Patent Publication Number: US-2023150471-A1

Title: Vehicle brake actuator and electromechanical brake

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Priority Application No. 102021129963.2, filed Nov. 17, 2021 and German Patent Application No. 102022119397.7, filed Aug. 2, 2022, the disclosure of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to a vehicle brake actuator and an electromechanical brake. 
     BACKGROUND 
     In electromechanical brakes, a brake-application force by which corresponding friction pads are placed in engagement with the brake disc is affected by a brake piston that is driven by an electric motor via a spindle drive. Here, the brake-application force is affected by way of a displaceability of the brake piston. The brake-application force that is provided gives rise to a reaction force in the opposite direction, which reaction force must be accommodated by a force-supporting device of the brake. This means that a brake actuator must be provided which firstly ensures displaceability of the brake piston but secondly can accommodate the reaction force that arises as a result of the brake-application force. In order to ensure these different functionalities, known brake actuators have a multiplicity of individual components that must be separately installed. The production of the brake actuator and of the brake thus involves great outlay. 
     There is therefore a demand to eliminate or at least alleviate the disadvantages of the prior art. 
     SUMMARY 
     According to one aspect, a vehicle brake actuator for an electromechanical brake is provided. The vehicle brake actuator comprises a brake housing, a spindle drive which is arranged in the brake housing and which has a spindle and a spindle nut mounted on the spindle, and a brake piston and a pot sleeve. The brake piston is movable between a retracted and a deployed position in order to apply a brake pad to a brake rotor. The pot sleeve has an interior space in which the brake piston is at least partially guided in axially displaceable fashion. The pot sleeve has a base and is pushed in its longitudinal direction into the brake housing and is mounted radially therein. 
     The spindle drive is configured to ensure linear displaceability of the brake piston relative to the spindle. Due to the spindle drive, the brake piston that acts as spindle nut can be moved in an axial direction. The brake piston can thus exert a brake-application force on at least one brake pad of the brake, such that frictional engagement with a brake disc can be generated. This means that the spindle can be rotated about the axis of rotation, and that this rotation causes a translational movement of the brake piston along the axial direction in order to provide brake-application forces for at least one brake pad. The generated brake-application forces give rise to oppositely oriented reaction forces, which generally have eccentric force components. 
     The vehicle brake actuator configured in this way creates a preassemblable subassembly of the brake, which is self-contained and delimited with respect to other components of the brake. For example, the pot sleeve can also ensure that the vehicle brake actuator can be sealed off with respect to other components of the brake. 
     Additionally, the vehicle brake actuator can, by way of the pot sleeve, be installed as a whole into the brake housing of the brake in a single assembly step. Here, the vehicle brake actuator is installed into the brake housing, and subsequently mounted therein, by simply being pushed in. The outlay on production is thus reduced. 
     Furthermore, owing to a dual functionality of the brake piston, radial structural space is saved in a radial direction relative to the axis of rotation of the spindle. The saving of radial structural space makes it possible to provide a pot sleeve that ensures a self-contained form of the vehicle brake actuator, Furthermore, the saving of radial structural space makes it possible to enlarge the core diameter of a thread of the spindle nut in a radial direction. For example, the core diameter can be enlarged without this causing an enlargement of the structural space required for the brake as a whole along the radial direction. 
     The enlargement of the core diameter has the effect that the force engagement point for eccentric force components of the reaction forces that arise as a result of the brake-application forces are shifted outwards in a radial direction. As a result, the eccentric force components are diminished in terms of their effect. This directly gives rise to a stabilization of the orientation and mounting of the components of the vehicle brake actuator. Altogether, the vehicle brake actuator configured in this way makes possible an improved exertion of force on the brake piston and thus on the brake pad of the brake, and reduced wear. 
     The pot sleeve comprises a side wall adjacent to the base. The brake piston is at least partially received in the interior space of the pot sleeve. The interior space is defined by a free internal volume enclosed by the side wall and the base of the pot sleeve, which internal volume is delimited by the side wall and the base. Since the brake piston is displaceable along the axial direction, it can generally also be only partially arranged in the interior space of the pot sleeve, and may at least partially extend beyond said interior space. 
     In one exemplary arrangement, the base of the pot sleeve is configured to accommodate reaction forces that arise as a result of the brake-application forces. The accommodated reaction forces can then be transmitted onwards from the base of the pot sleeve. 
     The pot sleeve is optionally arranged in a rotationally secured manner in the brake housing of the vehicle brake actuator. For example, positive engagement between the brake housing and the pot sleeve may be provided, which prevents a rotation of the pot sleeve relative to the brake housing. 
     For the rotational securing of the pot sleeve may involve a tongue-and-groove connection or a tangential pin connection. 
     Alternatively or in addition, the pot sleeve may also be radially pressed into the brake housing. Rotational securing of the pot sleeve relative to the brake housing is thus likewise ensured. 
     The pot sleeve and the brake piston are optionally accommodated in the brake housing. The pot sleeve has an axial stop by which it is supported on the brake housing when the brake is actuated, for example when the brake is closed and/or when the brake is opened. In this way, the reaction forces can be transmitted from the base of the pot sleeve via the side wall of the pot sleeve to the brake housing. The entire brake housing thus acts as a force-supporting device with regard to the reaction forces that are to be absorbed. 
     A “closing” is to be understood to mean an actuation of the brake in the case of which the brake-application force is increased at least in certain phases; an “opening” is to be understood to mean an actuation of the brake in the case of which the brake-application force is withdrawn at least in certain phases. Here, an actuation of the brake may comprise successive phases of “closing” and “opening”, for example in the context of anti-lock braking control. 
     The stop is optionally a radial shoulder formed integrally on the pot sleeve or is a fastening arrangement attached to the pot sleeve. 
     In one exemplary arrangement, the radial shoulder may be integral with a side wall of the pot sleeve. 
     In one exemplary arrangement, the fastening arrangement comprises a circlip. The circlip may for example be arranged in a radial groove of the pot sleeve. The circlip may also be of multi-layer form. 
     The spindle is optionally supported axially on the base of the pot sleeve when the brake is actuated. It can thus be ensured that the reaction force is transmitted from the spindle, via the base of the pot sleeve and the side wall thereof, to the brake housing. 
     For example, a spindle bearing with a bearing contact surface is arranged between the base of the pot sleeve and the spindle, which spindle bearing is configured to accommodate radial reaction forces when the brake is actuated. The spindle bearing also makes it possible to compensate eccentric force components of the reaction force. 
     For example, the spindle bearing has rotational symmetry. In this way, the spindle bearing can be of aft-round uniform design with respect to the axis of rotation of the spindle. 
     In one exemplary arrangement, the bearing contact surface of the spindle bearing is of spherical shape. 
     A spherical bearing contact surface is to be understood to mean a bearing surface that has a spherical contour. For example, the spherical bearing contact surface may be of convex or concave shape. A restoring force in the direction of an axis of rotation of the spindle is then effected by the curvature of the spherical bearing contact surface. Here, the spherical contour ensures that the restoring force increases with increasing distance of the force engagement point from the axis of rotation of the spindle. This means that, with suitable selection of the force engagement point, greater restoring forces are effected, which force the spindle into an orientation along the axis of rotation. 
     In one exemplary arrangement, the spindle comprises, at a brake pad side, a shank portion of thickened cross section, which on the outer shell has the mechanism screw of the spindle drive. Furthermore, the spindle has a drive shaft projection of smaller cross section in relation to said shank portion, and has a transition portion between the shank portion and the drive shaft projection. The spindle bearing bears against a contact surface provided by the transition portion. In other words, the radial extent of the spindle varies along the axial direction, specifically such that the spindle has a relatively small radial extent at the end situated opposite the brake pad and has a relatively large radial extent at the end at the brake pad side. Since the transition portion of the spindle is arranged between these portions and constitutes a narrowing of the spindle in terms of the radial extent, the outer surface of the transition portion can advantageously be utilized for contact with the spindle bearing. 
     In one exemplary arrangement, the contact surface of the transition portion of the spindle may be rotationally symmetrical. 
     In one exemplary arrangement, the contact surface of the transition portion of the spindle is of spherical shape and corresponds to the bearing contact surface of the spindle bearing. 
     By virtue of the fact that the contact between the spindle and the spindle bearing is provided in the region of the transition portion of the spindle, the spindle bearing delimits the thickened shank portion in the direction of the drive shaft projection. If the core diameter of the thickened shank portion is smaller than the outer diameter of the spindle bearing, it is ensured by the spindle bearing that a separate thread run-out of the spindle drive in the direction of the transition portion can be avoided. In this way, length advantages along the axial direction can be realized even in the case of large thread pitches of the spindle drive. Furthermore, the outlay on the manufacture of the vehicle brake actuator is reduced. 
     Optionally, the spindle bearing is an axial bearing via which the axial reaction forces of the spindle are accommodated. The axial bearing may comprise an axial rolling bearing. The axial bearing ensures the rotatability of the spindle relative to the pot sleeve without this involving an increased friction moment. 
     The spindle bearing may, on the side situated opposite the spherical bearing contact surface, have a planar contact surface on a bearing ring by way of which said spindle bearing is supported axially on the adjacent rolling elements. In this way, the spindle bearing, with the spherical bearing contact surface and the opposite planar contact surface, ensures the most uniform possible contact between the rolling elements and the bearing ring, because the rotational degrees of freedom transversely with respect to the axis of rotation of the spindle are not eliminated, and therefore microscopic and macroscopic angular offsets, or eccentric applications of force, can be compensated. 
     The spherical bearing contact surface of the spindle bearing and/or the complementary contact surface on the transition portion may be of convex or concave shape, 
     It is advantageous if one of the two contact surfaces, that is to say either the spherical bearing contact surface of the spindle bearing or the complementary contact surface of the transition portion, is of convex shape, whereas the other of the two contact surfaces is of concave shape. 
     Optionally, the spherical bearing contact surface of the spindle bearing has a first curvature radius and the complementary contact surface of the transition portion has a second curvature radius. The first curvature radius and the second curvature radius are advantageously different. This leads to linear contact (on a circular line) between the complementary contact surface and the bearing contact surface, for example in a situation without application of force. If the brake-application force is generated and the reaction forces thus arise, then, proceeding from the linear contact, areal contact between the contact surfaces arises with increasing force owing to elastic flattening of the surfaces. Close contact thus arises between the contact surfaces. It can thus be ensured that the centring action is intensified with increasing force. 
     In one exemplary arrangement, at least a first centre of the first or of the second curvature radius has a radial offset relative to the respective axis of rotation (spindle bearing or spindle). Owing to the radial offset, the circular line that describes the contact between the spherical bearing contact surface and the complementary contact surface of the transition portion is enlarged in terms of its diameter in a radial direction relative to the axis of rotation of the spindle. The contact angle between the contact surfaces is also enlarged. An enlargement of the contact angle and of the diameter of the circular curve reduce the contact pressure in the contact zone. Wear is thus advantageously reduced. 
     It is optionally also possible for both centres of the first and of the second curvature radius to have a radial offset relative to the axis of rotation of the spindle. In this way, the circular line that describes the contact can additionally be adapted as required. 
     In one exemplary arrangement, the spindle bearing, configured as an axial bearing, is supported on the base of the pot sleeve. The pot sleeve is oriented such that the open end is arranged in the direction of the brake disc and of the brake pad, that is to say at the brake pad side, and such that the base of the pot sleeve is arranged oppositely in relation thereto in an axial direction. This means that the brake-application forces that are generated act in an axial direction along the open end of the pot sleeve, whereas the reaction forces that arise as a result act in the direction of the base. By virtue of the fact that the axial bearing is supported on the base, the axial bearing is thus arranged between the base and the spindle along the direction of action of the reaction forces. In this way, the axial bearing can effectively accommodate the reaction forces. 
     In one exemplary arrangement, the base of the pot sleeve has an elevated plateau that extends axially from the base in the direction of the brake rotor. In this way, the spindle bearing can be positioned further into the interior of the brake piston. The axial length of a brake caliper of the brake can thus be shortened. In this way, the structural space required in an axial direction can be reduced. 
     A bearing disc is arranged axially between the base of the pot sleeve and the rolling elements of the spindle bearing, which bearing disc is pressed into the pot sleeve so as to be secured against rotation by frictional engagement and/or positive engagement. The pot sleeve, owing to its geometry, is a more complex component than the bearing disc. By the bearing disc, the base of the pot sleeve can be protected against damage by the axial bearing (if this were in direct contact with the base), which damage could generally be caused in the case of a worn axial bearing and under the action of the reaction forces. Thus, if required, it is merely necessary to exchange the bearing disc or the entire axial bearing, but not necessarily the pot sleeve. 
     In one exemplary arrangement, the bearing disc may have two opposite planar contact surfaces, of which one is in contact with the base of the pot sleeve and one is in contact with the rolling elements. This yields the additional advantage that the outlay on manufacturing in order to ensure the quality of the contact surface of the base of the pot sleeve can be lower. 
     The rolling elements of the axial bearing then roll, at one side, on the planar contact surface of the bearing ring at the brake-pad-side end of the spindle bearing, and, at the other side, on a planar contact surface of the bearing disc, which likewise forms a bearing ring. 
     In order to realize a radially even more compact construction, the brake piston is formed as a spindle nut by virtue of the spindle thread being formed on its inner side. The circumferential wall of the brake piston with the circumferential surface thus transitions integrally into the thread of the spindle in order to simultaneously form the spindle nut. The brake piston may consequently be configured as a single piece. 
     Optionally, a rotational locking arrangement is provided between the pot sleeve and the brake piston that is accommodated in linearly displaceable fashion in said pot sleeve. The rotational locking arrangement ensures the linear displacement of the brake piston by preventing a rotation of the brake piston relative to the pot sleeve. 
     In one exemplary arrangement, the rotational locking arrangement comprises an elongated hole with which a rotational securing element engages. 
     In one exemplary arrangement, at the brake pad side, a seal is provided between the brake piston and the pot sleeve. In this way, the interior space provided by the pot sleeve can be sealed off with respect to other parts of the brake housing. For example, the spindle drive arranged in the interior space of the pot sleeve is thus protected against contamination. 
     Optionally, the brake piston has, at the brake pad side, an end wall that presses against a brake pad when the brake is closed. The end wall may have a circular-ring-shaped end surface. In this way, the force engagement point of the brake-application force that acts on the brake pad is shifted radially outward, allowing an already more uniform application of load to the brake pad. The application of force to the brake pad is thus improved. 
     The brake housing has or forms a brake caliper. 
     Optionally, the thread of the brake piston has a core diameter that is greater than an outer diameter of the spindle bearing. In this way, the force engagement point for the eccentric force components of the reaction force is shifted outwards along the radial direction to such an extent as to be arranged radially outside the spindle bearing. This results in the effect of the eccentric force components being reduced, and these can, overall, be compensated by the spindle bearing. In this way, the orientation and mounting of the components of the vehicle brake actuator are improved, which likewise allows an optimization of the application of force to the brake piston. 
     In order to be implement such a large core diameter of the brake piston, sufficient radial structural space must be provided (without the structural space of the brake as a whole being enlarged), which in the present case is achieved by virtue of the brake piston also combining the functionality of the spindle nut. 
     The spindle drive has a recirculating ball screw. In a recirculating ball screw, balls transmit the force between the spindle and the brake piston, which acts as a spindle nut. Friction and wear are reduced owing to the rolling movement of the balls. 
     A recirculating ball screw has no self-locking action. This means that, owing to elasticities inherent in the system, the brake piston also automatically moves back into the fully retracted position when it is no longer being actively forced into a deployed position by a motor, for example an electric motor. In the fully retracted position of the brake piston, the brake-application force is fully withdrawn, such that the brake is fully “open”. 
     A rotation of the spindle is ensured by an electric motor and a reduction gearing that meshes with the drive shaft projection of the spindle. 
     The pot sleeve in which the spindle is mounted optionally has a positively engaging displaceable connection to the gearing that is utilized for the drive of the spindle. Centring of the gearing of the drive relative to the pot sleeve is thus ensured. 
     In one exemplary arrangement, the positively engaging connection between the pot sleeve and the gearing of the drive has a shaft-hub connection with a spline toothing or a tongue-and-groove connection. 
     In one exemplary arrangement, the pot sleeve together with the brake piston is sealed off with respect to the brake housing of the brake by a dust cap in the form of a corrugated bellows. A sealing function of the dust cap is ensured over an entire axial stroke movement of the screw drive. In this way, it is possible for the spindle drive to be protected against contamination. 
     According to a further aspect, an electromechanical brake is also provided, having an electric motor for actuating the brake, for dosing and/or for opening the brake, which electric motor is coupled in torque-transmitting fashion to the brake piston, and having a vehicle brake actuator as described above. 
     The electromechanical brake may be configured to serve as a vehicle brake with brake pads and a brake disc. 
     According to a further aspect, a vehicle having an electromechanical brake as described above is also provided. 
     Optionally, the vehicle may comprise a motor vehicle, that is to say a road-going vehicle. Alternatively, the vehicle may also comprise other vehicle types, for example aircraft, ships, two-wheeled vehicles, motorcycles, or the like. Overall, in the present case, a vehicle is to be understood to mean an apparatus that is configured for transporting articles, freight or people between different destinations. Examples of vehicles are land-going vehicles such as motor vehicles, electric vehicles, hybrid vehicles or the like, rail vehicles, aircraft, or watercraft. In the present context, vehicles may be regarded as road-bound vehicles, such as cars, trucks, buses or the like. 
     All features discussed with regard to the various aspects may, individually or in (sub-) combination, be combined with other aspects. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The disclosure and further advantageous exemplary arrangements and refinements thereof will be described and discussed in more detail below on the basis of the examples illustrated in the drawings. In the drawings: 
         FIG.  1    shows a simplified schematic cross-sectional view of an electromechanical brake according to the disclosure having a vehicle brake actuator according to the disclosure according to a first exemplary arrangement of the disclosure, 
         FIG.  2    shows a simplified schematic cross-sectional view of an electromechanical brake according to the disclosure having a vehicle brake actuator according to the disclosure according to a further exemplary arrangement, 
         FIG.  3    shows a simplified schematic illustration of the connection between the vehicle brake actuator according to the disclosure and the electromechanical actuating unit according to an exemplary arrangement of the disclosure, 
         FIG.  4    shows a simplified schematic illustration of the connection between the vehicle brake actuator according to the disclosure and the electromechanical actuating unit according to a further exemplary arrangement of the disclosure, 
         FIG.  5    shows a simplified schematic cross-sectional view of the pot sleeve of the vehicle brake actuator according to the disclosure, 
         FIG.  6    shows a simplified schematic illustration of the vehicle brake actuator according to the disclosure according to an exemplary arrangement of the disclosure, 
         FIG.  7    shows a simplified schematic frontal view of parts of the electromechanical brake according to the disclosure, 
         FIG.  8    shows a simplified schematic illustration of the vehicle brake actuator according to the disclosure according to a further exemplary arrangement of the disclosure, 
         FIG.  9    shows a simplified schematic exploded view of a cross section of the pot sleeve and of the brake housing of the vehicle brake actuator according to the disclosure, and 
         FIG.  10    shows a simplified schematic cross-sectional view of the rotational securing arrangement between the pot sleeve and the brake housing of the vehicle brake actuator according to the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description in conjunction with the appended drawings, in which identical elements are denoted by the same reference designations, is intended as a description of different exemplary arrangements of the disclosed subject matter, and is not intended to represent the only arrangements. Each exemplary arrangement described in this disclosure serves merely as an example or for illustration, and is not to be interpreted as being preferred or advantageous in relation to other exemplary arrangements. 
     All features disclosed below with regard to the exemplary arrangements and/or the appended figures may, individually or in any desired sub-combination, be combined with features of the aspects of the present disclosure, including features of preferred exemplary arrangements, assuming that the resulting combination of features is meaningful to a person skilled in the art in the technical field. 
       FIG.  1    shows a simplified schematic cross-sectional view of an electromechanical brake  10  having a vehicle brake actuator  12  according to a first exemplary arrangement. 
     The brake  10  comprises a brake housing  14  with a brake caliper  16  as part of the brake housing  14 . The brake housing  14  may at least partially also be assigned to the vehicle brake actuator  12 . The brake caliper  16  surrounds a brake disc  18 , for example a brake disc rotor, which is enclosed in an axial direction by two brake pads  20 ,  22 . The inner brake pad  20  along the axis of rotation  24  of the vehicle brake actuator  12  is actively subjected to a brake-application force Fz by the vehicle brake actuator  12 . In the present case (in the ideal situation of compensated transverse forces), the axis of rotation  24  of the vehicle brake actuator  12  also corresponds to the cylinder axis of the brake housing  14  and the brake disc axis of rotation of the brake disc  18 . 
     The axially displaceable brake caliper  16  ensures that the outer brake pad  22  in the axial direction is likewise subjected to the brake-application force Fz. Here, the brake-application force Fz is distributed substantially uniformly, in terms of magnitude, between the inner brake pad  20  and the outer brake pad  22 . Thus, for both brake pads  20 ,  22 , owing to the pressing force that is provided, frictional engagement with the brake disc  18  can be ensured, which frictional engagement is utilized for the deceleration or immobilization of a vehicle. 
     The brake  10  furthermore has an electromechanical actuating unit  26  that is utilized, together with the vehicle brake actuator  12 , to generate the brake-application force Fz. Relative to the vehicle brake actuator  12 , the electromechanical actuating unit  26  is arranged on the opposite side in relation to the brake disc  18  along the axis of rotation  24 . The electromechanical actuating unit  26  comprises at least one electric motor  28  and one reduction gearing  30 . 
     The components of the electromechanical actuating unit  26  are accommodated by the brake housing  14 , which may be configured as a skeleton-like frame composed of metal or of fibre-reinforced plastic. The electromechanical actuating unit  26  forms a closed, separately installable subassembly  32 . 
     The vehicle brake actuator  12  comprises a spindle  34  with a drive shaft projection  36 , with a second shank portion  38  at a brake pad side, and with a transition portion  40  that is arranged between the drive shaft projection  36  and the shank portion  38  along the axis of rotation  24  of the spindle  34 . The diameter of the drive shaft projection  36  of the vehicle brake actuator  12  along the radial direction is smaller than the diameter of the shank portion  38  along this direction. Correspondingly, the spindle  34  narrows in terms of its diameter in the region of the transition portion  40 . 
     The vehicle brake actuator  12  furthermore has a brake piston  42  that is configured as a spindle nut. The spindle drive  44  of the vehicle brake actuator  12  is in the present case configured as a recirculating ball screw that has no self-locking action. Here, the spindle drive  44  comprises a mechanism screw  46  in which balls  48  are arranged and roll. The spindle  34  and the brake piston  42  have mutually corresponding raceway parts. The balls  48  can, along the ball raceways  50  of the mechanism screw  46 , allow a translational movement of the brake piston  42  relative to the spindle  34  along the axis of rotation  24 . For this purpose, the ball raceways  50  are formed at least partially in the shank portion  38  of the spindle  34  and in the brake piston  42 . 
     The diameter of the ball raceways  50  corresponds, taking into consideration manufacturing tolerances and required gap dimensions, to the diameter of the balls  48 . 
     The translational movement of the brake piston  42  in the direction of the brake disc  18  causes the brake piston  42  to be moved in the direction of the inner brake pad  20  and thus ensures that the brake-application force Fz is actively applied to the inner brake pad  20 . 
     The vehicle brake actuator  12  furthermore comprises a pot sleeve  54  that has a side wall  56  and a base  58 . The open end of the pot sleeve  54  is arranged at a brake pad side along the axis of rotation  24 . This means that the base  58  is provided at the opposite end of the pot sleeve  54  in relation to the brake disc  18 . The base  58  has a passage hole  60  for the drive shaft projection  36  of the spindle  34 , which is held in said passage hole by a radial bearing  62 . 
     The side wall  56  and the base  58  define an interior space  64  of the pot sleeve  54 , in which at least the spindle  34  and the brake piston  42  are at least partially arranged. Owing to the linear displaceability of the brake piston  42 , this can also be arranged at least partially outside the interior space  64 . 
     The pot sleeve  54  makes it possible for the vehicle brake actuator  12  to be configured as a separate subassembly  66 . The brake housing  14  has, for the subassembly  66 , a corresponding receiving space  68  in which the subassembly  66  can be positioned and thus mounted radially and axially therein. 
     Within the vehicle brake actuator  12 , the brake piston  42  is guided linearly, and secured against rotation, relative to the brake housing  14  and the pot sleeve  54  by a rotational locking arrangement  70 . For this purpose, the brake piston  42  may have an axial groove that engages with a rotational securing element. 
     Here, the rotation of the spindle  34  is ensured by the electric motor  28 , which engages with the drive shaft projection  36  of the spindle  34  via the reduction gearing  30 . The rotation of the spindle  34  in conjunction with the rotational blocking of the brake piston  42  ensures a translational movement of the brake piston  42 . This movement is transmitted to the brake pads  20 ,  22 . The brake-application force Fz that is generated is proportional to the torque that is imparted to the drive shaft projection  36  by the electric motor  28  and the reduction gearing  30 . 
     Owing to the brake-application force Fz that is generated, a reaction force Fr that is opposed to the brake-application force Fz arises along the axis of rotation  24 . Owing to the elastic expansion of the components of the brake  10 , an angular offset may generally arise between the brake disc axis of rotation and the cylinder axis of the brake housing  14 , such that the reaction force Fr has eccentric force components, These eccentric force components can lead to an instability of the components of the vehicle brake actuator  12  along the radial direction, if the core diameter DK of the thread of the brake piston  42  is smaller than the outer diameter DL of a bearing that is intended to accommodate the reaction force Fr. 
     Thus, the elimination of an otherwise conventional separate spindle nut, by virtue of the fact that the brake piston  42  assumes the function of said spindle nut, has the effect that the brake piston  42  can be enlarged in a radial direction. In this way, despite an unchanged radial structural space of the brake  10 , it is made possible to enlarge the core diameter DK. 
     In one exemplary arrangement, the core diameter DK can be radially enlarged so as to be greater than the outer diameter DL of a spindle bearing  72  of the vehicle brake actuator  12  in a radial direction, which spindle bearing accommodates the reaction force Fr. It is thus made possible for the force engagement point of the eccentric force components of the reaction force Fr to be shifted radially outwards to such an extent that the effect of the eccentric force components is diminished, and the compensation by the spindle bearing  72  is ensured even without special bearing geometries of the spindle bearing  72 . Thus, the orientation and mounting of the individual components of the vehicle brake actuator  12 , and the application of force to the brake pads  20 ,  22 , are improved. 
     In the present case, the spindle bearing  72  is of rotationally symmetrical design, and is configured as an axial bearing. 
     In the present case, the spindle bearing  72  has, on a bearing ring  73 , a bearing contact surface  74  which faces towards the transition portion  40  and which is in contact with a complementary contact surface  76  provided by the transition portion  40  of the spindle  34 . The bearing contact surface  74  and the contact surface  76  may be planar. For example, the bearing contact surface  74  and the contact surface  76  may extend perpendicular to the axis of rotation  24  (not shown here). 
     In order to further improve the compensation of the eccentric force components of the reaction force Fr, the bearing contact surface  74  of the spindle bearing  72  and the contact surface  76  of the transition portion  40  are of spherical shape in the present exemplary arrangement. 
     In this exemplary arrangement, one of the two contact surfaces of this contact, that is to say either the spherical bearing contact surface  74  of the spindle bearing  72  or the complementary contact surface  76  of the transition portion  40 , is of concave shape, whereas the other is of convex shape. 
     In one exemplary arrangement, the contact surfaces  74 ,  76  have different curvature radii, whereby, in the situation without application of force, linear contact in the form of a circular line between the bearing ring of the spindle bearing  72  and the transition portion  40  of the spindle  34  is ensured. The centre of the circular line is congruent with the axis of rotation  24  of the spindle  34 . With increasing reaction force Fr, elastic flattening of the contact surfaces  74 ,  76  has the effect that the linear contact widens to become areal contact. 
     In order for the diameter of the circular line at the midpoint of the contact angle to be made as large as possible, the centre of the curvature radius of the spherical bearing contact surface  74  and/or the centre of the curvature radius of the complementary contact surface  76  may each have an offset, along the radial direction, with respect to the respective axis of rotation of the spindle bearing  72  or of the spindle  34 . Such an offset has the effect that the diameter of the circular line is enlarged, and the contact between the contact surfaces  74 ,  76  is shifted outwards in a radial direction. It is thus made possible for restoring forces of greater magnitude in the direction of the axis of rotation  24  of the spindle  34  to be generated. For example, the enlargement of the contact angle and of the diameter of the circular line has the effect that the contact pressure in the contact zone between the contact surfaces  74 ,  76  is reduced. The centring action of the spherical bearing contact surface  74  of the bearing ring  73  of the spindle bearing  72  is thus improved. 
     The spindle bearing  72  furthermore has a planar contact surface  78 , which is arranged oppositely in relation to the bearing contact surface  74  along the axis of rotation  24 . 
       FIG.  1    illustrates rolling elements  80  of the spindle bearing  72 , which rolling elements roll, at a motor side, on a bearing disc  82  which has planar contact surfaces situated oppositely along the axis of rotation  24  and which is pressed into the pot sleeve  54  so as to be secured against rotation by frictional engagement and/or positive engagement. One of the contact surfaces of the bearing disc  82  is in contact with the base  58  of the pot sleeve  54 . 
     Thus, the reaction force Fr that arises is, from the shank portion  38  of the spindle  34 , accommodated by the base  58  of the pot sleeve  54  via the spindle bearing  72 . 
     In the region of the brake-pad-side end of the pot sleeve  54 , this has, in the present exemplary arrangement, a radially integrally formed shoulder  83  which is formed integrally with the side wall  56  and which provides a stop  84  and by means of which the pot sleeve  54  is supported on the brake housing  14 . Thus, the reaction force Fr that is accommodated by the base  58  of the pot sleeve  54  is transmitted via the side wall  56  and the stop  84  to the brake housing  14 . 
     In order to protect the spindle drive  44 , the pot sleeve  54  has a radially internally situated groove in which a seal  86  is arranged and which acts between the pot sleeve  54  and the brake piston  42 . 
     The pot sleeve  54  and the brake piston  42  each additionally have a radially externally situated groove in which an additional seal  88  in the form of an encircling corrugated bellows is arranged. In this way, the subassembly  66  of the vehicle brake actuator  12  is sealed off with respect to other parts of the brake  10 . The seal  88  is configured to ensure the sealing action over the entire movement travel (stroke) of the brake piston  42 . 
     In the present case, at the brake pad side, the brake piston  42  comprises an end wall  90  with an end surface of circular-ring-shaped form, which is provided for the application of force to the inner friction pad  20 . The circular ring shape ensures an optimized force distribution of the brake-application force Fz over the receiving surface  92  of the inner friction pad  20 . 
     The spindle drive  44  comprises ball return guides  94  that are integrated within the spindle  34 . 
     In a pre-assembly step, both the mechanism screws  46  of the spindle  34  and the ball return guides  94  integrated in the spindle  34  can be fully filled with balls  48 . The brake piston  42  can subsequently be pushed onto the spindle  34 . 
     By the ball return guides  94 , which are integrated in the spindle  34 , of the spindle drive  44 , it is also ensured that, whilst providing the same stroke, the spindle drive  44  can be configured to be axially shorter than in the case of known and spindle drives without integrated ball return guides. The reason for this is the possibility for the spindle bearing  72 , on which the spindle drive  44  is supported at the open end of the brake piston  42 , to be able to project a certain distance into the brake piston  42  when the latter is in the retracted state, without the overlap of the balls  48  being eliminated. 
     In the present case, the pot sleeve  54  furthermore has an elevated plateau  96  which extends axially in the direction of the brake-pad-side end of the pot sleeve  54  proceeding from the base  58  of the pot sleeve  54 . By the elevated plateau  96 , it is made possible for the spindle bearing  72  and the bearing disc  82  to be positioned axially closer to the brake-pad-side end of the pot sleeve  54 . The axial length of the brake caliper  16  of the brake  10  can thus be shortened. In this way, the structural space required in an axial direction can be reduced. 
       FIG.  2    shows a simplified schematic cross-sectional view of an electromechanical brake  10  having a vehicle brake actuator  12  according to a further exemplary arrangement. The exemplary arrangement shown here substantially corresponds to the preceding exemplary arrangement. Therefore, only the differences will be discussed. 
     In this exemplary arrangement, the pot sleeve  54  of the vehicle brake actuator  12  comprises, instead of a radially integrally formed shoulder  83 , a radially externally situated groove  98  in which a fastening  100  is arranged, which provides the stop  84  with respect to the brake housing  14 . In the present case, the fastening  100  is a circlip. 
     This exemplary arrangement provides the additional advantage that the pot sleeve  54  can generally be pushed axially into the brake housing  14  from both sides. In this way, the installation of the pot sleeve  54  is simplified. 
     Furthermore, the pot sleeve  54  in this exemplary arrangement does not have an elevated plateau  96 . The base  58  of the pot sleeve  54  substantially has an axial extent that remains uniform with increasing radial distance to the axis of rotation  24  of the spindle  34 . As a result, the pot sleeve  54  has a simpler geometry, whereby the outlay on production is reduced. 
       FIG.  3    shows a simplified schematic illustration of the connection between the vehicle brake actuator  12  and the electromechanical actuating unit  26  according to an exemplary arrangement. 
     By a positively engaging connection  102  that is displaceable along the axis of rotation  24 , the pot sleeve  54  is coupled to the electromechanical actuating unit  26  such that the reduction gearing  30  is centred relative to the pot sleeve  54 . In this exemplary arrangement, the displaceable positively engaging connection  102  comprises a shaft-hub connection  104  with a spline toothing  106  for transmitting torque. 
       FIG.  4    shows a simplified schematic illustration of the connection between the vehicle brake actuator  12  and the electromechanical actuating unit  26  according to a further exemplary arrangement. The exemplary arrangement shown here substantially corresponds to the preceding exemplary arrangement. Therefore, only the differences will be discussed. 
     As an alternative to the shaft-hub connection  104 , the pot sleeve  54  in this embodiment has a tongue-and-groove connection  108 . The tongue, in this case in the form of a bolt, is in this case pressed into an associated bore that is formed into the base-side end surface of the pot sleeve  54 . 
       FIG.  5    shows a simplified schematic cross-sectional view of the pot sleeve  54 . 
     The figure shows the passage hole  60  in the base  58  of the pot sleeve  54 , which passage hole is provided for the drive shaft projection  36 . Proceeding from the base  58 , the elevated plateau  96  extends in the direction of the brake-pad-side end of the pot sleeve  54 . Furthermore, the pot sleeve  54  according to this exemplary arrangement has a radially integrally formed shoulder  83 . 
     The rotational locking arrangement  70 , which acts between the pot sleeve  54  and the brake piston  42 , comprises an elongated hole  110  into which a rotational securing element engages. 
       FIG.  6    shows a simplified schematic illustration of the vehicle brake actuator  12  according to an exemplary arrangement. 
     The figure shows that a sliding block  112  is provided, which is positioned in the elongated hole  110  of the rotational locking arrangement  70  and allows linear displaceability of the brake piston  42  with respect to the pot sleeve  54 , but which prevents a rotation of the brake piston  42  relative to the pot sleeve  54 . 
     The end stops  114 ,  116  of the elongated hole  110  for the sliding block  112  define the stroke of the maximum possible movement travel of the brake piston  42  (without brake pads). 
       FIG.  7    shows a simplified schematic frontal view of parts of the electromechanical brake  10 . 
     The brake housing  14  and the pot sleeve  54  are shown. The pot sleeve  54  is rotationally secured relative to the brake housing  14 . The rotational securing means  118  involves positive engagement, which is implemented in the present case by way of a tangential pin connection  120 . By virtue of the fact that the pot sleeve  54  is rotationally secured relative to the brake housing  14 , the brake piston  42  is rotationally secured relative to the brake housing  14  indirectly via the rotational locking arrangement  70 . It is thus ensured that the brake piston  42  does not rotate relative to the brake pad  20 , whereby an optimized application of force to the brake pad  20  is ensured. 
       FIG.  8    shows a simplified schematic illustration of the vehicle brake actuator  12  according to a further exemplary arrangement. 
     The pot sleeve  54  has, in turn, a groove  98  in which a fastening arrangement  100  can be arranged in order to provide the stop  84  for the coupling to the brake housing  14 . 
     It can also be seen that the spline toothing  106  is variable with regard to the number of splines. 
       FIG.  9    shows a simplified schematic exploded view of a cross section of the pot sleeve  54  and of the brake housing  14 . 
     It can be seen that the brake housing  14  has a receiving space  68  which corresponds to the pot sleeve  54  and which is provided by way of an at least partially circular cylindrical inner contour  122 . The pot sleeve  54  can this be pushed in an axial direction, with an oversize, into the receiving space  68  of the brake housing  14 . The pot sleeve  54  is subsequently radially mounted in the receiving space  68 . 
     If the pot sleeve  54  does not have a radially integrally formed shoulder  83  but instead has a radially externally situated groove  98  for a fastening arrangement  100 , then the pot sleeve  54  can be pushed into the receiving space  68  in axially opposite directions. The installation of the pot sleeve  54 , and of the subassembly  66  of the vehicle brake actuator  12  as a whole, is thus simplified. 
     Alternatively, the pot sleeve  54  may also be radially pressed into the receiving space  68 . By way of a pressing-in operation, rotational securing  118  of the pot sleeve  54  relative to the brake housing  14  can be ensured even without a tangential pin connection  120 . 
     In this exemplary arrangement, the rotational securing  118  of the pot sleeve  54  relative to the brake housing  14  is however ensured by positive engagement by a tongue-and-groove connection  124 . This is illustrated in  FIG.  10    by way of a simplified schematic cross-sectional view of the rotational securing means  118  between the pot sleeve  54  and the brake housing  14 .