Abstract:
A spindle gear unit ( 10 ), for an adjusting mechanism in a motor vehicle seat, includes a housing ( 20, 22 ), a spindle nut ( 40, 140, 240 ) cooperating with a spindle ( 30 ). The spindle nut ( 40, 140, 240 ) has external toothing ( 44, 144, 244 ) and has at least one bearing surface ( 46, 146, 246 ) for rotatably mounting the spindle nut ( 40, 140, 240 ) in the housing ( 20, 22 ). A thrust washer ( 50, 150, 250 ) is put on and encompasses the bearing surface ( 46, 146, 246 ). A screw ( 70 ) is rotatably mounted in the housing ( 20, 22 ) and has a worm gear ( 72 ) which is in engagement with the external toothing ( 44, 144, 244 ). The thrust washer ( 50, 150, 250 ) is pressed onto the spindle nut ( 40, 140, 240 ). A vehicle seat is also provided with the spindle gear unit for driving a seat rail of a length adjuster of the vehicle seat.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a United States National Phase Application of International Application PCT/EP2014/051707 filed Jan. 29, 2014 and claims the benefit of priority under 35 U.S.C. §119 of German Patent Applications 10 2013 001 804.8 filed Jan. 30, 2013 and 10 2013 207 665.7 filed Apr. 26, 2013, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a spindle gear unit for an adjusting mechanism in a motor vehicle, in particular in a motor vehicle seat, comprising a housing, a spindle nut for cooperation with a spindle, wherein the spindle nut has an external toothing and the spindle nut has at least one bearing surface for rotatably mounting the spindle nut in the housing, a thrust washer which is positioned on the bearing surface and encompasses said bearing surface and a worm which is rotatably mounted in the housing and has a worm gear which is in engagement with the external toothing of the spindle nut. 
         [0003]    The invention further relates to a vehicle seat. 
       BACKGROUND OF THE INVENTION 
       [0004]    A generic spindle gear unit is disclosed in DE 103 62 040 B4. A thrust washer absorbing axial forces, which, on the one hand, bears in the axial direction against a spindle nut and is connected fixedly in terms of rotation thereto and which, on the other hand, is supported in the axial direction on a bearing bush of a gear housing, comprises a projection which engages in a corresponding recess of the spindle nut and, as a result, forms a rotational locking. The rotational locking prevents noise being generated by relative movements between the thrust washer and the spindle nut. The threading of the projection of the thrust washer into the recess of the spindle nut requires a corresponding alignment of the thrust washer relative to the spindle nut and thus involves an additional operating step when mounting the spindle gear unit. Additionally, problems may arise in terms of quality control due to damage and the formation of chips on the spindle nut during the mounting of the gear unit by the projection of the thrust washer. 
         [0005]    DE 10 2005 001 333 A1 discloses a spindle gear unit with thrust washers which sit on projections but are not pressed onto said projections. 
         [0006]    A spindle gear unit comprising a spindle nut is disclosed in DE 10 2007 027 410 A1, said spindle nut comprising two bearing surfaces and an external toothing arranged between the bearing surfaces. One bearing surface of the spindle nut is mounted by means of five washers in a complex manner. For mounting the second bearing surface a thrust washer is provided. The washers and the thrust washer are located with clearance on the associated bearing surfaces and are not pressed onto said bearing surfaces. 
       SUMMARY OF THE INVENTION 
       [0007]    An object of the invention is based on improving a spindle gear unit for an adjusting mechanism of the type mentioned in the introduction, in particular providing a gear unit construction which is simple to mount, in which at least one thrust washer is connected fixedly in terms of rotation to a spindle nut, in particular without the thrust washer having to have a projection. 
         [0008]    As the thrust washer is pressed onto the spindle nut, in particular onto a projection of the bearing surface of the spindle nut, during the mounting process the thrust washer may be supplied without positional orientation and alignment. The thrust washer may additionally be a simple, planar component and less complex than conventional thrust washers with a projection. By being pressed from outside, a smooth surface may additionally be ensured on the running surface of the thrust washer relative to the bearing bushes. 
         [0009]    The term “pressed” is to be understood as an interference fit (press fit) in which before the joining process the largest dimension of the bore of the thrust washer is always smaller than the smallest dimension of the geometry of the spindle nut onto which the thrust washer is applied. “Shrink-fitted” which is known per se and which is based on the principle of thermal expansion is also intended to be understood hereinafter by the term “pressed”. 
         [0010]    Particularly low production costs are achieved when the at least one bearing surface has a circular cylindrical external contour, the central axis thereof being aligned with a rotational axis of the spindle nut. Alternatively, however, bearing surfaces may also be provided which deviate from the circular shape as is disclosed, for example, in DE 103 27 654 A1. 
         [0011]    The bearing surface may comprise, in addition to the external contour serving for mounting the spindle nut, further portions which are preferably arranged in the axial direction adjacent to the external contour, for example grooves or projections, i.e. diametral stepped portions. 
         [0012]    If the spindle nut comprises just two bearing surfaces, the external toothing being arranged therebetween, two thrust washers may be pressed simultaneously in opposing directions. The resulting forces on the spindle nut are then mutually cancelled out. 
         [0013]    Pushing the thrust washer onto the spindle nut may be achieved in a particularly simple manner by the thrust washer comprising an opening configured as a central hole with a diameter which is slightly larger than the external diameter of the external contour for the rotatable mounting of the spindle nut. The diameter of the opening is preferably slightly smaller than the external diameter of a projection of the bearing surface onto which the thrust washer is pressed. Preferably, the difference in diameter is 0.05 mm to 0.2 mm. 
         [0014]    Pushing the thrust washer onto the external contour of the bearing surface is achieved in a particularly simple manner by the projection being configured in a transition region between the bearing surface and the external toothing. The thrust washer may be initially pushed easily onto the bearing disk until the thrust washer finally reaches the projection and is pushed onto said projection. A chamfer on the end of the bearing surface remote from the external toothing simplifies the pushing of the thrust washer onto the bearing surface, by the thrust washer being centered and threaded-on by the chamfer. 
         [0015]    The projection preferably protrudes at least partially over the external contour of the bearing surface. However, the projection does not have to have a circular cross section but, for example, may also have a polygonal or toothed configuration. 
         [0016]    By pressing the thrust washer onto the projection of the spindle nut, a non-positive connection is produced between the thrust washer and the spindle nut. An alternative or additional positive connection may be achieved in that the extent of the external toothing in at least one axial direction is defined in a radially internal region of the external toothing by a front face oriented in the radial direction, and at least one retaining tip of the external toothing in a radial outer region of the external toothing protrudes in the axial direction over the front face in the direction of the thrust washer and the at least one retaining tip engages positively in a recess of the thrust washer. 
         [0017]    Preferably, a plurality of retaining tips are provided, said retaining tips being uniformly distributed over the periphery of the spindle nut, in particular each tooth of the external toothing forms a retaining tip in each of the two axial directions. The two thrust washers accordingly have correlating recesses which are formed, in particular, by pressing the thrust washer onto the spindle nut. The formation of the recesses may be achieved particularly effectively by the strength of the material of the spindle nut being greater than the strength of the material of the thrust washer. 
         [0018]    A recess in the form of a groove in the transition region between the bearing surface and the external toothing of the spindle nut may receive chip material which may form when the thrust washer is pressed on. The groove is preferably configured in each case adjacent to one of the two front faces of the spindle nut, in particular between one of the projections and the associated front face. 
         [0019]    A vehicle seat which is provided with a spindle gear unit according to the invention, in particular for driving a seat rail of a longitudinal seat adjuster and/or for driving a height adjuster, has cost advantages and as a result greater commercial value relative to a conventional vehicle seat. 
         [0020]    In a particularly cost-effective manner the thrust washers may be designed as planar stamped parts. The thrust washers in this case are preferably designed with a uniform material thickness and to be rotationally symmetrical, with a circular external diameter and a hole positioned centrally thereto. The internal diameter of this hole is designed as a simple press fit for the projection of the bearing surface. 
         [0021]    The invention is described in more detail hereinafter with reference to a figure for the prior art and two advantageous exemplary embodiments shown in the remaining figures. The invention, however, is not limited to these exemplary embodiments. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    In the drawings: 
           [0023]      FIG. 1  is an exploded view of a spindle gear unit known from the prior art; 
           [0024]      FIG. 2  is a perspective view of a spindle nut of a first exemplary embodiment of a spindle drive according to the invention; 
           [0025]      FIG. 3  is a view of the spindle nut corresponding to  FIG. 2  comprising a thrust washer partially pushed on during mounting; 
           [0026]      FIG. 4  is a view corresponding to  FIG. 3  with the thrust washer fully pressed on; 
           [0027]      FIG. 5  is a side view of a part of the spindle nut of the first exemplary embodiment; 
           [0028]      FIG. 6  is a section through the detail VI of  FIG. 5 ; 
           [0029]      FIG. 7  is a perspective view of a spindle nut of a second exemplary embodiment; 
           [0030]      FIG. 8  is a side view of a part of the spindle nut of the second exemplary embodiment; and 
           [0031]      FIG. 9  is a section through the detail IX of  FIG. 8 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]      FIG. 1  shows a spindle gear unit  10  that is known from the prior art. 
         [0033]    The spindle gear unit  10  comprises a housing which is made up of a first housing part  20  and a second housing part  22 . The two housing parts  20 ,  22  in the present case are connected together by four screws  24  provided in each case with a self-tapping external thread. Each of the four screws  24  passes through one respective through-hole  22   a  in the second housing part  22  and is screwed with its self-tapping external thread in one respective circular cylindrical hole  20   a  of the first housing part  20 . 
         [0034]    The housing  20 ,  22  forms an internal space and bearing regions for, on the one hand, a spindle nut  40  and, on the other hand, a worm  70  which together form a worm gear stage. The rotational axis of the spindle nut  40  defines an axial direction which is frequently oriented approximately in the direction of travel in spindle gear units for longitudinal seat adjusters in vehicles. The housing  20 ,  22  is continuously open in the axial direction for receiving a spindle  30  which in  FIG. 1  is shown only schematically by a dashed line. The spindle  30  has along its axial extent an external thread for cooperating with the spindle nut  40 . To this end, the spindle nut  40  has an internal thread  42  which is in engagement with the external thread of the spindle  30 . An external toothing  44  of the spindle nut cooperates with a worm gear  72  of the worm  70 . 
         [0035]    Viewed in the axial direction, the spindle nut  40  has on both sides of the external toothing  44  in each case a bearing surface  46  which substantially comprises a cylindrical external contour  46   d  which has an external diameter which is smaller than the external diameter of the external toothing  44  at the lowest points of the teeth, i.e. smaller than the internal circle of this external toothing  44 . A planar thrust washer  50  with a circular opening  50   a  is positioned on each of the two outer bearing surfaces  46 , said thrust washer comprising two main surfaces spaced apart from one another by a material thickness of the thrust washer, in each case facing outwardly and oriented perpendicular to the axial direction. The two main surfaces are preferably fully coated with a lubricating lacquer, in particular with PTFE. 
         [0036]    The thrust washer  50  has a projection  52  which protrudes axially but also could be configured radially. The axial projection  52  engages in the mounted state between two teeth of the external toothing  44 , whereby a rotational locking of the thrust washer is achieved relative to the external toothing  44 . This rotational locking may have a small degree of clearance which may be adjusted, for example, by adapting the dimensions of the projection  52 . In principle, however, the thrust washer  50  is coupled to the rotational movement of the spindle nut  40  due to the projection  52 . 
         [0037]    A bearing bush  60  is located on the two outer bearing surfaces  46 , in each case in the vicinity of the main surface of each thrust washer  50  remote from the external toothing  44 , said bearing bush comprising a ring  61  which by its basic geometry substantially corresponds to the thrust washer  50  and which has a circular cylindrical collar  62  of smaller external diameter, facing away from the external toothing  44 . The internal diameter of the collar  62  approximately corresponds to the external diameter of the associated bearing surface  46 . A lug  64  protrudes in the radial direction from the collar  62  of the bearing bush  60 . The bearing bush  60  is preferably made of a metallic bearing material. 
         [0038]    In the first housing part  20  and the second housing part  22  in each case semi-circular bearing grooves are provided for receiving the bearing bushes  60 . The housing  20 ,  22  also has a recess which receives the lug  64  so that the bearing bush  60  is not able to not rotate relative to the housing  20 ,  22 . 
         [0039]    During the operation of the spindle gear unit  10 , a relative rotation takes place between the bearing bush  60  connected fixedly in terms of rotation to the housing  20 ,  22  and the thrust washer  50  which is connected fixedly in terms of rotation to the spindle nut  40  rotating relative to the housing  20 ,  22 . Due to the axial forces, frictional forces occur in this case between the bearing bush  60  and the thrust washer  50  which may be kept as low as possible by a suitable material pairing. 
         [0040]    Moreover, the worm  70  is rotatably mounted in the housing  20 ,  22 . The axis of the worm  70  extends substantially at right angles and is offset to the axis of the spindle nut  40  and the spindle  30 . The worm  70  has a worm gear  72  on its outer circumference and on the inside a polygonal receiver for receiving a driving shaft, in particular a resilient shaft. The worm  70  is preferably rotatably mounted by a ball bearing on each of its axial ends respectively in one specific bearing opening  20   b ,  22   b  in the housing  20 ,  22 . A first bearing opening  20   b  is incorporated in this case in the first housing part  20  and a second bearing opening  22   b  is incorporated in the second housing part  22 . Additionally, bearing bushes, not shown in FIG.  1 —similar to the bearing bushes  60 —may be provided for mounting the worm gear in the housing  20 ,  22 . 
         [0041]    In a manner known per se, the gear unit is encompassed by two shells  90  made of rubber or a corresponding material suitable for noise damping and is accommodated in a substantially U-shaped angle bracket  95  which is fastened, for example, to or in a rail profile of a longitudinal seat adjuster for a vehicle. 
         [0042]    A spindle nut  140  of a first exemplary embodiment of a spindle gear unit according to the invention is shown in  FIGS. 2 to 6 , the construction thereof—provided not described differently hereinafter—corresponding to the spindle gear unit  10  of the prior art described above. The components which are different from the prior art have reference numerals increased by 100. 
         [0043]    The spindle nut  140  which in basic construction and mode of operation substantially corresponds to a spindle nut  40  of the prior art, has an external toothing  144  for cooperating with the worm gear  72  of the worm  70 . In the axial direction, the spatial extent of the external toothing  144  in both directions in a radial inner region, the diameter thereof being slightly smaller than the tip circle diameter of the external toothing  144 , is defined by one respective substantially planar front face  144   b . In the radial outer region of the external toothing  144 , said external toothing respectively protrudes slightly over the associated front face  144   b  to the side in the axial direction. As a result, each tooth of the external toothing  144  on both sides has one respective retaining tip  144   a  protruding over the associated front face  144   b , which preferably has an axial extent of a few tenths of a millimeter. 
         [0044]    Viewed in the axial direction on both sides of the external toothing  144 , the spindle nut  140  in each case has a bearing surface  146  which comprises an external contour  146   d  for the rotatable mounting of the spindle nut  140 , the basic geometry thereof being circular cylindrical, and which has an external diameter which is smaller than the external diameter of the external toothing  144  at the lowest points of the teeth, i.e. smaller than the internal circle of this external toothing  144 . 
         [0045]    In the transition regions to the front faces  144   b , i.e. between the external contour  146   d  and the front face  144   b , the bearing surfaces  146  in each case comprise a peripheral projection  146   a . In the region of the projection  146   a  the diameter of the bearing surfaces  146  is slightly larger than in the region of the external contours  146   d.    
         [0046]    The diameter of the projection  146   a  is preferably 0.05 mm to 0.2 mm larger than the diameter of the external contour  146   d.    
         [0047]    A peripheral groove  146   b  between the front face  144   b  and the projection  146   a  serves for receiving chips, which are produced in the process of pressing the thrust washer  150  onto the projection  146   a  described hereinafter. 
         [0048]    A planar, circular thrust washer  150  with a circular opening  150   a  is positioned on each of the two outer bearing surfaces  146 , said thrust washer comprising two main surfaces spaced apart from one another by the material thickness of the thrust washer  150 , in each case facing outwardly and oriented perpendicular to the axial direction. The central point of the circular opening  150   a  is identical to the central point of the circular thrust washer  150 . The diameter of the opening  150   a  corresponds to the diameter of the external contour  146   d  of the bearing surface  146  or is slightly larger. The diameter of the opening  150   a , however, at least before mounting, is smaller than the diameter of the projection  146   a , preferably by 0.05 mm to 0.02 mm. As a result, when mounting the spindle gear unit  10  the thrust washer  150  may be pushed over the external contour  146   d  of the bearing surface  146  without damaging said surface. Subsequently during the mounting process, however, the thrust washer  150  may simply press against the external contour  146   d.    
         [0049]    The thrust washer  150  differs from a thrust washer  50  of the prior art described above, therefore, in the design of the rotational locking to the spindle nut  140 . The thrust washer  150  is coupled to the rotational movement of the spindle nut  140 , by the opening  150   a  of the thrust washer  150  being located on the projection  146   a  with a press fit, due to the described difference in diameter. 
         [0050]    One end of each bearing surface  146  remote from the external toothing  144  has a chamfer  146   c  which is configured so that, during the mounting of the spindle gear unit, the pushing of the thrust washer  150  onto the bearing surface  146  is simplified. 
         [0051]    The thrust washer  150  is designed as a planar stamped part. The strength and/or hardness of the thrust washer is reduced relative to the strength and/or hardness of the projection  146   a  and the external toothing  144 . After supplying the two thrust washers  150  onto both bearing surfaces  146 , the two thrust washers  150  are pushed axially toward one another in the direction of the respectively associated front face  144   b , and subsequently pressed onto the projections  146   a . The softer material of the thrust washers  150  in this case is pushed onto the harder projection  146   a . The retaining tips  144   a  of the external toothing in the present case penetrate the thrust washer  150 , preferably sufficiently far until a main surface of the thrust washer  150  bears flat against the front face  144   b  of the external toothing  144 . By the penetration of the retaining tips  144   a  into the thrust washer  150  a positive driving is ensured by the spindle nut  140 . 
         [0052]    Pressing the thrust washer  150  onto the projection  146   a  may result in the formation of chips. The resulting chips are received in the groove  146   b.    
         [0053]    Naturally, the supply of the thrust washer  150  may take place separately during the mounting process, without positional orientation being necessary. 
         [0054]    A spindle nut  240  of a second exemplary embodiment of a spindle gear unit according to the invention is shown in  FIGS. 7 to 9 , the construction thereof—provided not described differently below—corresponding to the spindle gear unit  10  of the prior art described above. The components which are different from the prior art have reference numerals increased by 200. 
         [0055]    A connection which is fixed in terms of rotation between the spindle nut  240  and a thrust washer  250  takes place exclusively in a non-positive manner via a press fit between a projection  246   a  and the thrust washer  250 . The thrust washer  250  bears flat against a front face  244   b  of the spindle nut  240 , in the present case against a front face  244   b  of an external toothing  244 . In contrast to the first exemplary embodiment, geometric shapes which act in the same manner as the retaining tips  144   a  are not provided on the spindle nut  240 . 
         [0056]    The remaining features and mounting steps of the second exemplary embodiment correspond to the first exemplary embodiment. The components of the second exemplary embodiment, therefore, bear reference numerals which are increased by 100 relative to the first exemplary embodiment. The differences between the first exemplary embodiment and the second exemplary embodiment, therefore, are limited to the presence or absence of retaining tips. 
         [0057]    In particular, an internal thread  242 , two bearing surfaces  246 , a groove  246   b , a chamfer  246   c , an external contour  246   d  and in each case an opening  250   a  in the two thrust washers  250  correspond to the described components of the first exemplary embodiment. 
         [0058]    In a modification of the second exemplary embodiment, retaining tips are provided but they do not penetrate into the thrust washers  250 . The connection which is fixed in terms of rotation between the spindle nut  240  and the thrust washer  250  takes place exclusively in a non-positive manner via the press fit between the projection  246   a  and the thrust washer  250 . 
         [0059]    The features disclosed in the above description, the claims and the drawings may be significant both individually and also in combination for implementing the invention in its various embodiments. 
         [0060]    While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.