Hydraulic braking system and procedure

Abstract

Hydraulic brake system (1) comprising at least one wheel brake cylinder (2-1 - 2-4); a primary brake pressure generator (3) which is hydraulically coupled to the at least one wheel brake cylinder (2-1 - 2-4) in a separable manner and is configured to pressurize the at least one wheel brake cylinder (2-1 - 2-4) by means of a hydraulic fluid; a master brake cylinder (4) which has at least one first pressure chamber (5) and is hydraulically coupled to the at least one wheel brake cylinder (2-1 - 2-4); and a secondary brake pressure generator (7) which is coupled to the first pressure chamber (5) of the master brake cylinder (4) and is configured to pressurize the first pressure chamber (5) of the master brake cylinder (4);wherein the secondary brake pressure generator (7) can be controlled independently of the primary brake pressure generator (3), and with a hydraulic fluid reservoir (8) which is hydraulically coupled to the first pressure chamber (5) of the master brake cylinder (4) via a first hydraulic connection (9-1) and which is hydraulically coupled to an inlet (10) of the secondary brake pressure generator (7) either via the same line through which the primary pressure generator 3 is coupled to the hydraulic fluid reservoir 8, or directly via a separate line, coupled to the hydraulic fluid reservoir 8.

Description

The present invention relates to a hydraulic braking system and a method for operating a hydraulic braking system. State of the art In modern vehicles, a variety of driver assistance systems support the driver in controlling the vehicle. In passenger cars, systems are increasingly being used that relieve the driver of accelerating, braking, and steering in various situations. When the driver is completely relieved of vehicle control, this is referred to as highly automated or autonomous driving. In highly automated driving, the driver can engage in activities other than controlling the vehicle. Therefore, the driver cannot monitor the vehicle's movement and surroundings. This means that, in the event of necessary braking, the driver may not be available to intervene. Consequently, the braking system of such a vehicle must meet high availability requirements. German patent DE 102 33 196 discloses a braking system comprising a hydraulically actuated brake cylinder for actuating a brake. The system further comprises a pressure control cylinder with which the pressure in the wheel brakes can be adjusted. The pressure control cylinder can be actuated by means of an electronic adjusting device. If the pressure control cylinder fails, no support force can be provided by an assistance system. Such a failure could, for example, be due to engine failure, in which case pressure increase with assistance is no longer possible, but only by the driver using muscle power alone. DE 10 2012 205 859 A1 discloses a hydraulic brake system in which an electrically controllable pressure supply device is provided with at least one suction port and one pressure port, the suction port of which is connected to one of the pressure chambers of a master brake cylinder and the pressure port of which is connected to the brake circuit belonging to the pressure chamber. Document DE 10 2011 076 675 A1 discloses a method for controlling an electro-hydraulic “brake-by-wire” braking system with an electrically controllable pressure supply device, which comprises a cylinder-piston arrangement whose piston can be actuated by an electromechanical actuator, which enables an improvement of the pressure supply device functions. Disclosure of the invention The present invention discloses a hydraulic braking system with the features of claim 1 and a method with the features of claim 9. Accordingly, the following is provided: A hydraulic brake system with at least one wheel brake cylinder, a primary brake pressure generator which is hydraulically coupled to the at least one wheel brake cylinder in a separable manner and is designed to pressurize the at least one wheel brake cylinder by means of a hydraulic fluid, a master brake cylinder which has at least one first pressure chamber and is hydraulically coupled to the at least one wheel brake cylinder, and a secondary brake pressure generator which is coupled to the first pressure chamber of the master brake cylinder and is designed to pressurize the first pressure chamber of the master brake cylinder, wherein the secondary brake pressure generator can be controlled independently of the primary brake pressure generator. Furthermore, the following is provided: A method for operating a hydraulic brake system according to one of the preceding claims, comprising providing an error signal indicating a fault of the primary brake pressure generator, hydraulically disconnecting the primary brake pressure generator from the at least one wheel brake cylinder in response to the error signal, and controlled generation of a predetermined pressure in the at least one wheel brake cylinder by means of the secondary brake pressure generator in response to the error signal. The underlying insight of the present invention is that, due to increasing integration, modern braking systems may only have one primary pressure generator and therefore the availability for highly automated driving may be too low. The underlying idea of ​​the present invention is to take this knowledge into account and to provide a way to generate pressure in a highly integrated braking system with a secondary pressure generator, so that a braking function can be provided independently of a driver of the vehicle when the primary pressure generator is not available. The present invention provides that a secondary pressure generator, independent of the primary pressure generator, is provided in the braking system, which is designed solely to pressurize the first pressure chamber of a master brake cylinder of the braking system. In conventional braking systems, the first pressure chamber of the master cylinder is typically coupled to at least one of the wheel cylinders. If, for example, a second pressure chamber is provided in the master cylinder, this is usually coupled to another of the wheel cylinders. Since, in such a dual-chamber design, the pressure in the first pressure chamber is also transferred to the second, a dual-circuit braking system can be provided with a single master cylinder. With the aid of the second pressure generator of the present invention, pressure can be built up in the first pressure chamber of the master brake cylinder independently of brake actuation by the driver or the primary pressure generator. This simultaneously builds up pressure in those wheel brake cylinders that are coupled to the first pressure chamber. Since the pressure in the first pressure chamber of a master brake cylinder with a second pressure chamber is also transferred to the second pressure chamber by a floating piston in the master brake cylinder, pressure is also built up in those wheel brake cylinders which are coupled to the second pressure chamber. The present invention therefore makes it possible to provide a high availability of the braking system, even if the driver cannot be used as a fallback in the event of a failure of the primary pressure generator. Advantageous embodiments and further developments are described in the dependent claims and in the description with reference to the figures. According to the invention, the hydraulic brake system has a hydraulic fluid reservoir which is hydraulically coupled to the first pressure chamber of the master brake cylinder via a first hydraulic connection and which is hydraulically coupled to an inlet of the secondary brake pressure generator. This enables a simple supply of hydraulic fluid to the master brake cylinder. In one embodiment, an output of the secondary brake pressure generator is hydraulically coupled to the first hydraulic connection. In this embodiment, the pressure built up by the secondary pressure generator is introduced into the brake system between the hydraulic fluid reservoir and the master brake cylinder. As a result, during normal operation of the brake system, the secondary pressure generator is not subjected to the operating pressure of the brake system. In one embodiment, the output of the secondary brake pressure generator is coupled to a second hydraulic connection, which links the first pressure chamber of the master cylinder to at least one of the wheel cylinders. In this embodiment, the pressure generated by the secondary pressure generator is introduced into the brake system between the master cylinder and the wheel cylinders connected to the first pressure chamber of the master cylinder. This allows fluid volume to be actively transferred into the brake system even when the driver has already depressed the brake pedal and, for example, the intake port of the first pressure chamber of the master cylinder is already blocked. This arrangement also makes it possible to continue transferring fluid volume into the brake circuits even when the brakes are already applied, thus generating high braking force even in vehicles with high fluid volume capacity in the wheel cylinders. In one embodiment, the hydraulic brake system has a first interruption device which is arranged in the first hydraulic connection and is configured to control the flow of hydraulic fluid into the hydraulic fluid reservoir. With the aid of the interruption device, which can be designed, for example, as a valve, it is possible to prevent the pressure generated by the secondary pressure generator from being discharged into the reservoir. In one embodiment, the hydraulic brake system has a primary computing unit configured to control the primary brake pressure generator. Furthermore, the hydraulic brake system has a secondary computing unit configured to control the secondary brake pressure generator, in particular a motor of the secondary brake pressure generator, especially in the event of a failure of the primary brake pressure generator. If two independent computing units are provided, it is still possible to control the secondary pressure generator and build up pressure even if the primary computing unit fails. In one embodiment, the secondary computing unit is coupled to the first interrupting device and is configured to control the first interrupting device. If both the secondary pressure generator and the first interrupting device are controlled by the secondary computing unit, this simplifies the control of the braking system in the event of a failure of the primary pressure generator. In one embodiment, the primary and secondary computing units are arranged in different control units. This increases the availability of both the primary and secondary computing units, since a failure of a single control unit does not lead to the failure of both computing units. In one embodiment, the primary and secondary computing units each have a separate power supply. This further increases the availability of both units, as a single power supply failure does not cause both units to fail. In one embodiment, the secondary brake pressure generator comprises a single-circuit pump, in particular a single-piston pump. This makes it possible to provide a less complex and easily controlled secondary brake pressure generator. In one embodiment, the secondary brake pressure generator is designed to generate a maximum brake pressure that corresponds at least to the maximum service brake pressure of the hydraulic brake system, in particular 100 bar to 200 bar. This allows the entire service brake pressure range of the brake system to be covered by the secondary brake pressure generator. In one embodiment, the method involves the cyclic activation of the first interrupting device at a predetermined frequency when the specified pressure is generated by the secondary brake pressure generator, so that the flow of hydraulic fluid into the hydraulic fluid reservoir occurs and is interrupted cyclically. This makes it possible, even in the event of a fault in the primary pressure generator or a control unit of the primary pressure generator (which, for example, controls valves in the brake system accordingly when executing an ABS function), to still cyclically build up and release pressure in the brake circuits and continue to provide an ABS (anti-lock braking system) function. The above embodiments and further developments can be combined with one another as appropriate. Further possible embodiments, further developments, and implementations of the invention also include combinations of features of the invention described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention. Brief description of the drawings The present invention is explained in more detail below with reference to the exemplary embodiments shown in the schematic figures of the drawings. These show: Fig. 1 a block diagram of one embodiment of the hydraulic braking system according to the invention; Fig. 2 a block diagram of another embodiment of the hydraulic braking system according to the invention; Fig. 3 a block diagram of another embodiment of the hydraulic braking system according to the invention; Fig. 4 a block diagram of another embodiment of the hydraulic braking system according to the invention; and Fig. 5 a flowchart of one embodiment of the method according to the invention. In all figures, identical or functionally equivalent elements and devices – unless otherwise specified – have been provided with the same reference numerals. Embodiments of the invention Fig. 1 shows a block diagram of an embodiment of the hydraulic brake system 1 according to the invention. The hydraulic brake system 1 has a wheel brake cylinder 2-1, which is hydraulically coupled to a primary brake pressure generator 3 and to a master brake cylinder 4. Further wheel brake cylinders are indicated by three dots. The wheel brake cylinder 2-1 can be pressurized by means of a hydraulic fluid via both the primary pressure generator 3 and the master brake cylinder 4. The wheel brake cylinder 2-1 is coupled to a first pressure chamber 5 of the master brake cylinder 4. In further embodiments, the master brake cylinder 4 can additionally have a second pressure chamber 6, which can be hydraulically coupled to further wheel brake cylinders, for example. Such an embodiment is shown, for example, in Figures 2-4. Finally, the hydraulic brake system 1 has a secondary brake pressure generator 7, which is hydraulically coupled to the first pressure chamber 5 of the master brake cylinder 4. The brake pressure generator 7 can thereby pressurize the first pressure chamber 5 of the master brake cylinder 4, e.g. also by means of the hydraulic fluid. According to the present invention, the secondary brake pressure generator 7 can be controlled independently of the primary brake pressure generator 3. Separate control can be provided, for example, by two separate control units in one embodiment, each of which controls one of the brake pressure generators 3 and 7. In a further embodiment, separate energy sources can also be provided for the primary brake pressure generator 3 and the secondary brake pressure generator 7. In one embodiment, both the primary brake pressure generator 3 and the secondary brake pressure generator 7 can include pumps, in particular pumps driven by an electric motor. In one embodiment, the pump of the secondary brake pressure generator 7 can, for example, be a particularly simple single-piston pump. In one embodiment, the secondary brake pressure generator 7 can be designed to generate a maximum pressure corresponding to the maximum brake pressure required in the hydraulic brake system 1. The secondary brake pressure generator 7 is therefore designed to cover or operate the entire operating pressure range of the hydraulic brake system 1. In one embodiment, the maximum pressure that can be generated by the secondary brake pressure generator 7 can be, for example, above 100 bar, and in particular between 100 bar and 200 bar. In Fig. 1, the secondary brake pressure generator 7 and the wheel brake cylinder 2-1 are each coupled to the master brake cylinder 4 via separate connections. This arrangement is merely exemplary and may differ from that shown in Fig. 1 in further embodiments. Fig. 2 shows a block diagram of a further embodiment of the hydraulic brake system 1 according to the invention. The hydraulic brake system 1 of Fig. 2 is based on the hydraulic brake system of Fig. 1 and has a large number of additional components. The master brake cylinder 4 of Fig. 2 additionally has a second pressure chamber 6. This allows the pressure in the first pressure chamber 5 of the master brake cylinder 4 to be transferred to the second pressure chamber 6 via a floating piston 16 of the master brake cylinder 4. Therefore, pressure can also be indirectly generated in the second pressure chamber 6 via the secondary brake pressure generator 7. Figure 2 shows a hydraulic fluid reservoir 8 containing a hydraulic fluid. The hydraulic fluid reservoir 8 is coupled to an inlet of the first pressure chamber 5 and an inlet of the second pressure chamber 6 of the master brake cylinder 4. For example, the hydraulic fluid reservoir 8 can each be coupled to the vent hole of the respective pressure chamber 5, 6. The hydraulic fluid reservoir 8 is further coupled to a primary pressure generator 3, which includes a motor coupled to a pump and a check valve. One outlet of the first pressure chamber 5 of the master brake cylinder 4 is coupled to two wheel brake cylinders 2-1 and 2-2. Wheel brake cylinder 2-1 can, for example, be located on a front left wheel of a vehicle, and wheel brake cylinder 2-2 can be located on a rear right wheel of a vehicle. One outlet of the second pressure chamber 6 of the master brake cylinder 4 is coupled to two wheel brake cylinders 2-3 and 2-4. For example, wheel brake cylinder 2-3 can be located on a left rear wheel of a vehicle and wheel brake cylinder 2-4 can be located on a right front wheel of a vehicle. An interruption device 12, which is designed, for example, as a valve, in particular as a controllable valve, is arranged between the hydraulic fluid reservoir 8 and the inlet of the first pressure chamber 5. Furthermore, a pedal 22 is coupled to the master brake cylinder 4, via which, for example, the driver of a vehicle can control the braking system 1. A large number of valves 20-1 - 20-13 are arranged in the connections between the individual components of the hydraulic brake system 1. A valve 20-1 is arranged between the outlet of the first pressure chamber 5 and a brake pedal simulator. Furthermore, a valve 20-2 is arranged between the outlet of the second pressure chamber 6 and the two wheel brake cylinders 2-3, 2-4. A valve 20-4 is arranged between the first pressure chamber 5 and the wheel brake cylinders 2-1, 2-2. Additionally, a valve 20-4, 20-5, is arranged between the primary pressure generator 3 and one of the connections between the pressure chambers 5, 6 and the valves 20-2, 20-3. Finally, an inlet valve 20-6 - 20-9 is arranged between each of the pressure chambers 5 and 6 and the individual wheel brake cylinders 2-1 - 2-4. An outlet valve is arranged between each of the wheel brake cylinders 2-1 - 2-4 and the hydraulic fluid reservoir 8. Valves 20-1 to 20-13, during normal operation of the brake system, i.e., with the primary pressure generator 3 fully functional, serve to implement functions such as normal enhanced braking, ESP, and ABS. Figure 2 also shows a number of pressure transducers for the electronic detection of pressures in the brake system 1, which, for the sake of clarity, have not been labeled with their own reference numbers. In Fig. 2, the secondary pressure generator 7, which has a motor and a pump 15 driven by the motor, is coupled to the brake system in such a way that the inlet 10 of the pump 15 is coupled to the hydraulic fluid reservoir 8 via the same line through which the primary pressure generator 3 is also coupled to the hydraulic fluid reservoir 8. In other embodiments, the inlet 10 of the pump 15 can also be coupled to the hydraulic fluid reservoir 8 in any other way, e.g. directly via a separate line. The output 11 of the pump 15 is coupled to the line which couples the interrupting means 12 to the inlet of the first pressure chamber 5. Finally, Fig. 2 shows a primary computing unit 13 and a secondary computing unit 14. The primary computing unit 13 is coupled to the primary pressure generator 3 to control it. The primary computing unit 13 can include or control components such as power output stages, which drive the motor of the primary pressure generator 3. Furthermore, the primary computing unit 13 can, for example, read the pressure transducers and other sensors present in the brake system 1 to control the primary pressure generator and the valves 20-1 - 20-13. The primary computing unit 13 of Fig. 2 is further configured to output an error signal 30 if an error occurs in the primary printer 3 or the primary computing unit 13 that affects the normal operation of the brake system 1. The fault signal 30 can be received, among other things, by the secondary processing unit 14. The secondary processing unit 14 can then control the interrupting device 12 and the secondary pressure generator 7, so that the function of the hydraulic brake system 1 can be maintained even in the event of a fault in the primary pressure generator 3. In addition to the fault signal, the secondary processing unit 14 can also receive further control signals from higher-level vehicle systems, which specify to the secondary processing unit 14 which braking function is required. If the secondary computing device 14 is to build up pressure in the wheel brake cylinders 2-1 - 2-4, it closes the interrupting means 12 and builds up pressure in the first pressure chamber 5 of the master brake cylinder via the pump 15. This pressure is transferred to the second pressure chamber 6 and via both pressure chambers 5, 6 to the wheel brake cylinders 2-1 - 2-4. In such a case, the primary pressure generator 3 can be decoupled from the wheel brake cylinders 2-1 - 2-4 via the valves 20-4 and 20-5 to prevent interference. The secondary computing unit 14 can also represent an ABS functionality, for example, by cyclically controlling the interrupting device 12. In the embodiment shown in Fig. 2, during normal operation, i.e. when the primary pressure generator 3 is fully functional, the secondary pressure generator 7 is not subjected to the pressure that is built up in the brake circuits of the brake system 1 by the primary pressure generator 3. In further embodiments, the primary computing unit 13 does not generate the error signal 30 itself. For example, a monitoring device may be provided which monitors the primary computing unit 13 and the primary printer 3. For example, the function of the primary computing unit 13 and the primary printer 3 may be cyclically polled or monitored. The error signal 30 can be transmitted to the secondary computing unit 14, for example, via a vehicle bus system or via discrete lines. The computing units 13, 14 can, in one embodiment, be arranged as independent control units in a vehicle. Alternatively, the computing units 13, 14 can also be arranged as components (hardware or software) in one or more control units already present in the vehicle. Fig. 3 shows a block diagram of a further embodiment of the hydraulic brake system 1 according to the invention. The hydraulic brake system 1 of Fig. 3 is based on the hydraulic brake system 1 of Fig. 2 and differs from it in that the outlet 11 of the pump 15 of the secondary pressure generator 7 is coupled to the outlet of the first pressure chamber 5 of the master brake cylinder 4. The connection is made between the valve 20-3 and the outlet of the first pressure chamber 5. When the driver of the vehicle presses the brake pedal 22, the sniffing bore of the first pressure chamber 5 of the master brake cylinder 4 is closed and no more pressure can be introduced into the first pressure chamber 5 at the inlet of the first pressure chamber 5. The arrangement shown in Fig. 3 makes it possible to introduce pressure into the brake circuits or the first pressure chamber 5 with the secondary pressure generator 7 even when the brake pedal 22 has already been actuated by the driver. The embodiment of Fig. 3 can also be used in normal operation, i.e. when the primary pressure generator 3 does not malfunction, to introduce additional volume into the wheel brake cylinders 2-1 - 2-4 or to build up a higher pressure in the wheel brake cylinders 2-1 - 2-4. Especially in vehicles that have a high volume capacity in the wheel brake cylinders 2-1 - 2-4, the braking performance can be increased as a result. Fig. 4 shows a block diagram of a further embodiment of the hydraulic brake system 1 according to the invention. The hydraulic brake system 1 of Fig. 4 is based on the hydraulic brake system 1 of Fig. 3 and differs from it in that the outlet 11 of the pump 15 of the secondary pressure generator 7 is not directly coupled to the outlet of the first pressure chamber 5 of the master brake cylinder 4, but rather after the valve 20-3. The connection is therefore made between the valve 20-3 and the wheel brake cylinders 2-1 and 2-2. The embodiment shown in Fig. 4 allows volume or hydraulic fluid to be transferred to the corresponding brake circuit during active operation of the brake system 1, in which valve 20-3 is closed. In such operation, valves 20-4 and 20-5 can be opened, thus allowing volume or hydraulic fluid to be transferred to the second brake circuit in a dual-circuit system. This enables all wheel brake cylinders 2-1 to 2-4 to be pressurized with hydraulic fluid. This allows volume to be introduced into the brake system 1 via the secondary pressure generator 7 even during active operation. Furthermore, the pressure build-up dynamics during active operation of the brake system 1 can be improved, as the displaced plunger volume of the brake system 1 and the volume supplied by the secondary pressure generator 7 are added together. Figures 2-4 each show dual-circuit brake systems 1. However, it can be seen from Figures 2-4 that the secondary pressure generator 7 is always directly hydraulically connected to the first brake circuit. Therefore, in further embodiments, the present invention can also be designed as a single-circuit brake system 1 with only one brake circuit. Fig. 5 shows a flowchart of an embodiment of the inventive method for operating a hydraulic brake system 1 according to the invention. The procedure provides for the provision of an error signal 30 (S1) if a fault occurs in the primary brake pressure generator 3. The fault can be a mechanical, electrical, or any other fault that prevents pressure from being built up in the wheel brake cylinders 2-1 - 2-4 of the hydraulic brake system 1 by the primary brake pressure generator 3. Finally, in the at least one wheel brake cylinder 2-1 - 2-4, a predetermined pressure is built up by means of the secondary brake pressure generator 7 in response to the provision S1 of the fault signal 30, S2. If the fault signal 30 is provided, in one embodiment the primary brake pressure generator 3 is hydraulically disconnected from the at least one wheel brake cylinder 2-1 - 2-4. This can be achieved, for example, by a suitable arrangement and control of valves 20-1 - 20-13. In one embodiment, a first interruption means 12 can be controlled during the generation of the predetermined pressure by means of the secondary brake pressure generator 7 in such a way that the flow of hydraulic fluid into a hydraulic fluid reservoir 8 of the hydraulic brake system is prevented. This enables effective pressure build-up in the wheel brake cylinders 2-1 - 2-4. In addition to a simple pressure build-up, a cyclical pressure build-up can also be provided. In one embodiment, the first interrupting device 12 can be cyclically activated at a predetermined frequency when the specified pressure is generated by the secondary brake pressure generator 7, so that the flow of hydraulic fluid into the hydraulic fluid reservoir 8 occurs cyclically and is interrupted. This allows a form of anti-lock braking system (ABS) to be provided even in the event of a failure of the primary brake pressure generator 3. Although the present invention has been described above with reference to preferred embodiments, it is not limited thereto, but can be modified in many ways. In particular, the invention can be altered or modified in many ways without deviating from the core of the invention.

Claims

Hydraulic brake system (1) comprising at least one wheel brake cylinder (2-1 - 2-4); a primary brake pressure generator (3) which is hydraulically coupled to the at least one wheel brake cylinder (2-1 - 2-4) in a separable manner and is configured to pressurize the at least one wheel brake cylinder (2-1 - 2-4) by means of a hydraulic fluid; a master brake cylinder (4) which has at least one first pressure chamber (5) and is hydraulically coupled to the at least one wheel brake cylinder (2-1 - 2-4); and a secondary brake pressure generator (7) which is coupled to the first pressure chamber (5) of the master brake cylinder (4) and is configured to pressurize the first pressure chamber (5) of the master brake cylinder (4);wherein the secondary brake pressure generator (7) can be controlled independently of the primary brake pressure generator (3), and with a hydraulic fluid reservoir (8) which is hydraulically coupled to the first pressure chamber (5) of the master brake cylinder (4) via a first hydraulic connection (9-1) and which is hydraulically coupled to an inlet (10) of the secondary brake pressure generator (7) either via the same line through which the primary pressure generator 3 is coupled to the hydraulic fluid reservoir 8, or directly via a separate line, coupled to the hydraulic fluid reservoir 8. Hydraulic brake system according to claim 1, wherein an output (11) of the secondary brake pressure generator (7) is hydraulically coupled to the first hydraulic connection (9-1); or wherein the output (11) of the secondary brake pressure generator (7) is coupled to a second hydraulic connection (9-2) which couples the first pressure chamber of the master brake cylinder (4) to at least one of the wheel brake cylinders (2-1 - 2-4). Hydraulic braking system according to one of claims 1 and 2, comprising a first interrupting means (12) which is arranged in the first hydraulic connection (9-1) and is configured to control a flow of hydraulic fluid into the hydraulic fluid reservoir (8). Hydraulic brake system according to one of the preceding claims, comprising a primary computing device (13) configured to control the primary brake pressure generator (3); and comprising a secondary computing device (14) configured to control the secondary brake pressure generator (7), in particular a motor of the secondary brake pressure generator (7), especially in the event of a fault of the primary brake pressure generator (3). Hydraulic braking system according to the preceding claims 3 and 4, wherein the secondary computing device (14) is coupled to the first interrupting means (12) and is configured to control the first interrupting means (12). Hydraulic braking system according to one of the preceding claims 4 and 5, wherein the primary computing device (13) and the secondary computing device (14) are arranged in different control units. Hydraulic braking system according to any one of the preceding claims 4 to 6, wherein the primary computing device (13) and the secondary computing device (14) each have a separate power supply. Hydraulic brake system according to one of the preceding claims, wherein the secondary brake pressure generator (7) comprises a single-circuit pump (15), in particular a single-piston pump; and / or wherein the secondary brake pressure generator (7) is configured to generate a maximum brake pressure which corresponds at least to the maximum service brake pressure of the hydraulic brake system (1), in particular more than 100 bar. Method for operating a hydraulic brake system (1) according to one of the preceding claims, comprising: providing (S1) a fault signal (30) indicating a fault of the primary brake pressure generator (3); and generating (S2) a predetermined pressure in the at least one wheel brake cylinder (2-1 - 2-4) by means of the secondary brake pressure generator (7) in response to the fault signal (30). Method according to claim 9, further comprising: controlling the first interrupting means (12) when generating the predetermined pressure by means of the secondary brake pressure generator (7), so that a flow of hydraulic fluid into the hydraulic fluid reservoir (8) is prevented. Method according to one of claims 9 and 10, further comprising: cyclic actuation of the first interruption means (12) when generating the predetermined pressure by means of the secondary brake pressure generator (7) at a predetermined frequency, such that a flow of hydraulic fluid into the hydraulic fluid reservoir (8) takes place cyclically and is interrupted.

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