BRAKE ACTUATOR UNIT AND ELECTROMECHANICAL BRAKE

Abstract

The present disclosure relates to a brake actuator unit for an electromechanical brake and to an electromechanical brake. The brake actuator unit comprises a spindle, a spindle nut, and a spindle bearing, which receives the spindle, has a spherical bearing contact surface and absorbs the axial reaction forces of the spindle when the brake is actuated.

Claims

1. A brake actuator unit for an electromechanical brake, having a spindle, a spindle nut, a brake piston, and a spindle bearing, which receives the spindle, has a spherical bearing contact surface and absorbs the axial reaction forces of the spindle when the brake is actuated.

2. A brake actuator unit according to claim 1, wherein a cup sleeve is provided which has a base and which accommodates the brake piston and the spindle nut in its interior space

3. A brake actuator unit according to claim 2, wherein the spindle bearing is supported on the base of the cup sleeve.

4. A brake actuator unit according to claim 2, wherein the spindle bearing is an axial rolling bearing, via which axial reaction forces of the spindle are absorbed.

5. A brake actuator unit according to claim 4, wherein a bearing disc of the spindle bearing rests against the base of the cup sleeve, which bearing disc is pressed into the cup sleeve in a manner such that it is secured against rotation by frictional engagement.

6. A brake actuator unit according to claim 2 wherein a brake housing is provided, in which the cup sleeve, the spindle nut and the brake piston are accommodated, wherein the cup sleeve has an axial stop, which supports the cup sleeve on the brake housing when the brake is actuated.

7. A brake actuator unit according to claim 6, wherein the stop is a radial shoulder formed on the cup sleeve.

8. A brake actuator unit according to claim 6, wherein the cup sleeve is inserted axially into the brake housing and is supported radially in the brake housing.

9. A brake actuator unit according to claim 2, wherein a rotary lock is provided between the cup sleeve and the spindle nut, which is accommodated therein in a linearly movable manner and allows a linear movement of the spindle nut but prevents a rotation of the spindle nut relative to the cup sleeve.

10. A brake actuator unit according to claim 2, wherein a seal is provided on a brake pad side between the brake piston and the cup sleeve.

11. A brake actuator unit according to claim 6, wherein the brake housing has a brake caliper.

12. A brake actuator unit according to claim 1, wherein the spindle has, on a brake pad side, a cross-sectionally thickened shank section, which has a thread of the spindle on an outer circumferential surface and has a drive shaft extension, which is smaller in cross section than the said shank section, as well as a transitional section between the shank section and the drive shaft extension, wherein the spherical bearing contact surface rests against a complementary contact surface on the transitional section.

13. A brake actuator unit according to claim 1, wherein the spherical bearing contact surface has a first radius of curvature, wherein a complementary contact surface has a second radius of curvature, and wherein the first radius of curvature and the second radius of curvature are different.

14. A brake actuator unit according to claim 13, wherein at least a first center of the first radius of curvature or of the second radius of curvature has a radial offset relative to a rotation axis of the spindle.

15. An electromechanical brake having an electric motor for actuating the brake, which is coupled to the spindle nut in a torque-transmitting manner and having a brake actuator unit according to claim 1.

16. A brake actuator unit according to claim 7, wherein the cup sleeve and comprises a radial groove and wherein a snap ring is arranged in the radial groove.

17. A brake actuator unit according to claim 6, wherein the brake housing has a recess that corresponds at least partially to an outer contour of the cup sleeve.

18. A brake actuator unit according to claim 4, wherein a bearing disc of the spindle bearing rests against the base of the cup sleeve, wherein said bearing disc is pressed into the cup sleeve in a manner such that it is secured against rotation by positive engagement.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0042] The disclosure provides greater detail below with reference to the examples illustrated in the drawings, In the drawings:

[0043] FIG. 1 shows a simplified schematic cross-sectional view of an electromechanical brake according to the disclosure having a brake actuator unit according to the disclosure, and

[0044] FIG. 2 shows a simplified schematic cross-sectional view of the contact surfaces of the spindle bearing and of the spindle.

DETAILED DESCRIPTION

[0045] The following detailed description in conjunction with the appended drawings identical numbers refer to identical elements,

[0046] All of the features disclosed below and/or the accompanying figures can be combined, alone or in any subcombination, with features of the present disclosure provided that the resulting combination of features is worthwhile for a person skilled in the art.

[0047] FIG. 1 shows a simplified schematic cross-sectional view of an electromechanical brake 10 having a brake actuator unit 12.

[0048] The brake 10 comprises a brake housing 14 with a brake caliper 16. The brake caliper 16 surrounds a brake disc 18, in particular a brake disc rotor, which is bordered in the axial direction by two brake pads 20, 22. The inner brake pad 20 along the rotation axis 24 of the brake actuator unit 12 is subjected actively to an application force Fz by the brake actuator unit 12. In the present case (in the ideal case of compensated transverse forces), the rotation axis 24 of the brake actuator unit 12 also corresponds to the cylinder axis of the brake housing 14 and the brake disc axis of rotation of the brake disc 18.

[0049] The axially movable brake caliper 16 ensures that the brake pad 22 which is on the outside in the axial direction is likewise acted upon by the application force Fz. In this case, the application force Fz is distributed substantially uniformly in terms of magnitude between the inner brake pad 20 and the outer brake pad 22. Thus, as a result of the contact pressure force provided, frictional engagement with the brake disc 18 can be ensured for both brake pads 20, 22, said engagement being used to decelerate or hold a vehicle.

[0050] The brake 10 furthermore has an electromechanical actuating unit 26, which is used to produce the application force Fz together with the brake actuator unit 12. Relative to the brake actuator unit 12, the electromechanical actuating unit 26 is arranged opposite the brake disc 18 along the rotation axis 24. The electromechanical actuating unit 26 comprises at least one electric motor 28 and a reduction gear assembly 30.

[0051] The components of the electromechanical actuating unit 26 are accommodated by the brake housing 14, which can be designed as a skeleton-like frame made of metal or of fibre-reinforced plastic. The electromechanical actuating unit 26 forms a dosed subassembly 32 that can be assembled separately.

[0052] The brake actuator unit 12 comprises a spindle 34 with a drive shaft extension 36, a shank section 38 on the brake pad side and a transitional section 40, which is arranged between the drive shaft extension 36 and the shank section 38 along the rotation axis 24 of the spindle 34. The diameter of the drive shaft extension 36 of the brake actuator unit 12 is smaller along the radial direction than the diameter of the shank section 38 along this direction. The spindle 34 tapers correspondingly with respect to its diameter in the region of the transitional section 40.

[0053] The brake actuator unit 12 furthermore has a spindle nut 42. In the present case, the spindle drive 44 of the brake actuator unit 12 is designed as a recirculating ball screw, which is free of self-locking. The spindle drive 44 comprises a thread 46, in which balls 48 are arranged and roll. The spindle 34 and the spindle nut 42 have mutually corresponding race parts, which together form the thread 46. The balls 48 can permit a translational movement of the spindle nut 42 along the rotation axis 24 with respect to the spindle 34 along the ball races 50 of the thread 46. For this purpose, the ball races 50 are formed at least partially in the shank section 38 of the spindle 34 and of the spindle nut 42.

[0054] The diameter of the ball races 50 corresponds to the diameter of the balls 48, taking into account manufacturing tolerances and required gap dimensions.

[0055] Owing to the fact that the spindle nut 42 and the brake piston 52 are separate components, it is possible in the present case to dispense with the need to integrate a ball return mechanism for the balls 48 into the spindle 34. This reduces the manufacturing outlay for the spindle 34.

[0056] As a result of the translational movement of the spindle nut 42 in the direction of the brake disc 18, the brake piston 52 is moved in the direction of the inner brake pad 20 and thus ensures the active application of the application force Fz to the inner brake pad 20.

[0057] Here, the rotation of the spindle 34 is ensured by the electric motor 28, which is in engagement with the drive shaft extension 36 of the spindle 34 via the reduction gear assembly 30. The gradients of the spindle drive 44, in particular of the ball races 50, then have the effect that the rotation of the spindle 34 brings about a translational movement of the spindle nut 42. This movement is transmitted to the brake pads 20, 22 via the brake piston 52. The generated application force Fz is proportional to the torque which is produced at the drive shaft extension 36 by the electric motor 28 and the reduction gear assembly 30.

[0058] The brake actuator unit 12 further comprises a cup sleeve 54, which has a side wall 56 and a base 58. The open end of the cup sleeve 54 is arranged on the brake pad side along the rotation axis 24. This means that the base 58 is arranged at the opposite end of the cup sleeve 54 from the brake disc 18. The base 58 has a through-hole 60 for the drive shaft extension 36 of the spindle 34, which is held therein via a radial bearing 62.

[0059] The cup sleeve 54 is coupled in such a way to the electromechanical actuating unit 26, via a positive connection which is movable along the rotation axis 24, that the reduction gear assembly 30 is centred with respect to the cup sleeve 54. The movable positive connection can comprise, for example, a shaft-hub connection with spline toothing or a slot-and-key connection.

[0060] The side wall 56 and the base 58 define an interior space 64 of the cup sleeve 54, in which at least the spindle 34, the spindle nut 42 and the brake piston 52 are at least partially arranged. Owing to the linear mobility of the spindle nut 42 and of the brake piston 52, these components may also be arranged at least partially outside the interior space 64.

[0061] The cup sleeve 54 makes it possible to design the brake actuator unit 12 as a separate subassembly 66. For the subassembly 66, the brake housing 14 has a corresponding receiving space 68, in which the subassembly 66 can be positioned and is thus supported radially and axially therein.

[0062] Within the brake actuator unit 12, the spindle nut 42 is guided linearly and secured against rotation with respect to the brake housing 14 and the cup sleeve 54 via a rotary lock 70. For this purpose, the cup sleeve 54 can have an axial groove which is in engagement with a projection on the spindle nut 42 which forms the rotary lock 70.

[0063] As a result of the generated application force Fz, a reaction force Fr, which is opposite to the application force Fz, occurs along the rotation axis 24. Owing to the elastic expansion of the components of the brake 10, an angular misalignment can generally occur between the brake disc axis of rotation and the cylinder axis of the brake housing 14, with the result that the reaction force Fr has off-centre force components. These off-centre force components can lead to instability of the components of the brake actuator unit 12 along the radial direction, particularly if the core diameter of the spindle drive 44 is smaller than the outside diameter of a bearing which is intended to absorb the reaction force Fr.

[0064] In the present case, therefore, the brake actuator unit 12 comprises a rotationally symmetrical spindle bearing 72 embodied as an axial bearing with a bearing ring 73 which has a spherical bearing contact surface 74 arranged on the brake pad side. The spindle bearing 72 is in contact with the transitional section 40 of the spindle 34, which has a contact surface 76 complementary to the spherical bearing contact surface 74.

[0065] The bearing ring 73 furthermore has a planar contact surface 78, which is arranged opposite the spherical bearing contact surface 74 along the rotation axis 24.

[0066] Furthermore, the brake actuator unit 12 has rolling elements 80, which are in contact with the planar contact surface 78.

[0067] Arranged between the axial bearing 80 and the base 58 of the cup sleeve 54 there is, in addition, a bearing disc 82, which has opposite planar contact surfaces along the rotation axis 24 and is pressed into the cup sleeve 54 in a rotationally secure manner by frictional and/or positive locking. One of the contact surfaces of the bearing disc 82 is in contact with the base 58 of the cup sleeve 54. The rolling elements 80 roll on the other of the two contact surfaces of the bearing disc 82.

[0068] Thus, the reaction force Fr which occurs is transmitted from the shank section 38 of the spindle 34, via the transitional section 40, to the spherical bearing contact surface 74 of the spindle bearing 72, and from there is absorbed by the base 58 of the cup sleeve 54 via the rolling elements 80 and the bearing disc 82.

[0069] In the region of the end of the cup sleeve 54 on the brake pad side, the said sleeve has a radially formed shoulder 84, which is formed integrally with the side wall 56, acts as a stop 85 and via which the cup sleeve 54 is supported on the brake housing 14. Thus, the reaction force Fr absorbed by the base 58 of the cup sleeve 54 is transmitted to the brake housing 14 via the side wall 56 and the stop 85.

[0070] The shoulder 84 can optionally also be implemented by a snap ring arranged in a radial groove of the side wall 56 of the cup sleeve 54.

[0071] In order, in particular, to protect the spindle drive 44, the cup sleeve 54 furthermore has an inner radial groove in which a seal 86 is arranged and which acts between the cup sleeve 54 and the brake piston 52.

[0072] Since the outside diameter 88 of the spindle bearing 72 is greater than the core diameter of the spindle nut 42, it is possible to dispense with a separate thread run-out for the spindle nut 42 in the region of the shank section 38. This function is implemented by the spindle bearing 72. It is thereby possible to save installation space along the rotation axis 24, that is to say in the axial direction, especially if the ball races 50 of the spindle drive 44 have high thread pitches.

[0073] FIG. 2 shows a simplified schematic cross-sectional view of the contact surfaces 74, 76 of the spindle bearing 72 and of the spindle 34.

[0074] Along its rotation axis 90, the spindle bearing 72 has the spherical bearing contact surface 74 on the brake pad side and, opposite thereto, the planar contact surface 78 for contact with the rolling elements 80.

[0075] The spherical bearing contact surface 74 has a first radius of curvature R1.

[0076] Between the drive shaft extension 36 and the shank section 38 along the rotation axis 24, the spindle 34 has the transitional section 40, which has a contact surface 76 complementary to the spherical bearing contact surface 74.

[0077] The complementary contact surface 76 has a second radius of curvature R2.

[0078] In the ideal case (compensated transverse forces), the rotation axis 90 of the spindle bearing 72 coincides with the rotation axis 24 of the spindle 34.

[0079] At least one of the spherical bearing contact surface 74 and the complementary contact surface 76 is convex, while the other is concave.

[0080] The first radius of curvature R1 and the second radius of curvature R2 may be equal, thereby providing surface contact between the contact surfaces 74, 76.

[0081] However, the first radius of curvature R1 and the second radius of curvature R2 can be different, with the result that, in the case where no force is applied, line contact in the form of a circular line 92 occurs between the contact surfaces 74, 76. The centre of the circular line 92 is congruent with the rotation axis 24 of the spindle 34. As the reaction force Fr increases, elastic flattening of the contact surfaces 74, 76 leads to the line contact expanding to surface contact.

[0082] In order to make the diameter of the circular line 92 as large as possible at half the contact angle 94, the centre 96 of the first radius of curvature R1 and/or the centre 98 of the second radius of curvature R2 can in each case have an offset V2 along the radial direction with respect to the respective rotation axis 90, 24. Such an offset V1. V2 has the effect that the diameter of the circular line 92 is increased and the contact between the contact surfaces 74, 76 is displaced radially outwards. This makes it possible for restoring forces that are greater in terms of magnitude to be generated in the direction of the rotation axes 90, 24. In particular, the enlargement of the contact angle 94 and of the diameter of the circular line 92 leads to a reduction in the contact pressure in the contact zone between the contact surfaces 74, 76. The centring effect of the spherical bearing contact surface 74 of the spindle bearing 72 is thereby improved.