Abstract:
An axial adjusting device comprising two discs which are rotatable relative to one another, which are supported coaxially relative to one another and between which there are guided balls in pairs of ball grooves whose depth varies across the circumference. Of the discs, one is axially supported and one is axially displaceable against resilient returning forces of spring means. At least one of the discs is rotatingly drivable by a driving motor. For load reducing purposes, at least two balls are guided in each of the pairs of ball grooves.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to an axial adjusting device comprising two discs which are rotatable relative to one another, which are supported coaxially relative to one another and between which there are guided balls in pairs of ball grooves whose depth varies across the circumference. One disc is axially supported and the other disc is axially displaceable against resilient returning forces of spring means. At least one of the discs is rotatingly drivable by a driving motor.  
           [0002]    The rotatingly driven disc can, at the same time, be the axially displaceable one but this is an exception. Usually, the supported disc is rotatingly driven and the axially displaceable disc supported, in turn, via the balls on the supported disc in a rotationally fast way.  
         BACKGROUND OF THE INVENTION  
         [0003]    For actuating the axial adjusting device, the driving motor is driven in a first direction of rotation. At least one of the discs may be coupled to the driving motor, via a reduction stage and rotated. The axially displaceable disc which is supported in turn on the axially supported disc is axially displaced against the resilient returning forces of the spring means.  
           [0004]    The balls which contact end stops in the pairs of ball grooves and which, at the same time, are positioned in the deepest groove portions move to flatter groove portions as a result of the rotation of the discs relative to one another., as a result of which the discs are pressed apart.  
           [0005]    If the driving motor is driven in the opposite direction or de-energized, the resilient returning forces of the spring means acting on the axially displaceable disc cause the latter to be pushed back. At least one rotatingly drivable disc is actively rotated back by the driving motor or via the effect of the balls in the ball grooves until the balls in their pairs of ball grooves stop against the end stops.  
           [0006]    The balls in the ball grooves are subjected to high pressure forces so that ball damage (pittings) cannot be excluded. This may result in the balls being blocked and also in damage to the ball grooves.  
         OBJECT OF THE INVENTION  
         [0007]    It is therefore the object of the present invention to provide a design which reduces the load on the balls and on the ball grooves.  
           [0008]    The objective is achieved in that in each pair of ball grooves there are guided at least two balls. A larger number of balls per pair of grooves is possible, but the amount of rotation of the discs relative to each other should not be overly restricted. The individual ball grooves can be radially offset and circumferentially overlapping and partially run parallel to one another. As a result, although a larger number of balls is used, the amount of rotation can be sufficiently large.  
           [0009]    The larger number of balls reduces the specific load so that, optionally smaller balls and thus flatter ball grooves can be used. As a result, the axial length of the device can also be reduced.  
         SUMMARY OF THE INVENTION  
         [0010]    According to a preferred embodiment it is proposed that there are provided three pairs of ball grooves. Furthermore, it is proposed that there is provided a ball cage which holds the at least two balls in each pair of ball grooves at a circumferential distance from one another between the discs. In addition, it is advantageous that the cross-section of the ball grooves deviate from the shape of a circular arch, with the balls each having a two-point contact with the individual ball grooves. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 a  illustrates the axial adjusting device in an axial section with multiple ball bearings on ball grooves.  
         [0012]    [0012]FIG. 1 b  illustrates the axial adjusting device in an axial view.  
         [0013]    [0013]FIG. 2 a  illustrates one of the discs according to FIG. 1 in an axial view in an embodiment with five ball grooves,  
         [0014]    [0014]FIG. 2 b  illustrates a ball groove shape as a detail in longitudinal section.  
         [0015]    [0015]FIG. 3 a  illustrates the second one of the discs according to FIG. 1 with three ball grooves in an axial section.  
         [0016]    [0016]FIG. 3 b  illustrates the ball groove shape in a cross-section. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    [0017]FIG. 1 a  illustrates an axial adjusting device in accordance with the invention in a mounted condition. The end of a motor shaft  12  extends from a housing projection  13  of a driving motor  11 . The housing projection  13  is inserted into a centering bore  101  in a housing wall  102 . A shaft journal  14  with a driving pinion  15  is mounted on the shaft end  12 . A bearing journal  18  is inserted into a bore  103  in the housing wall  102 , with a sleeve pinion  19  being directly supported via two needle bearings  41  and  42  on the bearing journal  18 . A gearwheel  20  which engages the pinion  15  is pressed onto the sleeve pinion  19 . The sleeve pinion  19 , by means of its toothing, engages a toothed segment  22  which is firmly connected to a first disc  24  of the adjusting device. The disc  24  is rotatably supported via a needle bearing  23  on a projection  21  of a coupling cover  25  on which it is axially supported via an axial bearing  26 , a disc  27  and a securing ring  18 .  
         [0018]    The rotatingly drivable disc  24  cooperates with a further disc  29  which is slidingly supported on a projection  16  at the disc  24  and which is supported via an axial bearing  30  and a disc  31  on pressure springs  33  in the coupling cover  25 . The pressure springs  33  contain pressure pins  32  which form the adjusting members. The faces of the discs  24  and  29  which face one another comprise pairs of grooves  34  and  39  whose depths vary around the circumference and in which there run balls  35  which are held in a ball cage  36 . Each of the grooves extends from a first stop with the greatest groove depth to a second stop with the smallest groove depth. The disc  29  comprises a radial projection  37  with a guiding claw  38 . The guiding claw  38  glides in a longitudinally displaceable way on the holding pin  40  which is firmly inserted into a bore  105  in a housing wall  106  and which, in this way, holds the axially displaceable disc  29  in a rotationally fast way.  
         [0019]    [0019]FIG. 1 b  illustrates an axial view of the axial adjusting device of FIG. 1 a  with the reference numbers also being the same. FIGS. 1 a  and  1   b  show that a leaf spring  81 , whose free end cooperates with a stop curve  82  at the tooth segment  22  of the first disc  24 , is bolted to the projection  37  of the disc  29 . The end of the leaf spring  81  first glides along the stop curve  82 , generating friction forces, until it stops at a stop  83  at the tooth segment  22 , with the leaf spring  81  being shortened during further rotation. The leaf spring effectively engages the stop  83  prior to the balls reaching the end stops in the ball grooves.  
         [0020]    [0020]FIGS. 2 a  and  2   b  show the disc  29  in illustration A in an axial view, with the projection  37  and the guiding claw  38  being identifiable as details. The shape of the ball grooves  39  can be seen in detail. There are provided five uniformly circumferentially distributed, equally long ball grooves  39  which extend from a first end stop  71  of the greatest depth at the end A to a second end stop  72  of the smallest depth at the end B. The ball grooves in a matching disc  24 , in a plan view, provide an identical image, so that, if the parts are assembled as specified, the pairs of grooves can be made to overlap by means of their first ends A, with one ball resting at the first end stops  71  and with the discs assuming their closest positions relative to one another. A rotation of the discs relative to one another causes the balls in both grooves of a pair of grooves to move to the ends B, as a result of which the axially movable one of the discs moves away from the axially supported disc until another ball rests against the second end stops  72 .  
         [0021]    [0021]FIG. 2 b  shows the track shape in a longitudinal section wherein the ball stops  71  and  72  are provided at the deepest point A and, respectively, at the flattest point B of the ball groove  39  and have the shape of a spherical shell.  
         [0022]    [0022]FIG. 3 a  shows the disc  24  in an axial view, provided with balls, with the tooth segment  22  being visible as a detail. There are provided three equally long, uniformly circumferentially distributed ball grooves  34  which extend from a first axial end stop  71  of the greatest depth at the end A to a second end stop  72  of the smallest depth at the end B. The ball grooves in a matching disc  29 , in a plan view, form an identical image, so that if the components are assembled as specified, the pairs of grooves can be made to overlap by means of their first ends A. The ball grooves each contain two balls  35  which are held at the illustrated circumferential distance from one another by a cage (not illustrated). One ball  35  is positioned close to the second end stop B, in which case the discs are positioned furthest away from one another. A rotation of the discs relative to one another causes the balls  35  in both grooves of a pair of grooves to move to the end stops A, as a result of which the axially movable one of the discs approaches the axially supported disc until the respective other one of the balls stops against the first end stops A.  
         [0023]    [0023]FIG. 3 b  shows the track shape in a cross-sectional view. The ball groove  34 , above a base  43  with a smaller diameter than that of the ball  35 , comprises two flanks  44  and  45  which open in a V-like way and which form two contact points  46  and  47  with the ball.