Motorized piston-cylinder device for a braking system of a vehicle and method for operating a braking system of a vehicle with a motorized piston-cylinder device

Abstract

Motorized piston-cylinder device (10) for a braking system of a vehicle comprising: a motor (12); and a housing (14) with a control pressure chamber (16) formed therein and a compensation chamber (18) formed therein, between which a piston (20) is adjustably arranged; wherein a first opening (28) on the actuating pressure chamber (16) is designed such that the actuating pressure chamber (16) can be or is hydraulically connected to at least one wheel brake cylinder of the brake system via at least one line (30) that can be or is connected to the first opening (28), and wherein the piston (20) is adjustable by means of operation of the motor (12) such that brake fluid can be displaced from the actuating pressure chamber (16) via the first opening (28) to the at least one wheel brake cylinder, characterized in that in the housing (14) there is additionally formed a return chamber (22) which is delimited by an adjustable counter-piston (24) which is connected to the piston (20) via at least one spring (26) extending through the compensation chamber (18), wherein a second opening (34) on the return chamber (22) is designed such that the return chamber (22) can be or is hydraulically connected to the at least one wheel brake cylinder and / or at least one storage chamber of the brake system which is hydraulically connected to the at least one wheel brake cylinder via at least one further line (36) which can be or is connected to the second opening (34) in such a way that brake fluid can be sucked from the at least one wheel brake cylinder and / or the at least one storage chamber into the return chamber (22).

Description

[0001] The invention relates to a motorized piston-cylinder device for a braking system of a vehicle. The invention also relates to a hydraulic unit for a braking system of a vehicle and a braking system for a vehicle. Furthermore, the invention relates to a method for operating a braking system of a vehicle with a motorized piston-cylinder device. State of the art

[0002] A motorized piston-cylinder device according to the features of the preamble of claim 1 is already known from DE 10 2011 080 312 A1. This differs from the invention in that it does not have an additional counter-piston and thus, in particular, no counter-piston connected to the piston via at least one spring extending through the compensation chamber.

[0003] The latter also applies to the subject matter disclosed in DE 10 2009 055 244 A1.

[0004] DE 102011 004 140 A1 also describes a braking system and a method for regulating pressure in the braking system. The braking system comprises a piston-cylinder unit, referred to as a compensating device, with two chambers formed in a common bore of a housing. A piston, adjustable by a motor, is arranged between the two chambers. The first chamber, whose volume can be adjusted by the piston, is connected to the wheel brake cylinders via lines to receive brake fluid. Disclosure of the invention

[0005] The invention provides a motorized piston-cylinder device for a braking system of a vehicle having the features of claim 1, a hydraulic unit for a braking system of a vehicle having the features of claim 6, a braking system for a vehicle having the features of claim 7 and a method for operating a braking system of a vehicle having a motorized piston-cylinder device having the features of claim 8. Advantages of the invention

[0006] The present invention expands the functions that can be performed by a motorized piston-cylinder device. The motorized piston-cylinder device according to the invention can be used not only to build up brake pressure in at least one wheel brake cylinder, but can also be used to reduce brake pressure in the at least one wheel brake cylinder and / or to empty at least one storage chamber hydraulically connected to the at least one wheel brake cylinder. In particular, when using the motorized piston-cylinder device according to the invention, the fact that, in order to build up brake pressure, the actuating pressure chamber automatically "pulls up" the (active) return chamber by adjusting the piston, which thus provides the same volume as the provided brake volume, can be advantageously utilized.Thus, by means of a simple release of a hydraulic connection between the at least one wheel brake cylinder and / or the at least one storage chamber and the return chamber, the brake fluid volume to be transferred for pressure build-up / emptying can be automatically sucked into the return chamber.

[0007] The advantageous multifunctionality of the motorized piston-cylinder device according to the invention supports the development of an integrated braking system. At the same time, the motorized piston-cylinder device fulfills the pressure build-up function of a brake booster, such as an electromechanical brake booster.

[0008] The present invention eliminates the need to equip a braking system with at least one return pump. This allows the driver to reliably brake their vehicle without having to endure the disadvantages of a conventional return pump, such as noise pollution from pump noise and / or vibration / pulsation of the brake pedal.

[0009] In an advantageous embodiment, a third opening on the control pressure chamber and a fourth opening on the return chamber are configured such that the control pressure chamber is hydraulically connected to the return chamber via at least one intermediate line that is connectable or connectable between the third opening and the fourth opening, and brake fluid can be drawn from the return chamber into the control pressure chamber. This makes it easy to return the piston (to its initial position) after a pressure buildup by emptying the return chamber while simultaneously filling the control pressure chamber.

[0010] Advantageously, the motorized piston-cylinder device comprises a first valve, via which the first opening on the actuating pressure chamber can be selectively sealed or opened, and / or the motorized piston-cylinder device comprises a second valve, via which the second opening on the return chamber can be selectively sealed or opened. By opening the first valve, a pressure build-up can be specifically brought about in the at least one wheel brake cylinder while simultaneously adjusting the piston. By closing the first valve, an undesirable shift of brake fluid from the at least one wheel brake cylinder into the actuating pressure chamber can be prevented. Likewise, by opening the second valve, brake fluid can be sucked from the at least one wheel brake cylinder and / or the at least one storage chamber into the return chamber.The suction process can be reliably stopped / terminated by closing the second valve.

[0011] Additionally, the motorized piston-cylinder device can comprise a third valve, via which the third opening in the control pressure chamber can be selectively sealed or opened, and / or a fourth valve, via which the fourth opening in the return chamber can be selectively sealed or opened. This also allows for reliable control of the brake fluid transfer between the control pressure chamber, the return chamber, and an optionally connected brake fluid reservoir.

[0012] In an advantageous development, the motorized piston-cylinder device comprises an integrated simulator, whose simulator chamber and spring chamber, with at least one simulator spring, are formed in a common bore with the actuating pressure chamber, the compensation chamber, and the return chamber. By integrating the simulator into the motorized piston-cylinder device, the installation space required for a braking system equipped with it can be reduced.

[0013] The advantages described above are also ensured in a hydraulic unit for a braking system of a vehicle with a corresponding motorized piston-cylinder device.

[0014] Furthermore, the advantages mentioned are also realized in a braking system for a vehicle with a corresponding motorized piston-cylinder device and / or such a hydraulic unit.

[0015] Furthermore, the described advantages can be realized by implementing the method for operating a braking system of a vehicle with a motorized piston-cylinder device. The method can be further developed according to the above-described embodiments of the motorized piston-cylinder device. Short description of the drawings

[0016] Further features and advantages of the present invention are explained below with reference to the figures. They show: Fig. 1 is a schematic representation of an embodiment of the motorized piston-cylinder device; Fig. 2 a schematic representation of an embodiment of the braking system; and Fig. 3 a flowchart for explaining an embodiment of the method for operating a braking system of a vehicle with a motorized piston-cylinder device. Embodiments of the invention

[0017] Fig. 1 shows a schematic representation of an embodiment of the motorized piston-cylinder device.

[0018] The Fig. The motorized piston-cylinder device 10 schematically illustrated in Figure 1 can be used in a braking system of a vehicle, such as an ABS / ASR / ESP braking system. However, it should be noted that the applicability of the motorized piston-cylinder device 10 is not limited to a specific braking system type.

[0019] The motorized piston-cylinder device 10 comprises a motor 12 and a housing 14 with a control pressure chamber 16 and a compensation chamber 18 formed therein, between which a piston 20 is adjustably arranged. Furthermore, a return chamber 22 is additionally formed in the housing 14, which is delimited by an adjustable counter-piston 24, which is adjustably arranged between the return chamber 22 and the compensation chamber 18. The counter-piston 24 is connected to the piston 20 via at least one spring 26 extending through the compensation chamber 18.

[0020] A first opening 28 is formed on the actuating pressure chamber 16 such that the actuating pressure chamber 16 is hydraulically connectable or connected to at least one wheel brake cylinder (not shown) of the braking system via at least one line 30 that is connectable or connected to the first opening 28. The piston 20 is adjustable at least in an adjustment direction 32 by operation of the motor 12 such that a first volume of the actuating pressure chamber 16 delimited by the piston 20 can be reduced. In this way, brake fluid can be displaced from the actuating pressure chamber 16 via the first opening 28 (and the at least one line 30 connected thereto) to / into the at least one wheel brake cylinder. By operating the motor 12, a brake pressure present in the at least one wheel brake cylinder can thus be increased (in particular independently / decoupled from a driver's braking application).The motorized piston-cylinder device 10 thus reliably fulfills the function of a brake booster (or an external power brake).

[0021] A second opening 34 is formed on the return chamber 22 such that the return chamber 22 can be or is hydraulically connected to the at least one wheel brake cylinder and / or to at least one accumulator chamber of the brake system hydraulically connected to the at least one wheel brake cylinder via at least one further line 36 that can be or is connected to the second opening 34. A brake pressure buildup in the at least one wheel brake cylinder by adjusting the piston 20 in the adjustment direction 32, while simultaneously blocking the hydraulic connection (established by means of the at least one further line 36 between the return chamber 22 and the at least one wheel brake cylinder and / or the at least one accumulator chamber), keeps a second volume of the return chamber 22 constant, thus enlarging the compensation chamber 18 while simultaneously tensioning the at least one spring 26.This process can also be described as the automatic opening of the return chamber 22 when brake pressure builds up. A subsequent release of the hydraulic connection realized by means of the at least one further line 36 causes brake fluid to be (automatically) sucked into the return chamber 22 from the at least one wheel brake cylinder and / or the at least one storage chamber. The return chamber 22 can thus also be described as an active return chamber 22, which (in a closed braking system) takes on the function of a conventional return pump. A braking system equipped with the piston-cylinder device 10 therefore does not require a return pump. Instead, return can be carried out by means of the piston-cylinder device 10 without pump noise and / or pulsations / vibrations occurring on the brake pedal.The integration of the return pump functionality realized in the motorized piston-cylinder device 10 can also reduce the installation space required by the braking system equipped with it, as the mounting volume for at least one return pump and its motor, which would otherwise be required, is eliminated. Furthermore, the motorized piston-cylinder device 10 combines ABS functionality with that of a brake booster.

[0022] In the embodiment of the Fig. 1, the motorized piston-cylinder device 10 also has a third opening 38 on the control pressure chamber 16 and a fourth opening 40 on the return chamber 22. The openings 38 and 40 are designed such that the control pressure chamber 16 can be or is hydraulically connected to the return chamber 22 via at least one intermediate line 42 that can be or is connected between the third opening 38 and the fourth opening 40. Thus, brake fluid can be drawn from the return chamber 22 into the control pressure chamber 16 via the openings 38 and 40 and the at least one connected intermediate line 42. To build up brake pressure in the at least one wheel brake cylinder, the piston 20 can thus be adjusted from an initial position along the adjustment direction 32 by operating the motor 12.Openings 28 and 40 can be used to return the piston 20 while simultaneously reducing the size of the return chamber 22 and correspondingly increasing the size of the control pressure chamber 16. Thus, the piston 20 can be returned to its initial position even without operating the motor 12. The motor 12 therefore only needs to be operable in one direction of rotation. This allows the motorized piston-cylinder device 10 to be equipped with a comparatively cost-effective motor 12.

[0023] Advantageously, the motorized piston-cylinder device 10 can have a (built-in / inserted) first valve 44, via which the first opening 28 on the actuating pressure chamber 16 can be selectively sealed or opened. Accordingly, the motorized piston-cylinder device 10 can also have a (built-in / inserted) second valve 46, via which the second opening 34 on the return chamber 22 can be selectively sealed or opened. As an alternative to valves 44 and 46 built into / inserted in the motorized piston-cylinder device 10, at least one corresponding valve 44 and 46 can also be inserted in the at least one line 30 and / or in the at least one further line 36 for controlling the desired brake fluid displacements between the motorized piston-cylinder device 10 and the at least one wheel brake cylinder, or the at least one storage chamber.

[0024] In addition, the motorized piston-cylinder device 10 can have a (built-in / inserted) third valve 48, via which the third opening 38 on the control pressure chamber 16 can be selectively sealed or opened. Furthermore, a (built-in / inserted) fourth valve 50 can be present at the fourth opening 40 of the return chamber 22, via which the fourth opening 40 can be selectively opened or closed. As an alternative to built-in / inserted valves 48 and 50, however, at least one corresponding valve 48 or 50 can also be used in the at least one intermediate line 42 to ensure or prevent a transfer of brake fluid from the return chamber 22 into the control pressure chamber 16.

[0025] The at least one valve 44 to 50 can, for example, be a separating valve. Alternatively, a continuously adjustable / continuously controllable valve can also be used for the at least one valve 44 to 50.

[0026] The advantages of the motorized piston-cylinder device 10 are also ensured in a hydraulic unit for a braking system of a vehicle equipped therewith.

[0027] Fig. 2 shows a schematic representation of an embodiment of the braking system.

[0028] The Fig. The braking system for a vehicle schematically illustrated in Figure 2 is equipped with a further development of the motorized piston-cylinder device 10 described above. As in the above description, the control pressure chamber 16, the compensation chamber 18, the (active) return chamber 22, together with the pistons 20 and 24, are formed in a common bore 52 of the housing 14. However, the bore 52 is divided by a fixed partition 54, on the first side of which the chambers 16, 18, and 22 are located. Integrated into the part of the bore 52 located on the second side of the fixed partition 54 is a simulator having a simulator chamber 56 and a spring chamber 58 with at least one simulator spring 60. Between the simulator chamber 56 and the spring chamber 58 is a simulator piston 62, which is supported by the fixed partition 54 by means of the at least one simulator spring 60.

[0029] The motorized piston-cylinder device 10 thus fulfills the functions of a simulator in addition to the functions of brake pressure boosting and return already explained above. For this purpose, the simulator chamber 56 is connected to at least one pressure chamber of a master brake cylinder 66 of the braking system via at least one first isolating valve 64. Opening the first isolating valve 64 ensures that the driver displaces brake fluid into the simulator chamber 56 by actuating a brake actuation element 68 connected to the master brake cylinder 66, such as a brake pedal 68. At the same time, the wheel brake cylinders (not shown) can be hydraulically decoupled from the at least one pressure chamber of the master brake cylinder 66 by closing a second isolating valve 68. The driver thus no longer brakes into the wheel brake cylinders.The brake pressure present in the wheel brake cylinders can thus be adjusted independently of the driver's actuation of the brake actuation element 68. For example, this can be used to convert the vehicle's kinetic energy into electrical energy by operating a generator during the braking process requested by the driver. If the generator cannot be used for regenerative braking, the brake pressure present in the wheel brake cylinders can be increased by operating the motor 12 to adjust the piston 20 in the adjustment direction 32.Despite the hydraulic decoupling of the driver from the wheel brake cylinders, it is still ensured that the driver has an advantageous / standard brake actuation feeling (pedal feeling) in that the brake fluid displaced into the simulator chamber 56 enables its volume increase and thus an adjustment of the simulator piston 62 under compression of at least one simulator spring 60.

[0030] Preferably, the first isolation valve 64 is designed as a normally closed valve, while the second isolation valve 68 is a normally open valve. During a fallback level, the simulator chamber 56 is hydraulically decoupled from the master brake cylinder 66, and the second isolation valve 68 opens. Even in the event of a vehicle electrical system failure, the driver still has the option of applying the brakes to all wheel brake cylinders via the master brake cylinder 66 and thus bringing the vehicle to a safe stop using the driver's braking force.

[0031] The braking system of the Fig. 2 also has the valves 44 to 50 inserted into the piston-cylinder device 10 or arranged separately therefrom. Via the first valve 44, the control pressure chamber 16 is connected to the wheel inlet valves 70, via which a brake fluid transfer, schematically represented by the arrows 72, from the control pressure chamber 16 into at least one of the wheel brake cylinders can be controlled. Via the second valve 46, the return chamber 22 is connected to the wheel outlet valves 74, which can be used to release a brake fluid transfer, schematically represented by the arrows 76, from at least one of the wheel brake cylinders into the return chamber 22. Due to the fact that the braking system is equipped with the wheel inlet valves 70 and the wheel outlet valves 74, a brake pressure build-up or a brake pressure reduction can be carried out optionally for each wheel in the wheel brake cylinders.However, it should be noted that equipping the braking system with the wheel inlet valves 70 and the wheel outlet valves 74 is merely an example. The piston-cylinder device 10 can also be used in a braking system without wheel inlet valves 70 and without wheel outlet valves 74.

[0032] Via the valves 48 and 50, the control pressure chamber 16 and the return chamber 22 are also connected to an intake line 80 connected to a brake fluid reservoir 78, which opens into the at least one intermediate line 42. As schematically represented by the arrows 82, a brake fluid exchange is thus also possible between the brake fluid reservoir 78 (with the atmospheric pressure present therein) and the control pressure chamber 16, or the return chamber 22.

[0033] Optionally, the brake system can also have at least one pre-pressure sensor 84 and / or at least one pressure sensor 86. Likewise, at least one brake actuation element sensor 88, such as a pedal travel sensor, a rod travel sensor, a differential travel sensor, a brake force sensor, and / or a brake pressure sensor, can be installed on or in the brake system. However, equipping the brake system with the sensors 84 to 88 listed here is optional.

[0034] For example, a rapid braking logic can be implemented in the braking system by keeping the second isolation valve 68 open during the first milliseconds of a braking operation in order to build up system pressure using the driver's braking force. Only after the first milliseconds of the braking operation is the second isolation valve 68 closed, and the piston-cylinder device 10 assumes the pressure position by operating the motor 12 and the corresponding adjustment of the piston 20. It is again pointed out that during the pressure position / brake pressure boosting carried out by the piston-cylinder device 10, an "active reservoir" of the return chamber 22 is drawn up, which corresponds to a volume of the brake fluid displaced for the brake pressure buildup. From the closing of the second isolation valve 68 and a simultaneous opening of the first isolation valve 64, the driver brakes into the simulator chamber 46.During this phase, the brake pressure is built up / reduced exclusively by means of the piston-cylinder device 10.

[0035] Fig. 3 shows a flowchart for explaining an embodiment of the method for operating a braking system of a vehicle with a motorized piston-cylinder device.

[0036] The method described below can be carried out, for example, using the piston-cylinder device described above, a further development thereof, or a braking system equipped therewith. However, it should be noted that the feasibility of the method is not limited to the use of the previously described embodiments. Instead, the method can be carried out using one of a variety of different motorized piston-cylinder devices, which have a motor and a housing with a control pressure chamber formed therein, a compensation chamber formed therein, and a return chamber formed therein, wherein a piston adjustable by means of the motor is arranged between the control pressure chamber and the compensation chamber, and the return chamber is delimited by an adjustable counter-piston which is connected to the piston via at least one spring extending through the compensation chamber.

[0037] In a method step S1 of the method, the piston is adjusted by operating the motor to increase the brake pressure in at least one wheel brake cylinder of the brake system. This occurs in such a way that brake fluid is displaced from the actuating pressure chamber to the at least one wheel brake cylinder via at least one line connected to a first opening of the actuating pressure chamber.

[0038] In a method step S2, the at least one wheel brake cylinder and / or at least one accumulator chamber of the brake system hydraulically connected to the at least one wheel brake cylinder is emptied. This occurs by opening a hydraulic connection between a second opening on the return chamber and the at least one wheel brake cylinder and / or the at least one accumulator chamber. In this way, brake fluid is drawn from the at least one wheel brake cylinder and / or the at least one accumulator chamber into the return chamber via at least one additional line connected to the second opening. In particular, an ABS function can be executed / supported by means of method step S2.

[0039] For example, to release the hydraulic connection between the second opening on the return chamber and the at least one wheel brake cylinder and / or the at least one storage chamber, at least one valve arranged in or adjacent to the second opening can be opened. By closing the at least one valve arranged in or adjacent to the second opening, the hydraulic connection can be interrupted and method step S2 can be suspended / terminated. The other valves described above can also be used to carry out the method.

[0040] Optionally, a further method step S3 can be performed to return the piston (to its initial position prior to the execution of method step S1). For this purpose, a further hydraulic connection between a third opening in the control pressure chamber and a fourth opening in the return chamber is opened in such a way that brake fluid is drawn from the return chamber into the control pressure chamber via at least one intermediate line connected between the third opening and the fourth opening of the return chamber.

[0041] Regarding the further possible procedural steps of the procedure, reference is made to the above explanations.

Claims

[1] Motorized piston-cylinder device (10) for a braking system of a vehicle comprising: a motor (12); and a housing (14) with a control pressure chamber (16) formed therein and a compensation chamber (18) formed therein, between which a piston (20) is adjustably arranged; wherein a first opening (28) on the actuating pressure chamber (16) is designed such that the actuating pressure chamber (16) can be or is hydraulically connected to at least one wheel brake cylinder of the brake system via at least one line (30) that can be or is connected to the first opening (28), and wherein the piston (20) is adjustable by means of operation of the motor (12) such that brake fluid can be displaced from the actuating pressure chamber (16) via the first opening (28) to the at least one wheel brake cylinder, characterized by , that in the housing (14) there is additionally formed a return chamber (22) which is delimited by an adjustable counter-piston (24) which is connected to the piston (20) via at least one spring (26) extending through the compensation chamber (18), wherein a second opening (34) on the return chamber (22) is designed such that the return chamber (22) can be or is hydraulically connected to the at least one wheel brake cylinder and / or at least one storage chamber of the brake system which is hydraulically connected to the at least one wheel brake cylinder via at least one further line (36) which can be or is connected to the second opening (34) in such a way that brake fluid can be sucked from the at least one wheel brake cylinder and / or the at least one storage chamber into the return chamber (22). [2] Motorized piston-cylinder device (10) according to claim 1, wherein a third opening (38) on the control pressure chamber (16) and a fourth opening (40) on the return chamber (22) are designed such that the control pressure chamber (16) can be or is hydraulically connected to the return chamber (22) via at least one intermediate line (42) that can be or is connected between the third opening (38) and the fourth opening (40), and brake fluid can be sucked from the return chamber (22) into the control pressure chamber (16). [3] Motorized piston-cylinder device (10) according to claim 1 or 2, wherein the motorized piston-cylinder device (10) comprises a first valve (44) via which the first opening (28) on the actuating pressure chamber (16) can be selectively sealed or opened, and / or the motorized piston-cylinder device (10) comprises a second valve (46) via which the second opening (34) on the return chamber (22) can be selectively sealed or opened. [4] Motorized piston-cylinder device (10) according to claim 2 or 3, wherein the motorized piston-cylinder device (10) comprises a third valve (48) via which the third opening (38) on the actuating pressure chamber (16) can be selectively sealed or opened, and / or the motorized piston-cylinder device (10) comprises a fourth valve (50) via which the fourth opening (40) on the return chamber (22) can be selectively sealed or opened. [5] Motorized piston-cylinder device (10) according to one of the preceding claims with an integrated simulator, the simulator chamber (56) and spring chamber (58) of which are formed with at least one simulator spring (60) in a common bore (52) with the actuating pressure chamber (16), the compensation chamber (18) and the return chamber (22). [6] Hydraulic unit for a braking system of a vehicle with a motorized piston-cylinder device (10) according to one of the preceding claims. [7] Braking system for a vehicle with a motorized piston-cylinder device (10) according to one of claims 1 to 5 and / or a hydraulic unit according to claim 6. [8] Method for operating a braking system of a vehicle with a motorized piston-cylinder device (10) with a motor (12) and a housing (14) with a control pressure chamber (16) formed therein, a compensation chamber (18) formed therein and a return chamber (22) formed therein, wherein a piston (20) adjustable by means of the motor (12) is arranged between the control pressure chamber (16) and the compensation chamber (18), and wherein the return chamber (22) is delimited by an adjustable counter-piston (24) which is connected to the piston (20) via at least one spring (26) extending through the compensation chamber (18), comprising the steps: Increasing a brake pressure in at least one wheel brake cylinder of the brake system by adjusting the piston (20) by means of an operation of the motor (12) such that brake fluid is displaced from the actuating pressure chamber (16) via at least one line (30) connected to a first opening (28) of the actuating pressure chamber (16) to the at least one wheel brake cylinder (S1); and Emptying the at least one wheel brake cylinder and / or at least one storage chamber of the brake system hydraulically connected to the at least one wheel brake cylinder by releasing a hydraulic connection between a second opening (34) on the return chamber (22) and the at least one wheel brake cylinder and / or the at least one storage chamber such that brake fluid from the at least one wheel brake cylinder and / or the at least one storage chamber is sucked into the return chamber (22) via at least one further line (36) connected to the second opening (34) (S2). [9] Method according to claim 8, wherein in order to release the hydraulic connection between the second opening (34) on the return chamber (22) and the at least one wheel brake cylinder and / or the at least one storage chamber, at least one valve (46) is opened which is arranged in or adjacent to the second opening (34). [10] Method according to claim 8 or 9, wherein the piston (20) is moved back by opening a further hydraulic connection between a third opening (38) on the actuating pressure chamber (16) and a fourth opening (40) on the return chamber (22) in such a way that brake fluid is sucked from the return chamber (22) into the actuating pressure chamber (16) via at least one intermediate line (42) connected between the third opening (38) and the fourth opening (40) of the return chamber (22).

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