Method for operating a braking system, and braking system

Abstract

The invention relates to a method for operating a braking system of a motor vehicle, wherein, based on parameters of two brake circuits, capability indicators indicating the current capability of the brake circuit in question are calculated. The invention also relates to a braking system for carrying out such a method.

Description

[0001] Method for operating a braking system and braking system

[0002] The invention relates to a method for operating a braking system of a motor vehicle and an associated braking system.

[0003] Braking systems are typically used in motor vehicles to decelerate them in a targeted manner. For this purpose, a braking system typically comprises brakes, each of which acts on at least one wheel of the vehicle.

[0004] It is an object of the invention to provide a method for operating a braking system of a motor vehicle, which, for example, enables improved control of a braking system. It is also an object of the invention to provide a braking system for implementing such a method. This is achieved according to the invention by a method and a braking system according to the respective main claims. Advantageous embodiments can be found, for example, in the respective subclaims. The content of the claims is incorporated into the content of the description by express reference.

[0005] The invention relates to a method for operating a braking system of a motor vehicle. The motor vehicle typically has at least two axles, each typically having at least two wheels. The braking system has a first braking circuit and a second braking circuit. Each braking circuit typically has one or more brakes, each of which is assigned to at least one wheel. Each braking circuit is typically designed to apply braking torque to the wheels of exactly one axle or multiple axles of the motor vehicle. The brakes are preferably exclusively friction brakes. Each braking circuit is preferably designed to apply braking torque to the wheels exclusively by means of the friction brakes.

[0006] The procedure comprises the following steps:

[0007] Determining one or more first parameters of the first brake circuit, Determining one or more second parameters of the second brake circuit,

[0008] Calculating a first capability indicator from the first parameters, and

[0009] Calculate a second capability indicator from the second parameters.

[0010] Such a process can provide capability indicators that can contribute to better management of the braking system. For example, the capability indicators can provide an indication of how the capabilities of the two brake circuits currently behave, either absolutely or relative to each other, and / or how they develop over time. This allows the braking system to be controlled in a targeted manner to achieve specific states or to specifically control the load on the two brake circuits.

[0011] A braking system is typically understood to be a system in a motor vehicle which is used to specifically brake, i.e. decelerate, the vehicle. This is typically a system which is not directly integrated into a drive engine and therefore does not act as an engine brake. An axle typically comprises at least two wheels which are typically arranged in the same position along a longitudinal direction of the vehicle. In passenger cars, one wheel is typically attached to each side of the vehicle. Larger vehicles such as trucks or buses may also have dual tires, so that, for example, there can be two wheels on one axle. These can be designed, for example, so that a single brake acts on both wheels on one side. Alternatively, each wheel can be assigned its own brake.Typically, each brake acts on the wheel or wheels assigned to it.

[0012] The brakes are typically friction brakes. They can be disc brakes or drum brakes, for example. However, other designs, such as eddy current brakes, can also be used.

[0013] According to one embodiment, each brake circuit is assigned to exactly one axle. In this case, the brakes of this brake circuit act only on the wheels of this axle and not on the wheels of any other axle. However, a brake circuit can also be assigned to multiple axles of the motor vehicle. For example, a brake circuit can be assigned to the wheels of a twin axle, i.e., a combination of two axles arranged one behind the other at a short distance. Typically, in the embodiment presented here, a brake circuit acts either on all brakes of an axle or on no brakes of an axle.

[0014] The first parameters are those that affect the first brake circuit. The second parameters are those that affect the second brake circuit. In other words, the first parameters characterize the first brake circuit, and the second parameters characterize the second brake circuit. These parameters can, for example, be those described below.

[0015] If the brakes are exclusively friction brakes and the brake circuits are designed to apply braking torque exclusively by means of the friction brakes, the parameters necessarily originate exclusively from components related to the effect of one or more friction brakes. The parameters therefore do not originate from components that initiate braking by means of a recuperative electric motor. The braking system considered here is, in particular, a pneumatic braking system, a hydraulic braking system, a braking system with electrically actuated friction brakes, or a combination thereof. Such a braking system can be used together with an electric motor, which can also brake by recuperation, but which is not considered a component of the braking system.A friction brake is specifically defined as a brake in which two components that move relative to each other rub against each other. This converts part of the kinetic energy into heat.

[0016] The capability indicators provide information about the current capabilities or other status of the respective brake circuit. In particular, the capability indicators can be used to specifically control the braking system, for example, to adopt specific operating states or to specifically influence wear. Other goals, such as reducing particulate matter emissions, can also be advantageously achieved using the capability indicators. This will be discussed in more detail below. In any case, the mere presence of the calculated capability indicators represents a significant innovation compared to known braking systems, enabling improved control of the braking system and thus producing a beneficial effect.

[0017] In particular, a capability indicator can be calculated using a calculation rule implemented as an algorithm and / or a mathematically specified formula.

[0018] According to one embodiment, the method further comprises the following step: dividing a braking torque request between the first brake circuit and the second brake circuit depending on the first capability indicator and the second capability indicator.

[0019] This allows the two capability indicators to be used specifically to distribute a braking torque request between the two brake circuits. A braking torque request is typically a request to decelerate the vehicle, which can come from a driver of the motor vehicle or from a vehicle control system such as a driver assistance system or autonomous vehicle control. The task of the braking system is typically to implement this braking torque request so that the motor vehicle decelerates as desired. The distribution of this braking torque request between the two brake circuits can advantageously be carried out depending on the two capability indicators. This can, for example, be used to specifically control the wear on the two brake circuits or to achieve certain other goals.

[0020] A first target range can be predetermined for the first capability indicator. A second target range can be predetermined for the second capability indicator. The target ranges can be desired value ranges of the respective capability indicator, i.e., which indicate that the respective brake circuit is functioning normally and is not subject to any particular wear. The target ranges can, in particular, be fixedly specified so that they are not changed while a motor vehicle in which the brake system is installed is driving or during operation of the brake system. The same can apply to other ranges disclosed herein, i.e., in particular, the adaptation range and warning range.Accordingly, if the first capability indicator lies within the predetermined first target range and the second capability indicator lies within the predetermined second target range, a braking torque request can be divided between the first brake circuit and the second brake circuit independently of the first capability indicator and / or the second capability indicator. In other words, it is not necessary to consider the two capability indicators with regard to their exact value if both lie within the respective target range. In this case, other optimization criteria can be used. For example, these can be optimization criteria aimed at minimizing wear or minimizing brake dust emissions. Regenerative braking on an axle can be taken into account.This can, for example, reduce the braking force of a brake circuit if braking due to recuperation also occurs on the axle on which brakes of this brake circuit are located. Recuperation typically involves the use of an electric machine to generate electrical energy from the motor vehicle's excess kinetic energy. In particular, the greater the braking force acting on the same wheels or the same wheel due to recuperation, the more the braking force generated by the braking system can be reduced. A braking torque request can also be divided between the first brake circuit and the second brake circuit depending on the vehicle's load. This allows the load to be taken into account, which can be detected, for example, using suitable sensors. This can result in gentler and / or more comfortable braking.All these procedures are particularly useful when, as already mentioned, the first capability indicator lies in a predetermined first target range and the second capability indicator lies in a predetermined second target range.

[0021] In particular, when the braking system interacts with recuperative braking, which can be generated, for example, by an electric motor, in particular on a rear axle, it can be provided that a braking request is implemented exclusively with recuperation, if this is possible, i.e. as long as the maximum braking torque that can be applied by recuperation is greater than the braking request.

[0022] In particular, for vehicle speeds that are greater than a speed threshold, which may be, for example, at least 5 km / h or at most 9 km / h, or 7 km / h, it can be provided that, in the event that the maximum braking torque that can be applied by recuperation is not sufficient, initially only brakes on the front axle are used in addition, in particular as long as the braking torque to be applied to the front axle corresponds to a deceleration that is at most as large as a deceleration threshold of, for example, 0.1 g.

[0023] In particular, the braking torque applied to the front axle can be limited to a maximum of half the maximum braking torque that can be generated through recuperation. A proportion other than half can also be used.

[0024] If the vehicle's speed is lower than the speed threshold, a different deceleration threshold can be used. This deceleration threshold can be higher than if the speed threshold is exceeded. For example, it can be 0.15 g.

[0025] If the required braking torque is greater than the maximum braking torque that can be applied by recuperation plus the braking torque that can be applied to the front axle by the braking system up to the deceleration threshold, the braking torque to be applied by the braking system can be divided between the front and rear axles in a predetermined ratio, for example 60:40.

[0026] The strategies just described, in conjunction with recuperation, can be used independently of other measures described herein. They can be used particularly when driving forward and reversing.

[0027] Ranges can be predetermined in such a way that they are permanently stored in a control system. However, adjustments can also be provided, for example, while the braking system is in operation or during workshop visits.

[0028] Adaptation ranges can be provided for the capability indicators. These adaptation ranges are typically value ranges that indicate that the respective brake circuit, while not yet in a critical state, is in a state that is at least less desirable than a state in which the respective capability indicator is within the target range. This particularly justifies measures to influence the respective brake circuit so that its capability indicator moves back toward the target range.

[0029] In particular, if the first capability indicator lies in a predetermined first adaptation range and / or if the second capability indicator lies in a predetermined second adaptation range, a braking torque request can be distributed between the first brake circuit and the second brake circuit using a distribution factor. This can be determined in particular as a function of the first capability indicator and / or the second capability indicator. This makes it possible to take into account how the current capabilities of the two brake circuits currently relate to one another. In particular, a braking torque request can be distributed between the two brake circuits in such a way that the brake circuit whose capability indicator is currently in the adaptation range is specifically loaded in such a way that its capability indicator moves back towards the target range.For example, a reduced load can be applied to such a brake circuit. This applies particularly if the other capability indicator is within the target range. If, for example, one capability indicator is within the target range and the other capability indicator is within the adaptation range, the brake circuit whose capability indicator is within the adaptation range can be subjected to less load, so that its capability indicator moves back toward the target range.

[0030] In particular, with each change in the distribution factor, the distribution factor can remain constant for a braking torque request, or for a predetermined number of at least two braking torque requests. This ensures that the distribution factor is not constantly changed, but rather that it is first waited to see whether the most recent change in the distribution factor has the desired influence on the capability indicators. For example, the predetermined number can be two, three, four, five, ten, fifteen, twenty or more braking torque requests. A braking torque request is typically understood to mean the request for a braking torque in an operating situation of a motor vehicle, which begins, for example, with a braking torque being requested and ends with no further braking torque being requested.In typical operating situations, such a period extends over several seconds, although in special situations, such as long downhill stretches, a longer braking torque requirement may be present. In particular, the distribution factor can have only a limited range of values. This can prevent excessive loading of one of the brake circuits.

[0031] The adaptation area and the target area of ​​a respective capability indicator can in particular be directly adjacent to one another and can in particular be different from one another.

[0032] In particular, the distribution factor can be modified in such a way that more braking torque is applied by the brake circuit for which the respective capability indicator indicates a lower load than the other brake circuit. This allows the brake circuit with the higher capabilities to be subjected to a greater load. In particular, this can help balance the load on the two brake circuits.

[0033] In particular, the distribution factor can be determined such that the brake circuit for which the respective capability indicator indicates a lower load applies the majority of the braking torque. This can also be used to appropriately ensure that the load on the two brake circuits is balanced.

[0034] It can be provided that a respective warning range is defined for each capability indicator. This is typically a range in which a critical condition of the respective brake circuit is assumed. The respective warning range can in particular be directly adjacent to the adaptation range and / or different from the adaptation range and / or different from the target range. In particular, it can be provided that the warning range, the adaptation range and the target range together cover the entire possible value range of the respective capability indicator. The adaptation range can in particular be arranged between the warning range and the target range. The aforementioned ranges are in particular directly adjacent to one another and / or do not overlap.In particular, it can be provided that if the first capability indicator lies within a predetermined first warning range and / or if the second capability indicator lies within a predetermined second warning range, a warning message is issued and / or the braking system is degraded. A warning message can be used to specifically warn a driver. This can be, for example, an acoustic or visual warning message. It can be a warning message that is further processed, for example, in vehicle electronics and leads to defined reactions, and / or a warning message that is sent to a central unit such as a fleet monitoring system or a workshop.A degradation of a braking system means, in particular, that the braking system switches to a different operating mode in which, for example, certain functions are deactivated, such as those that are not absolutely necessary for the safety of a motor vehicle. This can, for example, reduce the load on the braking system. It can also, for example, limit the functions of the motor vehicle so that, for example, a certain maximum speed can no longer be exceeded.

[0035] In particular, it can be provided that, in the case of a degraded braking system, the braking torque distribution between the first brake circuit and the second brake circuit is adjusted such that the front axle locks before the rear axle locks. This can increase the braking force on the front axle, which is typically where the increased load occurs during braking. In the case of a degraded braking system, it can also be provided that a brake circuit with at least one failed brake does not apply any braking torque. In this case, it can be taken into account if a brake has failed completely, for example due to a mechanical break, so that the corresponding brake circuit no longer applies any braking torque and the other brake circuit ensures the full application of the braking torque. This can increase road safety because there is no attempt at using a failed brake for braking.In particular, it can be provided that when a brake failure is detected, the capability indicator of the corresponding brake circuit is changed so that it is in the warning range.

[0036] According to one possible embodiment, in at least one or several wear periods, a braking torque requirement is divided between the first brake circuit and the second brake circuit in such a way that a braking torque is predominantly applied by the brake circuit for which the capability indicator indicates a higher load. By defining such wear periods, a brake circuit can be worn down in a targeted manner, i.e. the brake circuit which is already subject to a higher load is specifically placed under a higher load, so that one of the two brake circuits can be specifically subjected to greater wear. This can, for example, protect the other brake circuit. This can, for example, have a positive effect on maintenance intervals, since maintenance of the deliberately more heavily worn brake circuit will soon be required anyway and the other brake circuit has a longer maintenance interval.A wear period can be understood as a period in which such an operating strategy is used.

[0037] In particular, in the case of a braking torque request that exceeds a threshold value and / or a braking torque request for which distribution between the brake circuits is not possible, the brake circuits can be controlled independently of the capability indicators. Such control can, in particular, take precedence over any other potentially implemented procedures for distributing a braking torque request between the two brake circuits. In the event that a threshold value is exceeded and / or distribution between the brake circuits is not possible, it is advantageous to disregard any considerations for specifically influencing the braking system and to apply the braking torque request in full.This prevents the braking torque requirement from being fully applied due to a potentially necessary split of the braking torque demand for conscious management of the braking system, which could compromise the road safety of the vehicle. Possible parameters are described below. These can be used, in particular, in the calculation of the capability indicators. These can be used individually or in any combination.

[0038] According to one embodiment, an energy input into the brakes of the first brake circuit and / or an energy dissipation from the brakes of the first brake circuit are parameters of the first brake circuit. According to one embodiment, an energy input into the brakes of the second brake circuit and / or an energy dissipation from the second brakes of the second brake circuit are parameters of the second brake circuit. An energy input and an energy dissipation can be measured, for example, using sensors and / or calculated using models. For example, an applied braking force, a vehicle speed, a vehicle load, an outside temperature, or the current wear of a respective brake can be taken into account.

[0039] The parameters of the first brake circuit and / or the second brake circuit can in particular comprise one or more entries in the following list: temperature of one or more brakes, temperature of one or more electrical components, state of wear of one or more brakes or other components, friction partners of one or more brakes, energy input into one or more brakes, energy dissipation from one or more brakes, assigned mass of one or more brakes, one or more characteristic values ​​of a torque control of at least one brake, one or more characteristic values ​​of a force setting of at least one brake.

[0040] A temperature of a brake or an electrical component can in particular result from a model by means of which the temperature can be calculated. Alternatively, a temperature can be measured using a temperature sensor. A wear state can, for example, take into account the current thickness of a brake pad. This can, for example, be calculated using a model or can be measured using a sensor. Friction partners can in particular be materials used which rub against one another in friction brakes. Energy input and energy dissipation can in particular be calculated using suitable models, as a result of which a conclusion can be drawn about the respective temperature of the components. An assigned mass is in particular a mass which is available to absorb heat generated during braking.This associated mass can typically absorb this type of heat and release it into the environment over a longer period of time even after braking. Torque control is typically a control system that ensures that a specific braking torque is applied. This is also referred to as a "closed loop." Force adjustment typically involves setting a specifically desired braking force on a brake. This is also referred to as an "open loop." Corresponding controls or settings can, in particular, have characteristic values ​​that are stored or implemented in the respective control systems. These can be fixed or variable. For example, they can be adjusted during operation of a motor vehicle.

[0041] The electrical components mentioned may include sensors, actuators, or electronic assemblies. Their temperature or other conditions can influence the availability and reliability of the associated brake circuit.

[0042] In particular, the first brake circuit and the second brake circuit can act on different axles. This can, in particular, ensure that the measures described herein act in an axle-specific manner. Such a division is typically also referred to as a black-white division. According to a respective embodiment, the first brake circuit has at least one first brake actuator and / or the second brake circuit has at least one second brake actuator. The first brake actuator and the second brake actuator can, in particular, be controllable independently of one another. By means of these brake actuators, a respective pressure in the brake circuit, for example a hydraulic pressure, can be generated and adjusted. By using separate brake actuators, different pressures can be used in the respective brake circuits.

[0043] In particular, the first brake actuator can be a hydraulic brake actuator that applies pressure to the brakes of the first brake circuit. In particular, the second brake actuator can be a hydraulic brake actuator that applies pressure to the brakes of the second brake circuit. Such a hydraulic brake actuator can be, for example, a hydraulic pump that can deliver continuously, or it can be, for example, a linear actuator, which typically ensures a discontinuous pressure buildup.

[0044] The first brake circuit can have one or more brakes that can be actuated by an electromechanical brake actuator. The second brake circuit can have one or more brakes that can be actuated by an electromechanical brake actuator. An electromechanical brake actuator is typically an actuator that actuates a brake without the interposition of a hydraulic system, for example, by means of an electric motor or an electromagnet. In particular, a control or supply via electrical current can be converted directly into a braking force.

[0045] Typically, each brake can only be controlled either electrically or hydraulically. However, combined hydraulic and electrical control is also possible. A brake circuit can be purely hydraulic, purely electric, or a combination of electric and hydraulic. In particular, it can be provided that the first capability indicator shows a load and / or remaining braking capacity of the first brake circuit. In particular, it can be provided that the second capability indicator shows a load and / or remaining braking capacity of the second brake circuit. By displaying a load, the capability indicator can show how high the current load on the respective brake circuit already is. By displaying a remaining braking capacity, it can be shown what potential is currently available for applying a braking force.This can be reduced, for example, if the temperature of friction brakes is already quite high due to a load on the brake circuit or, in the worst case, if a brake has failed.

[0046] In particular, the load on the first brake circuit can be higher the lower the remaining braking capacity of the first brake circuit is. In particular, the load on the second brake circuit can be higher the lower the remaining braking capacity of the second brake circuit is. Braking capacity is typically understood as a maximum braking torque that can be applied or an integrated measure of the braking torque that can be applied and the time over which this braking torque can be applied.

[0047] In particular, it can be provided that the first capability indicator is calculated exclusively from the first parameters and / or exclusively from parameters of the first brake circuit. In particular, it can be provided that the second capability indicator is calculated exclusively from the second parameters and / or exclusively from parameters of the second brake circuit. This can prevent properties of the other brake circuit from influencing the brake circuit under consideration.

[0048] In particular, the first capability indicator can be a numerical value. In particular, the second capability indicator can be a numerical value. The use of a numerical value allows the parameters under consideration to be summarized in a single value that summarizes the current capability of the respective brake circuit. In particular, the numerical value can be a single number or a suitable electronic representation thereof. A numerical value is therefore typically a one-dimensional value.

[0049] The invention further relates to a braking system for a motor vehicle, wherein the braking system has a first brake circuit, a second brake circuit, and a control device. The control device is configured to carry out a method as described herein. The invention further relates to a non-volatile computer-readable storage medium on which program code is stored, upon execution of which program code a processor executes a method described herein. With regard to the method, all embodiments and variants described herein can be used.

[0050] In particular, the braking system or a braking system with which the method described herein is carried out can be a by-wire braking system. In such a system, there is typically no hydraulic connection between a brake pedal actuated by a driver and the wheel brakes, at least not during normal operation. Rather, the driver's braking command is sensed and implemented by electrically operated pressure generators, actuators, or other units. Nevertheless, a hydraulic fallback level can be provided for emergencies, such as in particular in the event of a power failure, in which a hydraulic connection exists between a driver-operated master brake cylinder and the wheel brakes.

[0051] In principle, more than two brake circuits can be used. This can be the case, for example, if a vehicle has more than two axles. The explanations given for the two brake circuits described so far then apply accordingly to additional brake circuits.

[0052] In general, it should be noted that brake-by-wire braking systems generally allow the adjustment of wheel braking torques independent of the driver's applied braking force. For example, a central pressure regulator can be used to ensure the same hydraulic brake pressure in all four wheel brakes, thus preventing the brake force distribution from changing from the brake force distribution established by the wheel brake parameters on the front and rear axles. However, there are also braking systems that allow for axle-specific adjustment of the wheel braking torques.

[0053] Future braking systems that use, for example, electromechanical wheel brakes on all four wheels are also suitable for implementing axle- or even wheel-specific brake force distribution.

[0054] If such systems simulate a conventional static brake force distribution by distributing the requested total braking torque between the front and rear axles using a fixed distribution factor, the system advantages of axle-specific brake force distribution can only be utilized to a limited extent. For example, different thermal behavior of the front and rear wheel brakes cannot be counteracted. This is particularly the case if, for example, the wheel braking torque is controlled at the rear wheel brakes (closed loop), while the brake pressure or application force is controlled at the front wheel brakes (open loop). For example, it is not possible to select the wheel brakes in a situation-dependent manner to prioritize the implementation of the braking request, especially in such a way that optimization goals such as low emissions of particulate matter from brakes or tires are pursued.In addition, it may be difficult or impossible to take into account a regenerative braking torque in electrified vehicles if it only acts on one axle.

[0055] Further features and advantages will become apparent to those skilled in the art from the exemplary embodiment described below with reference to the accompanying drawings. These show:

[0056] Fig. 1 : a braking system, and

[0057] Fig. 2: Value ranges of capability indicators. Fig. 1 shows a purely schematic block diagram of a braking system 5 according to an embodiment of the invention.

[0058] The braking system 5 has a first brake circuit 10 and a second brake circuit 20. The first brake circuit 10 has a first brake 11 and a second brake 12. The second brake circuit 20 also has a first brake 21 and a second brake 22. For example, the first brake circuit 10 can be assigned to a front axle, and the second brake circuit 20 can be assigned to a rear axle. The respective first brake 11, 21 can, for example, be assigned to a respective left wheel. The respective second brake 12, 22 can be assigned to a respective right wheel. However, other distributions are also possible.In any case, the architecture of such a braking system 5 can be abstractly described by two independent brake circuits for the front and rear axles, with each brake circuit essentially consisting of two wheel brakes, but depending on the specific technical design, one or two brake actuators and one or two electronic control units. However, other designs are also possible in principle.

[0059] The braking system 5 further comprises a control device 30. This is configured to execute a method according to the invention according to at least one exemplary embodiment. A specific implementation will be discussed in detail below.

[0060] The braking system 5 further comprises a functional module 40 for detecting the driver's braking request. This is coupled to a sensor system 42 for detecting the driver's braking request. Sensor values ​​can thus be transmitted to the functional module 40, whereby a braking torque request based on a driver's braking request can be sent to the control device 30. Additionally or alternatively, for example, a braking torque request from a driver assistance system or an autonomous vehicle control system can be transmitted to the control device 30. As shown, bidirectional communication is possible between the control device 30 and the two brake circuits 10, 20. In particular, the control device 30 can transmit a respective request to apply a braking torque to each of the two brake circuits 10, 20 or ensure that a braking torque is applied accordingly.For this purpose, for example, hydraulic wheel brakes, electromechanical wheel brakes, electric pressure regulators for a respective hydraulic system, and / or valves or other devices can be controlled. In particular, parameters can be sent from the respective brake circuits 10, 20 to the control device 30, which can be used to calculate capability indicators for the respective brake circuits 10, 20. This will be discussed in more detail below.

[0061] It should be noted that the control device 30 is shown only schematically here and can, for example, also be integrated into other components or functionally divided.

[0062] Sensor system 42 can, for example, detect the driver's braking request. This generates signals that indicate, for example, the actuation travel and / or the actuation force of a brake pedal. Function module 40 can use such signals to calculate a requested total braking torque that should be applied to decelerate the vehicle.

[0063] In the control device 30, a distribution of the requested total braking torque to torque requirements for the two brake circuits 10, 20 can be carried out depending on the situation.

[0064] In addition to the driver braking request detection, further information, which is schematically represented by reference numeral 50, can also be input into the control device 30 and used accordingly.

[0065] In a concrete technical implementation, for example, a signal exchange between the components shown and / or other components can be realized via a communication interface such as a CAN bus.

[0066] In principle, an implemented brake force distribution should be stable, especially in the sense that it does not result in over-braking of one axle, resulting in a loss of driving stability (e.g., if the rear axle is over-braked) or steerability (e.g., if the front axle is over-braked). As long as wheel slip control is available for the wheels of both axles, this can ensure stability and steerability. Brake force distribution can then also be selected based on criteria other than stability.

[0067] In contrast to conventional pedal-coupled systems, brake-by-wire braking systems typically support wheel slip control without irritating the driver.

[0068] Based on brake-by-wire braking systems that allow axle-specific adjustment of the wheel braking torques, a method can be implemented that provides for adaptation of the brake force distribution based on capability indicators of the brake circuits 10, 20. These capability indicators can be understood as part of an interface between a brake force distribution and the brake circuits 10, 20.

[0069] Fig. 2 shows a diagram in which a first capability indicator BI1 and a second capability indicator BI2 are plotted. These can each assume a value between 0% and 100%. The first capability indicator BI1 is assigned to the first brake circuit 10 and is calculated from parameters of the first brake circuit 10. The second capability indicator BI2 is assigned to the second brake circuit 20 and is calculated from parameters of the second brake circuit.

[0070] The capability indicators BI1 and BI2 are expressed as percentages. A value of 100% indicates that there are no restrictions within the respective brake circuit 10, 20, and the use of its brakes or actuators can be freely defined. A value of the respective capability indicator BI1 and BI2 below 100% can indicate that restrictions exist within the system or are predicted to occur with constant use.

[0071] Implementation of a requested braking torque should be carried out by the braking system 5 completely within the physical limits, even if the values ​​of the respective capability indicator BI1, BI2 are below 100%. This ensures that, particularly during emergency braking, the maximum possible braking of the vehicle is always achieved, even if restrictions have already been detected and this is indicated by a value of one or both capability indicators BI1, BI2 of less than 100%. The capability indicators BI1, BI2 should be used in particular by the control device 30 to enable brake force distribution and to influence requested braking torques or to change their distribution between the two brake circuits 10, 20.

[0072] As can be seen in Fig. 2, three value ranges are specified for the two capability indicators BI1, BI2. These are a target range ZB, an adaptation range AB and a warning range WB. These ranges are represented as two-dimensional ranges for the combination of both indicators and, in a one-dimensional view, define a first target range ZB1, a first adaptation range AB1 and a first warning range WB1 for the first capability indicator BI1 as well as a second target range ZB2, a second adaptation range AB2 and a second warning range WB2 for the second capability indicator BI2. The target range ZB is selected such that it can be assumed that there are no restrictions to be observed for the respective brake circuit 10, 20 if the respective capability indicator BI1, BI2 is in the target range ZB.In particular, in the event that both capability indicators BI1, BI2 are in the target range ZB, a control of the braking system 5, in particular a distribution of a braking torque request to the braking circuits 10, 20, can thus take place without taking into account the capability indicators BI1, BI2.

[0073] The adaptation range AB is selected such that a value of the respective capability indicator BI1, BI2 in the adaptation range AB indicates that measures should be taken to bring the respective capability indicator BI1, BI2 back into the target range ZB, but that there is still no immediate restriction in the functionality, in particular no safety-critical restriction.

[0074] If a capability indicator BI1, BI2 is in the warning range WB, this indicates that there is a critical restriction in the functionality of the respective brake circuit 10, 20 and that a response should be made, for example by means of a warning message or a degradation of the brake system 5.

[0075] Typically, the control device 30 should ensure that the capability indicators BI1, BI2 remain within the target range ZB during normal vehicle use. This may mean, in particular, that the capability indicators BI1, BI2 of the brake circuits 10, 20 fall below the ideal value of 100% by at most a certain amount.

[0076] In this target range, e.g., of the capability indicators BI1, BI2, the control device 30 can distribute a braking torque request to the brake circuits 10, 20 according to general optimization criteria. For example, if a regenerative braking torque is present on one axle, the other axle can be used completely or largely to build up friction torque. This strategy serves to achieve even tire wear. If the brake circuits 10, 20 are equipped in such a way that different behavior is exhibited with regard to the emission of brake dust, the requested braking torque can be generated completely or largely via the brake circuit 10, 20 with the lower brake dust emission. The braking force distribution can also be adapted to a load condition of the motor vehicle. This can occur in particular if a load condition can be provided from another functional module.Determining a load factor or load condition is generally possible indirectly by correlating vehicle deceleration with the effective total braking torque or by directly measuring methods, such as using sensors for the suspension travel. Load detection methods generally allow a load condition to be taken into account when distributing brake forces.

[0077] If a capability indicator BI1, BI2 falls below the lower limit of the target range ZB into the adaptation range AB, the task of the control device 30 is to shift the distribution toward the axis currently showing the higher capability indicator BI1, BI2. The goal here is to develop the capability indicators BI1, BI2 of the front and rear wheel brake systems or the two brake circuits 10, 20 back toward the target range ZB.

[0078] Reasons for a capability indicator BI1, BI2 dropping into the adaptation range can be, for example, the wear condition or the current thermal load of the respective brake circuit 10, 20. The calculation rule for the capability indicators BI1, BI2 based on such or other parameters is typically part of the software implemented on the control device 30 and / or on separate, not-shown control devices of the brake circuits 10, 20. The calculation rule typically depends on the specific brake technology used. This will be explained in more detail below.

[0079] One possible implementation of the adaptation of the brake force distribution can be done, for example, as described below. a denotes a current distribution factor, where typically a < 1 . This can mean, in particular, that the requested wheel braking torques Tfront, Trear for the front and rear axles, i.e., for the first brake circuit 10 and the second brake circuit 20, result from a total braking torque request Ttotai as follows: Tfront — 1 / 2 Q Ttotal

[0080] Trear = 1 / 2 ( 1 -C() Ttotal-

[0081] If the capability indicators BI1, BI2 are in the adaptation range AB, the distribution factor a can, for example, be incremented by an amount A if BI2 < BI1 (shift forwards), or decremented by an amount A if BI1 < BI2 (shift backwards).

[0082] However, the step-by-step incrementation or decrementation is typically only repeated after a sufficient number of braking operations in order to be able to observe the effect of the changed braking force distribution on the capability indicators BI1, BI2.

[0083] Typically, a limitation of the adjustment range of the distribution parameter a is required. This prevents a particularly one-sided load from occurring.

[0084] The redistribution of braking force just described is particularly effective under the assumption that the capability indicators BI1, BI2 of the two brake circuits 10, 20 do not decrease simultaneously in real vehicle usage scenarios, but that either the first brake circuit 10 or the second brake circuit 20 still has potential, particularly expressed by a higher capability indicator BI1, BI2. Ensuring this is a task of a robust overall design of the braking system 5.

[0085] If, despite robust design and possible adaptation, a strong drop in one or both capability indicators BI1, BI2 occurs, ie the value pair BI1, BI2 is in the warning range WB, this can be used to provide the driver with an early warning of a possible impending (partial) failure of the braking system 5.

[0086] If such a partial failure occurs, this can be communicated, in particular, to the control device 30 and / or other components as a degradation state of the first brake circuit 10 and / or the second brake circuit 20 and / or the braking system 5. Such degradation states can be taken into account in the braking force distribution, in particular through the following strategies:

[0087] Setting a stable brake force distribution in the event of a failure of the anti-skid control (ABS) function. Stable brake force distribution here means, in particular, that the distribution factor a is selected according to the mass distribution and the dimensioning of the wheel brakes so that the rear axle never locks before the front axle.

[0088] Take into account the failure of a front or rear wheel brake, for example no redistribution to the axle with the failed wheel brake.

[0089] Consideration of the failure of the wheel brakes of one axle (no redistribution possible).

[0090] The calculation method used to calculate the capability indicators BI1 and BI2 depends on the technology used. Differences exist, in particular, between electromechanical and electrohydraulic brake actuators, between disc brakes and drum brakes, and between brake actuators with open-loop and closed-loop control of the wheel braking torques.

[0091] For example, the following parameters can be used to calculate the capability indicators BI1 and BI2:

[0092] wear and tear,

[0093] Temperature of electrical components such as sensors, actuators or electronic assemblies.

[0094] In electromechanical brake actuators with open-loop control of the wheel braking torque, an actuator force F is usually generated by adjusting the travel distance s of a linear actuator. Elasticity, which can be described by a characteristic curve F(s), can typically be included in the calculation of the capability indicator BI1, BI2, since high elasticity (above the normal characteristic) indicates heavy loading. This applies analogously to electrohydraulic brake actuators with open-loop control of the wheel braking torque, whereby a hydraulic pressure p replaces the actuator force F and the hydraulic volume displacement V replaces the travel distance s.

[0095] In brake actuators with closed-loop control of the wheel braking torque, a braking torque can be measured directly or indirectly (for example, via an effective support force), and the actuator force can be adjusted accordingly to achieve the requested wheel braking torque. Fluctuations in the transfer behavior between actuator force and wheel braking torque can be compensated in this way. In particular, this can also mean that the actuator control is capable of determining the characteristics of this transfer behavior (for example, a C* parameter). A drop in such characteristics, for example during brake fading (a reduction in the effectiveness of the wheel brake due to high load and the associated high temperature), can therefore be used to influence the capability indicator.

[0096] In particular, a method for adaptive brake force distribution is presented here, which is based in particular on by-wire braking systems suitable for axle-specific control of braking torques. Using capability indicators, a brake force distribution can be influenced, for example, such that the brake force distribution is selected within the design target range of the capability indicators according to the criteria of minimal or uniform tire wear and / or minimal brake dust emissions. Within an adaptation range of the capability indicators, a gradual adjustment of the brake force distribution can take place so that the wheel brakes on the more heavily loaded axle are relieved. If the capability indicators of the wheel brakes on an axle drop significantly, an early warning can be issued.Degradation states, such as the failure of individual or multiple wheel brakes or the failure of the slip control function, can be taken into account when determining the brake force distribution. Approaches for determining the capability indicators for various types of wheel brake actuators are also described herein.

[0097] The advantages of the procedure described here lie in particular in the utilization of the flexibility of the specified class of by-wire braking systems with regard to axle-specific brake force distribution. In particular, the method described here can achieve a reduction in tire wear through even use of the front and rear axles. Likewise, the brake force distribution can be selected to reduce the emission of particulate matter. By applying the method described here for adapting the brake force distribution, it is possible to orient the thermal design of the wheel brakes of one axle more closely to typical vehicle usage scenarios and, in the event of excessive loads, to generate a greater braking force with the wheel brakes of the other axle, provided that this other axle has sufficient reserves.

[0098] The steps mentioned in the method according to the invention can be carried out in the specified order. However, they can also be carried out in a different order, as long as this is technically reasonable. The method according to the invention can be carried out in one of its embodiments, for example, with a specific combination of steps, in such a way that no further steps are carried out. However, in principle, further steps can also be carried out, even those not mentioned.

[0099] It should be noted that features may be described in combination in the claims and the description, for example, to facilitate understanding, although they may also be used separately. Those skilled in the art will recognize that such features may also be combined independently with other features or combinations of features. References in subclaims may indicate preferred combinations of the respective features, but do not exclude other combinations of features.

[0100] Features are presented below in a structured manner. These can be combined with each other and with other features disclosed herein. These features do not constitute the claims of the application. However, they may represent independent aspects of the invention.

[0101] 1. A method for operating a braking system (5) of a motor vehicle, wherein the motor vehicle has at least two axles, each with at least two wheels, wherein the braking system (5) has at least a first braking circuit (10) and a second braking circuit (20), wherein each braking circuit (10, 20) has one or more brakes (11, 12, 21, 22), each of which is assigned to at least one wheel, and wherein each braking circuit (10, 20) is designed to apply braking torque to the wheels of exactly one axle or several axles of the motor vehicle, wherein the method comprises the following steps:

[0102] Determining one or more first parameters of the first brake circuit (10),

[0103] Determining one or more second parameters of the second brake circuit (20),

[0104] Calculating a first capability indicator (BI1 ) from the first parameters, and

[0105] Calculate a second capability indicator (BI2) from the second parameters.

[0106] 2. Method according to feature 1 , which further comprises the following step:

[0107] Distributing a braking torque request between the first brake circuit (10) and the second brake circuit (20) depending on the first capability indicator (BI1) and the second capability indicator (BI2). Method according to one of the preceding features, wherein, if the first capability indicator (BI1) lies in a predetermined first target range (ZB1) and the second capability indicator (BI2) lies in a predetermined second target range (ZB2), distributing a braking torque request between the first brake circuit (10) and the second brake circuit (20)

[0108] - regardless of the first capability indicator (BI1) and the second capability indicator (BI2), and / or

[0109] - using optimization criteria, and / or

[0110] - taking into account regenerative braking on one axle, and / or

[0111] - takes place depending on a loading state of the motor vehicle. Method according to one of the preceding features, wherein, if the first capability indicator (BI1) lies in a predetermined first adaptation range (AB1) and / or if the second capability indicator (BI2) lies in a predetermined second adaptation range (AB2), a braking torque request is distributed between the first brake circuit (10) and the second brake circuit (20) by means of a distribution factor which is determined as a function of the first capability indicator (BI1) and / or the second capability indicator (BI2). Method according to feature 4, wherein after each change in the distribution factor, the distribution factor for a braking torque request, or for a predetermined number of at least two braking torque requests, remains constant.Method according to one of features 4 or 5, wherein the distribution factor is changed in the event of a change such that more braking torque is applied by the brake circuit (10, 20) for which the respective capability indicator (BI1, BI2) indicates a lower load than by the other brake circuit (10, 20). Method according to one of features 4 to 6, wherein the distribution factor is determined such that the brake circuit (10, 20) for which the respective capability indicator (BI1, BI2) indicates a lower load applies the predominant part of the braking torque. Method according to one of the preceding features, wherein, if the first capability indicator (BI1) lies in a predetermined first warning range (WB1) and / or if the second capability indicator (BI2) lies in a predetermined second warning range (WB2), a warning message is issued and / or the braking system (5) is degraded.Method according to feature 8, wherein, in a degraded braking system (5), a braking torque distribution between the first brake circuit (10) and the second brake circuit (20) is adjusted such that the front axle locks before the rear axle locks, and / or a brake circuit (10, 20) with at least one failed brake (11, 12, 21, 22) does not apply any braking torque. Method according to one of the preceding features, wherein, in at least one or several wear periods, a braking torque requirement is distributed between the first brake circuit (10) and the second brake circuit (20) such that a braking torque is predominantly applied by the brake circuit (10, 20) for which the capability indicator (BI1, BI2) indicates a higher load.Method according to one of the preceding features, wherein, in the case of a braking torque request that is greater than a threshold value and / or in the case of a braking torque request for which distribution among the brake circuits (10, 20) is not possible, the brake circuits (10, 20) are controlled independently of the capability indicators. Method according to one of the preceding features, wherein an energy input into the brakes (11, 12) of the first brake circuit (10) and an energy removal from the brakes (11, 12) of the first brake circuit (10) are parameters of the first brake circuit (10), and / or wherein an energy input into the brakes (21, 22) of the second brake circuit (20) and an energy removal from the brakes (21, 22) of the second brake circuit (20) are parameters of the second brake circuit (20).Method according to one of the preceding features, wherein the parameters of the first brake circuit (10) and / or the second brake circuit (20) comprise one or more of the entries in the following list:.

[0112] - temperature of one or more brakes (11, 12, 21, 22),

[0113] - Temperature of one or more electrical components,

[0114] - wear condition of one or more brakes (11, 12, 21, 22) or other components,

[0115] - friction partner of one or more brakes (11, 12, 21, 22),

[0116] - Energy input into one or more brakes (11, 12, 21, 22),

[0117] - Energy dissipation from one or more brakes (11, 12, 21, 22),

[0118] - assigned mass of one or more brakes (11, 12, 21, 22),

[0119] - one or more characteristic values ​​of a torque control of at least one brake (10, 12, 21, 22),

[0120] - one or more characteristic values ​​of a force setting of at least one brake (10, 12, 21, 22). Method according to one of the preceding features, wherein the first brake circuit (10) and the second brake circuit (20) act on mutually different axes. Method according to one of the preceding features, wherein the first brake circuit (10) has at least one first brake actuator and the second brake circuit (20) has at least one second brake actuator, wherein the first brake actuator and the second brake actuator can be controlled independently of one another. Method according to feature 15, wherein the first brake actuator is a hydraulic brake actuator which applies pressure to brakes (11, 12) of the first brake circuit (10), and / or wherein the second brake actuator is a hydraulic brake actuator which applies pressure to brakes (21, 22) of the second brake circuit (20).Method according to one of the preceding features, wherein the first brake circuit (10) has one or more brakes (11, 12) which can be actuated by means of an electromechanical brake actuator, and / or wherein the second brake circuit (20) has one or more brakes (21, 22) which can be actuated by means of an electromechanical brake actuator.Method according to one of the preceding features, wherein the first capability indicator (BI1) indicates a load and / or a remaining braking capacity of the first brake circuit (10), and / or wherein the second capability indicator (BI2) indicates a load and / or a remaining braking capacity of the second brake circuit (20), and / or wherein the load on the first brake circuit (10) is higher, the lower the remaining braking capacity of the first brake circuit (10), and / or wherein the load on the second brake circuit (20) is higher, the lower the remaining braking capacity of the second brake circuit (20).Method according to one of the preceding features, wherein the first capability indicator (BI1) is calculated exclusively from the first parameters and / or exclusively from parameters of the first brake circuit (10), and / or wherein the second capability indicator (BI2) is calculated exclusively from the second parameters and / or exclusively from parameters of the second brake circuit (20). Method according to one of the preceding features, wherein the first capability indicator (BI1) is a numerical value, and / or wherein the second capability indicator (BI2) is a numerical value. Braking system (5) for a motor vehicle, wherein the braking system (5) comprises: a first brake circuit (10), a second brake circuit (20), and a control device (30) which is configured to carry out a method according to one of the preceding features. List of reference symbols.

[0121] BI1 first capability indicator

[0122] BI2 second capability indicator

[0123] E.g. target area

[0124] AB adaptation area

[0125] WB warning area

[0126] 5 Braking system

[0127] 10 first brake circuit

[0128] 11 first brake

[0129] 12 second brake

[0130] 20 second brake circuit

[0131] 21 first brake

[0132] 22 second brake

[0133] 30 Control device

[0134] 40 Function module

[0135] 42 Sensor technology

[0136] 50 more information

Claims

Patent claims 1. A method for operating a braking system (5) of a motor vehicle, wherein the motor vehicle has at least two axles, each with at least two wheels, wherein the braking system (5) has at least a first braking circuit (10) and a second braking circuit (20), wherein each braking circuit (10, 20) has one or more brakes (11, 12, 21, 22) which are exclusively friction brakes and are each assigned to at least one wheel, and wherein each braking circuit (10, 20) is designed to apply braking torque to the wheels of exactly one axle or several axles of the motor vehicle exclusively by means of the friction brakes, the method comprising the following steps: Determining one or more first parameters of the first brake circuit (10), Determining one or more second parameters of the second brake circuit (20), Calculating a first capability indicator (BI1 ) from the first parameters, and Calculate a second capability indicator (BI2) from the second parameters.

2. The method according to claim 1, further comprising the step of: Distributing a braking torque request between the first brake circuit (10) and the second brake circuit (20) depending on the first capability indicator (BI1) and the second capability indicator (BI2).

3. Method according to one of the preceding claims, wherein, if the first capability indicator (BI1) lies in a predetermined first target range (ZB1) and the second capability indicator (BI2) lies in a predetermined second target range (ZB2), a distribution of a braking torque request between the first brake circuit (10) and the second brake circuit (20) - regardless of the first capability indicator (BI1) and the second capability indicator (BI2), and / or - using optimization criteria, and / or - taking into account regenerative braking on one axle, and / or - depends on the loading condition of the vehicle.

4. Method according to one of the preceding claims, wherein, if the first capability indicator (BI1) lies in a predetermined first adaptation range (AB1) and / or if the second capability indicator (BI2) lies in a predetermined second adaptation range (AB2), a braking torque request is divided between the first brake circuit (10) and the second brake circuit (20) by means of a distribution factor which is determined as a function of the first capability indicator (BI1) and / or the second capability indicator (BI2).

5. The method according to claim 4, wherein after each change in the distribution factor, the distribution factor remains constant for a braking torque request, or for a predetermined number of at least two braking torque requests.

6. Method according to one of claims 4 or 5, wherein the distribution factor is changed in the event of a change such that more braking torque is applied by the brake circuit (10, 20) for which the respective capability indicator (BI1, BI2) indicates a lower load than for the other brake circuit (10, 20).

7. Method according to one of claims 4 to 6, wherein the distribution factor is determined such that the brake circuit (10, 20) for which the respective capability indicator (BI1, BI2) indicates a lower load applies the predominant part of the braking torque.

8. Method according to one of the preceding claims, wherein, if the first capability indicator (BI1) is in a predetermined first warning range (WB1) and / or if the second capability indicator (BI2) is in a predetermined second warning range (WB2), a warning message is issued and / or the braking system (5) is degraded.

9. The method according to claim 8, wherein, in the case of a degraded braking system (5), a braking torque distribution between the first braking circuit (10) and the second braking circuit (20) is set such that the front axle locks before the rear axle locks, and / or a braking circuit (10, 20) with at least one failed brake (11, 12, 21, 22) does not apply any braking torque.

10. Method according to one of the preceding claims, wherein in at least one or some wear periods, a braking torque request is divided between the first brake circuit (10) and the second brake circuit (20) in such a way that a braking torque is predominantly applied by the brake circuit (10, 20) for which the capability indicator (BI1, BI2) indicates a higher load. 11 . Method according to one of the preceding claims, wherein in the case of a braking torque request which is greater than a threshold value and / or in the case of a braking torque request for which a distribution to the brake circuits (10, 20) is not possible, the braking circles (10, 20) are controlled independently of the capability indicators.

12. Method according to one of the preceding claims, wherein an energy input into the brakes (11, 12) of the first brake circuit (10) and an energy dissipation from the brakes (11, 12) of the first brake circuit (10) are parameters of the first brake circuit (10), and / or wherein an energy input into the brakes (21, 22) of the second brake circuit (20) and an energy dissipation from the brakes (21, 22) of the second brake circuit (20) are parameters of the second brake circuit (20).

13. Method according to one of the preceding claims, wherein the parameters of the first brake circuit (10) and / or the second brake circuit (20) comprise one or more of the entries in the following list: - temperature of one or more brakes (11, 12, 21, 22), - Temperature of one or more electrical components, - wear condition of one or more brakes (11, 12, 21, 22) or other components, - friction partner of one or more brakes (11, 12, 21, 22), - Energy input into one or more brakes (11, 12, 21, 22), - Energy dissipation from one or more brakes (11, 12, 21, 22), - assigned mass of one or more brakes (11, 12, 21, 22), - one or more characteristic values ​​of a torque control of at least one brake (10, 12, 21, 22), - one or more characteristic values ​​of a force setting of at least one brake (10, 12, 21, 22).

14. Method according to one of the preceding claims, wherein the first brake circuit (10) and the second brake circuit (20) act on mutually different axes.

15. Method according to one of the preceding claims, wherein the first brake circuit (10) has at least one first brake actuator and the second brake circuit (20) has at least one second brake actuator, wherein the first brake actuator and the second brake actuator can be controlled independently of one another.

16. The method according to claim 15, wherein the first brake actuator is a hydraulic brake actuator which applies pressure to brakes (11, 12) of the first brake circuit (10), and / or wherein the second brake actuator is a hydraulic brake actuator which applies pressure to brakes (21, 22) of the second brake circuit (20).

17. Method according to one of the preceding claims, wherein the first brake circuit (10) has one or more brakes (11, 12) which can be actuated by means of an electromechanical brake actuator, and / or wherein the second brake circuit (20) has one or more brakes (21, 22) which can be actuated by means of an electromechanical brake actuator.

18. Method according to one of the preceding claims, wherein the first capability indicator (BI1) indicates a load and / or a remaining braking capacity of the first brake circuit (10), and / or wherein the second capability indicator (BI2) indicates a load and / or a remaining braking capacity of the second brake circuit (20), and / or wherein the load of the first brake circuit (10) is higher, the lower the remaining braking capacity of the first brake circuit (10), and / or wherein the load on the second brake circuit (20) is higher, the lower the remaining braking capacity of the second brake circuit (20) is.

19. Method according to one of the preceding claims, wherein the first capability indicator (BI1) is calculated exclusively from the first parameters and / or exclusively from parameters of the first brake circuit (10), and / or wherein the second capability indicator (BI2) is calculated exclusively from the second parameters and / or exclusively from parameters of the second brake circuit (20).

20. Method according to one of the preceding claims, wherein the first capability indicator (BI1) is a numerical value, and / or wherein the second capability indicator (BI2) is a numerical value.

21. Braking system (5) for a motor vehicle, the braking system (5) comprising: a first brake circuit (10), a second brake circuit (20), and a control device (30) configured to carry out a method according to one of the preceding claims.

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