Abstract:
The invention relates to a transmission drive unit ( 10 ), especially for adjusting a mobile part in the motor vehicle. Said drive unit comprises a drive assembly ( 42 ) driving, by means of a drive element ( 40 ), a drive wheel ( 18 ) received on a spindle. The drive wheel ( 18 ) is rotatably received in a support tube ( 14 ) having a seat ( 52 ) for a securing device ( 54 ) for diverting crash forces. At least one circular or annular support element ( 62 ) can be secured between an axial end ( 60 ) of the support tube ( 14 ) and the seat ( 52 ) in order to mechanically reinforce the support tube ( 14 ). Said support element can be retrofitted and separately installed.

Description:
RELATED ART 
       [0001]    The present invention relates to a transmission drive unit with a support tube, in particular for adjusting a movable part in a motor vehicle, and a method for manufacturing such a transmission drive unit, according to the preamble of the independent claims. 
         [0002]    Publication EP 0 759 374 A2 made known a device for adjusting a seat in a motor vehicle, which may absorb considerably greater forces than during normal operation. Forces such as these may be caused, e.g., by 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 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. If the plastic transmission housing is unable to withstand the strong flow of force, it is held by the metallic support part using an additional counternut. The disadvantage of this design is that a complex support structure is required in addition to the entire transmission housing, which increases the number of components and requires additional installation space. 
         [0003]    Publication EP 1 223 073 A2 makes known a spindle drive, with which additional support elements are installed in the transmission housing to absorb crash forces. In a further exemplary embodiment, a support disk is located inside an injection-molded worm wheel to prevent the spindle from tearing out of the transmission housing. The disadvantage of this embodiment is that the entire transmission housing and/or the worm wheel must be redesigned for different crash requirements. For very strong loads, e.g., an additional support collar is located around the transmission housing. These design changes are associated with high tool costs, so adapting the spindle drive to different crash requirements is also associated with high costs. 
       ADVANTAGES OF THE INVENTION 
       [0004]    The inventive transmission drive unit and its inventive manufacturing method with the features of the independent claims have the advantage that, by locating the drive wheel of the spindle in a support tube, a separate standardized assembly is created that is independent of the drive assembly. By eliminating a conventional transmission housing, with which the driven element of the drive assembly and the drive wheel of the spindle are both located in a closed housing, the transmission drive unit, as a modular system, may be adapted—very flexibly—to different strength requirements. The same drive assembly may always be used, since the mechanical interface for transferring the drive torque also remains the same for different crash requirements. Since all of the crash forces are absorbed by the support tube and are diverted to the fastening device, only the support tube is adapted to the different strength requirements. By using a standardized support tube, with which different support elements may be integrally formed, a very high level of flexibility of the spindle drive is attained, in a very cost-effective manner. Advantageously, the cylindrical support elements may be subsequently attached in the support tube, fully independently of the installation of the spindle and its drive wheel in the support tube. Tests have shown that, when a crash occurs, the highest loads on the support tube occur between the receptacle for the fastening device and the corresponding axial end of the support tube. The crash resistance may therefore be increased in a particulary effective manner by reinforcing the support tube using the support element at least in the region between the receptacle and the axial end of the support tube located closest to the receptacle. The introduction of force is advantageously distributed evenly around the entire circumference of the support tube. 
         [0005]    Advantageous refinements and improvements of the features indicated in the independent claims are made possible by the measures listed in the subclaims. When the support element includes, e.g., a circular recess, the support element may be attached very easily on the outer circumference of a round support tube, in order to stabilize it. With this design of the support element as an outer ring, it may also be installed before the spindle is installed on the support tube. This design is also suited, in particular, for a plunger spindle, in the case of which the spindle extends out of the support tube at both axial ends. 
         [0006]    In an alternative embodiment, the support element is attached inside the support tube, to the inner wall surface, in order to reinforce it. The support element may be designed as an inner ring or a complete disk. A support disk stabilizes the support tube to an even greater extent. These diverse support elements may be connected very easily with the standard support tube in accordance with the particular strength requirements. A further advantage of the inwardly located support element is that no additional work is created, i.e., the support element is located inside the installation space that is required anyway, and it does not create any additional, disturbing edges. 
         [0007]    The support element with a thread may be screwed into or onto the support tube particularly easily. To this end, the support tube includes—on its outer circumferential surface and/or its inner wall, at least in the region between the receptacle and the axial end located closer thereto—a thread, which engages in a corresponding thread of the support element. As an alternative, the support element includes a self-tapping or self-cutting thread that forms a counter-thread in the support tube when installed in the support tube. 
         [0008]    In an alternative embodiment, the support element may also be bonded or welded to the support tube, or it may be caulked with the support tube via cold deformation. With these connection methods, the support tube and the support elements may also have a non-circular cross section. 
         [0009]    Due to the modular design of the support tube, the standard support tube may be made of an easily formed deep-drawn metal, and the support rings used to provide strong crash resistance may be made of a stronger material, e.g., hardened steel. 
         [0010]    A fastening bolt is a widely used customer interface for connecting the spindle drive to the motor vehicle; it may be rotatably supported in a hole-shaped receptacle in the support tube. The crash forces that act on a seat, for instance, are transferred to the support tube via the fastening bolt in the receptacle. By designing the fastening device as a pivot bolt, the spindle is hingedly supported between the part to be adjusted and the body, thereby resulting in a greater degree of freedom of the adjusting motion. 
         [0011]    It is particularly favorable when the support element is inserted axially on or in the support tube until it bears axially against the fastening bolt, at least when an external force is applied. As a result, the forces are transferred directly from the fastening bolt to the support element, thereby enabling the spindle—with its drive wheel—to be held in the support tube. 
         [0012]    The spindle can be supported very favorably in the support tube by providing axial projections on the drive wheel, which is supported on the spindle. The axial projections are accommodated in a pot-shaped bearing receptacle of the support tube and/or an end plate fastened therein. The pot-shaped bearing receptacles may simultaneously support the spindle radially and axially. When the at least one end plate is made of plastic, it may interact, e.g., with a spherical, metallic axial stop of the spindle with minimal friction. 
         [0013]    In a preferred embodiment, the spindle with the receptacle for the fastening device, which is supported in the support tube, is a first preassembled assembly, which may be coupled very easily via a coupling device with a standardized drive assembly, e.g., an electric motor with an armature worm. To transfer force to the drive element of the spindle, the driven element of the drive assembly extends through an opening in the support tube. Since the recess in the support tube is relatively small, the support tube may absorb high forces without the spindle being torn out of the support tube. This inventive transmission drive unit therefore does not include a classical transmission housing that encloses the driven wheel of the drive and the drive wheel of the transmission, but rather includes a largely closed support tube, with the driven element being fixed in place relative thereto using the coupling device. To attach the coupling device, further recesses are formed in the support tube, for example, into which a fastening means of the coupling device engages for fixation. The drive assembly with its driven element is located completely outside of the flow of forces that occurs during a crash. 
         [0014]    When the support element is loaded in the axial direction relative to the fastening device, the support element may dig directly into the support tube in order to fix itself in position. This results in the elimination of an additional fastening process of the support element, such as bonding, welding, or material deformation. Given that the support element bears against the fastening element with preload, the force of the fastening element may be transferred to the support element and, therefore, to the support tube with no axial play. 
         [0015]    It is advantageous to manufacture the support element as a circular clamping disk that has an edge around its entire circumference that clamps tightly in the wall of the support tube. If the edge is designed with a sharp edge, it may dig into the tube wall in such a manner that it may not be displaced. With this embodiment, the step of forming a thread on the support element and/or the support tube is eliminated. 
         [0016]    To attain an axial preload relative to the fastening device, the plate-shaped clamping disk is shaped axially away from the fastening device in its outer radial region. As a result, the outer edge may more easily engage in the material of the support tube when the clamping disk is installed, the central region of the clamping disk being pressed against the fastening device. A support element of this type may be manufactured very cost-favorably as a bent blank. 
         [0017]    For higher strength requirements, several clamping disks—depending on the need—may be fixed in position in the support tube such that they bear axially against each other. As a result, all of the installed clamping disks are involved in the transfer of force to the support tube around their circumference. Since the clamping disks are plate-shaped, they may be stacked on top of each other in a form-fit manner, so that they bear flat against each other and stabilize each other against deformation. 
         [0018]    In addition, a force-transmission disk may be inserted between the at least one support element and the fastening device, the force-transmission disk having, e.g., a greater resistance to deformation than the support elements. As a result, the force of the, e.g., bolt-shaped fastening device may be transferred to a larger circular surface and forwarded to the support elements. As a result, the axially acting force is transferred to a large surface and, therefore, evenly to the entire circumference of the support elements. 
         [0019]    The inventive manufacturing method according to independent claim  16  has the advantage that the assembly with the support tube is installed separately from the drive assembly. As a result, after the fastening means are installed on the support tube, they may be easily adapted to the particular strength requirement using the support elements. A modular system of this type, with which different drive assemblies may also be used, is very cost-favorable and customer-friendly. 
         [0020]    The support elements may be very easily varied in terms of shape and material without having to change the design and assembly process of the transmission drive unit. 
         [0021]    Via the inventive process for installing the support elements, which are designed as clamping disks, the clamping disks are fixed securely in position in the support tube in one process step, simultaneously with the insertion of the clamping disks. The clamping disks are pressed axially against the fastening device with a specifiable contact pressure, which causes the clamping disks to dig into the wall surface of the support tube with axial preload. Depending on the strength requirement, one or more clamping disks may be installed in one working step. 
     
    
     
       DRAWING 
         [0022]    Various exemplary embodiments of an inventive transmission drive unit are presented in the drawing, and they are described in greater detail in the description below. 
           [0023]      FIG. 1  shows a cross section through an inventive transmission drive unit, 
           [0024]      FIG. 2  shows a side view of an assembly with the support tube, which may be installed separately, 
           [0025]      FIG. 3  shows a cross section of the assembly in  FIG. 2 , and 
           [0026]      FIG. 4  shows a further embodiment according to  FIG. 2 , in a cross-sectional view. 
       
    
    
     DESCRIPTION 
       [0027]    Transmission drive unit  10  shown in  FIG. 1  is composed of a first assembly  12 , with which a spindle  16  with a drive element  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 receptacle  22  for drive wheel  18  on an end region  20 . Spindle  16  extends out of support tube  14  through opening  24  in pot-shaped bearing receptacle  22  and is connected with the body, e.g., via a counternut, which is not shown. With this exemplary embodiment, 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 pot-shaped 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, e.g., using plastic, directly onto spindle  16  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  and is connected with first assembly  12  using a coupling device  44 . Support tube  14  has a projection  46 , which is used to position support tube  14  relative to coupling device  44 , and into which a fixing element  48  of coupling device  44  engages. To transfer the torque from drive assembly  42  to separate assembly  12 , support tube  14  has 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 , which serves as a housing for separate assembly  12 , also includes a receptacle  52  into which a fastening device  54 , e.g., a pivot bolt  55 , may be slid. With this fastening device  54 , support tube  14  is hingedly connected with an adjusting part  58  in the motor vehicle, e.g., a not-shown seat or a seat part that is adjusted relative to another seat part. 
         [0028]    Support elements  62  are attached to support tube  14  between receptacle  52  and an end  60  of support tube  14  located closer thereto. A first support element  62  is designed as outer ring  64 , which rests in an outer circumferential surface  66  of support tube  14 . Inside support tube  14 , a further support element  62  is designed as circular disk  68 , which bears against inner wall  70  of support tube  14 . In the top half of the drawing, support elements  62  are connected with support tube  14 , e.g., via welds  72 . The lower half of the drawing shows an attachment of support element  62  using caulking  74  via plastic material deformation. 
         [0029]    If a compression force  80  acts on spindle  16  when an accident occurs in axial direction  76 , spindle  16  is supported via drive wheel  18  in pot-shaped bearing receptacle  22  of support tube  14 . Compression force  80  is transferred via support tube  14  to fastening device  54 , thereby resulting in a high material load between receptacle  52  and end  60  of support tube  14 . These strong forces are absorbed by one or more support elements  62 , which therefore increase the absorption of force by support tube  14  without it being destroyed. As a result, spindle end  26  and, therefore, part  58  to be adjusted, remain in their intended places when a crash occurs. 
         [0030]      FIG. 2  and  FIG. 3  show a further exemplary embodiment of a spindle drive  10 , with which support elements  62  include a thread  78  that interacts with a corresponding counter-thread  79  on support tube  14 . Support elements  62  are inserted in axial direction  76  onto or into support tube  14  until fastening device  54  bears axially against support elements  62 . As shown in the cross-sectional view in  FIG. 3  (along III-III in  FIG. 2 ), an outer thread  79  and an inner thread  79  are formed on support tube  14 , onto which support elements  62  may be easily screwed on or off. Support element  62 , which bears against inner wall  70 , is designed as inner ring  65 , through which, e.g., a plunger spindle  16  passes. When attaching support element  62  using a thread  78 , force  80  is introduced into support tube  14  via threads  78 ,  79  around the entire circumference of support tube  14 , thereby preventing a partial increase in tension in the region of receptacle  52 , and utilizing previously unloaded regions of support tube  14 . 
         [0031]    In a further variant, support elements  62  include self-cutting threads  78 , which form counter-threads  79  in support tube  14  when they are turned in support tube  14 . In this example, fastening device  54  bears axially against end plate  28 , so that compression forces that act on spindle  16  are also absorbed via fastening bolt  54 . In this design, end plate  28  has a constant outer diameter along its entire axial length  29 , thereby increasing its mechanical stability. To transmit torque, recess  50  in support tube  14  is rectangular in shape, so that worm  39  may mesh with drive wheel  18 . Only separate assembly  12  is shown in  FIGS. 2 and 3 ; it may be installed completely independently of drive assembly  42 . Coupling device  44  is then installed on preassembled assembly  12  via recess  46 . Coupling device  44  fixes drive assembly  42  in position relative to support tube  14 , to transfer torque. Support elements  62  may be installed, e.g, at the end of the installation of separate assembly  12 , or once transmission drive unit  10  has been fully assembled. When support part  62  is designed as an outer ring  64 , it may be installed on support tube  14  before spindle  16  is inserted into support tube  14 . A further exemplary embodiment is shown in  FIG. 4 , with which support elements  62  are designed as clamping disks  81 . Support elements  62  are designed as circular disks  68 , which point away from fastening device  54  in the axial direction on a radially outer edge region  83 . As a result, support elements  62  are plate-shaped in design, with a flat central region  86  and an angled, outer edge region  83 . On its outer circumference  82 , support element  62  includes an edge  84 , which, in the installed state, is dug into inner wall  70  of support tube  14 . Edge  84  may have an angle of, e.g., 90°, or it may have a sharp edge, e.g., with a burr. In  FIG. 4 , three clamping disks  81 , for example, are installed in support tube  14  such that they bear axially against each other. Each clamping disk  81  digs into support tube  14  with its edge  84 . A force-transmission disk  88  is located between support elements  62  and fastening device  54 , which is more stable in design than support elements  62 . Force-transmission disk  88  has, e.g., a greater thickness  94 , or it is made of a stronger material. As a result, the force that is transferred in a straight line from pivot bolt  55  to force-transmission disk  88  is forwarded across a large surface area to circular supporting elements  62 . It is thereby ensured that acting axial force  80  is forwarded evenly to entire circumference  82  of support elements  62 . Force-transmission disk  88  is not attached radially to support tube  14 , for instance, but is inserted loosely into support tube  14 . When clamping disks  81  are installed axially, they are pressed against force-transmission disk  88 , which, in turn, are pressed against fastening device  54 . Central planar region  86  of clamping disks  81  therefore bears against fastening device  54 , the preload being specified via the press-in force of clamping disks  81 . 
         [0032]    A spindle nut  90  is located on spindle  16 , which is connected with a part  58  to be adjusted, e.g., a vehicle seat. When a crash occurs, a tension force  80  acts on spindle  16  via part  58  to be adjusted, thereby resulting in strong forces being produced between support tube  14  and fastening device  54 . To prevent, e.g., fastening bolt  54  from tearing out, force  98  of fastening bolt  55  is transferred around circumference  82  of support elements  62  to end  60  of support tube  14 . 
         [0033]    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 receptacle  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 . Likewise, the invention is not limited to the use of a pivot bolt  55  as fastening device  54 . Instead, support tube  14  may also include another type of receptacle  52  for attachment to body/adjustable part  58 . For example, a plunger spindle  16  may also be supported in support tube  14 . Both pot-shaped bearing receptacles  22  then include an opening  24 , through which spindle  16  extends. The device used to transfer torque is not limited to a worm gear pair  19 ,  39 . Torque may also be transferred, e.g., using a spur gear. The shape and material used for support elements  62  is selected depending on the strength requirement. One or more support elements  62  may be attached, as necessary. The cross section of support tube  14  is not limited to a circle. When support tube  14  is cylindrical in design, support element  62  may simply be designed as a subsequently added base surface or wall reinforcement.