BRAKE-ACTUATOR FOR A VEHICLE, IN PARTICULAR COMMERCIAL VEHICLE, AND BRAKE SYSTEM THEREWITH

Abstract

A brake actuator (1) for a vehicle includes a housing (5) and a piston (7) movably mounted inside the housing (5) and configured to reciprocate along a stroke axis (S) between a retracted position and an extended position for applying and releasing a braking force to and from a brake mechanism (101) of the vehicle. An electric motor (3) is operatively coupled to the piston (7) and configured to move the piston (7) rod between the retracted and extended positions such as to apply and release the braking force.

Claims

1. A brake actuator (1) for a vehicle, comprising: a housing (5), a piston (7) movably mounted inside the housing (5) and configured to reciprocate along a stroke axis (S) between a retracted position and an extended position for applying and releasing a braking force to and from a brake mechanism (101) of the vehicle, and an electric motor (3) operatively coupled to the piston (7) and configured to move the piston (7) rod between the retracted and extended positions to apply and release the braking force.

2. The brake actuator (1) of claim 1, wherein the piston (7) is slidably supported in the housing (5), configured to move along the stroke axis (S) and to pivot from the stroke axis (S) within a predetermined angle ().

3. The brake actuator (1) of claim 1, wherein the electric motor (3) is coupled to a screw drive (19), and the screw drive (19) is coupled to the piston (7) and configured to transfer a rotational drive movement of the electric motor (3) into a linear movement of the piston (7).

4. The brake actuator (1) of claim 3, wherein the rotating element (21) comprises a rotational axis (R) parallel to the stroke axis (S) and the nut (23) is driven along the rotational axis (R) by rotation of the rotating element (21).

5. The brake actuator (1) of claim 3, wherein the rotational axis (R) is coaxial with the stroke axis (S)

6. The brake actuator (1) of claim 3, wherein the screw drive (19) comprises a rotating element (21) and a nut (23), wherein the rotating element (21) and the nut (23) are in threaded engagement, wherein the rotating element (21) or the nut (23) rests against the piston (7).

7. The brake actuator (1) of claim 6, wherein the rotating element (21) is rotatably mounted in the housing (5), and the nut (23) is a running nut movably mounted to the rotating element (21) and rests against the piston (7).

8. The brake actuator (1) of claim 6, comprising a number of guide elements (25) that are located in the housing (5), oriented parallel to the rotational axis (R) of the rotating element (21) and engage the nut (23) to prevent rotation of the nut (23).

9. The brake actuator (1) of claim 3, wherein the nut (23) comprises an end face that faces the piston (7) and comprises a convexly shaped surface portion (25).

10. The brake actuator (1) of claim 9, wherein the convexly shaped portion (25) has a cylindrical shape to facilitate planar pivoting movement of the piston (7), or wherein the convexly shaped portion (25) has a spherical shape to facilitate three-dimensional pivoting movement of the piston (7).

11. The brake actuator (1) of claim 1, wherein the electric motor (3) is coupled to the screw drive (19) by at least one of: a toothed gear drive, a belt drive (27), a chain drive, a planetary gear, and a worm gear.

12. The brake actuator (1) of claim 1, wherein the housing (5) comprises a first chamber (9), preferably a pressure chamber, and a second chamber (11), preferably a non-pressure chamber, wherein the first chamber (9) and the second chamber (11) are sealed against and separated from one another by the piston (7).

13. The brake actuator (1) of claim 12, wherein the first chamber (9) comprises a port (41) for connecting the first chamber (9) to a pressure source.

14. The brake actuator (1) of claim 12, comprising at least one of: a check valve (39) communicating with the second chamber (11) to reduce elevated pressure inside the second chamber (11) when the piston (7) moves towards the extended position, or a return valve, preferably mounted to the piston (7), to compensate vacuum building up inside the second chamber (11) when the piston (7) moves towards the retracted position.

15. A brake system (100) of a vehicle, the brake system comprising: a brake actuator (1) according to claim 1, a brake mechanism (101) operatively coupled to the brake actuator (1), and an electronic control unit (105) operatively coupled to the brake actuator (1).

16. The brake system (100) of claim 15, wherein the electronic control unit (105) is configured to control the brake actuator (1) such that the electric motor (3) actuates the piston (7) when at least one of a parking brake function and a service brake function, is activated.

17. The brake system (100) of claim 15, wherein the brake mechanism (101) comprises: at least one brake pad (102) being subject to wear, and a wear sensor (103) operatively coupled to the electronic control unit (105) and configured to measure the wear of the brake pad (102) and to provide a signal representative of the wear measurement, wherein the electronic control unit (105) is configured to control the electric motor (3) of the brake actuator (1) such as to adjust at least one of the retracted and extended positions of the piston (7) as a function of the signal representative of the wear measurement.

18. The brake system (100) of claim 15, wherein the piston (7) of the brake actuator (1) has a maximum stroke length defined by the retracted position and the extended position, and wherein the brake actuator (1) is configured to communicate to the electronic control unit (105) a signal representative of the maximum stroke length.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In the drawings,

[0032] FIG. 1 shows a schematic 3-dimensional view of a brake actuator according to a preferred embodiment;

[0033] FIG. 2 shows a schematic planar cross-sectional view of the brake actuator of FIG. 1;

[0034] FIG. 3 shows a first schematic detail view of a locking unit of the brake actuator of FIGS. 1 and 2;

[0035] FIG. 4 shows a second schematic detail view of a locking unit of the brake actuator of FIGS. 1 and 2;

[0036] FIG. 5 shows a third schematic detail view of a locking unit of the brake actuator of FIGS. 1 and 2;

DETAILED DESCRIPTION OF THE DRAWINGS

[0037] FIGS. 1 and 2 shows a brake actuator 1 in accordance with a preferred embodiment. The brake actuator 1 comprises an electric motor 3 which is attached to a housing 5 and preferably housed integrally therewith. Inside the housing, a piston 7 is mounted for reciprocal movement between a retracted position (to the left in FIGS. 1 and 2) and an extended position (towards the right in FIGS. 1 and 2). The piston 7 sealingly abuts against an inside wall 8 of the housing 5 and separates a first chamber 9 from a second chamber 11.

[0038] In the second chamber 11, a return spring 13 is mounted and effective to move the piston 7 towards the retracted position.

[0039] The housing 5 of the brake actuator can be mounted to a wheel assembly of a vehicle by using bolts 15 or other suitable fastening elements.

[0040] Mounted to the housing 5 is a drive head 17 that houses a screw drive 19. The screw drive 19 comprises a rotatably mounted spindle 21 and a nut 23. The nut 23 and the spindle 21 engage one another with correspondingly shaped male and female threads, respectively. For ease of legibility, the threads are not shown. The nut 23 is prevented from rotational movement by a pair of guide elements 25 aligned in parallel to a rotational axis R of the screw drive 19. The rotational axis R in FIG. 1 is also coaxial to the stroke axis S of the piston 7.

[0041] The screw drive 19 is coupled to the electric motor 3 by a belt drive 27. The belt drive 27 comprises a tooth pinion 29 coupled directly to the drive shaft (not shown) of the electric motor 3, a tooth wheel 31 coupled to the spindle 21 and a tooth belt 33 connecting the tooth pinion 29 and the tooth wheel 31. The drive shaft of the electric motor 3 has an axis A that is oriented parallel to the rotation axis R, i.e. stroke axis S of the piston 7. As can be seen from the Figs., the layout of the entire belt drive 27 and screw gear 19 is very compact in the direction of axis R. As can in particular be seen from FIG. 2, the nut 23 comprises an end face 35 having a convexly shaped surface portion 25. The convexly shaped surface portion 25 may be of a cylindrical shape or a spherical shape. The convex shape of the surface portion 25 ensures that even when the piston 7 is pivoted away from the stroke axis at an inclination angle , proper contact between the nut 23 and the piston 7 is still ensured, as long as the inclination angle is within a pre-determined range.

[0042] In the peripheral region of the piston 7, a radially expandable sealing element 37 is positioned such that it sealingly abuts against the inside wall 8 of housing 5. The elasticity of the sealing element 37 preferably is such that as long as the pivoting angle of the piston 7 with respect to the stroke axis S is within the pre-determined range, the sealing element 37 still sealingly abuts against the sealing wall 8 of the housing 5.

[0043] During movement of the piston 7, the volume in particular of the second chamber 11 will decrease or increase, depending on the direction of movement of the piston 7. If the piston 7 is moved towards the extended position (right side in FIG. 2), the volume in the second chamber 11 decreases and elevated pressure may build up. To prevent this from impeding the piston movement, the housing 5 comprises a check valve 39 for venting elevated pressure from the second chamber 11.

[0044] In a preferred embodiment, the actuator 1 may additionally comprise a pressure port 41 configured to establish a fluid connection to a pressure source. Doing so turns the first chamber 9 into a pressure chamber. Thus, piston movement may selectively effected electrically, pneumatically or electro-pneumatically. The pressure port is schematically depicted on a sidewall of the brake actuator 1. It is to be understood that the pressure port may alternatively be located on another part of the brake actuator, such as for example on the drive head 17 next to the belt drive 27.

[0045] A return valve (not shown) may be integrated into the piston 7. The return valve preferably is configured to compensate vacuum building up in the second (non-pressure) chamber 11 when the piston 7 moves towards the retracted position.

[0046] The brake actuator shown in FIGS. 1 and 2 is part of a brake system 100 of a vehicle (not shown). The brake system 100 comprises a brake mechanism 101 which is operatively coupled to the brake actuator and actuated by the piston movement of the piston 7 in the direction of the stroke axis S. The brake mechanism 101 comprises a brake pad 102 which is subject to wear. In one preferred embodiment, the brake system 100 comprises a wear sensor 103 which is configured to monitor the wear status of the brake pad 102 and transmit a signal representative of the wear to an electronic control unit 105. Additionally or alternatively, the brake actuator 1 is configured to determine the maximum stroke of the piston 7 when actuated by the electric motor 3 and to transmit a signal representative of the maximum stroke length to the electronic control unit 105 in accordance with the preferred embodiments described herein above.

[0047] The electronic control unit 105 may use either of these signals, if both are present in the embodiment, or just one signal, whichever is present in the respective embodiment, to determine the need for replacement of the brake pad 102. Also, the electronic control unit 105 may adjust the control parameters for the electric motor 3 of the brake actuator 1 to compensate for increasing wear of the brake pad 102, e.g. by adjusting the extended position and retracted position of the piston 7. This way, it can be ensured that the piston 7 is extended far enough in order to create sufficient braking force even with a partially worn out brake pad. Likewise, it is possible to have the piston 7 retract only as far as is needed in view of the wear of the brake pad 7 such that slack between the brake pad and the corresponding counterpart, for example a brake disc, is kept at a minimum.

[0048] FIGS. 3 to 5 show a locking unit 43 of the brake actuator 1. The tooth wheel 31 has at least one, and preferably a plurality of teeth 47 that are dedicated to providing a locking function for the belt drive 27. This is realized by trigger 51 that is pivotably mounted in the drive head 17 and held by a holder 55. Preferably, the trigger 51 comprises a visible pivot point. The trigger 51 is configured to rotate around the pivot point, and is preferably actuated by an electromagnetic actuator 53. The locking unit 43 prevents an unwanted backward rotation of spindle 21 (see FIG. 2) and tooth wheel 31 after parking force application. The trigger 51 is shown in a locked position in which it engages a recess 45 between two adjacent teeth 47.

[0049] When the driver wants to release the parking brake, the electromagnetic actuator 53 is actuated and the trigger 51 is moved from the locked position, preferably in outward direction away from tooth wheel 31, into a release position. Due to the reaction force of the brake and the force of the return spring 13, and particularly due to a non-self-locking thread of the spindle, the piston 7 through the nut 23 (cf. FIG. 2) may rotate the gear in backward direction, until reaching the released position of the piston. This movement can also be (if needed, e.g. to speed up this process) assisted by backward rotation of the electric motor 3.

[0050] To mechanically release the parking brake, the trigger 51 is equipped with a latch (51a, FIG. 4) which can be pressed-in from the outside of the brake actuator 1 (using e.g. screwdriver or some other thin and long tool or rod) through an access hole 57 communicating with the outside of the drive head 17. This action generates a rotation of the trigger 51 in the same way as it was done by the electromagnetic actuator, but with mechanical (human) force instead of electricity.

[0051] FIG. 5 shows the access hole 57 on the external surface of drive head 17. In regular truck usage this hole should be covered (by e.g. rubber plug) to prevent the contamination ingress into the gear mechanism, and removed if mechanical release action is necessary.

[0052] Overall, the Figs. of the preferred embodiment described herein above show a very compact design of an electric brake actuator which can serve multiple purposes, the parking brake function among others.

[0053] While the above description constitutes the preferred embodiments of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.

LIST OF REFERENCE SIGNS (PART OF DESCRIPTION)

[0054] 1 brake actuator [0055] 3 electric motor [0056] 5 housing [0057] 7 piston [0058] 8 inside wall, housing [0059] 9 first chamber (pressure chamber) [0060] 11 second chamber (non-pressure chamber) [0061] 13 return spring [0062] 15 bolt [0063] 17 drive head [0064] 19 screw drive [0065] 21 spindle [0066] 23 nut [0067] 25 guide element [0068] 27 belt drive [0069] 29 toothed pinion [0070] 31 toothed wheel [0071] 33 toothed belt [0072] 35 end face [0073] 37 seal [0074] 39 check valve [0075] 41 port [0076] 43 locking unit [0077] 45 recess [0078] 47 tooth [0079] 51 trigger [0080] 51a latch [0081] 53 electromagnetic actuator [0082] 57 access hole [0083] 100 brake system [0084] 101 brake mechanism [0085] 102 brake pad [0086] 103 wear sensor [0087] 105 electronic control unit [0088] A rotational axis, electric motor [0089] R rotational axis, screw drive [0090] S stroke axis [0091] angle