Abstract:
The invention relates to a thrust washer ( 28 ) for an electric machine ( 10, 12 ) intended to be arranged on a shaft ( 16 ) between a bearing ( 18 ) and a rotor ( 14 ), preferably a rotating electrical contact element ( 24 ) impacted by brushes ( 38 ), and/or a disk pack ( 36 ) of the rotor ( 14 ). The thrust washer ( 28 ) is provided with an area for sealing having two end faces ( 32, 34 ). On each end face ( 32, 34 ), at least one radial abutment section ( 50, 52 ) for the bearing ( 18 ), or the rotor ( 14 ), is provided. The thrust washer ( 28 ) according to the invention is characterized in that it is made of at least one hard component ( 54 ) and one soft component ( 56 ), wherein the part of the radial abutment section ( 50, 52 ) abutting the rotor ( 14 ) and/or the bearing ( 18 ) is formed by the soft component (56).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a thrust washer for an electric machine for arranging on a shaft between a bearing and a rotor, preferably a rotating electric contact element, which is influenced by brushes, or rather a laminate stack of the rotor, wherein the thrust washer comprises a region for providing a sealing arrangement with two end faces, and at least one radial contacting section for the bearing and the rotor respectively is provided on each end face. A thrust washer of this type for an electric machine can be arranged on a shaft between a bearing and a rotor, in particular between a rotating electrical contact element, which is influenced by brushes, or rather a laminate stack of the rotor. The thrust washer comprises a region for providing a sealing arrangement with two end faces and has on each end face at least one contacting section for the bearing and/or the rotor. 
         [0002]    Electric motors such as those generally used for heating and air-conditioning motors are required to fulfill stringent requirements with regard to noise. The noise level of said electric motors is greatly influenced by the so-called longitudinal oscillation of the armature that is excited by way of the longitudinal play of generally a few one-tenth millimeters that occurs in the electric motor during operation. So-called thrust washers are located in the electric motor and are arranged between the non-moving bush bearings and the rotating armature or rotor and said thrust washers by virtue of their material characteristics such as wear-resistance, surface, serviceable life etc.—reduce the friction. As a result of the likewise high requirements for a long serviceable life, in other words good wear resistance, the material, generally an elastic synthetic material, for example polyester elastomer, has a comparatively small amount of intrinsic elasticity. It is also known to install corrugated washers or corrugated rings. However, corrugated washers or corrugated rings only function when in contact between the non-moving parts and the rotating parts. 
         [0003]    It is possible by means of skillful selection of the elasticity and damping of the thrust washer to modify the excitation of the axial oscillation to such an extent that said axial oscillation is damped during operation and thus does not cause any noise production. DE 10 2004 044 340 A1 discloses for example a thrust washer of the type mentioned above for an electric machine, in which the contacting sections of the two end faces are mutually connected by way of resilient sections that are embodied on the thrust washer. 
       SUMMARY OF THE INVENTION 
       [0004]    The object of the invention is to provide a thrust washer for an electric machine that further improves the damping of the longitudinal oscillation of the armature with respect to existing thrust washers in conjunction with a cost reduction and further reduces the noise production. 
         [0005]    The thrust washer in accordance with the invention for an electric machine has the advantage that the damping of the longitudinal oscillation of the armature can be improved in conjunction with reducing the noise production without using additional parts (for example corrugated rings). In addition, the wear resistance is increased and the machine construction is simple. For this purpose, the thrust washer is embodied in an inventive manner from at least one hard component and at least one soft component, wherein the part of the radial contacting section that lies on the rotor and/or bearing of the electric machine is embodied by the soft component. High axial forces can be absorbed in this manner during operation by way of the hard component, whereas the soft component acts against the longitudinal oscillation of the armature and prevents a corresponding excitation. 
         [0006]    In addition, it is provided that the contacting section comprises at least two planes that are spaced apart in the axial direction of the shaft, wherein a first plane is formed by the part of the contacting section that lies on the bearing or rotor and at least a second plane is arranged between the first plane and the returning region, wherein the second plane is embodied from both the soft component and the hard component. By virtue of this arrangement the force is introduced over an elastic region—namely the first plane that is embodied as the soft component—and the damping behavior is further improved. The hard component of the second plane effectively prevents the soft component of the first plane from being damaged in the case of high axial forces. For this purpose, the soft component and the hard component are arranged in an advantageous manner between the first plane and a region for returning lubrication means in the axial direction of the shaft on the same second plane. As an alternative thereto, the soft component and the hard component between the first plane and the region for returning the lubrication means in the axial direction of the shaft are however also spaced apart from each other in such a manner that the hard component extends further in the direction of the first plane than the soft component, nonetheless it remains below the level of the first plane. In this manner, it is possible to provide a defined stop in the axial direction until damping by means of the soft component is ensured. 
         [0007]    In order to avoid having to provide an additional sealing function with respect to oil penetrating from the bearing in the direction of the rotor, in particular the commutator, the soft component is in an advantageous manner embodied in a circumferential manner at its inner diameter, preferably over the entire axial extension of its shaft-side contacting region between the two radial contacting regions. 
         [0008]    In an advantageous embodiment of the invention the hard component and the soft component are embodied from the same material, for example Hytrel. Consequently, the thrust washer can be embodied as one piece, wherein the hardness (quoted in Shore D) of the hard component and of the soft component differ by at least Shore D=5. The axial rigidity is clearly reduced in this manner and consequently a damping process is possible in the axial direction for example by using two Hytrel materials (or corresponding materials that have comparable intrinsic damping, abrasion hardness and temperature stability). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention is explained by way of example hereinunder with reference to  FIGS. 1 and 2 , wherein like reference numerals in the figures indicate like components that have like functions. The figures in the drawing, the description of the figures and the claims comprise numerous features in combination. A person skilled in the art will also consider these features individually and combine said features to form further expedient combinations. In particular, a person skilled in the art will also combine the features of different exemplary embodiments to form further expedient combinations. 
           [0010]    In the drawing: 
           [0011]      FIG. 1  illustrates a longitudinal sectional view of an electric machine according to the prior art and 
           [0012]      FIG. 2  illustrates a perspective view of a thrust washer in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    A part of a rotating electric machine  10  according to the prior art is illustrated in a simplified manner in a longitudinal sectional view in  FIG. 1 . The electric machine  10  is an electromotor  12  that is used in a motor vehicle for example in a window lifter, a wiper drive, preferably a heater and blower drive etc. However, it can also be a generator. 
         [0014]    The electromotor  12  comprises a wound rotor  14  that is arranged on a shaft  16 . The shaft  16  is mounted with two bearings  18 . The bearings  18  in the present exemplary embodiment are sintered cup and ball bearings or rather bush bearings that are saturated with oil. However, other bearings  18 , such as ball bearings or similar can also be used. The bearings  18  are in each case arranged in end plates  22  that are located on the two end faces of a housing  20  of the electromotor  12 . 
         [0015]    A thrust washer  28  having a receiving bore  30  for the shaft  16  is arranged between one of the bearings  18  and a commutator  26  that is used as an electric contact element  24 , wherein the thrust washer  28  preferably lies with its first end face  32  on the bearing  18  and with its second end face  34  on the commutator  26  and preferably has a press-fit on the shaft  16 . A sealing arrangement is created on the shaft  16  by means of the press-fit. A further thrust washer  28  is arranged between the other bearing  18  and the rotor  14  or rather a laminated core  36  or the collar  37  of an insulating laminate disk of the laminate stack  36 . However, this further thrust washer can also be omitted or a differently formed thrust washer can be provided. The rotor is supported in the axial direction of the shaft  16  on the bearings  18  by way of the one thrust washer  28  or the two thrust washers  28 . 
         [0016]    It is also possible in place of the commutator  26  to provide a collector of the generator as an electric contact element  24 . In both cases, the electric contact elements  24  are contacted by way of brushes  38  that are guided in brush holders  40 , wherein the brush holders  40  are fastened to a brush carrier  42  of the electric machine  10  by way of fastening brackets. 
         [0017]      FIG. 2  illustrates an enlarged view of the thrust washer  28  in accordance with the invention. Said thrust washer comprises a region  44  for returning the lubrication means to the bearing  18 . For this purpose, the thrust washer  28  extends in an annular manner over the end face  46  of the bearing  18  (cf. also  FIG. 1  regarding this), which end face faces the thrust washer. The thrust washer comprises on the outer rim an axially protruding edge  48  for the purpose of returning the lubricating means, for example oil, to the bearing  18 . In addition, the edge  48  acts as a protection for the commutator  26  against the lubricating means. The annular region  44  can alternatively also be embodied in a conical or arched manner, and—as illustrated in FIG.  1 —can extend in the shape of a hood over the bearing  18  in order to influence the return flow of the oil. Likewise, the thrust washer  28  can comprise further axial circumferential protrusions on the side of the annular region  44 , which side faces the bearing  18 , for the purpose of returning the lubricating means, but these will not be described here in detail. It is essential that a sealing region is provided which seals the rotor  14 , in particular the commutator  26 , from any possible oil flow from the bearing  18 . 
         [0018]    A radial contacting section  50  for the bearing  18  is embodied on the first end face  32  of the thrust washer  28  and a radial contacting section  52  for the rotor  14  is embodied on the second end face  34 . The rotor  14  or rather armature can contact the contacting section  52  directly or by means of the commutator  26 . It is provided in accordance with the invention that the thrust washer  28  is embodied from at least one hard component  54  and a soft component  56 , wherein the part of the contacting section  52  that is lying on the rotor  14  is embodied by the soft component  56 . This part is furthermore divided into individual circle segments  58  for the purpose of contacting the rotor  14 . 
         [0019]    The contact section  52  comprises two planes  60  and  62  that are spaced apart in the axial direction of the shaft  16 , wherein the first plane  60  is embodied by the circle segments  58  of the contacting section  52 , which circle segments lie on the rotor  14 . The second plane  62  is arranged between the first plane  60  and the region  44  for returning the lubricating means and is embodied from both the soft component  56  and the hard component  54 , whereas the region  44  for returning the lubricating means is embodied solely by the hard component  54 . By virtue of this arrangement the force is introduced over an elastic region—namely the first plane  60  that is embodied as the soft component  56 —and the damping behavior is further improved. The hard component  54  of the second plane  62  effectively prevents the soft component  56  of the first plane  60  from being damaged in the case of high axial forces. 
         [0020]    It is evident in  FIG. 2  that the hard component  54  and the soft component  56  of the second plane  62  are arranged in the axial direction on the same level. However, as an alternative thereto, the two components  54 ,  56  can also be spaced apart from each other in the axial direction of the shaft  16  in such a manner that the hard component  54  extends further in the direction of the first plane  60  than the soft component  56 , nonetheless it remains below the level of the first plane  60 . In this manner, it is possible to achieve a defined stop in the axial direction until the damping by means of the soft component  56  is ensured. 
         [0021]    In order to avoid having to provide an additional sealing function with respect to oil penetrating from the bearing  18  in the direction of the rotor  14 , in particular in the direction of the commutator  26 , the soft component  56  is in an advantageous manner embodied in a circumferential manner at its inner diameter, over the entire axial extension of its shaft-side contacting region  64  between the two radial contacting regions  50 ,  52 . 
         [0022]    It is particularly advantageous if the hard component  54  and the soft component  56  are embodied from the same material, for example Hytrel. In this manner, the thrust washer  28  can be embodied as one piece, wherein the hardness (quoted in Shore D) of the hard component  54  and of the soft component  56  differ by at least Shore D=5. The axial rigidity is clearly reduced in this manner and consequently a damping process is possible in the axial direction by using two Hytrel materials, for example Hytrel 5555 HS (Shore D=55 +/−2) with a 2K contour of Hytrel 4056 TPC-ET (Shore D max=40) or corresponding materials that have comparable intrinsic damping properties, abrasion resistance and temperature stability. 
         [0023]    Reference is finally made to the fact that the illustrated exemplary embodiment is not limited to  FIGS. 1 and 2  but rather that application geometries and arrangements that differ therefrom are also feasible within the electric machine  10 . In addition, the dimensional ratios illustrated in the figures between the thrust washers  28  in accordance with the invention and the remaining components of the electric machine  10 , in particular the bearings  18  and the rotor  14 , do not as such have any influence on the invention. The same applies for the shape and size of the circle segments  58  of the first plane  60  and also of the hard component  54  and the soft component  56  of the second plane  62  of the second contacting region  52 . It is further mentioned that as an alternative thereto or supplementary thereto the first contacting region  50  can also be embodied in the structural design of the second contacting region  52 .