METHOD FOR IDENTIFYING FAULTS IN A BRAKE ASSEMBLY OF A MOTOR VEHICLE, AND MOTOR-VEHICLE BRAKING SYSTEM

Abstract

A method for identifying a fault in a brake assembly of a motor vehicle, including: ascertaining a first estimated value of a brake temperature based on an applied brake pressure; registering a series of measured temperature values by a temperature sensor spaced from the brake assembly; determining a second estimated value of the brake temperature based on the series of measured temperature values; comparing the first estimated value and the second estimated value; and deciding, based on the comparing of the first and second estimated values, whether there is a fault. Also described is a related motor vehicle braking system.

Claims

1-14. (canceled)

15. A method for identifying a fault in a brake assembly of a motor vehicle, the method comprising: ascertaining a first estimated value of a brake temperature based on an applied brake pressure; registering a series of measured temperature values by a temperature sensor spaced from the brake assembly; determining a second estimated value of the brake temperature based on the series of measured temperature values; comparing the first estimated value and the second estimated value; and deciding, based on the comparing of the first and second estimated values, whether there is a fault.

16. The method of claim 15, wherein the ascertaining of the first estimated value of the brake temperature is carried out based on the applied brake pressure and an instantaneous wheel speed.

17. The method of claim 15, wherein the determining of the second estimated value of the brake temperature is carried out based on the series of measured temperature values and a function.

18. The method of claim 17, wherein the function includes an extrapolation function.

19. The method of claim 15, wherein the determining of the second estimated value of the brake temperature is carried out based on a gradient, which is ascertained based on the series of measured temperature values.

20. The method of claim 15, wherein the fault occurs if the second estimated value differs from the first estimated value by at least a predetermined deviation.

21. The method of claim 20, wherein the predetermined deviation amounts to between 10% and 30% of the first estimated value.

22. The method of claim 17, wherein the function has at least one function parameter, and wherein the at least one function parameter is at least one parameter determined experimentally or by measurement.

23. The method of claim 17, wherein the function has at least one function parameter, and wherein the at least one function parameter is at least one parameter determined by computation or by computer-based simulation.

24. The method of claim 17, wherein the function has at least one function parameter, and wherein the at least one function parameter is a parameter determined by a learning process.

25. The method of claim 24, wherein the at least one function parameter includes an initial value that is adapted in a plurality of cycles based on the first and second estimated values.

26. A motor-vehicle braking system, comprising: a brake assembly; a control system for applying a brake pressure in the brake assembly; a sensor which is spaced from the brake assembly and configured for registering a series of measured temperature values; and a signal-processing unit configured to perform the following: ascertaining a first estimated value of a brake temperature based on an applied brake pressure; determining a second estimated value of the brake temperature based on the series of measured temperature values; comparing the first estimated value and the second estimated value; and deciding, based on the comparing of the first and second estimated values, whether there is a fault.

27. The motor-vehicle braking system of claim 26, wherein the sensor is arranged on a wheel-carrier, on a brake anchor or on a wheel axle of the motor vehicle.

28. The motor-vehicle braking system of claim 26, wherein the signal-processing unit and the control system are formed integrally with one another or separately from one another.

29. The method of claim 20, wherein the predetermined deviation amounts to at least 10% of the first estimated value.

30. The method of claim 20, wherein the predetermined deviation amounts to at least 20% of the first estimated value.

Description

[0023] Exemplary embodiments of the invention will be described in the following with reference to the appended drawings.

[0024] FIG. 1 shows a braking system of a motor vehicle according to an exemplary embodiment of the invention, in a block diagram.

[0025] FIG. 2 shows a flowchart of a method for identifying faults in a brake assembly of a motor vehicle according to an exemplary embodiment of the invention.

[0026] FIG. 3 shows a temperature diagram with exemplary profile curves of a first and of a second estimated value over time.

[0027] FIG. 1 shows a braking system 2 of a motor vehicle according to an exemplary embodiment of the invention. The braking system 2 exhibits a brake assembly 4, a control system 6 and a deceleration transducer 8. The brake assembly 4 is arranged on a wheel 9 of a motor vehicle (not represented).

[0028] The control system 6 exhibits a control unit 10 and a valve arrangement 12. The control unit 10 is connected to the valve arrangement 12 via an electrical connection 14, for instance a CAN bus. The control system 6 has been set up to apply or impose a desired brake pressure to or on the brake assembly 4 by means of the valve arrangement 12 via a compressed-air line 16. The control unit 10 and the valve assembly 12 may have been integrally formed or provided separately from one another.

[0029] The deceleration transducer 8 exhibits a brake pedal 18 which is connected both to an electrical sensor 20 and to a pneumatic sensor 22. The electrical sensor 20 registers the position of the brake pedal 18 and communicates this position to the control unit 10 via an electrical signal line 24. The pneumatic sensor 22 is connected to a compressed-air supply 26 and also to the valve arrangement 12 via a compressed-air line 28. The pneumatic sensor 22 has been set up to register the position of the brake pedal 18 and to make available a corresponding control pressure for the valve arrangement 12 in the compressed-air line 28 on the basis of the position of the brake pedal 18.

[0030] As explained above, the control unit 10 is connected to the electrical sensor 20 via the electrical signal line 24. The control unit 10 has been set up to calculate a desired brake pressure on the basis of the position of the brake pedal 18, as registered and communicated by the electrical sensor 20, and to communicate this desired brake pressure to the valve assembly 12 via the connection 14.

[0031] The valve arrangement 12 has been set up to receive the desired brake pressure, on the one hand electrically from the control unit 10 via the connection 14, and on the other hand pneumatically via the compressed-air line 28. In addition, the valve arrangement 12 is likewise connected pneumatically to the compressed-air supply 26 and connected electrically to a wheel-speed sensor 30 which is arranged on the wheel 9, spaced from the brake assembly 4. As an alternative to, or in addition to, the wheel-speed sensor 30, further sensors—such as, for instance, a temperature sensor 32—may have been arranged at the place shown. In particular, the temperature sensor 32 may have been arranged on a brake anchor, on a steering knuckle or wheel-carrier, or on the wheel axle, which may be by means of a holder mounted thereon. The wheel-speed sensor 30 and the temperature sensor 32 may also have been arranged at different positions, spaced from the brake assembly 4.

[0032] For the sake of completeness, it should be mentioned that both the pneumatic sensor 22 and the valve arrangement 12 exhibit an outlet port 32 and 34, respectively, to the atmosphere, via which the pressure in the respective component—that is to say, in the pneumatic sensor 22 and in the valve arrangement 12—can be let out.

[0033] In the block diagram of FIG. 1, the brake assembly 4 has been represented schematically as a unit. The term “brake assembly” encompasses any type of brake device that is suitable to exert, by means of an applied brake pressure, a braking action on a wheel or on elements of a vehicle rotating with a wheel.

[0034] If a brake pressure is applied to the brake assembly 4, the latter heats up during a braking procedure. A “braking procedure” in this connection describes the length of time for which a brake pressure has been applied to the brake assembly 4 and generates a braking action. During the braking procedure the brake assembly 4 heats up. The temperature prevailing in the brake assembly is designated herein as the brake temperature. If the brake temperature becomes too high, for instance as a result of excessively long and/or intense braking procedures, the thermal loading may cause damage to the brake assembly 4—in the case of motor-vehicle brakes, in particular to brake discs and brake pads—and, where appropriate, may diminish the braking performance. A damaging increased brake temperature may also be caused by mechanical faults in the brake assembly 4, for instance by rubbing of the brake pads against the brake disks. In addition, defective components on the wheel suspension—for instance, bearings on the wheel hub—may cause an unwanted heating of the brake assembly 4, which can result in damage and/or in a diminution of the braking action.

[0035] In order to avoid such damage to the brake assembly 4, such an evolution of temperature should be detected as early as possible. As a result, appropriate measures can be taken before damage to the brake and/or a diminution of the braking action occurs.

[0036] For the purpose of identifying faults, the braking system 2 exhibits a signal-processing unit 40. In the exemplary embodiment shown in FIG. 1, the signal-processing unit 40 has been configured as part of the control unit 10. It is also possible that the signal-processing unit 40 has been arranged at another place in the braking system 2, in particular outside the control system 6. The functionality of the signal-processing unit 40 may also have been realized at an entirely different place in the motor vehicle, for instance as part of a central motor-vehicle computer. Since the signal-processing unit 40 or, to be more exact, the functionality of the signal-processing unit relates to the identification of faults in the braking system 2, it is regarded as part of the braking system 2 also in the case last described.

[0037] FIG. 2 shows a method for identifying faults in the brake assembly 4 according to an exemplary embodiment of the invention on the basis of a flowchart.

[0038] In a first step S1, a first estimated value T1 of a temperature of the brake assembly 4, hereinafter designated as the brake temperature TB, is ascertained. The first estimated value T1 is ascertained on the basis of a brake pressure applied to the brake assembly 4, for example by the energy supplied to the brake assembly 4 being calculated with the aid of the brake pressure. The first estimated value T1 can be ascertained with the aid of the heating characteristic and the cooling characteristic of the brake assembly 4. For the ascertainment of the first estimated value T1, only the heating by virtue of the brake pressure actively applied to the brake assembly 4 is accordingly taken into consideration. Furthermore, a normal—that is to say, fault-free—functioning of the brake assembly 4 is assumed for the ascertainment of the first estimated value T1.

[0039] For the purpose of determining the first estimated value T1, the wheel speed that is registered by the wheel-speed sensor 30 (see FIG. 1) can additionally be taken into consideration. In addition, further factors—such as, for instance, the ambient temperature—can be taken into consideration.

[0040] In a second step S2, a series of measured temperature values TR is registered with the aid of the temperature sensor 32 (see FIG. 1). The temperature sensor 32 is spaced from the brake assembly 4 and may, for instance, have been integrated into the wheel-speed sensor 30 or arranged directly adjacent thereto.

[0041] The temperature sensor 32 permanently registers or senses a temperature TS applied thereto. The series of measured temperature values TR features two or more measured temperature values that were registered by the temperature sensor 32 over a certain period of time. The measured temperature values that the series of measured temperature values TR comprises may be temporally directly consecutive temperatures. The series of measured temperature values TR may comprise measured temperature values that exhibit regular or irregular temporal intervals from one another. The temperature TS registered by the temperature sensor 32 does not correspond to the brake temperature TB of the brake assembly 4 but is dependent on said brake temperature—that is to say, there is a correlation between the temperature TS registered by the temperature sensor 32 and the brake temperature TB.

[0042] On the basis of the series of measured temperature values TR, a second estimated value T2 of the brake temperature TB is determined in a next step S3. For this purpose, a function—such as, for instance, an estimating function, an extrapolation function, etc.—can be applied to the series of measured temperature values TR.

[0043] After determination of the two estimated values T1, T2 of the brake temperature TB, the two estimated values T1, T2 are compared with one another in a step S4. The magnitude of a deviation between the two estimated values T1, T2 is determined, for instance by ascertaining a difference between the first estimated value T1 and the second estimated value T2. On the basis of the result of this comparison, it is decided whether a fault—that is to say, an abnormal temperature in the brake assembly 4—obtains. For this purpose, the ascertained deviation is compared with a predetermined threshold value Δ. The threshold value Δ is a value that the deviation is maximally permitted to amount to in order that no fault is detected.

[0044] If the deviation is equal to or greater than the threshold value Δ (“yes” in step S4), it is decided that a fault obtains. In a step S5, it is then checked whether the second estimated value T2 is greater than the first estimated value T1. If the second estimated value T2 is greater than the first estimated value T1 (“yes” in step S5), in a step S6 a fault message is output, stating that there is a fault in the brake assembly 4. The output of the fault message can be effected via a warning light to the driver of the motor vehicle or by a warning text for the driver, or in any other suitable manner. Subsequently the method is concluded.

[0045] If the second estimated value T2 is less than the first estimated value T1, in a step S7 a fault message is output, stating that there is a measurement error and/or a fault in the measuring system. Subsequently the method is concluded.

[0046] If the deviation is less than the threshold value Δ (“no” in step S4), it is decided that no abnormal temperature behavior obtains, and the method is concluded.

[0047] A pass of the method is repeated in the manner of a loop, so long as the vehicle is actively in operation.

[0048] Such a method is carried out by a signal-processing unit. As described above, the signal-processing unit may have been provided separately from the control system 6 of the brake assembly 4 (see FIG. 1) or may have been integrated into the control system 6. The signal-processing unit may, for instance, have been integrated into the control unit 10 of the control system 6.

[0049] In further embodiments, it is conceivable that the function in step S3 that is applied to the series of measured temperature values (TR) has at least one function parameter that can be determined in different ways.

[0050] One possibility for determining the function parameter or parameters is an experimental determination or, to be more exact, a determination by measurements, for instance in the form of measurements of the vehicle on a test rig. The function parameter determined in this way is then stored in a vehicle data record and can be retrieved therefrom during the method.

[0051] A further possibility for determining the function parameter or parameters is a computational determination, for instance by means of computer-based simulations. The function parameter determined in this way is then stored in the vehicle data record and can be retrieved therefrom during the method.

[0052] Yet another possibility for determining the function parameter or parameters is by a learning process. The learning process starts with a predetermined initial value for the function parameter, which is adapted by several learning cycles during the learning process on the basis of the first and second estimated values T1, T2. After completion of the learning process, the function parameter determined in this way is stored in the vehicle data record and can be retrieved therefrom during the method. Such a learning process can be started in different ways; for instance, said process is enabled already at the time of the EoL check (EoL=End of Line), or it has been enabled in advance in the case of new control instruments, or it can be started via a method for diagnosis of the vehicle.

[0053] As in the exemplary embodiment shown in FIG. 2, the deviation between the two estimated values T1, T2 can be ascertained on the basis of the magnitude of the difference between the first estimated value T1 and the second estimated value T2. In this connection, the threshold value Δ is a temperature specification. But alternatively it is also conceivable to specify the deviation in relation to the first estimated value T1 as a percentage. In this case, the threshold value Δ is a percentage specification and is calculated in accordance with the following formula (1):

(|T1−T2|)/T1*100   (1)

[0054] FIG. 3 shows a temperature diagram in which an exemplary temperature profile T1(t) of the first estimated value T1 and an exemplary temperature profile TS(t) of the associated temperature TS of the temperature sensor 32 over time have been represented.

[0055] At the start of operation of the vehicle, both the first estimated value T1 and the temperature TS of the temperature sensor 32 correspond to the ambient temperature T0, since the brake has not yet been subjected to a braking pressure and is still “cold”, so to speak. At a time t1, a brake pressure is applied to the brake assembly 4, and the first estimated value T1 rises correspondingly. At time t3, the braking procedure has been concluded—that is to say, no brake pressure is applied to the brake assembly 4 any longer—and the brake temperature TB falls again. At the times without actively applied brake pressure, the profile of the estimated value T1 is based on the cooling characteristics of the brake assembly 4.

[0056] The profile of the temperature TS of the temperature sensor 32 begins to rise, only slightly delayed, at a time t1′, since the temperature sensor 32 is spaced from the brake assembly 4. An increase in temperature in the brake assembly 4 leads, only with a slight time-delay, also to an increase in temperature at the temperature sensor 32. Overall, it can be discerned that under normal conditions the temperature profile TS(t) of the temperature TS of the temperature sensor 32 exhibits increases and decreases in temperature always slightly delayed relative to curve profile T1(t).

[0057] A second estimated value T2(t2) is ascertained for time t2 on the basis of the series of temperature values TR(t2). For this purpose, in the exemplary embodiment shown in FIG. 3 the trend of six measured values recently registered by the temperature sensor 32 is taken into consideration. The second estimated value T2(t2) is determined on the basis of this trend. In particular, the determination of the second estimated value is undertaken with the aid of a function that has as input variable the gradient of the curve through the measured values taken into consideration. This approach takes advantage of the following consideration. A heating of the brake—that is to say, an increase in the brake temperature—leads to a delayed increase in the temperature TS measured at the temperature sensor. However, the gradient of the instantaneously measured temperature TS already contains information as to how high the brake temperature TB in the brake assembly is right now. A comparatively high brake temperature TB is associated with a comparatively high gradient. By experiments, simulations or learning processes, it can be ascertained which gradient at the temperature sensor is related to which brake temperature. A good estimate for the brake temperature can consequently be made from the gradient and/or from other information in the series of temperature values TR.

[0058] For the temperature profiles shown, the second estimated value T2(t2) at time t2 is very close to the first estimated value T1(t2). Here the difference is less than the threshold value Δ. It is therefore decided in the method in step S4 that no fault obtains at time t2.

[0059] On the basis of the series of temperature values TR(t4), for time t4 a second estimated value T2(t4) is ascertained which lies distinctly above the first estimated value T1(t4). Here the difference is greater than the threshold value Δ. It is therefore decided in the method in step S4 that a fault obtains at time t4. In step S5 of the method it is decided for time t4 that the fault is present in the brake assembly 4, since T2(t4) is greater than T1(t4), and the corresponding fault message is output (step S6). At time t4, the second estimated value T2(t4) indicates that the brake temperature TB existing in the brake assembly is distinctly above the value that would be expected in the case of normal functioning, namely distinctly above the first estimated value T1(t4). This result of the comparison leads to the conclusion that a faulty operation of the brake assembly obtains.

THE LIST OF REFERENCE SYMBOLS IS AS FOLLOWS:

[0060] 2 braking system [0061] 4 brake assembly [0062] 6 control system [0063] 8 deceleration transducer [0064] 9 wheel [0065] 10 control unit [0066] 12 valve arrangement [0067] 14 electrical connection [0068] 16 compressed-air line [0069] 18 brake pedal [0070] 20 electrical sensor [0071] 22 pneumatic sensor [0072] 24 electrical signal line [0073] 26 compressed-air supply [0074] 28 compressed-air line [0075] 30 wheel-speed sensor [0076] 32 temperature sensor [0077] T0 ambient temperature [0078] T1 first estimated value [0079] T2 second estimated value [0080] TR series of measured temperature values [0081] TS temperature of the sensor [0082] Δ threshold value [0083] T1(t) curve profile of T1 over time [0084] TS(t) curve profile of TS over time [0085] S1, S2, S3, S4, S5, S6, S7 method steps [0086] t1, t1′, t2, t3, t4 times