Procedure for checking a vehicle's braking system

Abstract

In a method for checking a vehicle's brake system for leaks, a brake application request (W) is detected while the vehicle is stationary. The brake application request (W) is modified by a predefined pressure profile (70) that includes a pressure (p) above a detection threshold (pS), and an electrofluidic pressure generation unit is activated with the predefined pressure profile (70). Pressure values ​​(pa) assigned to a first and / or a second brake circuit are recorded and compared with the predefined pressure profile (70), whereby deviation values ​​(Δp) are determined. Fault indicators are detected if at least one deviation value (Δp) exceeds a predefined threshold.

Description

The invention relates to a method for checking a vehicle's braking system for leakage. A known method for this purpose is part of a hydraulic test sequence, which is performed automatically during maintenance, for example. However, this method naturally does not allow for the regular detection of leaks or low compression in the hydraulic lines before starting a journey. Currently, a key focus for fault detection during normal driving is a brake fluid level sensor, which, however, can only detect a low fluid level in the brake fluid reservoir. Locating a leak in the brake system is not possible with this method. Furthermore, such sensors are expensive. However, especially with the increasingly common braking systems that do not have hydraulically separated and therefore redundant brake circuits, it is important to detect leaks early in order to ensure safe driving. Such braking systems are common, for example, in vehicles for autonomous or semi-autonomous driving. The object of the invention is therefore to present a flexibly applicable, simple and cost-effective method for checking a vehicle's braking system. This problem is solved by a method for checking a vehicle's braking system for leaks, wherein the braking system has a first and a second brake circuit, each with at least one pressure port, and each of the pressure ports can be coupled to an associated brake actuator of a wheel of the vehicle, as well as an electrofluidic pressure generation unit that is in fluid communication with the first and the second brake circuits, comprising the steps of: - detecting a braking request when the vehicle is stationary, - modifying the braking request by a predefined pressure profile that includes a pressure above a detection threshold, and controlling the electrofluidic pressure generation unit with the predefined pressure profile, - acquiring pressure values ​​that are associated with the first and / or the second brake circuit, - comparing the pressure values ​​with the predefined pressure profile and determining deviation values, and - detecting a fault indication.if at least one deviation value exceeds a predetermined threshold. During braking while the vehicle is stationary, the absolute magnitude of the braking force, as long as it exceeds the desired braking force, has no effect on the vehicle's behavior. Therefore, such braking maneuvers can be used to selectively modify the braking process through a predetermined pressure profile, tailored to testing the braking system. The pressure profile can be precisely adjusted, both in terms of the brake pressure level and its duration, so that the vehicle user is not disturbed by the brake system test, yet a reliable assessment of the brake system's condition can still be made. If the measured pressure value in the brake system does not correspond to the expected pressure profile, it is therefore clearly identifiable that a fault exists, since the precise adjustment of the brake pressure ensures that the braking process involves a pressure above the fault detection threshold. The detection threshold should be designed so that a leak in one of the brake circuits is noticed within the time available for inspection, and optionally also so high that excessively low compression in one of the brake circuits can be detected during the inspection. Furthermore, it is ensured that the check is always linked to brake application. Automated tests performed at times without deliberate brake application can then be optionally omitted. One indication of a fault is, for example, that the pressure specified by the pressure curve is not reached or is only reached with a delay, because hydraulic fluid leaks out or the desired compression cannot be achieved due to air in the hydraulic system. In general, this method for checking the brake system can detect leaks or low compression, possibly broken down into specific brake circuits or sub-circuits of a brake circuit. The brake system may still include a brake fluid level sensor that measures the level of brake fluid in the pressure fluid reservoir. However, a more cost-effective fluid level monitoring system can be used, or the brake fluid level sensor can be omitted entirely if the described procedure is carried out regularly. In braking systems where the electrofluidic pressure generation unit normally provides the braking force, no additional components are required to implement the procedure. The predetermined pressure profile, which replaces the braking request, is then applied to the brake circuits by the electrofluidic pressure generation unit. The electrofluidic pressure generation unit can, for example, be a conventional plunger. The steps for carrying out the procedure can easily be stored as software in the memory of a suitable control unit of the braking system. Optionally, the determined pressure values ​​and error indicators are also stored in the control unit's memory, so that a temporal progression of the brake system's behavior can be monitored and potential sources of error can be identified early. A separate hydraulic test sequence for leakage or compression detection can optionally be omitted. In one aspect, the predefined pressure profile involves amplifying the braking request by a gain factor. The detected braking request is amplified sufficiently to generate a pressure above the detection threshold. Such a pressure profile can be traversed in a short time. Testing using such a predefined pressure profile is subsequently referred to as a dynamic brake system test. This method is applicable, for example, when the braking request correlates with a change in driving mode at the start of a journey. For instance, in automatic vehicles, the driver must depress the brake pedal to switch from park to drive mode. This braking request, i.e., the depressurization of the brake pedal, can be used to determine a predefined pressure profile with a gain factor, apply it to the electrofluidic pressure generation unit, and record the pressure values ​​of all or individual brake circuits. The time required for this is short enough not to be noticeable during the driving mode change. In this way, a routine check of the braking system can be performed before starting a journey, thus increasing driving safety. Furthermore, this allows for automated checks, for example after bleeding the brake system, changing the brake fluid or changing the brake pads, to be carried out directly at the start of the next journey, in order to ensure that the brake system was not damaged during such a process and that no air has entered the hydraulic lines. In another aspect, the predefined pressure profile involves the automated execution of a predetermined pressure curve. Here, the pressure profile is precisely known, as it is completely predefined. For example, a maximum pressure is quickly built up and held constant for a certain period. This increases the measurement accuracy. This type of test usually takes more time than simply increasing the braking force, but the accuracy can be higher, or it allows for the sequential testing of multiple brake circuits or sub-circuits. Testing with such a predefined pressure profile is also referred to as a static brake system test. A good opportunity to use a predefined pressure profile in the form of a predefined pressure curve arises when the braking request correlates with a change in driving mode at the end of a journey. For example, similar to starting a journey, in automatic vehicles the driver must depress the brake pedal to switch from driving mode back to park mode. Since the vehicle remains stationary in park mode as planned, a longer period of time can be used to check the braking system unnoticed by the user, which can even extend significantly beyond the time the driver depresses the brake pedal. This provides sufficient time for a complete and thorough check of the braking system at the end of the journey. Such braking maneuvers while stationary also occur in electric vehicles, for example, due to the nature of driving mode changes. Hydraulic brakes are rare in electric vehicles, as the aim is to recover braking energy primarily through recuperation by the electric motor. However, the hydraulic braking system (intended at least for emergencies) can be easily tested during braking maneuvers when changing driving modes without any loss of recuperated electrical energy. The described procedure is also feasible for autonomously or semi-autonomously driving vehicles. In this case, the braking request when changing driving modes at the start and end of a journey is not triggered by the vehicle user, but by the autonomous system; however, the procedure is otherwise identical. It is also conceivable, upon detection of a fault indication, especially in suspected cases, to use hydraulic braking during normal driving, where the brake pressure exceeds the detection threshold, to verify the suspected fault. In this case, however, the brake pressure curve is not modified relative to the braking request; instead, the braking request is simply compared with the achieved pressure value. If each brake circuit is connected to the electrofluidic pressure generation unit via its own brake circuit valve, and only the corresponding brake circuit valve is opened for separate measurement, all brake circuits can be tested separately. If several or all brake circuits are to be tested simultaneously, all corresponding brake circuit valves must be opened. To perform a staged check, the entire brake system is first tested. For this, all brake circuit valves are opened so that pressure is applied to all brake circuits simultaneously. If no deviation above the threshold value is detected in the measured pressure values, the brake system is assumed to be functioning correctly, and the check can be completed. However, if a fault indication, i.e., a deviation value above the threshold, is detected, one of the brake circuits, for example, the first brake circuit, is checked separately in the next step. For this purpose, the brake circuit valve to the other, i.e., the second, brake circuit is closed, so that the pressure is only applied to the first brake circuit being measured. If no deviations to be taken into account are found during this measurement, i.e., deviation values ​​above the threshold, the first brake circuit is classified as functioning correctly. Accordingly, it is also concluded that the second brake circuit is faulty. However, if a deviation value exceeds the threshold during this measurement, it is recognized that the first brake circuit is defective. In this case, the brake circuit valve for the first brake circuit is closed and the one for the second brake circuit is opened, and the second brake circuit is checked separately. If no deviation exceeding the threshold value is detected, the second brake circuit is considered to be functioning correctly. However, if a fault is detected during this measurement as well, it is assumed that both brake circuits are defective and that there is a serious fault in the brake system. If, however, only one of the brake circuits is defective, it is possible to classify the fault as less serious and, if necessary, to continue operating the brake system via the electrofluidic pressure generation unit only with the properly functioning brake circuit. In known braking systems, each brake circuit can be connected to multiple brake actuators, typically those of two vehicle wheels. Usually, all brake actuators are located in their own sub-circuit with separately controllable valves. These separately controllable valves are, for example, familiar valves from the anti-lock braking system (ABS). Therefore, it is usually possible to test individual sub-circuits within the brake circuits. To test an individual sub-circuit, only the valves of the respective sub-circuit are opened. Thus, the step-by-step procedure described above can be further refined by checking the individual sub-circuits of a brake circuit found to be faulty by opening and closing the corresponding ABS valves. This check then provides fault indicators for the individual brake actuators of the vehicle, simplifying repairs. Since most checks do not reveal any faults, the check is already completed after testing the entire system and can be carried out in a short period of time, e.g. at the start of the journey. In one aspect, the fault indicators are categorized according to their relevance to the operation of the braking system and can include less serious and serious fault indicators. Upon detection of a serious fault indicator, the affected brake circuit or a sub-circuit of the affected brake circuit is optionally isolated, whereas upon detection of a less serious fault indicator, the braking system continues to operate, e.g., via the electrofluidic pressure generation unit. The categorization of error indicators can be easily achieved by using different threshold values ​​for the deviation values. In the case of a less serious fault, the braking system can continue to operate normally, with pressure generation provided by the electrofluidic pressure generation unit, using the remaining properly functioning brake circuits or sub-circuits. The vehicle user will then notice virtually no difference in driving behavior; most importantly, the brake force assistance provided by the electrofluidic pressure generation unit remains available. For example, the system only switches to push-through operation in the event of a serious fault indication. In this mode, the braking force is no longer supplied via the electrofluidic pressure generation unit, but rather via a brake master cylinder connected to the brake pedal. This master cylinder requires the driver to apply the braking force manually, purely mechanically, using only their foot pressure. This results in a less comfortable driving experience, which can be avoided in many cases by the procedure described above. If, for example, a check at the start of a journey only suggests low compression or a leak, it is possible to automatically perform a brake system check at the end of the journey. Here, it would be conceivable, for instance, to check all brake circuits and / or sub-circuits individually using a predefined pressure curve and compare the data obtained with previously stored data to detect a fault, such as a gradual development of pressure loss. Such a suspected fault arises, for example, if the achieved brake pressure is too low or drops too sharply, but is still at the lower end of normal operating conditions and / or the deviation value only minimally exceeds the threshold. For example, a message is stored in the control unit to perform a static brake system test at the end of the journey. This method can also detect a false positive dynamic brake system test performed at the start of a journey. This can be done without informing the driver and causing them alarm with a false positive warning message. A check using one of the described procedures can be performed and repeated at specific times, for example, at each drive module change when starting the vehicle, occasionally when changing drive modes when switching off the vehicle, or as needed, whereby the request can originate from the vehicle user and / or the braking system. For example, a dynamic braking system test can be performed by amplifying the braking request by a gain factor at the start of each journey. It is also possible to perform a static braking system test at specific intervals by driving through a pressure curve at the end of a journey. This allows, for example, a more detailed inspection of the braking system in case of suspected problems. To isolate a brake circuit or sub-circuit, for example the corresponding brake circuit valve and / or the corresponding ABS valves of the affected brake circuit or sub-circuits are kept permanently closed. Pressure measurement can be performed by acquiring pressure values ​​using pressure sensors at the individual vehicle wheels and / or by a pressure sensor that measures the output pressure of the electrofluidic pressure generation unit. In the first case, it would be conceivable to check several brake circuits or sub-circuits in parallel, at least to obtain an initial assessment of the signs of a fault. However, due to the sequential procedure described above, the method can also be easily implemented in brake systems without their own pressure sensors on the brake actuators. The invention is described in more detail below with reference to an exemplary embodiment and the accompanying figures. The figures show: - Fig. 1 a schematic representation of a vehicle's braking system with which a method according to the invention can be carried out; - Fig. 2 a schematic representation of a braking process of the method according to the invention when the vehicle is stationary with a predetermined pressure profile and an increase in braking force by a gain factor; - Fig. 3 a schematic representation of a braking process of the method according to the invention when the vehicle is stationary with a predetermined pressure profile and traversing a predetermined pressure curve; - Fig. 4 a schematic representation of hydraulic service braking during normal driving without a predetermined pressure profile; and - Fig. 5 a schematic representation of a sequence of a method according to the invention. Fig. 1 shows a braking system 10 for carrying out a braking procedure and a procedure for checking the braking system. For the sake of clarity, not all identical components are labelled with reference symbols. The braking system 10 is designed for a vehicle with four wheels 12 (rear right, front left, front right, and rear left). All four wheels 12 can be braked using the braking system 10. For this purpose, the braking system 10 has a total of four pressure connections 20, each for a brake actuator 22 per wheel 12. Each brake actuator 22 can be selectively pressurized and depressurized using the braking system 10. To actuate the braking system 10, the vehicle has a brake pedal 23, via which the driver can indicate a braking request W (see also Fig. 2, Fig. 3 to Fig. 4), which corresponds to a specific braking force and thus a deceleration of the vehicle. In this example, the brake system 10 is designed for a brake-by-wire system. The braking request W is therefore transmitted electronically from the brake pedal 23 to an electrofluidic pressure generation unit 24 of the brake system 10 in a known manner, which then provides the corresponding pressure in the brake system 10. The electrofluidic pressure generation unit 24 is a known plunger and essentially comprises an electric drive motor 26, which is coupled to a piston-cylinder unit 28 with a linearly movable piston 30. The piston 30 is guided in a cylinder 32 with two chambers, which can be supplied with pressure fluid from a pressure fluid reservoir 36 via a supply line 34 and can also feed pressurized pressure fluid into a main line 38. This design also allows, in a known manner, the piston 30 to feed pressurized pressure fluid into the main line 38 both when moving away from the drive motor 26 and when moving towards the drive motor 26. In the illustrated embodiment, the electrofluidic pressure generation unit 24 acts on the main line 38 via a first supply valve 46 and a second supply valve 48.The piston-cylinder unit 28 is also designed to receive pressurized fluid from the main line 38. The electrofluidic pressure generation unit 24 outputs hydraulic fluid at a known pressure. A pressure sensor 40 is arranged in the main line 38, which detects the actual hydraulic pressure established in the main line 38. The pressure sensor 40 and the drive motor 26 of the electrofluidic pressure generation unit 24 are connected to a control unit 44, which receives sensor data from the pressure sensor 40 and can control the drive motor 26. Optionally, 22 additional pressure sensors 41 are arranged on the individual brake actuators, which are also connected to the control unit 44. The control unit 44 is designed to control the electrofluidic pressure generation unit 24, more precisely its drive motor 26, in such a way that a desired hydraulic pressure is specified in the main line 38, even in a predetermined time profile. The brake pedal 23 is also mechanically coupled to a master cylinder unit 50 for purely mechanical emergency operation (so-called push-through operation). The master cylinder unit 50 comprises, for example, a fluidic brake master cylinder equipped with a first piston and a second piston, in a known manner. The master cylinder unit 50 is fluidically connected to the pressure fluid reservoir 36. The main cylinder unit 50 is used in normal operation only to generate the braking request W. For this purpose, it is coupled to a simulator unit 52 in addition to the brake pedal 23 in a known manner. By means of both the electrofluidic pressure generation unit 24 and the main cylinder unit 50, a volume flow of pressure fluid taken from the pressure fluid reservoir 36 can be selectively pressurized in the main line 38. The main line 38 leads to two brake circuit valves 54 and 56, which define a first brake circuit 58 and a second brake circuit 60. By closing one of the brake circuit valves 54 or 56, the two brake circuits 58 and 60 can be fluidically decoupled and individually connected to the main line 38. The first brake circuit 58 includes the pressure connections 20 for the rear right and front left wheels 12. The second brake circuit 60 accordingly includes the pressure connections 20 for the front right and rear left wheels 12. Under normal operating conditions, both brake circuits 58 and 60 are pressurized. However, it is possible to operate the brake system 10 with only one brake circuit 58 or 60 and still safely decelerate the vehicle. Flow-wise towards the pressure ports 20, a pressure modulation unit 62 is connected to the two brake circuit valves 58, 60 in each brake circuit 58, 60. Together with the control unit 44 and the brake actuators 22, this unit provides the functionality of an anti-lock braking system (ABS) in a known manner. Each pressure port 20 is assigned a valve 64, which here is an ABS shut-off valve, and a valve 66, which here is an ABS drain valve. Such valve configurations are known per se and are therefore not described in detail. To check the functionality of the brake system 10, especially for leaks or air in the hydraulic lines, a suitable program is stored in a non-volatile memory of the control unit 44, with which appropriate test procedures can be carried out. The steps of a possible test procedure are shown by way of example in Fig. 5. To check the brake system 10, a brake application is generally used when the vehicle is stationary. Generally, in an automatic vehicle, this involves a brake application that occurs automatically when changing driving modes at the start of a journey from park mode to driving mode, and at the end of a journey from driving mode to park mode. The control unit 44 detects such a change in driving mode and, if necessary, initiates a verification procedure. The application of the brakes during a change of driving mode is detected as a brake request W. The brake request W is generated either by the driver of the vehicle pressing the brake pedal 23, or by an autonomous control unit (not shown) sending a corresponding signal to the electrofluidic pressure generation unit 24. In a first variant, the brake system 10 is checked as a dynamic brake system test (see Fig. 2). This dynamic brake system test is performed at the start of the journey and optionally every time the driving mode changes from park mode to driving mode. In the dynamic brake system test, the braking force defined by the braking request W is increased by a suitable amplification factor f (shown in Fig. 2 for a pressure p corresponding to the braking force). This ensures that the pressure p exceeds a defined detection threshold pS. The detection threshold pS is chosen such that sufficient pressure build-up occurs in the hydraulic lines of the brake system 10 to reliably detect faults, i.e., air inclusions or leaks, within the time available for the brake system test. The pressure p of the hydraulic fluid delivered to the main line 38 thus follows a pressure profile 70 over time t, specified by the control unit 44, which corresponds to the braking request W amplified by a factor of f. The pressure p is specified with sufficient accuracy at every time t by the electrofluidic pressure generation unit 24, but is not regulated here. The pressure profile 70 is therefore precisely known. The pressure sensor 40 (and / or optionally the pressure sensors 41) measures the actual pressure pa in the main line 38 over the course of the brake system test. The deviations between the specified pressure curve 70 and the actually measured pressure pa are recorded and evaluated as one or more deviation values ​​Δp. Optionally, all brake circuits 58 and 60 of the brake system 10 are checked simultaneously. For this purpose, both brake circuit valves 54 and 56 are opened, so that both brake circuits 58 and 60 are pressurized. Additionally, the valves 64 of sub-circuits 72 are open, while the valves 66 are closed, so that all four sub-circuits 72 (each comprising a brake actuator 22, a valve 64, and a valve 66) are pressurized. If an excessively large deviation value Δp is detected during the inspection, the affected brake circuit 58, 60 or sub-circuit 72 is optionally deactivated and decoupled from the rest of the brake system 10. For this purpose, suitable valves are, for example, permanently closed or open by the control unit 44 until the defect has been rectified. In a second variant, the check is carried out as a static brake system test (see Fig. 3). This static brake system test is performed here, for example, when changing driving modes at the end of a journey. When the vehicle is parked, more time is available than at the start of the journey, so the total duration of the static brake system test may be longer than that of the dynamic brake system test. For the static brake system test, the detected braking request W is replaced by a predefined pressure profile 70, which is formed by a pressure curve defined with respect to its temporal progression and absolute pressure level. This pressure curve is automatically traversed by the electrofluidic pressure generation unit 24. Within this pressure curve, a maximum pressure is rapidly built up and maintained constant for a predefined period. As with the dynamic brake system test, the current pressure pain of the main line 38 is measured by the pressure sensor 40 (and / or optionally by the pressure sensors 41) and deviations are recorded and evaluated as deviation values ​​Δp and stored in the control unit 44. It is possible to perform a static brake system test at every change of driving mode from driving mode to parking mode at predetermined time intervals or upon input from a vehicle user. Optionally, hydraulic braking operations occurring during normal driving, in which the brake pressure rises above the threshold value pS, without any change in the braking request W, can also be used to check the brake system 10 (indicated in Fig. 4). During such braking operations, the applied pressure is also predetermined by the electrofluidic pressure generation unit 24, while the actual pressure pa is measurable by the pressure sensor 40. Fig. 5 shows a possible procedure for checking the brake system 10. At the start of the journey, in a first step (100), it is detected that a brake application has occurred while the vehicle is stationary during a driving mode change with a braking request (W). Now, in step 102, a dynamic brake system test is performed as described above in the first variant. Optionally, all brake circuits (58, 60) of brake system 10 are checked simultaneously. The braking request W is replaced by the specified pressure profile 70, in which the detected braking request W is amplified by the amplification factor f. Deviations of the currently measured pressure from the specified pressure curve 70 are recorded as deviation values ​​Δp and evaluated by the control unit 44. If the deviation value Δp remains below a predefined threshold, the control unit 44 determines that the brake system 10 is functioning correctly. A corresponding log entry is then recorded in the permanent memory of the control unit 44. The brake system 10 continues to operate normally. The check remains unnoticed by the vehicle user. However, if the deviation value Δp exceeds the threshold, the control unit 44 decides that a fault sign has been detected and the proper functioning of the brake system 10 is impaired. In this case, a static brake system test is performed directly as step 104. This brake system test is only performed here for the first brake circuit 58. For this purpose, the brake circuit valve 56 is closed, so that only the first brake circuit 58 is pressurized. The control unit 44 controls the electrofluidic pressure generation unit 24 so that it outputs the specified pressure curve 70 as described above. The current pressure pa is measured by the pressure sensor 40, and the deviation is determined and evaluated as the deviation value Δp. If no fault is detected, the second brake circuit 60 is isolated, for example, by keeping the brake circuit valve 56 closed during further driving. The brake system 10 is then operated exclusively with the first brake circuit 58, but still via the electrofluidic pressure generation unit 24. Thus, the brake system 10 can continue to be used in a limited normal operating mode. In addition, a warning message is issued and a corresponding entry is stored in the memory of control unit 44. However, if a fault sign is detected for the first brake circuit 58, a further static brake system test is performed for the second brake circuit 60 (step 106). If this remains error-free, the fault lies in the first brake circuit 58, and this is isolated, as described above analogously for the second brake circuit 60. The brake system 10 continues to operate in restricted normal operation using only the second brake circuit 60. Of course, the second brake circuit 60 could also be checked first. However, if a fault also occurs in the second brake circuit 60, the control unit 44 decides, optionally depending on the magnitude of the deviation values ​​Δp, whether the brake system 10 can still be operated in purely mechanical push-through mode via the master cylinder unit 50 and switches the valves of the brake system 10 accordingly. Here too, an error message is issued and an entry is stored in the memory of the control unit 44. The error indicators are optionally categorized, for example into suspected cases, less serious error indicators and serious error indicators. Suspected cases describe deviation values ​​Δp that, for example, are only slightly above the threshold value and thus represent only a minor deviation of the current pressure pa from the specified pressure curve 70. Suspected cases are indications that a defect could develop. However, the brake system 10 can continue to operate normally under observation. If a suspected case is detected at the start of the journey, it is possible to automatically perform a static brake system test at the end of the journey to verify this suspected case. Furthermore, control unit 44 can initiate a further check during suitable hydraulic braking operations during normal operation. Corresponding entries are stored in the memory of control unit 44, allowing the development of a potential fault to be tracked over time. A less serious fault indication is, for example, a leak or insufficient compression in only one brake circuit 58, 60 or only certain sub-circuits 72. In this case, it is usually possible to continue operating the brake system 10 via the electrofluidic pressure generating unit 24, if necessary by isolating the affected sub-circuits 72 of the affected brake circuit 58, 60. Serious fault signs, on the other hand, describe, for example, leaks in both brake circuits 58, 60 and cause the control unit 44 at least to switch the brake system 10 into an emergency operation in which pressure generation is only purely mechanical via the brake pedal 23 and the master cylinder unit 50. In addition, for less serious and serious fault indicators, warning messages are issued to the vehicle user and corresponding entries are made in the memory of control unit 44.

Claims

Method for checking a vehicle's brake system (10) for leakage, wherein the brake system (10) has a first and a second brake circuit (58, 60), each with at least one pressure port (20), wherein each of the pressure ports (20) can be coupled to an associated brake actuator (22) of a wheel (12) of the vehicle, and an electrofluidic pressure generation unit (24) which is in fluid communication with the first and the second brake circuit (58, 60), comprising the steps: - detecting a braking request (W) when the vehicle is stationary, - modifying the braking request (W) by a predetermined pressure profile (70) which includes a pressure above a detection threshold (pS), and controlling the electrofluidic pressure generation unit (24) with the predetermined pressure profile (70), - acquiring pressure values ​​(pa) that are associated with the first and / or the second brake circuit (58, 60).- Comparing the pressure values ​​(pa) with the specified pressure curve (70) and determining deviation values ​​(Δp), and - Determining an error indicator if at least one deviation value (Δp) exceeds a specified threshold. Method according to claim 1, wherein the predetermined pressure profile (70) comprises an amplification of the braking request (W) by an amplification factor (f). Method according to one of the preceding claims, wherein the braking request (W) correlates with a driving mode change at the start of the journey. Method according to one of the preceding claims, wherein the predetermined pressure profile (70) comprises the automated traversal of a predetermined pressure curve. Method according to one of the preceding claims, wherein the braking request (W) correlates with a change in driving mode towards the end of the journey. Method according to claims 3 and 5, wherein the fault indicators include suspected cases and, if a suspected case is detected at the start of the journey, an automated check of the braking system (10) is carried out at the end of the journey. Method according to one of the preceding claims, wherein each brake circuit (58, 60) is in flow communication with the electrofluidic pressure generation unit (24) via its own brake circuit valve (54, 56) and for separate measurement only the brake circuit valve (54, 56) to the corresponding brake circuit (58, 60) is opened. Method according to one of the preceding claims, wherein each brake circuit (58, 60) can be coupled to several brake actuators (22) and all brake actuators (22) are located in a separate sub-circuit (72) with separately controllable valves (64, 66) and only the valves (64, 66) of the respective sub-circuit (72) are opened. Method according to one of the preceding claims, wherein the fault signs are categorized according to their relevance for the operation of the brake system (10) and include less serious and serious fault signs, and upon detection of a fault sign, the affected brake circuit (58, 60) or a sub-circuit of the affected brake circuit (58, 60) is isolated, and upon detection of a less serious fault sign, the brake system (10) continues to be operated via the electrofluidic pressure generation unit (24). Method according to one of the preceding claims, wherein the detection of pressure values ​​(pa) is carried out by pressure sensors (41) on the individual brake actuators and / or by a pressure sensor (40) that detects an output pressure of the electrofluidic pressure generating unit (24).

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