Abstract:
A spindle drive ( 10 ), in particular for adjusting a movable part ( 58 ) in a motor vehicle, includes a drive assembly ( 42 ), which drives a drive wheel ( 18 ) supported on a spindle ( 16 ). The drive wheel ( 18 ) is rotatably supported in a support tube ( 14 ) that includes a receptacle ( 52 ) for a fastening device ( 54 ) for diverting crash forces. A guide tube ( 64 ) that accommodates the spindle ( 16 ) and overlaps axially with the support tube ( 14 ) is located coaxially with spindle ( 16 ).

Description:
CROSS-REFERENCE 
     The invention described and claimed hereinbelow is also described in PCT/EP2007/050134, filed on Jan. 8, 2007 and DE 10 2006 006 925.0, filed Feb. 14, 2006. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119 (a)-(d). 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a spindle drive with a support tube, in particular for adjusting a movable part in a motor vehicle. 
     Publication EP 0 759 374 A2 makes known a device for adjusting a seat in a motor vehicle, which may absorb considerably greater forces than it does during normal operation. Forces such as these are generated, e.g., during a traffic accident. It is important that the vehicle seat remain fixedly connected with the body, to ensure that the protective measures (seat belt, air bag) provided for the vehicle occupants may perform their intended function. With the device described above, a counternut that accommodates a threaded spindle is fixedly connected with the body. The threaded spindle is driven via a worm gear pair by an electric motor, which is fixedly connected with the seat. The transmission housing of the worm gear pair is made of plastic and is connected with the drive motor via a further housing part. When the drive motor is actuated, the threaded spindle rotates and displaces the transmission housing, including the drive motor and seat, relative to the counternut. To prevent the transmission housing from tearing loose from the threaded spindle, e.g., when an accident occurs, an additional, metallic, U-shaped support part is provided, which connects the transmission housing via a hinged fastening bolt with the drive motor and, therefore, the seat. The disadvantage of this design is that the U-shaped support part is unable to prevent the spindle from buckling when it is compression loaded. 
     SUMMARY OF THE INVENTION 
     The inventive device and the inventive method have that advantage that, due to the nested configuration of the guide tube relative to the support tube, the flow of force that acts on the spindle may be introduced with practically no torque directly from the guide tube to the support tube and into the customer&#39;s fastening device. The spindle is therefore reliably prevented from buckling, thereby making it possible to absorb greater crash forces. In addition, the axially moved spindle nut may be guided reliably in the guide tube during normal adjustment operation. 
     Due to the measures listed in the dependent claims, advantageous refinements and improvements of the embodiments described in the independent claims are made possible. It is particularly advantageous to design the support tube and the guide tube with circular cross sections, since this makes it possible to insert the two tubes into each other in a form-fit manner. When the guide tube and the support tube are designed concentric with the spindle axis, the two tubes may be joined in each other very easily; this connection is particularly tolerance-insensitive to being displaced in the center. 
     A particularly strong resistance to crumpling is attained when the guide tube bears radially directly against the support tube in a certain overlap region. The crumpling resistance may be affected along the length of the overlap region. 
     In an alternative embodiment, an adapter element is inserted radially between the support tube and the guide tube. The adapter element, which is designed, e.g., as a peg-shaped ring, may be slid onto the support tube, and the guide tube may then be slid onto the peg-shaped adapter element. The diameter of the guide tube may thereby be adapted to the dimensions of a counternut located on the spindle. 
     Via the peg-shaped design of the adapter element or the end of the support tube, a jacket surface may be created to bear radially against the inside of the guide tube, while simultaneously forming an axial stop for the guide tube. Based on the material selected for the receiving peg, e.g., a press fit may be realized between the guide tube and the support tube. 
     The peg-shaped adapter element, or the end of the support tube, may be designed simultaneously as an axial stop for the spindle nut, thereby damping it gently. 
     When a rotatable counternut that is connected, e.g., with the part to be adjusted is located on the spindle, the counternut may be braced radially by the guide tube when it undergoes linear motion. Depending on the application, the outer jacket surface of the counternut may bear against the inner surface of the guide tube, or it may be located at a slight distance away therefrom. 
     It is particularly advantageous when the guide tube is reliably fastened on the support tube via the installation of the transmission housing. To this end, the transmission housing—which includes, e.g., a main body and a cover—may be installed radially in the manner of a collar around the two tubes, which have been inserted into each other. 
     It is particularly favorable when no additional, separate connection means are required to fasten the guide tube relative to the support tube. This may be attained, e.g., by forming recesses in the support tube and the guide tube, into which the radial projections of the transmission housing engage in a form-fit manner. Via the installation of the, e.g., two-pieced transmission housing, the guide tube is installed opposite to the support tube at the same time when the transmission housing parts are connected. The two tubes are therefore fastened in position relative to the transmission housing. 
     When the fastening means between the transmission housing and the support tube with the guide tube are designed symmetrical with the drive wheel located on the spindle, the spindle may extend out of the transmission housing in one or the other direction without changing the design of the individual components. As a result, the spindle motor, which is designed as a modular system, may be adapted for different installation positions without any additional effort. 
     The peg-shaped end of the support tube may be designed, e.g., as one piece with the support tube, or as a separate component that is inserted in the support tube or is attached in the support tube. The radial inner surface of the peg-shaped end serves to radially and axially support the drive wheel, and the outer jacket also serves to accommodate the guide tube and/or an adapter element. When the pot-shaped end plate is designed as one piece with the support tube, it may be advantageously designed very cost-favorably using a deep-drawing method in one working step. 
     With the inventive method for manufacturing the spindle drive, the support tube with the guide tube inserted thereon is a pre-fabricated module, onto which the transmission housing may then be installed. The installation process for the module with the guide tube requires an insubstantial amount of adaptation relative to the module without the guide tube. 
     Due to the symmetrical design of the fastening means on the spindle module relative to the transmission housing, the installation position of the spindle may be easily rotated by 180°. No design changes need to be made to the individual components. The fastening means between the transmission housing and the support tube-guide tube module may be easily varied and adapted. It is particularly favorable that the guide tube module is fixed in position relative to the transmission housing in one working step when the transmission housing is installed. The transmission housing may be joined, e.g., by screwing, clipping, welding, or pressing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention are presented in the drawing and are described in greater detail in the description below. 
         FIG. 1  shows a first exemplary embodiment of a spindle drive, in a cross section, and 
         FIG. 2  shows a further exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Spindle drive  10  shown in  FIG. 1  is composed of a first assembly  12 , with which a spindle  16  with a drive wheel  18  located thereon is supported in a support tube  14 . Support tube  14  is manufactured, e.g., using deep drawing, and includes a pot-shaped bearing seat  22  for drive wheel  18  on an end region  20 . Spindle  16  extends out of support tube  14 , through an opening  24  in pot-shaped bearing seat  22 . The other spindle end  26  is located inside support tube  14  and is supported axially and radially via an end shield  28  that is attached inside support tube  14 . Spindle end  26  includes, e.g., a spherical stop surface  30 , which rests axially against end shield  28 . Optionally, a stiffer thrust washer  32  may be located in end shield  28 . In this exemplary embodiment, drive wheel  18  is designed as worm wheel  19 , which includes axial projections  34  for radial support. Drive wheel  18  is injection-molded using plastic directly onto spindle  16 , or it is non-rotatably attached thereto, and includes toothing  36  that meshes with a driven element  40  of a drive assembly  42 . Drive assembly  42  is designed as an electric motor  43  that includes a transmission housing  46 , which is connected with first assembly  12  using a coupling device  44 . An inner contour  49  of transmission housing  46  encloses an outer contour  15  of assembly  12 . To transfer the drive torque from drive assembly  42  to separate assembly  12 , support tube  14  includes a radial recess  50  into which driven element  40  engages. Driven element  40  is designed, e.g., as worm  39 , which is located on an armature shaft  41  of electric motor  43 . Support tube  14 , as the standard component, practically forms a housing for separate assembly  12 , on which various a receptacle  52  for a fastening device  54  is located. For example, a pivot bolt  55 , as fastening device  54 , may be slid into receptacle  52 , in the center of support tube  14 . With fastening device  54 , support tube  14  is connected—e.g., in a hinged manner—with a part  58  to be adjusted in the motor vehicle, e.g., a not-shown seat or a seat part that is adjusted relative to another seat part. 
     Spindle  16 , which extends out of support tube  14 , is located in a guide tube  64 , which is inserted on end  20  of support tube  14 . Support tube  14  and guide tube  64  overlap in a overlap region  60 , the length  62  of which may be specified depending on the requirements for crumple resistance. End  20  of support tube  14  is pot-shaped in design and forms, with its inner surface  66 , bearing seat  22  for drive wheel  18  and, with its outer surface  68 , a peg-shaped receiving element  70  for guide tube  64 . Guide tube  64  and support tube  14 , and/or receiving peg have a circular cross section, so that tubes  64  and  14  engage in each other while remaining centered relative to spindle axis  17 . With this design, guide tube  64  bears directly and radially against outer surface  68  of support tube  14 . Support element  64  includes an end face  72 , which bears axially against a stop  74  of support tube  14 . A counternut  76  is rotatably supported on spindle  16 . Counternut  76  is displaced linearly along spindle axis  17  when spindle  16  is rotated. Counternut  76  includes an outer jacket surface  78 , which may be supported against inner wall  80  of guide tube  64 . On an end  82  facing away from support tube  14 , counternut  76  extends out of guide tube  64  and is connected, e.g., with body  84 . 
     If a compression force  86  acts on spindle  16  along spindle axis  17  as the result of an accident, spindle  16  is braced laterally against guide tube  64 , which is connected with support tube  14  in a crumple-proof manner via receiving peg  70 . If spindle  16  crumples to the side, torques that are produced are diverted to fastening device  54  via support tube  14 . As a result, spindle end  16  and, therefore, part  58  to be adjusted, remain in their intended positions when a crash occurs. 
       FIG. 2  shows a further embodiment of a spindle drive  10 , with which an adapter element  88  is located on support tube  14 , on which guide tube  64  is located with an overlap region  60 . Adapter element  88  is designed in the shape of a peg with a circular cross section and performs the function of end  20 —designed as receiving peg  70 —of support tube  14  in  FIG. 1 . Guide tube  64  bears radially directly against adapter element  88 , which is located radially between guide tube  64  and end  20  of support tube  14 . A collar  87  of adapter element  88  forms axial stop  74  for guide tube  64 . Adapter element  88  includes an axial stop  75  opposite to collar  87 , against which counternut  76  is damped upon impact. End  27  of spindle  16  that extends through guide tube  64  includes a stop for counternut  76 . Guide tube  64 , which has been inserted onto support tube  14 , forms a single module  13 , which is connected with drive assembly  42  after it has been joined on its outer contour  49 . To this end, drive assembly  42  includes a transmission housing  46  with an inner contour  15 , on which radial projections  90  are located, which engage in corresponding radial recesses  92  and  93  of support tube  14  and guide tube  64 . Radial projections  90  form—together with recesses  92  and  93 —fastening means  89  of coupling device  44  for module  13 . In further embodiments, fastening means  89  may be formed by other form-fit connections. In  FIG. 2 , fastening means  89  are located symmetrically to a central plane  94  of drive wheel  18 , thereby enabling module  13  to be installed such that it is rotated by 180°, without redesigning any of the individual components. For example, recesses  92  and  93  with corresponding radial projections  90  are formed with the same axial distance  96  from central plane  94 . Transmission housing  46  includes a main body  47  and a cover  48 , which are installed radially to module  13  and are interconnected. When the two transmission housing parts  47  and  48  are connected, support tube  14  and guide tube  64  of module  13  are simultaneously attached to transmission housing  46  via fastening means  89 . 
     In a variation that is shown in the lower half of  FIG. 2 , pot-shaped end  20  of support tube  14  is designed as a separate component  98 , which is joined as bearing seat  22  in cylindrical support tube  14 . Component  98  performs the same function as receiving peg  70  of the embodiment that is designed as one piece with the support tube. 
     It should be noted that, with regard for the exemplary embodiments presented in the figures and the description, many different combinations of the individual features are possible. For example, support tube  14  may be manufactured using different methods, and it may have different specific designs. Instead of being designed as an integrally formed, pot-shaped bearing seat  22 , support tube  14  may also be designed as a smooth cylindrical tube in which two separate end shields  28  for supporting spindle  16  are located. Spindle  16  is preferably supported via drive wheel  18  supported thereon, although, in one variation, it may also be supported via bearing surfaces that are integrally formed directly on spindle  16 . The device used to transfer torque from drive assembly  42  is not limited to a worm gear pair  19 ,  39 . Torque may also be transferred, e.g., using a spur gear. The specific shape and material used for receiving peg  70  are selected depending on the strength requirement. Receiving peg  70  may be designed as an adapter element  88  if necessary. Receiving peg  70  may also have a stepped or tapered design. The cross section of support tube  14  and guide tube  64  is not limited to a circle. The cross section may also be, e.g., rectangular or elliptical (for tolerance compensation). Given a cylindrical design of support tube  14 , however, guide tube  64  may be reliably centered relative to spindle axis  17 .