Brake system and method for controlling a brake system

Abstract

A brake system may include a first pressure supply unit having an electromotive drive and arranged to supply pressure medium to first and second brake circuits; a motor-pump unit to supply pressure medium to at least one of the brake circuits; a second pressure supply unit, connected to the motor-pump unit via first and second hydraulic lines and arranged to supply pressure medium to at least one of the brake circuits; and a valve unit. The second pressure supply unit may be connected via a third hydraulic line to at least one of the brake circuits. The valve unit may include at least one feed valve via which the third hydraulic line may be at least partially reversibly shut off. An isolating valve may be disposed in at least one of the hydraulic lines to at least partially reversibly shut off the at least one hydraulic line.

Claims

1. A brake system, comprising: a first pressure supply unit, with an electromotive drive, which is configured to supply pressure medium to at least one first brake circuit and to at least one second brake circuit, a motor-pump unit configured to supply pressure medium to at least one of the brake circuits, a second pressure supply unit which is configured to supply pressure medium to least one of the brake circuits, wherein the second pressure supply unit is connected to the motor-pump unit via at least one first hydraulic line and via at least one second hydraulic line, and wherein the second pressure supply unit comprises a main brake cylinder with exactly one piston and exactly one piston chamber, wherein the main brake cylinder comprises at least one expansion bore connected to a reservoir via a hydraulic line and comprises two ring seals, wherein the at least one expansion bore is arranged between the ring seals, and wherein a throttle is arranged in the hydraulic line between the reservoir and the expansion bore, and a valve unit, wherein at least one of the brake circuits is connected to the second pressure supply unit via at least one third hydraulic line, wherein the valve unit comprises at least one feed valve via which the third hydraulic line is enabled to be at least partially reversibly shut off, and wherein an isolating valve is arranged in at least one of the hydraulic lines, via which the at least one of the hydraulic lines is enabled to be at least partially reversibly shut off.

2. The brake system according to claim 1, wherein at least one first isolating valve is arranged in the first hydraulic line, wherein the third hydraulic line and the first isolating valve are arranged in such a way that pressure medium from the second pressure supply unit passes into the second brake circuit via the first isolating valve and/or at least one second isolating valve is arranged in the second hydraulic line, wherein the second isolating valve is arranged such that a valve seat connection of the second isolating valve is hydraulically connected to the second brake circuit, and wherein the first isolating valve or the second isolating valve is a normally open valve.

3. The brake system according to claim 2, further comprising at least one third isolating valve, which is arranged and configured in such a way that in a closed state of the at least one third isolating valve, the first brake circuit is hydraulically decoupled from the first and second pressure supply unit, wherein the at least one third isolating valved is arranged such that a valve seat connection of the at least one third isolating valve is hydraulically connected to the first brake circuit, wherein the at least one third isolating valve and/or the at least one feed valve is a normally open valve.

4. The brake system according to claim 2, wherein the at least one first isolating valve is arranged in such a way that a valve seat connection of the at least one first isolating valve is hydraulically connected to the at least one second isolating valve and, via a fourth isolating valve, to the first pressure supply unit.

5. The brake system according to claim 4, wherein the first and second hydraulic line are enabled to be reversibly separated from the first pressure supply unit using the fourth isolating valve, and wherein the fourth isolating valve is arranged and designed in such a way that the first and second hydraulic line are disconnected from the first pressure supply unit in a closed state of the fourth isolating valve, and wherein the fourth isolating valve is a normally closed valve.

6. The brake system according to claim 2, wherein the third hydraulic line is connected to the first hydraulic line and, via the first isolating valve, to the second hydraulic line.

7. The brake system according to claim 2, wherein a travel simulator is provided, which is connected to the second pressure supply unit, and which includes two sealing elements.

8. The brake system according to claim 1, wherein the reservoir comprises a level sensor configured to detect a fill level of pressure medium within the reservoir, wherein a float with a magnet is arranged within the reservoir, the position of which float is enabled to be detected wirelessly, via detection of a magnetic field.

9. The brake system according to claim 8, wherein a control unit of the brake system is configured to perform a diagnosis to determine tightness of seals of the first and/or second pressure supply units, and/or to determine the existence of a leak, based on signals of the level sensor, wherein the electromotive drive of the first pressure supply unit has a redundant 3-phase electrical connection to enable actuation by a control unit.

10. The brake system according to claim 1, further comprising at least one pressure relief valve for component protection, wherein the pressure relief valve is in fluid connection with a working chamber of the first pressure supply unit.

11. The brake system according to claim 1, wherein the first hydraulic line and/or the second hydraulic line are connected to the reservoir via respective suction valves.

12. The brake system according to claim 1, further comprising an actuating element arranged on the second pressure supply unit, wherein the piston is actuatable by the actuating element.

13. The brake system according to claim 1, wherein the first pressure supply unit with a first piston-cylinder unit and the second pressure supply unit with a second piston-cylinder unit are arranged in a housing in such a way that a longitudinal axis of the first piston-cylinder unit is substantially perpendicular to a longitudinal axis of the second piston-cylinder unit.

14. A method for controlling a brake system that includes a first electromotively driven pressure supply unit arranged to supply pressure medium to at least first and second brake circuits, a motor-pump unit, a second pressure supply unit connected to the motor-pump unit via first and second hydraulic lines and arranged to supply pressure medium to at least one of the first or second brake circuits, wherein the second pressure supply unit comprises a main brake cylinder with exactly one piston and exactly one piston chamber, wherein the main brake cylinder comprises at least one expansion bore connected to a reservoir via a hydraulic line and comprises two ring seals, wherein the at least one expansion bore is arranged between the ring seals, and wherein a throttle is arranged in the hydraulic line between the reservoir and the expansion bore, the method comprising: a. providing a first pressure at a first connection point for connection to the first brake circuit; b. providing a second pressure at a second connection point for connection to the second brake circuit; c. detecting a first fault condition corresponding to a loss of pressure medium in the first brake circuit; d. closing at least a first isolating valve in response to the detection of the first fault condition, such that the first pressure supply unit is hydraulically decoupled from the first connection point.

15. The method according to claim 14, further comprising diagnosing a tightness of the first isolating valve by: closing the first isolating valve and a second isolating valve; building up pressure using the first pressure supply unit; and measuring a pressure at least over a predetermined time interval.

16. The method according to claim 14, further comprising detecting a second fault condition corresponding to an at least partial failure of an ESP unit, wherein, in response to the detection of the second fault condition, the following are performed: reading in measurement signals of the ESP unit a via at least one bus; and implementing a control strategy for valves of the ESP unit, taking into account the measurement signals.

17. The method according to claim 14, further comprising: detecting a third fault condition corresponding to failure of the first pressure supply unit and/or failure of the second brake circuit, wherein the following are performed in response to the detection of the third fault condition: controlling valves in such a way that the first brake circuit is enabled to be supplied with pressure medium from the second pressure supply unit in order to brake a first axle of a vehicle; and simultaneously actuating a vehicle electric motor on a second axle in order to brake the second axle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The foregoing summary, as well as the following detailed description of the preferred invention, will be better understood when read in conjunction with the appended drawings:

(2) FIG. 1 is a schematic circuit diagram of a first exemplary embodiment of the brake system according to the invention with two isolating valves and one feed valve;

(3) FIG. 2 is a schematic circuit diagram of a second exemplary embodiment of the brake system according to the invention with four isolating valves and one feed valve;

(4) FIG. 3 is a schematic circuit diagram of a variation of the first exemplary embodiment;

(5) FIG. 4 is a schematic circuit diagram of a further exemplary embodiment of the brake system according to the invention;

(6) FIGS. 5a and 5b are schematic side views of a structural unit of the brake system; and

(7) FIG. 6 is a schematic circuit diagram of an ESP unit.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1 shows a schematic circuit diagram of a brake system 2 comprising a first module (referred to as X-Boost) and a second module. The first modulethe X-Boosthas a first pressure supply unit 6 with an electromotive drive 8 as well as a second pressure supply unit 14 with a main brake cylinder 22 and an actuating element 26 with a brake pedal. Furthermore, a valve device with various solenoid and check valves is provided.

(9) The second module comprises an electrically driven motor-pump unit 90 (also referred to as an ESP unit) having a pump with an electromotive drive 91also referred to as a third pressure supply unit. The motor-pump unit 90 may be any ESP unit. A suitable ESP unit is described in detail in DE 10 2014 205 645 A1. Alternatively, a standard ABS unit without ESP function can be used as the second module.

(10) The two modules (X-boost and ESP unit) are set up to supply pressure medium to two brake circuits BK1 and BK2, wherein the modules are preferably connected hydraulically in series. In one exemplary embodiment, the X-Boost is attached to the bulkhead of a vehicle, to which the second module (ESP unit) is connected via hydraulic lines at two hydraulic interfaces or connection points (see thick black dots in FIG. 1 in relation to BK1, BK2).

(11) The first pressure supply unit 6 is connected to the first brake circuit BK1 or the corresponding interface via a first hydraulic line HL1. Furthermore, a second hydraulic line HL2 is provided for connecting the first pressure supply unit to the second brake circuit or the corresponding interface.

(12) In accordance with the invention, the second pressure supply unit 14 of the X-Boost has only one main brake cylinder 22 with a piston 24 and a piston chamber 23. In the exemplary embodiment, the second pressure supply unit 14 is of single-circuit design and is connected to the brake circuit BK1 or the corresponding hydraulic interface via a third hydraulic line HL3 and a feed valve 69. A fluid connection to the second hydraulic line HL2 leads via a first isolating valve BP1. The second pressure supply unit 14 can be disconnected from the brake circuits BK1, BK2 by closing the feed valve 69 in such a way that in normal brake-by-wire operation without faults (e.g., without brake circuit failure) the actuating unit 26 acts only on a travel simulator 28.

(13) In the exemplary embodiment according to FIG. 1, the brake circuits BK1 and BK2 can be isolated via the first isolating valve BP1 (preferably normally open). In accordance with the invention, in the event of a failure of the first pressure supply unit 6, the main brake cylinder 22 of the second pressure supply unit 14 can thus be connected either to the first brake circuit BK1 only or to the first and second brake circuits BK1, BK2 by opening the first isolating valve BP1. For this emergency operation, the feed valve 69 is designed as a normally open valve. If current is still applied, the valve is opened so that the second pressure supply unit 14 is no longer hydraulically decoupled from the brake circuits BK1, BK2.

(14) The first pressure supply unit 6 also optionally acts on the second brake circuit BK2 (first isolating valve BP1 closed) or both brake circuits BK1, BK2 (first isolating valve BP1 open or normally open). In normal operation, the first isolating valve BP1 is open so that the first pressure supply unit 6 supplies both brake circuits BK1, BK2 with pressure and the second pressure supply unit 14 is decoupled from the first brake circuit BK1 by the closed feed valve 69. If it is determined that volume is being lost from the brake circuits BK1, BK2, the brake circuit BK1 can be decoupled from the first pressure supply unit 6 by means of the first isolating valve BP1, so that in the event of a leak in the first brake circuit BK1, the second brake circuit BK2 can continue to be operated without loss of hydraulic medium.

(15) In the exemplary embodiment, the first isolating valve BP1 is embodied as a solenoid valve, wherein the ball seat of the isolating valve BP1 is connected via a connection (valve seat connection) to the portion of the hydraulic line that leads to the first pressure supply unit 6. This means that the first isolating valve BP1 can be reliably closed by energization even in the event of failure of the first brake circuit BK1 and is not forced open by higher pressures during operation of the first pressure supply unit 6.

(16) The second pressure supply unit 14 feeds the travel simulator 28 via an expansion hole in a wall of the main cylinder 22 when the actuating element 26 is actuated, so that a progressive haptic resistance in the form of a return force can be felt as a function of a magnitude of the actuation of the actuating element 26. The magnitude of actuation in this context is understood to be how firmly and/or how far a driver actuates the actuating element 26, which is configured as a brake pedal, and thus pushes the piston 24 into the main brake cylinder 22. Progressive haptic resistance is also referred to as pedal characteristic.

(17) A travel simulator valve 29 may be provided to shut off the connection to the travel simulator 28 (indicated in FIG. 1).

(18) The second pressure supply unit 14 has at least one expansion bore 38, which is connected to a storage container 40 via hydraulic lines. The storage container 40 is also part of the brake system 2.

(19) In the exemplary embodiment, a check valve RVHZ as well as a throttle DR may be arranged in the hydraulic line between the expansion bore and the storage container 40. By means of this check valve RVHZ as well as the first pressure supply unit 6, it is possible to perform a diagnosis of a state of preservation of sealing elements arranged within the first pressure supply unit 6 as well as within the travel simulator 28. When testing the seal of the main brake cylinder 22, the travel simulator valve 29if presentcan be closed.

(20) As shown, the main brake cylinder 22 has two sealing elements 42a, 42b, which are ring seals. The expansion bore 38 is arranged between the two sealing elements 42a, 42b. A throttle DR is arranged in the connection between the expansion bore 38, which is arranged between the two sealing elements 42a, 42b, and the storage container 40.

(21) The flow rate of the throttle DR is dimensioned so that the pedal characteristic is not significantly changed if the sealing element 42a fails (3 mm pedal travel in 10 s). In addition, a temperature-related volume compensation of the pressure medium can take place via the throttle DR.

(22) During ABS operation of the motor-pump unit 90, high pressure peaks can occur in the brake circuits BK1 and BK2, which can place a considerable load on the first pressure supply 6. A pressure relief valve V is connected to the piston chamber of the first pressure supply unit 6 via a bore in the variant according to FIG. 1, so that the high pressure peaks are reduced and damage to the system is avoided.

(23) A suction valve NV is also in fluid connection to the piston chamber of the first pressure supply unit 6 and enables the replenishment of pressure medium from the storage container 40. Thus, the first pressure supply unit 6 can independently introduce additional pressure medium into the brake circuits BK1, BK2. An additional expansion hole provided in the cylinder of the first pressure supply unit 6 enables volume compensation in the initial position of the piston of the first pressure supply unit 6.

(24) The motor-pump unit 90 is shown only schematically in FIG. 1. It ultimately supplies four wheel brakes RB1, RB2, RB3 and RB4. In the schematic diagram, the wheel brakes RB1, RB2 serve a front axle VA of the vehicle and the wheel brakes RB3 and RB4 serve a rear axle HA of the vehicle. A drive electric motor is located on the rear axle HA of the vehicle to drive the vehicle. The vehicle may be an all-electric vehicle or a hybrid vehicle.

(25) The first brake circuit BK1 is connected to the wheel brakes RB1 and RB2, and the second brake circuit BK2 is connected to the wheel brakes RB3 and RB4. For the hydraulic arrangement shown in FIG. 1, a corresponding assignment is advantageous.

(26) The motor-pump unit 90 further also includes a control unit 95 (ECU-ESP).

(27) Similarly, the second pressure supply unit 14 has a circuit board or PCB, which includes a level sensor NST that detects the position of a magnetic float NS within the storage container 40. The PCB further has sensors 30a, 30b for detecting pedal travel and a travel difference between the piston 24 and the pedal travel.

(28) To provide additional pressure medium for the motor-pump unit, a suction valve 70b is provided in the first brake circuit BK1 and connects the pump of the motor-pump unit 90 to the storage container 40.

(29) If the pump of the motor-pump unit 90 requires pressure medium for the second brake circuit BK2, this can be supplied from the storage container 40 via the suction valve 70c.

(30) Thus, the two brake circuits BK1, BK2 are each connected to the storage container 40 by their respective hydraulic lines HL1, HL2 via a suction valve 70b or 70c respectively for sucking in pressure medium. To achieve optimum suction of the pressure medium, the suction valve 70c preferably has a diameter in the range from 30 mm to 50 mm and in particular a diameter of 40 mm.

(31) Optionally, the exemplary embodiment has a control of the air clearance between brake pads and disc brake. The wheel brakes RB1, RB2, RB3, RB4 (see FIG. 1) can be designed as frictionless wheel brakes RB1, RB2, RB3, RB4. In a brake-by-wire system, disc brakes with brake pads that are spaced apart with an air clearance without pressure in the brake system allow the friction resistance to be reduced. This can be achieved by using rollback seals, return springs or by actively retracting the brake pads by generating negative pressure. Document EP 2225133 A2 describes the possibility of generating a corresponding negative pressure by means of the first pressure supply unit 6 and is hereby explicitly incorporated in respect of this disclosure.

(32) The first pressure supply unit 6 can be used to measure the air clearance in the wheel brake RB1, RB2, RB3, RB4, which varies during operation, on a wheel-specific or brake circuit-specific basis by evaluating the pressure profile. In accordance with the invention, a corresponding measurement can be carried out during servicing, but also during operation of the vehicle. Preferably, the measurement is carried out when the vehicle is stationary or after braking.

(33) With the known air clearance values of the wheel brakes RB1, RB2, RB3, RB4, the air clearance is then first quickly overcome by means of a piston travel control of the first pressure supply unit 6 when the wheel brake RB1, RB2, RB3, RB4 is activated. In this respect, the use of a brushless motor as the electromotive drive 8 of the first pressure supply unit 6 with a small time constant is preferable, since the overcoming of the air clearance can be realized without the driver noticing this when the brake is applied.

(34) In addition, the brake system 2 can be controlled so that the vehicle electric motor TM1 acts in the phase of the air clearance. Thus, a braking effect is generated immediately when the brake is applied.

(35) In one exemplary embodiment of the invention, differences in the air clearances of the wheel brakes RB1, RB2, RB3, RB4 are compensated for by controlling inlet valves of the second module (ESP unit) and/or using the electric motor of one or more vehicle axles to generate a braking effect to start braking. The air clearance can generally be used to reduce or avoid stick-slip effects of new brake systems at low speeds.

(36) In one exemplary embodiment, the brake system 2 according to the invention implements a stutter braking in the event of a failure of the ESP unit. By moving the piston of the first pressure supply unit 6 back and forth between an upper and lower pressure range, wheel locking is avoided and steerability is maintained.

(37) In one exemplary embodiment, 1-channel ABS operation is implemented additionally or alternatively. For this purpose, measurement signals such as pressure and wheel speeds can be read in via an interface to the control unit 95 of the ESP unit.

(38) The automated stutter braking results in sufficient braking distances (approximately 200% of the braking distance with ABS compared with full wheel-specific ABS) and acceptable stability by maintaining steerability. In conventional brake systems (WO 2011/098178) that offer this emergency function, actuation of the pedal can cause the wheels to lock because actuation via the brake pedal acts directly on the piston of the main brake cylinder, which is moved back and forth during the stutter braking function.

(39) The brake system according to the invention can provide this emergency function without the disadvantages of conventional systems, since the brake pedal according to one aspect of the invention acts only on piston 24 and is isolated from the brake circuits BK1, BK2 via the feed valve 69. Thus, in the brake system according to the invention, the function of the automated stutter braking cannot be disturbed by the driver.

(40) As an alternative or in addition to the stutter braking, single-channel ABS operation with select low control can be implemented. This leads to a further deterioration of the braking distance (approximately 400% braking distance compared to the braking distance with a full wheel-specific ABS), but to unrestricted vehicle stability. In accordance with the invention, measured values, e.g. pressure and wheel speed, for 1-channel ABS operation can be read in by the ESP unit 95 via an interface, e.g., CAN interface.

(41) To further increase the availability of the brake system 2 according to the invention as shown in FIG. 1, the electromotive drive 8 of the first pressure supply unit 6 is connected to the control unit 9 (ECU DV) of the X-boost via two redundant three-phase strings, and the electronics are (partially) redundant. For example, two B6 bridges can be provided for each string. Furthermore, in at least one exemplary embodiment, the electronics are connected to two redundant power supplies. In this way, the probability of failure of the electromotive drive 8 can be reduced by a factor of 4-10 and the fault condition (failure of the first pressure supply unit 6) can be further significantly reduced.

(42) The control unit of the ESP unit 95 and the control unit 9 (ECU DV) of the X booster are communicatively connected to one another via a CAN bus CAN. In this respect, it is possible to send control commands to the motor-pump unit 90 which cause actuation of the drive 91 and/or the valves provided (see also FIG. 6).

(43) With the brake system 2 according to FIG. 1, the following safety-relevant redundancies can be realized: ensuring sufficient braking effect to meet legal requirements in the event of brake circuit failure, failure of a) the second pressure supply unit 14, b) the first pressure supply unit 6 or c) first pressure supply unit 6 and the third pressure supply unit (simultaneously), i.e. also meeting legal requirements in the event of double failures: fault condition 1failure of the third pressure supply unit (motor-pump unit 90): deceleration due to brake boost via the first pressure supply unit 6 in both brake circuits BK1, BK2; fault condition 2failure of third pressure supply unit and brake circuit BK1: deceleration due to brake boost via first pressure supply unit 6, e.g., at rear axle; fault condition 3failure of the third pressure supply unit and the second brake circuit BK2: deceleration due to second pressure supply unit 14, e.g., at the front axle (first isolating valve BP1 closed) fault condition 4failure of the first pressure supply unit 6: deceleration due to brake boost via the third pressure supply unit; fault condition 5failure of the first pressure supply unit 6 and the first brake circuit BK1 or the second brake circuit BK2: deceleration by brake boost via the third pressure supply unit in one of the brake circuits BK1, BK2, possibly supported by vehicle electric motor TM1 on one axle; fault condition 6failure of the first pressure supply unit 6 and the third pressure supply unit: braking by main brake cylinder on front axle VA and optionally by drive electric motor on rear axle HA; fault condition 7failure of the vehicle electrical system: braking by second pressure supply unit 14 if necessary on front axle VA and rear axle HA; electronic braking force distribution (EBV) in the event of failure of the ESP unit by generating pressure in the first brake circuit BK1 via the third pressure supply unit and generating pressure in the second brake circuit BK2 via the first pressure supply unit 6 with the first isolating valve BP1 closed and controlling the first pressure supply unit 6 via sensors of the second pressure supply unit 14. This requires an S/W brake circuit split, i.e. the wheels of the front axle VA are connected to the first brake circuit BK1 and the wheels of the rear axle HA to the second brake circuit BK2; control of the air clearance between brake pads and disc brake; 1-channel ABS operation or realization of automated stutter braking.

(44) FIG. 2 shows an alternative embodiment of the X-booster according to FIG. 1. In contrast to the exemplary embodiment according to FIG. 1, a second isolating valve TVBK2 is provided in the second hydraulic line HL2 in FIG. 2. This second isolating valve TVBK2 enables the second brake circuit BK2 to be hydraulically decoupled from the first pressure supply 6. Thus, the first pressure supply 6 can selectively provide pressure medium in the first brake circuit BK1 or in the second brake circuit BK2 or in both brake circuits. When volume loss is detected in the second brake circuit BK2, this can be decoupled.

(45) Furthermore, the exemplary embodiment according to FIG. 2 differs in that a third isolating valve BP2 is provided in the first hydraulic line between the first isolating valve BP1 and the connection point for the first brake circuit BK1. Preferably, this third isolating valve BP2 is arranged such that the third hydraulic line opens into the first hydraulic line HL1 in a hydraulic connection between the first isolating valve BP1 and the third isolating valve BP2. The third isolating valve BP2 makes it possible to decouple the first brake circuit BK1 hydraulically from both the first pressure supply unit 6 and the second pressure supply unit 14. Thus, when the first pressure supply unit 6 fails, it is possible to feed pressure medium into the second brake circuit from the second pressure supply unit 14 via the feed valve 69, the first isolating valve BP1 and the second isolating valve TVBK2. If the third isolating valve BP2 is closed, no pressure medium is supplied to the first brake circuit.

(46) With the brake system 2 according to FIG. 2, the following safety-related redundancies can be realized: ensuring a sufficient braking effect in the event of failure of the one or more pressure supply units, fault conditions 1-7: see embodiment 1; fault condition 8failure of the feed valve 69 (e.g., leaking) or failure of the electrical control: closure of third hydraulic line HL3 by the isolating valves BP1 and BP2 so that the travel simulator is fully effective; first pressure supply unit 6 and ESP unit set pressures in the wheel brakes; further degree of freedom: optional feeding of the pressure of the main brake cylinder into brake circuit BK1 or BK2 in the event of a brake circuit failure. electronic brake boost (EBV) in the event of failure of the ESP unit by generating pressure in brake circuit BK1 via the second pressure supply unit 14 and by generating pressure in brake circuit BK2 via the first pressure supply unit 6 when the first isolating valve BP1 is closed and by controlling the pressure supply via the sensor system of the second pressure supply unit 14. S/W brake circuit distribution is required for this purpose and the braking force distribution in the brake circuits is controlled via the isolating valves BP1, BP2 and TVBK2. In accordance with the invention, the piston of the first pressure supply unit 6 can be controlled in forward and return stroke motion to apply a suitable pressure. Optionally, pressure adjustment can be performed via PWM control of the valves, in particular the isolating valves; 2-channel ABS operation in which, depending on road conditions, the system switches between a select low control (wheel lock pressure of the wheel with the poorer adhesion conditions per brake circuit determines the pressure to be set) and a select high control (wheel lock pressure of the wheel with the better adhesion conditions per brake circuit determines the pressure to be set). air clearance control is already implemented in the exemplary embodiment according to FIG. 1. The exemplary embodiment according to FIG. 2 offers the additional potential to compensate for the unequal air clearance in the wheel brakes RB1, RB2, RB3, RB4 of the brake circuits BK1, BK2 by appropriate preliminary control before the brake booster operation by sequential opening of the isolating valves BP1, TVBK2. Alternatively, PWM operation can also be used so that different flow cross-sections to the brake circuits BK1, BK2 can be set and thus the unequal air clearance can be compensated for simultaneously. An S/W brake circuit split is suitable here. This method is easy to implement because the brake circuit isolating valves are part of the X-Boost module and can be implemented without any time delay or susceptibility to errors (e.g., use of an interface between X-Boost and ESP unit). For example, the brake system can be designed in such a way that no air clearance is provided at the brake pads on the front axle and air clearance is provided on the rear axle. Thus, even a failure of the first pressure supply unit 6 does not lead to a delay in braking when pressure is generated by the actuation unit and acts on the wheel brakes RB1, RB2, RB3, RB4 of the front axle VA in accordance with the invention. In addition, a greater braking effect can be generated with the front axle VA.

(47) FIG. 3 shows a variation of the exemplary embodiment according to FIG. 1. Here, the brake circuits are swapped. It should be obvious to a person skilled in the art that similar advantages to those already explained in conjunction with the exemplary embodiments for FIGS. 1 and 2 can be achieved with a corresponding modification of the invention.

(48) FIG. 4 shows a schematic circuit diagram of a further exemplary embodiment of the inventive brake system 2 with the first pressure supply unit 6, which has an electromotive drive 8 and a transmission, and with a motor-pump unit 90, shown in FIG. 4 only schematized by a rectangle.

(49) The brake system 2 further comprises a second pressure supply unit 14. The second pressure supply unit 14 is described in detail in the application with the application file number PCT/EP2018/072363 of the applicant, to which reference is made at this juncture.

(50) Similarly to the exemplary embodiment according to FIG. 1, the second pressure supply unit 14 has a main brake cylinder 22 and a piston 24. An actuating element 26 is arranged on the piston 24 and is only partially shown in FIG. 4 and is designed, for example, as a brake pedal.

(51) In addition, the brake system 2 shown in FIG. 4 has a travel simulator 28 that is hydraulically connected to the second pressure supply unit 14.

(52) Sensors 30a, 30b detect a brake pedal travel and a travel difference between actuating element 26 and piston 24. The actuating element 26 acts on the piston 24 via a spring element. The sensors 30a, 30b are preferably integrated in the second pressure supply unit 14 and are part of a pedal interface there that is not described in more detail here.

(53) The signal generated by the sensors 30a, 30b contains information about a differential travel and thus a control signal for the first pressure supply unit 6, so that the latter applies a pressure medium to the first brake circuit BK1 and the second brake circuit BK2 as a function of the signal generated by the sensors 30a, 30b. Alternatively or additionally, the two brake circuits BK1, BK2 are supplied with the pressure medium located inside the main brake cylinder 22. Thus, in the exemplary embodiment, the second pressure supply unit 14 is set up in such a way that the two brake circuits BK1, BK2 are at least indirectly supplied with the pressure medium.

(54) Furthermore, when the actuating element 26 is actuated, the second pressure supply unit 14 feeds the travel simulator 28 via an expansion hole in a wall of the main brake cylinder 22, so that a progressive haptic resistance in the form of a return force can be felt as a function of a magnitude of the actuation of the actuating element 26. The magnitude of actuation in this context is understood to be how firmly and/or how far a driver actuates the actuating element 26, which is in the form of a brake pedal, and thus pushes the piston 24 into the main brake cylinder 22. Progressive haptic resistance is also referred to as pedal characteristic.

(55) Furthermore, the second pressure supply unit 14 comprises a spring 36, which is arranged with one end on the piston 24 and with the other end on the main brake cylinder 22. The spring 36 may also be part of the spring characteristic of the travel simulator 28 and thus part of the pedal characteristic.

(56) The second pressure supply unit 14 has at least one, in the exemplary embodiment two, expansion bores 38, which are connected to a storage container 40 via hydraulic lines. The storage container 40 is also part of the brake system 2 in the exemplary embodiment according to FIG. 4.

(57) In one embodiment, a check valve RV (not shown) may be arranged in the hydraulic line between the expansion bore 38 and the storage container 40. Furthermore, such a check valve RV (not shown) can also be arranged in a hydraulic line between the first pressure supply unit 6 and the storage container 40. By means of this check valve RV as well as the first pressure supply unit 6, it is possible to perform a diagnosis of a state of preservation of sealing elements arranged within the first pressure supply unit 6 as well as within the travel simulator 28.

(58) Furthermore, the main brake cylinder 22 has two sealing elements 42a, 42b that are redundant to each other and are designed as ring seals. One of the two expansion bores 38 is arranged between the two sealing elements 42a, 42b. A throttle DR is arranged in the connection between the expansion bore 38, which is arranged between the two sealing elements 42a, 42b, and the storage container 40.

(59) The throttle DR is dimensioned in respect of its flow rate so that the pedal characteristic is not significantly changed in the event of failure of one of the two sealing elements 42a, 42b (3 mm pedal travel in 10 s). In addition, a temperature-related volume compensation of the pressure medium can take place via the throttle DR.

(60) In the exemplary embodiment according to FIG. 4, as in FIGS. 1 and 2, the brake system 2 is designed redundantly with regard to a failure of the first pressure supply unit 6. For this purpose, in the event of failure of the first pressure supply unit 6 for a braking process, the ABS/ESP unit 90 takes over in such a way that it sucks in pressure medium from the storage container 40 by means of the pump P and supplies it to the brake circuits BK1 and BK2. In other words, the pump P of the ABS/ESP unit 90 assumes the function of the brake booster at least as an alternative in the event of failure of the first pressure supply unit 6. For this purpose, the hydraulic lines HL1 and HL2 are each hydraulically connected to the storage container 40 via a hydraulic line.

(61) The first pressure supply unit 6 has a piston 44, which has an expansion hole 46. The pressure medium is drawn in via a hydraulic line by means of which the first pressure supply unit 6 is connected to the storage container 40 (only partially shown in FIG. 4).

(62) The dimensioning of the first pressure supply unit 6 can be staggered in such a way that one full stroke of the piston 44 corresponds to a volume intake of one of the two brake circuits BK1, BK2.

(63) In turn, the first pressure supply unit 6 can alternatively be made correspondingly or smaller in volume (piston and stroke).

(64) A pressure build-up and/or pressure reduction in the first brake circuit BK1 and second brake circuit BK2 takes place via a control unit 9, to which the signal of the pedal travel sensors 30a, 30b is transmitted and then the electromotive drive 8 is controlled by the control unit 9 as a function of the transmitted signal. For receiving the signal of the pedal travel sensors 30a, 30b, the control unit has signal inputs (not shown). Furthermore, the control unit has two connections (also not shown) for electrical supply to a connection to a vehicle electrical system of the motor vehicle.

(65) Normally, the first pressure supply unit 6 delivers a volume with a pressure in the range of 80 bar to 120 bar to the brake circuits BK1 and BK2. This pressure range substantially corresponds to a wheel lock limit. That is to say, at a higher pressure the wheels would lock. If a higher pressure is nevertheless required, pump P of ABS/ESP unit 90 is switched on and a pressure build-up to approximately 200 bar is generated. However, this increased pressure build-up takes place with correspondingly lower power and is therefore slower than the pressure build-up with the first pressure supply unit 6. This is permissible because the pressure build-up up to 200 bar is only relevant for fading cases and does not have to take place as quickly as the pressure build-up up to the locking limit (e.g., for implementing emergency braking functions). The pump P of the ABS/ESP unit 90 is thus preferably designed for 200 bar, and the first pressure supply unit 6 is preferably designed for 80-120 bar.

(66) If the first pressure supply unit 6 fails during a braking process, the piston 44 is pushed back under pressure so that the braking pressure can be completely reduced. If a self-locking transmission is used for the piston 44 (e.g. in the form of a trapezoidal spindle with plastic nut), such a pressure reduction is not possible. In this case, a normally closed solenoid valve is provided in the first brake circuit BK1 with connection to the storage container (not shown).

(67) Furthermore, the brake system 2 has a valve unit 50 which is arranged and, in particular, connected by means of hydraulic lines between the second pressure supply unit 14 and the ABS/ESP unit to the motor-pump unit 90. Furthermore, the first pressure supply unit 6 is connected to the valve unit 50. Thus, the valve unit 50 acts in the manner of a distributor and enables the flow paths of the pressure medium already described above. The valve unit 50 also has check valves (not shown here for reasons of simplification) and pressure sensors.

(68) The auxiliary piston chamber 23 of the second pressure supply unit 14 is connected to the motor-pump unit 90 by means of a hydraulic supply line HL3 via the valve 69. Specifically, downstream of the valve 69, a first hydraulic line HL1 and a second hydraulic line HL2 are provided, which are connected in parallel with each other and are connected to the motor-pump unit 12. In other words, the hydraulic supply line HL3 downstream of the valve 69 splits into the first hydraulic line HL1 (which forms part of the first brake circuit BK1) and the second hydraulic line HL2 (which forms part of the second brake circuit BK2). Furthermore, a valve TV1, TV2 is arranged in each of the first hydraulic line HL1 and the second hydraulic line HL2, by means of which the first hydraulic line HL1 and the second hydraulic line HL2 can be at least partially reversibly shut off.

(69) To increase the suction power of the pump P in the brake circuit BK1 in the motor-pump unit 90, a suction valve 70b is provided which connects the pump P in the brake circuit BK1 of the motor-pump unit 90 to the storage container 40. The motor-pump unit 90 can then also draw in pressure medium from the storage container 40 via the first hydraulic line HL1, the valve 69, the hydraulic supply line HL3, auxiliary piston chamber 23 and expansion bore 38. The suction power of the pump P in the brake circuit BK1 in the motor-pump unit 90 is then also not reduced by a hydraulic flow resistance of the valve TV1 or of the valve combination TV1/TV11.

(70) The suction power of the pump P in the brake circuit BK2 in the motor-pump unit 90 when sucking in pressure medium from the storage container 40 via the valve TV2, the hydraulic line HL2, the valve 69 and the auxiliary piston chamber 23, is determined primarily by the hydraulic flow resistance of the valve TV2. To increase the suction power of the pump P in the brake circuit BK2 in the motor-pump unit 90, a suction valve 70c is provided which connects the second hydraulic line HL2 to the storage container 40. The pump P in the brake circuit BK1 of the motor-pump unit 90 can then also draw in pressure medium from the storage container 40 via the second hydraulic line HL2 and the suction valve 70c.

(71) Furthermore, a fourth hydraulic line HL4 branches off from the first hydraulic line HL1. The fourth hydraulic line HL4 hydraulically connects the first brake circuit BK1 and the first pressure supply unit 6. A fourth isolating valve 74 is arranged within the fourth hydraulic line HL4, by means of which the hydraulic connection between the first brake circuit BK1 and the first pressure supply unit 6 can be at least partially reversibly disconnected. In the event of a leak of the pressure relief valve 80, the fourth isolating valve 74 can be closed so that the brake circuit BK1 does not fail.

(72) An essential feature of the brake system 2 according to FIG. 4 is that no further pressure supply unit is required. The brake system 2 thus only has the first pressure supply unit 6 and the second pressure supply unit 14, which supply the two brake circuits BK1, BK2 with pressure medium.

(73) In the fallback option, the second pressure supply unit 14 can be switched to one or both brake circuits BK1, BK2 via the valves TV1 and TV2 in the event of a failure of the first pressure supply unit 6, so that either one or both brake circuits BK1, BK2 is/are supplied with pressure medium by the second pressure supply unit 14. In the event of a failure of the control unit 9, both brake circuits BK1, BK2 are effective.

(74) FIG. 5a and FIG. 5b illustrate one way in which the individual components of the X-booster, in particular the first and second pressure supply units 6, 14 and the associated valves, in particular the isolating valves 74, PD1, BP1, TV1, BP2, TVBK2, TV2, can be arranged in a housing.

(75) FIG. 5a and FIG. 5b show in simplified form the basic elements of the assembly with electromotive drive 8, second pressure supply unit 14, in particular the HCU block 114 with the main brake cylinder 22, the first pressure supply unit (ECU), storage container 40 and other components (SH2, motor sensor and motor sensor housing).

(76) The first pressure supply unit 6 has the electromotive drive 8, for example a spindle drive, as shown in FIG. 1, and a piston housing 108. The piston housing 108 is mounted on the HCU block 114 via a screw connection 101.

(77) The spindle drive with piston 24 is arranged within the HCU block 114. In accordance with the invention, the piston stroke of the first pressure supply unit 6 can be very small, since the dimensioning of the electromotive drive 8 is designed for both a low pressure level, e.g., 120 bar, and a correspondingly smaller volume. A higher pressure level and also additional volume can be provided by the ESP unit. The valves required for the described function are also integrated in the HCU block 114.

(78) Further integrated into the HCU block 114 is the SH2, which is connected to the actuating element 26. The HCU block 114 is connected to a mounting flange 102, which is screwed to the end wall 104 of the brake booster with mounting bolts 103.

(79) The control unit 9 (ECU) with housing 113 is mounted on the HCU block 114.

(80) The plug connector ST of the control unit 9 (ECU) is connected to the PCB. The PCB also carries the level sensor NS. The level sensor NS is designed to measure linearly so that even small leakage flows are detected. It detects the magnetic float NS or its position in the storage container 40. For the highest safety requirements, the level sensor NS can also be designed redundantly. The prerequisite for the described exemplary embodiment (without plug connector) is a corresponding arrangement of the storage container 40 behind the PCB (with respect to the drawing plane of FIG. 5b). This arrangement allows an extremely short overall length, which is advantageous in the event of a head-on collision.

(81) The hydraulic connection lines 105 to the ESP unit for the brake circuits BK1, BK2 2 can be realized on the motor side or alternatively on the front side, preferably at an angle of approximately 45. This facilitates assembly.

(82) The plug connector ST is disposed above the HCU block 114. In the illustrated exemplary embodiment, a travel simulator housing 117 is separately formed and not integrated into the HCU block 114. Instead, a screw connection is provided to allow the position of the travel simulator 28 to be adjusted. This saves volume in the HCU block 114.

(83) One aspect of the invention is that the first and second pressure supply unit 6, 14 are arranged substantially perpendicular to each other in the described housing. Due to the orientation of the pistons of the pressure supply units 6, 14, these have a direction of extension which are designated as L6 (=longitudinal axis of the first pressure supply unit 6) and L14 (=longitudinal axis of the second pressure supply unit 14) in FIGS. 5a and 5b. These two axes L6, L14 are perpendicular to each other in the shown exemplary embodiment, whereby a very compact arrangement of the pistons can be achieved. As can be seen from FIG. 5a, 5b, the longitudinal axes L6 and L14 do not lie in the same plane, but are arranged in two parallel-offset-planes. If the longitudinal axes L6 and L14 are mapped onto a common plane, the perpendicular course is obtained. The offset can be in the range of 1 to 15 cm.

(84) FIG. 6 shows a schematic circuit diagram of ESP unit with the motor-pump unit 90 for use in the brake system 2 according to the invention. The ABS/ESP unit is known with the main components pump P with motor 91, the valves HSV1 and HSV2, USV1 and USV2, the inlet and outlet valves EV and AV associated with the wheel brakes RB1, RB2, RB3, RB4, and the storage chamber (SpK). This system is described in many publications and patent applications. It is already on the market as an e-booster and is used mainly in electric and hybrid vehicles, because here the control of the brake system takes place in cooperation with the braking torque of the generator, i.e. recuperation.

(85) In one exemplary embodiment of the invention, the ESP unit can have a bidirectional valve HSV1, so that pressure can be released from the wheel brakes RB3, RB4 via this valve HSV1 in the event of a fault, bypassing the pump P. This design is particularly advantageous in conjunction with the selective pressure control in the brake circuits BK1, BK2.

(86) In particular, an aspect of the invention in this embodiment may be that the control unit 9 is communicatively connected to the control unit 95 (ECU-ESP) of the ESP unit and, to achieve the safety aspects already described, at least the intake and outlet valves AV are controllable by the control unit 9.

(87) By saving a pressure supply unit, a further cost reduction is achieved compared to the embodiments of brake systems 2 described, for example, in the prior art.

(88) At this juncture, it should be pointed out that all parts described above are to be regarded individuallyeven without features additionally described in the particular context, even if these have not been explicitly identified individually as being optional features in the particular context, e.g., by use of the following wording: in particular, preferably, for example, e.g., possibly, round brackets, etc.and in combination or any sub-combination as independent embodiments or further developments of the invention as defined in particular in the introduction to the description as well as in the claims. Deviations from this are possible. Specifically, it should be noted that the wording in particular or round brackets do not denote features that are mandatory in the particular context.

(89) It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.

LIST OF REFERENCE SIGNS

(90) 2 Brake system 6, DV1 First pressure supply unit 8 Electromotive drive 9 Control unit (ECU) 10 Transmission 14, BE Second pressure supply unit 22 Main brake cylinder 23 Piston chamber 24 Piston 26 Actuating element 28, WS Travel simulator 28a, 28b Sealing element of the travel simulator 29 Travel simulator valve 30a, 30b Pedal travel sensor 32 Travel simulator piston 34 Spring element of the travel simulator 36 Spring 38 Expansion hole of the second pressure supply unit 40, VB Storage container 42a, 42b Auxiliary piston sealing element 44 Piston of the first pressure supply unit 46 Expansion hole of the piston of the first pressure supply unit 48 Control unit 50 Valve unit 62 Sensor element 69, FV Feed valve 70b, 70c, 80d, RV1, RV2, NV Suction valve 74, PD1 Fourth isolating valve 80, V Pressure relief valve 90, DV2 Motor-pump unit 91 Drive 95 ESP unit control unit 101 Screw connection 102 Mounting flange 103 Mounting bolt 104 End wall 105 Connection lines 108 Piston housing 110 Sensor element 113 Control unit housing 114 HCU Block 117 Travel simulator housing B1, B2 Electrical connections (three-phase) P Pump M Motor BP1, TV1 First isolating valve TVBK2, TV2 Second isolating valve BP2 Third isolating valve RB1, RB2, RB3, RB4 Wheel brake DR Throttle BK1 First brake circuit BK2 Second brake circuit HL1 First hydraulic line HL2 Second hydraulic line HL3 Third hydraulic line HL4 Fourth hydraulic line L6 Longitudinal axis of the first pressure supply unit L14 Longitudinal axis of the second pressure supply unit VA Front axle HA Rear axle TM1 Vehicle electric motor RVHZ Check valve CAN CAN1 bus ST Plug connector NS Float NST Level sensor HSV1, HSV2, USV1, USV2 ESP unit valves AV Outlet valve EV Inlet valve SpK Storage chamber