Method of forming a precision ball track

Abstract

A method for forming a precision ball groove track in a part, especially in an outer race member of a universal joint. The method includes the steps of forming a recess groove in the ball race groove track and ball finish machining the ball race groove track to a predetermined precision shape, the recess reducing groove groove reducing the wear on the finish machining tool used during the finish machining step.

Description

This is a continuation of application Ser. No. 588,514, filed Mar. 12, 1984, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to methods for forming precision ball race groove tracks in a part, especially in the outer race member of a universal joint.

There are many mechanical parts having ball race groove tracks formed therein for engagement with bearing balls. The ball race groove tracks may be produced by various methods including formation of the ball race groove track with the part when the part is forged or cast, grinding, machining or cold forming the track into a rough workpiece, or cold forming or forging an initial roughly proportioned track during the formation process for the part and subsequently grinding or machining the formed ball track into a precision shape. The last mentioned methods are the most common when a precision shape for the ball race groove track is required since an accurately dimensioned ball race groove is produced without a substantial waste of material. Furthermore, these methods of producing a ball race groove cause less wear on the grinding machining tool than is the case when the ball race groove track is ground in a workpiece not having an initially formed ball race groove track therein.

Precision ball race groove tracks are required, for example, for universal joints of the type having spherically engaged inner an outer race members coupled to each other by a plurality of bearing balls disposed in ball engaging meridian race grooves in the inner and outer race members. Examples of this type of universal joint may be found in U.S. Pat. No. 2,046,584, issued July 7, 1936 to Alfred H. Rzeppa and in U.S. Pat. No. 1,665,280, issued Apr. 10, 1928 to the same inventor. A significant advantage of this type of construction for a universal joint is that it has a constant velocity property. That is, the speed of rotation of the shaft interconnected with the inner race member is the same as that of the shaft interconnected with the outer race member, regardless of the relative angular position between the inner and outer race members within a predetermined range of tracks ball groove tracks 18 and 30 to predetermined precision shapes.

More particularly, as shown in FIG. 3 with respective to a preselected first ball groove track 18a, the recess 32 is preferably formed at the apex of the first or second ball groove track with which it is associated, since the greatest grinding or machining resistance force is experienced at the apex of the track. Thus, the grinding or machining tool used in a finishing operation on the preselected first ball groove track 18a will experience substantially less wear than is the case when the recess 32 is omitted.

The recess 32 preferably has a substantially greater width w than its depth d, relative to the preselected first ball groove track 18a so as to provide a substantial lessening of the wear on the machining or grinding tool used, without substantially weakening the outer race member 12. For example, the width w of the recess 32 may be two to four times the dimension of the depth d. Furthermore, the recess 32 extend extends circumferentially about a portion of the preselected first ball groove track 18a such as to define a predetermined angle theta θ of arc relative to the preselected first ball groove track. The preselected angle theta θ is chosen such as to minimize the wear on the machining or grinding tool yet permit a sufficient remaining surface for the contact between the preselected first ball groove track 18a and the bearing ball 20 disposed therein. In the example illustrated, the preselected angle theta θ is approximately twenty degrees (20°) though it may range from approximately ten degrees to approximately thirty degrees (10°-30°) of arc.

According to the method of the present invention, the outer race member 12 is initially formed by a casting or forging process, having the preselected first ball groove track 18a formed therein having a formed surface 36 with a formed radius r₁. A subsequent grinding or machining operation is performed on the preselected first ball groove track 18a, such as to produce a ground surface varying within preselected tolerances between a minimum ground surface 38 having a minimum ground radius r₂ and a maximum ground surface 40 having a maximum ground radius r₃. The depth d of the recess 32 is selected so as to exceed the difference between the maximum ground radius r₃ and the formed radius r₁, so that the grinding or machining tool never encounters the base 44 of the recess 32.

The remaining first ball groove tracks 18 and second ball groove tracks 30 of the inner and outer race members 22 and 12, respectively, are formed in an analogous manner to the formation of the preselected first ball groove track 18a, as described above.

It should be noted that the method according to the present invention is more advantageously applied to the outer race member 12 than it is to the inner race member 22. The first ball groove tracks 18 for the outer race member 12 are typically proportioned, relative to the bearing balls 20, such that the bearing balls engage a surface of the ball groove track generally not including the apex of the track. This is done so as to maximize the amount of bearing surface between the bearing balls 20 and the outer race member 12. Thus, the removal of a porton portion of the first ball groove tracks 18, by the provision of a recess 32 in each of the tracks, removes a portion of the first ball groove track not experiencing any load. Thus, the method according to the present invention, when applied to the manufacture of an outer race member 12 of a constant velocity universal joint 10, increases the effective life of the grinding or machining tool used by removing that portion of the formed surface 36 of the first ball groove tracks 18 that offers the greatest resistance to the machining or grinding tool without affecting the functional engagement between the bearing ball 20 and the first ball groove track 18 associated therewith.

In contrast, the second ball groove tracks 30 of the inner race member 22 are typically proportioned in a manner providing substantial contact adjacent the apex of the second ball groove track. Accordingly, when an inner race member 22 is made according to the method of the present invention, as described above, the area of greatest contact between the bearing ball 20 and the second ball groove track 30 associated therewith will be on either side of the recess 34.

Therefore, for some applications, only the outer race member 12 would be formed according to the method of the present invention while the inner race member 22 would be formed according to prior art methods. Alternatively, the recess 34 formed in each second ball groove track 30 of the inner race member 22 may be formed at locations other than the apex of the second ball groove track. For example, two recesses, not shown in the drawing, may be formed in each of the second ball groove tracks 30, the two recesses being disposed a predetermined angular distance away from the apex of the second track associated therewith, on opposite sides of the apex.

The above description constitutes the best mode contemplated by the inventor hereof at the time of filing for carrying out the present invention. The above detailed description is merely exemplary of the present invention since variations therefrom within the spirit of the present invention will be apparent to those skilled in the art after reading the above description in conjunction with the drawing appended hereto. For example, the grinding or machining step according to the present invention may be accomplished by using a single pass or a multiple pass with a grinding wheel. Such variations are included within the intended scope of the claims appended hereto.

Claims

1. A method of forming a precision ball race groove track in a race member of a universal joint, said method comprising the steps of:

forming said race member with a formed ball race groove track and with a recess groove extending substantially along the apex of said formed ball race groove track, said recess groove having a base that will not come into contact with a finishing tool used to finish machine said ball race groove track; and

finish machining said formed ball race groove track to a predetermined precision shape to produce said precision ball race groove track by moving said ball race groove track into contact with the finishing tool such that the finishing tool contacts said ball race groove track to thereby finish machine said ball race groove track without coming into contact with said base of said recess groove extending along said formed ball race groove track.

2. The method as claimed in claim 1 wherein said race member comprises a spherical inner race member, said spherical inner race member comprising a plurality of ball engaging ball race groove tracks, said precision ball race groove track comprising at least one of said plurality of ball engaging ball groove tracks.

3. The method as claimed in claim 1 wherein said race member comprises a spherical outer race member, said spherical outer race member comprising a plurality of ball engaging ball race groove tracks, said precision ball race groove track comprising at least one of said plurality of ball engaging race groove tracks.

4. The method as claimed in claim 1 wherein said recess groove extends along the apex of has substantially constant depth along its length in relation to said formed ball race groove track.

5. The method as claimed in claim 1 wherein said recess groove has a width substantially larger than its depth relative to said formed ball race groove track.

6. The method as claimed in claim 1 wherein said recess groove has a predetermined depth substantially larger than the depth of said predetermined precision shape obtained by said finish machining step.

7. The method as claimed in claim 1 wherein said recess groove extends circumferentially between ten and thirty degrees of arc relative to said formed ball race groove track.

8. A method of forming an outer race member of a universal joint having an inner race member and a plurality of ball engaging race groove tracks in said inner and outer race members, said method comprising the steps of:

forming a cavity in said outer race member, said cavity having a plurality of spaced apart ball race groove tracks formed therein, each of said plurality of spaced apart ball race groove tracks having a recess groove formed in the apex thereof, said recess groove having a base that will not come into contact with a finishing tool used to finish machine said ball race groove track; and

finish machining each of said plurality of spaced apart ball race groove tracks to a predetermined precision shape to produce a plurality of precision ball race groove tracks by moving said ball race groove track into contact with the finishing tool such that the finishing tool contacts said ball race groove track to thereby finish machine said ball race groove track without coming into contact with the base of said recess groove extending along each of said plurality of spaced apart ball race groove tracks.

9. The method as claimed in claim 8 wherein each said recess groove has a width substantially larger than its depth relative to the respective one of said plurality of spaced apart ball race groove tracks associated therewith.

10. The method as claimed in claim 8 wherein each said recess groove has a predetermined depth substantially larger than said predetermined precision shape obtained by said finish machining step.

11. The method as claimed in claim 8 wherein each said recess groove extends circumferentially between ten and thirty degrees of arc relative to the respective one of said plurality of spaced apart ball race groove tracks associated therewith.

12. A method of forming an inner race member of a universal joint having an outer race member and a plurality of spaced apart ball engaging race groove tracks in said inner and outer race members, said method comprising the steps of:

forming an inner race member having an outer spherical surface and a plurality of spaced apart ball race groove tracks formed thereon, each of said plurality of spaced apart ball race groove tracks having a at least one recess groove formed in substantially at the apex thereof, said at least one recess groove having a base that will not come into contact with a finishing tool used to finish machine said ball race groove track; and

finish machining each of said plurality of spaced apart ball race groove tracks to a predetermined precision shape to produce a plurality of precision ball race groove tracks by moving said ball race groove track into contact with the finishing tool such that the finishing tool contacts said ball race groove track to thereby finish machine said ball race groove track without coming into contact with the base of said at least one recess groove extending along each of said plurality of spaced apart ball race groove tracks.

13. The method as claimed in claim 12 wherein each said recess groove has a width substantially larger than its depth relative to the respective one of said plurality of spaced apart ball race groove tracks associated therewith.

14. The method as claimed in claim 12 wherein each said recess groove has a predetermined depth substantially larger than said predetermined precision shape obtained by said finish machining step.

15. The method as claimed in claim 12 wherein each said recess groove extends circumferentially between ten and thirty degrees of arc relative to the respective one of said plurality of spaced apart ball race groove tracks associated therewith.

16. The method as claimed in claim 12 wherein said at least one recess groove comprises two recess grooves, each recess groove of said two recess grooves being located adjacent said apex of each of said ball race groove tracks on either side of said apex. 17. The method as claimed in claim 12 wherein said at least one recess groove is located adjacent said apex of each of said ball race groove tracks on at least one side of said apex. 18. The method as claimed in claim 12 wherein said at least one recess groove comprises one recess groove, said recess groove being located at said apex of each of said ball race groove tracks.