Method for operating a brake system and brake system

Abstract

The invention relates to a method for operating a brake system of a motor vehicle, in which a capability indicator is calculated on the basis of parameters of two brake circuits, which capability indicator indicates the current capability of the respective brake circuit. The invention also relates to a brake system for carrying out the method.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for operating a brake system of a motor vehicle and to a related brake system. BACKGROUND

[0002] Brake systems are generally used in motor vehicles in order to decelerate the vehicle in a targeted manner. To this end, the brake system generally has brakes which act on at least one wheel of the motor vehicle, respectively. SUMMARY

[0003] It is an object of the present application to provide a method for operating a brake system of a motor vehicle which, for example, enables an improved brake system control. It is a further object of the present application to provide a brake system for carrying out the method. The above objects are achieved according to the present application by the method and the brake system according to the respective independent claims. Advantageous design schemes can be derived, for example, from the respective dependent claims. The content of the claims is incorporated into the content of the description by explicit reference.

[0004] The present application relates to a method for operating a brake system of a motor vehicle. The motor vehicle generally has at least two axles, each of which generally has at least two wheels, respectively. The brake system has a first brake circuit and a second brake circuit. Each brake circuit generally has one or more brakes which are assigned to at least one wheel, respectively. Each brake circuit is generally configured to apply a brake torque to the wheels of exactly one axle or a plurality of axles of the motor vehicle. The brakes are preferably friction brakes. Each brake circuit is preferably configured to apply a brake torque to the wheels exclusively by means of friction brakes.

[0005] The method comprises the following steps: - determining one or more first parameters of the first brake circuit, - determining one or more second parameters of the second brake circuit, - calculating a first capability indicator from the first parameters, - calculating a second capability indicator from the second parameters.

[0006] By means of this method, a capability indicator can be provided which can contribute to a better management of the brake system. For example, the capability indicator can indicate the capability of the two brake circuits in terms of an absolute performance at the moment or a relative performance with respect to each other and / or a trend of this capability over time. The brake system can thus be operated in a targeted manner in order to achieve a certain state or to operate the load of the two brake circuits in a targeted manner.

[0007] A braking system is generally understood as a system in a motor vehicle used for targeted deceleration (i.e., reducing vehicle speed). Here, it typically refers to a system that is not directly integrated into the power unit, i.e., it does not act as a brake for the power unit. An axle typically includes at least two wheels, which are usually arranged in the same position along the longitudinal direction of the vehicle. In passenger cars, one wheel is typically mounted on each side of the vehicle. In larger vehicles (such as trucks or buses), dual-tire configurations may also exist, where, for example, two wheels may be present on one side of an axle. These wheels can be implemented, for example, such that a single brake acts on both wheels on one side. Alternatively, each wheel may be assigned its own brake. Typically, each brake acts on one or more wheels to which it is assigned.

[0008] The brake is typically a friction brake. For example, it can be a disc brake or a drum brake. However, other implementations, such as eddy current brakes, can also be used.

[0009] According to one embodiment, each braking circuit is assigned to exactly one axle. In this case, the brakes of that braking circuit act only on the wheels of that axle and not on the wheels of the other axle. However, a braking circuit can also be assigned to multiple axles of a motor vehicle. For example, a braking circuit can be assigned to the wheels of a tandem axle (i.e., a combination of two axles arranged in succession at a short distance). In this embodiment, a braking circuit typically either acts on all the brakes of an axle or does not act on any of the brakes of an axle.

[0010] The first parameter is a parameter related to the first braking circuit. The second parameter is a parameter related to the second braking circuit. In other words, the first parameter characterizes the first braking circuit, and the second parameter characterizes the second braking circuit. The parameters may also be, for example, those described below.

[0011] If all brakes are friction brakes and the braking circuit is constructed to apply braking torque solely through friction brakes, then the parameters must necessarily originate only from components related to the action of one or more friction brakes. Therefore, the parameters, in particular, do not originate from components that achieve braking via a regenerative motor. The braking systems considered in this paper are, in particular, pneumatic braking systems, hydraulic braking systems, braking systems with electrically operated friction brakes, or combinations thereof. Such braking systems can be used in conjunction with motors, which can also perform regenerative braking, but are not considered part of the braking system. Here, a friction brake is specifically understood as a brake in which two relatively moving components rub against each other. This converts a portion of the kinetic energy into heat energy.

[0012] Capability indicators reveal the current capability or other state of the corresponding braking circuit. Capability indicators are particularly useful for targeted control of the braking system, such as entering a specific operating state or specifically influencing wear. Other objectives, such as reducing dust emissions, can also be advantageously achieved with the help of capability indicators. This will be explained in detail below. In any case, the existence of calculated capability indicators is itself a significant innovation compared to known braking systems, enabling optimized control of the braking system and producing beneficial effects.

[0013] The calculation of ability indicators can be carried out, in particular, by using algorithmic calculation rules and / or mathematically prescribed formulas.

[0014] According to one implementation, the method further includes the step of: allocating braking torque demand to a first braking circuit and a second braking circuit based on a first capability index and a second capability index.

[0015] Therefore, these two capability indicators can be used specifically to distribute braking torque demand to the two braking circuits. Braking torque demand is typically the need to decelerate the vehicle, and it can originate from the driver or vehicle control systems, such as driver assistance systems or automated driving control systems. The braking system's task is usually to execute this braking torque demand, causing the vehicle to decelerate in a desired manner. Here, the distribution of braking torque demand to the two braking circuits can advantageously be based on these two capability indicators. This allows for, for example, targeted control of wear in the two braking circuits, or the achievement of other specific objectives.

[0016] A first target range can be preset for a first capability indicator. A second target range can be preset for a second capability indicator. The target range can be the expected numerical range of the corresponding capability indicator, i.e., the numerical range indicating that the corresponding braking circuit is operating normally without abnormal wear. The target range can be preset in a fixed manner so that it does not change during the driving of the vehicle equipped with the braking system or during the operation of the braking system. Other ranges disclosed herein, i.e., particularly the adaptation range and the warning range, can also be applied to this rule. Accordingly, when the first capability indicator is within the preset first target range and the second capability indicator is within the preset second target range, the allocation of braking torque demand to the first braking circuit and the second braking circuit can be carried out independently of the first capability indicator and / or the second capability indicator. In other words, when both capability indicators are within their respective target ranges, it is not necessary to consider the specific numerical values ​​of the capability indicators. In this case, other optimization criteria can be used. For example, optimization criteria aimed at minimizing wear or minimizing brake dust emissions may be involved. Regenerative braking on the axle can be considered. Thus, for example, when regenerative braking is also performed on the axle where the brakes of the braking circuit are arranged, the braking force of the braking circuit can be reduced.

[0017] Regeneration typically refers to converting excess kinetic energy of a motor vehicle into electrical energy using an electric motor. In particular, the greater the regenerative braking force applied to the same wheels, the greater the reduction in braking force generated by the braking system. The distribution of braking torque demand to the first and second braking circuits can also be related to the vehicle's load condition. This can be considered, for example, by load detection using suitable sensor devices. Therefore, gentler and / or more comfortable braking can be achieved. As mentioned above, all these methods are particularly applicable when the first capability indicator is within a preset first target range and the second capability indicator is within a preset second target range.

[0018] Especially when the braking system works in conjunction with regenerative braking (which can be generated, for example, by a motor, especially on the rear axle), it can be stipulated that, whenever feasible, the maximum braking torque applied by regenerative braking is greater than the braking demand, and the braking demand is achieved solely through regenerative braking.

[0019] Especially for situations where the vehicle speed is greater than the speed threshold (e.g., at least 5 km / h or at most 9 km / h, or 7 km / h), it can be stipulated that: if the maximum braking torque that can be applied by regenerative braking is insufficient, the brakes at the front axle should be used first, especially when the deceleration corresponding to the braking torque to be applied at the front axle is not higher than the deceleration threshold (e.g., 0.1g).

[0020] In particular, the braking torque required at the front axle can be limited to half of the maximum braking torque that can be generated by regenerative braking. Other ratios other than half can also be used.

[0021] If the vehicle speed is below the speed threshold, another deceleration threshold can be used. This deceleration threshold can be higher than the deceleration threshold when the speed threshold is exceeded, for example, it can be 0.15g.

[0022] If the required braking torque is greater than the sum of the maximum braking torque that regenerative braking can apply and the braking torque that can be generated on the front axle by the braking system before reaching the deceleration threshold, then the braking torque that the braking system needs to apply can be distributed to the front axle and the rear axle in a preset ratio, such as 60:40.

[0023] The strategies described above, when used in conjunction with regenerative braking, can be used independently of other measures described herein. These strategies are particularly useful when the vehicle is moving forward and backward.

[0024] The scope can be preset to be stored in the control system. However, adaptation can also be specified, for example, during braking system operation or during factory maintenance.

[0025] An appropriate adaptation range can be set for the capability indicators. The adaptation range typically indicates that although the corresponding braking circuit is not in a dangerous / critical state, its state is at least not as ideal as the state in which the corresponding capability indicator is within the target range. This especially demonstrates the necessity to take measures to act on the corresponding braking circuit to change its capability indicator back towards the target range.

[0026] Especially when the first capability index is within a preset first adaptation range and / or the second capability index is within a preset second adaptation range, the braking torque demand can be allocated to the first and second braking circuits via an allocation coefficient. This allocation coefficient can be determined based on the first and / or second capability indexes. This allows consideration of the relative current capabilities of the two braking circuits. The allocation of braking torque demand to the two braking circuits can be specifically implemented by applying a targeted load to the braking circuit whose capability index is currently within the adaptation range, causing its capability index to shift back towards the target range. For example, the load on this braking circuit can be reduced. This is particularly applicable when the other capability index is within the target range. For example, if one capability index is within the target range and the other is within the adaptation range, then, for example, the braking circuit whose capability index is within the adaptation range can have its load reduced, causing its capability index to shift back towards the target range.

[0027] Specifically, after each change in the allocation coefficient, the coefficient remains constant for a single braking torque demand or for at least two predetermined braking torque demands. This ensures that the allocation coefficient does not change frequently, but rather allows for observation of whether the most recent change has the expected impact on the capability indicators. For example, the predetermined number could be two, three, four, five, ten, fifteen, twenty, or more braking torque demands. Here, braking torque demand is generally understood as the demand for braking torque in a motor vehicle operating scenario, which begins, for example, when a braking torque demand is made and ends when the demand ceases. In typical operating scenarios, this period typically lasts several seconds, and in special scenarios, such as during prolonged downhill driving, the braking torque demand may last even longer. The allocation coefficient can also have only a limited numerical range. This prevents one braking circuit from being subjected to excessive load.

[0028] The applicable range and target range of the corresponding capability indicators can be directly adjacent, and can also be different from each other.

[0029] Specifically, the distribution coefficient can be adjusted when changes occur so that the braking torque is applied more by the braking circuit whose load, as indicated by the capability index, is lower than that of the other braking circuit. This allows for targeted increases in the load on the currently more capable braking circuit. Therefore, it particularly promotes load balancing between the two braking circuits.

[0030] Specifically, the allocation factor can be determined such that the braking torque applied by the braking circuit with the lower load, as indicated by the corresponding capacity index, constitutes the majority of the braking torque. This also allows for appropriate load balancing between the two braking circuits.

[0031] It can be specified that a corresponding warning range is defined for each capability indicator. This typically involves the range from which the critical state of the corresponding braking circuit begins. The corresponding warning range may 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 specified that the warning range, adaptation range, and target range together cover the entire possible numerical range of the corresponding capability indicator. Here, the adaptation range is particularly positioned between the warning range and the target range. The mentioned ranges are particularly directly adjacent to each other and / or do not overlap. In particular, it can be specified that a warning message is output and / or the braking system is degraded when the first capability indicator is in a preset first warning range and / or the second capability indicator is in a preset second warning range. The warning message can be used to specifically alert the driver. Here, for example, acoustic or optical warning messages may be involved. Warning messages may involve, for example, further processing in the vehicle's electronic systems and causing a specific reaction, and / or warning messages sent to a central unit (e.g., a fleet monitoring system or a repair shop). Degradation of the braking system specifically means that the braking system switches to another operating mode in which, for example, certain functions (e.g., functions not essential for the safety of the motor vehicle) are disabled. This can, for example, reduce the load on the braking system; it can also, for example, limit the vehicle's functions so that, for example, it cannot exceed a certain maximum speed.

[0032] Specifically, it can be stipulated that, when the braking system is degraded, the braking torque distribution between the first and second braking circuits is adjusted so that the front axle locks up before the rear axle. This increases the braking force on the front axle, which typically bears a higher load during braking. When the braking system is degraded, it can also be stipulated that the braking circuit with at least one failed brake does not apply braking torque. In this case, the scenario of complete brake failure (e.g., due to mechanical damage) can be considered, so that the corresponding braking circuit no longer applies braking torque, while another braking circuit applies the full braking torque. This improves traffic safety because there is no attempt to use the failed brake. Specifically, it can be stipulated that when brake failure is detected, the capability index of the corresponding braking circuit is changed to the warning range.

[0033] According to one feasible implementation, the braking torque demand is distributed to the first and second braking circuits in at least some wear cycles by ensuring that the braking torque is primarily applied by the braking circuit with the higher load indicated by the capability index. By defining such wear cycles, one braking circuit can be worn in a targeted manner, i.e., the load on an already heavily loaded braking circuit can be intentionally increased, thereby intentionally accelerating the wear of one of the two braking circuits. This, for example, can protect the other braking circuit. This can also, for example, have a positive impact on maintenance intervals, since the braking circuit whose wear is intentionally accelerated is already in need of maintenance, while the other braking circuit receives a longer maintenance interval. Here, the wear cycle can be understood as the time period during which such an operating strategy is employed.

[0034] Especially when the braking torque demand exceeds a threshold and / or when the braking torque demand cannot be allocated to the braking circuit, the braking circuit is manipulated regardless of the capability index. Such adjustments are particularly preferable to all other possible methods of allocating the braking torque demand to both braking circuits. If the threshold is exceeded and / or cannot be allocated to the braking circuit, it is advantageous to disregard considerations of targeted impacts on the braking system and instead apply the full braking torque demand. This avoids the possibility that the braking torque demand might not be fully applied due to the intentional management of the braking system, thus jeopardizing the traffic safety of the motor vehicle. Possible parameters will be described below. These parameters can be incorporated into the calculation of the capability index and can be used individually or in any combination thereof.

[0035] According to one embodiment, the energy input to and / or energy output from the brakes of the first braking circuit are parameters of the first braking circuit. According to one embodiment, the energy input to and / or energy output from the brakes of the second braking circuit are parameters of the second braking circuit. The energy input and energy output can be measured by sensors and / or calculated based on a model, for example. Here, for example, the applied braking force, vehicle speed, vehicle load, ambient temperature, or the corresponding current wear of the brakes can be considered.

[0036] The parameters of the first braking circuit and / or the second braking circuit may in particular include one or more of the following parameters: - The temperature of one or more brakes, - The temperature of one or more electrical components, - The wear condition of one or more brakes or other components. - Friction pairs of one or more brakes, - Energy input to one or more brakes, - Energy output from one or more brakes, - The relevant mass of one or more brakes, - One or more characteristic values ​​for the torque regulation of at least one brake. - One or more characteristic values ​​of the force setting of at least one brake.

[0037] The temperature of brakes or electrical components can be derived, for example, through a model, by which the temperature can be calculated. Alternatively, the temperature can be measured by a temperature sensor. Wear conditions can be considered, for example, the current thickness of the brake pads. This wear condition can be derived, for example, through model calculation or sensor measurement. Friction pairs can specifically refer to the materials used in friction brakes that rub against each other. Energy input and energy output can be derived, for example, through a suitable model calculation, from which the corresponding temperatures of the components can be inferred. Related mass can be used, in particular, to absorb the heat generated during braking. Related mass is typically capable of absorbing such heat and also dissipates it to the surrounding environment for a considerable period after the braking process. Torque regulation is typically a regulation that ensures the application of a specific braking torque; this is also known as a "closed loop." Force setting is typically setting the correct desired braking force on the brake; this is also known as an "open loop." The corresponding regulation or setting can have characteristic values, which are stored or implemented in the corresponding control system. Characteristic values ​​can be fixed or variable. Characteristic values ​​can be adapted, for example, during the operation of the motor vehicle.

[0038] The aforementioned electrical components may be, for example, sensors, regulating motors / servo motors, or electronic components, whose temperature or other conditions may affect the corresponding availability and reliability of the assigned braking circuit.

[0039] The first and second braking circuits can act on different axles in particular. This allows the measures described herein to be applied to specific axles. This allocation is often referred to as black-and-white allocation. According to a corresponding embodiment, the first braking circuit has at least one first brake actuator, and / or the second braking circuit has at least one second brake actuator. The first and second brake actuators can be operated independently of each other. With these brake actuators, corresponding pressures, such as hydraulic pressure, can be generated and set in the braking circuits. By using separate brake actuators, different pressures can be applied in the respective braking circuits.

[0040] Specifically, the first brake actuator can be a hydraulic brake actuator that applies pressure to the brake in the first brake circuit. Similarly, the second brake actuator can be a hydraulic brake actuator that applies pressure to the brake in the second brake circuit. Such hydraulic brake actuators can be, for example, a hydraulic pump capable of continuous delivery, or, for example, a linear actuator typically used for intermittent pressure build-up.

[0041] The first braking circuit may have one or more brakes that can be operated by an electromechanical brake actuator. The second braking circuit may have one or more brakes that can be operated by an electromechanical brake actuator. The electromechanical brake actuator is typically an actuator that operates the brake without hydraulic intervention, for example, by means of an electric motor or electromagnet. Here, in particular, the control or supply can be directly converted into braking force by means of electric current.

[0042] Typically, each brake can only be operated electrically or hydraulically. However, in principle, a combination of hydraulic and electric operation is also possible. The braking circuit can be implemented as purely hydraulic, purely electric, or a combination of both. Specifically, a first capability index can be specified to indicate the load and / or remaining braking capacity of the first braking circuit. In particular, a second capability index can be specified to indicate the load and / or remaining braking capacity of the second braking circuit. By indicating the load, the capability index can indicate the current load level of the corresponding braking circuit. By displaying the remaining braking capacity, it can indicate the potential currently available for applying braking force. This potential may be reduced due to excessive temperature of the friction brake caused by the braking circuit load or, in worst-case scenario, brake failure.

[0043] Specifically, the lower the residual braking capacity of the first braking circuit, the higher its load. Similarly, the lower the residual braking capacity of the second braking circuit, the higher its load. Here, braking capacity is generally understood as the maximum applicable braking torque, or a combined indicator of the applicable braking torque and the time for which it can be applied.

[0044] Specifically, it can be specified that the first capability index is calculated solely based on the first parameter and / or solely based on the parameters of the first braking circuit. Similarly, it can be specified that the second capability index is calculated solely based on the second parameter and / or solely based on the parameters of the second braking circuit. This prevents the characteristics of the corresponding other braking circuit from affecting the braking circuit under consideration.

[0045] Specifically, the first capability indicator can be numerical. Similarly, the second capability indicator can also be numerical. Using numerical values ​​allows the parameters under consideration to be summarized into a single value, which comprehensively reflects the current capability of the corresponding braking circuit. The numerical value can be a single number or its suitable electronic representation. Therefore, numerical values ​​are typically one-dimensional.

[0046] The present invention also relates to a braking system for a motor vehicle, wherein the braking system has a first braking circuit, a second braking circuit, and a control device configured to implement the methods described herein. The present invention also relates to a non-volatile computer-readable storage medium having program code stored thereon, wherein, when the program code is executed, a processor performs the methods described herein. Accordingly, all embodiments and variations described herein may be employed.

[0047] Specifically, the braking system, or the braking system used to implement the methods described herein, can be a brake-by-wire system. In such systems, there is typically no hydraulic connection between the driver-operated brake pedal and the wheel brakes, at least not during normal operation. Instead, the driver's braking intention is sensed and implemented via an electrically operated pressure generator, actuator, or other unit. Nevertheless, a hydraulic backup stage can be provided for emergencies, particularly in the event of a power failure, in which a hydraulic connection exists between the driver-operated master brake cylinder and the wheel brakes.

[0048] In principle, more than two braking circuits can also be used. This may be the case, for example, when a vehicle has more than two axles. In this case, the implementation scheme previously given for the two described braking circuits is correspondingly applicable to other braking circuits.

[0049] In general, it should be noted that brake-by-wire systems, in principle, allow the wheel braking torque to be set independently of the driving force applied. For example, a central pressure regulator can be used to ensure that the hydraulic braking pressure in all four wheel brakes is the same, thus preventing changes to the braking force distribution based on the initial settings of the wheel brakes on the front and rear axles. However, there are also braking systems that can set the wheel braking torque for each axle.

[0050] For example, advanced braking systems that use electromechanical wheel brakes on all four wheels are also suitable for distributing braking force to each axle or even to each wheel.

[0051] If a conventional static braking force distribution is simulated in such a system by distributing the required total braking torque to the front and rear axles with a fixed distribution coefficient, the system advantages of braking force distribution to each axle can only be utilized to a limited extent. For example, it is impossible to cope with the different thermal characteristics of the front and rear wheel brakes. This is especially true when wheel braking torque regulation (closed loop) is used at the rear wheel brakes, while braking pressure or clamping force regulation (open loop) is used at the front wheel brakes. For example, it is impossible to advantageously select wheel brakes to prioritize braking intentions based on the situation, that is, it is especially impossible to pursue optimization goals such as reducing dust emissions from brakes or tires. Furthermore, if regenerative braking torque only acts on one axle, it is difficult or impossible to consider regenerative braking torque in electric vehicles. Attached Figure Description

[0052] Other features and advantages will become apparent to those skilled in the art from the embodiments described below in conjunction with the accompanying drawings. Wherein: Figure 1 The braking system is shown; Figure 2 The numerical range of the capability indicators is shown. Detailed Implementation

[0053] Figure 1 A block diagram of a braking system 5 according to an embodiment of the present invention is shown purely schematically.

[0054] Braking system 5 has a first braking circuit 10 and a second braking circuit 20. The first braking circuit 10 has a first brake 11 and a second brake 12. Similarly, the second braking circuit 20 has a first brake 21 and a second brake 22. For example, the first braking circuit 10 can be assigned to the front axle, and the second braking circuit 20 can be assigned to the rear axle. The corresponding first brakes 11 and 21 can, for example, be assigned to the corresponding left wheels. The corresponding second brakes 12 and 22 can be assigned to the corresponding right wheels. However, other assignments are also possible. In any case, the architecture of this braking system 5 can be abstractly described as two independent braking circuits for the front and rear axles, wherein each braking circuit in principle consists of two wheel brakes, but depending on the specific technical embodiment, it may consist of one or two brake actuators and one or two electronic control units, or have the aforementioned components. However, other embodiments are also feasible in principle.

[0055] The braking system 5 also includes a control device 30. This control device is configured to implement the method according to the invention according to at least one embodiment. Specific embodiments will be discussed in detail below.

[0056] The braking system 5 also includes a functional module 40 for detecting the driver's braking intention. This functional module is coupled to a sensor device 42 for detecting the driver's braking intention. Sensor values ​​can then be transmitted to the functional module 40, allowing a braking torque demand to be sent to the control device 30 based on the driver's braking intention. Additionally or alternatively, braking torque demands, for example, from a driver assistance system or a vehicle automatic control system, can be transmitted to the control device 30. As shown, the control device 30 is capable of corresponding bidirectional communication with the two braking circuits 10, 20. In particular, the control device 30 can transmit a corresponding demand for applying braking torque to each of the two braking circuits 10, 20, or ensure the corresponding application of braking torque. For this purpose, for example, hydraulic wheel brakes, electromechanical wheel brakes, electric pressure regulators and / or valves or other devices for the corresponding hydraulic system can be operated. The corresponding braking circuits 10, 20 can send parameters to the control device 30, which can be used to calculate the capability indicators of the corresponding braking circuits 10, 20. This will be described in detail below.

[0057] It should be noted that the control device 30 shown here is only schematic and may also be integrated into other components or have its functions separated.

[0058] Sensor device 42 can be used to detect, for example, the driver's braking intention. A signal is generated here, which indicates, for example, the travel and / or force of the brake pedal. Functional module 40 can calculate, based on such signals, the total required braking torque to decelerate the vehicle.

[0059] In the control device 30, the total required braking torque can be distributed according to the torque requirements of the two braking circuits 10 and 20 as needed.

[0060] In addition to detecting the driver's intention to brake, other information, schematically shown by reference numeral 50, can also be input into the control device 30 and used accordingly.

[0061] In one specific implementation, signal exchange between the illustrated components and / or other components may be achieved, for example, via a communication interface (such as a CAN bus).

[0062] In principle, the established braking force distribution should remain stable, especially to avoid excessive braking of the axles that could lead to loss of driving stability (e.g., excessive braking of the rear axle) or loss of steering ability (e.g., excessive braking of the front axle). As long as both axles have wheel anti-slip adjustment capabilities, stability and steering ability can be ensured. In this case, braking force distribution can also be selected based on standards other than stability criteria.

[0063] Unlike traditional pedal coupling systems, brake-by-wire systems typically support wheel anti-slip adjustment without interfering with the driver.

[0064] Based on a brake-by-wire system that allows for individual axle setting of wheel braking torque, a method can be implemented that specifies braking force distribution based on capability indicators of braking circuits 10 and 20. These capability indicators can be understood as part of the interface between braking force distribution and braking circuits 10 and 20.

[0065] Figure 2 A graph is shown illustrating the plotting of a first capability index BI1 and a second capability index BI2. These indices can take values ​​between 0% and 100%. Here, the first capability index BI1 is assigned to the first braking circuit 10 and calculated based on the parameters of the first braking circuit 10. The second capability index BI2 is assigned to the second braking circuit 20 and calculated based on the parameters of the second braking circuit.

[0066] Here, capability indicators BI1 and BI2 are expressed as percentage values. A value of 100% indicates that there are no limitations within the corresponding braking circuits 10 and 20, and the use of their brakes or actuators can be freely defined. A value of less than 100% for the corresponding capability indicators BI1 and BI2 indicates that there are limitations within the system, or that limitations are expected to occur under continuous use.

[0067] Even if the values ​​of the corresponding capability indices BI1 and BI2 are below 100%, the braking system 5 should still fully achieve the required braking torque within its physical limits. This ensures, especially during emergency braking, that the vehicle's maximum possible deceleration is always achieved, even if a limitation has been identified and indicated by one or both capability indices BI1 and BI2 being below 100%. The capability indices BI1 and BI2 should be used, in particular, by the control device 30 to achieve braking force distribution and influence the required braking torque, more precisely, to alter its distribution between the two braking circuits 10 and 20.

[0068] like Figure 2As shown, three numerical ranges are defined for the two capability indicators BI1 and BI2. These involve the target range ZB, the adaptation range AB, and the warning range WB. These ranges are displayed as a two-dimensional range combining the two indicators. In a one-dimensional view, a first target range ZB1, a first adaptation range AB1, and a first warning range WB1 are defined for the first capability indicator BI1, and a second target range ZB2, a second adaptation range AB2, and a second warning range WB2 are defined for the second capability indicator BI2. The target range ZB is chosen such that when the corresponding capability indicators BI1 and BI2 are within the target range ZB, there are no limitations to consider for the corresponding braking circuits 10 and 20. Therefore, especially when both capability indicators BI1 and BI2 are within the target range ZB, the control of the braking system 5 can be performed without considering the capability indicators BI1 and BI2, particularly the distribution of braking torque requirements between braking circuits 10 and 20.

[0069] The adaptation range AB is selected in such a way that the values ​​of the corresponding capability indicators BI1 and BI2 are within the adaptation range AB, indicating that measures should be taken to bring the corresponding capability indicators BI1 and BI2 back to the target range ZB. However, at this time, there are no direct limitations on the function, especially no limitations that endanger security.

[0070] If the capability indicators BI1 and BI2 are in the warning range WB, it indicates that the function of the corresponding braking circuits 10 and 20 has dangerous or critical limitations, and a response should be taken, for example, by issuing a warning message or degrading the braking system 5.

[0071] Typically, the control device 30 should ensure that the capability indices BI1 and BI2 are within the target range ZB when the vehicle is in normal use. This in particular means that the capability indices BI1 and BI2 of the braking circuits 10 and 20 are at most only one fixed value lower than 100% of the ideal value.

[0072] Within the target range ZB of capability indices BI1 and BI2, control device 30 can allocate braking torque demand to brake circuits 10 and 20 according to general optimization criteria. For example, when regenerative braking torque exists at one axle, the frictional torque can be generated entirely or primarily by the other axle. This strategy aims to achieve uniform tire wear. If brake circuits 10 and 20 are designed to exhibit different performance in terms of brake dust emissions, the required braking torque can be generated entirely or primarily by brake circuits 10 and 20 with lower brake dust emissions.

[0073] The braking force distribution can also be matched to the load state of the motor vehicle. In particular, when the load state can be provided by other functional modules, the above matching can be carried out. In principle, the load factor or load state can be indirectly determined by the correlation between the vehicle deceleration and the effective total braking torque, or by direct measurement methods such as using sensors for the spring travel of the chassis. The load recognition method allows, in principle, the load state to be taken into account during braking force distribution.

[0074] If the ability indices BI1, BI2 drop below the lower limit of the target range ZB and enter the adaptation range AB, the task of the control device 30 is to distribute the steering to the axle with the currently higher displayed ability indices BI1, BI2. The goal is to make the ability indices BI1, BI2 of the front and rear wheel braking systems, more precisely the two braking circuits 10, 20, change again in the direction of the target range ZB.

[0075] The reasons for the ability indices BI1, BI2 dropping into the adaptation range may, for example, be the wear state or the current thermal load of the relevant braking circuits 10, 20. The calculation rules for calculating the ability indices BI1, BI2 based on such or other parameters are usually part of the software implemented on the control device 30 and / or on separate control units (not shown) of the braking circuits 10, 20. The calculation rules usually depend on the specific braking technology used. This will be explained in detail below.

[0076] A feasible solution for adapting the braking force distribution can be described as follows, for example. α represents the current distribution coefficient, where generally α < 1. This may particularly mean that the required wheel braking torques T front 、T rear of the front and rear axles (i.e., the first braking circuit 10 and the second braking circuit 20) are derived from the total braking torque requirement T total in the following way:

[0077] If the ability indices BI1, BI2 are in the adaptation range AB, then, for example, when BI2 < BI1 (front shift), the distribution coefficient α can be increased by an amount Δ, or when BI1 < BI2 (rear shift), the distribution coefficient α can be decreased by an amount Δ.

[0078] However, here, in order to be able to observe the influence of the changed braking force distribution on the ability indices BI1, BI2, the stepwise increase or decrease is usually only repeated after a sufficient number of braking processes.

[0079] 通常应规定对分配参数α调整范围的限制。这防止出现特别是单侧的负载。

[0080] The aforementioned redistribution of braking force is particularly effective under the following assumption: in actual vehicle use scenarios, the capability indices BI1 and BI2 of the two braking circuits 10 and 20 will not decrease simultaneously; rather, either the first braking circuit 10 or the second braking circuit 20 will still possess potential, particularly as reflected by higher capability indices BI1 and BI2. The robust overall design of the braking system 5 should ensure this.

[0081] Although the design is robust and adaptation has been performed where necessary, if one or both capability indicators BI1 and BI2 still drop significantly, i.e., the BI1 and BI2 values ​​are in the warning range WB, this can be used to warn the driver in advance that the braking system 5 may be about to experience (partial) failure.

[0082] In the event of such a partial failure, the degraded state of the first braking circuit 10 and / or the second braking circuit 20 and / or the braking system 5 can be communicated to the control device 30 and / or other components. This degraded state can be taken into account during brake force distribution, particularly through the following strategies: - Set a stable braking force distribution when the Anti-Slip Regulation (ABS) function fails. Here, stable braking force distribution specifically means selecting the distribution coefficient α based on the mass distribution and wheel brake specifications, thereby ensuring that the rear axle never locks up before the front axle.

[0083] - Consider the failure of the front or rear wheel brakes, for example, not redistributing braking force to the axle with the failed wheel brakes.

[0084] - Consider the failure of a wheel brake on an axle (unable to be redistributed).

[0085] The calculation rules for capability indicators BI1 and BI2 are related to the technology used. In particular, there are differences between electromechanical and electrohydraulic brake actuators, between disc and drum brakes, and between brake actuators with open-loop and closed-loop control of wheel braking torque.

[0086] In general, the following parameters can be used to calculate capability metrics BI1 and BI2: - Wear condition; - Temperature of electrical components (such as sensors, regulating motors, or electronic components).

[0087] For electromechanical brake actuators with open-loop control of wheel braking torque, the actuator force F is typically established by setting the linear actuator's travel distance s. The elasticity, which can be described by the characteristic curve F(s), is usually included in the calculation of the capability indices BI1 and BI2, because high elasticity (exceeding normal characteristics) indicates a larger load. The situation is similar for electro-hydraulic brake actuators with open-loop control of wheel braking torque, where the actuator force F is replaced by the hydraulic pressure p, and the travel distance s is replaced by the hydraulic displacement V.

[0088] For brake actuators employing closed-loop control of wheel braking torque, the braking torque can be measured directly or indirectly (e.g., through effective support force), and the actuator force can be adjusted accordingly to achieve the required wheel braking torque. This compensates for fluctuations in the transmission characteristics between the actuator force and the wheel braking torque. In particular, this also means that actuator adjustment can determine characteristic values ​​of the transmission characteristics (e.g., C). -Parameter). Therefore, a decrease in such characteristic values ​​(e.g., during brake fade - wheel brakes experience reduced performance due to high loads and the resulting high temperatures) can be used to assess the impact on performance indicators.

[0089] This paper proposes an adaptive brake force distribution method, particularly based on a brake-by-wire system that specifically adjusts the braking torque for each axle. Brake force distribution can be influenced by capability indicators, for example, by selecting a distribution based on minimum tire wear or uniform wear and / or minimum brake dust emissions within a specified target range of the capability indicators. The brake force distribution can be progressively adjusted within the adaptive range of the capability indicators, thereby reducing the load on the wheel brakes of heavily loaded axles. A warning can be issued when the capability indicator of a wheel brake on one axle drops significantly. Degradation states, such as indicating the failure of single or multiple wheel brakes or the failure of anti-slip adjustment, can be considered when determining the brake force distribution. This paper also describes methods for determining capability indicators for different types of wheel brake actuators.

[0090] The advantages of the method described in this paper lie particularly in the flexibility of the aforementioned types of brake-by-wire systems in distributing braking force to each axle. Specifically, the method described herein reduces tire wear by using the front and rear axles evenly. Braking force distribution can also be selectively chosen, thereby reducing dust emissions. By applying the braking force distribution adaptation method described herein, the thermal design of one axle's wheel brakes can be better suited to the vehicle's typical operating scenarios, and under loads exceeding these scenarios, if the other axle has sufficient reserve capacity, more braking force can be generated using the wheel brakes of the other axle.

[0091] The steps mentioned in the method according to the invention may be performed in a specified order. However, they may also be performed in other orders where technically reasonable. The method according to the invention may be performed according to one of its embodiments (which, for example, has a specific combination of steps) without the need to perform other steps. However, other steps, including those not mentioned, may also be performed in principle.

[0092] It should be noted that the claims and description may describe combinations of features, for example, for ease of understanding, but these features may also be used individually. Those skilled in the art will recognize that such features may also be combined independently with other features or combinations of features. References in dependent claims may indicate preferred combinations of the corresponding features, but do not exclude other combinations of features.

[0093] The features will be presented in a structured manner below. These features can be combined arbitrarily with each other and with other features disclosed herein. These features are not claims of this application, but may constitute independent aspects of the invention.

[0094] 1. A braking system (5) for operating a motor vehicle, characterized in that The motor vehicle has at least two axles, each of the at least two axles having at least two wheels, and the braking system (5) has at least a first braking circuit (10) and a second braking circuit (20). Each braking circuit (10, 20) has one or more brakes (11, 12, 21, 22) respectively distributed to at least one wheel, and each braking circuit (10, 20) is configured to apply braking torque to the wheels of exactly one or more axles of a motor vehicle. The method includes the following steps: - Determine one or more first parameters of the first braking circuit (10), - Determine one or more second parameters of the second braking circuit (20), - Calculate the first capability index (BI1) based on the first parameter. - Calculate the second capability index (BI2) based on the second parameter.

[0095] 2. The method according to feature 1, The method further includes the following steps: - Based on the first capability index (BI1) and the second capability index (BI2), the braking torque demand is allocated to the first braking circuit (10) and the second braking circuit (20).

[0096] 3. The method according to any one of the foregoing features, - When the first capability indicator (BI1) is within the predetermined first target range (ZB1) and the second capability indicator (BI2) is within the predetermined second target range (ZB2), The method for distributing the braking torque demand to the first braking circuit (10) and the second braking circuit (20) is as follows: - Unrelated to the first capability indicator (BI1) and the second capability indicator (BI2), and / or - Use optimization criteria and / or - Consider regenerative braking on the axle, and / or - Related to the load status of motor vehicles.

[0097] 4. The method according to any one of the foregoing features, - When the first capability index (BI1) is in a predetermined first adaptation range (AB1) and / or when the second capability index (BI2) is in a predetermined second adaptation range (AB2), the braking torque demand is allocated to the first braking circuit (10) and the second braking circuit (20) by means of an allocation coefficient, which is determined according to the first capability index (BI1) and / or the second capability index (BI2).

[0098] 5. The method according to feature 4, - After each change of the allocation coefficient, the allocation coefficient remains constant for a single braking torque demand or for at least two predetermined braking torque demands.

[0099] 6. The method according to feature 4 or 5, - The change in the distribution coefficient when it changes causes the braking torque to be applied more by the following braking circuits (10, 20): the load indicated by the corresponding capacity index (BI1, BI2) of the braking circuit is lower than that of the other braking circuit (10, 20).

[0100] 7. The method according to any one of features 4 to 6, - The distribution coefficients are determined such that the main portion of the braking torque is applied by braking circuits (10, 20) whose corresponding capacity indices (BI1, BI2) indicate lower loads.

[0101] 8. The method according to any one of the foregoing features, - If the first capability indicator (BI1) is in the predetermined first warning range (WB1) and / or the second capability indicator (BI2) is in the predetermined second warning range (WB2), output a warning message and / or degrade the braking system (5).

[0102] 9. The method according to feature 8, In the case of degraded braking system (5), - Adjust the braking torque distribution between the first braking circuit (10) and the second braking circuit (20) so that the front axle locks up before the rear axle locks up. and / or - Braking circuits (10, 20) with at least one failed brake (11, 12, 21, 22) do not apply braking torque.

[0103] 10. The method according to any one of the foregoing features, - In at least one or more wear cycles, the braking torque demand is distributed to the first braking circuit (10) and the second braking circuit (20) in such a way that the braking torque is applied primarily by the braking circuit (10, 20) with the higher load indicated by the capability indicators (BI1, BI2).

[0104] 11. The method according to any one of the foregoing features, - When the braking torque demand is greater than the threshold and / or when the braking torque demand cannot be allocated to the braking circuit (10, 20), manipulate the braking circuit (10, 20) regardless of the capability index.

[0105] 12. The method according to any one of the foregoing features, - The energy input to the brakes (11, 12) of the first braking circuit (10) and the energy output from the brakes (11, 12) of the first braking circuit (10) are parameters of the first braking circuit (10). and / or - The energy input to the brakes (21, 22) of the second braking circuit (20) and the energy output from the brakes (21, 22) of the second braking circuit (20) are parameters of the second braking circuit (20).

[0106] 13. The method according to any one of the foregoing features, - The parameters of the first braking circuit (10) and / or the second braking circuit (20) include one or more of the following parameters: - The temperature of one or more brakes (11, 12, 21, 22), - The temperature of one or more electrical components, - The wear condition of one or more brakes (11, 12, 21, 22) or other components. - Friction pairs of one or more brakes (11, 12, 21, 22), - Energy input to one or more brakes (11, 12, 21, 22), - Energy output from one or more brakes (11, 12, 21, 22), - The relevant mass of one or more brakes (11, 12, 21, 22), - One or more characteristic values ​​for torque adjustment of at least one brake (10, 12, 21, 22), - One or more characteristic values ​​of the force setting of at least one brake (10, 12, 21, 22).

[0107] 14. The method according to any one of the foregoing features, - The first braking circuit (10) and the second braking circuit (20) act on different axles.

[0108] 15. The method according to any one of the foregoing features, - The first braking circuit (10) has at least one first braking actuator, and the second braking circuit (20) has at least one second braking actuator. - The first brake actuator and the second brake actuator can be operated independently of each other.

[0109] 16. The method according to feature 15, - The first brake actuator is a hydraulic brake actuator, and it applies pressure to the brakes (11, 12) of the first brake circuit (10). and / or - The second brake actuator is a hydraulic brake actuator, and applies pressure to the brakes (21, 22) of the second brake circuit (20).

[0110] 17. The method according to any one of the foregoing features, - The first braking circuit (10) has one or more brakes (11, 12) that can be operated by means of an electromechanical brake actuator. and / or - The second braking circuit (20) has one or more brakes (11, 12) that can be operated by means of an electromechanical brake actuator.

[0111] 18. The method according to any one of the foregoing features, - The first capability index (BI1) indicates the load and / or remaining braking capacity of the first braking circuit (10). and / or - The second capability index (BI2) indicates the load and / or remaining braking capacity of the second braking circuit (20). and / or - The lower the residual braking capacity of the first braking circuit (10), the higher the load on the first braking circuit (10). and / or - The lower the residual braking capacity of the second braking circuit (20), the higher the load on the second braking circuit (20).

[0112] 19. The method according to any one of the foregoing features, - The first capability index (BI1) is calculated solely based on the first parameter and / or solely based on the parameters of the first braking circuit (10). and / or - The second capability index (BI2) is calculated based solely on the second parameter and / or solely on the parameters of the second braking circuit (20).

[0113] 20. The method according to any one of the foregoing features, - The first competency indicator (BI1) is numerical. and / or - The second capability indicator (BI2) is numerical.

[0114] 21. A braking system (5) for a motor vehicle, wherein the braking system (5) comprises: - First braking circuit (10) - Second braking circuit (20) - A control device (30) configured to perform the method according to any one of the preceding claims.

[0115] List of reference numerals

[0116] BI1 First Capability Indicator

[0117] BI2 Second Capability Indicator

[0118] ZB Target Range

[0119] AB compatibility range

[0120] WB Warning Range

[0121] 5. Braking System

[0122] 10 First Braking Circuit

[0123] 11 First Brake

[0124] 12 Second Brake

[0125] 20 Second Braking Circuit

[0126] 21 First Brake

[0127] 22 Second Brake

[0128] 30 Control device

[0129] 40 Functional Modules

[0130] 42 Sensor Device

[0131] 50 Other Information

Claims

1. Method for operating a brake system (5) of a motor vehicle, the motor vehicle having at least two axles, each having at least two wheels, the brake system (5) having at least a first brake circuit (10) and a second brake circuit (20), each brake circuit (10, 20) having one or more brakes (11, 12, 21, 22), each being a friction brake and being assigned to at least one wheel, each brake circuit (10, 20) being configured to apply a brake torque to the wheels of exactly one axle or a plurality of axles of the motor vehicle by means of the friction brakes only, the method comprising the steps of: - 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 index (BII) from the first parameters, - calculating a second capability index (BI2) from the second parameters.

2. Method according to claim 1, characterized in that the method further comprises the step of: - distributing a brake torque demand to the first brake circuit (10) and the second brake circuit (20) depending on the first capability index (BII) and the second capability index (BI2).

3. Method according to any of the preceding claims, characterized in that - when the first capability index (BII) is in a predetermined first target range (ZB1) and the second capability index (BI2) is in a predetermined second target range (ZB2), the brake torque demand is distributed to the first brake circuit (10) and the second brake circuit (20) in such a way that - it is independent of the first capability index (BII) and the second capability index (BI2), and / or - an optimization criterion is used, and / or - regenerative braking on the axles is taken into account, and / or - it is related to a load state of the motor vehicle.

4. Method according to any of the preceding claims, characterized in that - when the first capability index (BII) is in a predetermined first adaptation range (AB1) and / or when the second capability index (BI2) is in a predetermined second adaptation range (AB2), the brake torque demand is distributed to the first brake circuit (10) and the second brake circuit (20) by means of a distribution factor, which is determined depending on the first capability index (BII) and / or the second capability index (BI2).

5. Method according to claim 4, characterized in that - the distribution factor remains constant for one brake torque demand or for a predetermined number of at least two brake torque demands after each change of the distribution factor.

6. Method according to claim 4 or 5, characterized in that - the change of the distribution factor at the change is such that the brake torque is applied more by the brake circuit (10, 20) whose respective capability index (BII, BI2) indicates a lower load than the other brake circuit (10, 20).

7. Method according to any of claims 4 to 6, characterized in that - the distribution factor is determined such that a major part of the braking torque is applied by the brake circuit (10, 20) whose respective capability indicator (BI1, BI2) indicates a lower load.

8. The method according to any one of the preceding claims, characterized in that, - a warning message is output and / or the brake system (5) is downgraded in the event that the first capability indicator (BI1) is in a predetermined first warning range (WB1) and / or the second capability indicator (BI2) is in a predetermined second warning range (WB2).

9. The method according to claim 8, characterized in that, in the event of a downgrade of the brake system (5), - the distribution of the braking torque between the first brake circuit (10) and the second brake circuit (20) is adjusted such that a lock-up of the front axle occurs before a lock-up of the rear axle, and / or - the brake circuit (10, 20) having at least one failed brake (11, 12, 21, 22) does not apply a braking torque.

10. The method according to any one of the preceding claims, characterized in that, - in at least one or at least some wear cycles, the braking torque demand is distributed to the first brake circuit (10) and the second brake circuit (20) in such a way that the braking torque is mainly applied by the brake circuit (10, 20) whose capability indicator (BI1, BI2) indicates a higher load.

11. The method according to any one of the preceding claims, characterized in that, - in the event of a braking torque demand greater than a threshold value and / or in the event that the braking torque demand cannot be distributed to the brake circuits (10, 20), the brake circuits (10, 20) are actuated independently of the capability indicators.

12. The method according to any one of the preceding claims, characterized in that, - the energy input into the brakes (11, 12) of the first brake circuit (10) and the energy output from the brakes (11, 12) of the first brake circuit (10) are parameters of the first brake circuit (10), and / or - the energy input into the brakes (21, 22) of the second brake circuit (20) and the energy output from the brakes (21, 22) of the second brake circuit (20) are parameters of the second brake circuit (20).

13. The method according to any one of the preceding claims, characterized in that, - the parameters of the first brake circuit (10) and / or the second brake circuit (20) comprise one or more of the following parameters: - the temperature of one or more brakes (11, 12, 21, 22), - the temperature of one or more electrical components, - the wear state of one or more brakes (11, 12, 21, 22) or other components, - the friction pair of one or more brakes (11, 12, 21, 22), - the energy input into one or more brakes (11, 12, 21, 22), - the energy output from one or more brakes (11, 12, 21, 22), - the associated mass of one or more brakes (11, 12, 21, 22), - the temperature of one or more brakes (11, 12, 21, 22), - the temperature of one or more electrical components, - the wear state of one or more brakes (11, 12, 21, 22) or other components, - the friction pair of one or more brakes (11, 12, 21, 22), - the energy input into one or more brakes (11, 12, 21, 22), - the energy output from one or more brakes (11, 12, 21, 22), - the associated mass of one or more brakes (11, 12, 21, 22). - one or more characteristic values of the force setting of the at least one brake (10, 12, 21, 22), - one or more characteristic values of the force setting of the at least one brake (10, 12, 21, 22).

14. The method according to any one of the preceding claims, characterized in that - the first brake circuit (10) and the second brake circuit (20) act on different axles from one another.

15. The method according to any one of the preceding claims, characterized in that - 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, - the first brake actuator and the second brake actuator can be actuated independently of one another.

16. The method according to claim 15, characterized in that - the first brake actuator is a hydraulic brake actuator and exerts a pressure on the brakes (11, 12) of the first brake circuit (10), and / or - the second brake actuator is a hydraulic brake actuator and exerts a pressure on the brakes (21, 22) of the second brake circuit (20).

17. The method according to any one of the preceding claims, characterized in that - one or more brakes (11, 12) of the first brake circuit (10) can be actuated by means of an electromechanical brake actuator, and / or - one or more brakes (11, 12) of the second brake circuit (20) can be actuated by means of an electromechanical brake actuator.

18. The method according to any one of the preceding claims, characterized in that - the first capability indicator (BI1) indicates the load and / or the residual braking capacity of the first brake circuit (10), and / or - the second capability indicator (BI2) indicates the load and / or the residual braking capacity of the second brake circuit (20), and / or - the lower the residual braking capacity of the first brake circuit (10), the higher the load of the first brake circuit (10), and / or - the lower the residual braking capacity of the second brake circuit (20), the higher the load of the second brake circuit (20).

19. The method according to any one of the preceding claims, characterized in that - the first capability indicator (BI1) is calculated exclusively on the basis of the first parameter and / or exclusively on the basis of parameters of the first brake circuit (10), and / or - the second capability indicator (BI2) is calculated exclusively on the basis of the second parameter and / or exclusively on the basis of parameters of the second brake circuit (20).

20. The method according to any one of the preceding claims, characterized in that - the first capability indicator (BI1) is a numerical value, and / or - the second capability indicator (BI2) is a numerical value.

21. A brake system (5) for a motor vehicle, wherein The brake system (5) has - a first brake circuit (10), - a second brake circuit (20), - a control device (30) which is configured to carry out the method according to any one of the preceding claims.

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