Brake actuator for an electromechanical wheel brake and electromechanical wheel brake for a vehicle

Abstract

The invention relates to a brake actuator (1) for an electromechanical wheel brake (10) and to a wheel brake for a vehicle having such a brake actuator. The brake actuator is equipped with a servomotor device (2) for moving a brake pad (11) relative to a friction partner (12); and a return spring device (3) for returning the brake pad (11), wherein the return spring device (3) is mechanically operatively connected to the servomotor device (2).

Description

[0001] The present invention relates to a brake actuator for an electromechanical wheel brake and to an electromechanical wheel brake for a vehicle having such a brake actuator. State of the art

[0002] Drum brakes with various actuation types are common in modern vehicles. Drum brakes in passenger cars are typically hydraulically actuated, while pneumatic actuation is typical in trucks. Electromechanical actuators are also increasingly gaining attention. In passenger cars, it is mandatory that the brake generates a minimum braking torque by retracting the disc / drum brake pads when de-energized. Due to friction in the brake system, return springs are typically used for this requirement in drum brakes. These are usually mounted directly on the brake shoes.

[0003] For example, DE 10 2021 203 003 A1 describes an electromechanical actuating unit for a motor vehicle brake, in particular a drum brake.

[0004] A disadvantage of such known automotive brakes, however, is that the return of the brake actuator is negatively affected by friction and detent points, and the resulting self-locking effect. Self-locking can be divided into functional and intrinsic self-locking.

[0005] Even if individual gear stages and transmission points in the power flow are not self-locking in themselves, functional self-locking can still occur through the transmission of the individual frictional torques. The magnitude of the frictional torque and the level of the effective transmission ratio are particularly important here. Relevant frictional torques are usually present in electric motors in particular. Permanent magnet synchronous machines (PMSMs) are often used due to their otherwise favorable properties, for example due to power-to-weight ratio or cost. The permanent magnets create a cogging torque that counteracts the return movement. Relevant frictional torques also occur in gear stages with poor efficiency. Some gear types, such as worm gears, have poor efficiency due to a high sliding component.

[0006] Some gear designs, such as screw drives, have a direction-dependent efficiency and can exhibit intrinsic, self-locking properties in one drive direction. The efficiency in the self-locking direction is then zero. Disclosure of the invention

[0007] The invention provides a brake actuator for an electromechanical wheel brake having the features of claim 1 and an electromechanical wheel brake for a vehicle having the features of claim 10.

[0008] According to a first aspect of the invention, a brake actuator for an electromechanical or electromechanically actuated wheel brake is provided. The brake actuator comprises a servomotor device for moving a brake pad relative to a friction partner and a return spring device for returning the brake pad, wherein the return spring device is mechanically operatively connected to the servomotor device.

[0009] According to a second aspect of the invention, an electromechanical wheel brake for a vehicle is provided. The electromechanical wheel brake comprises a brake actuator according to the first aspect of the invention and a brake pad movable by the brake actuator.

[0010] One idea underlying the present invention is to relocate the return spring device from outside the brake actuator to inside the brake actuator. The return spring arranged outside the brake actuator, as previously customary, can either be omitted or made significantly weaker. The return spring device according to the invention can be arranged at various locations on the rotary part of the brake actuator. The following applies: the closer the return spring device is arranged to the source of the frictional torque, the less spring force is lost due to efficiency losses in the transmission points. The smaller the transmission ratio between the return spring device and the source of the frictional torque, the smaller the required spring force.For example, the brake pad of the electromechanical wheel brake can be actively moved by the brake actuator according to the invention both in an actuation direction and in a relief direction of the brake pad.

[0011] The present invention can improve the effect of the spring force with respect to return. Thus, otherwise unfavorable transmission, motor, and parking brake concepts can be used, and the efficiency of the brake actuator can be improved. Furthermore, a benefit of the present invention is that transmission concepts with a self-locking mechanism or a self-locking transmission element, for example, corresponding worm gears or trapezoidal spindles, can be used, since the driving and return of the self-locking transmission element or the transmission concept with self-locking occur in the same direction. This increases the freedom in transmission design.

[0012] Furthermore, the reduced spring force required for the return spring mechanism increases the efficiency of the brake actuator. This allows the actuator mechanism to be designed more compactly than previously possible, while reliably ensuring return. Furthermore, safe return is simplified for motors with higher cogging torques.

[0013] Advantageous embodiments and further developments emerge from the further subclaims and from the description with reference to the figures of the drawing.

[0014] According to a further development of the invention, the return spring device is integrated into the actuator device. This means that the return spring device acts directly on a primary source of the friction torque, i.e., the actuator device. In this way, the functional self-locking effect can be reduced. For example, the actuator device is designed as a rotary electric motor.

[0015] According to a further development of the invention, the brake actuator further comprises a screw drive for converting a rotational movement of the actuator motor device into a translational movement of the brake pad, wherein the return spring device is integrated into the screw drive or a gear arranged kinematically between the actuator motor device and the screw drive. The screw drive can be designed, for example, as a ball screw drive or a trapezoidal screw drive.

[0016] According to a further development of the invention, the actuator device and the return spring device are provided on the same drive side, so that the same efficiency is achieved for applying and releasing the wheel brake. In this way, intrinsic self-locking, i.e., a self-locking property, can be irrelevant for the resetting of the brake actuator. Thus, a very high gear ratio can be provided per stage, so that gear stages can be eliminated. The efficiency is, in particular, not equal to zero. Furthermore, lower requirements can be placed on the gearing and its bearings. For example, the actuator device and the return spring device are provided on the same drive side of a transmission concept or transmission element with a direction-dependent efficiency.

[0017] A self-locking mechanism combined with the return spring device allows for the integration of a parking brake or parking brake function. This can reduce complexity, weight, and / or cost.

[0018] According to a further development of the invention, the return spring device is designed as a spiral drive spring. This allows for a reduction in the installation space for the return spring device. Furthermore, the spiral drive spring can act directly on a motor shaft of the actuator device without significant additional mechanical effort.

[0019] According to a further development of the invention, the spiral mainspring has an inner end and an outer end, with the inner end allowing approximately 3 to 30 revolutions relative to the outer end between a relaxed state of the spiral mainspring and a maximally tensioned state. If the spiral mainspring is designed for a few revolutions, operating ranges such as overcoming clearance and pressing brake pads can be provided. The revolutions preferably correspond to the motor revolutions of the motor shaft.

[0020] According to a further development of the invention, the inner end is mechanically firmly connected to a motor shaft of the actuator device, and the outer end is operatively connected to a housing.

[0021] According to a further development of the invention, the outer end forms a switchable spring stop, which is designed to decouple, in particular completely decouple, the spiral drive spring from the housing. In this way, a parking brake function can be integrated into the brake actuator. The switchable spring stop can have a pin for displacing the outer end, or the switchable spring stop can be designed as a pin that can be displaced parallel to the motor shaft. Such electronic wear adjustment can significantly reduce the space required for the spiral drive spring.

[0022] An operating procedure for providing the parking brake function can, for example, include the following steps: - Turn the brake actuator back to a position where the coiled mainspring is completely relaxed and thus disengaged from the spring stop. By appropriately coordinating individual wheel brakes, rolling away can be prevented even when one wheel brake is completely released. - Retraction of the switchable spring stop. - Driving the brake actuator without tensioning the spiral mainspring to a predetermined braking force and switching off the brake actuator when the predetermined braking force is reached. - Retracting the brake actuator to release the parking brake. - Reconnect the spiral drive spring in the clearance area. Braking force can then be regenerated. A suitable sequence of individual wheel brakes can again prevent the vehicle from rolling away.

[0023] In addition, the spring force of the coiled mainspring for the parking brake can be adjusted. Alternatively or additionally, the spring force can be adjusted by preload to respond to varying friction conditions and / or degradation effects over the service life, thus providing an ideal spring force.

[0024] According to a further development of the invention, the outer end has a form-locking body which is designed to engage a further position by rotation when a predetermined force is reached, wherein the housing has a plurality of recesses into which the form-locking body can engage. The plurality of recesses are arranged, for example, circumferentially on the housing. The form-locking body is preferably triangular or similarly shaped. By means of such mechanical wear adjustment, the required installation space for the spiral drive spring can be significantly reduced. In particular, if the brake actuator is designed to be self-locking, the integration of the parking brake functionality can be achieved by changing the effect of the spiral drive spring between the motor shaft and the housing using the form-locking body.

[0025] Optionally, the return spring device, in particular the spiral-shaped mainspring, can have a degressive characteristic curve. This allows the spring force to remain essentially constant throughout the operating range. Compared to conventional linear springs, this allows for a reduction in parasitic spring force for relatively large actuator travels.

[0026] The electromechanical wheel brake is designed, for example, as an electromechanical drum brake or as an electromechanical disc brake. Short description of the drawings

[0027] The invention is explained below with reference to the figures of the drawings. The figures show: Fig. 1 a schematic representation of an electromechanical drum brake for a vehicle according to an embodiment of the invention with a brake actuator according to an embodiment of the invention; Fig. 2 a schematic representation of a brake actuator according to a further embodiment of the invention with a parking brake function by a switchable spring stop; Fig. 3 a schematic representation of a brake actuator according to a further embodiment of the invention with a mechanical wear adjustment; Fig. 4 a graph illustrating a spring characteristic curve of spiral-shaped mainsprings.

[0028] In the figures, the same reference numerals designate identical or functionally equivalent components, unless otherwise stated. The numbering of process steps is for clarity and generally does not imply a specific chronological order. In particular, several process steps can be performed simultaneously. Description of the embodiments

[0029] Further advantages, features and details of the invention will become apparent from the following description, in which various embodiments are described in detail with reference to the drawing.

[0030] Fig. 1 shows a schematic representation of an electromechanical drum brake 10 for a vehicle with a brake actuator 1.

[0031] The electromechanical drum brake 10 comprises, for example, a brake actuator 1 and two brake pads 11, which can be moved by the brake actuator 1.

[0032] The brake actuator 10 comprises a servomotor device 2 for moving the two brake pads 11 relative to a friction partner 12. The servomotor device 2 can be designed, for example, as an electric motor. The friction partner 12 can correspond to a brake drum.

[0033] Furthermore, the brake actuator 10 comprises a return spring device 3 for returning the brake pads 11, wherein the return spring device 3 is mechanically operatively connected to the actuator device 2. The actuator device 2 and the return spring device 3 are provided, for example, on the same drive side, so that the same efficiency is achieved for applying and releasing the wheel brake. In this way, an intrinsic self-locking feature, i.e., a self-locking property, can be irrelevant for the return of the brake actuator 1. Thus, a very high gear ratio can be provided per stage, so that gear stages can be eliminated. The efficiency is, in particular, not equal to zero.

[0034] Furthermore, the brake actuator 10 comprises, for example, a screw drive 4 designed as a ball screw drive for converting a rotational movement of the actuator device 2 into a translational movement of the brake pad 11, wherein the return spring device 3 is integrated in the ball screw drive 4 or a gear 5 arranged kinematically between the actuator device 2 and the ball screw drive 4.

[0035] The return spring device 3 can be arranged at various locations on the rotary part of the brake actuator 1, in particular on a motor shaft of the servomotor device 2 or the ball screw drive 4. A return spring arranged outside the brake actuator 1 for resetting the brake pad 11, as is usually provided in known drum brakes, can be omitted here or made significantly weaker.

[0036] Fig. 2 shows a schematic representation of a brake actuator 1 with a parking brake function by a switchable spring stop 8.

[0037] The brake actuator 1 can in particular have the features of the brake actuator according to Fig. 1. In particular, Fig. 2 illustrates a sectional view of the actuator device 2. Here, the return spring device 3 is integrated into the actuator device 2. This means that the return spring device 3 acts directly on a main source of the friction torque, usually the actuator device 2. The return spring device 3 is designed as a spiral drive spring. The spiral drive spring 3 can act directly on a motor shaft 6 of the actuator device 2 without any significant additional mechanical effort.

[0038] The spiral mainspring 3 has an inner end 3a and an outer end 3b. Between a relaxed state of the spiral mainspring 3 and a maximum tensioned state, the inner end 3a allows approximately 20 to 30 revolutions relative to the outer end 3b. These revolutions correspond to the motor revolutions of the motor shaft 6. The inner end 3a is mechanically fixed to the motor shaft 6, while the outer end 3b is operatively connected to a housing 7.

[0039] As in Fig. As shown in Figure 2, the outer end 3b forms a switchable spring stop 8, which is designed to completely decouple the spiral drive spring 3 from the housing 7. In this way, a parking brake function can be integrated into the brake actuator 1. The switchable spring stop 8 can have a pin for displacing the outer end 3b, which can be displaced parallel to the motor shaft 6. Such electronic wear adjustment can significantly reduce the installation space required for the spiral drive spring 3.

[0040] Fig. 3 shows a schematic representation of a brake actuator 1 with a mechanical wear adjustment

[0041] The brake actuator 1 can in particular have the features of the brake actuator according to Fig. 1. In particular, Fig. 3 illustrates a sectional view of the actuator device 2. Here, the return spring device 3 is integrated into the actuator device 2. This means that the return spring device 3 acts directly on a main source of the friction torque, i.e., the actuator device 2. The return spring device 3 is designed as a spiral drive spring. The spiral drive spring 3 can act directly on a motor shaft 6 of the actuator device 2.

[0042] The spiral mainspring 3 has an inner end 3a and an outer end 3b. Between a relaxed state of the spiral mainspring 3 and a maximum tensioned state, the inner end 3a allows approximately 20 to 30 revolutions relative to the outer end 3b. These revolutions correspond to the motor revolutions of the motor shaft 6. The inner end 3a is mechanically fixed to the motor shaft 6, while the outer end 3b is operatively connected to a housing 7.

[0043] As in Fig. As shown in Figure 3, the outer end 3b has a positive locking body 9, which is designed to engage a further position upon reaching a predetermined force by rotation, wherein the housing 7 has a plurality of recesses into which the positive locking body 9 can engage. The plurality of recesses are arranged circumferentially on the housing 7, for example. The positive locking body 9 is preferably triangular or similarly shaped. Through such mechanical wear adjustment, the required installation space for the spiral drive spring 3 can be significantly reduced. In particular, if the brake actuator 1 is designed to be self-locking, the integration of the parking brake functionality can be achieved by changing the effect of the spiral drive spring 3 between the motor shaft 6 and the housing 7 by the positive locking body 9.

[0044] Fig. 4 shows a graph illustrating a spring characteristic of spiral-shaped mainsprings 3.

[0045] The graph illustrates a torque M of the motor shaft over a number of motor revolutions # n of the motor shaft. For example, a working range of the Fig. 2 and Fig. 3 usable spiral mainspring at 7 to 20 motor revolutions # n. In addition, a hysteresis HY of the spiral mainspring between a winding A and a return R of the spiral mainspring is illustrated.

[0046] The present invention is applied here merely by way of example to a drum brake, but is not limited to this type of brake. Rather, the present invention can be applied to all electromechanically actuated brakes, such as electromechanical disc brakes or the like.

[0047] Although the present invention has been explained above using exemplary embodiments, it is not limited thereto but can be modified in a variety of ways. In particular, combinations of the above embodiments are also conceivable. 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] DE 10 2021 203 003 A1

[0003]

Claims

[1] Brake actuator (1) for an electromechanical wheel brake (10), comprising: a servomotor device (2) for moving a brake pad (11) relative to a friction partner (12); and a return spring device (3) for returning the brake pad (11), wherein the return spring device (3) is mechanically operatively connected to the servo motor device (2). [2] Brake actuator (1) according to claim 1, wherein the return spring device (3) is integrated in the servo motor device (2). [3] Brake actuator (1) according to claim 1 or 2, further comprising a screw drive (4) for converting a rotational movement of the servomotor device (2) into a translational movement of the brake pad (11), wherein the return spring device (3) is integrated in the screw drive (4) or a gear (5) arranged kinematically between the servomotor device (2) and the screw drive (4). [4] Brake actuator (1) according to one of the preceding claims, wherein the servo motor device (2) and the return spring device (3) are provided on the same drive side, so that the same efficiency is achieved for applying and releasing the wheel brake. [5] Brake actuator (1) according to one of the preceding claims, wherein the return spring device (3) is designed as a spiral-shaped drive spring. [6] Brake actuator (1) according to claim 5, wherein the spiral drive spring (3) has an inner end (3a) and an outer end (3b), wherein the inner end (3a) allows approximately 3 to 30 revolutions relative to the outer end (3b) between a relaxed state of the spiral drive spring (3) and a maximum tensioned state. [7] Brake actuator (1) according to claim 6, wherein the inner end (3a) is mechanically fixedly connected to a motor shaft (6) of the servo motor device (2), and wherein the outer end (3b) is operatively connected to a housing (7). [8] Brake actuator (1) according to claim 6 or 7, wherein the outer end (3b) forms a switchable spring stop (8) which is designed to decouple, in particular completely decouple, the spiral-shaped drive spring (3) from the housing (7). [9] Brake actuator (1) according to one of the preceding claims, wherein the outer end (3b) has a positive locking body (9) which is designed to engage a position further by rotation when a predetermined force is reached, wherein the housing (7) has a plurality of recesses into which the positive locking body (9) can engage. [10] Electromechanical wheel brake (10) for a vehicle, comprising a brake actuator (1) according to one of the preceding claims, and a brake pad (11) which is movable by the brake actuator (1).

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