Abstract:
The invention relates to an electromechanical disk brake which has a switchable freewheel in order to be configured as a parking brake. The switchable freewheel includes a clamping roller freewheel having rollers for locking a motor shaft of an electric motor of the brake. A locating bearing of the motor shaft of an electric motor, and the freewheel are accommodated on a cover of a housing of the electric motor, and all the electric connections of the disc brake are routed via the cover. The number of components used can be reduced considerably by the integrated design. Moreover, the positional tolerances of the freewheel in relation to the motor shaft can be reduced with the aid of the invention.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/EP 2006/062910 filed on Jun. 6, 2006. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an electromechanical brake, which is provided in particular as a vehicle brake for a motor vehicle. 
     2. Description of the Prior Art 
     Brakes of this kind are intrinsically known. In order to actuate them, i.e. in order to press a friction brake lining against a rotatable brake body to be braked, the brakes have an electromechanical actuating device equipped with an electric motor and a rotation/translation converting transmission via which the electric motor is able to press the friction brake lining against the brake body. Often, a reduction gear train is connected between the electric motor and the rotation/translation converting transmission. It is customary for the rotation/translation converting transmission to be a screw mechanism. Other mechanisms, for example a rack-and-pinion drive or a cam that the electric motor is able to pivot via the reduction gear train, thereby causing it to press the friction brake lining against the brake body can also be used to convert the rotating drive motion of the electric motor into a translating movement in order to press the friction brake lining against the brake body. It is also conceivable to use an electromagnet in lieu of the electric motor. In the case of a disc brake, the brake body is a brake disc. In the case of a drum brake, it is a brake drum. 
     One example of an electromechanical brake of this kind is disclosed in DE 102 55 192 A1. To modify the known brake into an auxiliary brake (parking brake), the known brake is equipped with a switchable freewheel, which in the engaged position, locks a motor shaft of the electric motor to prevent it from rotating in a releasing direction of the brake. The locking can occur directly on the motor shaft or indirectly, for example on a transmission shaft. In an actuation or application direction of the brake, the motor shaft is able to rotate freely even when the freewheel is engaged, thus allowing the brake to be actuated but not released. When the freewheel is disengaged, the motor shaft is able to rotate in both rotation directions. It is thus possible to apply and release the brake like a service brake. In the known brake, the freewheel is coaxially flange-mounted to a housing that accommodates the electric motor and the rotation/translation converting transmission. 
     SUMMARY OF THE INVENTION 
     The brake according to the invention has a housing that accommodates the electric motor. The housing can also accommodate an optional reduction gear train and/or the rotation/translation converting transmission. A cover is attached to the end of the housing and, according to the invention, constitutes a bearing plate with a bearing for the motor shaft of the electric motor. The freewheel of the brake according to the invention is also accommodated on or in the cover. This integrated design of the cover of the housing for the electric motor reduces the number of individual components and simultaneously reduces the assembly costs of the brake according to the invention. The positional accuracy of the freewheel in relation to the motor shaft is increased since the bearing for the motor shaft is situated in the cover on which or in which the freewheel is also accommodated. It is possible to maintain a high degree of precision of the axial position of the motor shaft in relation to the freewheel. The high degree of axial precision is important in order to assure a reliable switching of the freewheel and avoid an unintended switching of the freewheel. The invention also assures an exact maintenance of an installation angle of the freewheel. The invention enables a compact embodiment of the brake. 
     The brake according to the invention can be equipped with a self-amplifying device, which converts a friction force exerted by the rotating brake body against the friction brake lining pressed against it during braking into a compressive force that presses the friction brake lining against the brake body in addition to a compressive force exerted by the actuating device, thus increasing the braking force. Examples of possible mechanical self-amplifying devices include wedge or ramp mechanisms or lever mechanisms. Other self-amplifying devices, for example hydraulic ones, are also conceivable. 
     The electromechanical brake according to the invention can be a disc brake, a drum brake, or another brake design. 
     Advantageous embodiments and modifications of the invention disclosed in claim  1  are the subject of the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in greater detail below in conjunction with an exemplary embodiment shown in the drawings, in which: 
         FIG. 1  is a sectional depiction of an electromechanical brake according to the invention; and 
         FIG. 2  is a cross section through a cover of a housing of the brake from  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The brake according to the invention, which is shown in the drawing and labeled as a whole with the reference numeral  1  is a disc brake. It has an electromechanical actuating device  2  equipped with an electric motor  3 , a multi-stage gear train and reduction gear train that will be explained below, and a rack-and-pinion drive or other rotation translation converting transmission. The electric motor  3 , the reduction gear train, and the rotation/translation converting transmission constitute an electromechanical actuating device of the brake  1 . The electric motor  3  has a stator  5  with stator windings  6  and a rotor  7  on a motor shaft  8 . The electric motor  3  is an electronically commutated direct-current motor (brushless BLDC motor), but the invention does not absolutely require it to be. The electric motor  3  is accommodated in a housing  9  into which the stator  5  is press-fitted or fixed in some other way. The motor shaft  8  is supported in the housing  9  in rotary fashion at one end by a movable bearing  10 , i.e. with axial play. In the exemplary embodiment depicted and described here, a roller bearing is used as the movable bearing  10 . 
     At the other end, the housing  9  is closed by a cover  11  that is manufactured, for example, out of steel or a material of comparable strength. The cover  11  constitutes a bearing plate of a fixed bearing  12  of the electric motor  3 . In the exemplary embodiment of the invention depicted and described here, the fixed bearing  12  is embodied in the form of a ball bearing with balls  13  that are secured in rotary fashion in a ball cage  14 . A circumferential groove with a circular cross section that is ground into an axial through opening in the cover  11  constitutes an outer bearing ring  15  of the fixed bearing  12 . An inner bearing ring of the fixed bearing  12  is split in a plane radial to the motor shaft  8 : one half of the inner bearing ring is comprised of a bearing surface  16  with a circular cross section that is ground into an annular step on the motor shaft  8 . A second bearing surface  17 , also with a circular cross section, is embodied on a nut  18  that is screwed onto the motor shaft  8 . The bearing surface  16  of the motor shaft  8  and the bearing surface  17  of the nut  18  combine to form a circumferential groove with a circular cross section and constitute the inner bearing ring  16 ,  17  of the fixed bearing  12 . A bearing play can be adjusted by rotating the nut  18  on the motor shaft  8 ; for example, the nut  18  is secured against rotation on the motor shaft  8  by a screw-locking varnish. 
     In lieu of the above-described bearing construction of the fixed bearing  12 , the rotary support of the motor shaft  8  in the cover  11  constituting the bearing plate can also be embodied in other ways. For example, a roller bearing can be press-fitted onto the motor shaft  8  and inserted into an annular step in the axial hole in the cover  11  and can be secured there with a retaining ring (not shown). 
     A pinion  19  that is rotationally secured to the motor shaft  8  and is manufactured, for example, by means of grinding, meshes with a large gear  20 , which is supported in a rotationally secured fashion on a first transmission shaft  21 . The transmission shaft  21  can be followed by other transmission stages and a brake-applying mechanism for a wheel brake, which mechanism can be actuated in any fashion. 
     The housing  9  in which the electric motor  3  is accommodated is part of a not otherwise shown brake caliper of the brake  1 , which is embodied in the form of a disc brake. The housing  9  can also be attached to the brake caliper. The housing  9  accommodates not only the electric motor  3 , but also the entire actuating device, including the brake-applying mechanism. The brake caliper, of which only a fraction is depicted, namely the housing  9 , is embodied in an intrinsically known fashion as a floating caliper, i.e. it is guided so that it is able to move transversely in relation to a brake disc that is not shown. As a result, when one friction brake pad is pressed against one side of the brake disc, a second friction brake pad situated on the other side of the brake disc in the brake caliper is pressed in an intrinsically known fashion against the other side of the brake disc so that the brake disc is braked on both sides. 
     As is clear from  FIG. 2 , a switchable freewheel  31  is accommodated on or in the cover  11 . The freewheel  31  is embodied in the form of a clamping roller freewheel with rollers  32  serving as the clamping or locking elements. Other designs of the freewheel  31  are also possible. The rollers  32  are situated distributed around the motor shaft  8  of the electric motor  3 . They are accommodated in recesses of a roller cage  33  that is situated in an annular intermediate space between the motor shaft  8  and the cover  11 . Spring elements  34 , which are likewise situated in the recesses of the roller cage  33 , act on the rollers  32  in the circumference direction so that the rollers  32  are lifted away from the motor shaft  8 . The rollers  32  roll in pockets  35  in the axial bore of the cover  11 . In this case, a bottom surface of the pockets  35  constitutes a bearing surface for the rollers  32 . The bottom surfaces of the pockets  35  constituting the bearing surfaces extend in spiral fashion in relation to the motor shaft  8 . Through rotation of the roller cage  33  around the motor shaft  8 , the rollers  32  of the freewheel  31  roll in the pockets  35  and move in spiral fashion toward the motor shaft  8 . If the rollers  32  are resting against the pockets  35  and against the motor shaft  8 , then the spiral course of the pockets causes the rollers  32  to prevent the motor shaft  8  from rotating in one rotation direction. This rotation direction is a releasing direction of the brake  1 . The motor shaft  8  is, however, able to rotate in the applying direction. The above-described rotated position of the roller cage  33  is the engaged, locked position of the freewheel  31  in which the freewheel  31  locks to prevent a rotation of the motor shaft  8  in the releasing direction, but permits an actuation of the brake  1 . 
     If the roller cage  33  is rotated back into its starting position and the spring elements  34  lift the rollers  32  away from the motor shaft  8 , then the freewheel  31  is disengaged and the motor shaft  8  can rotate freely in both rotation directions. 
     In order to rotate the roller cage  33  and therefore to engage the freewheel  31 , the freewheel  31  is equipped with an electromagnet  36 , which has a winding  37  and an armature  38 . A housing  39  of the electromagnet  36  is integrally joined to the cover  11  of the housing  9  of the electric motor  3 . A cover  40  that closes the housing  39  of the electromagnet  36  constitutes a yoke of the electromagnet  36 , which closes the magnetic flux path. The electromagnet  36  switches the freewheel  31  by means of a tappet  41  that is situated tangential to the roller cage  33  of the freewheel  31 . The tappet  41  engages a cam  42  that protrudes radially outward from the roller cage  33 ; the opposite side of this cam is acted on by a spring element  43  in the form of a helical compression spring, which is accommodated in a pocket in the cover  11 , outside of the roller cage  33 , and is supported in the cover  11 . When current is supplied to the coil  37  of the electromagnet  36 , this exerts traction on the armature  38  and, via the tappet  41 , pushes against the cam  42  of the roller cage  33  of the freewheel  31 . This rotates the roller cage  33  into the engaged position as described above. In the engaged position of the freewheel  31 , the brake  1  can be applied further, but cannot be released. If the brake  1  is actuated while the freewheel  31  is engaged, a mechanical stress builds up, which keeps the rollers  32  of the freewheel  31  clamped between the motor shaft  8  and the cover  11  even if the electromagnet  36  is no longer supplied with current. The brake  1  is therefore kept in the actuated position even when it is without current and can thus be used as an auxiliary brake. In order to release the actuated brake  1 , the electric motor  3  actuates it, which releases the mechanical prestressing so that the spring element  43  rotates the roller cage  33  of the freewheel  31  back into the disengaged position. The motor shaft  8  is then able to rotate freely and the brake  1  can be released and used as a service brake. The cover  11 —which is equipped with the pockets  35  for the rollers  32 , cooperates with the rollers  32  and together with the rollers  32 , prevents the motor shaft  8  from rotating in the releasing direction of the brake  1  when the freewheel  31  is engaged—constitutes part of a locking mechanism of the freewheel  31 . 
     The cover  11  of the housing  9  contains all of the electrical lines of both the electric motor  3  and the electromagnet  36 ; the electrical lines are brought together in one or more electrical plugs that are not shown in the drawing. This has the advantage of achieving a simple electrical connection of the electric components of the brake  1  according to the invention. 
     The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.