Abstract:
The invention relates to a regulating device, in particular a motor vehicle parking brake with a regulating unit having a power-operated drive. To provide a regulating device which enables simple cable balancing, it is proposed that a hollow shaft be moved against a torsionally resistant stop as a function of the spring force of an elastic element, when the parking brake is released. The axial position of the stop thus ensures that an adequate cable bias force is always present.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a regulating device, in particular a motor vehicle parking brake with a regulating unit comprising a power-operated drive. 
   During the operation of a parking brake, it is necessary to adjust the length of the brake cable, due to wear of the brake shoes for example or the settling behavior of the brake cable for example. This is to avoid essentially unnecessary cable travel when the brake cable is tightened so that said brake cable can be tightened in a quick and reliable fashion. 
   Mechanical adjustment devices are known from the prior art, which are mostly integrated into the force flow of the brake pull cable as a type of “mechanical series connection”. The fundamental concept behind these types of adjustment devices is based on two teeth interlocking with each other and transmitting the cable force. As soon as the teeth are no longer interlocking with each other, the force flow is interrupted. Generally one of the teeth is designed as a rack and the other tooth as a latch. In this way, the latch engages in a specific tooth on the rack depending on wear. 
   With power-actuated parking brakes, electromotive parking brakes with a spindle drive for example, the adjustment takes place by means of path measurement in conjunction with corresponding control of the drive. The disadvantage with this is that path measurement and control of the drive require relatively expensive and error-prone components. 
   SUMMARY OF THE INVENTION 
   The object of the invention is to provide a regulating device, in particular a motor vehicle parking brake, with a regulating unit having a power-operated drive, which enables simple cable balancing. 
   This object is achieved by means of a regulating device according to claim  1 . Advantageous embodiments of the invention are specified in the subclaims. 
   The regulating device according to the invention has a regulating unit with a power-actuated drive, a telescopic device in a housing or the like which can be moved axially in the longitudinal axis of the regulating unit, comprising a hollow shaft and a spindle shaft, which is axially connected to said hollow shaft by means of a rotary feed connection and which activated the brake pull cable, a drive connection between the power-actuated drive and the hollow shaft, an axial feed support between the hollow shaft on the one hand and the housing on the other hand via an elastic element which is stationary in relation to the spindle shaft and the brake pull cable and arranged parallel in the direction of the hollow shaft, and is axially loaded by the feed support and thus can be longitudinally deformed in an axial fashion. 
   A regulating device with these features is known from the former German patent application of the applicant with the official reference number 103 61 127.4. The complete disclosure of this former patent application is incorporated here into the disclosure of the current patent application. 
   According to the present invention, in addition to the regulating device known from the former patent application, the regulating device has a torsionally resistant axial stop to restrict the rotation of the hollow shaft. Rotation of the hollow shaft is thus stopped when the brake pull cable is released, when a specific cable bias force defined by the elastic element is reached. 
   A basic concept behind the invention is to provide cable balancing even in power-actuated parking brakes, which is essentially based on a mechanical system. Complicated, expensive and error-prone steps such as path measurement and control of the drive can thus be significantly reduced and/or completely dispensed with. 
   According to the invention, provision is made for a mechanical adjustment device to be integrated into the spindle drive of the spindle shaft actuating the brake pull cable. The simple structural design means that no control system is necessary to set a specific release force for the brake pull cable. Rather a defined minimum cable bias force is always present when the brake pull cable is released. 
   This is achieved structurally in that during the release process, the hollow shaft is pushed against the axial stop by means of the longitudinally deformable elastic element, if the cable force, in other words the force acting on the brake pull cable, is smaller than the bias force of the elastic element. The extent of the cable bias force can be adjusted by selecting the elastic element depending on the application in question. 
   In other words it is proposed that a hollow shaft be moved against a torsionally resistant stop as a function of the spring tension, when the parking brake is released. The axial position of the stop thus ensures that an adequate cable bias force is always present. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The invention and further advantageous embodiments according to the subclaims are described below with reference to the schematically represented exemplary embodiments, which are explained in more detail with reference to the drawings, in which: 
       FIG. 1  shows a first embodiment of a regulating device with a tightened brake pull cable in a longitudinal section, 
       FIG. 2  shows the regulating device according to  FIG. 1  in a perspective representation with a partially cut-out housing, 
       FIG. 3  shows an enlarged partial view from  FIG. 2 , 
       FIG. 4  shows the regulating device according to  FIG. 1  with a released brake pull cable in a longitudinal section, 
       FIG. 5  shows the regulating device according to  FIG. 4  in a perspective representation with a partially cut-out housing 
       FIG. 6  shows an enlarged partial view from  FIG. 5 , 
       FIG. 7  shows a second embodiment of a regulating device with a released brake pull cable in a longitudinal section, 
       FIG. 8  shows a third embodiment of a regulating device with a released brake pull cable in a longitudinal section, 
       FIG. 9  shows a fourth embodiment of a regulating device with a tightened brake pull cable in a longitudinal section, 
       FIG. 10  shows the regulating device according to  FIG. 9  in a perspective representation with a partially cut-out housing, 
       FIG. 11  shows an enlarged partial view from  FIG. 10 , 
       FIG. 12  shows the regulating device according to  FIG. 9  with a released brake pull cable in a longitudinal section, 
       FIG. 13  shows the regulating device according to  FIG. 12  in a perspective representation with a partially cut-out housing, 
       FIG. 14  shows an enlarged partial view from  FIG. 13 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As shown in  FIG. 1 , an axially moveable telescopic device is accommodated by a housing  1  with an axially closing housing cover  2 , said telescopic device having a hollow shaft  3  and a spindle shaft  5  connected to said hollow shaft by means of a rotary feed connection, operating a brake pull cable  4  and connected at its left end to a brake pull cable  4 . 
   An elastic element  6  in the form of a spiral spring concentrically enclosing the hollow shaft  3  and/or the spindle shaft  5  is provided as a feed support for the hollow shaft  3 , said spiral spring being positioned as a compression spring, with its one end resting against a shoulder  8  of the housing  1 , by means of a fixed axial thrust bearing  7 , and with its other axial end resting against a circumferential flange  9  of the hollow shaft  3 . 
     FIG. 1  shows a brake position with a tightened brake pull cable. When the telescopic device is driven in the sense of a movement of the brake pull cable  4  to the right, i.e. in the sense of a tightening of a motor vehicle parking brake (not shown in further detail here), the elastic element  6  is compressed by pressure against the axial bearing  7 . 
   A torque is thereby transmitted from an electric motor  10  of a regulating unit  11  (see.  FIG. 2 ), via a transmission system (not shown in further detail) to an axially moveable drive transmission wheel  12  in the form of a toothed wheel, with a fixed drive connection to the hollow shaft  3 . The hollow shaft  2 , made to rotate by the drive transmission wheel  12 , has an internal thread  13 . An axial feed movement of the spindle shaft  3  is achieved by means of this internal thread  13  via the intermeshing external thread  14  of the spindle shaft  5 . 
   A stop element  15  in the form of trapezoidal toothing around the hollow shaft edge is attached on the axial end of the hollow shaft  3  opposite the brake pull cable  4 , see  FIG. 2 . The housing cover  2  is configured in the manner of a sleeve to accommodate the spindle shaft  5 . At the edge of the sleeve a stop  16  also in the manner of trapezoidal toothing is arranged to interact with the stop element  15  of the hollow shaft  3 . The trapezoidal toothing in the housing cover  2  is not completely shown for illustration reasons. Counter-clockwise rotation is not possible due to the asymmetrical saw-tooth type of toothing used, whilst clockwise rotation, in other words the retightening of the parking brake can be effected at any time. 
   In a tightened state the trapezoidal toothing is not engaged, so that rotation of the hollow shaft  3  is possible in both directions, see  FIG. 3 . 
   In order to release the brake cable, counter-clockwise rotation of the hollow shaft  3  is effected by means of the electric motor  10  so that the spindle shaft  5  moves counter-clockwise. The load acting on the brake pull cable  4  reduces as the release path increases. At the same time, the elastic element  6  expands. The load reduction causes the hollow shaft  3  and the drive transmission wheel  12  to be pushed to the right in the direction of the stop  16  by means of the spring force of the elastic element  6 . 
   If the force (cable force) acting on the brake pull cable  4  is smaller than the bias force of the supporting elastic element  6  (spring force) at the axial bearing  7 , the hollow shaft  3  is pushed with its stop element  15  against the stop  16  on the housing cover  2 , see  FIG. 4 . Further rotation in the release direction is prevented by the specific configuration of the stop mechanism and the cable force does not therefore drop below a defined value. The engaged trapezoidal toothing is shown in  FIGS. 5 and 6 . 
     FIG. 7  shows a further embodiment of a regulating device with a released brake pull cable  4 , in which a sensor  17  connected to the hollow shaft  3  is provided. The elastic element  6  is thereby supported between the axial bearing  7  and the sensor  17 , so that the sensor  17  can serve to determine the spring path already covered and thus the axial position of the hollow shaft  3 . This information is preferably used to ensure gentle engagement of the trapezoidal toothing at the stop  16 . To this end the electric motor  10  is for example controlled such that the rotational speed and/or the regulating speed is reduced shortly before the stop  16 . 
     FIG. 8  shows a further embodiment in a released position, the stop element  18  not being directly attached to the hollow shaft  3  but rather to the drive transmission wheel  12 . Accordingly, the stop  16  in the housing cover  2  is also configured on a sleeve  19  encompassing the hollow shaft  3 . In this embodiment the drive transmission wheel  12  is fixed to the hollow shaft  3 . One Particular advantage of this embodiment is the ease with which the stop element  18  can be produced in conjunction with the manufacture of the drive transmission wheel  12 . 
     FIGS. 9 to 14  show a further embodiment of the regulating device. This differs from the previous embodiment on the one hand in that in addition to the first elastic element  6  which serves as a spring for the bias force of the brake pull cable  4 , a second elastic element  20  is provided. This second elastic element  20  which is similarly configured in the form of a spiral spring serves as a spring for a force sensor. Both the first and the second elastic elements  6 ,  20  are thereby supported on the axial bearing  7  on the one hand and on the sensor  21  of the force sensor on the other hand, which is arranged on the hollow shaft  3 . When the parking brake is tightened or released, the hollow shaft  3  and thus also the sensor  21  moves axially to the left or right. The path thereby covered is detected via the sensor pick-up  21  and provides a measure for the tightening force and/or braking force exerted by the electric motor  10  via the drive transmission wheel  12 , the hollow shaft  3  and the spindle shaft  5  on the brake pull cable  4 . In other words, conclusions can be drawn from this path information about the cable force in the tightened state. 
   Furthermore this embodiment differs in that the stop  22  in the housing cover  2  is not fixed, but is configured on an axially moveable sleeve-type counter-element  23 . In the brake position shown in  FIG. 9 , the spindle shaft  5  pushes the counter-element  23  to the right against the spring force of a third elastic element  24 , which is similarly configured as a spiral spring and is supported on the counter-element  23  on the one hand and on the housing cover  2  on the other hand.  FIGS. 10 and 11  show the brake position with its released trapezoidal toothing. 
   In the case of a locked brake pull cable the trapezoidal toothing engages further to the right, since the spindle shaft  5  pushes the counter-element  23  to the right as a result of the support at the brake pull cable  4 . The position of the sensor pick-up  21  is thus different from its position when the brake pull cable is released. It is thus possible to detect the locking of a brake pull cable  4  during release. By way of example, the driver of the motor vehicle can be informed of locking by means of a warning light. 
   When the brake position is released, the spindle shaft  5  moves to the left and relieves the load on the counter-element  23 , so that the third elastic element  24  expands. The hollow nut  3  thus moves back to the right, see  FIG. 12 . If the cable force is smaller than the spring force of the second elastic element  20 , the stop element  15  engages at the counter-element  24  and further rotation in the release direction is prevented. 
   If the brake pull cable  4  is locked during release, the spindle shaft  5  would not move to the left during release either. The sensor pick-up  21  would thus move further to the right than would be the case with a brake cable that is not locked. Locking could be detected in a simple fashion by evaluating the path signal of the sensor pick-up  21 . 
   The spring system comprising the first, second and third elastic elements  6 ,  20 ,  24  is thus tailored to the application in that different path points of the axial path of the hollow shaft  3  are assigned different resulting spring strengths. So for example, a first path point “cable released” is defined by the “disengaging” of the second elastic element  20 . From this point onwards the hollow shaft  3  is only supported by the first elastic element  6 , which pushes the hollow shaft  3  against the stop. Reaching the stop then defines a second path point “stop with defined cable bias force”. If the stop point moves, because the third elastic element  24  is pushed against the first elastic element  6 , a further path point “stop moved” is thereby defined.