JP4858456B2 - Camshaft manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a camshaft having a cam lobe. In particular, the present invention relates to a technique for polishing a cam surface of a cam lobe.

  A camshaft having a cam lobe is attached to, for example, an automobile engine and used to open and close an intake valve and an exhaust valve. The cam surface of the cam lobe is in direct contact with an intake valve or an exhaust valve, or a rocker arm (hereinafter sometimes referred to as a passive member) connected to the intake valve or the exhaust valve. Therefore, the cam surface is required to be smooth.

Patent Document 1 describes a technique for forming a cam lobe. In this technique, a cam lobe is formed into a target shape by bringing the rotated grindstone into contact with the cam surface and rotating the cam shaft.
After forming the cam lobe into a desired shape, the cam surface of the cam lobe is polished by a polishing grindstone. Thereby, the cam surface of the cam lobe is finished smoothly.

Japanese Patent Laid-Open No. 3-86459

In an automobile engine or the like, it is preferable that a sound (operation sound) generated during operation is small. The inventors of the present invention have conducted research on engine operating noise, and have confirmed that one of the causes of operating noise is camshaft vibration. Furthermore, as a result of intensive studies, the present inventors have confirmed that minute surface irregularities are also formed on the polished cam surface, and the camshaft vibrates due to this.
Therefore, if the minute surface irregularities can be eliminated from the cam surface, the camshaft will not vibrate, and the operating noise resulting therefrom can be prevented. However, it is virtually impossible to completely eliminate the surface irregularities formed by polishing. Even if minute surface irregularities exist on the cam surface, there is a need for a technology that suppresses vibration of the camshaft and reduces operation noise caused by the vibration.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a technique for suppressing the vibration of the camshaft caused by surface irregularities on the cam surface and reducing the operation sound caused by the camshaft.

In order to solve the above problems, the present specification provides a method of manufacturing a camshaft having a cam lobe. This camshaft manufacturing method includes a polishing step of polishing the cam surface of the cam lobe with an abrasive. In the polishing step, the polishing conditions for polishing the cam surface are changed according to the position of the cam surface in the circumferential direction, and the pitch of the surface irregularities formed on the cam surface is changed according to the position of the cam surface in the circumferential direction. Make it different.
Here, the position of the cam surface in the circumferential direction means the position of the cam surface in the rotation direction of the cam lobe (camshaft).

For example, when the entire cam surface is polished with the polishing conditions fixed, the pitch of the surface irregularities formed on the cam surface is constant regardless of the position of the cam surface in the circumferential direction. In this case, since the force generated between the cam lobe and the passive member fluctuates at a constant frequency, the vibration of the camshaft is likely to be amplified, and a relatively loud operation sound is generated accordingly.
In contrast to the above, in the manufacturing method disclosed in this specification, the pitch of the surface unevenness formed on the cam surface is changed in the circumferential direction of the cam surface by changing the polishing conditions according to the position in the circumferential direction of the cam surface. It is made to differ according to the position in. In this case, since the fluctuation frequency of the force generated between the cam lobe and the passive member changes, the vibration of the camshaft is difficult to be amplified, and the accompanying operation sound becomes relatively small.
Various polishing conditions can be adopted as the polishing conditions to be changed. For example, the type of abrasive may be changed, and the pressing force of the abrasive may be changed. Alternatively, the sliding speed at which the abrasive is slid with respect to the cam surface may be changed.
According to the manufacturing method disclosed in this specification, it is possible to suppress the vibration of the camshaft caused by the surface unevenness of the cam surface, and to reduce the operation sound caused by the vibration.

In the above-described polishing step, it is preferable that the sliding speed at which the abrasive is slid with respect to the cam surface is changed according to the position of the cam surface in the circumferential direction.
According to this method, the pitch of the surface irregularities formed on the cam surface can be changed relatively freely.

When changing the sliding speed of the abrasive according to the position of the cam surface in the circumferential direction, the rotated abrasive is brought into contact with the cam surface, and the rotational speed of the abrasive is set to the position of the cam surface in the circumferential direction. It is preferable to change accordingly.
In this manufacturing method, it is only necessary to change control conditions such as a motor for rotating the abrasive, and the pitch of the surface irregularities formed on the cam surface can be made different with a simple configuration.

The present specification provides a method of manufacturing a camshaft having a plurality of cam lobes. This camshaft manufacturing method includes a polishing step of polishing the cam surface of the cam lobe with an abrasive. In the polishing step, the polishing conditions for polishing the cam surface are changed between at least two cam lobes, and the pitch of the surface irregularities formed on the cam surface is made different between the at least two cam lobes.

When the camshaft has a plurality of cam lobes, it is also effective to change the pitch of the surface irregularities formed on the cam surface in units of cams by changing the polishing conditions in units of cams. In this case, since the fluctuation frequency of the force generated between the cam lobe and the passive member changes for each cam, the vibration of the camshaft is difficult to be amplified, and the accompanying operation sound becomes relatively small.
Also with this manufacturing method, it is possible to suppress the camshaft vibration caused by the surface irregularities of the cam surface and to reduce the operating noise caused by it.

In the above-described polishing step, it is preferable that the sliding speed at which the abrasive is slid with respect to the cam surface is changed between at least two cam lobes.
According to this manufacturing method, the pitch of the surface irregularities formed on the cam surface can be changed relatively freely.

When the sliding speed of the abrasive is changed between at least two cam lobes, the rotated abrasive is brought into contact with the cam surface, and the rotational speed of the abrasive can be changed between at least two cam lobes. preferable.
According to this manufacturing method, it is only necessary to change control conditions such as a motor for rotating the abrasive, and the pitch of the surface irregularities formed on the cam surface can be made different with a simple configuration.

The present invention provides a manufacturing method of a cam shaft having a plurality of cam lobes. In this manufacturing method, in the polishing step of polishing the cam surface with an abrasive, the polishing conditions for polishing the cam surface are fixed between at least two cam lobes, and at least two starting points for starting the cam surface polishing are set. By changing along the circumferential direction between the cam lobes, the phase of the surface irregularities formed on the cam surface is made different between at least two cam lobes.
In the manufacturing method described above, it is not necessary to change the polishing conditions. In this case, surface irregularities having the same pitch are formed on the cam surface of each cam lobe. However, since the starting point for starting the polishing of the cam surface is changed for each cam, the phase of the surface unevenness differs among the cam lobes. In this case, since the phase of the force generated between each cam lobe and the passive member does not coincide with each other, the vibration of the camshaft is difficult to be amplified, and the accompanying operation sound becomes relatively small.
Also with this manufacturing method, it is possible to suppress the camshaft vibration caused by the surface irregularities of the cam surface and to reduce the operating noise caused by it.

In the manufacturing method described above, the at least two cam lobes are preferably a cam lobe group having the same phase.
If the surface irregularities with the same pitch are formed in the same phase in the cam lobe groups having the same phase, the vibration of the camshaft is particularly easily amplified. Therefore, it is possible to effectively suppress the vibration of the camshaft by amplifying the surface of the surface unevenness formed on the cam surface for each cam lobe in the cam lobe groups having the same phase.

When the cam lobe group is a cam lobe pair composed of two cam lobes, the starting point is changed in the circumferential direction between the cam lobe pairs by an integral multiple of the pitch of the surface irregularities expected from fixed polishing conditions and a half pitch. It is preferable.
In this manufacturing method, the surface unevenness formed on the cam surface of one cam lobe and the surface unevenness formed on the cam surface of the other cam lobe can be in an opposite phase relationship. In this case, the vibration caused by one cam lobe and the vibration caused by the other cam lobe cancel each other. The vibration of the camshaft is remarkably suppressed, and the operation sound can be reduced.

According to the manufacturing method described above, a new and useful camshaft can be manufactured. The first camshaft has a cam lobe, and the cam surface of the cam lobe is a polished surface polished by an abrasive, and the pitch of surface irregularities formed by polishing depends on the position in the circumferential direction. Change. The second camshaft has a plurality of cam lobes, and the cam surfaces of these cam lobes are polished surfaces polished by an abrasive, and surface irregularities formed by polishing between at least two cam lobes. Are different from each other. The third camshaft has a plurality of cam lobes, and the cam surfaces of these cam lobes are polished surfaces polished by an abrasive, and surface irregularities formed by polishing between at least two cam lobes. Are different in phase.
According to these camshafts, the vibration of the camshaft due to the surface irregularities of the cam surface is suppressed, and the operating noise due to it is reduced.

  According to the present invention, it is possible to realize an internal combustion engine that suppresses the vibration of the camshaft caused by the surface unevenness of the cam surface and has a low operating noise.

The technical features of the following examples are listed.
(Mode 1) In the polishing step, the abrasive is rotated and the cam lobe is rotated.
(Form 2) The camshaft has four pairs of cam lobes. Each cam lobe pair extends perpendicular to the rotation axis of the camshaft. The phase of the first cam lobe pair is orthogonal to the phase of the second cam lobe pair and the phase of the fourth cam lobe pair. The phase of the first cam lobe pair is opposite to the phase of the third cam lobe pair.

(First Reference Example)
A method for manufacturing a camshaft according to a first reference example will be described with reference to the drawings. In this reference example, a camshaft used for an automobile engine will be described. FIG. 1 is a plan view of a camshaft 10 manufactured by the manufacturing method of this reference example. As shown in FIG. 1, the camshaft 10 has a rotating shaft 12 and four pairs of cam lobes 14, 16, 18, and 20 (hereinafter referred to simply as cam pairs) attached to the rotating shaft 12. ing. The first cam pair 14 has a pair of cam lobes 14a and 14b (hereinafter, the cam lobes are simply referred to as cams).
FIG. 2 is a view of one cam 14a as viewed from the axial direction of the rotating shaft 12 (right side in FIG. 1). The cam 14a is formed with an arc-shaped top portion 14c having a relatively small curvature radius and an arc-shaped base portion 14d having a relatively large curvature radius. The top portion 14c and the base portion 14d are provided at positions opposite to each other with the rotating shaft 12 interposed therebetween, and both are connected via a straight line portion. The center of the arc of the base portion 14 d coincides with the center of the rotation shaft 12. The center of the arc of the top portion 14c is shifted from the center of the rotating shaft 12 toward the top portion 14c. The other cam 14b has the same shape as the one cam 14a described above. The phase of the top portion of the cam 14b with respect to the rotating shaft 12 is equal to the phase of the top portion 14c of the cam 14a.

  Each of the cams 16a to 20b of the cam pairs 16, 18, and 20 has the same shape as the cam 14a. Each of the cam pairs 16, 18, and 20 has an equal phase with respect to the rotating shaft 12. The phase of the cam pair 14 is perpendicular to the phase of the cam pair 16 and the phase of the cam pair 20. The phase of the cam pair 18 is in an opposite phase relationship to the phase of the cam pair 14.

Next, a method for manufacturing the camshaft 10 will be described. In the manufacturing method of the camshaft 10, first, a coarse intermediate product is formed by casting. Subsequently, the intermediate product is ground and molded, and the cam surface of each cam is polished. 3 and 4 are schematic views of the polishing device 30 for the camshaft 10.
As shown in FIG. 3, the polishing apparatus 30 includes a camshaft support portion 36 that supports both ends of the camshaft 10, a grindstone 34, and a grindstone support portion 32. The camshaft support portion 36 supports the camshaft 10 so as to be rotatable about the rotation shaft 12. The camshaft 10 supported by the camshaft support portion 36 is rotated by a motor (not shown). The camshaft 10 is rotated at a constant speed by a motor. The grindstone 34 is rotatably supported by the grindstone support portion 32. The grindstone 34 is rotated by a motor (not shown). Further, the grindstone 34 can move in the vertical direction (vertical direction in FIG. 3) according to the shape of each cam. As shown in FIG. 4, the polishing step is performed by bringing the grindstone 34 and the cam surface of each cam into contact with each other and sliding the grindstone 34 on the cam surface.

The rotational speed of the grindstone 34 changes according to the position of the cam surface in the circumferential direction. Thereby, the sliding speed with respect to the cam surface of the grindstone 34 is changed according to the position in the circumferential direction of the cam surface. When the sliding speed of the grindstone 34 with respect to the cam surface is changed, the pitch of minute surface irregularities formed by polishing changes. Therefore, when the sliding speed of the grindstone 34 with respect to the cam surface is changed according to the position in the circumferential direction of the cam surface, the pitch of the minute surface irregularities formed by polishing depends on the position in the circumferential direction of the cam surface. Can be different.
Here, the rotational speed of the grindstone 34 may be continuously changed according to the position of the cam surface in the circumferential direction, or may be changed stepwise according to the position of the cam surface in the circumferential direction. In this reference example, as shown in FIG. 2, the cam surface of the cam 14 a is divided into three ranges 22, 24, 26 along the circumferential direction, and the sliding speed of the grindstone 34 for each of the three ranges 22, 24, 26. Is changing. FIG. 5 is a graph showing the surface unevenness of the cam 14a in the circumferential direction of the cam surface. The horizontal axis in FIG. 5 indicates the phase angle with the midpoint of the base portion 14d being 0 °, and the phase angle increases toward the right. The vertical axis in FIG. 5 indicates the size of the surface irregularities (surface shape). As shown in FIG. 5, the pitch of the surface irregularities formed by polishing differs for each of the ranges 22, 24, and 26. Similarly, for the cams 14b to 20b, the sliding speed of the grindstone 34 is changed in three ranges along the circumferential direction of the cam surface, and surface irregularities having different pitches are formed in each range of the cam surface.

When the camshaft 10 is assembled to an automobile engine, the cam surface of each cam contacts a passive member (eg, a rocker arm). When the engine is driven, each cam rotates while its cam surface slides with the passive member. At this time, since the cam surface of each cam has minute surface irregularities formed at the time of polishing, an operation sound (sliding sound) is generated between the cam surface and the passive member. Here, for example, if the surface irregularities of the cam surface are formed at the same pitch over the entire circumference, the vibration of the cam shaft 10 is amplified, and the operation sound between the cam surface and the passive member is compared. Will become bigger. On the other hand, each cam surface of the camshaft 10 according to the present reference example has surface irregularities with different pitches for each of the ranges 22, 24 and 26 as shown in FIG. Can be prevented. Thereby, the operation sound generated between the cam surface and the passive member can be reduced.

(Real施例)
In the camshaft manufacturing method of the first reference example, the rotational speed of the grindstone 34 is changed in the circumferential direction of the cam in the cam surface polishing step of each cam. On the other hand, in the camshaft manufacturing method of this embodiment, the rotational speed of the grindstone 34 is constant. However, in the present embodiment, the position of the starting point for starting polishing is changed along the circumferential direction between the cams 14a and 14b of the cam pair 14. Specifically, in one cam 14a, polishing is started from the midpoint of the base portion 14d. In the other cam 14b, polishing is started from the position moved in the circumferential direction from the midpoint of the base portion.

FIG. 6 is a graph showing the state of surface irregularities of the cams 14 a and 14 b of the cam pair 14. The horizontal axis of FIG. 6 shows the phase angle with the midpoint of the base portion 14d being 0 °, and the phase angle increases toward the right. The vertical axis in FIG. 6 indicates the size of the surface irregularities (surface shape). A graph 50 indicated by a solid line in FIG. 6 shows an outline of the surface irregularity of the cam surface of one cam 14a. A graph 52 shown by a broken line in FIG. 6 shows an outline of the surface irregularity of the cam surface of the other cam 14b.
As shown in FIG. 6, since the rotational speed of the grindstone 34 is constant in this embodiment, surface irregularities due to polishing are formed on the cam surfaces of the cams 14a and 14b at a substantially constant pitch in the circumferential direction. . However, by moving the starting point for starting the polishing, the phase of the surface irregularities is different between the two. In particular, in this embodiment, the starting point for starting polishing is moved between the two cams 14a and 14b by a half pitch of the surface irregularities formed on the cam surface. Thereby, as shown in FIG. 6, the phase of the surface irregularities between the two cams 14a and 14b is in an opposite phase relationship. Here, the pitch of the surface irregularities formed on the cam surface is determined by the rotational speed of the grindstone 34 and the rotational speed of the camshaft 10 at the time of polishing (that is, the sliding speed of the grindstone 34 with respect to the cam surface). This is determined according to the polishing conditions such as the contact pressure, the material of the camshaft 10 and the grindstone 34. Therefore, the pitch of the surface irregularities formed on the cam surface can be predicted according to the polishing conditions by confirming in advance, for example, by experiments.

Similarly, the other cam pairs 16, 18, 20 are formed on the cam surface with a starting point for starting polishing of one cam 16a, 18a, 20a and a starting point for starting polishing of the other cams 16b, 18b, 20b. Move by half the pitch of the surface irregularities. Accordingly, the vibration phase of one cam 14a, 16a, 18a, 20a is opposite to the vibration phase of the other cam 14b, 16b, 18b, 20b. As a result, the vibrations of the cams 14a, 16a, 18a, and 20a are canceled out by the vibrations of the cams 14b, 16b, 18b, and 20b. Therefore, the vibration of the camshaft 10 is suppressed.
In the manufacturing method of the camshaft 10 of the present embodiment, the surface irregularities of the cam surfaces of the cam 14a and the cam 14b may not be in reverse phase. In this case, for example, the surface irregularities of the cam surfaces of the cams 14a, 14b, 16a, and 16b may have the same phase, and the surface irregularities of the cam surfaces of the cams 18a, 18b, 20a, and 20b may have the same phase. At this time, the phase of the surface irregularities of the cam surfaces of the cams 14a, 14b, 16a, 16b and the phase of the surface irregularities of the cam surfaces of the cams 18a, 18b, 20a, 20b are set to opposite phases or different phases. Alternatively, the surface irregularities of the cam surfaces of all the cams may have different phases.

( Second reference example)
In the manufacturing method of the camshaft 10 of the second reference example, the sliding speed of the grindstone 34 when the cam surface of each cam is polished is constant. On the other hand, the rotational speed of the grindstone 34 is changed for each cam to be polished. As a result, the camshaft 10 in which the pitch of the surface irregularities formed on the cam surface is different for each cam can be manufactured.
In this configuration, the period of vibration transmitted from the cam to the rotating shaft 12 differs depending on each cam. Therefore, the camshaft 10 does not resonate due to the vibration of each cam. It is possible to prevent the vibration of the camshaft 10 from being amplified.

In the manufacturing method of the camshaft 10 described above, the rotational speed of the grindstone 34 is changed in order to change the pitch of the surface irregularities formed by polishing. However, the pitch of the surface irregularities formed by polishing varies depending on other polishing conditions such as the contact pressure of the grindstone 34 to the cam surface, the material of the camshaft 10 and the grindstone 34, and the like. Therefore, for example, in the first reference example, after the cam surface of the cam 14a is polished at the same sliding speed with the same grindstone 34 over the entire circumference, each of the ranges 22 and 24 of the cam 14a is used with another grindstone. May be polished. Thereby, the pitch of the surface unevenness | corrugation in the circumferential direction of the cam surface of the cam 14a can be changed. In the second reference example, for example, the grindstone 34 may be changed for each cam. At this time, the grindstone used for each cam can be appropriately selected so that the pitch of the surface irregularities of the cam surface is different.
In the reference example described above, the rotational speed of the grindstone 34 is changed. However, for example, the rotational speed of each cam may be changed.

  In an automobile engine using the camshaft 10 described above, abnormal noise generated during driving is reduced. Therefore, for example, a sound insulation cover for preventing abnormal noise is not required. When the camshaft 10 vibrates, a rib or the like for preventing other components from resonating becomes unnecessary. Thereby, the weight of the automobile can be reduced. Further, the surface processing for reducing the surface unevenness of the cam surface is not required. Thereby, manufacturing cost and manufacturing time can be reduced.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
For example, the camshaft manufactured by the camshaft manufacturing method of the present embodiment can be used other than an automobile engine.
In addition, the camshaft 10 of this embodiment is integrally formed with the rotating shaft 12 and the cams 14a to 20b by casting. However, the camshaft may be formed by separately forming the rotating shaft and the cam. In this case, the polishing step may be performed before the step of assembling the rotating shaft and the cam.
In addition, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

The top view which shows the cam shaft of a present Example. The figure which looked at the cam lobe of the present Example from the axial direction of the rotating shaft. The schematic diagram of the polish device used at the polish process of this example. The part excerpt figure of the grinding | polishing apparatus used at the grinding | polishing process of a present Example. The graph which shows the surface unevenness | corrugation of the cam surface of the cam lobe of a 1st reference example. The graph which shows the surface unevenness | corrugation of the cam surface of the cam lobe of a present Example.

Explanation of symbols

10: Cam shaft 12: Rotating shafts 14, 16, 18, 20: Cam lobe pairs 14a, 14b, 16a, 16b, 18a, 18b, 20a, 20b: Cam lobe 14c: Top portion 14d: Base portion 30: Polishing device 32: Grinding stone Support part 34: Whetstone 36: Camshaft support part

Claims (3)

A method of manufacturing a camshaft having a plurality of cam lobes,
Having a polishing step of polishing the cam surface with an abrasive;
In the polishing step, the polishing conditions for polishing the cam surface are fixed between at least two cam lobes, and the starting point for starting the cam surface polishing is changed along the circumferential direction between the at least two cam lobes. A method of manufacturing a camshaft, characterized in that a phase of surface irregularities formed on a cam surface is made different between the at least two cam lobes. The method of manufacturing a camshaft according to claim 1 , wherein the at least two cam lobes are a cam lobe group having the same phase. The cam lobe group is a cam lobe pair consisting of two cam lobes,
The polishing step is characterized in that the starting point for starting the cam surface polishing is changed in the circumferential direction between the cam lobe pairs by an integral multiple and half pitch of the pitch of the surface irregularities expected from the fixed polishing conditions. The manufacturing method of 2 camshafts.

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