Electromechanical drum brake

Abstract

The invention relates to an electromechanical drum brake (10) for a motor vehicle. The electromechanical drum brake (10) comprises a drum (14) in which brake shoes (18) are arranged, wherein a threaded drive unit (30) driven by an electric motor (22) is arranged between the brake shoes (18) to spread them, converting the rotary motion of the electric motor (22) into a translational motion. The threaded drive unit (30) is arranged in a housing (46) such that it is displaceable in an axial direction relative to the housing (46).

Description

[0001] The present invention relates to an electromechanical drum brake for a motor vehicle. Furthermore, the invention relates to a motor vehicle having such an electromechanical drum brake. State of the art

[0002] Drum brakes with various actuation types are common in modern vehicles. Drum brakes are typically hydraulically actuated. Hydraulic pressure is built up in a double piston, which then expands, exerting a force on each brake shoe. The brake shoes are often only roughly positioned by a support bearing and return springs and can find their own position within the drum depending on tolerances and wear.

[0003] EP 1 095 834 B1 discloses, among other things, a drum brake for a motor vehicle. The drum brake has a drum in which two brake shoes are arranged, to which a brake lining is applied on the outside. Two levers are arranged between the brake shoes, by means of which the brake shoes can be pressed apart. At one end of the levers, these are connected to the brake shoes via a pin, whereas at the opposite end of the levers, an actuator is arranged, which is driven by an electric motor. The actuator comprises a reduction gear, which reduces the speed, and a ball screw drive.

[0004] The object underlying the invention is to provide an electromechanical drum brake which has an improved braking effect and which requires less construction effort.

[0005] The object is achieved by an electromechanical drum brake having the subject matter of patent claim 1. Preferred embodiments can be found in the dependent claims. Disclosure of the invention

[0006] The invention specifies an electromechanical drum brake for a motor vehicle. The electromechanical drum brake comprises a drum in which brake shoes are arranged. A screw drive unit driven by an electric motor is arranged between the brake shoes to spread the brake shoes. This screw drive unit converts the rotational movement of the electric motor into a translational movement. The electromechanical drum brake accordingly further comprises the electric motor and the screw drive unit. The screw drive unit is arranged in a housing such that it is displaceable relative to the housing in an axial direction of the screw drive unit.

[0007] The screw drive unit is preferably arranged at an upper end of the brake shoes. A force is applied to the brake shoes via the screw drive unit, allowing them to be spread apart. While the housing is fixed to the drum in the axial direction of the screw drive unit, the screw drive unit is movable relative to the drum in the axial direction. This means that the screw drive unit can move between the brake shoes. In response to a counterforce acting on the screw drive unit from the brake shoes, the screw drive unit is moved axially in such a way that a force balance is created between the brake shoes, allowing them to better develop their self-reinforcing properties. The brake shoes can therefore find their optimal position in the drum, allowing any tolerances in the drum and the positioning of the drum relative to the support bearing and actuator to be compensated for.This improves the braking effect of the drum brake and reduces braking torque fluctuations.

[0008] The screw drive unit can be designed in such a way that the adjustment travel of the screw drive unit also compensates for wear. This eliminates the need for separate wear adjustment. This reduces design effort and the associated manufacturing costs. Due to the axial mobility of the screw drive unit, only low axial forces are transferred to the drum. This further reduces design effort.

[0009] In a preferred embodiment of the invention, the housing is designed as a cylindrical sleeve. The cylindrical sleeve holds the screw drive unit in the radial direction of the screw drive unit. The two open sides of the cylindrical sleeve ensure that axial movement of the screw drive unit is not blocked. A cylindrical sleeve thus provides a simple housing in which the screw drive unit can move axially relative to the housing.

[0010] In a further preferred embodiment of the invention, the screw drive unit is a ball screw drive unit. A ball screw drive unit is a screw drive unit in which balls are arranged between the threads. Such a screw drive unit reduces friction between the spindle nut and spindle, so that less drive torque is required to rotate the spindle nut or spindle. The electric motor can therefore be made smaller. This reduces the unsprung mass on the wheel and improves ride comfort.

[0011] Preferably, an anti-rotation device for a spindle of the screw drive unit is formed via the brake shoe. In a screw drive unit, the spindle or spindle nut is typically secured against rotation. A anti-rotation device is provided for this purpose. By providing the anti-rotation device via the brake shoe to which the spindle is connected, a separate anti-rotation device is no longer necessary. This simplifies the design of the screw drive unit.

[0012] In an advantageous further development, the anti-rotation device is formed by a tongue-and-groove connection that runs in the direction of the longitudinal extension of the brake shoes, so that the brake shoes are movable along the longitudinal extension in the tongue-and-groove connection. The position of the brake shoe is not fixed. The brake shoe can therefore move in a groove direction. Such an anti-rotation device ensures that the brake shoe can be displaced. This also allows for a wear-related change in the position of the brake shoes during operation.

[0013] Advantageously, the screw drive unit is designed to be non-restrictive. A non-restrictive screw drive unit is one that automatically reverses when a force is applied to it. In the event of a failure, the brake can therefore automatically re-open after a braking maneuver, even if the electric motor is de-energized. This makes such a drum brake suitable for use as a service brake.

[0014] In a further advantageous embodiment, a housing toothing is arranged on the housing, via which the housing and the spindle nut can be driven. The housing toothing is either arranged as a separate part on the housing or can be formed by the housing itself. Thanks to the housing toothing, the housing can be used directly to drive the spindle nut. This means that the housing fulfills the function of both radially holding and driving the screw drive unit. Advantageously, the housing toothing is spur toothed. Spur toothing has the advantage of being simpler and therefore more economical to design and is quieter in operation.

[0015] According to a practical embodiment, the housing and the spindle nut have anti-rotation devices that prevent rotation of the spindle nut relative to the housing. The anti-rotation device ensures that the spindle nut rotates when the housing is driven.

[0016] This eliminates the need for separate components to provide anti-rotation protection between the housing and the spindle nut. This reduces the number of parts and manufacturing costs.

[0017] According to a further expedient embodiment, the anti-rotation device between the housing and the spindle nut is formed by a toothing extending in the axial direction, which enables axial movement of the spindle nut relative to the housing. The toothing is aligned such that the teeth of the toothing extend in the axial direction. Such a toothing easily forms an anti-rotation device, which also enables axial movement of the spindle nut relative to the housing. This allows the spindle nut to be driven via the housing despite its axial mobility.

[0018] Preferably, an axial bearing is arranged between the spindle nut and one of the brake shoes. The axial bearing can be used to decouple any rotation of the spindle nut from the brake shoe. Such an axial bearing thus provides a simple means for decoupling this movement.

[0019] The invention also provides a motor vehicle having the electromechanical drum brake according to the invention. Such a motor vehicle has the advantages and properties described above.

[0020] Embodiments of the invention are illustrated in the drawing and explained in more detail in the following description. It shows: Fig. 1 Electromechanical drum brake according to an embodiment of the invention, Fig. 2 Sectional view of an adjusting device with a screw drive unit according to an embodiment of the invention in a rest position, Fig. 3 Adjustment device according to Fig. 2 in a braking position of the drum brake, and Fig. 4 Perspective view of an embodiment of the electric motor and a gear unit.

[0021] In Fig. 1 shows an electromechanical drum brake 10 according to an embodiment of the invention. The electromechanical drum brake 10 has a drum 14 in which two brake shoes 18 are arranged opposite one another. An adjusting device 26 driven by an electric motor 22 is provided in the region of an upper end of the brake shoes 18. The brake shoes 18 can be spread apart via this adjusting device 26, so that a braking force can be applied.

[0022] Fig. 2 shows a sectional view of an adjusting device 26 with a screw drive unit 30 according to an embodiment of the invention in a rest position. The rest position is a position in which the brake shoes 18 are not spread and thus no braking force is applied. The adjusting device 26 has an adjusting device housing 34 in which the screw drive unit 30 is arranged. The screw drive unit 30 comprises a spindle nut 38 which surrounds a spindle 42. The spindle nut 38 is surrounded by a housing 46, via which the screw drive unit 30 is mounted to the adjusting device housing 34 via bearings 50. The housing 46 is designed as a cylindrical sleeve which has a housing toothing 58 on an outer peripheral surface 54 in a central region.

[0023] Contact pieces 62 for connection to the brake shoes 18 are arranged at both axial ends of the screw drive unit 30. The contact pieces 62 form a groove 66 extending in the longitudinal extent of the brake shoes 18, in which groove 66 a spring-shaped end (not shown) of the brake shoe 18 can be received. The groove 66, together with the spring of the brake shoe 18, forms an anti-rotation device for the spindle 42. The groove 66 also enables movement of the brake shoe 18. An axial bearing 70 is arranged between the spindle nut 38 and the contact piece 62, so that rotation of the spindle nut 38 is decoupled from the contact piece 62.

[0024] Fig. 3 shows the adjustment device 26 according to Fig. 2 in a braking position of the drum brake 10. In this position, the spindle 42 is moved out of the spindle nut 38. Accordingly, the two contact pieces 62 are further apart than in Fig. 2. The brake shoes 18 are thus spread to apply a braking force. In the figure, it can also be seen that the spindle nut 38 is axially displaced relative to the housing 46. The spindle nut 38 is thus held in the housing 46 so as to be movable in the axial direction. The housing 46 has an internal toothing 74 on an inner circumference, which engages with a corresponding spindle nut toothing 78 (see Fig. 4) engages the spindle nut 38, so that a rotational movement of the housing 46 can be transmitted to the spindle nut 38. The mobility of the screw drive unit 30 in the housing 46 creates a force balance between the brake shoes 18. The braking performance of the drum brake 10 is thereby improved.

[0025] In Fig.Figure 4 shows a perspective view of an embodiment of the electric motor 22 and a gear unit 82 of the electromechanical drum brake 10. This view shows the contact piece 62 at the axial end of the screw drive unit 30, which has the groove 66 for connection to the brake shoe 18. The electric motor 22 drives a gear 86, which interacts with the housing toothing 58 via an intermediate gear 90. As a result, the housing 46 and thus the spindle nut 38 can be driven via the electric motor 22. This figure also shows how the internal toothing 74 interacts with the spindle nut toothing 78. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 1 095 834 B1

[0003]

Claims

[1] Electromechanical drum brake (10) for a motor vehicle, comprising a drum (14) in which brake shoes (18) are arranged, wherein for spreading the brake shoes (18) between the brake shoes (18) a screw drive unit (30) driven by an electric motor (22) is arranged, which converts the rotary movement of the electric motor (22) into a translatory movement, characterized by that the screw drive unit (30) is arranged in a housing (46) in such a way that it is displaceable in an axial direction of the screw drive unit (30) relative to the housing (46). [2] Electromechanical drum brake (10) according to claim 1, characterized by that the housing (46) is designed as a cylindrical sleeve. [3] Electromechanical drum brake (10) according to claim 1 or 2, characterized by that the screw drive unit (30) is a ball screw drive unit. [4] Electromechanical drum brake (10) according to one of the preceding claims, characterized by that an anti-twist device (66) for a spindle (42) of the screw drive unit (30) is formed via the brake shoe (18). [5] Electromechanical drum brake (10) according to claim 4, characterized by that the anti-twist device (66) is formed by a tongue and groove connection which runs in the direction of a longitudinal extension of the brake shoes (18), so that the brake shoes (18) are movable along the longitudinal extension in the tongue and groove connection. [6] Electromechanical drum brake (10) according to one of the preceding claims, characterized by that the screw drive unit (30) is designed to be free of inhibition. [7] Electromechanical drum brake (10) according to one of the preceding claims, characterized by that a housing toothing (58) is arranged on the housing, via which the housing (46) and the spindle nut (38) can be driven. [8] Electromechanical drum brake (10) according to one of the preceding claims, characterized by that the housing (46) and the spindle nut (38) have anti-rotation means (74, 78) which block a relative rotation of the spindle nut (38) to the housing (46). [9] Electromechanical drum brake (10) according to claim 8, characterized by that the anti-rotation means (74, 78) between the housing (46) and the spindle nut (38) is formed by a toothing extending in the axial direction, which enables an axial movement of the spindle nut (38) relative to the housing (46). [10] Electromechanical drum brake (10) according to one of the preceding claims, characterized by that an axial bearing (70) is arranged between the spindle nut (38) and one of the brake shoes (18). [11] Motor vehicle comprising an electromechanical drum brake (10) according to one of the preceding claims.

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