Abstract:
An actuator for a motor vehicle with an electric motor having an output shaft, a gearbox that is connected to the output shaft that includes a spindle nut, and a spindle that engages the spindle nut. The spindle nut comprises one main portion and at least one axial socket. The axial socket: (a) is solidly connected to the main portion, more specifically is integral with the main portion, (b) comprises an internal thread cooperating with the spindle and (c) is configured to be radially elastic. An elastic element is provided which fits against the axial socket and pushes the internal thread thereof into engagement with the spindle.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to German Application No. DE 10 2006 039 809.2, filed Aug. 25, 2006, and German Application No. DE 10 2007 030 445.7, filed Jun. 29, 2007, both of which are expressly incorporated by reference in their entirety as part of the present disclosure. 
     BACKGROUND 
     The invention relates to an actuator for a motor vehicle, more specifically for a motor vehicle seat, according to the preamble of patent claim  1 . Such an actuator has been known from WO 03/068551 A1 and also from U.S. Pat. No. 3,617,021 A and from WO 86/06036. Additionally, the reader is referred to U.S. Pat. No. 6,073,893 A and to U.S. Pat. No. 6,322,146 B1. 
     The disadvantage of such actuators is that a certain clearance between spindle nut and spindle is unavoidable. This clearance is noticeable in practical use, for example during a change in the drive direction. Attempts have been made to make actuators of the type mentioned herein above having zero clearance. The reader is referred for example to the document EP 588 812 B1 which describes a spindle drive the spindle of which is motor rotated. It proposes two separate spindle nuts one of which fits against the left thread collars of the spindle thread and the other against the right thread collars of the spindle thread. 
     The invention aims at indicating an implementation of an actuator that is easy to realize in terms of construction and that comprises a zero clearance interaction, more specifically a zero clearance adjustable interaction, between the spindle nut and the spindle. 
     SUMMARY 
     The object is solved by providing an actuator for a motor vehicle including an electric motor having an output shaft, a gearbox that is connected to the output shaft and includes a spindle nut, and a spindle that engages the spindle nut. The spindle nut comprises a main portion and at least one axial socket. The axial socket: (a) is solidly connected to the main portion, (b) comprises an internal thread cooperating with the spindle and (c) is configured to be radially elastic. The actuator further includes an elastic element that fits against the axial socket and pushes the internal thread thereof into engagement with the spindle. In one aspect, the axial socket is integral with the main portion. 
     In accordance with the invention, there is provided at least one axial socket, one axial socket being preferably associated with the two axial ends of the spindle nut. The axial socket is preferably made integral with the spindle nut. The spindle nut may be made from metal and/or from plastic material. 
     The invention allows for a simple solution for zero clearance cooperation between the spindle nut and the spindle. In the region of the at least one axial socket, the elastic element urges the internal thread of the socket so far into the thread turns of the spindle that the flanks fit against each other on either side and that a zero clearance fit is achieved. 
     Generally speaking, what is achieved is that the functions of the spindle nut are distributed. The main portion absorbs the crash forces, the at least one axial socket is responsible for the zero clearance fit. The afore the applies in essence, for the axial socket also contributes to a certain extent to absorbing crash forces, although significantly less than the main portion. 
     The axial socket is preferably at least twice as elastically deformable in the radial direction as the main portion under the action of a radial force K. 
     In a preferred configuration, the at least one axial socket is solidly connected to the main portion. When made from plastic, the two are injection-molded together or made together in another way, when made from metal, the axial socket preferably has at least one slot for it to be sufficiently elastically deformable. In principle, such type slots are also suited for other materials and configurations of the axial socket. 
     The elastic element urges the axial socket into engagement with the thread of the spindle. This is how the zero clearance fit is achieved. The elastic element acts preferably over the entire circumference. It is sufficient that the axial socket is urged at one point so far into the thread turns of the spindle that a zero clearance fit is achieved there. 
     Preferably, the internal thread of the axial socket is made in one work step together with the inner thread of the main portion. Preferably, the two threads are disposed continuously one behind the other and are continuous. 
     Preferably, the axial socket has a smaller outer diameter than the main portion, more specifically an outer diameter amounting at the most to only about 80%, preferably only about 50% thereof. Between the axial socket and the main portion there is preferably located a step that may be used for accommodating a bearing, more specifically a ball bearing. 
     The spindle nut preferably has a toothed external surface feature that is provided only in the main portion and not on the axial socket. It is thereby preferred that the external surface feature is a worm wheel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages will become more apparent upon reviewing the appended claims and the following non restrictive description of embodiments of the invention, given by way of example only with reference to the drawing. In the drawing: 
         FIG. 1  shows a perspective illustration of a partially sectioned actuator of the invention; 
         FIG. 2  shows a perspective illustration of a combination of spindle and spindle nut similar to the configuration shown in  FIG. 1 , but now with recesses; 
         FIG. 3  shows a top view of a combination shown in  FIG. 2 ; and 
         FIG. 4  shows an axial sectional view taken along section line IV-IV in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a first exemplary embodiment and illustrates an electric motor  20  having an output shaft  22 . A worm  24 , which meshes a worm wheel  26 , is non-rotatably connected thereto. This worm wheel  26  is part of a spindle nut  28  that engages a spindle  30 . In operation, the spindle  30  is not rotated by the electric motor  20 . The described parts  24  through  30  form a two-stage gearing comprising a worm gearing and a spindle gearing mechanism. The arrangement described is state of the art. 
     The spindle nut  30  has a main portion  32  that carries the worm wheel  26  on its circumference. Insofar, the spindle nut  28  does not differ from prior art. Still, there is a difference which is that there is provided an axial socket  34  on either of the two axial ends of the main portion  32 , the socket having an outer diameter that is significantly smaller than that of the main portion  32 . The axial socket  34  is solidly connected to the main portion  32 ; in the concrete embodiment according to  FIG. 1 , it is integral with the main portion  32 . As can be seen from  FIG. 4 , which also applies to  FIG. 1 , the main portion has in a known way an inner thread  36  that engages with the thread of the spindle  30 . The axial sockets  34  each have an internal thread  38  that also cooperates with the spindle  30  and engages with the thread turns thereof. The axial sockets  34  are configured to be elastic in the radial direction, meaning they can be pushed more or less onto the spindle  30 . An elastic element  40  in the form of a ring-shaped spring is provided, the elastic element forming a surrounding grip around the respective associated axial socket  34 , as can be seen from the  FIGS. 2 through 4  showing the second exemplary embodiment as well as from  FIG. 1 . This elastic element  40  abuts the axial socket  34  and pushes at least a partial portion of this axial socket  34  in such a manner against the spindle that the internal thread  38  engages the thread turns of the spindle  32  with, as far as possible, zero clearance. It forms an almost entirely surrounding grip around the axial socket  34  and also encircles the spindle  30 . 
     The parts  24  through  28 , and in parts the spindle  30 , are disposed in a gear housing  42  that is shown in a partial sectional view in  FIG. 1 . It has opposite openings  44  for passage of the spindle  30 . In the portion of these openings  44  there are affixed protective parts  46  which partially enclose the spindle  30 , with very little clearance but freely, and protect it from dirt. They have a cylindrical inner wall with an inner diameter that corresponds to the diameter of the addendum circle of the spindle  30  plus one to three tenths of a millimeter. At need, the protective part  46  is provided on its inner wall with a cleaning device, e.g., flocked with fibers. 
     As can be seen from  FIG. 1 , outside of the protective parts  46  there are unprotected portions  48 ,  50  where the spindle  30  is freely accessible and also freely visible in  FIG. 1 . The axial length of each unprotected portion  48 ,  50  is smaller than the axial length of the protective parts  46 . The arrangement is chosen such that the position of the spindle  30  shown in  FIG. 1  is the central position. If the electric motor  20  is actuated in one direction of rotation, it transports the spindle  30  in one direction, it being hypothesized that it transports it leftward pursuant to arrow  52  in  FIG. 1 . This movement is only possible up to the point at which a fastening portion  54 , which is solidly connected to the spindle  30 , strikes the free end of the neighboring protective part  46 . In this condition, the unprotected portion  48  has migrated inside the protective part  46 , as it can be seen from  FIG. 1 , but it has not come into contact with the spindle nut  28 . 
     If the direction of rotation of the electric motor  20  is reversed, the same processes occur in the other direction, now a holding portion  56 , which is also connected to the spindle  30 , abuts the end of the left protective part  46  so that the movement is stopped. In this condition as well, the portion  50 , which is unprotected in  FIG. 1 , has not been displaced far enough to come into contact with the spindle nut  28 . Accordingly, the spindle nut  28  generally comes only into contact with protected thread portions. These protected portions cannot be contaminated with dust, dirt or other particles and remain clean. In particular motor vehicles that are used for a longer period of time are known to have their openly accessible gear parts increasingly contaminated. This only occurs with the unprotected portions  48 ,  50  which are irrelevant for the functioning of the actuator. 
     As shown in  FIG. 1 , the two protective parts  46  are retained in the position shown by a bracket  58  that is substantially configured in a U shape and forms a surrounding grip around the top of the gear housing  42 . For this purpose, they have a groove  60  for lateral arms of the elastic bracket  58  made from wire to engage. 
     The second exemplary embodiment shown in the  FIGS. 2 through 4  is not shown completely, these figures only showing the combination of spindle nut  28  and spindle  30  as well as the protective parts  46  that are illustrated in  FIG. 4 . The difference from the first exemplary embodiment is that the axial socket  34  now has a recess  62  that may also be configured to be a slot, a bight portion, a hole or a notch. The radial elasticity of the axial socket  34  is increased as a result thereof. It is possible to make the spindle nut  28  from metal, at least in parts from metal. 
     As shown in particular in  FIG. 4 , the axial socket  34  is quite thin, in any case significantly thinner than the main portion  32 . There, there is sufficient resistant material between the thread turns of the spindle  30  and the worm wheel  26 . In this portion, the spindle nut is configured like a prior art spindle nut  28 , meaning it can absorb crash forces. In the two axial sockets  34 , which are built according to the same principle, the wall is quite thin, it ranges from 1 through 3 mm, and appropriate measures have been further taken, for example material chosen, recess  62  provided and so on, for the axial sockets  34  to be at least partially sufficiently deformable for their internal thread  38  to completely mesh the thread turns of the spindle  30  without allowing axial clearance to occur. The threads have oblique flanks, e.g. trapezoidal engagement. 
     In the configuration shown in the  FIGS. 2 through 4 , the thread of the spindle nut  28  is continuous and made in the same work step, more specifically during injection molding. In  FIG. 1 , the two protective parts  46  are built substantially according to the same principle and have more specifically the same axial length. The axial length corresponds to about 65% of the axial length of the spindle nut  28  and ranges from 40 to about 80% of this axial length. 
     As shown in the  FIGS. 2 through 4  in particular, the axial socket  34  has a cylindrical intermediate piece  63  commencing at the main portion  32  and an outer portion  66  extending outward therefrom. It is this outer portion  66  that performs the function of compensating for the clearance. The intermediate piece  63  is slightly thicker than the outer portion  66 . The intermediate piece  63  is in particular suited for receiving a bearing  64  that abuts the gear housing  42 . 
     As shown in  FIG. 4 , each protective part  46  has an abutment surface  68  by which it contacts the gear housing. This abutment surface is limited either by a cylinder the cylinder axis of which passes through the centre of the spindle nut  28  and extends either parallel to the output shaft  22  or perpendicularly to the output shaft or by a ball the centre of which is in the center of the spindle nut  28 . Partially cylindrical outer surfaces or ball surfaces configured accordingly and mating the abutment surfaces  68  are provided on the gear housing  22 . Together with the protective parts  46 , the spindle  30  can be pivoted about this cylinder axis or about the center of the ball within a certain pivot range.