Abstract:
The invention relates to an electrical steering device for a motor vehicle, comprising an electromotor with a worm gear. Said worm gear consists of a worm and a worm wheel ( 14 ) which is coupled to an input shaft and which has a gear rim ( 23 ). The worm wheel ( 14 ) forms one of the two coupling parts of an elastic compensation coupling ( 14, 16 ) that are to be intercoupled, the other coupling part ( 16 ) being connected to the input shaft in a rotationally fixed manner. The two coupling parts ( 14, 16 ) are intercoupled by one or more elastic spacers ( 17 ) only.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an electrical steering system.  
         BACKGROUND INFORMATION  
         [0002]    Electrical steering systems may have an input shaft, that is mechanically linked to a steering handwheel, which is used to transmit a torque required for steering wheels to be steered. An output member is mechanically connected to the wheels to be steered. An electric motor, by which an auxiliary force may be exerted directly or indirectly on the output member, is positioned on the auxiliary force steering system. The input shaft and the output member are connected to each other via a torsionally flexible member so that between the input shaft and the output member a limited twisting motion is possible. In steering systems having a rack-and-pinion gear, the output member is designed as a driving pinion, and is mechanically connected via a gear rack to the steerable wheels of a motor vehicle. The gear rack is mechanically connected to a servo motor developed as an electric motor, via a reducing gear that may be designed as a worm gear. The output member is connected to an electric motor via the worm gear. The main components of the electric motor are a rotor and a stator. The stator is fixed to the housing, and the rotor is connected to a worm shaft of the worm gear via a drive shaft.  
           [0003]    Such an electrical steering system is described, for example, in German Published Patent Application No. 197 52 075. This electrical steering system is made up of an electrical motor-driven worm gear system in which the shaft of the worm is held elastically in the gear case. Play is provided between the worm wheel and the worm of the worm gear. The worm is supported shiftably in the axial direction, and is supported on the gear case via elastic elements. Because of this, the negative influences transmitted by the electric motor&#39;s actuating drive to the steering system may be reduced.  
           [0004]    The electrical steering system described in German Published Patent Application No. 197 52 075 has the disadvantage that noise reduction may be achieved, but not noise suppression. Furthermore, noises appearing at the limit stop during travel are not eliminated. Constant functioning cannot be guaranteed over the entire service life, since the elastic elements will have their characteristics changed by outer influences such as temperature and dirt.  
           [0005]    It is an object of the present invention to provide an electrical steering system which may ensure a constant functioning over its entire service life in view of the decoupling of structure-borne noise and damping of the limit stop.  
         SUMMARY  
         [0006]    The foregoing object may be attained by providing an electrical steering system as described herein.  
           [0007]    The foregoing object may be achieved by providing an axial and radial decoupling and torsion damping, e.g., by decoupling of structure-borne noise of the worm gear system from the steering spindle and the drive pinion. For this purpose, the worm wheel is arranged as a coupling part of an elastic compensation coupling, the other coupling part of which is formed as a flange which is connected, rotatably fixed, to the input shaft. The two coupling parts are coupled to each other by an elastic spacer, a specified limit stop being provided, which is achieved at a certain torque.  
           [0008]    This may make it possible to achieve an axial and radial decoupling of the ring gear of the worm wheel from the steering spindle. The rigidity of the ring gear with respect to the input shaft is able to be changed by adjusting the contour and form of the elastic spacer.  
           [0009]    Further aspects and features of the present invention are described below. However, the present invention is not limited to the feature combinations set forth below, but rather, further combination possibilities of features become apparent to one skilled in the art.  
           [0010]    The present invention is described in greater detail below with reference to an exemplary embodiment represented in the drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 illustrates the construction of an electrical steering system for motor vehicles, in a schematic representation.  
         [0012]    [0012]FIG. 2 is a longitudinal cross-sectional view through the electrical motor illustrated in FIG. 1.  
         [0013]    [0013]FIG. 3 is an exploded representation of the worm wheel illustrated in FIG. 2. 
     
    
     DETAILED DESCRIPTION  
       [0014]    In the exemplary embodiment in FIG. 1, the electrical steering system for motor vehicles includes a steering gear of a rack-and-pinion steering  1 . Such a rack-and-pinion steering  1  is generally conventional, and is therefore not explained in more detail here. An input shaft  2 , which is mechanically connected to a steering handwheel  4 , for example, via a steering column  3  provided with universal joints, bears a drive pinion of the rack-and-pinion steering.  
         [0015]    A gear rack of rack-and-pinion steering  1 , together with two drag rods  5  and  6 , form an output member which is connected mechanically to wheels to be steered. In addition, the gear rack forms the drive part of the steering system.  
         [0016]    By the use of such a steering system, a steering torque may be transmitted from steering handwheel  4  to the wheels to be steered.  
         [0017]    A supporting torque may be exerted on input shaft  2  by an electric motor  7 . In the exemplary embodiment illustrated in FIG. 1, electric motor  7  is positioned so that its axis is located perpendicular to the axis of input shaft  2 , and thus of the drive pinion. But its axis may also be positioned at a different angle to the axis of input shaft  2 . At the same or similar effect, electric motor  7  may be situated so that its axis is parallel to the axis of input shaft  2 , and thus also to that of the drive pinion or another part of steering column  3 . In both manners of positioning electric motor  7  described so far, it acts upon input shaft  2  using the drive pinion of rack-and-pinion steering  1 . Electric motor  7  may be positioned so that its axis is parallel or coaxial to the longitudinal direction of the gear rack of rack-and-pinion steering  1 .  
         [0018]    Electric motor  7  may be configured as an asynchronous motor. The asynchronous motor may be made up of a rotatable rotor  8  and a fixed winding  9 . The torque is produced by a rotating field specified from the outside via control and switching elements. Rotor  8  may be configured as a squirrel-cage rotor or as a squirrel-cage induction rotor. Since such an electric motor does not require permanent magnets, no magnetic field is generated during rotation of rotor  8 , when there is interference in the electrical or electronic part of the steering system, which would influence or hinder the rotary motion of rotor  8 . This may ensure that the power flow from steering handwheel  4  to the steered wheels is not impaired in case of interference.  
         [0019]    In the exemplary embodiment illustrated in FIG. 2, winding  9  of electric motor  7  is integrated directly into a housing  10  in a space-saving manner, and is protected from axial and radial motion by a stop  11  and an axially prestressed cover  12 .  
         [0020]    The torque produced by electric motor  7  is transmitted to input shaft  2  via a worm gear system made up of worm  13  and worm wheel  14 .  
         [0021]    [0021]FIG. 3 is an exploded view of the elastic compensation coupling, of which worm wheel  14  illustrated in FIG. 2 is a part.  
         [0022]    It has a ring gear  23 , in which worm  13  (FIG. 2) engages. The other coupling part of the elastic compensation coupling, e.g., flange  16 , is connected in a rotatably fixed manner to input shaft  2  (see FIGS. 1 and 2), e.g., by a connecting piece, the end face of which is marked  16   a , and the lateral surface of which is marked  24   d.    
         [0023]    The two parts  14  and  16  of the compensation coupling are supplemented by a ring-shaped, elastic spacer  17  having processes  20 . In the assembled state, inner surface  24   b  of spacer  17  is arranged on lateral surface  24   d  of the connecting piece of flange  16 . In this context, in each case two processes  20  encompass one of lugs  25  on flange  16 .  
         [0024]    Worm wheel  14  may be arranged with mirror symmetry, and thus may have the same aspect on the non-visible reverse side as on the front. After assembly, worm wheel  14  is supported on spacer  17 , which in turn is supported on the connecting piece of flange  16 . Inner surface  24   c  of worm wheel  14  thus rests on ring outer surface  24   a  of spacer  17 . Throat depths  26  of recesses  22  in worm wheel  14  are provided for processes  20  of spacer  17 . Processes  20  find accommodation in these throat depths  26 .  
         [0025]    Although, under certain circumstances, parts  14 ,  16 , and  17  may be sufficient for fulfilling the functions of an elastic compensation coupling, the front side of worm wheel  14  is complemented by a second spacer  27  and a second flange  28  to become an additional compensation coupling. In the assembled state, flanges  16  and  28  are connected to each other by studs  21 . In addition, an inner toothing of second flange  28  engages with a toothing of the connecting piece on flange  16 . In the assembled state, second elastic spacer  27  also rests on the connecting piece of flange  16 . These lugs of second flange  28  project in each case into the interstice between two closely adjacent processes  20  of spacer  27 .  
         [0026]    Then, for example, front contact surface  18   a  is arranged up against the rear side of second flange  28 . Rear side contact surface  18   b  of second spacer  27  is arranged up against contact surface  18   e  of a throat depth  26  in worm wheel  14 . Lateral contact surfaces  19   a ,  19   b  of spacer  17  and  27  rest against lateral contact surfaces  19   c ,  19   d  of lugs  25  and lateral contact surfaces  19   e ,  19   f  of throat depths  26  in worm wheel  14 .  
         [0027]    Processes  20  thus prevent lugs  25  from directly touching the lateral surfaces of throat depths  26  during the transmission of a torque in one or the other direction. Spacers  17 ,  27  are also arranged so wide that they prevent direct contact of parts  14  and  26  or  14  and  28  in the axial direction. And, since the ring-shaped parts of spacers  17 ,  27  are arranged between lateral surface  24   d  of flange  16  and inner surface  24   c  of worm wheel  14 , it is also provided in the radial direction that direct contact between the connecting piece of flange  16  and worm wheel  14  may be avoided. Spacers  17 ,  27  thus form buffers between flange  16  (and thereby input shaft  2 ) and worm wheel  14  both in the axial and the radial direction, and also in the tangential direction.  
         [0028]    However, the elastic buffering is not unlimited in the tangential direction, because recesses  22  in worm wheel  14 , through which studs  21  of flange  16  engage, are only a little larger (measured in the tangential direction) than studs  21 . This has the result that studs  21  and recesses  22  form mutual stops, which take effect when, during the transmission of an excessively large torque, processes  20  of spacers  17 ,  27  are squeezed together by a certain amount.  
         [0029]    List of reference numerals  
         [0030]    [0030] 1  rack-and-pinion steering  
         [0031]    [0031] 2  input shaft  
         [0032]    [0032] 3  steering column  
         [0033]    [0033] 4  steering handwheel  
         [0034]    [0034] 5  drag rod  
         [0035]    [0035] 6  drag rod  
         [0036]    [0036] 7  electric motor  
         [0037]    [0037] 8  rotor  
         [0038]    [0038] 9  winding  
         [0039]    [0039] 10  housing  
         [0040]    [0040] 11  limit stop  
         [0041]    [0041] 12  cover  
         [0042]    [0042] 13  worm  
         [0043]    [0043] 14  worm wheel  
         [0044]    [0044] 16  flange  
         [0045]    [0045] 17  spacer  
         [0046]    [0046] 18   a, b, c, d  contact surfaces  
         [0047]    [0047] 19   a, b, c, d  contact surfaces  
         [0048]    [0048] 20  process  
         [0049]    [0049] 21  stud  
         [0050]    [0050] 22  recess  
         [0051]    [0051] 23  ring gear  
         [0052]    [0052] 24   a, b, c, d  contact surfaces  
         [0053]    [0053] 25  lug  
         [0054]    [0054] 26  throat depth  
         [0055]    [0055] 27  second spacer  
         [0056]    [0056] 28  second flange