Method for operating a brake system

Abstract

The invention relates to a method for operating a brake system (1) which has a first control unit (3) and a second control unit (4) for adjusting a wheel brake (2) when the parking brake is activated. In the event of a fault in the first control unit (3), the brake system (1) is operated in a fallback mode (8) in which the wheel brake (2) is adjusted by means of the second control unit (4), wherein a status of the wheel brake (2) is monitored for a standby period, and wherein the standby period is adjusted according to the temperature of the wheel brake (2). The invention also relates to a computer program product for carrying out the method.

Description

[0001] Method for operating a braking system

[0002] The present invention relates to a method for operating a braking system. The invention also relates to a computer program product for operating such a braking system.

[0003] To implement a parking brake in a vehicle, a wheel brake of a braking system is adjusted to a position that blocks at least one associated wheel. The adjustment can be performed using a control unit of the braking system.

[0004] To increase reliability, such a braking system can have two such control units, which can be used redundantly, for example. If one of the control units is faulty, the other control unit can take over wheel brake adjustment when the parking brake is activated.

[0005] The present invention is concerned with the object of providing improved or at least different embodiments for a method for operating a braking system of the type mentioned above and for a computer program product for operating such a braking system.

[0006] Inventive proposals for solving the problem are found in the independent claims. Advantageous variants are the subject of the dependent claims.

[0007] The invention accordingly proposes, in a braking system with two control units used to adjust a wheel brake upon activation of a parking brake, that if one of the control units fails, the adjustment be carried out by the other control unit. The state of the wheel brake is monitored for a certain period of time and the wheel brake is readjusted if necessary, and this period is adjusted depending on the temperature of the wheel brake. Thus, during the aforementioned switchover from one control unit to the other control unit, thermally induced changes to the wheel brake, which could lead to a release from the desired position, are not only taken into account by means of the temperature, but the duration of the adjustment is also selected depending on the temperature.As a result, in addition to improved implementation of the parking brake and thus increased safety, there is also a demand-based operating time and thus more efficient operation of the braking system.

[0008] According to the invention, a method for operating a braking system with a wheel brake is proposed, wherein the braking system has a first control unit and a second control unit for adjusting the wheel brake in a position that blocks at least one wheel of an associated vehicle when a parking brake of the braking system is activated. This position is also referred to below as the locking position. This means that the first control unit and the second control unit serve to adjust the wheel brake when the parking brake is activated. According to the invention, a temperature of the wheel brake is determined. If both control units are error-free, the braking system is operated in an operating mode that is also referred to below as control mode. If one of the control units has a fault, for example, has failed or degraded, the braking system is operated in an operating mode that is also referred to below as fallback mode.In normal operation, when the parking brake is activated, the wheel brake is adjusted by the first control unit. In fallback operation, when the parking brake is activated, the wheel brake is adjusted by the second control unit. In fallback operation, the parking position is monitored for a certain period of time, and the wheel brake is readjusted if the wheel brake threatens to release from the parking position or releases. This period is also referred to below as the standby period. The standby period is adjusted depending on the measured temperature of the wheel brake.

[0009] An imminent release of the wheel brake from the locking position is assumed in particular if it can be assumed that a clamping force exerted by the wheel brake will be reduced above a defined threshold in order to reach the locking position.

[0010] In particular, the solution according to the invention takes into account those cases in which the wheel brake cools down after being adjusted to the locking position. This cooling leads to a reduction in the clamping force exerted to achieve the locking position, such that the wheel brake is no longer securely locked, causing the associated wheel to rotate and thus the associated vehicle to roll or to threaten to roll. The readjustment thereby adjusts the wheel brake in such a way that the locking of at least one wheel is achieved and / or continues to be ensured. The readjustment thus corresponds, for example, to re-tensioning the wheel brake.The temperature-dependent adjustment of the standby time thus ensures that such cooling does not lead to release from the locking position, even in fallback mode or when changing to fallback mode, or the probability of such release is at least reduced.

[0011] After the standby period has elapsed, the monitoring system, in particular the second control unit, is advantageously deactivated, with the wheel brake remaining in the locking position. The standby period thus expediently specifies a period after which the second control unit is deactivated, i.e., in particular, shut down. The adjustment, in particular the increase, of the standby period can be achieved by preventing this deactivation, in particular this shut-down, of the second control unit.

[0012] The adjustment of the standby time, which depends on the determined temperature, is conveniently carried out in an analogous manner in normal operation.

[0013] The transition from normal operation to fallback operation can be carried out in any way.

[0014] For example, fallback mode can also be activated if the first control unit detects a fault during or after the wheel brake is adjusted to the locking position. The switchover occurs during or after the wheel brake is adjusted by the first control unit. In this case, the second control unit can complete the locking position or simply be used for subsequent adjustment.

[0015] In principle, the respective control unit can be designed in any way.

[0016] For example, the respective control unit can have a microcontroller or be a microcontroller.

[0017] The parking brake is preferably implemented by means of a parking brake function of the respective control unit. At least the first control unit comprises a complete parking brake function. Advantageously, the second control unit also comprises a complete parking brake function.

[0018] The braking system can serve as a host or have a host in which the parking brake functions are stored, particularly integrated. The standby time can be adjusted depending on the temperature of the wheel brake when the wheel brake is moved to the locking position. This means that the temperature of the wheel brake is determined when the wheel brake is moved to the locking position, and the standby time is adjusted depending on this determined temperature.

[0019] In advantageous variants, the temperature of the wheel brake is continuously determined and the standby time is adjusted depending on the last determined temperature or temperatures.

[0020] For the standby duration, a control value is advantageously provided, which applies when the measured temperature falls below a specified threshold. If the measured temperature is below the threshold, the standby duration is set to the control value. Adjusting the standby duration thus corresponds to increasing the standby duration beyond the control value. The standby duration is therefore increased compared to the control value if the measured temperature of the wheel brake is at least equal to the threshold.

[0021] In principle, the control value can also be zero, meaning that the standby time is zero if the threshold value is undershot.

[0022] Advantageously, the control value corresponds to a minimum value that is greater than 0. This means that the standby time is greater than zero even if the threshold value is undershot.

[0023] It is conceivable to measure the temperature of the wheel brake in one of the

[0024] Control units are separate components of the braking system and / or in a

[0025] Control units can determine the wheel brake temperature from a higher-level unit, for example, in the host. It is also conceivable that, during normal operation, the first control unit determines the wheel brake temperature and stores it in the braking system. This storage is preferably carried out in a non-volatile memory. The wheel brake temperature is preferably determined continuously in the first control unit. In fallback mode, the temperature stored by the first control unit, in particular the most recently stored temperature, is used to adjust the standby time.

[0026] The standby time can be adjusted depending on the temperature last determined by the first control unit.

[0027] It is also conceivable to determine the current temperature of the wheel brake on the basis of the temperature last stored by the first control unit and to use the current temperature thus determined to adjust the standby time.

[0028] Alternatively or additionally, the second control unit can determine the wheel brake temperature during normal operation. In fallback mode, the temperature determined by the second control unit is used to adjust the standby time. Preferably, the wheel brake temperature is determined continuously by the second control unit.

[0029] In principle, the temperature in the control units can be determined in any way.

[0030] In particular, it is conceivable for at least one of the control units to determine the wheel brake temperature based on a model, for example, using vehicle variables such as wheel brake pressure, wheel speeds, and deceleration duration. The respective control unit preferably also serves to adjust the wheel brake for active release from the locked position when the parking brake is deactivated.

[0031] It is understood that the braking system may also comprise two or more such wheel brakes. The parking brake system may therefore comprise at least one wheel brake. When the parking brake is activated, the control units adjust at least one of the wheel brakes to the locking position.

[0032] The method, in particular the operating modes and / or the parking brake functions in the control units, is preferably implemented by means of a computer program product.

[0033] The computer program product includes instructions which, when the computer program product is executed by the braking system, cause the braking system to carry out the method.

[0034] The computer program product is expediently stored on a non-volatile memory, in particular of the braking system, for example the respective control unit.

[0035] Further important features and advantages of the invention emerge from the subclaims, from the drawings and from the associated description of the figures based on the drawings.

[0036] It is understood that the features mentioned above and those to be explained below can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the present invention. Preferred embodiments of the invention are illustrated in the drawings and explained in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

[0037] They show, schematically

[0038] Fig. 1 is a highly simplified, circuit diagram-like representation of a braking system,

[0039] Fig. 2 is a flow chart explaining a method for operating the braking system.

[0040] A braking system 1 shown as an example in Figure 1 is used to adjust at least one wheel brake 2 to brake an associated vehicle (not shown). In the exemplary embodiment shown and below, for the sake of simplicity, it is assumed that the braking system 1 has a single such wheel brake 2. The braking system 1 has two control units 3, 4, namely a first control unit 3 and a second control unit 4. By means of the control units 3, 4, the wheel brake 2 can be adjusted into a position blocking the at least one associated wheel, wherein the position is also referred to below as the locking position. The adjustment to the locking position occurs when a parking brake of the braking system 1 is activated. The activation of the parking brake is indicated in Figure 1 by a symbol comprising a hand and a circled "P".In the exemplary embodiments shown, the parking brake is implemented by means of at least one parking brake function 5, which is stored in the parking brake 1, which can serve as a host. In the exemplary embodiments shown, the parking brake function 5 is stored in the respective control unit 3, 4. The braking system 1 is able to determine a temperature of the wheel brake 2. For this purpose, the braking system 1 in the exemplary embodiments shown has at least one model-based temperature determination function 6, hereinafter also referred to as temperature function 6 for short. As can be seen from Figure 1, in the exemplary embodiments shown, the respective control unit 3 has a temperature function 6 purely by way of example. In the exemplary embodiments shown, the temperature of the wheel brake 2 is determined continuously, for example permanently or regularly, by means of the respective temperature function 6.

[0041] As indicated in Figure 1, the braking system 1 can be operated in two operating modes 7, 8. If both control units 3, 4 are fault-free, i.e. if both control units 3, 4 have neither failed nor degraded, the braking system 1 is operated in a first operating mode 7, which is also referred to below as normal operation 7. In normal operation 7, the parking brake is implemented by means of one of the control units 3, 4, in the exemplary embodiments shown by means of the first control unit 3. In normal operation 7, the wheel brake 2 is adjusted by means of the first control unit 3 when the parking brake is activated. If this control unit 3, 4, in this case the first control unit 3, is faulty, i.e. has an error, is degraded or failed, for example, the parking brake 2 is operated in a second operating mode 8, which is also referred to below as fallback operation 8.In fallback mode 8, the parking brake is implemented by the other control unit 3, 4, in this case by the second control unit 4. In fallback mode 8, the wheel brake 2 is adjusted by the second control unit 4 when the parking brake is activated. In control mode 7 shown in Figure 1, the first control unit 3 adjusts the wheel brake 2 to the locked position when the parking brake is activated. Accordingly, in Figure 1, the first control unit 3 is connected to the wheel brake 2. In fallback mode 8, the wheel brake 2 is adjusted by the second control unit 4 when the parking brake is activated, with the fallback mode 8 being indicated in Figure 1 by a dashed connection between the second control unit 4 and the wheel brake 2. The switch from control mode 7 to fallback mode 8 can also occur if the error in the first control unit 3 occurs during or after the wheel brake 2 is adjusted to the locked position.In this case, the wheel brake 2 is switched to the locking position during or after it has been adjusted to the fallback mode 8.

[0042] The method for operating the braking system 1 is explained below using the sequence shown as an example in Figure 2.

[0043] In the exemplary embodiment shown, the starting point is a procedural measure 100, in which the state of the control units 3, 4 is determined. This procedural measure 100 is also referred to below as conversion measure 100. If the result of conversion measure 100 is a fault-free state of both control units 3, 4, the braking system 1 is operated in normal mode 7. If the result of conversion measure 100 is the faulty state of the first control unit 3, the braking system 1 is operated in fallback mode 8.

[0044] As explained below by way of example, in fallback mode 8 the locking position is monitored for a duration by means of the second control unit 4 and the wheel brake 2 is readjusted if the wheel brake 2 threatens to release from the locking position or releases. An imminent release from the locking position is assumed, for example, if it can be assumed that a clamping force exerted by the wheel brake 2 will decrease above a defined threshold in order to reach the locking position. The duration is also referred to below as the standby duration. The standby duration is adapted depending on the determined temperature of the wheel brake 2. The readjustment of the wheel brake 2 is expediently carried out to prevent the wheel brake 2 from releasing in such a way that at least one associated wheel threatens to release or releases.The readjustment is carried out, for example, by adjusting the wheel brake 2 in such a way that the clamping force of the wheel brake 2 is increased.

[0045] In the embodiment shown in Figure 2, in fallback mode 8, a process measure 101 checks whether the parking brake is activated. This process measure 101 is also referred to below as query measure 101. If the result of query measure 101 is negative, i.e., if the parking brake is not activated or deactivated, the second control unit 4 is switched off or shut down in a process measure 102. The process measure 102 is also referred to below as switch-off measure 102. The switch-off measure 102 therefore also terminates the monitoring of the parking position and the readjustment of the wheel brake 2.

[0046] If the result of query measure 101 is positive, i.e., if the parking brake is activated, wheel brake 2 is moved to the locking position in a procedural measure 103, provided that wheel brake 2 is not already in the locking position. Procedural measure 103 is also referred to below as blocking measure 103. In a subsequent procedural measure 104, the determined temperature of wheel brake 2 is checked. Procedural measure 104 is also referred to below as adaptation measure 104. In the exemplary embodiment shown, depending on whether the determined temperature is below a threshold value, shutdown measure 102 is continued or operation of second control unit 4 is maintained. Thus, the standby duration is adjusted depending on the determined temperature, in the exemplary embodiment shown also depending on the threshold value.According to Figure 4, in the exemplary embodiment shown, shutdown measure 102 is continued if the result of adaptation measures 104 is that the determined temperature falls below the threshold value. If, on the other hand, the determined temperature is at least equal to or greater than the threshold value, the method returns to adaptation measure 104. This process is repeated until the temperature falls below the threshold value. This return to adaptation measures 104 or the repetition leads to the aforementioned temperature-dependent adjustment of the standby time. The system therefore waits until cooling of wheel brake 2 leads to the determined temperature falling below the threshold value. In particular, in the exemplary embodiment shown, the standby time is incrementally increased depending on the last determined temperature and is thus adjusted depending on the temperature.

[0047] As indicated in Figure 2, a procedural measure 105 may provide for a delay, i.e., waiting for a predetermined period, before the procedure returns to the adjustment measure 104. The procedural measure 105 may thus be referred to as a delay measure 105.

[0048] In the embodiment shown, the temperature of the wheel brake 2 is continuously determined and the standby time is adjusted depending on the last determined temperature.

[0049] It may be expedient to provide a control value for the standby duration, which applies even if the temperature determined during the standby duration is immediately below the threshold value. This means that if the temperature falls below the threshold value when the adjustment measures 104 are first executed, the standby duration is set to the control value, i.e., the shutdown measure 102 is only continued once the control value of the standby duration has expired. The control value therefore corresponds to a minimum value of the standby duration, with the adjustment of the standby duration being carried out, as described, by an increase compared to the control value. The control value is preferably greater than 0, so that the standby duration is always greater than zero.

[0050] In the exemplary embodiments shown, the most recently determined temperature or temperatures are used in the adaptation measure 104. The temperature or temperatures used in the adaptation measure 104 can be determined using the temperature model 6 stored in the second control unit 4. Alternatively or additionally, it is conceivable to continuously determine the temperature of the wheel brake 2 using the first control unit 3, for example using the temperature model 6 stored in the first control unit 3, and to provide at least the most recently determined temperature to the second control unit 4 or to store it in the braking system 1, so that the second control unit 4 has access to this stored temperature in the fallback mode 8. The second control unit 4 can then use the stored temperature in the fallback mode 8 to adjust the standby duration.

[0051] The implementation of the method, in particular the operating modes 7, 8, is implemented in particular by means of a computer program product. The computer program product comprises commands which, when the computer program product is executed by the braking system 1, cause the braking system 1 to execute the method.

Claims

Claims 1. Method for operating a braking system (1) with a first control unit (3) and a second control unit (4) for adjusting a wheel brake (2) in a locking position upon activation of a parking brake of the braking system (1), wherein the wheel brake (2) blocks at least one wheel of an associated vehicle in the locking position, - wherein a temperature of the wheel brake (2) is determined, - wherein in a control operation (7) in which the first control unit (3) and the second control unit (4) are fault-free, the wheel brake (2) is adjusted by means of the first control unit (3) when the parking brake is activated, - wherein the braking system (2) is operated in a fallback mode (8) in the event of a fault in the first control unit (3), in which the wheel brake (2) is adjusted by means of the second control unit (4) when the parking brake is activated, - whereby in fallback mode (8) the locking position is monitored for a standby period and the wheel brake (2) is readjusted if the wheel brake (2) threatens to release from the locking position or releases, - whereby the standby time is adjusted depending on the determined temperature of the wheel brake (2).

2. Method according to claim 1, characterized in that the standby time is adapted depending on the temperature of the wheel brake (2) when adjusting the wheel brake (2) to the locking position.

3. Method according to claim 1, characterized in that the temperature of the wheel brake (2) is continuously determined and the standby time is adjusted depending on the last determined temperature.

4. Method according to one of claims 1 to 3, characterized in that - that the standby time is set to a control value if the temperature of the wheel brake (2) is below a predetermined threshold, - that the standby time is increased compared to the control value if the temperature of the wheel brake (2) is at least equal to the threshold value.

5. Method according to claim 4, characterized in that a minimum value of the standby time greater than zero is selected as the control value.

6. Method according to one of claims 1 to 5, characterized in that - that in normal operation (7) the first control unit (3) determines the temperature of the wheel brake (2) and stores it in the brake system (1), - that in fallback mode (8) the temperature stored by the first control unit (3) is used to adjust the standby time.

7. Method according to claim 6, characterized in that in the fallback mode (8) the current temperature of the wheel brake (3) is determined on the basis of the temperature last stored by the first control unit (3) and the current temperature thus determined is used to adjust the standby time.

8. Method according to one of claims 1 to 7, characterized in that - that in control operation (7) the second control unit (4) determines the temperature of the wheel brake (2), - that in fallback mode (8) the temperature determined by means of the second control unit (4) is used to adjust the standby time.

9. Method according to one of claims 1 to 8, characterized in that the fallback mode (8) is switched over if the error of the first control unit 3 occurs during or after the adjustment of the wheel brake 2 to the locking position.

10. A computer program product comprising instructions which, when the computer program product is executed by a braking system (1) having a wheel brake (2) and a first control unit (3) and a second control unit (4), cause the system to carry out the method according to one of claims 1 to 9.

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