Abstract:
A reducing motor including a rotor with an armature shaft, a reducer housing ( 2 ) containing a gear wheel ( 3 ) engaging a worm on the shaft, and a shock absorber ( 5 ) housed in the gear wheel and rotationally integral therewith. The unitary shock absorber has circumferential notches ( 8 ) engageable both by radial flanges  87 ) on the gear wheel and by elements ( 10 ) for driving an output member ( 11 ), and chamfers ( 90 ) are provided on the edges of the notches to ensure gradual torque-dependent angular deflection of the shock absorber and make it easier to mount the same automatically on the hub of the gear wheel.

Description:
BACKGROUND OF THE INVENTION 
     The subject of the present invention is a geared motor unit, particularly for driving vehicle equipment such as window lifters, sunroofs, etc, and of the type comprising a rotor equipped with a rotor shaft, a reduction gearbox which contains a gearwheel in mesh with a worm belonging to the shaft and capable of driving an output member. 
     Geared motor units of this type are normally equipped with means for adjusting the axial play between one end of the rotor shaft and the wall of the box. This is because the axial play in the driveline mounted in the geared motor unit is due to the combination of dimensional spreads on the various parts on assembly (shaft, endstop, box, etc.) which, placed end to end, are not as long as their housing. 
     Hitherto this axial play has been compensated for manually using a screw housed in the end of the box facing the rotor shaft hole and which is immobilized by an adhesive which at the same time provides sealing. Such a method of adjustment is lengthy to perform, expensive, and increases the overall cost of manufacture of the geared motor unit. 
     It is also known practice (see U.S. Pat. No. 5,169,245) to achieve automatic compensation for the axial play in the driveline of the geared motor unit using a coil spring resting in an axial housing of the end of the box, and a system of end stops designed to limit the compressive axial loading experienced by the coil spring to a predetermined value. This limitation is achieved by a shoulder on the inside of the wall of the box, and against which a piston inserted between the end of the shaft and the coil spring abuts. 
     Patent Abstracts of Japan Vol. 018 No. 297 of 7.6.1994 also discloses a geared motor unit in which an end stop, fixed by welding to one end of the box, eliminates any axial play between the rotor shaft and the wall of the box. 
     These devices for compensating for the axial play have a drawback which lies in the fact that they are not able to eliminate the troublesome noise of the shaft which is caused when it changes its direction of rotation. 
     SUMMARY OF THE INVENTION 
     The object of the invention is therefore to eliminate this drawback by arranging the geared motor unit in such a way that these noises are completely eliminated. 
     According to the invention, the geared motor unit comprises means for eliminating, under a given compressive axial preload, any axial play between one end of the rotor shaft and the wall of the box. 
     According to one embodiment of the invention, the said means comprise a plug housed in the end of the box, and a piston inserted between the plug and the end of the shaft, the plug exerting the said compressive axial preload, set at the time of assembly, on the piston and on the shaft, and the box by melting the plastic of which the box is made into the said roughnesses; this melting may be obtained, for example, using a sonotrode, an ultrasonic-welding machine, or alternatively by high-frequency welding. 
     According to another possible embodiment of the invention, the geared motor unit comprises a metal plug mounted so that it can slide in an axial housing formed in the wall of the box facing the end of the shaft; irregularities are arranged on the surface of this plug in contact with the wall of the housing, and the plug is moved axially until it comes into abutment against the end of the shaft under a given compressive axial preload thrust, then immobilized in this position so as to eliminate any shaft play. 
     This type of embodiment therefore has no piston, the plug alone fulfilling the function of plug and piston of the previous embodiment, and being immobilized in the desired position to exert appropriate axial thrust on the shaft. 
     The basic idea underlying the invention therefore consists in eliminating the axial play left in geared motor units of the state of the prior art and in doing so under a given compressive axial preload or thrust, for example of the order of 100 newtons. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other specific features and advantages of the invention will become apparent during the course of the description which will follow, which is given with reference to the appended drawings which illustrate a number of embodiments thereof by way of non-limiting examples. 
     FIG. 1 is a view in longitudinal elevation and part section of a geared motor unit for driving motor vehicle equipment, equipped with a device for eliminating the axial play in its driveline according to the invention. 
     FIG. 2 is a view in cross section on  2 / 2  of FIG. 3, illustrating a first embodiment of the gear motor unit according to the invention. 
     FIG. 3 is a view in partial longitudinal section showing one end of the geared motor unit of FIG. 1 equipped with a device for eliminating the axial play of the shaft according to a first embodiment of the invention. 
     FIG. 4 is a view in partial longitudinal section similar to FIG. 3 illustrating a second embodiment of the device for eliminating axial play in the geared motor unit according to the invention. 
     FIG. 5 is a view in side elevation of an alternative form of the piston of FIGS. 3 and 4. 
     FIGS. 6,  7  and  8  are views similar to FIG. 3 of three other embodiments of the device for eliminating axial play at which the invention is intended. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The geared motor unit  1  illustrated in FIG. 1 is intended, in particular, for driving vehicle equipment such as electric window lifters. 
     It comprises, housed inside a casing  2 , a stator  3  which can be powered by electrical connections  4  in the known way, a rotor  5  equipped with a rotor shaft  6 , the ends of which are mounted in rolling bearings  7 ,  8 . This rotor shaft carries a worm  9  in mesh with a gearwheel  11  capable of driving an output member  12  which itself drives the equipment associated with the geared motor unit, for example a window lifter, a sunroof, etc. 
     The end  6   a  of the rotor shaft  6  passing through the bearing  7 , located near the worm  9  collaborates with a device  12  making it possible, under a given compressive axial preload F (FIG. 3) to eliminate any axial play between the end  6   a  of the shaft  6  and the wall  13  of the reduction gearbox  14 . 
     In the embodiment illustrated in FIGS. 2 and 3, the means which constitute the device  12  comprise a plug  15  made of an elastic material such as an elastomer, arranged in a terminal housing  17  at the end of the wall  13  and projecting axially from this housing  17 , towards the end  6   a  of the shaft  6 . The device  12  also comprises a piston  18  inserted between the plug  15  and the end  6   a  of the shaft  6 . Arranged on the peripheral surface of the piston  18 , in contact with the interior wall  13   a  of the end  13  of the box  14  are irregularities such as circular grooves  19  or, alternatively, a screw thread, notching, axial grooves, knurling, etc., the piston  18  being made of metal, whereas the box  14  is made of plastic. 
     When the geared motor unit is assembled, the piston  18  is pressed against the plug  15 , precompressing it so that it exerts a compressive axial preload thrust F of an appropriate value, such as about 100 newtons, on the piston  18  and on the end  6   a  of the shaft  6 . 
     Once this compressive preload F has been set to the desired value, the piston  18  is immobilized in the axial position that corresponds to the said compressive preload of the plug  15 , and this is done by heating the plastic of the end  13  of the box  14  facing the surface irregularities of the piston  18 , so that the molten plastic fills its grooves or channels  19 . Subsequent solidification of the plastic by cooling fixes the piston  18  permanently in this position at the end  13  of the box  14 . This melting of the plastic may be brought about by appropriate means, not depicted, such as an ultrasound generator or using high-frequency welding. 
     Once the piston  18  has been secured to the box  14  in this way, changes in direction of rotation of the rotor shaft  6  can no longer cause this shaft to move axially and therefore can no longer generate troublesome noise. 
     In the second embodiment illustrated in FIG. 4, the device  21  comprises a piston  22 , the peripheral surface irregularities of which, in contact with the interior wall  13   a , consist of two circular channels  23  formed on the edges of the piston  22  and separated by a cylindrical region  14 . Correspondingly, at least one duct  25  is arranged to the side of the piston  22  in the wall  13  of the box  14  and opens into an annular chamber  26  in the wall  13 , this chamber  26  itself opening onto the circular grooves  23 . 
     This device  21  for eliminating axial play in the shaft  6  is adjusted as follows: first of all, the compressive axial preload F of the plug  15  is adjusted to the desired value, so that the piston  22  is positioned exactly at the appropriate axial location, opposite the chamber  26 . Next, a liquid adhesive is injected into the lateral duct  25  so that it fills the chamber  26  and the channels  23 . The pressure with which the liquid adhesive is injected is arbitrary. After hardening, the adhesive entirely fills the channels  23 , the chamber  26  and the duct  25  thus hermetically sealed and immobilizes the piston  22  with respect to the wall  13  of the box  14 . As before, the piston  22  eliminates any axial play of the rotor shaft  6  and therefore any parasitic noise as the shaft changes direction of rotation. 
     In the alternative form of FIG. 5, the piston  27  has three circular channels  28 , the central cylindrical region  24  having been omitted. In other respects, the use of the piston  27  is entirely similar to that of the piston  22 . 
     In the alternative form of FIG. 6, the device  29  for eliminating the axial play of the shaft  6  comprises a piston  27  with a number of circular channels  28  and a peripheral counterbore  31  which is shaped so as to delimit, facing the channels  28 , complementary channels  32  which are formed in the wall  13  of the box  14 . This counterbore  31  and the grooves  28  can be filled with liquid adhesive via the side duct  25 , the piston  27  being immobilized by the solidified adhesive. 
     FIG. 7 illustrates a fourth embodiment of the invention in which the device  33  for eliminating the play of the shaft  6  comprises a metal plug  34  with a diameter greater than the diameter of the axial housing  35  formed in the wall  13  of the reduction gearbox  14  facing the end  6   a  of the shaft  6 . There are irregularities  36  on the surface of this plug  34  in contact with the wall of the housing  35 , for example knurling as depicted, or alternatively notching, etc. 
     The plug  34  is moved axially in the housing  35  by melting the plastic of the wall  13  using means which are known and have not been depicted, until this plug comes into abutment against the end  6   a  of the shaft  6  with a given compressive axial preload thrust F (for example 100 newtons). The position of the plug  34  before it is introduced is depicted in chain line in FIG.  7 . 
     The plug  34  is positioned axially at the precise desired location in order to place the shaft  6  under compressive preload using an ultrasonic-welding machine which causes the plastic of the wall  13  of the housing  35  to melt into the surface irregularities  36 . This machine is associated with a thrusting ram which defines the amount of compressive preload on the driveline. Immobilization is achieved by the hardening of the plastic when the ultrasonic transducer has been shut down. 
     FIG. 8 illustrates a fifth embodiment which constitutes an alternative form of FIG. 7, in which the plug  37 , preferably made of metal, has a smooth surface and is immobilized in its axial position, compressed against the end  6   a  of the shaft  6 , by solidified adhesive  38 . The latter is injected in the liquid state through an axial nozzle  39  formed in the wall  13  of the box  14  and which opens into the housing  35 . The liquid adhesive is injected under a given pressure and fills that part of the housing  35  which is located behind the plug  37 . 
     Use is made, for example, of a hot-melt adhesive, which melts at a temperature lower than the melting point of the plastic of which the box  14  is made (200° C.) at low pressure. 
     By way of an unlimiting numerical example, if the axial thrust F is 100 newtons, and the cross-sectional area S of the plug  37  is equal to 0.5 cm 2 , the pressure with which the adhesive is injected must be equal to 20 bar. 
     Injecting a plastic identical to that of the box  14  is difficult to envisage because it would have to be done at high pressure, which would entail a plug  37  of very low cross section. 
     The invention is not restricted to the embodiments described and its execution may be varied in a number of ways. Thus, the embodiment of FIG. 8 could be modified by completely opening the housing  35  to the outside of the box  14  as depicted in FIG. 7, by arranging surface irregularities (grooves, knurling, etc.) on the surface of the plug  37  and by forming a side nozzle and a counterbore in the wall  13  of the box  14  so that liquid adhesive can be injected against the periphery of the plug  37  once the plug has been correctly axially positioned at the desired location. To perform this positioning operation, the plug  37  is pushed by an exterior precompression ram and immobilized by injecting adhesive into its grooves, via the counterbore in the box. 
     The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specially described. For that reason the following claims should be studied to determine the true scope and content of this invention.