ELECTROMECHANICAL BRAKE ACTUATOR FOR ELECTROMECHANICAL BRAKE ARRANGEMENT

Abstract

An electromechanical brake actuator (100) is configured to move a service-brake rod (104) between a full-braking position (BP) and a drive position (DP). A parking-brake rod (112) is coupled to the service-brake rod and is movable between a first position (P1) for locking the service-brake rod (104) in the full-braking position (BP), and a second position (P2) where the service-brake rod (104) is free to be moved. A spring element (116) coupled to the parking-brake rod is arranged so that in a fully-compressed state (CS) the parking-brake rod is in the second position, and in a fully-released state (RS) the parking-brake rod is in the first position. A hydraulic unit (118) is operatively coupled to the parking-brake rod and configured, based on a parking-brake signal, to lock the parking-brake rod or allow a release of the spring element to the fully-released state.

Claims

1. Electromechanical brake actuator (100, 200, 300), comprising: a service-brake unit (102) including: a service-brake rod (104), for applying a variable braking force (F) to an external caliper (502); a service-actuation unit (106) that receives receive a service-brake signal (SS) and, in dependence thereof, moves the service-brake rod (104) to a position (P) between a full braking position (BP), at which a maximum braking force (Fmax) is applied to the caliper (502), and a drive position (DP), at which no braking force (F) is applied to the caliper (502); wherein the electromechanical brake actuator (100, 200, 300) further comprises: a parking-brake unit (110), including: a parking-brake rod (112) operatively coupled to the service-brake rod (104) and movable between a first position (P1), in which the parking-brake rod (112) is arranged to lock the service-brake rod (104) in a braking position (BP), and a second position (P2) in which the service-brake rod (104) is released from the braking position (BP) and free to be moved by the service-actuation unit (106); and a parking-actuation unit (114) comprising a spring element (116) operatively coupled to the parking-brake rod (112) and arranged so that in a fully-compressed state (CS) of the spring element (116) the parking-brake rod (112) is in the second position (P2), and in a fully-released state (RS) of the spring element (116) the parking-brake rod (112) is in the first position (P1), the parking-actuation unit (114) further comprising a hydraulic unit (118) that is operatively coupled to the parking-brake rod (112) and that receives a parking-brake signal (PS) and, in dependence thereof, locks the parking-brake rod (112) at a given position, and further allows a release of the spring element (116) to the fully-released state (RS).

2. The electromechanical brake actuator (100, 200, 300) of claim 1, wherein the hydraulic unit (118) includes a hydraulic cylinder (120) including a piston chamber (121) and a piston (122) arranged inside the piston chamber (121), the piston (122) being operatively coupled to the parking-brake rod (112), wherein the hydraulic unit (118) further includes a first chamber (124) and a second chamber (126a, 126b) in fluid communication with the first chamber (124) via a fluid passage (128), and wherein an electrically controlled valve unit (132) that receives the parking-brake signal (PS) is arranged and operates to selectively block and enable a flow (f) of an hydraulic fluid (130) via the fluid passage between the first chamber (124) and the second chamber (126a, 126b).

3. The electromechanical brake actuator (200) of claim 2, wherein the hydraulic cylinder (120) is a double acting cylinder (220), wherein the first chamber (124) and the second chamber (126a) are located inside the double acting cylinder (220) and separated by the piston (122).

4. The electromechanical brake actuator (300) of claim 2, wherein the hydraulic cylinder (120) is a single-acting cylinder (320), wherein the first chamber (124) is located inside the hydraulic cylinder (120) and the second chamber (126b) is a reservoir (126b) arranged outside the hydraulic cylinder (120).

5. The electromechanical brake actuator (100) of claim 2, wherein the electrically controlled valve unit (132) includes a manifold valve (134), in particular a 2/2-way solenoid valve (134) being operable in a first state (134.1) in which a first port (134a) of the manifold valve (134) in fluid communication with the first chamber (124) is connected to a second port (134b) of the manifold valve (134) in fluid communication with the second chamber (126a, 126b) and therefore a movement of the piston (122) inside the hydraulic cylinder (120) is enabled, and a second state (134.2) in which the first port (134a) is disconnected from the second port (134b) and therefore a movement of the piston (122) inside the hydraulic cylinder (120) is hindered.

6. The electromechanical brake actuator of claim 5, wherein the first state (134.1) is an unactuated state of the manifold valve (134) and the second state (134.2) is an actuated state of the manifold valve (134).

7. The electromechanical brake actuator (100) of claim 2, wherein the hydraulic unit (118) further includes a flow-control unit (136, 138) arranged between the electrically controlled valve unit (132) and the hydraulic cylinder (120) for controlling a flow amount (f) between the first chamber (124) and the second chamber (126a, 126b).

8. The electromechanical brake actuator (100) of claim 7, wherein the flow-control unit (138) is further configured to switch between two flow resistances values (R1, R2).

9. The electromechanical brake actuator (100) of claim 8, wherein the flow-control unit (138) is configured to set a first flow resistance value (R1) to a first flow path (f1) from the first chamber (124) to the second chamber (126a, 126b) and a second flow resistance value (R2) to a second flow path (f2) from the second chamber (126a, 126b) to the first chamber (124).

10. The electromechanical brake actuator (100) of claim 1, wherein the service-actuation unit (106) is further arranged and configured to compress the spring element (116) and to drive the parking-brake rod (112) to the second position (P2).

11. The electromechanical brake actuator (100) of claim 1, wherein the hydraulic unit (118) further comprises an emergency-release unit (140, 140a, 140b) that is operatively coupled to the parking-brake rod (112) and configured to drive the parking-brake rod (112) to the second position (P2) independently of the service-actuation unit (106).

12. The electromechanical brake actuator (100) of claim 11, wherein the emergency-release unit (140, 140a, 140b) comprises an emergency-release screw (140a) for moving the parking-brake rod (112).

13. The electromechanical brake actuator (100) of claim 12, wherein the emergency-release unit (140, 140a, 140b) further comprises a manual valve actuator (140b) for controlling the hydraulic unit (118) independently of the electric parking-brake signal (PS).

14. The electromechanical brake actuator (100) of claim 1, wherein the braking position (BP) parking-brake rod (112) is arranged to lock the service-brake rod (104) in a braking position (BP) corresponding to the full braking position.

15. The electromechanical brake actuator (100, 200, 300) of claim 1, wherein the hydraulic unit (118) locks the parking-brake rod (112) at a given position when a hydraulic valve (132) of the hydraulic unit (118) is switched to a close state, and the hydraulic unit (118) allows a release of the spring element (116) when a hydraulic valve (132) of the hydraulic unit (118) is in an open state.

16. The electromechanical brake actuator (100, 200, 300) of claim 15, wherein to operate the service-brake unit, the hydraulic valve (132) is switched to the open state and the service-brake actuator unit (106) drives the service-brake rod (104) to the drive position (DP), the parking-brake rod (112) to the second position, and the spring element (116) to the compressed state, and thereafter the hydraulic valve (132) is switched to the close state, whereby the parking brake rod (112) and the spring element (116) are held in the second position and the compressed state, respectively, thereby enabling controlled movement of the service-brake rod (104) between the drive position and the brake position.

17. The electromechanical brake actuator (100, 200, 300) of claim 2, wherein the hydraulic unit (118) is switchable between an open state and a close state, wherein the close state holds the parking-brake rod (112) and the spring element (116) in their current position at the time the hydraulic unit (118) is switched to the close state, wherein the piston (122) is held in place within the hydraulic unit (118) and fluid is blocked from flowing into or out of the hydraulic unit (118).

18. The electromechanical brake actuator (100, 200, 300) of claim 17, wherein a loss of power automatically switches the hydraulic unit (118) to the open state, and the spring element (116) drives the parking-brake rod (112) toward the first position, which drives the service-brake rod (104) to the braking position and provides an emergency braking function in the absence of control from the service-brake actuator (106).

19. An electromechanical brake arrangement (500), comprising: an electromechanical brake actuator (100, 200, 300) according to claim 1; a caliper (502) connected to the service-brake rod (104) and configured to apply a braking force (F) to a brake disc (503), the amount of the braking force (F) being dependent on a position (BP, DP) of the service-brake rod (104); and a brake control unit (504) in signal communication with the service-actuation unit (106) and the parking-actuation unit (114) and configured to generate and electrically provide the service-brake signal (SS) and the parking-brake signal (PS).

20. A commercial vehicle, in particular an electric commercial vehicle (1000), comprising an electromechanical brake arrangement (500) according to claim 19, wherein a respective brake disc (503) is connected to a corresponding wheel (1002) of the vehicle (1000).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Various aspects of the present disclosure are shown in the following drawings, in which:

[0032] FIG. 1. is schematic diagram of an electromechanical braking system including an electromechanical brake actuator according to a first embodiment of the present disclosure;

[0033] FIG. 2A is a schematic diagram of a hydraulic unit for use in an electromechanical brake actuator in accordance with the present disclosure;

[0034] FIG. 2B is a schematic diagram of an alternative hydraulic unit for use in an electromechanical brake actuator in accordance with the present disclosure;

[0035] FIG. 3 is a cross sectional view of an electromechanical brake actuator according to a second embodiment of the present disclosure;

[0036] FIG. 4 is a cross sectional view of an electromechanical brake actuator according to a third embodiment of the present disclosure; and

[0037] FIG. 5 is schematic diagram of a commercial vehicle according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0038] There are known combined emergency-brake and parking brake actuator for air disc brakes. In addition to a service chamber for service brake actuation, there is an additional parking chamber for the parking brake actuation. A spring is placed in this chamber. For normal usage of a service brake, pressure is applied to the parking chamber. The spring is compressed, hence no spring-force is applied on the pushrod. A clamping or braking force is generated by pressurizing the service chamber. Without pressure applied on the parking chamber, spring expand and generates a clamping force onto the pushrod. This functionality can be used for an emergency brake and park brake functionality: The spring will apply brake forces without any pressuring/energy supply to any of the chambers. In addition to that an emergency release functionality is integrated. In case of failure or service the spring can be compressed manually. A nut can be fastened in order to compress the spring. By this the brake is released manually.

[0039] The electromechanical brake actuator of the present disclosure offers an increased functionality similar to that of air-disc brakes, without the need to use a pneumatic system.

[0040] FIG. 1 shows a schematic diagram of an electromechanical braking system 500 including an electromechanical brake actuator 100 operatively coupled to a caliper 502 and controlled by a brake control unit 504 according to aspects of the present disclosure.

[0041] The electromechanical brake actuator 100 includes a service-brake unit 102 and a parking-brake unit 110. The service-brake unit 102 includes a service-brake rod 104 arranged and configured to apply a variable braking force F to the caliper. The service-brake rod 104 is actuated by a service-actuation unit 106 that is configured to receive a service-brake signal SS from the brake control unit and in dependence thereof, to move the service-brake rod 104 to a corresponding position P between a full braking position BP and a drive position DP. The full braking position is that position P at which a maximum braking force Fmax is applied to the caliper 502 and the drive position DP, at which a minimum, preferably no braking force F, is applied to the caliper 502. The service-actuation unit 106 may include a pinion-and-rack system for moving the service-brake rod 104. For instance, a rack element 109 is attached to the service-brake rod 104 and a pinion 108, driven for example by an electromotor (see FIG. 3 or 4), is used to move the service-brake rod 104 to the intended position indicated by the service-brake signal SS. The service-brake signal SS may for instance depend on a duration during which a braking pedal is pressed by the driver and/or on a force amount applied to the braking pedal. When the pressure or force amount applied to the pedal is reduced, the service-actuation unit moves the service-brake rod 104 towards the drive position DP and the amount of braking force applied F to the caliper 502 is reduced.

[0042] The electromechanical brake actuator 100 also includes a parking-brake unit 110, which includes a parking-brake rod 112 and a parking-actuation unit 114. The parking-brake rod 112 is operatively coupled to the service-brake rod 104 and is movable between a first position P1, in which the parking-brake rod 112 is arranged to lock the service-brake rod 104 in a braking position, preferably the full braking position BP, and a second position P2 in which the service-brake rod 104 is released from the braking position BP and free to be moved by the service-actuation unit 106. Thus, when the parking-brake rod 112 is in the second position P2, the service-brake rod 104 is free to be moved by the service-actuation unit 106 to any position P between the full-braking position BP and the drive position DP. When the parking-brake rod 112 is in the first position P1, the service-brake rod 104 is forced to be at the braking position, which is preferably the full-braking position BP. In this case, the service-brake rod 104 cannot be moved by the service-actuation unit. In embodiments where the braking position at which the service-brake rod 104 is forced when the parking-braking rod 112 is in the first position P1 is not the full-braking position FB, the service-braking rod may be movable by the service-actuation unit 106 to any position between the full braking position FB and the braking position. The service-actuation unit 106 is optionally further arranged and configured to compress the spring element 116 and to drive the parking-brake rod 112 to the second position P2.

[0043] In FIG. 1 the service-brake rod 104 and the parking-brake rod 112 are arranged longitudinally along a common longitudinal direction L. However, in alternative embodiments (not shown), the service-brake rod 104 is arranged in a direction different from a direction in which the parking-brake rod 112 is aligned.

[0044] The parking-brake unit 110 also includes a parking-actuation unit 114 for actuating the parking-brake rod 112. The parking-actuation unit 114 includes a spring element 116 that is operatively coupled to the parking-brake rod 112. The spring element 116 is arranged so that in a fully-compressed state CS of the spring element 116, the parking-brake rod 112 is in the second position P2, and in a fully-released state RS of the spring element 116, the parking-brake rod 112 is in the first position P1. The parking-actuation unit 114 further comprises a hydraulic unit 118 that is operatively coupled to the parking-brake rod 112 and configured to receive a parking-brake signal PS, for instance, from the brake control unit 504, for example in response to the driver actuating a parking-brake interface (not shown). In dependence on the received parking-brake signal PS, the hydraulic unit 118 is configured to lock the parking-brake rod 112 at a given current position, or to allow a release of the spring element 116 to the released state RS.

[0045] In the exemplary electromechanical brake actuator 100, the hydraulic unit 118 includes a hydraulic cylinder 120 including a piston chamber (121, see FIG. 3 or 4) and a piston 122 that is arranged inside the piston chamber 121. The piston 122 is operatively coupled to the parking-brake rod 112. The hydraulic unit 118 further includes a first chamber 124 and a second chamber. In a particular embodiment, as shown in FIG. 1, the second chamber 126a is inside the piston chamber 121. In an alternative embodiment, shown in FIG. 1 with a dotted line, the second chamber 126b is located outside the piston chamber 121. Thus, in the former case, the hydraulic cylinder 120 is a double acting cylinder wherein the first chamber 124 and the second chamber 126a are located inside the piston chamber 121 and separated by the piston 122. In the latter case, the hydraulic cylinder 120 is a single-acting cylinder, wherein the first chamber 124 is located inside the hydraulic cylinder 120 and the second chamber 126b is arranged outside the hydraulic cylinder 120.

[0046] The first chamber 124 and the second chamber 126a, 126b are in fluid communication via a fluid passage 128. An electrically controlled valve unit 132 is configured to receive the parking-brake signal PS and it is arranged and configured to control, i.e., to block and enable, a flow f of a hydraulic fluid 130 via the fluid passage 128 between the first chamber 124 and the second chamber 126a, 126b.

[0047] Typically the first chamber 124, whose volume depends on the position of the piston 122 is filled with hydraulic fluid, such as oil or any other suitable fluid. When the parking-brake rod 112 is moved from in the direction of the second position P2 (for example actuated by the service-actuation unit 106 via the service-brake rod 104), the volume of the first chamber 124 increases and hydraulic fluid 130 is drawn from the second chamber 216a, 126b for filling the added volume. This is possible only if the hydraulic unit 118 is in a state where a flow f through the fluid passage 128 is enabled. If not, the piston 122 will substantially remain at its position and the parking-brake rod 112 will practically not move in either direction, not even by the force exerted by the spring element 116. The amount of movement possible is given by the compressibility of the hydraulic fluid 130.

[0048] If the state of the hydraulic unit 118 changes and a flow f between the first chamber 124 and the second chamber 126a, 126b is enabled, the spring element 116 will be released towards its released state RS, driving the parking-brake rod 112 towards the first position P1 (and therefore the service-brake rod towards the (full) braking position). The volume of the first chamber will be reduced because the piston 122 is indirectly driven (i.e. by means of the parking-brake rod 112) by the spring element 116. The hydraulic fluid f flows out of the first chamber 124 and into the second chamber 126a, 126b.

[0049] Optionally, the hydraulic unit 118 includes a flow-control unit 136, for instance a throttle valve or a restrictor, that is arranged between the electrically controlled valve unit 132 and the hydraulic cylinder 120 and configured to control the flow amount f between the first chamber 124 and the second chamber 126a, 126b.

[0050] Also optionally, the hydraulic unit 118 further includes an emergency-release unit 140 that is operatively coupled to the parking-brake rod 112 and configured to drive the parking-brake rod 112 to the second position P2 independently of the service-actuation unit 106. In this particular example, the emergency-release unit 140 includes an emergency-release screw 140a for moving the parking-brake rod 112 and, optionally, a manual valve actuator 140b for controlling the hydraulic unit 118 independently of the electric parking-brake signal PS. For example, in the case of power loss, the electrically controlled valve unit 132 switches to an operating state in which a fluid communication between the first chamber 124 and the second chamber 126a, 126b is enabled. The compressed spring element 116 is then free to expand towards the fully-released stated RS, the parking-brake rod is moved towards the first position and the service-brake rod is locked at the (full) braking position BP. Since there is no power, the service-actuator unit 106 cannot operate the service-brake rod 104 towards the drive position DP. Should a user want to liberate the service-brake rod, he or she has the possibility to use emergency-release unit 140, for instance by actuating the emergency-release screw 140a to draw the parking-brake rod 112 from the first position P1 towards the second position P2.

[0051] In cases where the electrically controlled valve unit 132 blocks a fluid connection between the first chamber 124 and the second chamber 126a, 126b, the electrically controlled valve unit 132 may include a manual valve actuator 140b for controlling the hydraulic unit 118 independently of the electric parking-brake signal PS. Thus the state of the valve unit 132 can also be manually controlled to allow operation of the emergency-release unit 140.

[0052] In the electromechanical brake arrangement 500 of FIG. 1, the caliper 502 is connected to the service-brake rod 104 and configured to apply the braking force F to a brake disc of a vehicle (see FIG. 5). The amount of the braking force F depends on a current position P of the service-brake rod 104.

[0053] The brake control unit 504 is in signal communication with the service-actuation unit 106 and the parking-actuation unit 114 and configured to generate and provide the electric service-brake signal SS and the electric parking-brake signal PS to the service-actuation unit 106 and the parking-actuation unit 114 respectively.

[0054] Thus, FIG. 1 shows an exemplary electromechanical brake actuator 100 with a linear gear type (rack 109 and pinion 108 gear type for braking force F generation). The output shaft, i.e. a distal end of the service-brake rod 104, is designed to fulfill a linear movement along the longitudinal direction L in order to apply the braking force F, for instance, to a conventional brake caliper 502, known from former air disc brake. The combined parking brake functionality 112/114 is shown on the right-hand side of FIG. 1. As known for conventional air disc brakes, parking and emergency brake forces are generated via a spring and an additional parking brake pushrod, here referred to as parking-brake rod 112. This pushrod 112 is connected to a hydraulic unit 118 with a hydraulic cylinder 120. The cylinder 120 is controlled by the brake control unit 504 which provides a parking-brake signal PS, for controlling the spring element 116 and the valve unit 132. In order to release the parking brake, the spring 116 is to be compressed, for example via the service-actuation unit 106. To achieve this, valve unit 132 is to be switched to its open state. Afterwards, the service-actuation unit 106 is used to move both pushrods 104/112 to the right-hand side end-position, namely the drive position DP in the case of the service-brake rod 104 and the second position P2 in the case of the parking-brake rod 112. Due to this actuation via the service-actuation unit 106, this parking brake mechanism does not need a dedicated energy supply. Once the end-positions are reached, namely the drive-position DP and the second position P2, the valve unit 132 is to be switched to its close state. For parking brake functionality, a normal open valve (NO) is advantageous: In case of loss of supply of the actuator, the valve unit 132 will open automatically. The spring element 116 is released, and the braking force F is applied via spring element 116. Depending on applied safety case normal close and bi-stable valves units can be applied, too. The optional throttle valve 136 enables a smooth controlled movement of the parking-brake rod 112. A mechanism for emergency release 140 can be placed on the same parking-brake rod 112. Depending on valve type and failure mechanisms, a manual actuator 140b for the valve unit 132 can be provided. This is used to prevent a hydraulically locking of piston cylinder 120 whilst manual emergency release via known screw mechanism is performed.

[0055] FIG. 2A and FIG. 2B show respective pneumatic diagrams of a hydraulic unit for use in an electromechanical brake actuator in accordance with the present disclosure. The following discussion will be focused on those technical features that have not been discussed with respect to the hydraulic unit 118 of FIG. 1. The same reference numbers are used for those technical features that have an identical or similar function. The electrically controlled valve unit 132 of FIGS. 2A and 2B comprises a manifold valve 134, namely a 2/2-way solenoid valve 134. The 2/2-way solenoid valve is operable in an open first state 134.1 in which a first port 134a of the manifold valve 134 that is in fluid communication with the first chamber 124 (see FIG. 1) is connected to a second port 134b of the manifold valve 134 that is in fluid communication with the second chamber 126a, 126b (see FIG. 1). Therefore, in the first state 134.1, a movement of the piston 122 inside the hydraulic cylinder 120 is enabled (see FIG. 1). The 2/2-way solenoid valve is also operable in a closed second state 134.2, in which the first port 134a is disconnected from the second port 134b and therefore a movement of the piston 122 inside the hydraulic cylinder 120 is hindered (see FIG. 1). In particular, the open first state 134.1 is an unactuated state of the manifold valve 134 and the closed second state 134.2 is an actuated state of the manifold valve 134. This is advantageous because in case of a power failure, the manifold valve 134 will be automatically operated in the unactuated state thereby triggering the parking-brake functionality by driving the service-brake rod 104 to the (full) braking position BP.

[0056] Further, the manifold valves 134 of FIG. 2A and FIG. 2B are connected to a respective flow-control unit 136, 138, arranged between the electrically controlled valve unit 132 and the hydraulic cylinder 120. The flow-control units 136, 138 are configured to control a flow amount f1, f2 between the first chamber 124 and the second chamber 126a, 126b. In FIG. 2A, the flow control unit 136 is a throttle valve or restrictor 135. In FIG. 2B, the flow control unit 138 is further configured to switch between two flow resistances values R1, R2. In particular, the flow-control unit 138 is configured to set a first flow resistance value R1 to a first flow path f1 from the first chamber 124 to the second chamber 126a, 126b and a second flow resistance value R2 to a second flow path f2 from the second chamber 126a, 126b to the first chamber 124. The flow-control unit 138 comprises a first branch with a check valve 137a for blocking a flow f2 from the second chamber 126a, 126b to the first chamber 124 and a throttle valve 135 to limit said flow f1, and a second branch with a check valve 137b for blocking a flow f1 from the first chamber 124 to the second chamber 126a, 126b. Thus, the flow rates f1 and f2 are different, enabling, for example, a slower relaxation of the spring element 116 to the released state RS, which correlates to an engagement of the parking brake, and a faster (compared to the relaxation) tensioning of the spring element 116, which correlates to a release of the parking brake.

[0057] Thus, this particular mechanism can be used as a self-clamping parking brake. i.e. a parking brake designed to apply brake force to the caliper in case of power loss in the braking system.

[0058] In another embodiment (not shown), the electrically controlled valve unit comprises a bi-stable valve, wherein a parking-brake signal in the form of a pulse triggers a change in the state of the valve, which remains in said state until another pulse is provided, or, in a particular embodiment, a manual valve actuator is operated.

[0059] FIG. 3 shows a cross sectional view of an electromechanical brake actuator 200 according to a second embodiment of the present disclosure. The following discussion will be focused on those technical features that have not been discussed with respect to the electromechanical brake actuator 100 of FIG. 1. The same reference numbers are used for those technical features that have an identical or similar function. The service-brake unit 102 comprises an electromotor 105 configured to receive the service-brake signal SS, and, in dependence thereof to operate a set of gears 107 for turning a pinion 108 which cooperates with a linear rack 109 arranged on the service-brake rod 104. By operating the electromotor, the service-brake rod 104 can be moved to any position between a full braking position BP and a drive position DP, each of which is correlated to a maximum and a minimum (particularly a vanishing) braking force F that can be applied to a caliper.

[0060] A parking-brake rod 112 is operatively coupled to the service brake rod 104. It also includes a support element 115 that is arranged and configured to support the spring element 116 and to compress the spring element 116 when the parking-brake rod 112 moves towards the second position P2.

[0061] In the electromechanical brake actuator 200 of FIG. 3, the hydraulic cylinder is a double acting cylinder 220, wherein the first chamber 124 and the second chamber 126a are located inside the double acting cylinder 220 and separated by the piston 122 that is arranged within the piston chamber 121.

[0062] Alternatively, FIG. 4 shows a cross sectional view of an electromechanical brake actuator according to a third embodiment of the present disclosure. The following discussion will be focused on those technical features that have not been discussed with respect to the electromechanical brake actuators 100 and 200 of FIG. 1 and FIG. 3, respectively. The same reference numbers are used for those technical features that have an identical or similar function. In the case of the exemplary electromechanical brake actuator 300, the hydraulic cylinder is a single-acting cylinder 320, wherein the first chamber 124 is located inside the hydraulic cylinder 120 and the second chamber (not shown) is arranged outside the hydraulic cylinder 120. The second chamber is, in a particular embodiment, a reservoir.

[0063] FIG. 3 and FIG. 4 show two different embodiments of the electromechanical brake actuator of the present disclosure. The electromechanical brake actuator 200 provides a parking brake mechanism using double acting cylinder 220. For best usage of available space, the cylinder 220 is preferably integrated into the spring housing. The electromechanical brake actuator 300 of FIG. 4 provides a parking brake mechanism using single-acting cylinder 320. In this embodiment there is only one pressured hydraulic chamber inside the hydraulic cylinder 320. The design of the actuator is simplified and it also allows the integration of emergency release mechanics. As an advantage, the size of the electromechanical brake actuator can be reduced. However, an additional second chamber, such as reservoir, is to be provided, for instance, integrated in the housing.

[0064] In a particular embodiment (not shown) the elements of the flow control unit, optionally including the electrically controlled valve unit are integrated into a housing of the spring element.

[0065] Before the service brake can be applied, the parking brake mechanism, also referred to as emergency brake is to be put in operation. As described above, for the state of no energy supply, the spring element 116 is in its fully-released state RS and thus expanded. The brake is clamped because a braking force F is applied to the caliper via the service-brake rod 104. To release the brake, the valve unit 132 is switched to the open state, the service-brake rod 104 is moved to right-hand end position, i.e., towards the drive position by the service-actuation unit 106 which drives the parking-brake rod 112 towards the second position P2. Once end positions DP, P2 are reached, the valve unit 132 is switched to the close state.

[0066] FIG. 5 shows a schematic block diagram of an inventive commercial vehicle 1000 according to an embodiment of the present disclosure. The commercial vehicle 1000, in particular an electric commercial vehicle, includes an electromechanical brake arrangement 500, such as the electromechanical brake arrangement discussed with reference to FIG. 1. In the commercial vehicle 1000, a respective brake disc 503 is connected to a corresponding wheel 1002 of the vehicle 1000. The caliper 502 is actuated by the service-brake rod 104, which is configured to transfer a variable braking force F to the caliper 502, and thus to the brake disc 503.

[0067] While the service-actuation unit 106 drives the service-brake rod 104 and the parking-brake rod 112 to their respective final positions DP, P2, i.e. while the spring element 116 is being forced towards the fully-compressed state, no controlled brake force F can be applied to the wheels 1002, which can cause heavy safety issues. To avoid this, it is preferred that the wheels are to be put in operation sequentially. Starting at one wheel-end or two wheel-ends per axle the process explained above is applied. After completed, a brake force shall be applied to that particular wheel or wheel-end via service brake functionality. Now a first axle is in operation. Afterwards the same process can be applied to the next axle until all wheel-ends are in operation.

[0068] In summary, the present disclosure is directed to an electromechanical brake actuator configured to move a service-brake rod between a full-braking position and a drive position. A parking-brake rod is coupled to the service-brake rod and movable between a first position for locking the service-brake rod in the full-braking position, and a second position where the service-brake rod is free to be moved. A spring element is coupled to the parking-brake rod and arranged so that in a fully-compressed state the parking-brake rod is in the second position, and in a fully-released state, the parking-brake rod is in the first position. A hydraulic unit is operatively coupled to the parking-brake rod and configured, in dependence on a parking-brake signal, to lock the parking-brake rod, and also to allow a release of the spring element to the fully-released state.

[0069] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0070] In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality.

[0071] A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0072] Any reference signs in the claims should not be construed as limiting the scope.

REFERENCE NUMBERS (PART OF THE DESCRIPTION)

[0073] 100 Electromechanical brake actuator [0074] 102 Service-brake unit [0075] 104 Service-brake rod [0076] 105 Electromotor [0077] 106 Service-actuation unit [0078] 107 Gears [0079] 108 Pinion [0080] 109 Rack element; linear rack [0081] 110 Parking-brake unit [0082] 112 Parking-brake rod [0083] 114 Parking-actuation unit [0084] 115 Support element [0085] 116 Spring element [0086] 118 Hydraulic unit [0087] 120 Hydraulic cylinder [0088] 121 Piston chamber [0089] 122 Piston [0090] 124 First chamber [0091] 126a Second chamber; double acting cylinder [0092] 126b Second chamber; single acting cylinder [0093] 128 Fluid passage [0094] 130 Hydraulic fluid [0095] 132 Electrically controlled valve unit [0096] 134 Manifold valve; 2/2-way solenoid valve [0097] 134.1 First state of manifold valve [0098] 134.2 Second state of manifold valve [0099] 134a First port of manifold valve [0100] 134b Second port of manifold valve [0101] 135 Throttle valve; restrictor [0102] 136 Flow-control unit [0103] 137a Check valve [0104] 137b Check valve [0105] 138 Flow-control unit [0106] 140 Emergency-release unit [0107] 140a Emergency-release screw [0108] 140b Manual-valve actuator [0109] 200 Electromechanical brake actuator [0110] 220 Double acting cylinder [0111] 300 Electromechanical brake actuator [0112] 320 Single acting cylinder [0113] 500 Electromechanical braking system [0114] 502 Caliper [0115] 503 Brake disc [0116] 504 Brake control unit [0117] 1000 Commercial vehicle; electric commercial vehicle [0118] 1002 Wheel [0119] BP Full braking position of service-brake rod [0120] CS Fully compressed state of spring element [0121] DP Drive position of service-brake rod [0122] f flow [0123] f1 first flow [0124] f2 second flow [0125] F Braking force [0126] Fmax Maximum braking force [0127] L Longitudinal direction [0128] P Position [0129] P1 First position of parking-brake rod [0130] P2 Second position of parking-brake rod [0131] PS Parking-brake signal [0132] R1 First flow resistance value [0133] R2 Second flow resistance value [0134] RS Fully-released state of spring element [0135] SS Service-brake signal