Patent Publication Number: US-8528948-B2

Title: Auxiliary locking drive for a motor vehicle lock

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates to an auxiliary locking drive for a motor vehicle lock having its own drive housing and being located separately from the vehicle lock in the installed state, being coupled to the vehicle lock by way of a transmission, having a drive motor, and in the mounted state, the drive motor producing a linear driving motion that is transmitted to the vehicle lock by way of the transmission so that the vehicle lock can be transferred from a half-locked state into a main locked state by the driving motion. 
     2. Description of Related Art 
     Here, the expression motor vehicle lock is defined as all types of door/hood/trunk or hatch locks. 
     The vehicle lock is equipped with conventional latching elements, a latch and a ratchet, the ratchet keeping the latch in the main locked position and in the half-locked position. The ratchet is then in the engaged state. The latch can be moved into retaining engagement with a striker or the like which is located on the body. Here, the striker or the like can be assigned to the vehicle lock. 
     In the course of enhancing the ease of operation, current vehicle locks are provide with various automatic functions. They include, for example, a striker function in which the vehicle lock is transferred by motor from the half-locked state into the main locked state. It is advantageous that the user need move the motor vehicle door only to the half-locked state for locking and that this is possible with comparatively little effort. The counter-pressures of the door seal are not yet acting here. Only moving from the half-locked state into the main locked state is associated with the compression of the door seal, and thus, with a considerable expenditure of force; this takes place by means of an auxiliary locking drive. 
     Different versions for implementation of the auxiliary locking function are known. One version (German Patent DE 39 35 804 C2 and corresponding U.S. Pat. No. 5,158,330) calls for the striker which interacts with the latch to be moved by a motor for pulling the vehicle door tight. In another version (German Patent Application DE 102 39 734 A1 and corresponding U.S. Patent Application Publication 2004/0135378 A2), the latch can be moved by means of the locking aid by a motor from the half-locked position into the main locked position, and thus, the vehicle lock can be moved altogether from the half-locked state into the main locked state. 
     In the latter implementation of the auxiliary locking function, the auxiliary locking drive is activated when the latch reaches the half-locked position. For this purpose, there is a control unit in the form of an auxiliary locking control. 
     In the aforementioned arrangements, it has been found to be disadvantageous that the amount of installation space required in the region of the vehicle lock is undesirably high due to the integration of the auxiliary locking drive; this leads to major structural limitations. Furthermore, the modularity of the arrangement with respect to the implementation of the additional function “locking aid” is low. 
     In the known auxiliary locking drive which underlies the present invention (German Patent Application DE 10 2006 048 026 A1), the auxiliary locking drive is located separately from the vehicle lock and is coupled to the vehicle lock via a Bowden cable by drive engineering. This solves the problem of installation space in the region of the vehicle lock in a satisfactory manner and corresponds to a modular execution. 
     In any case, the problem of installation space in the known auxiliary locking drive has simply been shifted. Known auxiliary locking drives which are made in this way are of considerable size; this leads to corresponding installation space problems at the respective site away from the vehicle lock. Furthermore, the known auxiliary locking drives are of considerable weight. 
     SUMMARY OF THE INVENTION 
     Therefore, a primary object of the present invention is to embody and develop the known auxiliary locking drive such that the amount of installation space required and the weight of the auxiliary locking drive are reduced. 
     The aforementioned problem is solved in an auxiliary locking drive of the initially mentioned type in that the auxiliary locking drive for producing the linear driving motion has a feed gear mechanism which is connected downstream of the drive motor and that the feed gear mechanism is a spindle-nut gearing with a spindle and a spindle nut. 
     First of all, it is important that, by providing the auxiliary locking drive with a feed gear mechanism which is made as spindle-nut gearing to produce a linear driving motion, this leads to a minimum installation space requirement. Furthermore, this arrangement can be implemented with a minimum number of components, and additionally, leads to a low weight. 
     In accordance with a preferred configuration, the spindle is assigned to the drive side and the spindle nut is assigned to the driven side of the feed gear mechanism. This means that the spindle is driven by the drive motor, while the spindle nut runs along the spindle; this corresponds to the linear driving motion here. 
     An especially compact arrangement can be achieved by the spindle nut being assigned to the drive side and the spindle being assigned to the driven side of the feed gear mechanism. This means that, at this point, the spindle nut and not the spindle is driven by the drive motor. In an especially preferred embodiment, the drive shaft of the drive motor is made as a hollow shaft which, at the same time, forms the spindle nut of the feed gear mechanism. In this especially preferred embodiment, it is provided that the drive motor, with respect to driving the hollow shaft, is a direct electrical drive. In this case, the amount of installation space required can be minimized by the inter-nested arrangement of the drive motor and the feed gear mechanism. 
     In especially preferred configurations, the auxiliary locking drive in accordance with the invention can be easily designed or parameterized for the respective application. Different applications can require specifically different forces, speeds and feeds; this leads accordingly to different drive motors, intermediate gearing or feed gear mechanisms. Depending on the configuration, the drive housing and optionally the end piece of the Bowden cable must be adapted. This is especially easily possible by a telescoping configuration of the parts of the drive housing. 
     In accordance with further preferred embodiments, there is a lengthwise guide which is located parallel to the spindle and on which the spindle nut runs and there is a second spindle which is coupled to the drive shaft of the drive motor and which has a second spindle nut thread. These measures serve to prevent jamming of the spindle nut relative to the spindle even when the coupling of the core of the Bowden cable relative to the axis of the spindle is coupled off-center to the feed nut. 
     The invention is explained in detail below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the structure of the auxiliary locking drive in accordance with the invention in the installed state, 
         FIG. 2  is a cutaway side view of a first embodiment of the auxiliary locking drive of  FIG. 1 , 
         FIG. 3  is a cutaway side view of a second embodiment of the auxiliary locking drive as shown in  FIG. 1 , 
         FIG. 4  is a cutaway side view of a third embodiment of the auxiliary locking drive as shown in  FIG. 1 , 
         FIG. 5  shows the auxiliary locking drive of  FIG. 4  with a telescoping drive housing and telescoping end piece of the Bowden cable, and 
         FIG. 6  shows the auxiliary locking drive in accordance with the invention with two drive spindles. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The structure of an auxiliary locking drive in accordance with the invention which is shown in  FIG. 1  applies to all the embodiments shown in  FIGS. 2 to 4 . This auxiliary locking drive is assigned to a vehicle lock  1 . With respect to a broad understanding of the concept “motor vehicle lock” reference should be made to the Background part of this specification. 
     In all the illustrated embodiments, the auxiliary locking drive has its own drive housing  2  and is located separately from the vehicle lock  1  in the installed state. As can be seen in  FIG. 1 , the auxiliary locking drive is coupled to the vehicle lock  1  by way of a transmission means  3 . 
     As can be seen in detail in  FIGS. 2 to 4 , the auxiliary locking drive has a drive motor  4  which, in the mounted state, is able to produce a linear driving motion that is transmitted to the vehicle lock  1  by way of the transmission means  3 . This linear driving motion allows the vehicle lock  1  to be transferred from the half-locked state into the main locked state. These states were explained in the Background part of this specification. 
       FIGS. 2 to 4  also show, in three embodiments, that the auxiliary locking drive for producing the linear driving motion has a feed gear mechanism  5  which is connected downstream of the drive motor  4  and that the feed gear mechanism  5 , in all embodiments, is made as spindle-spindle nut gearing with a spindle  6  and a spindle nut  7 . 
     The vehicle lock  1  can be largely assigned to any locking elements in a vehicle lock. Preferably, the vehicle lock  1  is assigned to a vehicle door or hatch. The vehicle door can also be a sliding door. 
     The transmission means  3  preferably is a Bowden cable which, generally, has a cable core  8  and a cable sheath  9 . Depending on the available installation space, the use of other types of transmission means  3  are possible. One example of the implementation of the transmission means  3  is a simple cable pull. Another example of the implementation of the transmission means  3  is a rack with teeth in the vehicle lock  1  which can be caused to engage the latch  1 . Another example of the implementation of the transmission means  3  is a linkage which can also contain a universal coupling. It is fundamentally also possible to provide the transmission means  3  with a hydraulic connection. 
     Here, the driving motion is a linear driving motion. Accordingly, the use of spindle-spindle nut gearing for the feed gear mechanism  5  is especially advantageous. Depending on the configuration of the vehicle lock  1 , an adapted design of the auxiliary locking drive with respect to the scope of the driving motion and to the level of the driving force is necessary. 
     In all cases, first of all, the vehicle lock  1  has latching elements, the latch  10  and ratchet  11  as well as a striker  12  which is assigned to the latch  10 . The fundamental interaction of these components was explained in the Background part of this specification. 
     In the preferred embodiment shown in  FIG. 1 , the latch  10  can be moved into a half-locked position (not shown) and into the illustrated main locked position. For this purpose, the latch  10  has a pre-catch  13  and a main catch  14  which each of which can be caused to engage an engagement section  15  of the ratchet  11 . For the preferred configuration shown in  FIG. 1 , it is also such that the auxiliary locking drive, in the installed state, is coupled by drive engineering to the latch  10  and that the latch  10  can be moved by the driving motion produced by the auxiliary locking drive from the half-locked position into the main locked position so that the vehicle lock  1 , as a whole, can be moved from the half-locked position into the main locked position. In this connection, the auxiliary locking drive preferably first causes movement of the latch  10  into an overtravel position so that the ratchet  11  can engage. Then, the latch  10  drops back into the main locked position and is kept there by the ratchet  11 . In this arrangement, the core  8  of the Bowden cable  3  is preferably coupled to the latch  10 . 
     However, fundamentally, it is also possible for the auxiliary locking drive to act on the striker  12  instead of on the latch  10 . In this embodiment (not shown), it is provided that the striker  12 , for its part, can be moved into the half-locked position and into the main locked position, that the auxiliary locking drive, in the installed state, is coupled by drive engineering to the striker  12  and that the striker  12 , by the driving motion produced by the auxiliary locking drive, can be moved from the half-locked position into the main locked position so that the vehicle lock  1  altogether can be moved from the half-locked state into the main locked state. 
     Both versions of the vehicle locks  1  require transmission of a driving motion via the transmission means  3 , here via the Bowden cable  3 . In any case, the range of motion and the force required are different depending on the version; this has corresponding effects on the layout of the auxiliary locking drive. 
     The concept of “spindle-spindle nut gearing” and the terms “spindle” and “spindle nut” can be broadly understood in conjunction with the feed gear mechanism  5 . Fundamentally, it is provided here that the spindle  6  has a spindle thread and that the spindle nut  7  has a spindle nut thread. However, it can also be provided that either the spindle  6  or the spindle nut  7  have a corresponding thread. 
     In particular, it can be provided that the spindle  6  has a driver which engages the thread of the spindle nut  7 . Alternatively, it can also be provided that the spindle nut  7  has a driver which engages the thread of the spindle  6 . A “driver” is defined here as any shape which is suited to engaging a thread and as a result for advancing the spindle nut  7  or the spindle  6 . For example, the driver can be a simple projection or the like. 
     In conjunction with the threads of the spindle  6  and the spindle nut  7 , it is also pointed out that the pitch of the thread of the spindle  6  and/or the spindle nut  7  can change over its lengthwise extension. This can result in a mechanical advantage of the spindle-spindle nut drive, therefore of the feed gear mechanism  5 , changing over an auxiliary locking process. This can be advantageous depending on available installation space conditions. 
       FIG. 2  shows an arrangement in which the spindle  6  is assigned to the drive side and the spindle nut  7  is assigned to the driven side of the feed gear mechanism  5 . This means that the spindle  6  can be driven by the drive motor  4  and that the spindle nut  7  constitutes the output of the feed gear mechanism  5 . Accordingly, it is preferably provided that the transmission means  3 , here the core  8  of the Bowden cable  3 , in the mounted state, is coupled directly to the spindle nut  7 . Furthermore, here it is preferably such that the spindle nut  7  of the feed gear mechanism  5  is rotationally fixed, but able to move lengthwise. The locking element of the spindle nut  7  is addressed below. 
     In the preferred embodiment shown in  FIG. 2 , intermediate gearing  16  is connected downstream of the drive motor  4  and with its output side acts on the spindle  6 . However, fundamentally, it can also be provided that the drive shaft of the drive motor  4  (not shown), is coupled directly to the spindle  6 . In an especially preferred embodiment, the drive shaft of the drive motor  4 , itself, forms the spindle  6 . 
     In the embodiment shown in  FIG. 2 , therefore, the spindle  6  is driven, while the spindle nut  7  is rotationally fixed, but able to move lengthwise. As a result, here, the rotary motion of the spindle  6  is converted into a lengthwise motion of the spindle nut  7 . 
     For the locking element, there is a lengthwise guide  17  which is engaged by a projection  18  or the like of the spindle nut  7 . Accordingly, when the spindle  6  turns the spindle nut  7  moves up or down the length of the spindle.  FIG. 2  shows the initial position of the spindle nut  7 . The end position of the spindle nut  7  after completion of the auxiliary locking process is shown in broken lines. 
     Here, the spindle nut  7  is preferably made as a bushing which is sealed on the end face, which is at the bottom in  FIG. 2 . It is preferably such that this end face provides the coupling point  19  for the transmission means  3 , which in this case is the core  8  of the Bowden cable  3 . 
     In order to simplify the installation of the auxiliary locking drive, especially of the Bowden cable  3 , it is preferably provided that the spindle nut  7 . together with the transmission means  3 , here with the core  8  of the Bowden cable  3 , form a pre-mountable unit. In particular, it is provided that the spindle nut  7 , in the installed state, is inseparably connected to the transmission means  3 , here, to the core  8  of the Bowden cable  3 . It is possible for the spindle nut  7  to be produced by a plastic injection molding process and that the Bowden cable core  8  is embedded in the spindle nut  7  during that process. Other means of connection can be advantageously used as well. 
     In the preferred embodiment shown in  FIG. 2 , the drive motor  4 , intermediate gearing  16  which may be present and the feed gear mechanism  5  are arranged in succession in the drive housing  2 . In this connection, it is also preferable that these components are aligned relative to the drive shaft of the drive motor  4  and/or at the axle of the spindle  6 . 
     Another arrangement is shown in  FIG. 3 . Here, the drive motor  4  and the feed gear mechanism  5  in the drive housing  2  are located at least partially inter-nested in one another relative to the lengthwise extension of the auxiliary locking drive. This inter-nested arrangement can also relate to intermediate gearing  16  of  FIG. 2  which may be present in the  FIG. 3  arrangement as well. 
     Here, the spindle nut  7  is preferably assigned to the drive side and the spindle  6  is assigned to the driven side of the feed gear mechanism  5 . Different from the embodiment shown in  FIG. 1 , therefore, the spindle nut  7  is driven here by the drive motor  4 , while the spindle  6  runs along the spindle nut  7 . Here, the spindle  6  forms the output of the feed gear mechanism  5  and is accordingly coupled, preferably directly, to the transmission means  3 , which, in this case, is the core  8  of the Bowden cable  3 . 
     In this connection, it is also preferable that the spindle  6  of the feed gear mechanism  5  is arranged to be rotationally fixed, but able to move lengthwise. As a result, the rotary motion of the spindle  6  is converted into longitudinal motion of the spindle nut  7 . 
     The aforementioned inter-nesting of the individual components is achieved in the embodiment which is shown in  FIG. 3  by the drive shaft of the drive motor  4  being made as a hollow shaft and by the hollow shaft forming the spindle nut  7  of the feed gear mechanism  5 , and for this purpose, preferably has a spindle nut thread. Within the spindle nut  7  is the spindle  6 , the locking element again being formed by a type of projection  18  which runs in a lengthwise guide  17 . 
     It is apparent in  FIG. 3  that the amount of installation space required is especially small, viewed in the lengthwise extension of the auxiliary locking drive. This is achieved especially by the drive motor  4 , with respect to the driving of the hollow shaft, being made in the manner of a direct electrical drive. The hollow shaft, here the spindle nut  7 , therefore, at the same time, forms the rotor of the drive motor. 
     It can be further taken from  FIG. 3  that the spindle  6  of the feed gear mechanism  5  is located completely within the spindle nut  7 . Here, this preferably applies regardless of the position in which the auxiliary locking drive is found. 
     In the preferred embodiment shown in  FIG. 3 , it is of interest that the extension of the drive motor  4  corresponds altogether to the extension of the drive shaft or of the spindle nut  7 . This can be attributed first of all to the drive motor  4  being made in the manner of a direct electric drive. 
     In order to ensure installation as simple as possible, in one preferred configuration, the spindle  6  together with the transmission means  3 , here with the core  8  of the Bowden cable  3 , form a pre-mountable unit. The same applies here as was stated above regarding the spindle nut  7 . 
     It was already pointed out above that intermediate gearing  16  can be connected between the drive motor  4  and the feed gear mechanism  5 . This is shown schematically in  FIG. 2 . 
       FIG. 4  shows another preferred embodiment in which the intermediate gearing  16  is a planetary gearing system. The planetary gearing system generally has a sun wheel  20 , a planet gear carrier  21  and an internal gear  22 . Here, it is advantageous that the planetary gearing system enables an especially space-saving structure.  FIG. 4  also shows the planet gears  21   a  which are supported on the planet gear carrier  21 . 
     In an especially preferred configuration, one of the components comprised of the sun wheel  20 , planet gear carrier  21  and internal gear  21  are assigned to the drive motor  4 , especially the drive shaft of the drive motor  4 . Another of these components is accordingly assigned to the drive side of the feed gear mechanism  5 . The third of these components is finally braked or completely fixed, at least for auxiliary locking operation. 
     In this case, the sun wheel  20  is preferably assigned to the drive motor  4 , especially the drive shaft of the drive motor  4 . The internal gear  22  is formed by the drive housing  2  and is fixed accordingly. The planet gear carrier  21  is provided with an internal thread and thus forms the spindle nut  7 . The internal thread in the planet gear carrier  21  is located, in particular, on the web plate of the planet gear carrier  21 . However, fundamentally, it can also be provided that the spindle nut  7  is coupled directly to the planet gear carrier  21 . 
     In the embodiment shown in  FIG. 4 , again, the basic principle of the feed gear mechanism  5  as shown in  FIG. 3  is implemented. The rotation of the spindle nut  7  is converted into lengthwise motion of the spindle  6 . For this purpose, it is again provided that the spindle  6  is provided with a projection  18  which runs in a lengthwise guide  17  for locking the spindle against rotation while allowing it to move in a lengthwise direction. 
     In all of the illustrated embodiments, the drive housing  2  has a single, continuous section. However, fundamentally, it is also possible for the drive housing  2  to be composed of several housing components. For example, it can be advantageous to provide the internal gear  22  of the planetary gearing system  5  in a separate drive housing, especially to be able to provide a correspondingly wear-proof material for this purpose. 
     In all of the illustrated embodiments, it is also such that the end piece  23  of the Bowden cable is supported on the drive housing  2 . Here, support on a separate drive housing is also possible. It has been found to be especially advantageous if, as shown in  FIG. 4 , there is a lengthwise guide  17  for the locking element on this end piece  23  of the Bowden cable. 
     Finally, in all of the illustrated embodiments, it is such that the drive motor  4  is made as an electric drive motor. However, fundamentally, it is also possible for it to be a pneumatic or a hydraulic drive motor. 
     Quick mounting of the Bowden cable  3  acquires special importance here. This was already pointed out above. In addition to the proposed pre-mounting of the spindle  6  and the Bowden cable core  8  or the spindle nut  7  and Bowden cable core  8 , it is conceivable that a type of quick acting closure of the Bowden cable be implemented. The Bowden cable core  8  would be inserted into an opening in the spindle  6  and spindle nut  7  and clamped fast in a self-locking manner when pulled back. 
     Electrical control of the auxiliary locking process, in the illustrated embodiments, is especially simple. To start an auxiliary locking process, the electrical drive motor  4  is energized in the first direction until the latch  10  has been transferred into its main locked position, especially into its overtravel position. After turning off the drive motor  4 , the drive motor  4  is energized in the opposite direction until the spindle nut  7  or the spindle  6  reaches the initial position. It is fundamentally possible for there to be spring pretensioning, for example of the drive shaft of the drive motor  4 , which provides for the drive motor  4  returning automatically into the initial position without repeated energizing. 
     In one especially preferred configuration, the auxiliary locking drive, especially the drive motor  4  with the intermediate gearing  16  which is optionally connected downstream and the feed gear mechanism  5  which is connected further downstream, is not made to be self-locking. This especially has the advantage that the arrangement can automatically drop back from the overtravel position into the main locked position after the drive motor  4  is turned off, by the high counterpressure of the door seal which is then acting. 
     In another preferred configuration, it is provided that at least the inside of the drive housing  2  is made essentially rotationally symmetrical relative to the lengthwise extension of the auxiliary locking drive. Optimum use of the available installation space can also be achieved with it. 
     It can be summarized that extraordinarily small installation space requirements are associated with all the illustrated embodiments. Furthermore, the small number of parts allows an especially low weight. As a result, production, especially installation, is possible with especially low cost. 
     It was explained in the Background part of this specification that, depending on the application, a different layout of the auxiliary locking drive in accordance with the invention is necessary. In order to implement this layout with minimum effort, in the preferred embodiment shown in  FIG. 5 , it is provided that the drive housing  2  and the support of the Bowden cable sheath  9 , here of the end piece  23  of the Bowden cable, can be configured such that different drive motors  4 , different intermediate gearings  16  and different feed gear mechanisms  5 , each with different dimensions, can be used. In certain applications it may also be necessary to omit the intermediate gearing  16 . 
     The aforementioned configuration capacity is preferably implemented by the drive housing  2  being made in two parts for adaptation to the respective drive motor  4  and/or the respective intermediate gearing  16 . It can also be advantageous for the drive housing  2  to be composed of more than two parts. 
     For purposes of ease of configuration, at this point, it is preferable that the two parts  2   a ,  2   b  of the drive housing  2  are telescopic. In particular, this means that the first part  2   a  of the drive housing  2  can be slid over the second part  2   b  of the drive housing  2 . The overlapping of the two parts  2   a ,  2   b  of the drive housing  2  makes it possible to adapt the length of the drive housing  2  to the respectively chosen components. There can be interlocking for attachment of the two parts  2   a ,  2   b  of the drive housing  2  to one another. 
     The configuration illustrated in  FIG. 5  also shows that the end piece  23  of the Bowden cable can be telescoped relative to the drive housing  2  to adapt to the respective feed gear mechanism  5 . This can also be provided as an alternative to the telescoping capacity of the drive housing  2  instead of being in addition thereto. The telescoping capacity of the end piece  23  of the Bowden cable means that the end piece  23  of the Bowden cable can be slipped onto the drive housing  2  in different positions. Depending on the overlapping between the end piece  23  of the Bowden cable and the drive housing  2 , adaptation to the respective feed gear mechanism  5  is possible. This relates especially to the layout of the auxiliary locking drive for different actuation strokes. Here, there is also preferably an interlocking attachment between the end piece  23  of the Bowden cable and the drive housing  2 . 
     In certain applications, it can be advantageous for the core  8  of the Bowden cable  3  to be coupled to the spindle nut  7  off-center relative to the axle of the spindle  6 . Then, it is also preferable that the spindle  6  likewise arranged to off-center relative to the drive shaft of the drive motor  4 . 
     It is obvious that, for the aforementioned off-center arrangement, there is the danger of jamming of the spindle nut  7  relative to the spindle  6 . As a result, for this case, it is preferable that there is a lengthwise guide  17  which is located parallel to the spindle  6  to support the spindle nut  7 , on which guide the spindle nut  7  runs. The lengthwise guide  17  can be a guide rod which runs through the corresponding guide hole in the spindle nut  7 . However, a guide groove is also possible which is engaged by the spindle nut  7  with a correspondingly web shape. 
     In an especially preferred embodiment, in any case, it is provided that there is a second spindle  6   a  which is coupled to the drive shaft of the drive motor  4  and that the spindle nut  7  has a second spindle nut thread which is assigned to this second spindle  6   a . This can be seen in  FIG. 6 . 
     The embodiment shown in  FIG. 6 , similar to the embodiment shown in  FIG. 5 , has a drive motor  4 , a planet gear carrier  16  connected downstream, and spindle nut gearing  5  which is in turn connected downstream and which has two spindles  6 ,  6   a . The two spindles  6 ,  6   a  are coupled to the planet gear carrier  21  of the planetary gearing system by the planet gear carrier  21  having a spur gear which meshes with the spur gears of the two spindles  6 ,  6   a . In the preferred embodiment shown in  FIG. 6 , the two spindles  6 ,  6   a  turn in opposite directions so that the spindle thread must be accordingly oriented differently. 
     Here, the two spindles  6 ,  6   a  are preferably arranged symmetrically relative to the drive shaft of the drive motor  4 . With this symmetrical arrangement, the danger of jamming of the spindle nut  7  on one of the two spindles  6 ,  6   a  is extremely low. This increases the operating reliability of the auxiliary locking drive in accordance with the invention altogether.