Abstract:
The invention reduces vibration in a plastic element used in an electrical drive. The plastic element has a baseplate, at least two commutator brush boxes leading to a shaft passage channel which passes through the baseplate, and a bearing seat which is connected to the baseplate via at least one supporting arm for holding a shaft bearing. The invention provides for the entire contact area of the supporting arm with the baseplate to be arranged at a lateral distance from the commutator brush boxes.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2007/051150 filed on Feb. 7, 2007, 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a plastic element used in electrical drives, especially in vehicles, and preferably in power window systems. 
     2. Description of the Prior Art 
     A plastic element of this kind is shown for instance in German Patent Disclosure DE 100 06 350 A1. The plastic element has multiple functions. It forms a bearing seat for receiving a shaft bearing, in particular a collar bearing, in a manner fixed against relative rotation, for a drive shaft connected to the rotor of a direct current electric motor in a manner fixed against relative rotation. In addition, the plastic element has at least two diametrically opposed commutator brush boxes, extending orthogonally to a shaft passage channel for the drive shaft. These commutator brush boxes serve to receive commutator brushes or current inverter brushes, also called carbon brushes, which rest, diametrically opposite one another, radially on a commutator seated on the drive shaft. The commutator brushes are supported displaceably inside the commutator brush boxes and are supplied with direct current. The commutator brush boxes serve to deliver current to the rotor winding. 
     In the known plastic element, the commutator brush boxes are passed directly through two parallel supporting arms for mounting the bearing seat for the shaft bearing. The problem is that vibration, especially in the acoustical, audible range, is transmitted from the commutator brushes, resting on the drive shaft or on the commutator, directly to the shaft bearing via the supporting arms of the bearing seat and from the shaft bearing to the gearbox, resting on the shaft bearing, of the electrical drive. The gearbox forms a resonant body for the vibration emitted by the commutator brushes, and this leads to unwanted noise production. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The object of the invention is to propose an improved plastic element, with which the noise production of electrical drives can be reduced. 
     The invention is based on the concept of having the at least one supporting arm for mounting the bearing seat for the shaft bearing connect to the baseplate with lateral spacing from the commutator brush boxes. The contact area between the supporting arm and the baseplate is thus disposed entirely laterally offset from the commutator brush boxes, and not directly above them as in the prior art. Basically it does not matter whether the contact area of the supporting arm is spaced apart from and next to the commutator brush boxes, or whether the supporting arm is connected to the baseplate with lateral spacing above the commutator brush boxes or with lateral spacing below them. Primarily, what is important is only the lateral spacing of the entire contact area from the commutator brush boxes. As a result of the where the at least one supporting arm is disposed according to the invention, the commutator brush boxes and the bearing seat are decoupled from each other in terms of vibration. Because of this decoupling, the transmission of vibration from the commutator brushes to the bearing seat and thus to the gearbox is reduced, as a result of which the noise emission is reduced considerably in turn. 
     Preferably, the commutator brush boxes extend directly toward one another, or in other words have a common longitudinal center axis, which together with the longitudinal center axis of the shaft passage channel defines a common center plane. In this case, the connection point or contact area between the at least one supporting arm and the baseplate is spaced apart from an outer plane that extends parallel to the aforementioned center plane. The outer plane extends through the area of the commutator brush boxes that is located the farthest outward laterally; that is, it contains the outermost longitudinal axis of the commutator brush boxes, which extends parallel to the common longitudinal center axis of the commutator brush boxes. The farther away the supporting arm is connected to the baseplate laterally from the commutator brush boxes, the better is the vibrational decoupling between the bearing seat and the commutator brush boxes. 
     Preferably, the disposition of the supporting arm or supporting arms is made asymmetrically to the common center plane, especially in such a way that supporting arms for the bearing seat are provided only on one side of the center plane. 
     It has proved advantageous to provide four flexible arms, which receive the bearing in clamping fashion, as the bearing seat. The arms are preferably disposed on the order of a grasping hand, and upon introduction of the shaft bearing they bend elastically outward. 
     In a preferred embodiment, two arms each are combined into one U-shaped element, and the two U-shaped elements are preferably disposed symmetrically to a plane extending orthogonally to the common center plane. One arm of a U-shaped element is preferably located on each side of the center plane. 
     On each U-shaped element, in a refinement of the invention, one supporting arm is provided; to increase the stability, the two supporting arms can be connected to one another via a connecting bridge that is spaced apart from the baseplate. It is advantageous for the supporting arms to be disposed asymmetrically to the center plane, in particular in such a way that both supporting arms are disposed on one side of the center plane and are spaced apart from one another in the longitudinal direction of the commutator brush boxes. As a result of the asymmetrical disposition relative to the center plane, more space is obtained, which can be used for instance for the disposition of electronic components. 
     To lend the supporting arms a further functionality, it is advantageous that the supporting arms have a substantially L-shaped cross section; preferably, one leg of each supporting arm extends parallel to the commutator brush boxes, and the other leg extends in the direction away from the commutator brush boxes. Thus the two supporting arms form the corner edges of a U-shaped structure for receiving an electronic component, in particular a thermostatic switch. Preferably, different bearing elements are provided for a 24-V and for a 12-V thermostatic switch. 
     It is especially advantageous if the side faces of the commutator brush boxes, with a substantially rectangular and preferably square cross section, are each disposed at an angle of 45° from a plane extending parallel to the upper side of the baseplate. As a result, the vibrational decoupling between the bearing seat and the commutator brush boxes can be improved still further. 
     In a preferred embodiment, on at least one side face of the commutator brush boxes and preferably on all the side faces, linear guides extending in the longitudinal direction of the commutator brush boxes are provided for the commutator brushes. In contrast to a full-surface contact of the commutator brushes with the side faces of the commutator brush boxes as known from the prior art, tilting of the commutator brushes inside the commutator brush boxes can be prevented by means of the linear guide. Because of the linear guidance of the commutator brushes in the commutator brush box, the inside diameter of the commutator brush box is no longer identical to the spacing between the side faces of the commutator brush box. In the area between the commutator brushes and the side faces of the commutator brush boxes, raised areas may be present, such as an injection molding skin or a burr, without impairing the function. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and expedient embodiments will become apparent from the further claims, the description of the drawings, and the drawings themselves, in which: 
         FIG. 1  is a schematic view of the arrangement of a plastic element in an electrical power window system; 
         FIG. 2  shows the plastic element in a view from below; 
         FIG. 3  shows the plastic element in a side view; 
         FIG. 4  shows the plastic element in a top view; 
         FIG. 5  is an enlargement of the detail B in  FIG. 3 ; 
         FIG. 6  is a sectional view of the plastic element taken along the line A-A in  FIG. 3 ; and 
         FIG. 7  is a sectional view of the plastic element taken along the line C-C in  FIG. 4 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the drawings, identical components and components with the same function are identified by the same reference numerals. 
     In  FIG. 1 , a one-piece plastic element  1 , embodied as a die-cast part, is shown, with a baseplate  2  and a shaft passage channel  3 . A drive shaft  4  is extended through the shaft passage channel  3 . The drive shaft  4  is the rotor shaft of a direct current electric motor, not shown, that is received in a stator housing  5 . By means of a sintered bearing  6 , the drive shaft  4  is supported radially in the stator housing and can also be supported axially. 
     Spaced apart from the baseplate  2 , the one-piece plastic element  1  has a bearing seat  7 , comprising four arms  8 ,  9 ,  10 ,  11 , which form the parallel legs of two U-shaped elements  12 ,  13 . The arms  8 ,  9 ,  10 ,  11  serve to receive a shaft bearing  14 , embodied as a collar bearing in clamping fashion, for radially supporting the drive shaft  4 . With the aid of two struts  15 ,  16  of a gearbox  17 , the shaft bearing  14  is secured in the bearing seat  7 . 
     As can be seen from  FIG. 1 , the baseplate  2  is disposed between the stator housing  5  and the gearbox  17 . 
     The course of the drive shaft  4  in the region behind the shaft bearing  14  in the gearbox  17 , the latter shown only in fragmentary form, is not shown. For instance, the drive shaft  4  is connected in a manner fixed against relative rotation to a worm that meshes with a worm wheel supported rotatably in the gearbox  17 . On the end of the drive shaft  4  diametrically opposite the lower end in terms of  FIG. 1 , the drive shaft  4  can be supported in both the axial and the radial directions in the gearbox  17 . 
     The two U-shaped elements  12 ,  13  are connected to the upper side of the baseplate  2 , the side facing toward the bearing seat  7 , each via a respective supporting arm  18 ,  19 . 
     The baseplate  2  furthermore has two diametrically opposed commutator brush boxes  20 ,  21 , which extend orthogonally to the shaft passage channel  3 . They serve to receive commutator brushes, current inverter brushes, or carbon brushes. The brushes have the function of supplying current to the armature windings, not shown, of the direct current electric motor and for that purpose rest radially in a known manner on a commutator, not shown, that is connected to the drive shaft  4  and are of different polarities. 
     As seen from  FIG. 1 , the supporting arms  18 ,  19  are connected to the baseplate  2  with lateral spacing from the commutator brush boxes  20 ,  21  as well as slightly above a plane that extends parallel to the upper side of the baseplate and contains the common longitudinal center axis  24  of the commutator brush boxes  20 ,  21 . This contact area  28 , in the plane of the drawing, is disposed behind an outer plane  29  that is parallel to a center plane  23  and that contains the outer longitudinal axis  30  of the commutator brush boxes  20 ,  21 . The common center plane  23  is defined by the common longitudinal center axis  24  of the commutator brush boxes  20 ,  21  and by the axis of rotation of the shaft, that is, the longitudinal center axis  25  of the shaft passage channel  3 . The supporting arms  18 ,  19  extend substantially parallel to the center plane  23 . The disposition of the supporting arms  18 ,  19  is asymmetrical relative to the center plane  23 . All the supporting arms  18 ,  19  are disposed on one common side of the center plane  23 . The center plane  23  extends exactly through the middle of two diametrically opposed arms  8 ,  9  and  10 ,  11 , respectively, of the U-shaped elements  12 ,  13 . 
     It is also conceivable for the commutator brush boxes to be disposed at an angle to one another, so that the respective longitudinal center axes also extend at an angle to one another. In that case, two center planes are the result, which intersect preferably, but not necessarily, at the longitudinal center axis  25  of the shaft passage channel  3 . According to the invention, the supporting arms  18 ,  19  are disposed with lateral spacing from both these center planes and the outer planes that are parallel to these center planes. 
     From  FIGS. 2 through 7 , further details of the plastic element  1  of the invention can be seen.  FIG. 2  shows the plastic element  1  in a view from below. The longitudinal center axis  25  of the shaft passage channel  3  is shown, which is perpendicular to the plane of the drawing. The center plane  23  is also indicated, which also extends perpendicular to the plane of the drawing. In the view in  FIG. 2 , two spring domes  26 ,  27  can be seen. They serve to receive leg springs, not shown, with which the commutator brushes are subjected to spring force in the direction of the longitudinal center axis  25 . 
     In  FIG. 3 , the plastic element  1  is shown in a side view. The contact area  28  between the supporting arm  19  and the baseplate  2  can be seen. The entire contact area  28  is located with lateral spacing from the commutator brush boxes  20 ,  21 . In other words, the contact area  28  is spaced apart from the center plane  23  and is also outside and spaced apart from the outer plane  29 . The outer plane  29  extends parallel to the center plane  23  and intersects the commutator brush boxes in their laterally outermost region, and thus contains the outer longitudinal axis  30  of the commutator brush boxes  20 ,  21 . In the event that the commutator brush boxes do not have a common longitudinal center axis  24  but instead have longitudinal center axes that are at an angle to one another, then the outer planes are also at an angle to one another. According to the invention, the supporting arms  18 ,  19  then feed into the baseplate  2  in a manner that is laterally offset from these outer planes. 
     The arms  8 ,  9 ,  10 ,  11  supported by the supporting arms  18 ,  19 , or the bottom legs  31 ,  32  connecting the arms, are braced by the supporting arms  18 ,  19  in such a way that the area between the commutator brush boxes  20 ,  21  and the U-shaped elements  12 ,  13  is free of components or elements of the plastic element  1 . Electronic components, for instance, can be accommodated here. 
     As can be seen from  FIGS. 3 and 5 , the cross-sectional area of the commutator brush boxes is essentially square in shape and is disposed such that all the side walls of the commutator brush boxes  20 ,  21  are at an angle of 45° to the center plane  23  that extends perpendicular to the upper side of the baseplate. 
     In  FIG. 4 , the plastic element  1  is shown in a top view. The longitudinal center axis  25 , perpendicular to the plane of the drawing, of the shaft passage channel  3  can be seen, as can the center plane  23 . The arms  8 ,  11  are located in the plane of the drawing, to the left of the center plane  23 . The other two arms  9 ,  10  on the right of the center plane. Beside the two arms  9 ,  19  in  FIG. 4 , a connecting bridge  35  is shown between the supporting arms  18 ,  19 . The L-shaped cross section of the supporting arms  18 ,  19  can also be seen, each with one leg extending parallel to the center plane  23  and one leg extending perpendicular to the center plane  23  and pointing away from the commutator brush boxes  20 ,  21 . In the top view shown in  FIG. 4 , the supporting arms  18 ,  19  form a kind of U-shaped element, which is suitable for receiving thermostatic switches. Both larger 24-V thermostatic switches and smaller 12-V thermostatic switches can be inserted from above in the direction of the baseplate  2 . 
     In  FIG. 5 , the detail B of  FIG. 3  is shown. The commutator brush box  21  can be seen, with its four side walls at a 45° angle from the center plane  23 . On each side wall, there are two parallel linear guides  33 , extending in the longitudinal direction, or in other words the direction of the longitudinal center axis  24 , for guiding the commutator brushes. By means of the linear guides, seizing of the commutator brushes in the commutator brush box  21  is avoided. 
     In  FIG. 6 , a sectional view of the plastic element is shown along the line A-A in  FIG. 3 . The sectional plane is equivalent to the center plane  23 . Recesses  34  can be seen in the center region of the arms  9 ,  10 , for receiving the shaft bearing  14  (see  FIG. 1 ). 
     In  FIG. 6 , the connecting bridge  35  can be seen, extending spaced apart from the upper side of the baseplate  2  and located between the supporting arms  18 ,  19 ; it extends essentially parallel to the longitudinal center axis  24 . Providing this connecting bridge  35  increases the stability of the bearing seat arrangement. 
     In  FIG. 7 , a sectional view of the plastic element  1  along the line C-C in  FIG. 4  is shown. The connecting bridge  35  between the supporting arms  18 ,  19  is clearly seen. 
     The foregoing relates to the preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.