value. It is characterized by increasing the radius of curvature.
[0012]
[Action]
According to the configuration of the present invention, since the contact surface pressure per unit area between the cam profile and the contact surface of the driven body is reduced, the wear between the cam profile and the contact surface of the driven body can be reduced, and durability can be reduced. Can be improved. Further, the required overall change of the valve lift (lift curve), that is, to ensure the valve lift of the initial (lift curve), also because it required a change in the cam base circle, to ensure engine performance, In addition, the man-hours for manufacturing the cam lift portion are not sacrificed, and further, it is not necessary to change the layout of the entire cylinder head, the increase in man-hours for production can be avoided, and the cost can be reduced.
[0013]
【Example】
Embodiments of the present invention will be described in detail and specifically with reference to the drawings. 1 to 4 show an embodiment of the present invention. In FIG. 3, reference numeral 2 denotes a cam for operating an engine valve mechanism (not shown). The cam 2 is formed integrally with the cam shaft 4, and a cam profile 8 is formed on the outer peripheral surface by a cam lift portion 6 protruding from the same cam base circle BC as the outer peripheral surface of the cam shaft 4.
[0014]
In the cam profile 8, a minimum radius of curvature portion S is formed on the distal end side of the cam lift portion 6.
[0015]
In this minimum curvature radius region S, as shown in FIG. 2, the cam curvature radius RR is such that the contact surface pressure per unit area with the contact surface of the driven body (not shown) in contact with the cam profile 8 is reduced. It is formed larger than the setting, that is, the conventional cam curvature radius (indicated by the broken line in FIGS. 2 and 3).
[0016]
Further, the second-order differential value d2Y / dθ2 obtained by second-order differentiation of the valve lift Y (lift curve) is corrected by the following method so as to increase the curvature radius while maintaining the initial lift curve.
[0017]
As shown below, a positive change value and, if necessary, a negative change value are added before and after the minimum curvature radius angle θ1 of the second-order differential value d2y / dθ2 of the valve lift Y (lift curve). , Locally increasing the radius of curvature. That is, as shown in FIG. 1, the added amplitude is a at the wavelength A, the added amplitude is b at the wavelength B, and the amplitude is c at the wavelength C. Here, a ≦ 0, b ≧ 0, and c ≦ 0, and these relationships are about | a | ≈ | c | ≈ | b / 2 | or about A≈C≈B / 2.
[0018]
As shown in FIG. 4, the method for correcting the additional component of the second-order differential value d2y / dθ2 of the valve lift Y (lift curve) corrects the corresponding portion of the digital data of d2y / dθ2 on the computer. Then, the corrected d2y / dθ2 is integrated to recreate the valve lift Y (lift curve).
[0019]
Next, the operation of this embodiment will be described.
[0020]
The minimum curvature radius portion S having the minimum curvature radius angle θ1 varies depending on the valve operating system and the geometric dimension (shape) (for example, a driven body such as a direct hit type or a rocker arm). And if correction (b, B) is performed to the minimum curvature radius angle (theta) 1, the corrected minimum curvature radius will become larger than before (refer FIGS. 1-3).
[0021]
Negative change values (a, A,) and (c, C) are used for maintaining the smoothness of the periphery and the lift shape. When the positive change values (b, B) are small, (a, A ) (C, C) becomes smaller and may not need to be added.
[0022]
As a result of this modification, the minimum curvature radius RR is made larger than that of the prior art by only a local change of the rate of change d2Y / dθ2 of the cam profile 8 to obtain the cam shape shown in FIG.
[0023]
As a result, as shown in FIGS. 1 and 2, the minimum radius of curvature RR of the minimum curvature radius region S to ensure initial valve lift Y (lift curve), the contact surface per unit area of the contact surface of the driven member set the pressure is reduced, i.e., to mitigate the minimum radius of curvature RR to the extent that the sliding surface of the abrasion is acceptable (larger diameter than conventional), thereby securing the lift curve of the initial, thus The wear can be reduced and the durability of the cam 2 and the follower can be improved.
[0024]
Further, as shown in FIG. 4, if the correction of the additional component of d2Y / dθ2 is programmed, the correction is further simplified.
[0025]
In addition, it is not necessary to change the entire cam lift unit 6 and the cam base circle BC is not required to be changed, thereby eliminating the influence on the cam profile 8, thereby ensuring engine performance and creating the cam lift unit 6. The number of man-hours is not sacrificed, and the layout of the entire cylinder head is not required to be changed.
[0026]
【The invention's effect】
As is apparent from the above detailed description, according to the present invention, in order to reduce the contact surface pressure per unit area with the contact surface of the follower contacting the cam profile of the cam, the valve at the minimum radius of curvature portion of the cam profile. A positive change value that has the maximum amplitude at the minimum curvature radius angle is added to the second-order differential value of the lift, and is approximately half the amplitude of the positive change value and approximately half the working angle of the positive change value. in addition a negative change value with operating angle before and after the positive variation value, by increasing the local radius of curvature, the maximum amount of valve lift is the same, while ensuring the engine performance, and the cam profile Wear with the contact surface of the follower can be reduced, and durability can be improved.
[0027]
Further, the required overall change of the valve lift (lift curve), that is, to ensure the valve lift of the initial (lift curve), also because it required a change in the cam base circle, to ensure engine performance, The man-hours for creating the cam lift portion are not sacrificed, and further, it is not necessary to change the cylinder head layout, the increase in the man-hours for production can be avoided, and the cost can be reduced.
[Brief description of the drawings]
FIG. 1 is an enlarged view of a minimum radius of curvature portion in FIG.
FIG. 2 is a diagram illustrating a relationship between a valve lift and a cam curvature radius.
FIG. 3 is a configuration diagram of a cam.
FIG. 4 is an explanatory diagram of digital data correction.
FIG. 5 is a configuration diagram of a conventional cam.
FIG. 6 is a diagram showing a relationship between a conventional valve lift and a cam curvature radius.
[Explanation of symbols]
2 Cam 4 Cam shaft 6 Cam lift 8 Cam profile

Claims (1)

In a design method of a cam structure of a cam provided on a camshaft so as to operate an engine valve mechanism, in order to reduce a contact surface pressure per unit area with a contact surface of a follower contacting the cam profile of the cam In addition, a positive change value having a maximum amplitude at the minimum radius of curvature is added to the second-order differential value of the valve lift at the minimum radius of curvature portion of the cam profile, and the amplitude is approximately half the amplitude of the positive change value. The cam structure is designed to locally increase the radius of curvature by adding a negative change value having a working angle substantially half the working angle of the positive change value before and after the positive change value. Way .

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