Abstract:
The invention relates to a wiper drive for a rear window wiper of a motor vehicle, comprising a drive unit having a wiper shaft for the oscillating pivoting about a rotational axis, and having a protective cap surrounding the wiper shaft in an axial section, wherein the protective cap is connected to a housing of the drive unit by way of a radial press fit connection. The protective cap comprises a detent element engaging in a recess in the housing in order to absorb axial forces on the protective cap.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a wiper drive for a rear window wiper of a motor vehicle. 
     A wiper drive is an encapsulated drive unit for the oscillating pivoting movement of a wiper arm about an axis of rotation in order to guide a wiper blade connected to the wiper arm between two turning positions over a windshield and consequently to remove impurities or wet spots from said windshield. The wiper drive can be used in particular on a rear window wiper of a motor vehicle. Here, the wiper shaft is usually protected by means of a protective cap against penetrating moisture and foreign bodies. The protective cap is connected by means of a radial press connection to a cylindrical formation of a housing of the wiper drive, with the wiper shaft extending through the formation. The relatively hard protective cap is in turn surrounded by a soft rubber bush in the region of a lead-through through a vehicle body or through the windshield of the motor vehicle. The wiper drive is connected at elastically mounted suspension points to the body of the motor vehicle in order to provide insulation with respect to structure-borne noise and vibrations. 
     During the wiping operation, the wiper drive moves relative to the body of the motor vehicle owing to the wiper forces which occur. As a result of this movement, owing to a so-called pumping action, axial forces are exerted on the protective cap which attempt to free the protective cap from its press connection with the housing of the wiper drive and pull it off in the upward direction. Further axial forces can occur when an impulse acts in the axial direction on the wiper drive or the wiper arm, for example when banging closed a tailgate of the motor vehicle on which the wiper drive is fastened. 
     SUMMARY OF THE INVENTION 
     The object on which the invention is based is to provide an improved wiper drive which is better protected against axial loads in the region of a lead-through through the body of the motor vehicle. 
     A wiper drive according to the invention for a rear window wiper of a motor vehicle comprises a drive unit having a wiper shaft for pivoting in an oscillating manner about an axis of rotation and a protective cap which surrounds the wiper shaft over an axial portion, wherein the protective cap is connected by means of a radial press connection to a housing of the drive unit. The protective cap comprises a latching element which engages in a cutout in the housing in order to absorb axial forces on the protective cap. The cutout preferably extends in the housing in a direction which is radial with respect to the axis of rotation. 
     According to the invention, the known press connection between the protective cap and the housing only remains stressed to a small extent if at all in the axial direction. The strength of the connection between the protective cap and the housing can consequently also be maintained after long-time or intensive use of the wiper drive. Moreover, by virtue of the axial fixing of the protective cap by means of the latching element, a relative movement between the wiper shaft and the protective cap can be minimized. As a result, the wear behavior of a seal between the protective cap and the wiper shaft can be improved. 
     In a preferred embodiment, the latching element is designed, after engaging in the cutout, to exert an axial prestress on the protective cap. As a result, the connection between the protective cap and the housing can be further secured. 
     The latching element can have a hook portion with an axial and a radial bearing surface in each case for bearing against a corresponding bearing surface in the region of the cutout of the housing. Here, an angle between the axial and the radial bearing surface of the hook portion can be 90° or less. If the angle is less than 90°, an axial force which attempts to remove the protective cap from its press connection with the housing can be used to further strengthen an engagement between the hook portion and the housing such that the protective cap cannot be released even when the axial forces acting on it are large enough to release the press connection to the housing. 
     The latching element can comprise an elastically deformable spring portion, wherein the spring portion comprises two webs which are separated from one another. The webs can extend next to one another from a cylindrical portion of the protective cap in a radial and/or axial direction with respect to the hook portion described. The provision of at least two webs which are separated from one another makes it possible for the protective cap to be maintained fixed in the axial direction even if one of the webs should tear, break or diminish in its spring force. Moreover, improved accessibility to the hook elements can be provided in the region between the webs, such that a tool can be applied at this point in order to remove the latching element from the cutout in the housing and to withdraw the protective cap. 
     The spring portion can comprise a first, radial portion and a second, axial portion. As a result of the L-shaped spring portion, it is possible for spring properties to be predeterminable in an advantageous manner by correspondingly dimensioning individual portions of the spring portion. 
     The protective cap can comprise a torque support with a bearing surface, which extends in the circumferential direction of the protective cap, for bearing against a corresponding bearing surface of the housing. 
     Consequently, a correct rotational orientation of the protective cap can be imposed during assembly on the housing. The latching element can thus be improved in its holding reliability. Moreover, the torque support can contribute to absorbing rotational forces, with the result that the press connection of the protective cap with the housing can be further relieved of stress. 
     In one embodiment, the protective cap is formed in one piece with the latching element. As a result, assembly can be simplified and manufacturing costs can be reduced. Additional parts to achieve the effect according to the invention are not required. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       It is also possible to provide a plurality of latching elements which are arranged in different radial directions on the protective cap. Angles between the latching elements or between one of the latching elements and the torque support can be identical. The latching elements and the torque support can thus be distributed uniformly over the circumference of the protective cap. As a result, forces can be more uniformly transferred between the protective cap and the housing such that the durability of the protective cap and, in particular, of its latching elements can be improved. The invention will now be described more precisely with reference to the appended figures, in which: 
         FIG. 1  shows a wiper drive for a rear window wiper of a motor vehicle; 
         FIG. 2  shows a sectional view through the wiper drive from  FIG. 1 ; 
         FIG. 3  shows a protective cap for the wiper drive from  FIG. 1 ; 
         FIG. 4  shows detail views of a housing of the wiper drive from  FIG. 1 ; and 
         FIG. 5  shows a sectional view through the wiper drive from  FIG. 1  during assembly of the protective cap. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a wiper drive  100  for a rear window wiper of a motor vehicle  105 . The wiper drive  100  comprises a drive unit  110  with a housing  115  on which a drive motor  120  is mounted. A drive shaft  125  projects from the housing  115  in a vertical direction. What cannot be seen is a gear mechanism of the drive unit  110  which is accommodated in the housing  115  and transmits a movement of the electric motor  120  to the drive shaft  125 . The drive unit  110  is configured such that or is activated in such a way that the drive shaft  125  is rotated in an oscillating manner about an axis of rotation  130 . The drive shaft  125  has an upper shaft end which is configured for the torque-locking fastening of a wiper arm. 
     A lower axial portion of the drive shaft  125  is surrounded by a protective cap  135  which at a lower end comprises two latching elements  140  which engage in the radial direction in corresponding cutouts  145  in the housing which extend transversely with respect to the axis of rotation  130 . 
     The protective cap  135  has a lower portion from which the latching elements  140  extend, and an upper portion which has a smaller outside diameter than the lower portion. The two portions are substantially cylindrical. 
       FIG. 2  shows a sectional view through the wiper drive  100  from  FIG. 1 . There is represented a detail which comprises a region around the protective cap  135 . The latching elements  140  are not represented in  FIG. 2 . 
     The protective cap  135  has, in the region of its left end, a sealing lip  205  which is peripherally in contact with the drive shaft  125  in order to prevent moisture and/or impurities from penetrating a region within the protective cap  135 . For the same purpose, an O-ring  210  is situated on an inner side of the protective cap  135  in the region of the sealing lip  205 . The O-ring  210  is held in the axial direction to the left by the sealing lip  205  and in the axial direction to the right by a retaining ring  215 . The retaining ring  215  can be pressed with elastic stress into the interior of the protective cap  135  or fixedly mounted there by means of ultrasonic welding. 
     The protective cap  135  is preferably made of plastic, in particular a relatively hard plastic such as, for example, PA66. 
     In the region of a right end, the protective cap  135  is conically formed on its inner side. The housing  115  has an approximately tubular extension  220  which extends coaxially to the drive shaft  125  and the protective cap  135 . The extension  220  is likewise conical on its outer side, with the result that a press fit can be produced between the protective cap  135  and the extension  220  by the protective cap  135  in the illustration of  FIG. 2  being pushed with a predetermined axial force to the right onto the extension  220 . 
     There is an axial gap  230  in the region between a right axial end of the protective cap  135  and a shoulder  225  of the extension  220 . In an embodiment of the protective cap  135  having at least one latching element  140 , it is advantageous to reduce the axial gap  230  to 0, in order to prevent the protective cap  135  being moved as a result of operation, shaking or vibration in such a way that the press fit between the protective cap  135  and the extension  220  is released. 
       FIG. 3  shows a protective cap  135  having two latching elements  140  for the wiper drive  100  from  FIG. 1 . Here,  FIG. 3   a  shows a complete view of the protective cap  135  and  FIG. 3   b  shows an enlargement of a portion of the protective cap  135  with one of the latching elements  140 . 
     The two latching elements  140  enclose an angle of about 120° with respect to the axis of rotation  130 . A torque support  305  is situated offset at angles of about 120° with respect to the latching elements  140 . The torque support  305  is substantially formed by an axial extension having two bearing surfaces  310  which are situated substantially opposite one another in the circumferential direction of the torque support  305  around the axis of rotation  130 . The bearing surfaces  310  preferably extend in radial planes with respect to the axis of rotation  130 . 
     The latching element  140  comprises a spring portion  315  and a hook portion  320 . The spring portion  315  connects a lower end of a cylindrical portion of the protective cap  135  to the hook portion  320  and is formed by a first web  325  and a second web  330  which extend substantially parallel to one another. Each web  325 ,  330  comprises a first, radial portion  335  and a second, axial portion  340 . The radial portion  335  extends substantially perpendicularly to the axis of rotation  130  and forms an angle of about 90° with the axial portion  340 . 
     The hook portion  320  comprises an axial bearing surface  345  which points upwardly, and a radial bearing surface  350  which points inwardly with respect to the axis of rotation  130 . In other embodiments of the invention, the radial bearing surface  350  may also point outwardly in the radial direction. The bearing surfaces  345  and  350  enclose an angle with one another which is at most 90°, but preferably slightly less, for example about 85° or about 80°. 
       FIG. 4  shows detailed views of a housing  115  of the wiper drive  100  from  FIG. 1 . In  FIGS. 4   a  and  4   b , the housing  115  can be seen from different perspectives. 
     The extension  220  is supported by means of a number of radial webs  405  with respect to the remainder of the housing  115 . Two adjacent webs  405  form a cutout for receiving the torque support  305  of the protective cap  135 . Bearing surfaces  410  of the webs  405  that extend perpendicularly to the circumferential direction are designed to bear against the bearing surfaces  310  of the torque support  305 . 
     The webs  405  are connected to one another by means of an annular reinforcement  415  extending around the axis of rotation  130 . On a radial outer side, the cutout  145  is made in the radial direction in the reinforcement  415  in the region between two webs  405 . The cutout  145  forms an undercut on the housing  115 . 
       FIG. 5  shows a sectional view through the wiper drive  100  from  FIG. 1  while assembling the protective cap  135 . The region illustrated is limited to an area surrounding one of the latching elements  140 . To clarify the illustration, the first web  325  of the spring portion  315  of the latching element  140  is not illustrated.  FIG. 5   a  shows the protective cap  135  in a position in which the hook portion  320  of the latching element  140  is not yet completely latched into the cutout  145 , while in the illustration of  FIG. 5   b  the hook portion  320  is completely latched in. 
     In the position of the protective cap  135  shown in  FIG. 5   b , an outer boundary surface  505  of the reinforcement  415  is in contact with the radial bearing surface  350  of the hook portion  320  of the latching element  140 . An upper (in the axial direction) boundary surface  510  of the cutouts  145  which extends through the reinforcement  415  bears simultaneously against the axial bearing surface  345  of the hook portion  320  of the latching element  140 . 
     The latching element  140  is preferably dimensioned in such a way that the spring portion  315  of the latching element  140  exerts a downwardly directed prestress on the protective cap  135  when the axial gap  230  is zero and the hook portion  320  is completely latched in, as is illustrated in  FIG. 5   b . The prestressing is mainly maintained by the radial portion  335  of the web  330 . The press connection represented in  FIG. 2  between the extension  220  of the housing  115  and an end of the protective cap  135  corresponding thereto can consequently be reduced or even completely liberated in its loading by axial forces such that a releasing of the press connection in the operation of the wiper drive  100  is less probable or can be prevented.