Actuator for an electromechanical vehicle braking system and electromechanical vehicle braking system

Abstract

Actuator for an electromechanical vehicle braking system (10) with an electromechanically actuated service brake and an electromechanically actuated parking brake, with an electric motor (22) and a transmission (24) which has a first transmission element (241) and a second transmission element (242), wherein the two transmission elements (241, 242) are connected to one another in a torque-transmitting manner, wherein the first transmission element (241) is rotatable about an axis of rotation (D1) and can be translated in the direction of the axis of rotation (D1), and the second transmission element (242) is rotatable about the axis of rotation (D1), fixed in the direction of the axis of rotation (D1), and connected to the first transmission element (241) in a torque-transmitting manner via a connecting device (26), wherein the transmission (24) has a parking brake coupling device (30) which can be adjusted between an open state and a closed state and which has a first,rigidly arranged coupling element (301) and a second coupling element (302) operatively connected to the first gear element (241), wherein the first gear element (241) is displaced relative to the second gear element (242) above a predefined torque threshold in the direction of rotation and in the direction of the rotation axis (D1).

Description

[0001] The invention relates to an actuator for an electromechanical vehicle braking system with an electromechanically actuated service brake and an electromechanically actuated parking brake.

[0002] According to the current state of the art, a vehicle typically has a service brake and a parking brake. The service brake is typically applied by the driver via the brake pedal. The parking brake is often implemented as a separate electromechanical actuator and is usually activated by the driver via a separate switch. The actuator for providing the parking brake is typically attached to the brake caliper of a braking device and primarily prevents a parked vehicle from rolling away.

[0003] Furthermore, it is known from the prior art that the service brake is designed as a so-called brake-by-wire braking system, wherein the actuation of the brake pedal is detected by a sensor device and, based on this, an electric motor of an actuator that interacts with the service brake is actuated. In this case, the actuator in particular translates the brake pistons acting on the brake pads, whereby the brake pads are displaced relative to a brake disc that is firmly connected to a vehicle wheel and rotates together with the vehicle wheel during driving. As an alternative to the disc brake, the braking device can also be designed as a drum brake, wherein in this case too, the brake pads are displaced by an actuator depending on the sensor signal from a sensor device that detects the actuation of the brake pedal, thereby triggering a braking operation.

[0004] For example, DE 10 2011 086 152 A1 discloses an actuator for a vehicle braking system with an electromechanically actuated service brake and an electromechanically actuated parking brake. By displacing a drive pinion of an electric motor, the connection of the drive pinion to various components is adjusted, thereby switching between a service brake function, a parking brake function, and a play compensation function. The drive pinion is adjusted using several coils that interact with an armature attached to a drive shaft of the electric motor, to which the drive pinion is attached.Depending on the desired function, the corresponding coil is energized, creating a predefined magnetic field. The resulting magnetic field translates the armature, together with the drive shaft and the drive pinion, into the corresponding position. A disadvantage of such actuator designs is that additional coils with associated control functions are required to switch at least between the parking brake function and the service brake function. This, in turn, leads to relatively high assembly and manufacturing costs and a relatively large actuator size.

[0005] The object of the invention is to provide an actuator for an electromechanical vehicle braking system for the reliable provision of a service brake and a parking brake, which actuator can be designed in a space-saving, simple and cost-effective manner.

[0006] The problem is solved by the features of claim 1.

[0007] The actuator comprises at least one electric motor and a transmission. The transmission is interposed between the electric motor and a brake actuation unit, which interacts with a braking device, so that the transmission is connected to the electric motor on the drive side, i.e., to a drive pinion of the electric motor, and to the brake actuation unit on the output side, in a torque-transmitting manner.

[0008] The transmission has at least two transmission elements that are connected to one another via a connecting device for transmitting torque. The first transmission element is mounted for rotation about an axis of rotation and translationally displaceable in the direction of the axis of rotation. The second transmission element is arranged coaxially to the first transmission element and is thus mounted for rotation about the axis of rotation. In contrast to the first transmission element, the second transmission element is mounted for translationally fixed movement in the direction of the axis of rotation, so that translational displacement of the second transmission element is not possible.

[0009] When the vehicle is in operation, an actuation of the brake pedal is detected by a sensor device, and the electric motor is controlled by a control unit in accordance with the detected deflection of the brake pedal. The electric motor drives the gear wheel via the drive pinion, whereby the torque-transmitting connection between the gear elements caused by the connecting device causes the gear elements to rotate together about the axis of rotation. The brake actuation unit, which is operatively connected to the second gear element, is usually operatively connected to two brake pads in such a way that the output-side rotational movement leads to a translational movement of the brake pads, whereby the brake disc arranged between the brake pads is clamped between the two brake pads, and a braking effect is caused by the friction between the brake disc and the brake pads, which is dependent on the contact force.

[0010] The transmission also includes a parking brake clutch device, which, together with other components, serves to implement a parking brake. The parking brake clutch device includes two clutch elements. A first clutch element is rigidly arranged. A second clutch element is operatively connected to the first transmission element such that the second clutch element rotates and translates depending on the rotation and translational movement of the first transmission element.

[0011] To activate the parking brake, the electric motor is controlled in such a way that a torque provided by the electric motor exceeds a predefined torque threshold, whereby exceeding the torque threshold is only possible when the brake pads are in contact with the brake disc or the brake drum. The service brake is applied in a service brake torque range which lies below the torque threshold. By increasing the torque provided by the electric motor, i.e. by appropriately controlling the electric motor, above the predefined torque threshold and a corresponding design of the connecting device, the first gear element is displaced in the direction of rotation and translationally in the direction of the axis of rotation relative to the second gear element.Because the second clutch element is operatively connected to the first transmission element, the second clutch element is translationally displaced relative to the stationary first clutch element in such a way that the parking brake clutch device is moved from the open state to the closed state. When the parking brake clutch device is in the closed state, the parking brake is activated.

[0012] In the open state, the clutch elements are separated from one another, so that the actuator serves exclusively as a service brake. If a parking brake is activated while the vehicle is stationary, the actuator serves to activate the parking brake, whereby the parking brake clutch device is adjusted to the closed state by corresponding control of the electric motor. The electric motor is inactive in the closed state, whereby the parking brake clutch device remains in the closed state due to a holding force, which is composed in particular of the static friction between adjacent components, in particular the clutch elements, the components of the connecting device and the components of the actuating unit, and the cogging torque of the electric motor.The closed state is maintained until the first gear element is rotated by the electric motor in the opposite direction of rotation, thereby overcoming the static friction and eliminating the cogging torque of the electric motor.

[0013] This provides an actuator for an electromechanical vehicle brake which enables a service brake function and a parking brake function and can be designed in a space-saving, simple and cost-effective manner.

[0014] The parking brake clutch device is preferably a friction clutch, wherein both clutch elements each have a friction surface which abut one another in the closed state and are spaced apart from one another in the open state. This allows the parking brake clutch device to be designed simply and easily adjusted between the open and closed states, wherein to provide the closed state the two clutch elements only have to be moved translationally relative to one another until the two clutch elements abut one another. The relative positions of the two clutch elements in the direction of rotation do not have to be taken into account. Alternatively, the parking brake clutch device can be designed as a form-fitting clutch, wherein the two clutch elements are positively connected to one another in the direction of rotation in the closed state.For example, the parking brake coupling device could be designed as a dog clutch.

[0015] In a preferred embodiment, the second clutch element is manufactured in one piece with the first gear element. This allows the clutch element to be formed by the gear wheel, with the second clutch element being manufactured during the production of the first gear element. This reduces the manufacturing and assembly costs of the actuator. The first clutch element is preferably manufactured in one piece with an actuator housing.

[0016] Alternatively, the first coupling element is a separate element and is attached to the actuator housing.

[0017] Preferably, a spring element is provided which is designed and arranged such that the two coupling elements are pressed apart by the spring element. The spring element is preferably arranged between the first gear element and an actuator housing, wherein the first coupling element is arranged on the actuator housing. This reliably prevents the coupling elements from abutting one another in the open position. When the parking brake is activated, the axial force caused by the connecting device and the torque of the electric motor, i.e., the force in the direction of the rotational axis, exceeds the spring force of the spring element, causing the coupling elements to be displaced relative to one another, i.e., toward one another. The spring force is so low that, when the parking brake-coupling device is in the closed state, the spring force is not sufficiently high for the coupling parts to be moved apart.

[0018] In a preferred embodiment, the transmission elements each form a gearwheel, with the first transmission element being connected to a drive pinion of the electric motor, and the second transmission element being connected to a third transmission element configured as a gearwheel, which is operatively connected to a brake actuation unit. Alternatively, the second transmission element can be connected directly to the brake actuation unit.

[0019] Preferably, one of the gear elements has a bearing section on which the other gear element is mounted so as to be displaceable in the direction of rotation and in the direction of the rotation axis. The second gear element thus serves to support the first gear element, which can reduce the manufacturing and assembly effort of the actuator, since no additional component or no additional configuration, for example, of the actuator housing, is required to support the first gear component.

[0020] The connecting device is preferably arranged in the direction of the axis of rotation between the two gear elements. In a preferred embodiment, the connecting device is formed by at least one pocket formed on the first gear element, a counter-pocket formed on the second gear element, and a rolling element, preferably a sphere or a cylinder, arranged in the pocket and in the counter-pocket. The pocket and / or the counter-pocket has a ramp-like side wall such that, when the predefined torque threshold is exceeded, the rolling element moves out of the pocket and / or counter-pocket along the ramp-like side wall such that the two gear elements are displaced relative to one another in the direction of the axis of rotation and in the direction of rotation.

[0021] When the electric motor is operated in the service braking torque range, at least one rolling element remains in the pocket and the counterpocket due to the relatively steep, ramp-like sidewall, so that the two transmission elements rotate together during the service braking function, and no relative movement occurs between the transmission elements. Only when the predefined torque threshold is exceeded by the torque to be transmitted via the transmission elements, by controlling the electric motor accordingly, does a displacement of the rolling elements along the ramp-like sidewall of the pocket and / or the counterpocket result, causing the first transmission element to be displaced relative to the second transmission element in the direction of rotation and in the direction of the rotation axis.By displacing the first gear element, the second clutch element is moved toward the first clutch element, moving the parking brake clutch device into the engaged state, thus activating a parking brake function. By selecting the inclination, i.e., the angle to the horizontal, of the ramp-like side wall, the torque threshold and the holding force in the engaged state of the parking brake clutch device can be adjusted.

[0022] The object is further achieved by an electromechanical vehicle braking system comprising an actuator according to one of claims 1 to 11 and a braking device, wherein the actuator is operatively connected to at least one brake pad of the braking device via a brake actuation unit. The braking device can be either a disc brake or a drum brake.

[0023] The invention is explained in more detail below with reference to the accompanying drawings. In the drawings: Fig. 1 an electromechanical vehicle braking system in cross section, Fig. 2 a section of a connecting device of an actuator of the electromechanical vehicle braking system in cross section.

[0024] The Fig. 1 shows an electromechanical vehicle braking system 10. The electromechanical vehicle braking system 10 comprises an actuator 20, a brake actuation unit 50, and a braking device 70. The electromechanical vehicle braking system 10 is designed as a brake-by-wire system, wherein the actuator 20 is controlled depending on the position of a brake pedal 40. The position of the brake pedal 40 is detected by a sensor device 42, wherein the sensor signals of the sensor device 42 are processed in a control unit 44 and used to operate the actuator 20.

[0025] The actuator 20 has an electric motor 22 and a gear 24. The electric motor 22 comprises a stator and a rotor, wherein the stator is fastened, for example, to an actuator housing 21 and the rotor is rotatably mounted on the actuator housing 21 about a rotation axis D2. The rotor is rotationally fixedly connected to a drive shaft 221, wherein a drive pinion 222 is rotationally fixedly arranged on the drive shaft 221, such that the drive pinion 222 is driven via the drive shaft 221. The electric motor 22, i.e. the stator, is electrically connected to the control unit 44, such that the electric motor 22 is controlled by the control unit 44.

[0026] The transmission 24 is interposed between the electric motor 22 and the brake actuation unit 50, so that the transmission 24 is connected on the drive side to the electric motor 22, ie to the drive pinion 222 of the electric motor 22, and on the output side to the brake actuation unit 50 in a torque-transmitting manner.

[0027] The transmission 24 has three transmission elements 241, 242, 243. A first transmission element 241 is designed as a gear and meshes with the drive pinion 222, so that the first transmission element 241 is driven by the electric motor 22 during operation.

[0028] A second gear element 242 and a third gear element 243 are also designed as gears. The second gear element 242 is arranged coaxially to the first gear element 241 and is connected to the first gear element 241 via a connecting device 26 in a torque-transmitting manner, with the second gear element 242 meshing with the third gear element 243. The third gear element 243 is operatively connected to the actuating unit 50.

[0029] The first gear element 241 is rotatable about a rotation axis D1 and is mounted translationally in the direction of the rotation axis D1 on a bearing section 25 of the second gear element 242. The second gear element 242 is rotatable about the rotation axis D1 and is mounted fixedly in the direction of the rotation axis D1 on the actuator housing 21. The third gear element 243 is rotatable about a rotation axis D3 and is mounted fixedly in the direction of the rotation axis D3 on the actuator housing 21.

[0030] The connecting device 26, which connects the two gear elements 241, 243 in a torque-transmitting manner, is arranged in the direction of the axis of rotation D1 between the two gear elements 241, 242 and has a plurality of pockets 261 formed on the first gear element 241 and arranged distributed in the circumferential direction, a plurality of counter-pockets 262 formed on the second gear element 242 and arranged distributed in the circumferential direction, and a plurality of rolling elements 263, in particular spherical rolling elements, each arranged in a pocket 261 and in a counter-pocket 262.

[0031] A section of the connecting device 26 is shown in Fig. 2. The pockets 261 and the counter-pockets 262 are groove-like, with one side wall 281, 282 of each of the pockets 261 and counter-pockets 262 being ramp-like. When providing a braking function of the braking device 70, the rolling elements 263 rest against these side walls 281, 282.

[0032] The transmission 24 also has a parking brake clutch device 30, which is adjustable between an open state and a closed state. The parking brake clutch device 30 comprises two clutch elements 301, 302. A first clutch element 301 is rigidly arranged on the actuator housing 21 and has an annular friction surface 341. A second clutch element 302 is formed integrally with the first transmission element 241 and has an annular friction surface 342 facing the first clutch element 301. In the open state, the two clutch elements 301, 302 are spaced apart from one another, and a gap RS exists between the friction surfaces of the clutch elements 301, 302. The two coupling elements 301, 302 are pressed apart by a spring element 32 in order to ensure the gap RS in the open state, wherein the spring element 32 is arranged between the first gear element 241 and the actuator housing 21.In the closed state, the gap RS no longer exists and the coupling elements 301, 302 lie against each other via the friction surfaces 341, 342.

[0033] The brake actuation unit 50 comprises two actuation elements 501, 502 and a plurality of spherical rolling elements 52 connecting the actuation elements 501, 502 to one another. The first actuation element 501 is connected in a rotationally fixed manner to the third gear element 243 and has a plurality of ramp-like actuation pockets 54 in the circumferential direction, in which the rolling elements 52 are arranged. The second actuation element 502 is mounted for translational displacement and rests against the rolling elements 52 with a side facing the third gear element 243. With a side facing away from the third gear element 243, the second actuation element 502 is connected to a brake piston 72 of the braking device 70, which is designed as a disc brake and is also mounted for translational displacement. The brake piston 72 is fixedly connected to a brake pad 74, wherein the brake pad 74 interacts with a brake disc 76 of the braking device 70 for a braking function.

[0034] During normal driving of the vehicle, in which the service brake is required, an actuation of the brake pedal 40 is detected by the sensor device 42, and based on this, the electric motor 22 is controlled by the control unit 44 in accordance with the detected deflection of the brake pedal 40. The electric motor 22 drives the first gear element 241 via the drive pinion 222, wherein the gear elements 241, 242 rotate together about the rotation axis D1 via the connecting device 26. The third gear element 243 is driven by the second gear element 242, wherein the first actuating element 501 also rotates together with the third gear element 243.The rotational movement of the first actuating element 501 rotates the first actuating element 501 such that the rolling elements 52 move along the ramp-like actuating pockets 54, whereby the second actuating element 502, the brake piston 72, and the brake pad 74 are displaced translationally. As soon as a distance BS has been overcome, the brake pad 74 rests against the brake disc 76 and a braking effect is present. The braking effect is caused by the friction present between the brake disc 76 and the brake pad 74, which is dependent on the contact force, i.e., the torque provided by the electric motor 22. The service braking function can be provided by controlling the electric motor 22 in a service braking torque range.

[0035] To activate the parking brake, the electric motor 22 is controlled such that a torque provided by the electric motor 22 exceeds a predefined torque threshold, wherein the torque threshold can only be provided when the brake pads 74 are in contact with the brake disc 76. When the electric motor 22 is operated in the service brake torque range, i.e. below the torque threshold relevant for the parking brake, the rolling elements 263 remain in the pockets 261 and in the counter pockets 262 due to the relatively steep ramp-like side wall, so that the two gear elements 241, 242 rotate together during the service brake function and no relative movement takes place between the gear elements 241, 242.Only when the predefined torque threshold is exceeded by the torque to be transmitted via the gear elements 241, 242, by controlling the electric motor 22 accordingly, does a displacement of the rolling elements 263 along the ramp-like side wall of the pockets 261 and the counter-pockets 262 result, causing the first gear element 241 to be displaced in the direction of rotation and in the direction of the rotational axis D1 relative to the second gear element 242. The displacement of the first gear element 241 in the direction of the rotational axis D1 moves the second clutch element 302 toward the first clutch element 301, and the parking brake clutch device 30 is adjusted to the engaged state. This activates a parking brake function.

[0036] When the parking brake clutch device 30 has been moved to the engaged state, the electric motor 22 can be switched to an inactive state. Due to the existing static friction between the adjacent components, in particular the coupling elements 301, 302, the components of the connecting device 26, and the components of the actuating unit 50, and due to the cogging torque of the electric motor 22, the parking brake function is maintained even when the electric motor 22 is inactive. The parking brake function is maintained until the first gear element 241 is rotated in the opposite direction by the electric motor 22, thereby overcoming the static friction and eliminating the cogging torque of the electric motor 22. List of reference symbols 10 Electromechanical vehicle braking system 20 Actuator 21 Actuator housing 22 electric motor 221 drive shaft 222 drive pinion 24 gearboxes 241 First gear element 242 Second gear element 243 Third gear element 26 Connecting device 261 bag 262 Counter pocket 263 rolling elements 281 Ramp-like side wall of the pocket 282 Ramp-like side wall of the counter pocket 30 Parking brake coupling device 301 First coupling element 302 Second coupling element 32 spring element 341 Friction surface of the first clutch element 342 Friction surface of the second clutch element 40 Brake pedal 42 Sensor device 44 Control unit 50 operating unit 501 First actuating element 502 Second actuating element 52 rolling elements 54 Ramp-like actuation pocket 70 Braking device 72 brake pistons 74 brake pad 76 brake disc D1 First axis of rotation D2 Second axis of rotation D3 Third axis of rotation BS Way RS gap

Claims

[1] Actuator for an electromechanical vehicle braking system (10) with an electromechanically actuated service brake and an electromechanically actuated parking brake, with an electric motor (22) and a transmission (24) which has at least a first transmission element (241) and a second transmission element (242), wherein the two transmission elements (241, 242) are connected to one another in a torque-transmitting manner, characterized by , that the first gear element (241) is rotatable about a rotational axis (D1), translationally displaceable in the direction of the rotational axis (D1), and the second gear element (242) is rotatable about the rotational axis (D1), fixed in the direction of the rotational axis (D1), and connected to the first gear element (241) in a torque-transmitting manner via a connecting device (26), wherein the gear (24) has a parking brake coupling device (30) which is adjustable between an open state and a closed state, said coupling device having a first, rigidly arranged coupling element (301) and a second coupling element (302) which is operatively connected to the first gear element (241), wherein the connecting device (26) is designed such that the first gear element (241) is displaced relative to the second gear element (242) above a predefined torque threshold in the direction of rotation and in the direction of the rotational axis (D1) such that the coupling device connected to the first gear element (241) effectively connected,second coupling element (302) is displaced relative to the first coupling element (301) in the direction of the rotation axis (D1) such that the parking brake coupling device (30) is adjusted between the open state and the closed state., [2] Actuator according to claim 1, characterized by that the parking brake coupling device (30) is a friction clutch, wherein both coupling elements (301, 302) each have a friction surface (341, 342) which abut one another in the closed state and are spaced apart from one another in the open state. [3] Actuator according to claim 1 or 2, characterized by that the second coupling element (302) is made in one piece with the first transmission element (241). [4] Actuator according to one of the preceding claims, characterized by that the first coupling element (301) is fastened to an actuator housing (21) or is made in one piece with the actuator housing (21). [5] Actuator according to one of the preceding claims, characterized by that a spring element (32) is provided which is designed and arranged such that the two coupling elements (301, 302) are pressed apart by the spring element (32). [6] Actuator according to one of the preceding claims, characterized by that the gear elements (241, 242) each form a gearwheel, wherein the first gear element (241) is connected to a drive pinion (222) of the electric motor (22) and the second gear element (242) is connected to a third gear element (263) designed as a gearwheel, which is operatively connected to a brake actuation unit (50). [7] Actuator according to one of the preceding claims, characterized by that one of the gear elements (241, 242) has a bearing section (25) on which the other gear element (241, 242) is mounted so as to be displaceable in the direction of rotation and in the direction of the axis of rotation (D1). [8] Actuator according to one of the preceding claims, characterized by that the connecting device (26) is arranged in the direction of the axis of rotation (D1) between the two gear elements (241, 242). [9] Actuator according to claim 8, characterized by in that the connecting device (26) is formed by at least one pocket (261) formed on the first gear element (241), a counter-pocket (262) formed on the second gear element (242) and a rolling body (263) arranged in the pocket (261) and in the counter-pocket (262), wherein the pocket (261) and / or the counter-pocket (262) has a ramp-like side wall (281, 282) such that when the predefined torque threshold is exceeded, the rolling body (263) moves along the ramp-like side wall (281, 282) such that the two gear elements (241, 242) are displaced relative to one another in the direction of the axis of rotation (D1) and in the direction of rotation. [10] Actuator according to claim 9, characterized by that the rolling element (263) is a sphere or a cylinder. [11] Actuator according to one of the preceding claims, characterized by that the electric motor (22) is inactive when the parking brake coupling device (30) is in the closed state. [12] Electromechanical vehicle braking system with an actuator (20) according to one of claims 1 to 11, and a braking device (70), wherein the actuator (20) is operatively connected to at least one brake pad (74) of the braking device (70) via a brake actuation unit (50).

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