Pressure sensor calibration procedure and brake system

Abstract

The invention relates to a method for calibrating pressure sensors of an electrohydraulic braking system of a vehicle, wherein the braking system comprises a first module and a second module that can be controlled independently of the first module, wherein the first module comprises a brake pedal and a sensor system for detecting the required braking power, wherein the second module comprises inlet valves and outlet valves for actuating the wheel brakes of the vehicle, a first pressure sensor provided on the input side, a second pressure sensor, and at least one isolating valve provided between the first and second pressure sensors, wherein the method carries out the following steps for calibrating the pressure sensors, at least in the event of a defect in the first module for which no measured values ​​from the sensor system for detecting the required braking power are available: - closing at least one isolation valve; - Connecting the second pressure sensor to atmospheric pressure; - Calibration of the second pressure sensor while connected to atmospheric pressure; - Disconnecting the second pressure sensor from atmospheric pressure; - Opening the isolation valve; - Calibrating the first pressure sensor relative to the second pressure sensor with the isolation valve open.

Description

[0001] The invention relates to a method for pressure sensor calibration of an electrohydraulic braking system of a vehicle and to such a braking system.

[0002] Electro-hydraulic vehicle braking systems, which have an electrically operated pressure generator and electrically actuated valves for implementing hydraulic switching operations, are generally known.

[0003] Electro-hydraulic vehicle braking systems are already known that have several modules in order to ensure safe braking of the vehicle with the other module in the event of a malfunction in one module.

[0004] Such electrohydraulic vehicle braking systems can include a pedal unit with a hydraulic master brake cylinder, which, in the event of a malfunction in the braking system, generates pressure directly in the braking system via the hydraulic brake cylinder, thus decelerating the vehicle. In a fault-free state, the braking power desired by the driver is determined by a sensor on the brake pedal or the pedal unit comprising the brake pedal. However, if the module containing the pedal unit is defective, the additional module has one or more pressure sensors to measure the braking power applied by the driver via the master brake cylinder and convert this into the required pressure in the braking system via an electric pressure generator. Such a braking system is known from DE 10 2023 205 165 A1.

[0005] However, pressure sensors exhibit offset drift. This offset drift must be compensated for at certain intervals to ensure that the measured values ​​provided by the pressure sensors are offset-free and thus indicate the actual pressure.

[0006] Based on this, it is the object of the invention to provide a method by means of which a reliable calibration of the pressure sensors is possible even in the event of partial malfunctions of the braking system.

[0007] The object is achieved by a method having the features of independent patent claim 1. A hydraulic braking system is the subject of independent patent claim 13. Preferred embodiments are the subject of the dependent claims.

[0008] According to a first aspect, a method for calibrating pressure sensors of an electrohydraulic braking system of a vehicle is disclosed. The braking system comprises a first module and a second module that can be controlled independently of the first module. The first module is coupled to a brake pedal and has a sensor system for detecting the required braking power. The required braking power is communicated by the driver by acting on the brake pedal. The driver's braking power request can be detected via a pressure sensor that measures the pressure provided by a hydraulic cylinder of the brake pedal and a travel sensor that measures the brake pedal travel.

[0009] The second module has inlet valves and outlet valves for actuating the vehicle's wheel brakes, a first pressure sensor provided on the input side, a second pressure sensor, and at least one isolation valve provided between the first and second pressure sensors. The method performs the following steps to calibrate the pressure sensors, at least in the event of a defect in the first module, in particular where no measured values ​​from the sensor system are available to detect the required braking power: First, at least one isolation valve is closed. This closure of the isolation valve preferably hydraulically decouples the first and second pressure sensors from each other.

[0010] The second pressure sensor is then connected to atmospheric pressure. This provides atmospheric pressure to the pressure sensor, which can be used to calibrate the sensor.

[0011] During the connection to atmospheric pressure, the second pressure sensor is calibrated. The calibration is performed in such a way that the second pressure sensor outputs a measured value of 0 bar or essentially 0 bar after calibration.

[0012] After the second pressure sensor has been calibrated, it is decoupled from atmospheric pressure. This is done primarily by closing one or more valves, which—depending on the valve position—can establish or break a connection between the second pressure sensor and the pressure fluid reservoir.

[0013] Subsequently, at least one isolation valve provided between the first and second pressure sensors is opened. This hydraulically couples the first and second pressure sensors again.

[0014] Finally, the first pressure sensor is calibrated relative to the second pressure sensor, with the isolation valve open during this calibration.

[0015] The technical advantage of the proposed method is that it enables pressure sensor calibration, particularly offset adjustment, even when the first module of the braking system, which performs sensor calibration in a fault-free state, is malfunctioning, and therefore it cannot be determined whether a state necessary for calibration can be established. This allows the pressure sensors to be calibrated even in the event of a fault, thus accurately recording the braking performance desired by the driver, which is measured by the pressure sensors of the second module in the event of a fault.

[0016] According to one embodiment, calibration includes an offset adjustment of the first and second pressure sensors. This allows offset drift of the pressure sensors to be corrected, so that the pressure sensors display correct measured values ​​without any offset. This allows the pressure applied to the wheel brakes and the braking power desired by the driver to be determined relatively precisely and without offset influence.

[0017] According to one exemplary embodiment, the at least one isolating valve is designed to hydraulically decouple the first module from the second module. In the event of a malfunction, the second module can be decoupled from the first module via the isolating valve, so that the second module can apply pressure to the wheel brakes via its pressure generator. A pressure increase can be caused at the first pressure sensor via the hydraulic brake pedal assigned to the first module. The pressure applied via the brake pedal is detected by the first pressure sensor and converted via the pressure generator of the second module into a system pressure that can be applied to the wheel brakes. Alternatively, the at least one isolating valve can be designed as a circuit isolating valve for hydraulically separating two brake circuits of the braking system. This can be used, for example, to decouple the wheel brakes on the front axle from the wheel brakes on the rear axle.

[0018] According to one embodiment, the first pressure sensor is provided between the connection at which the first and second modules are hydraulically coupled and the at least one isolation valve. Thus, from the perspective of the first module, the first pressure sensor is located upstream of the isolation valve and, when the second module is hydraulically isolated from the first module by means of the isolation valve, can be used to measure the driver's braking power request communicated via the actuation of the brake pedal.

[0019] According to one embodiment, the connection to atmospheric pressure is established by opening at least one inlet valve of a wheel brake and by opening an outlet valve associated with this inlet valve, thereby establishing a connection to a pressure fluid reservoir. This allows a connection to the atmosphere to be established using valves already available in the brake system in order to calibrate the pressure sensors based on atmospheric pressure.

[0020] According to one exemplary embodiment, sensor calibration is only started when, with the parking brake not engaged, the first and second pressure sensors measure a pressure value lower than a predetermined pressure threshold. The pressure threshold is preferably selected such that it indicates no or only a low braking power request from the driver. This ensures that the calibration process is only initiated when no or only low braking of the vehicle is to occur. However, if the vehicle's parking brake is activated, sensor calibration can be started without taking into account the pressure value of the second pressure sensor, since it can be assumed that the vehicle can be braked by the parking brake alone when stationary and that the service brake is not required even when the driver presses the brake pedal.

[0021] According to one exemplary embodiment, the pressure threshold is set based on the maximum possible measured value offset according to the specifications of the first and / or second pressure sensor. If, for example, the first and / or second pressure sensor can have a maximum measured value offset of 7 bar, the pressure threshold is set, for example, to 7 bar or substantially 7 bar. This ensures that the calibration process is initiated even when the pressure sensor has experienced the maximum possible drift, i.e., the measured value supplied by the pressure sensor is not interpreted as a braking request from the driver up to the pressure threshold, but is not taken into account for initiating the calibration process.

[0022] According to one embodiment, the at least one isolation valve is only opened when the second pressure sensor indicates a pressure measurement value less than a lower pressure threshold for a defined period of time. It can therefore be assumed that the calibration of the second pressure sensor has been completed and that the calibration of the first pressure sensor can thus be initiated using the calibrated second pressure sensor.

[0023] According to one embodiment, during calibration of the first pressure sensor, a check is carried out to determine whether the absolute value of the gradient of the pressure measurement value of the first pressure sensor is smaller than a predetermined gradient threshold. A high gradient of the pressure measurement value of the first pressure sensor indicates that the pressures in the braking system are changing rapidly over time, for example, due to pumping of the brake pedal. With such fluctuating pressures, despite direct hydraulic coupling of the first and second pressure sensors, it cannot be ensured that the same pressure is always applied to the pressure sensor and thus that the first pressure sensor can be calibrated based on the measured value of the calibrated second pressure sensor. The gradient threshold can be used to define a limit above which gradient a sufficiently good calibration cannot be ensured.

[0024] According to one embodiment, the opening of the isolation valve and the calibration of the first pressure sensor relative to the second pressure sensor are initiated when the absolute gradient of the pressure measurement value of the first pressure sensor is smaller than a predetermined pressure measurement gradient threshold. This allows the start of the calibration of the first pressure sensor to be delayed or even completely prevented in the event of significant temporal fluctuations in the pressure in the brake system.

[0025] According to one exemplary embodiment, the braking power requested by the driver is detected by the second pressure sensor during the period between the calibration of the second pressure sensor and the calibration of the first pressure sensor, which has not yet been completed or has not yet been completed. As previously explained, the driver's braking request is generally detected by the first pressure sensor. However, if the second pressure sensor has already been calibrated but the first pressure sensor has not yet been calibrated or has not been fully calibrated, it is advantageous to detect the braking power requested by the driver using the already calibrated second pressure sensor. This enables more precise detection of the required braking power.

[0026] According to one exemplary embodiment, when the detection of the required braking power changes from the first pressure sensor to the second pressure sensor, or vice versa, a ramp-like transition is provided between the pressure measurement values ​​of the first and second pressure sensors. This ensures that, when the detection of the required braking power is transferred between the two pressure sensors, any jumps in the measured values ​​detected do not lead to a sudden change in the braking power of the wheel brakes, but rather a smooth, jump-free change is achieved through the ramp-like transition.

[0027] According to a further aspect, an electrohydraulic braking system for a vehicle is disclosed. The electrohydraulic braking system comprises a control unit for controlling the braking system, a first module, and a second module that can be controlled independently of the first module. The first module comprises a brake pedal and a sensor system for detecting the required braking power. The second module has inlet valves and outlet valves for actuating the wheel brakes of the vehicle, a first pressure sensor provided on the input side, a second pressure sensor, and at least one isolation valve provided between the first and second pressure sensors. The control unit is designed to perform the following steps for calibrating the pressure sensors in the event of a defect in the first module: - closing at least one isolation valve; - Connecting the second pressure sensor to atmospheric pressure; - Calibration of the second pressure sensor while connected to atmospheric pressure; - Disconnecting the second pressure sensor from atmospheric pressure; - Opening the isolation valve; - Calibrating the first pressure sensor relative to the second pressure sensor with the isolation valve open.

[0028] The terms “approximately”, “essentially” or “about” mean, in the sense of the invention, deviations from the exact value by + / - 10%, preferably by + / - 5% and / or deviations in the form of changes that are insignificant for the function.

[0029] Further developments, advantages, and possible applications of the invention will become apparent from the following description of exemplary embodiments and from the figures. All described and / or illustrated features, individually or in any combination, are fundamentally part of the invention, regardless of their summary in the claims or their reference back to them. The content of the claims is also incorporated into the description.

[0030] The invention is explained in more detail below with reference to exemplary embodiments and the figures. They show: Fig. 1 shows, by way of example, a schematic representation of an embodiment of an electro-hydraulic braking system of a vehicle; and Fig. 2 shows an example block diagram illustrating the method steps of a method for calibrating pressure sensors of an electro-hydraulic brake system.

[0031] Fig. 1 schematically shows an example of an electro-hydraulic braking system 1 of a vehicle.

[0032] The braking system 1 comprises a first independent module 100 and a second independent module 200, and a pressure fluid reservoir 7 under atmospheric pressure. The first module is controlled by the first control unit S100, and the second module by the second control unit S200. The first and second modules 100, 200 are structurally separate and can, for example, be arranged separately in the motor vehicle. The pressure fluid reservoir 7 is, for example, assigned to the first module 100 and arranged on it. The pressure fluid reservoir 7 contains a brake fluid as the pressure medium.

[0033] The first module 100 comprises a first, electrically actuated pressure generator 2. The first pressure generator 2 is designed, for example, as a hydraulic piston-cylinder arrangement and has, for example, a pressure chamber and a piston that can be displaced within the pressure chamber by an electric actuator in order to vary the volume of the pressure chamber and thereby apply pressure to the brake fluid located in the pressure chamber. The actuator can, for example, be an electric motor with a rotor position sensor.

[0034] The pressure chamber is connected to the interior of the pressure fluid reservoir 7 via a check valve 8. The check valve 8 is arranged in such a way that it allows a flow of brake fluid from the pressure fluid reservoir 7 into the pressure chamber, but prevents a backflow of the brake fluid from the pressure chamber into the pressure fluid reservoir 7. Via this check valve 8, the hydraulic piston-cylinder arrangement can draw brake fluid from the pressure fluid reservoir 7 when the piston has already advanced a great distance into the pressure chamber by moving the piston back (in Fig. 1 this corresponds to a movement of the piston to the left).

[0035] In addition, the first module 100 has a coupling valve 9. This coupling valve 9 is provided in a line that couples a pedal unit P to the second module 200. The coupling valve 9 is an electrically actuated valve, meaning that the position of the valve can be controlled by an electrical switching signal.

[0036] The pedal unit P has a master brake cylinder 20 with a brake pedal connected to it. This allows a driver to communicate a braking request and, in the event of a hydraulic fallback, also to build up brake pressure at the wheel brakes 3. The pedal unit P also has a simulator 21, which is connected to the master brake cylinder 20 via a simulator valve 22. The master brake cylinder 20 and simulator 21 are connected to the other hydraulic components of the braking system 1 via the isolation valve 9.

[0037] The second module 200 has a first port E1, which is connected to the interior of the pressure medium reservoir 7. Furthermore, the second module 200 has a second port E2, which is coupled to the output A of the first module 100.

[0038] The second module 200 comprises a second pressure generator 2', which is designed, for example, as a brake fluid pump. The brake fluid pump can comprise a pump pair driven by a common motor. The suction side of the second pressure generator 2' is fluidly connected to the port E1, and the pressure side of the second pressure generator 2' is fluidly connected to a connecting line 10, which establishes a connection to at least two brake circuits B1, B2 of the vehicle.

[0039] The brake circuits B1, B2 each apply braking force to a portion of the wheel brakes 3 of the vehicle, for example, the brake circuit B1 applies braking force to the wheel brakes 3 of the rear axle of the vehicle and the brake circuit B2 applies braking force to the wheel brakes 3 of the front axle.

[0040] Each wheel brake 3 is assigned an inlet valve 4 and an outlet valve 5. The inlet valves 4 are connectable on the inlet side to the first and second pressure generators 2, 2' via the connecting line 10. On the outlet side, the inlet valves 4 are each connected to a wheel brake 3. Pressurized brake fluid can thus be supplied to the wheel brakes 3 in a controlled manner via the inlet valves 4, thereby generating a braking force at the respective wheel.

[0041] The outlet valves 5 are coupled on the inlet side to the connecting line that runs between the respective wheel brake 3 and the inlet valve 4 assigned to that wheel brake 3. The outlets of the outlet valves 5 are connected to the pressure fluid reservoir 7 via a connecting line. The braking force in the wheel brakes 3 can thus be reduced via the outlet valves 5 by reducing the pressure.

[0042] The second module 200 also has a first isolation valve 11 and a second isolation valve 12. The first isolation valve 11 can be used to fluidically decouple the second module 200 from the first module 100, for example, if a leak or a failure of the control unit S100 of the first module 100 is detected. The circuit isolation valve 12 can be used to fluidically isolate the connecting line 10 and thus the two brake circuits B1, B2.

[0043] During normal braking operation, for example, the simulator valve 22 is open and the isolation valve 9 is closed, so that the master brake cylinder 20 is hydraulically connected to the simulator 21, but not to the brake circuits B1, B2 themselves. When the brake pedal is depressed, the brake fluid present in the master brake cylinder 20 is pressed into the simulator 21. The simulator 21 has, for example, a receiving chamber for the brake fluid. For example, a translationally displaceable cylinder is provided in the simulator 21, which can be displaced according to an increasing pressure-displacement characteristic curve. Thus, when the brake pedal is depressed, a driver feels an increasing counterforce generated by the simulator 21.

[0044] However, when the isolation valve 9 is closed, there is no direct hydraulic effect on the wheel brakes 3. Rather, the driver's braking request is detected via a travel sensor 20.1 provided on the master brake cylinder 20 and / or via a pressure sensor 6. The driver's braking request is then automatically implemented based on the measurement information from the travel sensor 20.1 and / or the pressure sensor 6, specifically via the first pressure generator 2 and / or the second pressure generator 2'. In other words, the braking power requested by the driver is implemented in normal braking operation by the sensors of the first module 100.

[0045] In the event that the first module 100 is defective, so that the required braking power can no longer be determined by the sensors of the first module 100, the hydraulic pedal unit P enables the brake force to be directly generated at the wheel brakes 3 via the master brake cylinder 20 itself, for example, if the first control unit has failed. For this purpose, the simulator valve 22 is closed and the isolation valve 9 is opened, allowing the pressure generated in the master brake cylinder 20 to be transmitted to the wheel brakes 3.

[0046] In the event of a malfunction of the first module 100, the required braking power is measured using a first pressure sensor 13 of the second module 200. Based on this measured value, the second pressure generator 2' and the inlet and outlet valves 4, 5 are appropriately controlled. The first pressure sensor 13 is preferably provided between the second port E2 of the second module 200 and the first isolation valve 11.

[0047] The second module 200 also has a second pressure sensor 14. This is preferably provided in the connecting line 10 between the second pressure generator 2' and the second isolation valve 12. The second pressure sensor 14 can thus measure the system pressure that can be applied to the wheel brakes 3 when the intake valves 4 open.

[0048] Pressure sensors, and thus also the first and second pressure sensors 13, 14 of the second module 200, exhibit an offset drift. In order to accurately measure the pressures applied by the first and second pressure sensors 13, 14, the pressure sensors 13, 14 must be recalibrated, thus correcting the offset drift. A correctly calibrated first pressure sensor 13 is particularly important when the braking power required by the driver cannot be provided using the sensors of the first module 100, for example, because the first control unit S100 assigned to the first module 100 has failed.

[0049] In the absence of a malfunction, the first and second pressure sensors 13, 14 are calibrated by hydraulically connecting them to atmospheric pressure via the sniffer hole S provided in the first module 100. However, in the event of a failure of the first control unit S100, it is not possible to ensure that the pressure sensors 13, 14 are connected to the atmosphere via the sniffer hole S.

[0050] In the following, a method for calibrating, in particular for offset adjustment of the pressure sensors 13, 14 without the need for connection to the atmospheric pressure via the first module 100, in particular the sniffer hole S provided there, is disclosed.

[0051] In the event that the first module 100 and / or the first control unit S100 have a fault which means that it cannot be ensured whether or when a connection of the first isolation valve 11 to the atmospheric pressure via the sniffer hole S is possible, the calibration of the first and second pressure sensors 13, 14 takes place without connecting these pressure sensors 13, 14 to the first module 100, but via the connection of the second module 200 via the first connection E1 to the pressure medium reservoir 7 and thus to the atmospheric pressure.

[0052] First, the second pressure sensor 14 is calibrated by connecting it to the atmospheric pressure present at the pressure fluid reservoir 7 by opening at least one inlet valve 4 and the associated outlet valve 5. Before the inlet valve 4 and the outlet valve 5 are opened, the first and / or second isolation valve 12, 13 is closed.

[0053] Once atmospheric pressure is applied to the second pressure sensor 14, this pressure sensor 14 is calibrated such that it outputs the measured value 0 bar or essentially 0 bar. In other words, the sensor offset of the second pressure sensor 14 is calibrated when atmospheric pressure is applied. It is understood that during this time, the second pressure generator 2' is not active, i.e., it does not deliver any brake fluid.

[0054] After calibrating the second pressure sensor 14, the at least one inlet valve 4 and the associated outlet valve 5 are preferably closed again.

[0055] The calibrated second pressure sensor 14 is then used to calibrate the first pressure sensor 13. For this purpose, the first and / or second isolation valve 11, 12 is opened, thus opening the hydraulic connecting line 10 between the first and second pressure sensors 14. After the first and second isolation valves 11, 12 are opened, the first pressure sensor 13 is calibrated relative to the second pressure sensor 14, preferably such that it displays the same or substantially the same measured value as the second pressure sensor 14. This allows the offset adjustment of the first pressure sensor 13 to be performed.

[0056] The following conditions or states are advantageous for the calibration of the first and second pressure sensors 13, 14: The calibration process is preferably only started when the first and second pressure sensors 13, 14 output a measured value less than a pressure threshold. The pressure threshold is preferably based on the maximum offset drift according to the specification of the pressure sensors 13, 14. For example, if the pressure sensors 13, 14 have a maximum offset drift of 7 bar, the calibration of the second pressure sensor 14 is only started when the measured value output by the first and / or second pressure sensors 14 is less than or equal to 7 bar. This ensures that the calibration is only initiated when no or only very low braking power is requested by the driver.

[0057] In the event that the vehicle's electronic parking brake is activated, the calibration can be started even if the measured values ​​are greater than the pressure threshold, since it can be assumed that the braking performance of the parking brake when the vehicle is stationary is sufficient to prevent the vehicle from rolling away.

[0058] Since the measured values ​​of the pressure sensors 13, 14 can fluctuate, the calibration of the first and / or second pressure sensors 13, 14 is preferably only terminated when they output a pressure measured value less than or equal to a lower pressure threshold over a defined period of time. The period of time can be, for example, 1 s, 2 s, or more. The lower pressure threshold can be, for example, 0.1 bar or less. For example, the second pressure sensor 14 is considered calibrated when the second pressure sensor 14 displays a measured value less than the lower pressure threshold over a period of 1 s or longer. If this condition is met, the calibration of the first pressure sensor 14 can be carried out based on the calibrated second pressure sensor 14.

[0059] Since the driver can create undesirable hydraulic conditions for calibration by pressing the brake pedal during calibration of the first pressure sensor 13, the calibration process of the first pressure sensor 13 is only started when the absolute value of the gradient of the pressure measurement value of the first pressure sensor 13 is less than a predetermined gradient threshold. This gradient threshold can be less than 1 bar / s, for example. Using the gradient threshold, it can be detected whether the driver, for example by pumping the brake pedal, is causing rapidly changing pressure conditions in the brake system 1. This makes offset compensation between the first and second pressure sensors 13, 14 impossible, since the pressure measurement values ​​of these sensors cannot change synchronously or with a time offset.

[0060] Should the absolute value of the gradient of the pressure measurement value of the first pressure sensor 13 change during its calibration, the calibration is continued until the pressure measurement value has no gradient or only a gradient smaller than a gradient threshold value.

[0061] In the event that the first module 100 and / or its control unit S100 has a malfunction, the driver's request is preferably detected using the first pressure sensor 13. In the event that the first pressure sensor 13 has not yet been calibrated, but the calibration of the second pressure sensor 14 has already taken place, the driver's request is detected using the second pressure sensor 14. Since a jump in the measured value can occur when the driver's request is transferred from the first pressure sensor 13 to the second pressure sensor 14 (due to the non-synchronous offset adjustment), a ramp-like transition is preferably carried out between the measured values ​​of the first and second pressure sensors 13, 14. This can prevent sudden changes in the measured driver's request from occurring due to insufficient offset adjustment.

[0062] Fig.2 shows a flow chart illustrating the method steps for calibrating the pressure sensors 13, 14 of the brake system 1.

[0063] First, the first and / or second isolation valve is closed (S10).

[0064] The second pressure sensor is then connected to the atmospheric pressure (S11).

[0065] After connecting the second pressure sensor to atmospheric pressure, the second pressure sensor is calibrated while connected to atmospheric pressure and thus measuring this atmospheric pressure (S12). This allows the pressure sensor's offset to be adjusted.

[0066] After the second pressure sensor has been calibrated, it is decoupled from atmospheric pressure (S13).

[0067] The isolation valve located between the first and second pressure sensors is opened so that the pressure sensors are hydraulically coupled (S14).

[0068] Finally, the first pressure sensor is calibrated relative to the second pressure sensor with the isolation valve open (S15). This is done by adjusting the offset of the first pressure sensor so that the first pressure sensor outputs the same or essentially the same measured values ​​as the second pressure sensor.

[0069] The invention has been described above using exemplary embodiments. It is understood that numerous changes and modifications are possible without departing from the scope of protection defined by the patent claims. List of reference symbols 1 braking system 2 first pressure generator 2' second pressure generator 3 wheel brakes 4 Inlet valve 5 Exhaust valve 6 Pressure sensor 7 Pressure medium reservoir 8 Check valve 9 Coupling valve 10 connecting cable 11 first isolation valve 12 second isolation valve 13 first pressure sensor 14 second pressure sensor 20 master brake cylinders 20.1 Position sensor 21 Simulator 22 Simulator valve 100 first module 200 second module A Exit B1 first brake circuit B2 second brake circuit E1 first connection E2 second connection P Pedal unit S sniffer hole S100 first control unit S200 second control unit

Claims

[1] A method for calibrating pressure sensors of an electrohydraulic braking system (1) of a vehicle, wherein the braking system (1) comprises a first module (100) and a second module (200) that can be controlled independently of the first module (100), wherein the first module (100) comprises a brake pedal and a sensor system for detecting the required braking power, wherein the second module (200) comprises inlet valves (4) and outlet valves (5) for actuating the wheel brakes (3) of the vehicle, a first pressure sensor (13) provided on the input side, a second pressure sensor (14), and at least one isolating valve (11, 12) provided between the first and second pressure sensors (13, 14), wherein the method carries out the following steps for calibrating the pressure sensors (13, 14), at least in the event of a defect in the first module (100): - closing the at least one isolation valve (11, 12) (S10); - connecting the second pressure sensor (14) to the atmospheric pressure (S11); - Calibrating the second pressure sensor (14) while connected to atmospheric pressure (S12); - decoupling the second pressure sensor (14) from atmospheric pressure (S13); - Opening the isolation valve (11, 12) (S14); - Calibrating the first pressure sensor (13) relative to the second pressure sensor (14) with the isolation valve (11, 12) open (S15). [2] Method according to claim 1, characterized by that the calibration comprises an offset adjustment of the first and second pressure sensors (13, 14). [3] Method according to claim 1 or 2, characterized by that the at least one isolating valve (11) is designed for hydraulically decoupling the first module (100) from the second module (200) or that the at least one isolating valve (12) is designed as a circuit isolating valve for hydraulically isolating two brake circuits (B1, B2) of the brake system (1). [4] Method according to one of the preceding claims, characterized by that the first pressure sensor (13) is provided between the connection (E2) at which the first and second modules (100, 200) are hydraulically coupled and the at least one isolating valve (11, 12). [5] Method according to one of the preceding claims, characterized by that the connection to atmospheric pressure is established by opening at least one inlet valve (4) of a wheel brake (3) and an outlet valve (5) associated with this inlet valve (4), wherein a connection to a pressure medium reservoir (7) is established when the inlet valve (4) and the outlet valve (5) are opened. [6] Method according to one of the preceding claims, characterized by that the sensor calibration is only started when a pressure measurement value smaller than a predetermined pressure threshold value is measured by the first and second pressure sensors (13, 14) when the parking brake is not engaged. [7] Method according to claim 6, characterized by that the pressure threshold is determined based on the maximum possible measured value offset according to the specification of the first and / or second pressure sensor (13, 14). [8] Method according to one of the preceding claims, characterized by that the opening of the at least one isolating valve (11, 12) only occurs when the second pressure sensor (14) indicates a pressure measurement value less than a lower pressure threshold value for a defined period of time. [9] Method according to one of the preceding claims, characterized by that during the calibration of the first pressure sensor (13) it is checked whether the absolute value of the gradient of the pressure measurement value of the first pressure sensor (13) is smaller than a predetermined gradient threshold value. [10] Method according to one of the preceding claims, characterized bythat the opening of the isolating valve (11, 12) and the calibration of the first pressure sensor (13) relative to the second pressure sensor (14) is started when the absolute gradient of the pressure measurement value of the first pressure sensor (13) is smaller than a predetermined pressure measurement value gradient threshold value. [11] Method according to one of the preceding claims, characterized by that during the period between the calibration of the second pressure sensor (14) which has already been carried out and the calibration of the first pressure sensor (13) which has not yet been carried out or has not yet been completed, the required braking power is detected by the second pressure sensor (14). [12] Method according to one of the preceding claims, characterized by that when the detection of the required braking power changes from the first pressure sensor (13) to the second pressure sensor (14) or vice versa, a ramp-like transition is provided between the pressure measurement values ​​of the first and second pressure sensors (13, 14). [13] An electrohydraulic braking system (1) for a vehicle, comprising a control unit for controlling the braking system (1), wherein the braking system (1) comprises a first module (100) and a second module (200) that can be controlled independently of the first module (100), wherein the first module (100) comprises a brake pedal and a sensor system for detecting the required braking power, wherein the second module (200) comprises inlet valves (4) and outlet valves (5) for actuating the wheel brakes (3) of the vehicle, a first pressure sensor (13) provided on the input side, a second pressure sensor (14), and at least one isolating valve (11, 12) provided between the first and second pressure sensors (13, 14), wherein the control unit is designed to carry out the following steps for calibrating the pressure sensors (13, 14) in the event of a defect in the first module (100): - closing the at least one isolating valve (11, 12); - connecting the second pressure sensor (14) to atmospheric pressure; - Calibrating the second pressure sensor (14) while connected to atmospheric pressure; - decoupling the second pressure sensor (14) from atmospheric pressure; - Opening the isolation valve (11, 12); - Calibrating the first pressure sensor (13) relative to the second pressure sensor (14) with the isolation valve (11, 12) open.

Images