Method for operating a braking system

Abstract

The present invention relates to a method for operating a braking system (1) comprising 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 braking system (1) is operated in a fallback mode (8) in which the adjustment of the wheel brake (2) is carried out by means of the second control unit (4), whereby a state of the wheel brake (2) is monitored for a standby period, and wherein the standby period is adjusted depending on the temperature of the wheel brake (2). The invention also relates to a computer program product for carrying out the method.

Description

[0001] The present invention relates to a method for operating a braking system. The invention also relates to a computer program for operating such a braking system.

[0002] To engage a parking brake in a vehicle, a wheel brake of the braking system is adjusted to a position that locks at least one of its associated wheels. This adjustment can be made using a control unit of the braking system.

[0003] To increase reliability, such a braking system can have two such control units, which can, for example, be used redundantly. If one of the control units is faulty, the other control unit can take over the adjustment of the wheel brakes when the parking brake is activated.

[0004] The present invention addresses the problem of providing improved or at least other embodiments for a method for operating a braking system of the aforementioned type and for a computer program product for operating such a braking system.

[0005] Inventive proposals for solving the problem are found in the independent claims. Advantageous variants are the subject of the dependent claims.

[0006] The invention therefore proposes that, in a braking system with two control units that are used to adjust a wheel brake when a parking brake is activated, in the event of a fault in one of the control units, the adjustment is carried out by the other control unit, whereby the state of the wheel brake is monitored for a certain period and the wheel brake is readjusted as necessary, and this period is adjusted depending on the temperature of the wheel brake. Thus, during the aforementioned switch from one control unit to the other, thermally induced changes to the wheel brake, which could lead to it releasing from the desired position, are not only taken into account by means of the temperature, but the duration of this consideration 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 a demand-based operating time and therefore more efficient operation of the braking system.

[0007] According to the invention, a method for operating a braking system with a wheel brake is proposed, wherein the braking system comprises a first control unit and a second control unit for adjusting the wheel brake to 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 hereinafter also referred to as the holding position. That is to say, 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, the temperature of the wheel brake is determined. If both control units are fault-free, the braking system operates in an operating mode, which is hereinafter also referred to as normal operation. If one of the control units has a fault, for example, if it has failed or degraded, the braking system operates in an operating mode, which is hereinafter also referred to as fallback operation.In normal operation, when the parking brake is engaged, the wheel brake is adjusted by the first control unit. In fallback mode, when the parking brake is engaged, the wheel brake is adjusted by the second control unit. In fallback mode, the locking position is monitored for a certain period, and the wheel brake is readjusted if it threatens to release from the locking position or does release. This period is subsequently referred to as the standby duration. The standby duration is adjusted depending on the measured temperature of the wheel brake.

[0008] A risk of the wheel brake releasing from the locked position is assumed in particular if it can be assumed that a clamping force exerted by the wheel brake in order to reach the locked position will dissipate over a defined threshold.

[0009] In particular, the solution according to the invention addresses 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 locking of the wheel brake is no longer guaranteed, resulting in or threatening to cause the associated wheel to rotate and the vehicle to roll away. The readjustment adjusts the wheel brake to ensure that the locking of at least one wheel is achieved and / or remains guaranteed. This readjustment is therefore equivalent, for example, to retensioning the wheel brake.The temperature-dependent adjustment of the standby time thus ensures that such cooling does not lead to any release from the locking position, even in fallback mode or when switching to fallback mode, or at least the probability of such a release is reduced.

[0010] After the standby period has elapsed, the monitoring system, in particular the second control unit, is advantageously deactivated, while the wheel brake remains in the locked position. The standby period thus expeditiously defines a duration after which the second control unit is deactivated, i.e., specifically shut down. Adjusting, in particular increasing, the standby period can be achieved by preventing this deactivation, in particular this shutdown, of the second control unit.

[0011] The adjustment of the standby time, which depends on the determined temperature, is expediently carried out in an analogous manner during normal operation.

[0012] The switch from normal operation to fallback operation can be carried out in any way.

[0013] For example, the system can also switch to fallback mode if the first control unit malfunctions during or after the wheel brake is moved into the locking position. This switchover occurs during or after the wheel brake is adjusted by the first control unit. In this case, the second control unit can either complete the locking process or simply be used for fine-tuning.

[0014] The respective control unit can, in principle, be designed in any way imaginable.

[0015] For example, the respective control unit may have a microcontroller or be a microcontroller.

[0016] The parking brake is preferably implemented by means of a parking brake function of the respective control unit. At least the first control unit includes a complete parking brake function. Advantageously, the second control unit also includes a complete parking brake function.

[0017] The braking system can serve as a host or have a host in which the parking brake functions are stored, in particular integrated.

[0018] The standby time can be adjusted depending on the temperature of the wheel brake when it is moved into the locking position. This means that the temperature of the wheel brake is determined when it is moved into the locking position, and the standby time is adjusted accordingly.

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

[0021] The standard value can in principle also correspond to zero, meaning that the standby time is zero if the threshold value is not exceeded.

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

[0023] It is conceivable to determine the temperature of the wheel brake in a component of the braking system separate from the control units and / or in a unit superior to the control units, for example in the host.

[0024] It is also conceivable that, during normal operation, the first control unit determines the temperature of the wheel brake and stores it in the brake system. This data is preferably stored in non-volatile memory. Preferably, the first control unit continuously determines the temperature of the wheel brake. In fallback mode, the temperature stored by the first control unit, particularly the last stored temperature, is used to adjust the standby time.

[0025] The standby time can be adjusted depending on the temperature last determined by the first control unit.

[0026] It is also conceivable to determine the current temperature of the wheel brake based on the temperature last stored by the first control unit and to use the current temperature thus determined to adjust the standby time.

[0027] Alternatively or additionally, the second control unit can determine the temperature of the wheel brake during normal operation. In fallback mode, the temperature determined by the second control unit is used to adjust the standby time. Preferably, the temperature of the wheel brake is determined continuously by the second control unit.

[0028] The temperature in the control units can, in principle, be determined in any way.

[0029] In particular, it is conceivable to determine the temperature of the wheel brake in at least one of the control units using a model-based approach, for example by means of vehicle parameters such as wheel brake pressure, wheel speeds and duration of deceleration.

[0030] The respective control unit is preferably also used to adjust the wheel brake for active release from the locked position when the parking brake is deactivated.

[0031] It goes without saying that the braking system can also include two or more such wheel brakes. The parking brake system can therefore include at least one wheel brake. When the parking brake is activated, the control units adjust at least one of the wheel brakes into the locked 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 executed by the braking system, cause the computer program product to execute the procedure.

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

[0035] Further important features and advantages of the invention will become apparent from the dependent claims, the drawings and 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 combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0037] Preferred embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein identical reference numerals refer to identical or similar or functionally identical components.

[0038] They show, each schematically Fig. 1. A highly simplified, circuit diagram-like representation of a braking system, Fig. 2. A flowchart to explain a procedure for operating the braking system.

[0039] With a Fig. In the exemplary embodiment shown in Figure 1, at least one wheel brake 2 is adjusted to brake an associated vehicle (not shown). For the sake of simplicity, in the illustrated embodiment and in the following, it is assumed that the brake system 1 has a single such wheel brake 2. The brake system 1 has two control units 3 and 4, namely a first control unit 3 and a second control unit 4. By means of the control units 3 and 4, the wheel brake 2 can be adjusted to a position that blocks at least one associated wheel, a position which is also referred to below as the locking position. The adjustment to the locking position occurs when a parking brake of the brake system 1 is activated. The activation of the parking brake is described in Fig. 1 is indicated by a symbol comprising a hand and a circled “P”. In the illustrated embodiments, 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 the host. In the illustrated embodiments, the parking brake function 5 is stored in the respective control unit 3, 4. The brake system 1 is capable of determining the temperature of the wheel brake 2. For this purpose, the brake system 1 in the illustrated embodiments has at least one model-based temperature determination function 6, hereinafter also referred to as temperature function 6. How Fig. As can be seen from Figure 1, in the illustrated embodiments, the respective control unit 3 has a temperature function 6. Using the respective temperature function 6, the temperature of the wheel brake 2 is continuously determined in the illustrated embodiments, for example, permanently or regularly.

[0040] As in Fig. As indicated in Figure 1, the brake system 1 can be operated in two operating modes 7 and 8. If both control units 3 and 4 are fault-free, i.e., neither control units 3 and 4 have failed or degraded, the brake system 1 operates in a first operating mode 7, which is subsequently also referred to as normal operation 7. In normal operation 7, the parking brake is applied by one of the control units 3 and 4, in the illustrated embodiments by the first control unit 3. In normal operation 7, the wheel brake 2 is adjusted by the first control unit 3 when the parking brake is activated. If this control unit 3 or 4, in this case the first control unit 3, is faulty, i.e., has a fault, is degraded, or has failed, the parking brake 2 operates in a second operating mode 8, which is subsequently also referred to as fallback operation 8.In fallback mode 8, the parking brake is applied by means of the other control unit 3, 4, in this case, the second control unit 4. In fallback mode 8, the wheel brake 2 is adjusted by means of the second control unit 4 when the parking brake is activated. In the... Fig. In the standard operating procedure shown in Figure 1, the first control unit 3 adjusts the wheel brake 2 to the locking position when the parking brake is activated. Accordingly, Fig. 1. The first control unit 3 is connected to the wheel brake 2. In fallback mode 8, the adjustment of the wheel brake 2 is carried out by means of the second control unit 4 when the parking brake is activated, whereby the fallback mode 8 is in Fig. 1 is indicated by a dashed line connecting the second control unit 4 to the wheel brake 2. The switch from normal operation 7 to fallback operation 8 can also occur if the fault of the first control unit 3 occurs during or after the wheel brake 2 is moved into the locking position. In that case, the switch to fallback operation 8 occurs during or after the wheel brake 2 is moved into the locking position.

[0041] The procedure for operating the brake system 1 is described below using the example in the Fig. The process is explained using two examples.

[0042] In the illustrated embodiment, the starting point is a process 100 in which the state of the control units 3 and 4 is determined. This process 100 is hereinafter also referred to as the changeover process 100. If the result of the changeover process 100 is a fault-free state of both control units 3 and 4, the braking system 1 is operated in normal operation 7. If the result of the changeover process 100 is a faulty state of the first control unit 3, the braking system 1 is operated in fallback operation 8.

[0043] As explained below, in fallback mode 8, the locking position is monitored for a certain period by means of the second control unit 4, and the wheel brake 2 is readjusted if it threatens to release from the locking position or does release. A release from the locking position is considered imminent, for example, if it can be assumed that a clamping force exerted by the wheel brake 2 to achieve the locking position will dissipate beyond a defined threshold. 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 2. The wheel brake 2 is expediently readjusted to prevent it from releasing, such that at least one associated wheel threatens to release or does release.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.

[0044] At the in Fig. In the embodiment shown in Figure 2, during fallback operation 8, a check is performed in a procedure 101 to determine whether the parking brake is activated. This procedure 101 is also referred to below as query procedure 101. If the result of query procedure 101 is negative, i.e., the parking brake is not activated or is deactivated, the second control unit 4 is switched off or shut down in a procedure 102. This procedure 102 is also referred to below as shutdown procedure 102. The shutdown procedure 102 thus also terminates the monitoring of the locking position and the readjustment of the wheel brake 2.

[0045] If the result of query measure 101 is positive, meaning the parking brake is activated, then in a procedure measure 103, the wheel brake 2 is moved into the locking position, unless it is already in the locking position. Procedure measure 103 is hereinafter also referred to as blocking measure 103. In a subsequent procedure measure 104, the determined temperature of the wheel brake 2 is checked. Procedure measure 104 is hereinafter also referred to as adjustment measure 104. In the illustrated embodiment, depending on whether the determined temperature is below a threshold value, the shutdown measure 102 is initiated, or the operation of the second control unit 4 is maintained. Thus, depending on the determined temperature, and in the illustrated embodiment also depending on the threshold value, the standby duration is adjusted accordingly. Fig. 4 In the illustrated embodiment, the shutdown measure 102 is executed if the result of the adjustment measures 104 is that the measured temperature falls below the threshold. If, on the other hand, the measured temperature is at least at the threshold, i.e., equal to or greater than the threshold, the procedure returns to adjustment measure 104. This process is repeated until the threshold is undershot. This return to adjustment measure 104, or the repetition, leads to the aforementioned temperature-dependent adjustment of the standby time. The process waits until cooling of the wheel brake 2 causes the measured temperature to fall below the threshold. In particular, in the illustrated embodiment, the standby time is incrementally increased depending on the last measured temperature and thus adjusted temperature-dependently.

[0046] As in Fig.As indicated in section 2, a delay, i.e., waiting for a predetermined period, may be provided for in procedural measure 105 before the procedure returns to adjustment measure 104. Procedural measure 105 can therefore be referred to as delay measure 105.

[0047] In the illustrated embodiment, the temperature of the wheel brake 2 is continuously determined and the standby time is adjusted depending on the last determined temperature.

[0048] It may be expedient to provide a setpoint for the standby duration, which applies even if the standby temperature is directly below the threshold. This means that if the temperature falls below the threshold during the initial execution of adjustment measures 104, the standby duration is set to the setpoint, and the shutdown measure 102 is only initiated once the setpoint for the standby duration has expired. The setpoint thus corresponds to a minimum standby duration, with the standby duration being adjusted as described by increasing it compared to the setpoint. The setpoint is preferably greater than 0, ensuring that the standby duration is always greater than zero.

[0049] In the illustrated embodiments, the last determined temperature(s) are used in the adaptation measure 104. The determination of the temperature(s) used in the adaptation measure 104 can be carried out 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 last determined temperature to the second control unit 4 or to store it in the brake system 1, so that the second control unit 4 has access to this stored temperature in fallback mode 8. The second control unit 4 can then use the stored temperature in fallback mode 8 to adjust the standby time.

[0050] The implementation of the procedure, in particular operating modes 7 and 8, is implemented primarily by means of a computer program. The computer program comprises instructions which, when executed by the braking system 1, cause the braking system 1 to execute the procedure.

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 holding position when a parking brake of the braking system (1) is activated, wherein the wheel brake (2) in the holding position blocks at least one wheel of an associated vehicle, - where a temperature of the wheel brake (2) is determined, - wherein in normal 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) in the event of a fault in the first control unit (3) is operated in a fallback mode (8) in which the wheel brake (2) is adjusted by means of the second control unit (4) when the parking brake is activated, - wherein 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 or releases from the locking position, - wherein the standby time is adjusted depending on the determined temperature of the wheel brake (2). [2] Method according to claim 1, characterized by , that the standby time is adjusted depending on the temperature of the wheel brake (2) when the wheel brake (2) is moved into the locking position. [3] Method according to claim 1, characterized by , that the temperature of the wheel brake (2) is continuously determined and the standby time is adjusted depending on the most recently determined temperature. [4] Method according to any one of claims 1 to 3, characterized by , - 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 standard value if the temperature of the wheel brake (2) corresponds at least to the threshold value. [5] Method according to claim 4, characterized by , that a minimum standby time greater than zero is chosen as the rule value. [6] Method according to any one of claims 1 to 5, characterized by , - 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 by, that in 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 any one of claims 1 to 7, characterized by , - that in normal 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 any one of claims 1 to 8, characterized by , that the system switches to fallback operation (8) if the fault of the first control unit 3 occurs during or after the adjustment of the wheel brake 2 to the locking position. [10] Computer program product comprising instructions which, when the computer program product is executed by a braking system (1) with a wheel brake (2) and a first control unit (3) and a second control unit (4), cause it to execute the method according to any one of claims 1 to 9.

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