Abstract:
The invention relates to a gear drive unit ( 10 ), in particular to adjust moveable parts in a motor vehicle, with a gear housing ( 15 ) and a shaft ( 18 ) positioned therein along a longitudinal axis ( 30 ), which shaft is supported on the housing ( 15 ) via an axial stopping face ( 35 ) on a counter stopping face ( 36 ), wherein at least one of the stopping faces ( 35, 36 ) is inclined perpendicular to the longitudinal axis ( 30 ) against a plane ( 42 ) by an angle of inclination ( 40 ) in order to generate an axial force, and a component ( 44 ), which cooperates with at least one of the stopping faces ( 35, 36 ), is arranged in a displaceable manner perpendicular to the longitudinal axis ( 30 ). In doing so, the coefficient of friction between the at least one stopping face ( 35, 36 ) and the component ( 44 ) is greater than the tangent of the angle of inclination ( 40 ).

Description:
BACKGROUND OF THE INVENTION 
   The invention starts with a gear drive unite, in particular for adjusting moveable parts in a motor vehicle. 
   A drive device for a windshield wiper system of a motor vehicle, which features a housing and an armature shaft positioned rotatably therein that has a worm, became known with DE 198 545 35 A1. Using an axial force generating device, a wedge slider is hereby displaced radially to the armature shaft in order to equalize the axial play of the armature shaft. The displacement force of the wedge slider is applied via a pre-stressed spring element, which presses the wedge slider radially against a limit stop of the armature shaft, thereby displacing the shaft axially until the axial play is equalized. On the other hand, with a great load to the armature shaft via a driven gear, an axial force occurs, which presses the armature shaft against the wedge slider and in doing so the wedge slider is pressed back radially away from the armature shaft against the spring element. This type of great permanent load on the spring element leads to a situation where its service life or its elastic properties are diminished and therefore the axial play of the armature shaft is no longer equalized so that it moves back and forth axially under load, which can produce unpleasant clicking noises. 
   SUMMARY OF THE INVENTION 
   The gear drive unit in accordance with the invention has the advantage that an axial force generating device is arranged in such a way that its coefficient of friction prevents a component that equalizes the axial play from receding radially. To do this, the geometry, the surfaces and the materials for the axial force generating device are selected in such a way that the coefficient of friction between a stopping face inclined by an angle of inclination against the perpendicular of the shaft and the surface of the component is greater than the tangent of the angle of inclination. In doing so, the component is displaced radially to the shaft as soon as the shaft has longitudinal play. Pushing back the component is prevented, however, by the frictional condition. As a result, an elastic element, which is used to displace the component, does not have to absorb any high restoring forces, which are initiated via the shaft on the component. Therefore, the elasticity of the elastic element is retained over its entire service life, thereby reliably eliminating the longitudinal play of the shaft over the entire service life. 
   In addition, the shaft longitudinal play is hereby eliminated without this longitudinal play having to be measured beforehand during the assembly of the device in order to equalize it, e.g., by means of selectively mounted equalizing plates. As a result, the number of stations on the assembly line is reduced and the assembly device is simplified. The axial force generating device can be manufactured using modular principles so that it is compatible with many different drive units. 
   Advantageous developments of the device are possible. Thus, the coefficient of friction between the surface of the component and the inclined stopping face is increased in an especially favorable way by forming a profile on one of the two friction surfaces. If, for example, a saw-tooth-like profile is formed on at least one of the surfaces, the component can be moved radially towards the shaft with less force, but can only be moved back radially again with a considerably higher expenditure of force. As a result, this type of structured surface leads to the elastic element for displacing the component not being excessively stressed. Therefore, the elastic element can be displaced back radially over the entire service life of the device in order to eliminate the axial play that is occurring. Because of forming such a profile on the friction surface between the component and the stopping face, the angle of inclination of the stopping face can be selected to be greater, thereby making greater travel available to equalize the shaft longitudinal play. In a preferred embodiment, one of the two stopping faces or the component can feature a stair-step-like surface, in which the “stepping surfaces” are aligned to be approximately perpendicular to the longitudinal axis of the shaft. As a result, a restoring force of the component radially away from the shaft is practically completely prevented with the effect of a axial force from the shaft. This produces a situation where no shaft longitudinal play is permitted even in the case of extreme loads on the shaft. 
   If the inclined surface forms a cone so that a truncated cone surface area is produced, the shaft is supported on a radially symmetrical surface, whereby the shaft remains very precisely centered radially symmetrically even under load. The purpose of the cone-shaped surface is so that at least one component can be displaced simultaneously from all sides uniformly towards the shaft axis. 
   It is particularly favorable if one of the stopping faces is embodied as one part together with the component. As a result, no additional stopping elements are required, thereby reducing assembly expenses. 
   If the component features a U-shaped design, then the component can be used in an especially favorable way also for a plunging-through shaft. In this case, the component is not arranged on the front side of a shaft, but surrounds the shaft and is supported, e.g., on a collar that is manufactured on it. This type of U-shaped component is also advantageous for the application of a shaft, which is supported with a stopping sleeve, because the U-shaped component surrounds the stopping sleeve in order to reduce the structural length of the drive. 
   In a preferred embodiment, the component is embodied to be annular and radially elastically tensile. As a result, this component slides on the basis of its pre-stress into the gap between the two stopping faces so that no additional elastic element, which acts on the component with a displacement force, is required. If such a component that is embodied as an elastic ring element is coupled with a stair-step-shaped stopping face, which is embodied as a cone, then the spring ring contracts in order to again equalize the increased axial play from the signs of wear. In the process, it is not necessary for the elastic ring element to be supported on the housing. 
   In order to reduce the structural length of the gear drive unit, the component can feature two separate wedge surfaces, which are connected to one another via a surface that is arranged perpendicular to the axis of the shaft. In doing so, the wedge-shaped component can be displaced back radially against the shaft over the course of time, whereby the structural height of the overall drive device is reduced by reducing the overall height of the component. In the process, the axial forces of the shaft are favorably absorbed very uniformly over a large diameter of the stopping face. 
   The axial force generating device in accordance with the invention can be arranged on both the front side or on a collar of the shaft, thereby guaranteeing a high variance for different designs of the gear drive unit. 
   If the shaft features a worm toothing, which meshes with a worm wheel for example, very high axial shaft forces occur, if for example a moveable part is moved against a limit stop. In just the same way, in the case of a spindle drive with thread toothing on the shaft, strong axial forces occur when accelerating or decelerating the moveable parts. The dynamic axial play that occurs in the process is equalized reliably and on a long-term basis via the device in accordance with the invention. 
   It is advantageous if the component is constantly guided back by a displacement force, which is applied by a pre-stressed elastic element. The stored energy of the spring element leads to a situation where such a self-adjusting axial play equalization presses the component with adequate force against the shaft over the entire service life of the gear drive. 
   It is especially favorable for assembly if the pre-mounted elastic element is pre-stressed directly with the fastening of the covering of the gear housing. Because of the radial assembly of the elastic element, no other auxiliary tools are required for this. 
   Even more favorable from a procedural point of view is if the elastic element is designed either as an integral part of the covering of the gear housing or the component since the elastic element is thereby directly positioned during assembly of the component or the gear housing covering and assembly is simplified by the reduction in the [number of] components. 
   If the component is embodied as one piece with the elastic element, it can be formed of a leaf spring for example. So that the wedge-shaped embodied leaf spring can absorb greater axial forces on their fore parts, it is embodied to be wavy in the area of the acting axial force for stability reasons. The free ends of the leaf spring simultaneously support the component in the process against the gear housing in order to guide the component back perpendicularly towards the shaft longitudinal axis. In this case, the component can be manufactured together with the elastic element very cost-effectively as a bent punch part. 
   The angle of inclination of the stopping face can be enlarged by a saw-tooth profile, thereby making greater travel available to equalize the shaft longitudinal play. 
   The drawings depict exemplary embodiments of a device in accordance with the invention and they are explained in greater detail in the following description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings show: 
       FIG. 1  A section of an exemplary embodiment of a gear drive unit. 
       FIG. 2  A schematic representation of the forces occurring in accordance with  FIG. 1 . 
       FIG. 3  An enlarged section of another exemplary embodiment in accordance with  FIG. 1 . 
       FIG. 4  Another exemplary embodiment during assembly of the component. 
       FIG. 5   a  A side view of the component from  FIG. 4 . 
       FIG. 5   b  A top view of the component from  FIG. 5   a.    
       FIG. 6   a  A side view of another component. 
       FIG. 6   b  A top view of the component in  FIG. 6   a.    
       FIG. 7  Another exemplary embodiment of an immersion spindle drive. 
       FIG. 8  The assembly of the component in accordance with  FIG. 7  is shown in cross-section. 
       FIG. 9   a  A side view of another component in accordance with  FIG. 8 . 
       FIG. 9   b  A top view of the component in accordance with  FIG. 9   a.    
       FIG. 10   a  A section of a gear drive unit with a stopping sleeve. 
       FIG. 10   b  A section of a gear drive unit with a stopping sleeve. 
       FIG. 10   c  A section of a gear drive unit with a stopping sleeve. 
       FIG. 11  A section of another exemplary embodiment with a stair-step-shaped cone as a stopping face. 
   

   DETAILED DESCRIPTION 
   The exemplary embodiment depicted in  FIG. 1  shows a section of a gear drive unit  10  in accordance with the invention in which an electric motor  12  (not shown in greater detail) drives via a worm gear  14  a shaft  18  embodied as a spindle  16 , which projects out of the gear housing  15  of the worm gear  14 . A worm wheel  20  featuring a collar  22  is formed on the shaft  18 . This collar  22  forms a first stopping face  24 , which is supported on a counter stopping face  26  of a stopping plate  28 , which is adjacent to the gear housing  15 . The shaft  18  that is positioned along a longitudinal axis  30  is supported with a fore part  32  on another stopping element  34  on the front side, which features a stopping face  35  on the side facing away from the fore part  32 . Embodied on the gear housing  15  is another stopping face  36 , which is inclined by an angle of inclination  40  against a plane  42  perpendicular to the longitudinal axis  30 . Arranged between the diagonal stopping face  36  and the stopping face  35  of the stopping plate  34  on the front side is a component  44 , which can be displaced perpendicular to the longitudinal axis  30  to eliminate the shaft longitudinal play. The component  44  is embodied to be wedge-shaped in the exemplary embodiment so that the wedge angle corresponds to the angle of inclination  40  of the inclined stopping face  36 . An elastic element  48  is arranged between the component  44  and a housing part  46  and the elastic element presses the component  44  radially into the gap  64  against the longitudinal axis  30 . 
   The operating principle of this axial force generating device is depicted schematically in  FIG. 2 . The stopping element  34  in this case is embodied as one piece with the component  44  so that the stopping face  35  is formed directly by the fore part  32  of the shaft  18 . When the shaft  18  is under load, an axial force  50  acts along the longitudinal axis  30  on the component  44 , which passes on this axial force  50  to the stopping face  36 . Resulting on the inclined stopping face  36  from the axial force  50  are a normal force  52  perpendicular to the stopping face  36  and a downhill slope force  54  parallel to the stopping face  36 , which pushes back the wedge-shaped component  44  against the elastic element  48  from the gap  64  between the shaft  18  and the stopping face  36 . A frictional force  56 , which is generated when displacing the component  44  against the stopping face  36 , acts against the downhill slope force  54 . In order to prevent the axial force  50  from pushing the component  44  back against a displacement force  58  applied by the elastic element  48  in the case of a strong axial load of the shaft, according to the invention, the frictional force  56  is greater than the maximum occurring downhill slope force  54  in the case of maximum axial load of the shaft  18 . This results mathematically in the tangent of the angle of inclination  40  being less than the coefficient of friction, which corresponds to the frictional force  56 . The coefficient of friction in this case is essentially determined by the selection of material and the surface quality of the surfaces that can be displaced against each other. 
     FIG. 3  depicts a component  44 , in which the coefficient of friction is increased via a saw-tooth profile  60  on a friction surface  62  between the component  44  and the diagonal stopping face  36 . In this case, the saw-tooth-like profile  60  is formed on the component, but can just as well be arranged on the diagonal stopping face  36  of the housing  15  or on the stopping face  35 . The saw-tooth profile  60  is formed in such a way that the wedge-shaped component  44  can be displaced perpendicularly toward the shaft  18  with less displacement force  58  of the elastic element  48  than [when] this is pressed back via the downhill slope force  54 . If the axial play increases again, e.g., due to wear of the stopping plate  34 , the component  44  is pushed further into the gap  64  between the stopping face  35  of the stopping plate  34  and the diagonal stopping face  36  of the housing  15  due to the elastic force  58  with which the elastic element  48  is supported against the housing part  46 . 
     FIG. 4  shows another exemplary embodiment in a representation in accordance with Section IV-IV in  FIG. 3 . The component  44  is embodied to be U-shaped, whereby in this case both legs are arranged against the fore part  32  of the shaft  18 . The elastic element  48  is embodied to be one piece as an integral part of the component  44 , whereby the one-piece component  44  is punched out of a steel sheet for example. During assembly, the component  44  is inserted into the gap  64  between the stopping plate  34  and the inclined stopping face  36  and the elastic elements  48  are pre-stressed with the fastening of a covering  66  of the housing  15 . The right half of the illustration shows the device  10  before assembly of the covering  66  and the left half of the illustration shows it after the covering  66  has been assembled. In doing so, the component  44  is pressed radially towards the shaft  18  with the force  58  of the elastic element  48 . For further equalization of the longitudinal play, the component  44  has a free displacement path  68  at its disposal via which the component  44  can be subsequently displaced. 
     FIGS. 5   a  and  5   b  depict the component  44  from  FIG. 4  again in a side view and a top view. The friction surface  62  of the component  44  is arranged against the plane  42  by the same angle of inclination  40  as the corresponding stopping face  36  of the housing  15 . The angle of inclination  40  and the overall length of the component  44  define a maximum travel  70  by which the shaft longitudinal play can be equalized at a maximum.  FIG. 5   b  depicts a maximum spring range  72  by which the elastic element  48  can be pre-stressed via the housing part  46  during assembly. This range  72  results in the force  58  with which the elastic element  48  presses the component  44  into the gap  64 . 
     FIGS. 6   a  and  6   b  depict a variation of the component  44  from  FIGS. 5   a  and  5   b , whereby a saw-tooth profile  60  is formed on the friction surface  62  of the wedge-shaped component  44  in this case. The U-shaped component  44  is embodied in this case to be wavy, as shown in  FIG. 6   b , in order to be able to absorb greater axial forces  50 . The maximum spring range  72  of the elastic element  48  is greater in this example whereby the component  44  is pressed against the longitudinal axis  30  with greater force  58 . 
     FIG. 7  depicts another exemplary embodiment of a gear drive unit  10  namely a plunging-through spindle motor, whose shaft  18  cannot be supported on its fore parts  32  on the end of the shaft  18 . In this case, an electric motor  12  drives a worm wheel  20  via a worm of the armature shaft and the worm wheel is positioned rotationally secured on the shaft  18 . Since the shaft  18  that is formed as a spindle  16  projects out of the gear housing  15  on both sides of the worm wheel  20 , the shaft  18  is positioned axially via two annular stopping faces  24 . 
   This is depicted in a section through the gear housing  15  in  FIG. 8 . The worm wheel  20  of the shaft  18  has a collar  22  on the one side, which forms a stopping face  24 , which is adjacent with the stopping face  26  of a stopping plate  28 , which is supported in turn on the gear housing  15 . On the axially opposite side of the worm wheel  20  it also has a collar  23 , which the shaft  18  also uses to support itself on a stopping plate  34  on this side. A stopping face  36  that is inclined against the plane  42  by the angle of inclination  40  and through which the shaft  18  penetrates is formed in this exemplary embodiment for equalizing the axial play. In this case, a wedge-shaped component  44  is inserted perpendicular to the shaft  18  between the stopping face  35  of the stopping plate  34  and the inclined stopping face  36  of the gear housing  15  in order to equalize the axial play between the shaft  18  and the housing  15  that is caused by manufacturing and operation. The component  44  has a wedge angle  40 , which corresponds to the angle of inclination  40  of the inclined stopping face  36 . Sharp edges  61  are formed on the friction surface  62  towards the stopping face  36  and these sharp edges correspond to a saw-tooth profile  60 . The component  44  is pressed into the gap  64  between the stopping plate  34  and the stopping face  36  with a force  58 , which is generated by the pre-stressed elastic element  48 . In this case, the element  44  cannot be embodied to be flat, as is possible with a support of the shaft  18  via its fore parts  32 , but the component  44  is embodied to be U-shaped or arched in order to surround the shaft  18 . 
   One variation of the U-shaped component  44  is depicted in  FIG. 9   a  and  FIG. 9   b  in a side view and a top view. The friction surface  62 , which is embodied in this case a smooth surface  63 , is subdivided into two offset regions in the side view, which are connected via a surface  76 , which runs parallel to plane  42 . With this embodiment the corresponding stopping face  36  has a correspondingly stepped wedge profile. In this connection the structural height  78  of the component  44  can be reduced without the angle of inclination  40  being reduced as a result.  FIG. 9   b  shows the component  44  in the top view with the partial friction surfaces  62  and the intermediate surfaces  76 , which run parallel to the plane  42 . The housing  15  (or alternatively also the approximately quadratic stopping plate  34 ) must have a correspondingly inclined stopping face  36  in the area of the U-shaped, formed friction surface  62 . It is essential that one of the two stopping faces  35  or  36  is inclined in accordance with the wedge angle  40  of the component. In one variation, the component is embodied as a two-sided wedge and the two stopping faces  35 ,  36  are each inclined by the one angle portion. 
     FIGS. 10   a  through  10   c  depict another exemplary embodiment in which a shaft  18  is positioned axially on its fore part  32  in a stopping sleeve  80 . An annular stopping face  35  is again formed on the stopping sleeve  80 , and the stopping face is adjacent to the arched embodied component  44  that surrounds the stopping sleeve  80 . The component  44  supports itself on the other hand via the friction surface  62  on the stopping face  36  that is inclined by the angle of inclination  40 . 
   The component  44  is again embodied to be one piece with the elastic element  48 , which supports itself on a covering  66  of the gear housing  15 . The one-piece component  44  is manufactured as a leaf spring  45  similar to in  FIGS. 5   a  and  5   b , whereby this leaf spring is embodied to be wedge-shaped particularly in the areas  84  in the insertion direction. The component  44  has a displacement path  68  at its disposal for equalizing the longitudinal play occurring during the operating time via which the component can be subsequently pushed into the gap  64  via the elastic force  58  of the elastic component  48 . 
     FIG. 11  shows another exemplary embodiment, in which the inclined stopping face  36  is embodied as a cone  90 . The shaft  18  features a collar  23 , which is adjacent to an annular stopping plate  34 . In this case, the inclined stopping face  36  is not embodied as a flat plane, but radially symmetrical as a truncated cone surface area  90 , which forms the angle of inclination  40  with the plane  42 . The shaft  18  penetrates the stopping face  36  in the center of this cone  90  so that this exemplary embodiment is also suitable for a plunging-through spindle  16 . The cone-shaped stopping face  36  features a stair-step-like profile  91  in this case so that the individual ring surfaces  92  run approximately parallel to the plane  42 . An elastic ring element  94 , via which the shaft  18  is supported on the housing  15 , is arranged as a component  44  between the stopping face  35  of the stopping plate  34  and the conical stopping face  36 . The elastic ring element  94  is comprised, e.g., of a put-together spiral spring  96 , which is mounted under pre-stress in a resting position  98  in the gear housing  15 . The annular spring  96  tensions as soon as it is shifted out of its resting position  98  into the gap  64  between the two stopping faces  36  and  35  and contracts so much until the axial play is equalized. If the axial play increases, e.g., due to wear, the spiral spring  96  can contract further radially in the gap  64 . When the shaft  18  exerts an axial force  50  on the component  44 , the formed-on, annular steps  92  prevent the component from being forced back out of the gap  64  radially away from the longitudinal axis  30  since no downhill slope force  54  results because of the parallel alignment of the ring surfaces  92  to the stopping plate  34 . In this connection, the frictional condition that the coefficient of friction is supposed to be greater than the tangent of the angle of inclination  40  of the conical surface  36  is guaranteed by the step-shaped profile. In an alternative embodiment, the stopping face  36  that is embodied as a cone  90  features a smooth surface  63 , and the component  44  is manufactured at least on its surface of a material that yields a high coefficient of friction in connection the surface of the cone  90 . In the case of the embodiment according to  FIG. 11 , no separate elastic element  48 , which is supported on a housing part  46 , is required either, but because of the elastic design of the component  44  as an annular spring  96 , the displacement force  58  is applied via the radial pre-stress of the elastic ring element  94 . 
   In another variation of this exemplary embodiment, instead of the elastic ring element  94 , several wedge-shaped components  44  are situated in the gap  64  between the step-shaped cone  90  and the stopping face  35  of the stopping plate  34 . In this case, it is preferred that the components  44  be embodied as circular ring segments, whose friction surface  62  also features step-shaped ring surface segments, which run approximately parallel to the ring surfaces  92  of the cone or to the plane  42 . These components are pressed into the gap  64  by means of elastic elements  48 , which are supported for example either on the gear housing  15 . Alternatively, one annular spring  96  is arranged around the components  44  on their radial outer surfaces, and the annular spring exerts a radial displacement force  58  on the wedge-shaped, stepped components  44  during contraction. 
   The axial force generating device in accordance with the invention is used preferably with plunge-through spindle drives, but it can also be used for supporting armature shafts with any drive elements or other drive components. In addition, the invention also includes individual features of the exemplary embodiments or any given combination of the features of different exemplary embodiments.