DE102006014269A1 - Hydraulic system`s functional test providing method for brake assembly of vehicle, involves measuring delivery rate of multi-piston pump, where multi-piston pump is tested at same time to check operability of individual pistons - Google Patents

Abstract

The method involves measuring a delivery rate of a multi-piston pump (SRP1), where the multi-piston pump is tested at the same time to check the operability of individual pistons. Decrease in pressure of a hydraulic system (10) is measured for determining leakage. The delivery rate of the multi-piston pump is measured by generating a pressure on pressure side of the multi-piston pump up to an intermediate value, where the pressure generation is continued up to a nominal value after a delay time. Independent claims are also included for the following: (1) a device for providing a functional test of a hydraulic system (2) a testing device for use in a method of providing functional test of a hydraulic system.

Description

State of technology

The The present invention relates to a method and a device for functional testing a hydraulic system, in particular a brake circuit with a multi-piston pump in a brake system of a vehicle as well a test device for carrying out the Process.

In Brake circuits of vehicles are now multi-piston pumps for power assistance or to increase used the brake pressure. While at conventional Brake control systems with a single-piston pump at the end of line testing or check after Repairs or in operation it is sufficient, the delivery rate It is also necessary to determine if the individual pistons are functional. In a multi-piston pump there is the possibility that a single piston inoperable or is functionally restricted, the overall performance of the multi-piston pump is still sufficient. In a single-piston pump, a so-called actuator test is performed to check the function carried out, wherein pressure is built up in the hydraulic system and the pump lag time is measured by the generator voltage of the pump motor, which conclusions on the quality the pump or its capacity and the filling level of the hydraulic system allows. Such a test is not sufficient for a multi-piston pump, since no statement about the correct function of all pump elements and their capacity can be taken.

task the present invention is therefore to provide a method with the functionality a hydraulic system with a multi-piston pump to be checked can.

epiphany the invention

• – Messen der Förderleistung der Mehrkolbenpumpe, wobei diese gleichzeitig auf Funktionsfähigkeit der einzelnen Kolben geprüft wird,
• – Messen des Druckabfalls des mit Druck beaufschlagten hydraulischen Systems zur Ermittlung von Leckagen.

This problem is solved by a method for functional testing of a hydraulic system, in particular a brake circuit with a multi-piston pump in a brake system of a vehicle, comprising the method steps

• - Measuring the flow rate of the multi-piston pump, which is simultaneously tested for operability of the individual pistons,
• - Measuring the pressure drop of the pressurized hydraulic system to detect leaks.

In An embodiment of the invention is provided that the measuring the delivery rate the multi-piston pump a pressure build-up on the pressure side of the multi-piston pump to an intermediate value, wherein the pressure build-up after a Delay Time continues to a nominal value.

In An embodiment of the invention provides that the delivery rate the multi-piston pump from the pressure gradient after the delay time until reaching the nominal value.

In An embodiment of the invention is provided that after reaching of the nominal value, a second delay time is waited for and then the measurement of the pressure drop of pressurized hydraulic system connects.

In An embodiment of the invention is provided that the hydraulic System includes a UPS and a HSV, with the HSV until reaching of the nominal value opened remains and the UPS until reaching the intermediate value partially is closed and closed after reaching the intermediate value becomes.

In An embodiment of the invention is provided that the functionality the individual piston on the basis of a frequency spectrum of pressure fluctuations tested in the hydraulic system becomes.

In An embodiment of the invention provides that the individual Piston as functional be classified when the frequency spectrum of pressure fluctuations Specified spectral lines with an integer multiple of the Pump speed comprises, wherein the largest multiple of the number of Piston corresponds to the multi-piston pump.

In An embodiment of the invention provides that at least one of the pistons classified as at least functional when one of the spectral lines is an integer multiple the pump speed is missing.

The advantage of the method according to the invention lies, in particular, in the fact that in the case of end-of-line testing in a production plant and after carrying out service work, it is possible to assess the quality of the hydraulic system in terms of pump delivery rate, pump function and internal leakages in one operation. In the method according to the invention, the monitoring of the multi-piston pump is integrated by a fast Fourier transformation (FFT) during the pressure build-up. The pressure gradient is detected by a control unit, over a definable leakage time, the internal pressure loss is determined. This makes it possible to have all the test steps for the hydraulic system in one procedure perform. The summary of the tests reduces the time required for testing in production and after the execution of service work. To the same extent, the process reliability of the tape end inspection increases after production. A further advantage is that the method according to the invention offers a simple tool for detecting the performance of the hydraulic system during and after service work (repair work or the like) on the hydraulic system.

• – Mittel zum Messen der Förderleistung der Mehrkolbenpumpe,
• – Mittel zum Prüfen der Funktionsfähigkeit der einzelnen Kolben,
• – Mittel zum Messen des Druckabfalls des mit Druck beaufschlagten hydraulischen Systems zur Bestimmung von Leckagen

umfasst.The problem mentioned above is also solved by a device for functional testing of a hydraulic system, in particular a brake circuit with a multi-piston pump in a brake system of a vehicle, characterized in that this

• Means for measuring the delivery rate of the multi-piston pump,
• - means for checking the operability of each piston,
• - means for measuring the pressure drop of the pressurized hydraulic system to determine leaks

includes.

The The aforementioned problem is also solved by a tester for use in a method according to the invention.

Short description the drawings

following is an embodiment of Present invention explained in more detail with reference to the accompanying drawings. there demonstrate:

1 a sketch of a hydraulic brake system with multi-piston pump of a vehicle;

2 a diagram of a pressure curve;

3a - 3c Frequency spectra of a pressure curve;

4 a frequency spectrum of the pressure curve at a badly tuned sampling frequency;

5 a flow diagram of the method according to the invention.

Embodiment (s) of the invention

1 shows a sketch of a hydraulic braking system of a vehicle, wherein the hydraulic brake system in two circles, these are referred to here as MC1 and MC2, is divided in a known manner. The circle MC2 is for actuating the brakes RR of the right rear seat and LR of the left rear wheel of the vehicle, the circle MC1 is for actuating the brake RF of the right front wheel and the brake LF of the left front wheel. The brakes are usually disc brakes, but may also be drum brakes or the like. In the present case, it is assumed that a four-wheeled vehicle. If more than four wheels are present, they can either be used on the dual-circuit brake system as in 1 can be traced back, or there may be more than two independent brake circuits. The with the reference number 10 designated vehicle brake system is connected to a dual-circuit master cylinder 1l connected, which comprises one or two independent master cylinder, which can be actuated by a brake pedal. The independent brake circuits MC1 and MC2 are described below using the example of the brake circuit MC1, the brake circuit MC2 is constructed identically. The first brake circuit MC1 comprises a hydraulic slave cylinder RF and a hydraulic slave cylinder LF. In the present example, the hydraulic slave cylinder RF is assigned to the right front wheel, the hydraulic slave cylinder LF to the left front wheel. The master cylinder 11 is via a hydraulic line to the master cylinder side pressure sensor 12 is arranged, connected to a first high-pressure switching valve HSV1. The first high-pressure switching valve HSV1 is closed in the de-energized state and opens when energized. It may be a dosable valve, a so-called continuous valve that can be brought between the open and closed positions in any position or a switching valve with only open or closed position. The first high-pressure switching valve HSV1 is connected to the suction side of a first hydraulic pump SRP1, which in the exemplary embodiment shown here is designed as a piston pump with three pump pistons per brake circuit MC1, MC2. The hydraulic pump SRP1 of the first brake circuit MC1 and a hydraulic pump SRP2 of the second brake circuit MC2 are driven by a common speed-torque-controllable electric pump motor M. The pressure and pumping power of the two hydraulic pumps SRP1 and SRP2 can be changed via the speed and torque of the controllable pump motor M. The pressure side of the hydraulic pump SRP1 is connected to the wheel brake cylinder RF via a valve RFEV and to the wheel brake cylinder LF via a valve LFEV. The valves RFEV and LFEV are opened in the de-energized state and are each bridged with a check valve, which allows a return flow from the wheel brake cylinders RF and LF. The wheel brake cylinder RF is connected via a valve RFAV, the wheel brake cylinder LF via a valve LFAV and both together via a check valve RVR1 with the suction side of the hydraulic pump SRP1 connected. The valves RFAV and LFAV are closed in the de-energized state. On the valves RFAV and LFAV side facing the check valve RVR1 a pressure accumulator A1 is arranged. At the wheel brake cylinder LF is a radbremszylinderseitiger pressure sensor 13 arranged. A changeover valve 1 allows separation of the high pressure side of the SRP1 hydraulic pump with the master cylinder 11 , The changeover valve 1 is bridged with a check valve that opens in the direction of the wheel brake cylinder.

The second hydraulic circuit MC2 is constructed identically to the first hydraulic circuit MC1, the valves and brake cylinders are designated accordingly. The wheel brake cylinder side pressure sensor is in the second hydraulic circuit MC2 with the reference numeral 14 designated. Otherwise, the indices 1 and 2 are respectively selected according to the numbering of the respective hydraulic circuit MC1 and MC2. Hereinafter, a braking operation will be explained with reference to the first hydra likkreises MC1. In a braking operation with brake booster, the first high-pressure switching valve HSV1 is opened, so that of the master cylinder 11 specified pressure on the hydraulic line on the suction side of the hydraulic pump SRP1 is applied. By opening the first changeover valve USV1 more or less, the pressure on the pressure side of the hydraulic pump SRP1 is regulated because the first changeover valve USV1 acts as a short circuit between the suction side and the high pressure side of the first hydraulic pump SRP1. The valves RFAV and LFAV serve to adapt the pressure of the respective wheel brake cylinders to different braking powers for each side, z. As well as within an ABS system.

For the functionality a vehicle brake system is in addition to the functionality all switchable valves and the pressure tightness of the supply lines the Function of the first and second hydraulic pump SRP1 and SRP2 of importance. The hydraulic pumps are here multi-piston pumps, which mentally as parallel connection of out-of-phase piston pumps, here three piston pumps shown can be. The following is an embodiment of a method with which the functionality all components used can be tested. The procedure will described using the example of the first hydraulic circuit MC1, the procedure in terms of the second hydraulic circuit MC2 and possibly further before Unillustrated hydraulic circuits are identical.

2 shows a diagram of the pressure p, it is here the pressure at the wheel brake cylinder LF, via the pressure sensor 13 measured over time. The pressure is plotted in bar, the time in seconds. In addition, the switching state of the respective valves is plotted. In the switching state of the valves only the energized state is applied in each case by a solid line with the respective rising and falling edge. The process begins at a time t0 with the unpressurized state. At this time, the pump motor M for driving the hydraulic pumps SRP1 and SRP2 is turned on and operated at a constant speed, for example, 1500 rpm. At the same time, the high-pressure switching valve HSV1 is switched on. The first switching valve USV1 is controlled from the time t0 to a value W (USV1), which corresponds to a pressure build-up to the value p1. The first switching valve USV1 is thus partially closed, this can be expressed as a percentage of the complete closing, so that the pressure p1 is built up in the stationary state on the pressure side of the hydraulic pump SRP1. In the case of the partially closed first changeover valve USV1, a return flow from the pressure side of the hydraulic pump SRP1 to the low-pressure side takes place via the first changeover valve USV1 and the first high-pressure switching valve HSV1. The stationary state, that is, when the pressure P1 is constructed as an intermediate value, can with the pressure sensor 12 be determined. The pressure P increases from time t0 to time t1 to the value (intermediate value) p1 by the value Δp1. As soon as the pressure p is stationary at the value p1, the detection of the pressure values is started and these are transformed into the frequency domain by means of Fast Fourier Transformation (FFT). The detection of the pressure values is completed at a time t2. At time t2, the pump motor M is activated to 100% and thus driven to full load. The first switching valve USV1 is also activated to 100%, thus fully closed. A current limit of the first changeover valve USV1 remains within the scope of conventional valve protection measures and to limit the maximum permissible system pressure. The buildup of pressure is then continued until time t3 and the attainment of a pressure value p2, then the time measurement for the flow rate measurement or flow rate test begins until a time t4. The pressure values of the pressure p are further cyclically determined until a pressure p3 is reached. The time t4 - t3 = Δt4 to reach a pressure difference p3 - p2 = Δp3 is a measure of the capacity of the hydraulic pump SRP1. The pump motor M is switched off at the time t4, at the same time the first high-pressure switching valve HSV1 is switched off, thus closed. At time t4, therefore, the first high-pressure switching valve HSV1 is closed, the first switching valve USV1 is closed and the hydraulic pump SRP1 is switched off. From time t4, a settling time Δt5 = t5-t4 waits until a time t5. With the time t5, the leak test begins, so it is checked whether the first hydraulic circuit MC 1 is tight. For this purpose, the pressure value p _LTA at the time t5 to the beginning of Le recorded at time t5. At the time t6, and thus after expiration of a time Δt6 = t6-t5, the pressure at the pressure sensor becomes 12 detected as pressure p _LTE . The differential pressure Δp4 = P _LTA -p _LTE is a measure of leakage flows within the first brake circuit MC1, for example by non-tightly closing valves or the like. At time t6, and thus at the end of the leakage test, the first changeover valve USV1 is switched off and thereby fully opened, all other valves and the pump motor M are switched on. Turning on all other valves means that the valves RFAV and LFAV are open. After reducing the pressure p at time t7, thus after a time .DELTA.t7 = t7 - t6, this period is 250 milliseconds in the following embodiment, the exhaust valves are switched off, after a further pump lag time .DELTA.t8 = t8 - t7 at time t8, the pump motor M. switched off, the time .DELTA.t8 is one second in the present embodiment.

At the end of the test described above, the controller sends the information to a tester that all pump elements of the tested circuit have been delivered, as well as the time Δt4 until the pressure difference Δp3 has been reached, and the pressure values p _LTA and p _LTE at the beginning and end of the test leakage test. During the entire test procedure, the brake must not be actuated, the master cylinder 11 may not be used. This can be z. B. be monitored by a query of the brake light switch (BLS). If the brake is actuated by applying pressure to the master brake cylinder 11 recognized, the test is considered failed. If the control request of the first changeover valve USV1 is too high, so that an overflow and a constant pressure below 30 bar can not take place, then the test is also considered as failed. The leakage check of the exhaust valves and the first changeover valve is an additional option of the pump function test. If the waiting times Δt5 and Δt6 are transferred with zero milliseconds, no leakage test takes place and the pump function test runs without delay.

During the pressure build-up by the hydraulic pump, pressure fluctuations arise, since a pressure build-up takes place only during each working stroke of one of the pistons. The pressure fluctuations have a frequency and amplitude, which are dependent on the pump speed and the number of working pistons. 3a , b and c show an example of a frequency spectrum of these pressure fluctuations. The pressure fluctuations are with the pressure sensors on the pressure side of the hydraulic pumps SRP1 and SRP2, these are the pressure sensors 13 respectively. 14 , detected. The detection of the pressure variables by means of the pressure sensors 13 respectively. 14 can be done both continuously and temporally discretely. By means of the thus detected pressure variables, a time profile of the pressure generated by the hydraulic pumps SRP1 and SRP2 can be determined. This time course can be temporarily stored in a memory, not shown, of a control unit. Based on the temporal pressure curve, the measured values can be transformed into the frequency domain by means of a fast Fourier transformation (FFT). Due to the pressure pulsations of the hydraulic pumps (multi-piston pumps) SRP1 or SRP2, the FFT must deliver a deflection in the nth harmonic of the pump speed. In case of failure of a piston element, it is therefore the rash at the (n-1) th harmonic. If a failure of a pump element is detected, then an external device, not shown, can be activated, which informs the driver of the failure acoustically and / or optically. However, it can also be provided that the driver is not informed until the failure of a plurality of pump elements, a pressure supply to the brake system or the brake circuit in critical driving situations is no longer possible. In addition, from the failure of a pump element can be stored in a control unit, not shown and kept retrievable for subsequent service work. This information can then z. B. be queried during a workshop visit or at a regular inspection. The control unit can be, for example, a brake control unit or a central on-board computer.

The clock cycle in the detection of the print sizes is for example one millisecond. Overall, then in the present exemplary embodiment of a three-piston pump per brake circuit sixteen measured values for each brake circuit sufficient to allow sufficient information about the functioning of the pump elements in the respective hydraulic pump SRP1 and SRP2. To reduce the noise, in each case an average value of, for example, five measured values is used. This results in a sampling rate of 5 milliseconds. These 5 milliseconds correspond to a sampling frequency of 1/5 milliseconds, ie 200 hertz. According to the sampling theorem, the highest scannable frequency is therefore 100 hertz (Nyquist frequency). The lowest scannable frequency results from the time grid, ie the number of measuring points times the sampling rate, here this is 16 × 5 milliseconds = 80 milliseconds. The lower sampling frequency, ie the lower limit frequency, is then 1/80 milliseconds = 12.5 Hertz. These 12.5 hertz simultaneously form the frequency grid of the FFT. In order to prevent a defective pump element from being erroneously detected by faults, the distance between the individual frequencies to be expected is increased. This distance, called the signal-to-noise ratio, is chosen as the optimum pump speed. In the present For example, the signal-to-noise ratio should be twice the frequency of the frequency spectrum of the FFT, ie 2 · 12.5 Hertz = 25 Hertz. This corresponds to the pump speed 25 · 60 = 1500 min ^-1 . Together, it results from the lower sampling frequency and the optimum pump speed that a measurement should be made at a pump speed of 1500 / min for a period of 80 milliseconds. This can be done by a special test drive or integrated into a pressure build-up that takes place anyway.

The selected parameters result in a correctly running piston pump and optionally deducting a noise floor, a frequency spectrum accordingly 3a , The x-axis represents the frequency in the grid of 12.5 hertz and the y-axis the intensity of the transformed signal. The frequency 8 corresponds to the Nyquist frequency of 100 hertz. Since the frequencies represent 9 to 15 reflections of the frequencies 1 to 7, the se are not further considered below. Frequency 6 represents in the present embodiment, the expected frequency at a pump motor speed of 25 Hertz, when all three pump elements work. In case of failure of a pump element, the rash disappears to frequency 6 (75 hertz) and it comes to the rash on frequency 4 (50 hertz). If it also comes to a failure of another pump element, so that only a functioning pump element is present, so a rash on frequency 2 (25 hertz) can be found.

If the pump speed is synchronized exactly with the sampling frequency, then the rashes in the fast Fourier transformation are most clearly visible. If the pump speed deviates from the sampling frequency, fluctuations also occur on adjacent frequencies, as in FIG 4 shown. Despite these additional rashes, a significantly higher rash is to be expected on the expected fundamental frequency 6. To prevent erroneous detection of a defective pump element, it is advantageous to choose the signal to noise ratio sufficient. Alternatively, it is possible to compare the spectral power density of the individual spectra with an expected value, including only the frequency with the highest spectral power density and suppressing adjacent frequencies. From the pump speed is the expected fundamental frequency, this is the frequency 6, known, as well as the expected multiples are known, so that adjacent frequencies can be suppressed.

For realizing the FFT algorithm with the proposed evaluation of sixteen measured values, sixteen-bit integer arithmetic can be used. Thus, sixteen measured values result in a memory requirement of 16 × 2 × 2 = 64 bytes due to the necessary complex calculation. These 64 bytes are sufficient to calculate the individual steps of the FFT. Additional memory is not needed. Thus, it is possible to represent the FFT with little effort in existing control devices. Sixteen measured values require 32 calculation steps (two-value FFT). Each individual calculation step comprises 4 × 16 bit multiplications or divisions as well as 4 × 16 bit additions followed by a shift. This results in different possibilities of realization for the calculation. It can be calculated in the complete FFT with 32 computational steps in one computing cycle, alternatively, a division of the FFT on four arithmetic cycles with eight computational steps can take place or it can be a division of the FFT to 32 arithmetic cycles, each with a calculation step. In a further embodiment, a modification is conceivable in which only eighth measured values are used. Conventional FFT controllers or PC programs operate at a high sampling rate compared to the expected frequencies. Thus, a plurality of measured values are recorded, which must be processed with appropriate computing power. By contrast, the small frequency raster of the high sampling frequency hits the measurement frequencies with high accuracy. By judicious choice of the ratios between sampling frequency and the expected measuring frequencies, a few (for example sixteen, as in the present exemplary embodiment, or only eight) measured values suffice. However, it is necessary for the measured values to be synchronized as accurately as possible with the sampling frequency. As in 4 As shown, there may be excursions at adjacent frequencies, which would never give a rash if the synchronization is good, if there is a deviation between the sampling frequency and the expected frequencies. If the next expected measuring frequency is set at an adequate signal-to-noise ratio, only an insignificant rash occurs in this case. It can thus be ensured that a deviation does not erroneously detect a defective pump element.

5 shows a flowchart of the method according to the invention. After starting the procedure in step 101 will be in step 102 the pump motor M is brought to a defined partial value (referred to here as x%) of the maximum speed and the maximum torque. At the same time, the first switching valve USV1 is partially closed, this is indicated here by a value y%. In step 103 is then checked whether the pressure p has reached a constant value p1. If this is the case, the pressure values p are detected between the periods t1 and t2 in the 5 millisecond time grid and processed by fast Fourier transformation (FFT) for a control unit (not shown here) (step 104 ). At time t2 will be in step 105 the pump model tor M to 100% of its output. At the same time, the first reversing valve USV1 is completely closed, thus 100% closed. In step 106 it is then checked whether the pressure p has reached the value p3. If this is the case, then in step 107 the pressure difference Δp3 and in step 108 the time difference .DELTA.t4 determined until reaching the pressure p3. In step 109 Then, the pump motor is switched off, thus brought to 0% of its power, at the same time the first high-pressure switching valve HSV1 is turned off, this is referred to here as HSV1 = 0. In step 110 Then the time .DELTA.t5 is waited, then in step 111 the pressure p is determined and stored as P _LTA at time t5, after the expiration of time .DELTA.t6 in step 112 the pressure p is measured and stored as P _LTE . In step 113 As a result, the first changeover valve USV1 is switched off and thus completely opened. At the same time all the exhaust valves and the pump motor M are turned on. After the time .DELTA.t7 in step 114 the exhaust valves are in step 115 switched off again after expiration of another time .DELTA.t8 in step 116 will be in step 117 the pump motor switched off, in step 118 then the relevant data is transmitted to a tester or the like, the method then ends in step 119 ,

One embodiment the method according to the invention has previously been described with reference to the first hydraulic circuit MC1, the method can be applied identically to the second hydraulic circuit MC2. It can both methods are carried out in parallel or in succession.

Claims (10)

Method for functional testing of a hydraulic system ( 10 , MC1, MC2), in particular a brake circuit (MC1, MC2) with a multi-piston pump (sRP1, sRP2) in a brake system of a vehicle, characterized in that this the steps - measuring the flow rate of the multi-piston pump (sRP1, sRP2), which at the same time on the functioning of the individual pistons - measuring the pressure drop of the pressurized hydraulic system ( 10 , MC1, MC2) for detecting leaks. Method according to claim 1, characterized in that that measuring the flow rate the multi-piston pump (sRP1, sRP2) builds up pressure on the pressure side the multi-piston pump (sRP1, sRP2) to an intermediate value (p1) wherein the pressure build-up after a delay time (t2-t1) up to a nominal value (p3) is continued. Method according to claim 2, characterized in that that the delivery rate the multi-piston pump from the pressure gradient (Δp / Δt) after the delay time (t2) until the nominal value (p3) has been reached. Method according to claim 2 or 3, characterized after reaching the nominal value (p3) a second delay time (t6-t5) is waited for and then the measurement of the pressure drop of the pressurized hydraulic system connects. Method according to one of the preceding claims, characterized in that the hydraulic system has at least one switching valve (USV1, US Pat. USV2) and a high pressure switching valve (HSV1, HSV2), wherein the HSV remains open until the nominal value (p3) has been reached and the UPS remains open until the end of the year Reaching the intermediate value is partially closed and after Reaching the intermediate (p1) is completely closed. Method according to one of the preceding claims, characterized characterized in that the operability of each piston based on a frequency spectrum of pressure fluctuations in the hydraulic System tested becomes. Method according to one of the preceding claims, characterized characterized in that the individual pistons classified as functional be when the frequency spectrum of the pressure fluctuations reported Spectral lines with an integer multiple of the pump speed includes, being the largest multiple the number of the piston corresponds to the multi-piston pump. Method according to one of the preceding claims, characterized characterized in that at least one of the pistons classified as at least functionally limited when one of the spectral lines is an integer multiple the pump speed is missing. Device for functional testing of a hydraulic system, in particular a brake circuit with a multi-piston pump in one Brake system of a vehicle, characterized in that this - Medium for measuring the delivery rate the multi-piston pump, - Medium for testing the functionality the single piston, - Medium for measuring the pressure drop of the pressurized hydraulic Systems for the determination of leaks includes. Tester for use in a method according to any one of claims 1 to 8.