Abstract:
An actuation unit for an electromechanically actuated disk brake for motor vehicles, arranged on a brake caliper ( 50 ) in which two brake linings ( 4, 5 ) interacting with lateral faces of a brake disk ( 6 ) are displaceable, one of the brake linings ( 4 ) being engageable by the actuation unit directly with the brake disk ( 6 ) by means of an actuating element ( 7 ). The actuation unit including an electric motor ( 1 ) and a reduction gear ( 2 ) operatively arranged between the electric motor ( 1 ) and the actuating element ( 7 ) and having a threaded spindle ( 17 ) which is driveable by the electric motor ( 1 ) and bears axially against the brake caliper ( 50 ). A rolling element bearing ( 33, 42, 63 ) and a force measuring device ( 30, 40, 60 ) having a deformable element ( 35, 43, 65 ) which is deformed when subjected to the force to be determined are arranged in the force flow between the threaded spindle ( 17 ) and the brake caliper ( 50 ). The threaded spindle ( 17 ) bearing against the deformable element of the force measuring device ( 30, 40, 60 ) via the rolling element bearing ( 33, 42, 63 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to German Patent Application Nos. 10 2010 001 986.0, filed Feb. 16, 2010, 10 2011 002 565.0, filed Jan. 12, 2011, and PCT/EP2011/051503, filed Feb. 3, 2011. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to an actuation unit for an electromechanically actuated motor vehicle disk brake. 
       BACKGROUND AND SUMMARY OF THE INVENTION 
       [0003]    An electromechanically actuated disk brake consisting of a floating caliper and an actuation unit with an electric motor and a roller-and-thread drive arranged on the caliper is known from DE 196 52 230 A1. A force measuring device by means of which the application force of the brake can be determined is arranged in the force flow between the caliper and the actuation unit, the force measuring device being arranged in a bore of the threaded spindle. 
         [0004]    WO 2004/083670 A1 discloses a generic actuation unit for an electromechanically actuated disk brake for motor vehicles, comprising an electric motor and a first reduction drive arranged operatively between the electric motor and an actuating element. A force measuring element may be arranged in the first reduction drive. More precise information on the arrangement and configuration of the force measuring element is not disclosed. 
         [0005]    It is the object of the present invention to provide an actuation unit for an electromechanically actuated disk brake of the type mentioned in the introduction which has high accuracy in determining the application force while being configured to be as simple and cost-effective as possible with regard to production. 
         [0006]    This object is achieved according to the invention by an actuation unit for an electromechanically actuated disk brake as claimed herein. 
         [0007]    The invention is based on the concept that a rolling element bearing and a force measuring device comprising at least one deformable element which deforms when subjected to the force to be determined are arranged in the force flow between the threaded spindle and the brake caliper, the threaded spindle bearing against the deformable element of the force measuring device via the rolling element bearing. A simple and compact structure is thereby achieved. 
         [0008]    The rolling element bearing is preferably in the form of a needle roller bearing. In the event of failure of the electro-mechanically actuated brake, the residual clamping force which is retained is thereby significantly reduced. 
         [0009]    According to an alternative preferred embodiment of the invention, the rolling element bearing is in the form of a tapered roller bearing or a ball bearing. Because tapered roller bearings and ball bearings have a lower coefficient of friction, the attainable residual clamping force can be further reduced. 
         [0010]    According to a preferred development of the invention, at least a part of the deformable element of the force measuring device is in the form of at least a part of the rolling element bearing. Through this “dual use” of the deformable element a reduced overall length can be achieved. In addition, the reduction of components achieved thereby leads to a cost optimization. As a result of the reduced number of components, any contour deviations on the contact surfaces occur less frequently or have a smaller influence, increasing the accuracy of the force measurement. Especially preferably, a part of the deformable element of the force measuring device and a part of the rolling element bearing are formed in one piece. 
         [0011]    In the case of a rolling element bearing with a first and a second bearing element between which rolling elements are arranged, a part of the deformable element of the force measuring device is preferably in the form of one of the bearing elements of the rolling element bearing. A contact surface between bearing element and deformable element of the force measuring device is thereby eliminated. 
         [0012]    Correspondingly, in the case of a needle roller bearing with bearing disks, a part of the deformable element of the force measuring device is preferably in the form of a bearing disk of the needle roller bearing. 
         [0013]    In the case of a tapered roller bearing or a ball bearing as the rolling element bearing, a part of the deformable element of the force measuring device is preferably in the form of a ball bearing ring of the ball bearing or a tapered roller bearing ring of the tapered roller bearing. 
         [0014]    In order to measure the deformation of the deformable element, which represents a measure for the application force of the brake, deformation sensors, for example in the form of strain gauges, are advantageously arranged on the deformable element. 
         [0015]    An advantage of the invention is that increased accuracy in determining the application force is attained. A simplified production process and/or a reduction in production cost is/are thereby also achieved. 
         [0016]    A further advantage of the invention is that a shorter overall length is achieved by combining force measuring device and bearing. The production costs for the actuation unit are also reduced by the smaller number of components. Furthermore, the influence of production inaccuracies is reduced. This increases the accuracy of the force measuring device and therefore of the determination of the application force. 
         [0017]    According to a further preferred embodiment of the invention, the reduction gear is in the form of a rolling body-and-thread drive, in particular a ball screw drive, with a threaded spindle driveable by means of the electric motor. 
         [0018]    It is also preferred that the actuation unit includes a second reduction gear, for example a rotation/rotation gear, arranged between the electric motor and a part of the reduction gear. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Further preferred embodiments of the invention are apparent from the dependent claims and from the following description with reference to figures, in which: 
           [0020]      FIG. 1  shows schematically an electromechanically actuated disk brake in accordance with the prior art, 
           [0021]      FIG. 2  shows schematically a partial view of a first exemplary embodiment of an actuation unit according to the invention for an electromechanically actuated disk brake, 
           [0022]      FIG. 3  shows schematically a partial view of a second exemplary embodiment of an actuation unit according to the invention for an electromechanically actuated disk brake, and 
           [0023]      FIG. 4  shows schematically a partial view of a third exemplary embodiment of an actuation unit according to the invention for an electromechanically actuated disk brake. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]      FIG. 1  shows an electromechanically actuated brake known from WO 2004/083670 A1, the caliper of which, shown in cross section, is mounted displaceably in a fixed support. A pair of friction linings (or pads)  4  and  5  is arranged in the brake caliper in such a way that they face towards the left-hand and right-hand lateral faces of a brake disk  6 . While the first friction lining  4  can be brought directly into engagement with the brake disk  6  by an actuation unit by means of an actuating element  7 , the second brake lining  5  is pressed against the opposite lateral face of the brake disk  6  through the effect of a reaction force exerted by the caliper upon actuation of the arrangement. 
         [0025]    The actuation unit, which is mounted on the brake caliper by means of fastening means (not shown), has a modular structure and consists essentially of four independent assemblies or modules, namely a drive unit  1 , a first reduction gear  2  actuating the first friction lining  4  and simultaneously converting a rotary motion into a translational motion, a second reduction gear  3  interposed between the drive unit  1  and the first reduction gear  2 , and an electronic control unit  8  (or ECU-only the mounting for electronic components is shown). 
         [0026]    The drive unit consists of an electric motor  1 , the stator  9  of which is arranged immovably in a motor housing  12  and the rotor  10  of which is connected to a shaft  13  which is operatively connected to the second reduction gear  3 . The first reduction gear  2  is in the form of a ball screw drive which is arranged in a transmission housing  14 . The ball screw drive consists in this case of a threaded nut  16  and a threaded spindle  17 , a plurality of balls, not designated in detail, being arranged between the threaded nut  16  and the threaded spindle  17 , circulating during rotary motion of the threaded spindle  17  and imparting an axial or translational motion to the threaded nut  16 . The threaded nut  16  has a two-part configuration and consists of a first part  18 , which forms the aforementioned actuating element  7 , and a second part  19  in which a recirculation region for the balls is formed, in which the balls can roll back without load to the start of the load-bearing track. The second reduction gear  3  is in the form, in the example, of a planetary gear set. 
         [0027]    The arrangement is implemented in such a way that the rotor  10  or the shaft  13  of the electric motor drives the threaded spindle  17  via the interposed second reduction gear  3 , while the first part  18  of the threaded nut  16  bears against the first friction lining  4 . The coupling of the first reduction gear  2  to the second reduction gear  3  is effected by means of a plug-in connection without radial stress which carries reference numeral  20  and may be configured, for example, as a splined connection. Two radial bearings  21  and  22  arranged in the motor housing  12  serve to mount the rotor  10 . 
         [0028]      FIG. 2  shows schematically a partial view of a first exemplary embodiment of an actuation unit according to the invention for an electromechanically actuated disk brake. Here, the region of the reduction gear  2  which converts rotary motion into translational motion, and its support against the brake caliper  50 , is shown on an enlarged scale. The threaded spindle  17  driven by electric motor  1  (not shown) bears against the brake caliper  50  via a needle roller bearing  33  and a force measuring device  30 . The needle roller bearing  33  is arranged between the spindle  17  and the force measuring device  30  and serves, inter alia, to transmit force between the spindle  17  and a deformable element  35  of the force measuring device  30 . The needle roller bearing  33  includes bearing disks  31  and  32 . The force measuring device  30  bears against the brake caliper housing  50 , via a further component  34  according to the exemplary embodiment in  FIG. 2 , and is arranged in particular rigidly, in particular non-rotatably, in the brake caliper (housing)  50 . The bearing disk  32  and the deformable element  35  of the force measuring device  30  are hardened. A needle roller bearing  33  is advantageous because of the small amount of installation space available. Deformable element  35  is designed to deform in reaction to actuation forces exerted by the actuation unit and is measured by a strain measuring device such as electric resistance strain gages. 
         [0029]      FIG. 3  shows schematically a partial view of a second exemplary embodiment of an actuation unit according to the invention for an electromechanically actuated disk brake. In this case the rolling bearing arranged between threaded spindle  17  and force measuring device  40  is in the form of a ball bearing  42 . Alternatively, the rolling bearing may be in the form of a tapered roller bearing (not shown). 
         [0030]    The arrangement of a ball bearing  42  or a tapered roller bearing in place of the needle roller bearing  33  is especially advantageous since ball and tapered roller bearings  42  inherently make possible a lower coefficient of friction. Needle roller bearings  33  inherently have a higher coefficient of friction, in particular when loaded with axial forces. The use of a ball or tapered roller bearing  42  therefore has the advantage that in the event of failure of the electromechanically actuated (service) brake the residual clamping force to be set can be reduced to a minimum. Above all, a ball bearing  42  has the further advantage of being very cost-effective in production. 
         [0031]    Through their construction, ball and tapered roller bearings  42  have a larger space requirement than needle roller bearings  33 . In order to reduce the space requirement, the force measuring device is advantageously configured in such a way that a part of the ball or tapered roller bearing, or the ball or tapered roller bearing itself, forms the deformable element  43  of the force measuring device  40 . 
         [0032]    In the second exemplary embodiment represented in  FIG. 3 , the ball bearing  42  is arranged between the threaded spindle  17  and the force measuring device  40 , the ball bearing  42  serving to transmit force between threaded spindle  17  and force measuring device  40 . The force measuring device  40  bears against the brake caliper housing  50 , via a further component  44  according to this exemplary embodiment. The ball bearing  42  comprises a first bearing ring  41  and a second bearing ring  43 , between which rolling balls  45  are arranged. The force measuring device  40  is configured in such a way that at least a part of its deformable element  43  forms part of the ball bearing  42 , namely the outer bearing ring  43  of the ball bearing  42 . Deformable element  43  features a circumferential groove as shown to promote desired deformation. 
         [0033]    In an actuation unit according to the first exemplary embodiment ( FIG. 2 ), the bearing disk  32  and the force measuring device  30  are in contact only via an annular edge (linear contact of the force measuring device  30 ), at least under low application forces. Through the production process of the bearing, the bearing disks  31 ,  32  and the deformable element  35 , small contour deviations (regarding parallelism, flatness) within the range of a few pm are possible, with the result that the deformation of the deformable element  35  of the force measuring device  30  does not take place homogeneously or linearly, so that the output signal has deviations from the ideal characteristic curve. This can lead in some cases to slightly reduced accuracy of the application force measurement. In the second exemplary embodiment, in comparison to the first exemplary embodiment, the outer bearing disk and the linear contact with the force measuring device are eliminated, so that any contour inaccuracies of the bearing disk and of the linear contact can have no influence, or less influence, on the signal of the force measuring device  40 . Accordingly, the measuring accuracy of the force measuring device  40  is increased according to the second exemplary embodiment. 
         [0034]    Through the use of a conventional ball bearing  42  and the configuration of the deformable element  43  of the force measuring device  40  as a part of the ball bearing  42  (bearing ring  43 ), the residual clamping force in the event of failure of the electromechanically actuated brake can be reduced, while the overall length remains the same or is even reduced in comparison to the use of a needle roller bearing. Furthermore, the influence of contour inhomogeneities is reduced by the reduced number of components (through the at least partial “integration” or “combination” of bearing  42  and force measuring device  40 ), whereby the accuracy of the force measuring device is increased. 
         [0035]      FIG. 4  shows schematically a partial view of a third exemplary embodiment of an actuation unit according to the invention for an electromechanically actuated disk brake. In this case the rolling bearing arranged between threaded spindle  17  and force measuring device  60  is in the form of a needle roller bearing  63 . The needle roller bearing  63  includes a first bearing disk  61 . The deformable element  65  of the force measuring device  60  is configured in such a way that it serves as the second bearing disk for the needle roller bearing  63 . A needle roller bearing  63  is advantageous on account of the small installation space available. Through the configuration of the deformable element  65  of the force measuring device  60  as a part of the needle roller bearing (bearing disk), the number of components is reduced, reducing the influence of contour inhomogeneities. The accuracy of the force measuring device  60  can thereby be increased. 
         [0036]    In the examples, the force measuring device  30 ,  40 ,  60  includes a deformable element, for example a deformable ring or a deformable disk made of steel on which electrical resistance strain gauges, for example made of silicon, are arranged to measure deformation. 
         [0037]    While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation, and change without departing from the proper scope and fair meaning of the accompanying claims.