Method for operating a brake system and brake system - Patents.com

Abstract

The invention relates to a method for operating a brake system (1) with a primary brake actuator (2) with a first control device (15) and a secondary brake actuator (3) with a second control device (16), the primary brake actuator (2) being driven starting from a first brake setting (6a, 11a). The first control device (15) and the second control device (16) and / or further control device (10, 21) are connected to each other via a communication means (7). With the second control device (16) and / or further control device (10, 21) it is checked whether a signal from the first control device (15) is received at the second control device (16) and / or further control device (10, 21) or whether a signal received at the second control device (16) and / or further control device (10, 21) from the first control device (15) has an error. If the signal is missing or erroneous, actuation of the secondary brake actuator (3) based on the second brake setting (6b, 11b) is disengaged or prevented (FIG. 1).

Description

[Technical field]

[0001] Background technology DE 10 2009 001 135 A1 discloses a method for operating a hydraulic vehicle brake system with an electromechanical brake booster and a wheel slip controller. The invention proposes operating the vehicle brake system by means of a brake booster, for example to limit the vehicle speed or to regulate the distance to the vehicle ahead or in situations where the brake pedal is not actuated, such as when parking. [Prior art documents] [Patent documents]

[0002] [Patent Document 1] DE 102009001135 A1 Summary of the Invention [Problem to be solved by the invention]

[0003] Disclosure of the Invention The present invention relates to a method for operating a brake system comprising a primary brake actuator with a first control device and a secondary brake actuator with a second control device, the primary brake actuator being driven starting from a first brake setting. [Means for solving the problem]

[0004] The first control device and the second control device and / or the further control device are connected to each other via communication means. With the second control device and / or the further control device it is checked whether a signal from the first control device has been received at the second control device and / or the further control device or whether the signal received at the second control device and / or the further control device from the first control device has an error. If the signal from the first control device is missing or has an error, the actuation of the secondary brake actuator based on the second brake setting is released or prevented.

[0005] This has the advantage that in a by-wire brake system comprising a first brake pressure generator, for example an electrically operated plunger or brake booster, and a second brake pressure generator, for example a hydraulic assembly as known as an ESP assembly, the two units capable of generating brake pressure are optimized in their interaction. In particular, it is important here that the two units can communicate with each other and that there is a suitable fallback level in case such communication is not possible or should be disabled, so that the vehicle can still be braked sufficiently. In this way, the safety of the brake system is increased. This is particularly important in by-wire brake systems where no mechanical hydraulic fallback level based on the driver braking force is provided for the driver to brake. If a communication problem is identified, the actuation of the secondary brake actuator can be intentionally released or prevented. This allows a situation-dependent operation of the two brake actuators.

[0006] In the embodiment of the invention, the primary brake actuator is driven on the basis of a first brake pressure setting via a first characteristic curve, which corresponds to the relationship between the first brake pressure setting and the internal control quantity to be adjusted of the primary brake actuator, in particular the rod travel, the transmission force or the motor current. The fact that the primary brake actuator can be driven on the basis of a first brake pressure setting and the secondary brake actuator on the basis of a second brake pressure setting has the advantage that, even in the event of a communication failure, the two brake actuators can be used on the basis of their respective directly supplied brake pressure settings and furthermore, the respective brake settings can be used in the event of a communication system failure or signal errors. This increases the overall availability of the brake actuators and leads to a more reliable implementation of the brake pressure settings and thus to a redundancy of the brake system.

[0007] As a further feature of the method, an error identification is carried out by means of the second control device and / or a further control device and a corresponding alternative reaction is initiated. The error identification makes it possible to individually omit a response to a detected communication problem. If it is determined in the scope of the error identification that the primary brake actuator is still fault-free, there is no need to discontinue the actuation of the primary brake actuator provided for normal pressure build-up, since there is a communication failure. However, if the error identification shows that there is a problem with or around the primary brake actuator, the secondary brake actuator can be additionally utilized in a manner appropriate to the situation.

[0008] Advantageously, for error detection, the brake pressure adjusted by the primary brake actuator on the basis of the first brake setting is read in by the second control device or by another control device. With the read in brake pressure, a plausibility check of the brake pressure is carried out by the second control device or by another control device for the second brake setting present in the second control device or by another control device. This has the advantage that a plausibility check of the pressure formed by the primary brake actuator on the basis of the first brake setting can be carried out by the secondary brake actuator on the basis of the second brake setting received there. In this way, communication failures can be handled.

[0009] Furthermore, in an advantageous embodiment of the method, the plausibility check can be carried out on the basis of a second characteristic curve and / or a characteristic map, which defines a relationship between the brake pressure and the second brake setting. By providing a characteristic curve, which allows the target brake pressure to be achieved independently of the first brake setting by means of a second brake setting in the secondary brake actuator or in a further brake control device, fault safety is increased.

[0010] In another configuration, the first and second brake settings are identical. In particular, the first and second brake settings come from the same supply source. This has the advantage that the first and second brake settings are identical in quantity, but are doubly supplied in different paths of independent brake actuators. The reliability of the brake system can thus be increased by corresponding validation tests.

[0011] Furthermore, it is advantageous if, during the plausibility check, no pressure or expected pressure is identified, within the scope of the error identification, a first error state is set, which indicates a defect in the primary brake actuator. Thus, based on the execution of a plausibility check whether pressure is not present at all or is present to an insufficient extent, an error around the primary damping factor can be associated.

[0012] Furthermore, as a first error state it may additionally be possible to indicate an error in the surroundings of the communication means or an error in the communication device of the primary brake actuator, which allows not only the identification of a defective primary brake actuator but also confirmation of the first error state in which the communication means does not function.

[0013] In an advantageous embodiment, if no pressure is identified within the scope of the plausibility check, the release of the drive of the secondary brake actuator based on the second brake setting (6b, 11b) takes place as an alternative reaction (304) by complete assumption of the brake pressure regulation by the secondary brake actuator. Alternatively, the release of the drive of the secondary brake actuator takes place as an alternative reaction by at least partial assumption of the brake pressure regulation if no expected pressure is identified, in particular if no expected pressure within the tolerance range of the characteristic curve between pressure and brake setting is identified. This allows the assumption of the secondary brake actuator as an alternative reaction to always be released to the required extent.

[0014] In another configuration, if during the plausibility check an expected pressure is identified, in particular an expected pressure within the tolerance range of the characteristic curve between pressure and brake setting, then in the context of the error identification a second error state is set, indicating an error in the communication means (7), which has the advantage that it is also possible to identify that the primary brake actuator is functional and that the error is due to a communication problem only.

[0015] In an advantageous embodiment, the pressure regulation by the secondary brake actuator as a fallback reaction is prevented in this case and the pressure regulation by the primary brake actuator is continued, so that the operation of the primary brake actuator which generates the brake pressure as normal can continue. The secondary brake actuator does not take over in this situation.

[0016] The invention further relates to a braking system comprising a primary brake actuator having a first control device and a secondary brake actuator having a second control device.Furthermore, there may be provided a further control device, the control device being configured to perform the method according to any one of claims 1 to 11.

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram showing a brake system. [Diagram 2] FIG. 2 is a diagram showing characteristic curves used in a brake system. [Diagram 3] 1 is a flow chart illustrating a method. [Figure 4] FIG. 1 illustrates two pressure-volume relationships for a primary brake actuator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] EMBODIMENTS OF THE PRESENTINVENTION In FIG. 1, a schematic diagram of a vehicle brake system 1 is shown. The brake system 1 comprises a primary brake actuator 2 and a secondary brake actuator 3. The primary brake actuator 2 can be, for example, an electromechanical brake actuator 2, which can generate a brake pressure in the wheel brakes of the vehicle by means of a hydraulic fluid. The electromechanical brake actuator 2 can also be provided in the form of an electromechanical brake booster device. The primary brake actuator 2 can also be understood as an electrically operated plunger piston, which can likewise generate a brake pressure in the connected wheel brakes. In contrast to a brake booster, in such a plunger system, the electrically operated plunger and the driver do not operate the wheel brakes at the same time, at least during normal operation. The driver rather generates a brake setting / demand by applying a load to a pedal simulator, which is then realized in the wheel brakes by the electrically operated plunger.

[0020] The hydraulic pressure can be generated, for example, in a master brake cylinder of the braking system of the motor vehicle. A secondary brake actuator 3 is usually arranged hydraulically downstream of such a master brake cylinder. Such a secondary brake actuator 3 can be, for example, the hydraulic mechanism of a brake pressure modulation unit. A brake pressure modulation unit can be understood to be, for example, an ESP system.

[0021] The brake system 1 is capable of providing both driver-dependent and driver-independent braking pressure.

[0022] If the braking settings 11a, 11b are driver-independent, they are formed by a system 10 of the vehicle. In this case, a braking request on the part of the system is usually realized. Examples of such systems are, in particular, a hill climbing assistance, a traffic jam assistance or an automatic following assistance. However, braking operations by the driver, for example via the brake pedal, can also be taken into account, although they are not directly converted into braking actions. The system 10 here can be a system 10 arranged in parallel to the brake system 1, for example a driving assistance system with appropriate distance sensor devices and environmental detection sensor devices, or a higher-level system 10, for example an overall vehicle control system which includes the brake system and the driving assistance system or is connected to and communicates with the brake system and the driving assistance system via communication means.

[0023] If the brake settings 6a, 6b are driver-dependent, the brake pressure provided by the primary brake actuator 2 or the brake pressure provided by the secondary brake actuator 3 depends on the driver's operation of an operating element 4, for example an operation of the brake pedal 4, which is in this case converted into a corresponding brake pressure by means of the primary brake actuator 2 and / or the secondary brake actuator 3. The brake demand settings 6a, 6b from the driver's side can also be effected via other operating elements 4, such as, for example, a jog dial, a slider or a lever.

[0024] The brake setting via the operating element 4 may be in the form of a magnitude of the actuation of the operating element 4 by the driver and is calculated by the control unit 5 by means of a suitable sensor device. The quantities for calculating the driver setting may be, for example, a displacement distance and / or an actuation force. The quantities for calculating the driver setting may also be quantities which are derived from the displacement distance and / or the actuation force or which can be derived from the displacement distance and / or the actuation force.

[0025] The control unit 5 transfers the driver-dependent braking settings to the respective controllers 15 and 16 of the primary brake actuator 2 and the secondary brake actuator 3, i.e. in the form of a driver setting 6a to the controller 15 of the primary brake actuator 2 and in the form of a driver setting 6b to the controller 16 of the secondary brake actuator 3. The braking settings 6a and 6b are identical quantities and are supplied to each of the primary brake actuator 2 and the secondary brake actuator 3 for redundancy purposes.

[0026] The further system 10 transfers driver-independent brake settings 11a and 11b to respective control devices 15, 16 of the primary brake actuator 2 and the secondary brake actuator 3, i.e. in the form of a driver setting 11a to the control device 15 of the primary brake actuator 2 and in the form of a driver setting 11b to the control device 16 of the secondary brake actuator 3. The brake settings 11a and 11b are also identical in quantity and are supplied to each of the primary brake actuator 2 and the secondary brake actuator 3 for redundancy purposes.

[0027] Both the case of the driver-dependent braking settings 6a, 6b and the case of the driver-independent braking settings 11a, 11b will be referred to as braking settings in the following.

[0028] The control device 15 of the primary brake actuator 2 and the control device 16 of the secondary brake actuator 3 are connected to each other via a communication system 7, for example a communication bus 7. Via such a communication system 7, the brake actuators 2, 3 involved can directly exchange signals with each other. Here, for example, the primary brake actuator 2 can transmit an error state 8 directly to the secondary brake actuator 3. If the primary brake actuator 2 transmits the error state 8 to the secondary brake actuator 3, for example, the secondary brake actuator 3 can take over and / or continue the braking that was previously performed by or with the primary brake actuator 2. Such a function is also called hydraulic boost compensation HBC. Here, the brake settings 6a, 11a present in the primary brake actuator 2 can also be transmitted to the secondary brake actuator 3 via the communication system 7, so that the brake pressure adjustment can be taken over accordingly.

[0029] However, if the communication via the communication system 7 is interrupted or if an error occurs in this communication, the braking settings can no longer be transferred reliably over this path.

[0030] For this purpose, the control device 16 of the secondary brake actuator 3 includes a monitoring function that can detect a breakdown in communication via the communication system 7 or can identify that an erroneous signal has been transmitted via the communication system 7. An erroneous signal is understood to mean a signal that falls outside a set validity value range provided for a given quantity. Similarly, a signal may have an error if its state is characterized or defined as not valid (e.g. by a set bit or index). In this way, the secondary brake actuator 3 makes it possible to deduce a problem in communication with the primary brake actuator 2.

[0031] A lack of reception of information at the secondary brake actuator 3 or reception of an erroneous signal at the secondary brake actuator 3 can have several causes: On the one hand, a failure of the primary brake actuator 2 may have occurred, which failure makes it impossible to transmit information, on the other hand, the communication system 7 itself may have an error or may have failed, for example due to a mechanical disconnection.

[0032] Error identification, ie mapping to a failure in the communication system or to a failure in the primary brake actuator 2, cannot be done on the individual bus connections alone.

[0033] In the following, a method is described which allows such error identification.

[0034] It is initially assumed that the primary brake actuator 2 is solely responsible for pressure formation or pressure regulation and that the brake settings 6a, 11a or 6b, 11b are supplied to the primary brake actuator 2 and to the secondary brake actuator 3, respectively. Here, it can be seen that the brake settings are supplied directly to the primary brake actuator 2 and to the secondary brake actuator 3.

[0035] In a first step 301, in the control device 16 of the secondary brake actuator 3, monitoring is performed as to whether any information is received from the primary brake actuator 2 via the communication system 7 at all or whether an erroneous signal is received via the communication system 7.

[0036] If the signal from the primary brake actuator 2 is missing or if this signal has an error, the brake system transitions to an operating mode in which the drive for adjusting the brake pressure of the secondary brake actuator 3 based on the brake settings 6b, 11b supplied to the secondary brake actuator 3 is released or blocked.

[0037] First, in the case of a communication failure or an erroneous signal, the drive of the secondary actuator 3 can be released (step 301a). For this purpose, the secondary actuator 3 can detect the brake pressure 13 present in the brake system 1 and compare it with the brake settings 6b, 11b. This can be done on the basis of a characteristic curve 17, which will be explained further in the following paragraphs and therefore will not be described here. If the brake pressure 13 deviates from the brake pressure expected on the basis of the brake settings 6b, 11b and the characteristic curve 17, possibly taking into account a tolerance range, the missing brake pressure can be applied by the secondary actuator. The pressure 13 is always read and present in the control device 16 of the secondary actuator, so that the brake pressure corresponding to the second brake setting 6b, 11b can always be adjusted. In this case, it may remain undetermined how the state of the primary actuator 2 is, whether communication via the communication system 7 is no longer possible or whether error-free communication with the secondary actuator is no longer possible.

[0038] In other words, each brake actuator 2, 3 forms the brake pressure with a specific brake setting 6a, 11a or 6b, 11b supplied to it. The secondary brake actuator 3 can now adjust the desired brake pressure taking into account the measured prevailing brake pressure 13. In this case, the primary brake actuator 2 forms the brake pressure by controlling an internal quantity of the primary brake actuator 2. In this case, further characteristic curves can be used which describe the brake setting 6a, 11a in relation to the actuation quantity of the primary brake actuator. The actuation quantity here can be, for example, the rod distance of the primary brake actuator (for example the output rod of the primary brake actuator), the transmission force or the motor current. The adjustable internal quantity is directly related to the pressure formed, which is shown by way of example in FIG. 4 by two pressure-volume characteristic curves 18, 19. The volume V shifted during the brake actuation is proportional to the rod distance s according to the relationship V=A*s, where A is the area of ​​the cylinder whose volume is shifted. The two pressure-volume characteristic curves shown are for example the front and rear wheels respectively, the front and rear brakes being connected respectively to brake cylinders operated by a primary brake actuator 2 .

[0039] The next method step 302 can be performed immediately after a communication failure or a signal with an error has been detected, ie it can follow after step 301 or after the already described step 301a.

[0040] Since the signal emanating from the primary brake actuator 2 has not been received at the secondary brake actuator 3 or since an erroneous signal has been received at the secondary brake actuator 3, in a next step 302 an additional monitoring can be carried out in the form of a plausibility check of the prevailing brake pressure 13 with the brake settings 6b, 11b supplied to the secondary brake actuator 3. This monitoring is also carried out on the control device 16 of the secondary brake actuator 3. This monitoring serves to check at what point in the brake system 1 an error exists, in other words to identify the error.

[0041] In the control device 16 of the secondary brake actuator 3, the brake pressure 13 formed by means of the primary brake actuator 2 is monitored, which can be determined by means of a pressure sensor 12 in the brake system 1, which can detect the pressure 13 available in the master brake cylinder or at another suitable location in the brake system 1. Thus, for example, an ESP pilot pressure sensor supplies a signal corresponding to the master brake cylinder.

[0042] The detected brake pressure can now be compared in the control device 16 of the secondary brake actuator 3 with the existing (driver-dependent or driver-independent) brake settings 6b, 11b. The comparison can take place, for example, with the aid of a characteristic map or characteristic curve 17 that is pre-stored in the vehicle. The characteristic map or characteristic curve 17 here does not necessarily have to be permanently provided in the vehicle, but can also be updated during operation or at specific intervals, for example at power-on or during inspection. Similarly, an adaptation of such a characteristic curve or characteristic map can also be carried out via the selection of the vehicle's operating mode. Thus, for example, via a selection switch in the vehicle, the vehicle can be operated in sport and comfort mode.

[0043] An example of a characteristic curve 17 is shown in Fig. 2. In Fig. 2, the course of a characteristic curve 17 of the brake pressure 13 depending on the brake settings 6a, 6b, 11a, 11b is shown. The brake pressure 13 increases as the brake settings 6a, 6b, 11a, 11b increase. Such characteristic curves 17 can be set to be the same for the driver-dependent brake settings 6a, 6b and the driver-independent brake settings 11a, 11b, but can also be different from one another. Only one characteristic curve 17 is shown here by way of example.

[0044] The above-mentioned plausibility check is carried out on the basis of a characteristic curve 17 which illustrates the relationship between the brake settings 6a, 6b, 11a, 11b and the desired pressure 13 as explained in Fig. 2. The plausibility check can be carried out in such a way that pressures within a certain tolerance range around the characteristic curve are still evaluated as acceptable, and only in the region 14 below the characteristic curve are they evaluated as unacceptable.

[0045] If, in the next step 303, a plausibility check shows that no pressure 13 is measured or, alternatively, that an acceptable pressure 13 is not measured despite the presence of a brake setting 6b, 11b with a setpoint brake pressure to be adjusted, then a fault in the environment of the primary brake actuator 2 is assumed. In other words, if no pressure is available or if there is insufficient pressure, then it must be assumed that there is a defect in the primary brake actuator 2. Here, errors in the bus communication 7 or in the communication device of the primary brake actuator 2 are also detected. This is because, in the event of a defect in the environment of the primary brake actuator 2, the primary brake actuator 2 itself must transmit a corresponding error message via its own communication device and the bus communication 7 to the secondary brake actuator 3, in particular its control device 16.

[0046] In the following step 304, a corresponding alternative reaction can be initiated, in which, if no brake pressure is present at all, the pressure build-up is taken over completely by the secondary brake actuator 3. However, in the alternative reaction in the case of the presence of brake pressures that are not permissible based on the characteristic curve 17 and its tolerance range, the secondary brake actuator 3 takes over at least part of the brake pressure build-up or brake pressure regulation, and the brake pressure 13 present corresponding to the characteristic curve 17 is regulated or controlled corresponding to the brake settings 6b, 11b supplied to the secondary brake actuator 3. To regulate the brake pressure 13, the brake pressure signal 13 can be regulated by the secondary brake actuator. In this way, the release of the at least partial brake pressure regulation by the two brake actuators 2, 3 can be coupled to a plausibility check and is not used in all operating situations.

[0047] If the plausibility check in step 305 shows that the correct pressure 13 is set or that the correct pressure 13 is set taking into account the characteristic curve 17 and the existing tolerances, then an error in the bus communication 7 only is determined. In this case, it is assumed that the primary brake actuator 2 is fault-free. Here, as an alternative reaction 306, the brake pressure formation is maintained in the primary brake actuator 2 and the secondary brake actuator 3 does not take over, i.e. the secondary brake actuator 3 is prevented from taking over. The method described above can be carried out and used in a vehicle without time limitations.

[0048] In the embodiment described so far, it is assumed that monitoring of the brake pressure 13 and error recognition in the control device 16 of the secondary brake actuator 3 takes place.

[0049] In another embodiment, it is also possible that the analysis of whether the brake pressure 13 generated by the primary brake actuator 2 and calculated by the secondary brake actuator 3 and the corresponding brake pressure sensor 12 conforms to the brake settings 6b, 11b is carried out on a control device other than the control device 16 of the secondary brake actuator 3. Similarly, other steps of the described method can also be executed on another control device. Furthermore, certain method steps can also be executed on a control device and other steps on at least one other device. For this purpose, the necessary signals must be supplied to the control devices involved.

[0050] On the one hand, the method steps can be at least partially taken over by a further control device provided in the vehicle, for example a control device 10 which is actually responsible for the driver assistance functions or, alternatively, a higher-level control device, for example a central computer of the vehicle. The data required to carry out the analysis on the further control device, for example the brake pressure 13 and the brake settings 6b, 11b, can be supplied to the further control device 10 via a suitable communication channel, for example via a communication network 7 (bus system) and also via wireless data transmission within the vehicle.

[0051] It is likewise conceivable to carry out an analysis as to whether the achieved brake pressure 13 corresponds to the brake settings 6b, 11b and to carry out further method steps outside the vehicle, for example in a control device 21 external to the vehicle or in a computer external to the vehicle, which in turn has access to corresponding data of the vehicle. The data here are the brake pressure 13 and the brake settings 6b, 11b. For this purpose, the brake demand settings 6b, 11b can also be directly provided to the control device 21 external to the vehicle or to the computer external to the vehicle. It is also possible for the brake settings 6b, 11b to be subsequently provided to the secondary brake actuator 3 and transmitted from the secondary brake actuator 3 to the control device 21 external to the vehicle or to the computer external to the vehicle. In this case, the data transmission to a control device external to the vehicle, for example to a cloud, can be carried out by suitable communication means, for example a data connection via the Internet.

[0052] Here, the alternative reaction in case of failure of the primary brake actuator 2, as shown in the first embodiment, can still be carried out by the secondary brake actuator 3 (either in the case of another control device 10 in the vehicle or in the case of a control device 21 external to the vehicle or a computer external to the vehicle). Likewise, a partial alternative reaction by the secondary brake actuator 3 can also be carried out if the primary brake actuator 2 is still partially generating a braking pressure. In other words, the difference between the target braking pressure and the braking pressure generated by the primary brake actuator is compensated by the secondary brake actuator 3, as already explained in the first embodiment.

[0053] If the brake system 1 comprises further brake elements in addition to hydraulic adjusting elements or actuators, i.e. in addition to the primary brake actuator 2 and the secondary brake actuator 3, these brake elements can likewise be used for the alternative reaction. Such further brake elements can be, for example, an electrically operable parking brake, an electric brake arranged on at least one wheel to be braked, or a generator of an electric or hybrid vehicle which generates a braking effect during recuperation. When using further brake actuators, for example a parking brake, a generator or an electric brake, for the alternative reaction, a common pressure regulation of the hydraulic pressure from the primary brake actuator 2 and the secondary brake actuator 3 can, under some circumstances, only be possible partially. In this case, a full or at least an additional complementary contribution to the further adjusting elements must be taken into account.

Claims

1. A method for operating a brake system (1) with a primary brake actuator (2) having a first control device (15) driven starting from a first brake setting (6a, 11a) and a secondary brake actuator (3) having a second control device (16), comprising: - said first control device (15) and said second control device (16) and / or further control devices (10, 21) are interconnected via communication means (7), using said second control device (16) and / or said further control device (10, 21), whether a signal is received from the first control device (15) at the second control device (16) and / or at the further control device (10, 21), or - whether the signal received at the second control device (16) and / or at the further control device (10, 21) from the first control device (15) has an error is inspected, - if the signal from the side of the first control device (15) is missing or has errors, the actuation of the secondary brake actuator (3) based on the second braking setting (6b, 11b) is released or prevented; A method for operating a brake system (1).

2. the primary brake actuator (2) is driven based on the first brake setting (6a, 11a) via a first characteristic curve (18, 19) corresponding to a relationship between the first brake setting (6a, 11a) and an internal control variable to be adjusted of the primary brake actuator (2), in particular a rod distance, a transmission force or a motor current of the primary brake actuator (2); The method of claim 1.

3. an error identification is performed using the second control device (16) and / or the further control device (10, 21) and an alternative reaction is initiated. The method according to claim 1 or 2.

4. For the error identification, the brake pressure (13) adjusted by means of the primary brake actuator (2) on the basis of the first brake setting (6a, 11a) is read by means of the second control device (16) or by means of the further control device (10, 21), - by means of the second control device (16) or the further control device (10, 21), a plausibility check (302) is carried out of the calculated brake pressure (13) for the second brake setting (6b, 11b) present in the second control device (16) or the further control device (10, 21), The method according to claim 3.

5. the plausibility check (302) is carried out on the basis of a second characteristic curve and / or characteristic map (17) defining a relationship between the brake pressure (13) and the second brake setting (6b, 11b), The method according to claim 4.

6. the first braking setting (6a, 11a) and the second braking setting (6b, 11b) are identical, in particular the first braking setting (6a, 11a) and the second braking setting (6b, 11b) are derived from the same supply source (4, 5, 10), 6. The method according to any one of claims 1 to 5.

7. if during said plausibility check (302) a pressure (13) or an expected pressure (13) is not identified, within the scope of said error identification a first error state is set which indicates a defect in said primary brake actuator (2); The method according to claim 4.

8. As the first error state, an error in the environment of the communication means (7) or an error in the communication device of the primary brake actuator (2) is additionally indicated. The method of claim 7.

9. As an alternative reaction (304), the release of the drive of the secondary brake actuator (3) based on the second brake setting (6b, 11b) if no pressure is identified within the scope of the plausibility check, this is carried out by complete takeover of the brake pressure regulation by the secondary brake actuator (3), by at least partially taking over the brake pressure regulation if an expected pressure (13) has not been identified, in particular if an expected pressure within the tolerance range of the characteristic curve (17) between pressure (13) and brake settings (6b, 11b) has not been identified, 9. The method according to claim 7 or 8.

10. if during the plausibility check (302) an expected pressure (13) is identified, in particular an expected pressure (13) within a tolerance range of a characteristic curve (17) between pressure (13) and brake setting (6b, 11b), then in the scope of the error identification a second error state is set, which indicates an error in the communication means (7), The method according to claim 4.

11. The pressure regulation by the secondary brake actuator (3) as an alternative reaction (306) is prevented, and the pressure regulation by the primary brake actuator (2) is continued. The method of claim 10.

12. 12. A brake system (1), comprising a primary brake actuator (2) having a first control device (15) and a secondary brake actuator (3) having a second control device and / or a further control device (16, 10, 21), the control device being configured to perform a method according to any one of claims 1 to 11.

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