Method for leak testing of a valve of an electro-hydraulic brake system

Abstract

The invention relates to a method for leak testing of a closed valve of a hydraulic brake system of a vehicle. The method comprises the following steps: - Determining a pressure-time integral value by summing several pressure difference values, which indicate the pressure difference present at the closed valve, over a period of time (S10); - Determining a leakage volume, which indicates the volume of brake fluid that has flowed through the closed valve during this period (S11); - Calculating a leakage conductance value of the valve based on the determined pressure-time integral value and the determined leakage volume (S12); - Check if there is a leakage from the closed valve, based on the calculated leakage conductance (S13).

Description

[0001] The invention relates to a method for leak testing a valve of an electro-hydraulic 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] To ensure the correct functionality of the electro-hydraulic braking system, hydraulic monitoring and hydraulic self-tests are performed. "Hydraulic monitoring" refers to the passive observation of braking system signals for fault detection. "Hydraulic self-test" refers to the active control of braking system actuators to test functionality. In particular, it can be monitored whether an electrically operated valve, which is controlled in such a way that it is in a closed state, is actually closed, i.e., whether it is not exhibiting significant leakage. This can be done, for example, by determining the valve's leakage conductance.

[0004] A problem with valve leak testing is that it is often inaccurate and difficult to reproduce. This is often due to the pressure level at the valve changing when the vehicle brake is applied, making it difficult to determine the valve's leakage conductance. This can be particularly problematic for isolation valves that hydraulically decouple a pedal unit from the rest of the braking system, as a leak in this isolation valve can lead to critical situations in which the vehicle cannot be braked or can only be braked with great difficulty.

[0005] Based on this, it is the object of the invention to provide a method by means of which a leakage test of a valve of a hydraulic brake system is possible with high accuracy and reproducibility.

[0006] 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 8. Preferred embodiments are the subject of the dependent claims.

[0007] According to a first aspect, a method for leak testing a closed valve of a hydraulic brake system of a vehicle is disclosed. The method comprises the following steps: First, a pressure-time integral value is determined. This is done by summing several pressure difference values ​​over a period of time, with each pressure difference value indicating the pressure difference existing at the closed valve at a specific point in time. Mathematically speaking, the pressure-time integral value is equal to the integral of the pressure difference values ​​over this period.

[0008] A leakage volume is then determined. The leakage volume indicates the volume of brake fluid that flowed through the closed valve during this period, i.e., the period during which the pressure difference values ​​were summed and to which the pressure-time integral value thus refers.

[0009] A leakage conductance of the valve is then calculated based on the determined pressure-time integral value and the determined leakage volume.

[0010] Finally, based on the calculated leakage conductance, it is checked whether there is a leak in the closed valve.

[0011] The technical advantage of the proposed method is that a very accurate and reproducible test of a valve for unwanted leaks can be carried out, regardless of temporal fluctuations in the pressure level at the valve to be tested and the duration of the application of the wheel brakes.

[0012] According to one embodiment, the valve is designed as a separating valve for decoupling a pedal unit of a hydraulic brake system from at least one wheel brake and at least one electric pressure generator that provides a system pressure to the at least one wheel brake. It is advantageous to be able to check this separating valve with high precision during brake application, since leaks can lead to an undesirable flow of volume into the pedal unit and thus to a falsified detection of the driver's braking request.

[0013] According to one embodiment, the pedal unit has a master cylinder actuatable by means of a brake pedal and a simulator. The simulator is designed to generate a counterforce when the brake pedal is actuated. With a pedal unit designed in this way, if the isolating valve leaks, brake fluid can be forced back into the master cylinder and the simulator. The measured values ​​determined by a sensor in the pedal unit are falsified by the volume of brake fluid forced back in, so that the sensor no longer detects the driver's actual braking request, but rather the measured values ​​are falsified, which can lead to critical driving situations, for example a very hard brake pedal and / or inadequate braking performance of the vehicle. Therefore, especially with this design of the pedal unit, it is very advantageous to detect a leak in the isolating valve as quickly as possible during the braking process.

[0014] According to one embodiment, the leakage test is performed while the brake pedal is being depressed. In other words, the pressure-time integral value and the leakage volume, as well as the leakage conductance, are determined during a braking operation, i.e., when a valve leak leads to undesirable volume flows due to the pressure buildup in the brake system. This allows a leak to be detected immediately during the braking operation, thus avoiding critical driving situations.

[0015] According to one embodiment, the pressure-time integral value is determined by summing several pressure difference values ​​over a period of time shorter than a braking operation performed by the driver of the vehicle. Preferably, the determination of the pressure-time integral value and the leakage volume, as well as the determination of the leakage conductance, are performed multiple times during a single braking operation, in particular iteratively during the entire or substantially entire braking operation. This allows for continuous monitoring of the valve's closing state, which is particularly advantageous when pressures in the braking system vary.

[0016] According to one embodiment, the leakage volume is determined based on measured values ​​from sensors in the pedal unit. This is advantageous because existing sensors, which are intended in particular for detecting the driver's braking request, can be used to check the valve for leaks.

[0017] According to one exemplary embodiment, the volume of brake fluid absorbed in the master cylinder is determined based on a displacement sensor of the master cylinder, and the volume of brake fluid absorbed in the simulator is determined based on pressure values ​​from a pressure sensor of the pedal unit and the pressure-volume characteristic curve of the simulator. The leakage volume is then determined by summing the volumes of brake fluid absorbed in the master cylinder and the simulator. This allows the leakage volume to be determined simply and relatively accurately using sensors located in the pedal unit itself.

[0018] According to an alternative embodiment, the leakage volume is determined based on the volume displaced by an electric pressure generator configured as a piston-cylinder unit during the period in which the pressure-time integral value is determined. Using the pressure generator as a volume measuring device is advantageous because an existing technical device is used both for pressure generation and as a volume measuring device, which reduces the technical effort required for leakage determination.

[0019] When determining the valve's leakage volume, the pressure-volume characteristic curve of the wheel brake calipers is preferably taken into account. This allows the leakage volume to be determined with greater accuracy.

[0020] According to a further aspect, an electrohydraulic braking system for a vehicle is disclosed. The electrohydraulic braking system comprises at least one electric pressure generator, at least one wheel brake, at least one valve, and a control unit for controlling the braking system. The control unit is configured to perform the following steps for leak testing of the valve: - Determining a pressure-time integral value by summing several pressure difference values, which indicate the pressure difference existing at the closed valve, over a period of time; - Determining a leakage volume that indicates the volume of brake fluid that flowed through the closed valve during this period; - Calculating a leakage conductance of the valve based on the determined pressure-time integral value and the determined leakage volume; - Check if there is a leakage of the closed valve based on the calculated leakage conductance.

[0021] According to one embodiment of the brake system, the valve is designed as a separating valve for decoupling a pedal unit of the electro-hydraulic brake system from at least one wheel brake and at least one electric pressure generator which provides a system pressure to the at least one wheel brake.

[0022] According to one embodiment of the brake system, the pedal unit has a master cylinder actuatable by means of a brake pedal and a simulator, wherein the simulator is designed to generate a counterforce upon actuation of the brake pedal.

[0023] 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.

[0024] 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.

[0025] 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 of a block diagram illustrating the method steps of a method for leak testing a valve of an electro-hydraulic brake system.

[0026] Fig. 1 schematically shows an example of an electro-hydraulic braking system 1 of a vehicle.

[0027] The braking system 1 comprises a first independent module 100 and a second independent module 200, as well as a pressure fluid reservoir 7 under atmospheric pressure. 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 thereon. A brake fluid is stored in the pressure fluid reservoir 7 as the pressure medium.

[0028] 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.

[0029] 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).

[0030] In addition, the first module 100 has a separating valve 9. This separating valve 9 is provided in a line that couples a pedal unit P to the brake circuits B1, B2. The separating valve 9 is an electrically actuated valve, meaning that the position of the valve can be controlled by an electrical switching signal.

[0031] For example, the wheel brakes 3 of the second brake circuit B2 are directly assigned to the first module 100. Each wheel brake 3 is assigned an inlet valve 4 and an outlet valve 5. The pressure at the wheel brakes 3 can be controlled by controlled opening or closing of the respective inlet valves 4 and an outlet valve 5.

[0032] The second module 200 is coupled to the first module 100 via a pair of inlet valves 4. As a result, wheel brakes 3 of the first brake circuit B1, which are assigned to the second module 200, can be supplied with pressurized fluid from the first module 100 in order to perform a braking operation.

[0033] 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 pair of pumps driven by a common motor.

[0034] A portion of the wheel brakes 3 of the vehicle can be subjected to braking force via the brake circuits B1, B2, for example the wheel brakes of a first vehicle axle via the brake circuit B1 and the wheel brakes of a second vehicle axle via the brake circuit B2.

[0035] As previously described, 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 pressure generator 2. 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 brake 3 in a controlled manner via the inlet valves 4, thereby generating a braking force at the respective wheel.

[0036] 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 outlet valves 5 can thus reduce the braking force in the wheel brakes 3 by reducing pressure, or even prevent a pressure buildup at the wheel brakes 3 entirely.

[0037] The first module 100 also has a valve 11 and a circuit isolation valve 12. The valve 11 forms an isolation valve by means of which the first pressure generator 2 can be fluidically decoupled from the first module 100 and thus from the brake circuits B1, B2.

[0038] The two brake circuits B1, B2 can be fluidically separated from each other using the circuit isolation valve 12. This is advantageous, for example, if a leak has been detected in a brake circuit B1, B2 and this brake circuit therefore needs to be hydraulically decoupled.

[0039] An electronic control unit 6 is provided to control the braking system 1. This control unit 6 can be used, in particular, to control the actuators, valves, and other components of the braking system in order to perform braking operations of the vehicle, but also to perform monitoring and testing in the braking system 1.

[0040] 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.

[0041] 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.

[0042] 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 23. 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 23, specifically via the first pressure generator 2 and / or the second pressure generator 2'.

[0043] By means of the pedal unit P, it is possible, if necessary, to generate a braking force directly on the wheel brakes 3 via the master brake cylinder 20 itself, for example, if the first and second pressure generators 2, 2' have failed. For this purpose, the simulator valve 22 is closed and the isolation valve 9 is opened, so that the pressure generated in the master brake cylinder 20 can be transmitted to the wheel brakes 3.

[0044] In the event that the isolation valve 9 is not fully closed despite being triggered to assume the closed state, for example due to a leak, pressurized brake fluid supplied by the first pressure generator 2 can flow into the pedal unit. The pressure building up in the pedal unit P is largely determined by the pressure-volume characteristic curve of the simulator 21. If the isolation valve 9 is leaking, the pressure in the pedal unit increases progressively if the driver keeps the brake pedal travel constant.

[0045] Since the driver request detection gives much greater weight to the brake pedal travel (i.e. the displacement of the piston of the master brake cylinder 20, measured by the travel sensor 20.1) than to the pressure provided by the pressure sensor 22, the target pressure in the brake circuits B1, B2 remains almost constant.

[0046] However, the driver must exert increasing force, so that the vehicle's braking behavior is classified as uncontrollable when the isolation valve 9 leaks. The driver is often no longer able to apply the necessary pedal force, as the pedal is forced back by the increasing pressure. This forced back leads to a reduction in the target pressure in brake circuits B1 and B2 due to the aforementioned overweighting of the brake pedal travel.

[0047] This can lead to a situation, for example, where the vehicle can no longer be kept stationary on a slope or can no longer be braked as desired during a long descent over a pass.

[0048] The following discloses a method for testing for a leak in a valve, in particular the isolation valve 9. This method can be used online, i.e., not only at the end of an ignition cycle or after an ignition cycle, but directly upon actuation of the wheel brakes 3 of the vehicle.

[0049] The method described below is particularly suitable for testing the isolation valve 9 for an existing leak, since this method offers a high level of accuracy even when the pressure level changes over time and the brake pedal is actuated during the determination of the measured values ​​required for the leak test.

[0050] Using the pressure sensor 23 of the pedal unit P and a pressure sensor 13 provided in the first module 100 and / or a pressure sensor 13' assigned to the second module 200, the time-dependent course of the pressure difference present at the isolating valve 9 can be determined. The pressure difference thus indicates the pressure difference between the pressure provided to the brake circuits B1, B2 and the pressure present in the pedal unit P. Based on the measured values ​​of the pressure sensors, a pressure-time integral value can be calculated. This pressure-time integral value is obtained by summing several pressure difference values ​​over time.

[0051] According to a first alternative, the leakage volume, i.e., the amount of brake fluid conveyed into the pedal unit P via the closed isolation valve, is determined based on measured values ​​of the pedal unit P itself. The brake fluid entering the pedal unit P due to the leak can be absorbed by both the master brake cylinder 20 and the simulator 21, with the absorption in the master brake cylinder 20 depending on the actuation of the brake pedal by the driver of the vehicle.

[0052] The volume introduced into the master brake cylinder 20 during the period to which the pressure-time integral value refers can be determined by the travel of the piston of the master brake cylinder 20. This travel is measurable via the travel sensor 20.1.

[0053] Simulator 21 typically does not have a displacement sensor. However, the volume introduced into the simulator can be estimated using the pressure measured by pressure sensor 22 and the pressure-volume characteristic curve of simulator 21.

[0054] The volume pushed back into the pedal unit P during the period to which the pressure-time integral value refers corresponds to the sum of the volumes introduced into the master brake cylinder 20 and into the simulator 21.

[0055] According to a second alternative, the leakage volume is determined by the volume displaced by the piston of the first pressure generator 2, which is designed as a piston-cylinder unit. The first pressure generator 2 has a displacement sensor by means of which the volume displaced by the piston in the period to which the pressure-time integral value refers can be determined. By taking into account the pressure-volume characteristic curve of the brake calipers of the wheel brakes 3, the volume displaced into the wheel brakes 3 can be advantageously determined. The leakage volume is determined by calculating the difference between the volume displaced by the piston of the first pressure generator 2 and the volume displaced into the wheel brakes 3. However, this estimate is less accurate than estimating the volume via the pedal unit P, since the switching of the intake valves and the air gap of the wheel brakes 3 result in volume tolerances that cannot be determined or can only be determined inaccurately.

[0056] After determining the pressure-time integral value and the leakage volume, the leakage conductance can be determined by division.

[0057] Based on this determined leakage conductance, a decision can be made as to whether the isolation valve 9 has closed as specified or whether it is leaking. The decision can be made, in particular, based on a threshold value for a permissible leakage conductance. Depending on this, countermeasures can be taken to ensure the safe functionality of the braking system 1.

[0058] It is understood that in addition to the isolation valve 9, other valves of the brake system 1 can also be tested for leakage based on the method according to the invention if the leakage volume passing through the respectively closed valve and the pressure difference at the valve can be measured.

[0059] Fig.Figure 2 shows a flow chart illustrating the process steps for leak testing a closed valve of a hydraulic brake system of a vehicle.

[0060] First, a pressure-time integral value is determined by summing several pressure differential values ​​over a period of time. The pressure differential values ​​indicate the pressure differential at the closed valve (S10).

[0061] A leakage volume is then determined. The leakage volume indicates the volume of brake fluid that flowed through the closed valve during this period (S11).

[0062] Based on the determined pressure-time integral value and the determined leakage volume, the leakage conductance of the valve is then calculated (S12).

[0063] Finally, based on the calculated leakage conductance, a check is carried out to determine whether a leakage of the closed valve is present (S13). This can be done, for example, by comparing the calculated leakage conductance with a specified leakage conductance or by comparing the calculated leakage conductance with a leakage conductance threshold.

[0064] 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 Control unit 7 pressure medium reservoir 8 Check valve 9 Isolating valve 11 first valve 12 Circuit isolation valve 13 Pressure sensor 20 master brake cylinders 20.1 Position sensor 21 Simulator 22 Simulator valve 23 Pressure sensor 100 first module 200 second module B1 first brake circuit B2 second brake circuit P Pedal unit

Claims

[1] Method for leak testing a closed valve (9) of an electro-hydraulic braking system (1) of a vehicle, the method comprising the following steps: - determining a pressure-time integral value by summing several pressure difference values, which indicate the pressure difference present at the closed valve (9), over a period of time (S10); - determining a leakage volume which indicates the volume of brake fluid which has flowed through the closed valve (9) during this period (S11); - Calculating a leakage conductance of the valve (9) based on the determined pressure-time integral value and the determined leakage volume (S12); - Check if there is a leakage of the closed valve (9) based on the calculated leakage conductance (S13). [2] Method according to claim 1, characterized bythat the valve (9) is designed as a separating valve for decoupling a pedal unit of the electro-hydraulic brake system (1) from at least one wheel brake (3) and at least one electric pressure generator (2, 2') which provides a system pressure to the at least one wheel brake (3). [3] Method according to claim 2, characterized by that the pedal unit (3) has a master cylinder (20) which can be actuated by means of a brake pedal and a simulator (21), wherein the simulator (21) is designed to generate a counterforce when the brake pedal is actuated. [4] Method according to one of the preceding claims, characterized by that the leakage test is carried out while the brake pedal is being operated. [5] Method according to one of the preceding claims, characterized bythat the pressure-time integral value is determined by summing several pressure difference values over a period of time which is shorter than a braking operation performed by the driver of the vehicle. [6] Method according to one of claims 2 to 5, characterized by that the leakage volume is determined based on measured values from sensors (20.1, 22) of the pedal unit. [7] Method according to claim 6, characterized by that the volume of brake fluid absorbed in the master cylinder (20) is determined based on a travel sensor (20.1) of the master cylinder (20) and the volume of brake fluid absorbed in the simulator (21) is determined based on pressure values of a pressure sensor (22) of the pedal unit and the pressure-volume characteristic curve of the simulator (21), and that the leakage volume is determined by summing the volumes of brake fluid absorbed in the master cylinder (20) and in the simulator (21). [8] Method according to one of claims 1 to 5, characterized bythat the leakage volume is determined based on the volume displaced by an electrical pressure generator (2) designed as a piston-cylinder unit in the period in which the pressure-time integral value is determined. [9] Method according to claim 8, characterized by that when determining the leakage volume of the valve, the pressure-volume characteristic curve of the brake callipers of the wheel brakes (3) is taken into account. [10] Electro-hydraulic braking system for a vehicle with an electric pressure generator (2, 2'), at least one wheel brake (3), at least one valve (9) and a control unit (6) for controlling the braking system (1), wherein the control unit (6) is designed to carry out the following steps for leak testing of the valve (9): - determining a pressure-time integral value by summing several pressure difference values, which indicate the pressure difference present at the closed valve (9), over a period of time; - determining a leakage volume which indicates the volume of brake fluid which has flowed through the closed valve (9) during this period; - Calculating a leakage conductance of the valve (9) based on the determined pressure-time integral value and the determined leakage volume; - Check if there is a leakage of the closed valve (9) based on the calculated leakage conductance. [11] Braking system according to claim 10, characterized by that the valve (9) is designed as a separating valve for decoupling a pedal unit of the electro-hydraulic brake system (1) from at least one wheel brake (3) and at least one electric pressure generator (2, 2') which provides a system pressure to the at least one wheel brake (3). [12] Braking system according to claim 11, characterized bythat the pedal unit has a master cylinder (20) which can be actuated by means of a brake pedal and a simulator (21), wherein the simulator (21) is designed to generate a counterforce when the brake pedal is actuated.

Images