Method for the production of a spindle nut of a spherical thread drive mechanism

Method for the production of a spindle nut (3) of a spherical thread drive mechanism, whereby the spindle nut (3) has at least one screw-shaped track (4) formed as a single piece on its inner circumference, whose threads (38) are limited by shoulders (6). The shoulder (6) is interrupted by a deflecting recess (23) at at least one deflecting position, in order to deflect balls (13) out of one thread into an adjacent thread (38). The method includes locating a tool arbor (56) in a hollow blank (57), whereby the tool arbor (56) has on its outer circumference a counter profile of the screw-shaped track (4) and a projecting part (59) for each deflecting recess. A tool operates on and reshapes the blank (57) from the exterior by exercising radial forces (F), whereby during the reshaping process the inner circumferential surface of the blank (57) is shaped according to the counter profile and to the projecting part (59) of the tool arbor (56) such that the screw-shaped track (4) and the deflecting recess (23) are formed.

BACKGROUND

The present invention relates to a method for the production of a spindle nut of a spherical thread drive mechanism.

From DE 31 00 349 C2, for example, a spherical thread drive mechanism of a spherical roll spindle and one of these encompassing bearing nuts under formation of an annular gap have been known, which have screw-shaped circular recessed tracks of the same slope facing one another. The threads of the tracks are separated from one another by means of corresponding screw-shaped circular raised shoulders. The tracks form spherical tracks that extend over an angle of circumference of approximately 360°, whereby bearing balls run in these spherical tracks. Each spherical track has an approximately S-shaped deflecting position, at which the balls are deflected out of one thread of the track into the adjacent thread. The spindle nut has an interruption in the shoulder at the deflecting position and a deflecting recess. The deflecting recess is necessary so that the balls can be raised over the corresponding shoulder of the spindle. The deflecting recesses are directly formed in the nut in an advantageous manner, such that these can be formed completely closed all around. The incorporation of the deflecting recesses can take place after the hardening of the spindle nut, for example, electrolytically or by means of electrical discharge machining.

This production of the deflecting recesses is very expensive for large runs of a series.

SUMMARY

The object of the present invention is to provide a method for the production of a spindle nut according to the invention, with which large lots can be produced in a cost-effective manner.

The method according to the invention provides for the following steps: arrangement of a tool arbor in a hollow blank, whereby the tool arbor has on its outer circumference a counter profile of the screw-shaped spherical track and a projecting part for each deflecting recess; providing a tool that operates on and reshapes the blank from the exterior by exercising radial forces, whereby during this reshaping process the inner circumferential surface of the blank is shaped according to the counter profile and to the projecting part of the tool arbor such that the screw-shaped spherical track and the deflecting recess are formed. During this process, material of the blank is displaced in order to produce the tracks and the deflecting recesses on the inner circumferential surface.

The method according to the invention can be carried out in a cost-effective manner. Well known reshaping methods suitable for the invention are, for example, kneading, cold forming by spinning, as well as fluid forming. The material of the blank is forced inwardly during this reshaping process and shaped to the contour of the tool arbor with the projecting parts. The well known kneading is suitable in a particular manner for the production of a spindle nut according to the invention, because rotationally unsymmetrical contours are easily produced by means of this method, whereby kneading jaws under radial impact action operate on the blank that is rotating relative to the kneading jaws and reshape them.

After the reshaping process, the tool arbor together with the projecting part is removed, after which the spindle nut can undergo a heat treatment. The spindle nut hardened in such a manner can be completed with additional component parts for the spherical thread drive mechanism. The method for the production of the spindle nut can take place with the subsequent heat treatment in production steps that follow one another, such that the spindle nuts according to the invention can be produced in a commercially efficient manner.

A device according to the invention for the implementation of the described method provides that the tool arbor has a recess in which the projecting part is formed as a stamp, which can be affixed in its extended position radially transverse outwards and inwards in comparison with the tool arbor, whereby the stamp is arranged in its extended position within the counter profile of the tool arbor. A problem-free removal is ensured with this device according to the invention. If the tool arbor is to be rotated forth out of the spindle nut in a screwing motion, the stamp is moved inward radially beforehand, such that a screwing motion is as problem-free as possible.

The tool arbor can be formed in a hollow manner for the operation of the stamp, whereby a connecting rod arranged in the hollow tool arbor works with the stamp, such connecting rod being held in its extended position in a primary connecting position of the connecting rod of the stamp. The connecting rod is then brought into a second connecting position for removal from the mold, which makes an inward shift of the stamp possible. However, the tool arbor can also be filled with hydraulic fluid in place of a connecting rod, which can be pressurized, whereby this hydraulic fluid works together with the stamp of this type, which is held in its extended position by means of the adjacent pressure. After taking away the pressure, the stamp can be removed radially inward, in order to rotate the tool arbor out of the spindle nut using a screwing motion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows the schematic assembly of a spherical roll spindle. The spindle1is encompassed by a bearing nut3by using an annular gap2. Depending on the type of a thread, a screw-shaped circular recessed track4is incorporated at the inner circumference of the nut3, which likewise faces a screw-shaped recessed track5on the outer side of the spindle1. Both of the tracks4,5have the same slope and the individual threads of the track4of the nut3or the track5of the spindle1are separated from one another by means of a corresponding screw-shaped circular raised shoulder6or7. The nut3can be sealed at the end sides against the spindle1with the help of strippers (wiper rings)8,9, and they can have a radially distant circumferential surface10at an end, with whose help the nut3can be fastened to an arbitrary component part11. In addition, cylindrical embodiments without a flange or with various other outer forms are possible. The flange10has, for example, a lubrication connection12for pouring a lubricant into the annular gap2.

The tracks4,5of the nut and the spindle that are facing one another form spherical tracks or spherical runs, in which balls13revolve to bear the spindle1, which is itself rotating. As a result of the annular gap2, the spindle1does not lie adjacent to the nut3, and it supports itself on it only by means of the balls13.

In each case, the spherical tracks extend over an angle of circumference of 360°. In order to obtain spherical tracks enclosed in themselves (these are plotted with dotted lines inFIG. 2), each spherical track contains an approximately S-shaped deflecting position16. At the same time, the deflecting positions16of the various spherical tracks are distributed equally over the circumference. A ball13entering from above inFIG. 3, from above the drawing plane (as is indicated with dotted lines inFIG. 4), for example in the thread of the track4of the nut3and in the facing thread39of the track5of the spindle1, rolls along these threads40of the track4of the nut3and is led back into the thread of the track of the spindle1facing it. This track leads through to the lower end inFIG. 3out of the drawing plane, and the ball rolls off above the drawing plane into the related thread areas of the nut3and the spindle1that are not visible, until it enters again above in the thread38of the nut and the thread39of the spindle. Viewed as a whole, in this manner one obtains a screw-shaped spherical track that runs over almost 360°, whereby the ends of the screw-shaped areas at the deflecting positions16are associated with one another. The course of spherical tracks of this type, in which the balls are led back internally, are well-known, such that nothing further about them should be suggested.

So that the balls13can be led back to the respective deflecting positions16, the shoulder6of the nut3has an interruption19at the deflecting position16. The dividing edges of these interruptions are designated with the reference numbers20and21. In addition, a deflecting recess23crossing the interruption19at the deflecting position16is incorporated into the wall of the nut3by means of a method described further below. The deflecting recess23is so deep that a ball that dips into it no longer touches the shoulder7of the spindle1. In this manner, the balls13can roll around in a radial direction outside the uninterrupted shoulder7of the spindle by means of the deflecting recess23and the interruption19of the shoulder6of the nut3. As a result, the balls13are located at the deflecting position16outside of interference with the track of the spindle1. After rolling through the deflecting recess16, the balls engage the track of the spindle1again and control it.

The measures described up until now are not yet sufficient to allow the balls to follow the path of the track to the deflecting position16. Namely, the balls12must still be prevented from rolling on straight ahead to the deflecting position16instead of the deflecting recess23. For this purpose, it is provided that deflecting surfaces reaching to both ends of the deflecting recess16in the track of the spindle and lifting these balls from this track into the deflecting recess are available, and that the spherical track is covered between the two deflecting surfaces on the spindle1by means of a covering that reaches into the annular gap2between nut3and spindle1. Therefore, the balls13are first diverted from one of the two deflecting surfaces from the spindle1to the deflecting recess23, after which they roll off from the covering, and after that come back again over the other deflecting surface in the track of the spindle. In a manner of speaking, both of the deflecting surfaces obstruct the balls from the path running on straight ahead, whereby one therefore requires a deflecting surface on both sides of the deflecting recess, because of course the spindle or the nut can rotate in both rotational directions, such that the balls must also be able to run through the spherical tracks in both directions.

The deflection of the balls13at the deflection positions16take place with the help of inserts. This involves insertion bodies35,36,37, which are represented in theFIGS. 3 and 4with thickly drawn lines, whereby only the insertion bodies35are complete, but the insertion bodies36,37are shown as cut. Two insertion bodies are associated with each deflection position16. An insertion body is arranged between two spherical tracks adjacent to one another or spherical runs. These two insertion bodies, for example the insertion bodies35,36, which are arranged for the deflection position containing the deflection recess23, are independent from one another and have a toric shape, in particular as appears graphically inFIG. 4. These toric bodies (which appear as essentially circular in the cross section) are curved corresponding to the tracks of the nut and of the spindle, which means they extend along an arc of a circle in the side view. One of the two insertion bodies, for example, the insertion body35, lies in the thread38of the track4of the nut3, as well as in the facing thread39of the track5of the spindle1. The other insertion body36is inserted into the adjacent thread40of the track4of the nut3, as well as into the track of the spindle facing this one, which is not visible inFIG. 4. Both of the insertion bodies35,36associated with the respective deflecting positions are therefore arranged in adjacent threads of the tracks of the nut and of the spindle, whereby they come to an end at the respective deflecting positions16coming from opposite sides. At the same time, both of the insertion bodies35,36face one another with their front sides at an angle, between which the respective deflecting recess23are located. In each case, these front sides, with their sections inserted into the track of the spindle1, are preferred for the formation of deflecting surfaces lifting the balls13out of the track5of the spindle1, and are cambered at an angle for the lateral control of the balls. InFIG. 3, in which the insertion bodies seen from the spindle are represented, the preferred sections41,42are visible, which, according toFIG. 4, seat nearly aground for the track5of the spindle1, whereby a clearance is present here. The front sides return out of these sections41,42in the longitudinal direction of the respective insertion bodies as seen towards the nut, whereby the dividing lines43,44of the front sides45,46running towards the nut are indicated with dotted lines in theFIGS. 3 and 4. At the same time, these front sides are positioned at an angle and cambered in such a manner that one obtains a flowing deflection of the balls in the deflecting recess23. In addition, each of the insertion bodies now contains a lateral projecting part47or48on the side of the interruption19relating to the deflecting recess23of the shoulder6of the nut3, whereby this projecting part runs up to the front side of the insertion body facing the respective deflecting position16. In addition, these projecting parts47,48stand in extension for the shoulder6of the nut3over the interruption19of this shoulder, on which the deflecting recess23is located, whereby the projecting parts47,48are arranged in the annular gap2between nut3and spindle1. As seen in the top view of the spindle, the projecting parts47,48(seeFIG. 3) have a lightly rounded outer contour, which passes over into the dividing lines of the related front sides of the insertion bodies in a flowing manner. The two projecting parts47,48, in each case belonging to an adjacent insertion body, face themselves with slight distance and in each case form a half of the covering of the spherical track for the spindle. Therefore, the balls are led inside the deflecting position on one hand at the bottom of the deflecting recess23and on the other hand not only at the cambered front side of the two insertion bodies, but also at the two projecting parts47,48.

Each insertion body, for example the insertion body35, extends itself inside the related threads38or39of the nut3or of the spindle1up to the deflecting position of the adjacent spherical track, as appears graphically inFIG. 3. At the same time, the insertion body on the other front side50, which is associated with this adjacent deflecting position, is correspondingly formed like the already described front side and, in addition, a corresponding lateral projecting part52is present there. In other words, one rotates the insertion bodies35,36,37around its transverse medial axis55running in a radial direction around 180°, thus exactly the same shape results in turn. In this manner, the halves from two insertion bodies are assigned to each deflecting position, while the respective other half of each insertion body is assigned to one of the two adjacent deflecting positions. Thus the insertion body35, for example, limits the deflecting position related to the deflecting recess23with its one front side45and the laterally facing projecting part47, and the deflecting position or related spherical track adjacent to the left inFIG. 3with its other front side50and the laterally facing projecting part51.

It can be seen that the areas of the spherical tracks of the spindle that are not covered, and the nut that is located in each case between two deflecting positions, are filled by the insertion bodies, such that no empty space is present, into which one can otherwise inadvertently pour in balls during the assembly, which were split during operation.

For fastening the insertion bodies it is provided that a radially projecting fastening pin52is affixed to them on the outer circumference, which is inserted into a corresponding tapped blind hole53of the nut. Alternatively, the insertion bodies can also be attached with adhesive or weld.

Ideally, the insertion bodies35,36,37can be produced as single pieces out of plastic or metal.

It can be yet further seen fromFIGS. 3 through 5that a continuous stepped surface54is present in the longitudinal direction on the outer circumference of the insertion bodies35,36,37, which passes over into the lower side of the respective lateral projecting part47,51facing the spindle1, in order to obtain an appropriate radial and axial clearance in the spherical track of the spindle.

FIG. 6shows in a schematic representation the production of the spindle nut3according to the invention, as well as a device according to the invention for carrying out the method. A tool arbor56is first introduced into a hollow blank57. The tool arbor56is provided with a counter profile (not represented here) on its outer shell surface for the track4of the spindle nut3. In addition, the tool arbor56is provided with a recess58, in which a radially arranged transverse stamp59is placed. As projecting part60, the stamp59forms the counter profile at the deflecting recess23at the inner circumferential surface of the spindle nut3. The tool arbor56is of a hollow design, whereby a connecting rod61is placed in the tool arbor56in an axial transverse manner. The connecting rod61is provided with a wedged surface62, which works together with a counter surface63of the stamp59.FIG. 6shows the stamp59in its extended position. External forces F now operate on the blank57, under which the material of the blank57is formed onto the contour of the tool arbor56with its stamp59. The force F is exerted over kneading jaws64, which are represented with dotted lines in theFIG. 4. The kneading jaws64carry out a compact stroke during a rotation relative to the blank57. This process is ended when the tracks4on the inner circumference of the blank57and the deflecting recess23are shaped. The connecting rod61is now axially shifted to the extent that the stamp59comes free. Now the stamp59can be shifted radially inwards. In this connection, the tool arbor56can then be un-screwed from the spindle nut3.

FIG. 7shows the same method as doesFIG. 6, but with a modified device for carrying out the method in comparison withFIG. 6. Here, instead of a connecting rod, hydraulic fluid65is poured into the hollow tool arbor56. The hydraulic fluid65can be pressurized. The stamp59is held in its position driven radially outward under the adjacent pressure. After the pressure is taken away, the stamp59can be shifted radially inward.