Abstract:
An actuator for a parking brake of a motor vehicle is provided, which includes an electric motor ( 1 ) whose rotor ( 20  has a threaded spindle ( 3 ) on which a spindle nut ( 4 ) is located. Between the threaded spindle ( 3 ) and the spindle nut ( 4 ), rolling bodies are in rolling engagement with threaded paths ( 6, 7 ) formed on the spindle nut ( 4 ) and on the threaded spindle ( 3 ). A cable pull ( 8 ) for actuating a brake acts upon the spindle nut ( 4 ).

Description:
BACKGROUND  
       [0001]     The present invention relates to an actuator for a parking brake of a motor vehicle. Parking brakes actuated with an actuator can be set automatically when parking and can be released automatically when starting to move again. These parking brakes can also be designated as active parking brakes.  
         [0002]     These usually electromechanical actuators comprise an electric motor, which sets the parking brake via a control element. The control element can comprise gearing. These actuators should enable quick release and application of the parking brake. The objective of the present invention is to provide an actuator of a parking brake for a motor vehicle, which has a simple design and can be actuated reliably.  
       SUMMARY  
       [0003]     The actuator according to the invention from claim  1  has the advantage that the rotor of the electric motor drives the threaded spindle directly, so that gearing between the rotor and the threaded spindle is eliminated. The known spindle nuts arranged on the threaded spindle operate with very low friction, because relative rotation between the spindle nut and the threaded spindle is performed with the rolling of rolling bodies on threaded paths of the spindle nut and the threaded spindle. The combination of the direct drive and rolling body threaded drive enables a drive with very high mechanical efficiency. The spindle nut interacting with the threaded spindle form a known rolling body threaded drive, which operates reliably. The actuator according to the invention has a compact and economic design due to the elimination of intermediate gearing. Due to the low friction losses, the electric motor can be small.  
         [0004]     The spindle nut is displaced in the axial direction when the threaded spindle rotates, because a rolling body threaded drive represents a rotary transmission gearing. The cable pull attached to the spindle nut is tightened by the axial displacement of the spindle nut through tensioning. Loosening is realized through an opposite movement of the spindle nut.  
         [0005]     The actuator according to the invention enables a biasing force of about 1600 N per wheel side. The tension path—thus the travel path of the spindle nut—can equal approximately 25 mm. The activation time can be reduced to about 700 milliseconds at a spindle rpm of approximately 1250 revolutions/min. Quick activation times are therefore possible.  
         [0006]     If the parking brake is activated, thus the actuator has been set, the vehicle is secured. If there is not a self-locking gear between the electric motor and the cable pull, then a locking device can be provided, which secures the rotor and/or the threaded spindle against rotation. This locking can be realized preferably in a mechanical way, for example, through positive-fit meshing of locking elements, of which one is fixed in rotation on the rotor and the other is fixed in the rotational directions of the rotor. For example, a displaceable piston can engage in a gap of a gear defined by teeth. The tensile load of the cable pull can exert a torque on the threaded spindle or the rotor. This torque is then received by the locking device. In the case of the piston, a tooth then presses against the piston. The piston is then held tight and rotation of the spindle nut is stopped.  
         [0007]     If the parking brake is to be released, first the cable pull is relaxed by actuating the electric motor, which has the result that the piston is no longer held tight. If a spring force is applied to the piston, the piston can be moved out from its locking position under this spring force. The parking brake is then released.  
         [0008]     If the parking brake is to be released, but the electric motor cannot be used due to loss of power, an emergency unlocking device is provided. With this emergency unlocking device, which can be operated, for example, by hand, the locking device can be disabled. For the locking device described as an example, it is necessary to remove the load of the toothed disk which is pressed against the piston, so that the piston can spring out of its locking position under the spring force. With the emergency locking device, now a torque is exerted by hand, which counteracts a torque exerted by the load of the cable pull. This means that the pressure is taken off the piston, so that the piston can spring out. The parking brake is then released.  
         [0009]     If, for example, the emergency unlocking device has a band, which wraps around the toothed disk and which, in the wrap-around area has a pocket, into which the teeth of the toothed disk project, first the toothed disk can rotate without coming into locking contact with the band. If the band is provided with a crosspiece, which can engage in a gap of the toothed disk, the emergency unlocking device can operate as follows. With one end, the band is fixed to a tension spring. At the other end it is now tightened. The band now moves along the periphery of the toothed disk, wherein the crosspiece engages in the gaps. For further movement of the band, the toothed disk is taken along and the piston of the locking device relaxes, so that this piston can spring out from the gap. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The invention is explained in more detail below with reference to an embodiment shown in a total of three figures. Shown are:  
         [0011]      FIG. 1 a  perspective view of an actuator according to the invention for a parking brake of a motor vehicle,  
         [0012]      FIG. 2 a  longitudinal section view of a part of the actuator according to  FIG. 1 , and  
         [0013]      FIG. 3  another perspective view of the actuator according to the invention from  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     The actuator according to the invention shown in  FIGS. 1 and 3  for a parking brake of a motor vehicle is provided with an electric motor  1 , having a rotor  2  with a threaded spindle  3 . A spindle nut  4  is arranged on the threaded spindle  3 . The spindle nut  4  is shown clearly in  FIG. 2  in a longitudinal section. It should be noted from  FIG. 2  that between the threaded spindle  3  and the spindle nut  4  there are rolling bodies  5  in rolling engagement with threaded paths  6 ,  7  formed on the spindle nut  4  and the threaded spindle  3 . The spindle nut  4  and the threaded spindle  3  form a ball screw  9 , wherein the rolling bodies are formed by balls  5   a , which circulate in endless ball raceways  10 . The ball raceways  10  are defined by the threaded paths  6 ,  7  of the threaded spindle  3  and the spindle nut  4 . The rotor  2  has two opposite ends, which are arranged on two sides of a motor housing  1   a  of the electric motor  1 . One of the threaded spindles  3  is attached to both ends of the rotor  2 . This threaded spindle  3  is coaxial to the rotor  2  and locked in rotation with this rotor. These two threaded spindles  3  have threaded path sections of opposing slope. A spindle nut  4  is arranged on each threaded path section. A cable pull support  4   a  is fixed to each spindle nut  4 . Cable pulls  8  are suspended in the two cable pull supports  4   a . The cable pulls  8  each engage one of the parking brakes of the motor vehicle. The parking brakes are not shown here.  FIG. 3  shows that the cable pull supports  4   a  are arranged displaceable along a connecting member  26  here shown only with dashed lines. This connecting member  26  is used as a rotational lock for the cable pull supports  4   a  and the spindle nut  4 .  
         [0015]      FIG. 3  further shows a locking device  11 , which prevents rotation of the rotor  2  and thus of the threaded spindle  3  when no current flows to the electric motor  1 . This locking device  11  has a first locking element  12  fixed in rotation with the rotor  2  and a movable second locking element  13 , wherein, in the locking position the two locking elements  12 ,  13  engage with a positive fit in each other for preventing rotation of the rotor  2 . The first locking element  12  has a toothed disk  15  locked in rotation with the rotor  2 . Several teeth  16  distributed over the extent of the disk form gaps  17  on the periphery of this toothed disk.  
         [0016]     The locking device  11  further comprises a frame-fixed electromagnet  14 , which is provided with the second locking element  13 . The locking element  13  moves into the locking position under the activation of the electromagnet  14 , wherein the locking position is reached when the second locking element  13  engages in the gap  17 . The second locking element  13  is here formed by a piston  18 . The piston  18  is acted on by a spring force and can be pushed against the spring force into the locking position through the activation of the electromagnet  14 .  
         [0017]     The ball screw  9  forms a control element, which is driven by the rotor  2 . Instead of the ball screw, other rotary transmission gears are also possible.  
         [0018]      FIG. 3  further shows an emergency unlocking device  19  for relaxing the locking device  11  from a load applied for tensioning the brake.  
         [0019]     This emergency unlocking device  19  has a band  20 , which is arranged perpendicular to the rotor axis and which wraps around a contact surface  21  arranged coaxial to the rotor axis. This contact surface  21  is formed on the toothed disk  15  and axial to two sides of the teeth  16 . The band  20  has legs or belts  23  extended in the longitudinal direction of the band  20 , wherein the belts  23  can be brought into contact with the contact surface  21 . The two legs or belts  23  define a large pocket  24 , which is bordered by a catch  22  along the band. This catch  22  is formed in the present example as a transverse crosspiece  22   a , which connects the two belts  23  to each other. One band end is attached to a tension spring  27 , which is supported, on its side, by a housing  25  fixed to the frame. The other band end engages a cable pull  28 . By tensioning the cable pull  28 , the band  20  contacts the contact surface  21  of the toothed disk  15  with its belts  23  and is moved relative to the toothed disk  15  in the counterclockwise direction, wherein this band is moved under deflection of the tension spring  27 .  
         [0020]     In the following, the function of the actuator according to the invention is described. For activating the not-shown parking brakes, the electric motor  1  is activated. Through rotation of the rotor  2  and the threaded spindles  3 , spindle nuts  4  are displaced in the axial direction along the threaded spindle  3 , that is, in the direction towards the motor housing  1   a . Under this displacement of the cable pull support  4   a , the cable pulls  8  are tensioned, wherein, as a result of activating the cable pulls  8 , the parking brakes are activated. If there is no current flowing to the electric motor  1 , the piston  18  of the locking device  11  moves into the closest possible gap  17 . The toothed disk  15 —and thus the rotor  2 —is now engaged and locked in its rotational position.  
         [0021]     For releasing the parking brake, first the piston  18  must be moved again out of the gap  17 . However, at first this can be made more difficult in that under a torque acting on the toothed disk  15 , one of the two teeth adjacent to the piston  18  presses against the piston  18 . For relaxing pressure, the electric motor  1  can be activated for a short time or optionally the emergency unlocking device  19  can be activated, if, for example, the electric motor  1  has failed. For this purpose, for example, in the passenger compartment there can be a handle attached to the cable pull  28  in order to be able to pull on the cable pull  28 . The band  20  is now pushed under the section of the cable pull  28 . The catch  22  of the band  20  shown in  FIG. 3  is finally led into a gap  17 . For further movement of the band, now the toothed disk  15  is now taken along by means of a positive engagement. Under these positive engagement measures, the piston  18  is now released from pressure. Finally, the pressure is reduced so far that the piston  18  springs back under the spring force and is led out of engagement with the gap  17 . Now, the toothed disk  15  can rotate again, that is, also the rotor  2  and the threaded spindle  3 . Now, the spindle nuts  4  can be displaced away from the motor housing  1   a  along the threaded spindle  3  under the relaxing of the cable pulls  8 , whereby the parking brakes are released.  
       LIST OF REFERENCE SYMBOLS  
       [0000]    
       
           1  Electric motor  
           1   a  Motor housing  
           2  Rotor  
           3  Threaded spindle  
           4  Spindle nut  
           4   a  Cable pull support  
           5  Rolling body  
           5   a  Ball  
           6  Threaded path  
           7  Threaded path  
           8  Cable pull  
           9  Ball screw  
           10  Ball raceway  
           11  Locking device  
           12  Locking element  
           13  Locking element  
           14  Electromagnet  
           15  Toothed disk  
           16  Tooth  
           17  Gap  
           18  Piston  
           19  Emergency unlocking device  
           20  Band  
           21  Contact surface  
           22  Catch  
           22   a  Transverse crosspiece  
           23  Belt  
           24  Pocket  
           25  Housing  
           26  Connecting member  
           27  Tension spring  
           28  Cable pull