Brake system for vehicle

Abstract

To provide a brake system (1) for a vehicle (100), the brake system (1) comprising brakes (2, 3) respectively associated with two axles (101, 102) of the vehicle (100), where the brake system (1) is actuated by means of a primary control instance (18) and a secondary control instance (19).SOLUTION: In the event of an error of the primary control instance (18), the supply of a hydraulic fluid to the brakes (3) of one of the axles (102) is interrupted. The invention also relates to a method for operating such a brake system (1), a computer program for implementing the method, and a vehicle (100) having such a brake system (1).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a braking system for a vehicle, which has corresponding brakes for the two axles of the vehicle. Furthermore, the present invention relates to a method for operating such a braking system. Furthermore, the present invention relates to a computer program product for implementing the method. Finally, the present invention relates to a vehicle equipped with such a braking system. [Background technology]

[0002] To brake a vehicle, a braking system is generally used, which has corresponding brakes for the different axles of the vehicle. Usually, one such brake of the braking system is assigned to each wheel of one axle of the vehicle. In this case, a simulator device is used to transmit the braking sensation to the vehicle driver when the brake pedal of the brake pedal device is actuated. In practice, the braking process is carried out via an electric motor actuator, which generates a hydraulic pressure in a circuit in which the brake is integrated, depending on the displacement of the brake pedal. This also usually results in an amplification of the braking action.

[0003] The actuation of such a brake system is generally carried out by means of at least one control instance, in the case of an error, as a rule, a brake pedal device is directly connected to the circuit, so that the vehicle driver generates hydraulic pressure in the circuit for braking directly and without amplification via the brake pedal. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention addresses the problem of providing improved or at least alternative embodiments of a braking system of the above-mentioned type, a method for operating such a braking system, a computer program product for implementing the method and a vehicle equipped with such a braking system, in particular, embodiments of the braking system, the method, the computer program product and the vehicle which are characterized by an improved braking action in the case of an error case. [Means for solving the problem]

[0005] The above object is achieved according to the invention by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims.

[0006] The above problem is therefore solved in a brake system for a vehicle, which has corresponding brakes for each of the two axles of the vehicle, by interrupting the supply of hydraulic fluid for braking one of these axles in the event of an error. As a result of this, a direct, unamplified actuation of the brakes via the brake pedal device of the brake system, which is carried out in the event of an error, requires a smaller adjustment of the brake pedal of the brake pedal device by the vehicle driver. In this case, the knowledge is used that in the event of an error, the pedal feel and thus the braking feel and braking effect change significantly. In particular, the brake pedal feels "softer" to the vehicle driver, i.e. feels less resistant, and the vehicle driver has to displace the brake pedal further to obtain an equivalent braking effect than in the absence of an error, in which case amplification is carried out. Furthermore, in the event of an error, due to the direct action, the deceleration until the braking effect is achieved is smaller. Overall, the occurrence of an error event in this way causes high irritation for the vehicle driver, which in itself can ultimately lead to a lower braking effect actually being achieved. This is countered according to the invention by isolating the brakes of one axle from the hydraulic fluid column between the brake pedal device and the brakes as described above, which directly results in an increased resistance in the hydraulic fluid column and therefore provides the brakes of the other axle with more hydraulic pressure for braking, thus resulting in a combination that not only improves the braking feel for the vehicle driver, but also improves the braking action.

[0007] According to the idea of ​​the invention, the brake system comprises two brakes, hereinafter also referred to as first axle-brakes, for a first axle of the vehicle. In this case, the first axle has two wheels, hereinafter also referred to as first axle-wheels. This means that the brake system comprises two first axle-brakes for respective first axle-wheels of the first axle of the vehicle. Furthermore, the brake system comprises two brakes, hereinafter also referred to as second axle-brakes, for a second axle of the vehicle. In this case, the second axle has two wheels, hereinafter also referred to as second axle-wheels. This means that the brake system comprises two second axle-brakes for respective second axle-wheels of the second axle of the vehicle. The brake system further comprises a circuit for providing hydraulic fluid to the brakes. The brake system has, for each first axle-brake, a corresponding first axle-inlet valve for inletting hydraulic fluid to the corresponding first axle-brake and a corresponding first axle-outlet valve for outletting hydraulic fluid from the corresponding first axle-brake in the circuit. Furthermore, the brake system has, for each second axle-brake, a corresponding second axle-inlet valve for inletting hydraulic fluid to the corresponding second axle-brake and a corresponding second axle-outlet valve for outletting hydraulic fluid from the corresponding second axle-brake in the circuit. In this case, the respective inlet valve is open when there is no current. This means that the respective inlet valve is open in the absence of further drive, whereby hydraulic fluid can flow towards the corresponding brake. Furthermore, the respective outlet valve is closed in the absence of current. This means that the respective outlet valve is closed in the absence of further drive, whereby the outlet of hydraulic fluid is blocked by the corresponding brake. A brake pedal device is arranged outside the circuit and is used to operate the brakes. In this case, the brake pedal arrangement can be connected to the circuit via at least one valve, also referred to in the following as circuit valve.The brake system further comprises a sensor device for determining a displacement distance of the brake pedal of the brake pedal device, i.e. the sensor device is configured to determine the displacement distance during operation. The brake system further comprises an electric motor-based actuator for providing a hydraulic fluid pressure in a circuit during operation, i.e. the aforementioned amplification is performed by the electric motor-based actuator. The brake system comprises two control instances, hereinafter also referred to as a primary control instance and a secondary control instance, for operating the brake system. The primary control instance is connected to the first axle-inlet valve and the first axle-outlet valve, whereby the primary control instance drives the first axle-inlet valve and the first axle-outlet valve during operation. Furthermore, the primary control instance is connected to the sensor device and to the electric motor-based actuator, whereby the primary control instance provides a hydraulic pressure according to the displacement distance by means of the electric motor-based actuator in a circuit. The secondary control instance is connected to the second axle-inlet valve and the second axle-outlet valve, whereby the secondary control instance drives the second axle-inlet valve and the second axle-outlet valve during operation. In this case, the brake system is configured such that, at least in the absence of an error in the primary control instance, the brake pedal arrangement is hydraulically disconnected from the circuit, whereby hydraulic pressure is provided in the circuit by means of an electric motor-type actuator depending on the displacement distance.Furthermore, the brake system is configured such that, in the event of an error in the primary control instance, the brake pedal arrangement is hydraulically connected to the circuit, whereby the brake pedal directly displaces hydraulic fluid in the circuit, whereby hydraulic pressure is provided in the circuit.Furthermore, the secondary control instance closes the second axle inlet valve, whereby hydraulic pressure in the circuit is provided to the first axle brake.

[0008] In the event of an error in the primary control instance, the actuation of the electric motor-based actuator, also referred to below as actuator for short, which is connected to the primary control instance is no longer carried out. The hydraulic intervention in the brake pedal arrangement is therefore no longer amplified. Due to the second axle inlet valve being closed, this leads in this case to a significantly improved pedal sensitivity for the vehicle driver and an improved braking action via the first axle brake.

[0009] The braking system advantageously comprises a simulator device connected to the brake pedal arrangement via a corresponding valve, also referred to hereinafter as simulator disconnection valve. The simulator device is configured to provide a resistance in the brake pedal arrangement during operation, which resistance is preferably dependent on the displacement distance of the brake pedal. Preferably, the simulator device displaces hydraulic fluid in the brake pedal arrangement in order to transmit a braking sensation to the vehicle driver.

[0010] In an advantageous embodiment, the primary control instance is decoupled from the second axle inlet valve and the second axle outlet valve, i.e. it cannot drive them, at least directly.

[0011] The actuation of the electric motor actuator and of all valves except the second axle inlet valve and the second axle outlet valve is preferably performed by a primary control instance.

[0012] In a preferred embodiment, the secondary control instance is decoupled from the first axle inlet valve and the first axle outlet valve.

[0013] If there are no errors, the braking system is fully functional.

[0014] If an error occurs in the secondary control instance, the second axle inlet valve is opened, since it is open when there is no current. Furthermore, the second axle outlet valve is closed, since it is closed when there is no current. This means that, using the primary control instance, the first axle brake can be operated in a regular manner via the actuator and the first axle inlet and first axle outlet valves. Both first axle brakes are thus fully available for braking and, in particular, for driving dynamics control.

[0015] Each control instance is usefully a controller or control device.

[0016] Each control instance may in principle be arbitrarily configured.

[0017] For example, each control instance may be a controller, and in particular, the primary control instance may be an ESP controller or part of an ESP controller.

[0018] It is also conceivable that the primary control instance and the secondary control instance are implemented in the same control device.

[0019] Preferably, in the absence of errors, the calculation of the actuation of the inlet and outlet valves is performed in the primary control instance and this is transmitted to the secondary control instance.

[0020] In this case, the secondary control instance can determine / calculate by itself the corresponding actuation of the second axle inlet valve and the second axle outlet valve.

[0021] Similarly, in the absence of errors, the actuation calculations may be performed entirely in the primary control instance, with only the results of the valve actuation for the second axle inlet valve and the second axle outlet valve being transmitted to the secondary control instance, thereby reducing the internal communication between the control instances.

[0022] A variant in which the brake system is further configured to close the simulator disconnection valve in the event of an error of the primary control instance is considered to be advantageous, so that the simulator device is disconnected from the brake pedal device, i.e. in this way there is no simulated resistance as a function of the displacement distance in the brake pedal device, which leads to a further improvement of the pedal feel and the braking action for the vehicle driver.

[0023] In a preferred embodiment, in the event of an error of the primary control instance, at least one parking brake actuator of the brake system can be used in order to achieve a braking action also at the second axle / wheel brake and / or to enhance the braking action at the first axle / wheel brake. This means that the brake system preferably has a parking brake actuator for at least one of the wheels, in particular for at least one of the second axle / wheel. In this case, the brake system is configured in such a way that in the event of an error of the primary control instance, at least one of the at least one parking brake actuator is actuated depending on the displacement distance of the brake pedal.

[0024] Each parking brake actuator is preferably of the electric type, which means that each parking brake actuator is preferably an electric parking brake actuator.

[0025] At least one parking brake actuator can thereby achieve a speed of, for example, 1.5 m / s2 The braking or deceleration action may be performed.

[0026] Preferably, the brake system has such a parking brake actuator for at least one of the second axle brakes, and in the event of an error of the primary control instance, operation of the parking brake actuator is performed depending on the displacement distance of the brake pedal.

[0027] Preferably, at least one of the at least one parking brake actuator is actuated only when the brake pedal deflection distance exceeds a predefined limit value, and the brake system is accordingly configured, which means that when the limit value is exceeded, a predefined braking force is provided by the at least one parking brake actuator.

[0028] Preferably, when a threshold value of the brake pedal displacement is exceeded, at least one of the at least one parking brake actuators of the second axle brake, preferably each, is first brought closer to the corresponding brake piston, i.e. the free distance is overcome. In this case, the threshold value is smaller than the limit value. With a further increase in the brake pedal displacement, the force share by the parking brake actuator is correspondingly increased.

[0029] The maximum force of the at least one parking brake actuator is preferably set such that the at least one parking brake actuator does not lock the corresponding wheel, in other words the maximum force is limited to a value less than the locking force.

[0030] Preferably, a reduction in the vehicle driver's braking desire, i.e. a reduction in the brake pedal displacement distance, results in a corresponding reduction in the braking force generated by means of the at least one parking brake actuator.

[0031] Advantageously, the actuation of the at least one parking brake actuator of the at least one parking brake actuator is performed stepwise as a function of the displacement distance of the brake pedal, which results in an improved braking action.

[0032] It is understood that the scope of the present invention includes not only the braking system but also a vehicle equipped with the braking system, where each axle has two wheels, i.e. the first axle has two first axle-wheels and the second axle has two second axle-wheels.

[0033] It is advantageous if the first axle is the front axle of the vehicle and the second axle is the rear axle of the vehicle, which has the advantage in particular that in the event of a failure of the primary control instance, the actuation of the first axle / brake and thus the front axle / brake is not amplified, but still allows some control of the driving dynamics.

[0034] It will be appreciated that braking systems and vehicles, as well as methods for operating braking systems, are within the scope of the present invention.

[0035] That is, in the method, in a state where there is no error in the primary control instance and the secondary control instance, the brake pedal device is hydraulically disconnected from the circuit and hydraulic pressure is provided in the circuit using an actuator depending on the displacement distance, and, in the event of an error in the primary control instance, the brake pedal device is hydraulically connected to the circuit and the supply of hydraulic fluid to the second axle-brake is disconnected, whereby the brake pedal device directly provides hydraulic pressure in the circuit and hydraulic pressure is provided to the first axle-brake.

[0036] Additionally, preferably at least one of the at least one parking brake actuator is operated in response to brake pedal displacement distance as described above.

[0037] The operation of the brake system, in particular the method, is preferably implemented by a computer program product, which is for example stored at least partially in the brake system and / or at least partially in the vehicle.

[0038] The computer program product includes instructions that, when executed by the braking system, cause the braking system to operate as described above.

[0039] Further important features and advantages of the invention emerge from the dependent claims, the drawings and the corresponding drawing description based on the drawings.

[0040] It is self-evident that the features mentioned above, and those to be further described below, can be used not only in the respective combinations described, but also in other combinations or alone, without departing from the scope of the invention.

[0041] Preferred embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description, in which like reference numbers refer to identical or similar components or functionally equivalent components. [Brief description of the drawings]

[0042] [Figure 1] FIG. 1 is a highly schematic circuit diagram of a vehicle braking system in an error-free state. [Diagram 2] FIG. 4 is a highly schematic circuit diagram of the brake system in another state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] The brake system 1 shown exemplarily in the drawings is used in a vehicle 100. The brake system 1 has two brakes 2, 3, respectively, for a first axle 101 and a second axle 102 of the vehicle 100. The brake 2 for the first axle 101 is also referred to as the first axle-brake 2 in the following, and the brake 3 for the second axle 102 is also referred to as the second axle-brake 3. Each brake 2, 3 is associated with a corresponding wheel 103, 104, not shown any further, of the corresponding axle 101, 102. The wheel 103 of the first axle 101 is also referred to as the first axle-wheel 103 in the following, and the wheel 104 of the second axle 102 is also referred to as the second axle-wheel 104 in the following. In the illustrated embodiment, the first axle 101 is a front axle 105 of the vehicle 100 and the second axle 102 is a rear axle 106 of the vehicle 100. The brake system 1 thus comprises two first axle-brakes 2 for respective first axle-wheels 103 of the first axle 101 and two second axle-brakes 3 for respective second axle-wheels 104 of the second axle 102. The brake system 1 further comprises a circuit 4 for providing hydraulic fluid and thus hydraulic pressure to the brakes 2, 3. In other words, braking is performed hydraulically with the brakes 2, 3. For each first axle-brake 2, the brake system 1 comprises a corresponding inlet valve 5 in the circuit 4 for inletting hydraulic fluid to the corresponding first axle-brake 2 and an outlet valve 6 for outletting hydraulic fluid from the corresponding first axle-brake 2. The respective inlet valve 5 is also referred to below as a first axle inlet valve 5 and the respective outlet valve 6 is also referred to as a first axle outlet valve 6. Similarly, for each second axle-brake 3, the brake system 1 has in the circuit 4 a corresponding inlet valve 7 for inletting hydraulic fluid to the corresponding second axle-brake 3 and an outlet valve 8 for outletting hydraulic fluid from the corresponding second axle-brake 3. The respective inlet valve 7 is also referred to below as a second axle inlet valve 7 and the respective outlet valve 8 is also referred to below as a second axle outlet valve 8. In this case, the respective inlet valve 5, 7 is open when there is no current, as indicated by a spring, which is not further shown in the drawings.This means that the respective inlet valve 5, 7 releases the inflow of hydraulic fluid to the corresponding brake 2, 3 without further actuation. In contrast, the respective outlet valve 6, 8 is closed when there is no current, as is also indicated by a spring, which is not further shown in the figures. This means that the respective outlet valve 6, 8 blocks the outflow of hydraulic fluid from the corresponding brake 2, 3 without further control. Outside the circuit 4, the braking system comprises a brake pedal arrangement 9 for operating the brake 2, 3, the brake pedal arrangement 9 comprising a brake pedal 10. In this case, actuation of the brake pedal 10 by the vehicle driver, i.e. by displacement of the brake pedal 10, usually results in a displacement of hydraulic fluid in a cylinder 12 of the brake pedal arrangement 9 by means of a piston 11, as shown in the figures. The brake pedal arrangement 9 can be connected to the circuit 4 via at least one valve 13, also referred to as circuit valve 13 in the following. If the at least one circuit valve 13 is closed (see FIG. 1), the brake pedal arrangement 9 is hydraulically isolated from the circuit 4. If at least one circuit valve 13 is open (see FIG. 2 ), the brake pedal arrangement 9 is hydraulically connected to the circuit 4. The brake system 1 comprises a sensor arrangement 14 for determining the displacement distance of the brake pedal 10. In the illustrated embodiment, the brake system 1 further comprises a simulator arrangement 15. The simulator arrangement 15 is hydraulically connected to the brake pedal arrangement 9 via a valve 16, also referred to as simulator disconnection valve 16 in the following. During operation, the simulator arrangement 15 provides a resistance in the brake pedal arrangement 9 that is dependent on the displacement distance of the brake pedal. In the illustrated embodiment, this is achieved by the simulator arrangement 15 displacing hydraulic fluid in the brake pedal arrangement 9. An electric motor-based actuator 17 of the brake system 1 is used to generate hydraulic pressure in the circuit 4. This is achieved depending on the displacement distance. The electric motor-based actuator 17 is also referred to as actuator 17 in the following for short.

[0044] To drive the brake system 1, the system 1 has two control devices 18, 19, also referred to as control instances 18, 19 in the following. One control instance 18 is also referred to as primary control instance 18 in the following, the other control instance 19 is also referred to as secondary control instance 19. In the illustrated embodiment, the control instances 18, 19 are realized in respective corresponding control devices 20, 21, purely by way of example. The primary control instance 18 is connected (not shown) to the first axle inlet valve 5, the first axle outlet valve 6 and the actuator 17, so that these can be driven by the primary control instance 18, respectively. By contrast, the primary control instance 18 is decoupled in the illustrated embodiment from the second axle inlet valve 7 and the second axle outlet valve 8. The primary control instance 18 is further connected (not shown) to the sensor device 14, so that the primary control instance 18 provides a hydraulic pressure in the circuit 4 as a function of the displacement distance by means of the actuator 17. The secondary control instance 19 is connected to the second axle-inlet valve 7, such that the secondary control instance 19 can actuate the second axle-inlet valve 7 during operation. Additionally, the secondary control instance 19 is connected to the second axle-outlet valve 8 in the illustrated embodiment, such that the secondary control instance 19 can actuate the second axle-outlet valve 8 during operation. The secondary control instance 19 is decoupled from the first axle-inlet valve 5 and the first axle-outlet valve 6 in the illustrated embodiment.

[0045] FIG. 1 shows the operation of the brake system 1 in the so-called "full system", i.e. in the absence of errors in the control instances 18, 19. In this error-free state, the brake pedal arrangement 9 is hydraulically disconnected from the circuit 4, i.e. at least one circuit valve 13 is closed. There is therefore no direct fluid connection between the brake pedal arrangement 9 and the circuit 4, as shown in FIG. 1 by the dashed line between the brake pedal arrangement 9 and the circuit 4. That is to say, in the error-free state, there is no column of hydraulic fluid between the brake pedal arrangement 9 and the brakes 2, 3. In the error-free state, the actuation of the brakes 2, 3 is carried out by hydraulic pressure provided in the circuit 4 by means of the actuator 17 as a function of the displacement distance of the brake pedal 10. This means that in the error-free state, amplification is carried out by means of the actuator 17. At the same time, in the illustrated embodiment, the simulator device 15 simulates for the vehicle driver that a corresponding braking process is carried out by means of a resistance in the brake pedal arrangement 9.

[0046] In contrast to this, in a faulty, in particular faulty, state of the primary control instance 18 shown in FIG. 2, the brake pedal device 9 is hydraulically connected to the circuit 4, i.e. the circuit valve 13 is open, whereby the aforementioned liquid column is formed. As a result, the brake pedal 10 directly displaces the hydraulic fluid in the circuit 4 and thus creates hydraulic pressure for the braking process in the circuit 4. Furthermore, the secondary control instance 19 closes the second axle-brake inlet valve 7, whereby hydraulic pressure in the circuit 4 is supplied to the first axle-brake 2 but not to the second axle-brake 3.

[0047] In the illustrated embodiment, the secondary control instance 19 is decoupled from the first axle inlet valve 5 and the first axle outlet valve 6 .

[0048] In the illustrated embodiment, in the event of an error in the primary control instance 18 , the simulator isolation valve 16 is closed, thereby isolating the simulator arrangement 15 from the brake pedal arrangement 9 .

[0049] As can be seen in the drawing, in the exemplary embodiment shown, the second axle-brake 3 is also assigned an electric actuator 22 of the parking brake function of the brake system 1, which electric actuator 22 is also referred to as parking brake actuator 22 in the following. In this case, if necessary, a braking action is also generated for the second axle-brake 3 and thus for the second axle-brake wheel 104 in the case of an error of the primary control instance 18, i.e. if the second axle-inlet valve 7 is closed. This is carried out in the exemplary embodiment shown as a function of the displacement distance of the brake pedal 10. In this case, the parking brake actuator 22 is preferably first moved towards a corresponding brake piston, not shown, of the corresponding second axle-brake 3 when a threshold displacement distance is exceeded, i.e. the free distance is overcome. If the displacement distance exceeds a limit value that is greater than the threshold, an actuation of the corresponding second axle-brake 3 is carried out by means of the corresponding parking brake actuator 22. In this case, the braking force exerted by means of the parking brake actuators 22 is always smaller than the force which would result in locking of the corresponding second axle-wheel 104. In this case, the actuation of the respective parking brake actuator 22 is preferably carried out stepwise depending on the displacement distance, if a limit value is exceeded.

[0050] The brake system 1 is configured accordingly to carry out the operations. In particular, the control instances 18, 19 or the control devices 20, 21 are configured accordingly. For this purpose, for example, a corresponding computer program product can be used, i.e. the computer program product comprises instructions for operating the brake system 1 as described above when executed by the brake system 1.

Claims

1. A brake system (1) for a vehicle (100), comprising: - said braking system (1) comprises two first axle brakes (2) for each first axle wheel (103) of a first axle (101) of said vehicle (100); - said braking system (1) comprises two second axle brakes (3) for each second axle wheel (104) of a second axle (102) of said vehicle (101); - said braking system (1) comprises a circuit (4) for providing hydraulic fluid to said brakes (2, 3), - said braking system (1) having, for each said first axle brake (2), a corresponding first axle inlet valve (5) for letting the hydraulic fluid in and a corresponding first axle outlet valve (6) for letting the hydraulic fluid out in said circuit (4); - said braking system (1) having, for each said second axle brake (3), a corresponding second axle inlet valve (7) for letting the hydraulic fluid in and a corresponding second axle outlet valve (8) for letting the hydraulic fluid out in said circuit; each of said inlet valves (5, 7) is open when there is no current and each of said outlet valves (6, 8) is closed when there is no current; - said braking system (1) comprises a brake pedal device (9) arranged outside said circuit (4) for operating said brakes (2, 3), said brake pedal device (9) being connectable to said circuit (4) via at least one circuit valve (13); said braking system (1) comprising a sensor device (14) for determining the displacement distance of a brake pedal (10) of said brake pedal device (9); - said braking system (1) comprises an electric motor actuator (17) which, during operation, provides hydraulic pressure in said circuit (4); - said braking system (1) comprising a primary control instance (18), said primary control instance (18) being connected to said first axle inlet valve (5) and said first axle outlet valve (6), whereby said primary control instance (18) drives said first axle inlet valve (5) and said first axle outlet valve (6) during operation; - the primary control instance is connected to the sensor device (14) and to the electric motor actuator (17), whereby the primary control instance (18) provides a hydraulic pressure in the circuit (4) by means of the actuator (17) according to the displacement distance; - said braking system (1) comprising a secondary control instance (19), said secondary control instance (19) being connected to said second axle inlet valve (7), whereby said secondary control instance (19) drives said second axle inlet valve (7) during operation; the braking system (1) is configured such that, at least in an error-free state of the primary control instance (18), the brake pedal device (9) is hydraulically disconnected from the circuit (4), whereby the hydraulic pressure is provided in the circuit (4) by means of the actuator (17) as a function of the displacement distance, said braking system (1) in the event of an error of said primary control instance (18), the brake pedal device (9) is connected to the circuit (4) such that the brake pedal (10), when actuated, displaces hydraulic fluid in the circuit (4), thereby providing hydraulic pressure in the circuit (4); the secondary control instance (19) closes the second axle inlet valve (7) so that the hydraulic pressure in the circuit (4) is supplied to the first axle brake (2); The brake system (1) further comprises:

2. the brake system (1) is configured to close a simulator isolation valve (16) in the event of an error in the primary control instance (18), thereby isolating a simulator device (15) from the brake pedal device (9).

2. The braking system of claim 1.

3. - the braking system (1) further comprises an electric parking brake actuator (22) for the second axle brake (3), the braking system (1) is configured such that, in the event of an error of the primary control instance (19), at least one of the at least one parking brake actuator (22) is actuated depending on the displacement distance; 3. A brake system according to claim 1 or 2.

4. the brake system (1) is configured such that at least one of the at least one parking brake actuator (22) is operated only when the displacement distance of the brake pedal (10) exceeds a predetermined limit value.

4. The braking system of claim 3.

5. the operation of at least one parking brake actuator (22) is performed stepwise depending on the displacement distance.

5. A brake system according to claim 3 or 4.

6. A method for operating a brake system (1) according to any one of claims 1 to 5, comprising the steps of: - in the absence of errors in the primary control instance (18) and in the secondary control instance (19), the brake pedal device (9) is hydraulically disconnected from the circuit (4) and hydraulic pressure is provided in said circuit (4) by means of an electromechanical actuator (17) depending on said displacement distance, - in the event of an error of the primary control instance (18), the brake pedal device (9) is hydraulically connected to the circuit (4) and the supply of hydraulic fluid to the second axle / brake (3) is disconnected, so that the brake pedal device (9) directly provides hydraulic pressure in the circuit, which is supplied to the first axle / brake (2); method.

7. - the braking system (1) is constructed as claimed in any one of claims 3 to 5, - in the event of an error of the primary control instance (19), at least one of the at least one parking brake actuator (22) is actuated depending on the displacement distance; The method according to claim 6.

8. 1. A computer program product comprising: The computer program product comprises instructions for operating the braking system (1) according to the method of any one of claims 5 to 7, when the computer program product is executed by the braking system (1) according to any one of claims 1 to 5. Computer program products.

9. a first axle (101) having two first axle-wheels (103); a second axle (102) having two second axle-wheels (104); A braking system (1) according to any one of claims 1 to 5, A vehicle (100) comprising:

10. the first axle (101) is a front axle (105) of the vehicle (100); The second axle (102) is a rear axle (106) of the vehicle (100).

10. The vehicle of claim 9.

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