SE509576C2 - Method and apparatus for testing the braking system of a vehicle - Google Patents

Abstract

The method involves building pressure up or lowering pressure in at least one of the wheel brakes using an electrically operated valve arrangement. A defined pressure is built up in at least one wheel brake for monitoring purposes in at least one defined operating state. The pressure is reduced again after a static pressure or force level has been reached. The static pressure or force level achieved is evaluated to detect undissolved gas in the brake fluid in the braking system. A static pressure or force level is determined as having been achieved when a certain time has elapsed after the start of the pressure build-up.

Description

Advantages of the invention.

The solution according to the invention guarantees operational reliability of an electro-hydraulic braking system with hydraulic emergency braking system. A special advantage is that this control can be performed already during normal operation of the brake system.

In an advantageous manner, an impermissible amount of undissolved gas is sensed in the bromine fluid of the well system.

Through the solution according to the invention, very small amounts of gas can be detected.

A special advantage in this context is that the test to be performed for gas detection can be performed within a very short period of time, of the order of 250 milliseconds.

A special advantage is that by evaluating the stationary pressure end value, the dynamic condition of the pressure increase does not have to be taken into account.

A particular advantage is that the amount or volume of the gas content of the brake fluid can be determined when the stationary pressure value constitutes a direct measure of the gas content.

An advantage is that no additional sensor equipment is required to carry out the monitoring. The monitoring is based solely on signals from existing SCO SOTCI.

A particular advantage is that time optimization of the test is possible taking into account temperature influences if the stationary pressure end value is taken when the pressure has swung into a predetermined tolerance band.

A special advantage is furthermore that the gas sensing is carried out by directional pressure build-up in the individual wheel brakes and that in this way different brake line areas can be independently examined with respect to unauthorized amounts of gas.

Additional advantages appear from the following description of the exemplary embodiments and from the dependent claims.

Drawing.

The invention is described in more detail below with reference to the embodiments shown in the drawing. Thereby showing ñg. 1 is a block diagram of an electrohydraulic braking system, in which, by means of a flow chart according to fi g. 2, the solution according to the invention is used within the framework of a preferred embodiment. I ñg. 3 finally shows the mode of operation of the solution according to the invention with the aid of time diagrams.

Description of the embodiments.

Pig. 1 shows a block diagram of an electrohydraulic braking system of a vehicle.

An electro-hydraulic control unit is denoted by 10, which controls a hydraulic brake system 12 provided with corresponding valve devices. For this purpose, input lines 14 - 16 connected to the electronic control unit 10 from measuring devices 18 - 20 for sensing the brake pressures, torques or forces, an input line 22 from at least one measuring device 24 for sensing the effect of the brake pedal and input lines 26 - 28 from measuring devices 30 - 32 for sensing additional operating parameters of the brake system resp. the vehicle such as wheel speeds, vehicle speed, etc. Via output lines, the electronic control unit 10 controls the electrically operable valves of the hydraulic brake system 12. For the sake of clarity, only the output lines 34 and 36 are shown, which control a pressure relief valve 38 and pressure boost valve 40 belonging to a wheel brake.

The pressure relief valve 38, which in the preferred embodiment in the unqualified state is in the closed position but in the equipped state is open, is inserted into a hydraulic line 42 shown in broken lines, which runs from a storage container 44 to the brake cylinder 46. correspondingly, the pressure boost valve 40, which in the preferred embodiment likewise assumes a closed position in the unqualified state but is open in the equipped state, is inserted into a hydraulic line 50, which runs from a pressure generating pump 52 to the wheel brake 46. On On the suction side, the pump 52 is connected via a hydraulic line 54 to a storage tank 56, which may be identical to the storage tank 44. A high-pressure media accumulator 58 is connected to the hydraulic line 50. Furthermore, the pressure in the wheel brake cylinders 46 can be influenced directly by the driver by actuating the brake pedal via a hydraulic line 60, which is partly connected to the wheel brake 46, and partly connected to the main brake cylinder (not shown). This connection is active only when there is a fault in the electrical system, which in fi g. 1 is symbolized by means of a coupling element 62.

For the sake of clarity, visas g is shown. 1 the hydraulic part of the brake system only for one wheel brake. Corresponding arrangements are available for at least the wheel brakes on the same axle or for all wheel brakes of the vehicle.

In normal operation, the electronic control unit 10 senses the driver's desire for braking from the degree of action of the brake pedal, which is received via line 22.

This is converted to a setpoint for the brake pressure to be set at the individual wheel brakes. By means of a pressure control circuit, this pressure is set taking into account the measured pressure by controlling the valves 38 and 40. In the case of pressure increase, pressure medium flows via the line 50 through the opened pressure increase valve 40 into the wheel brake 46 from the storage tank via the pump 52 and / or from the accumulator 58. Upon depressurization, the depressurization valve 40 is closed and the depressurization valve 38 is opened so that pressure medium flows back to the reservoir through the conduit 42. Furthermore, the electronic control unit 10 comprises a brake lock protection and / or drive wheel spin control device which, under monitoring 25 30 5 509 576 or drive spin tendency at at least one wheel can lower resp. increase the pressure in the corresponding wheel brake.

In addition to regulating the pressure in the wheel brakes, other advantageous embodiments realize the driver's desire for braking by regulating the braking torque, braking force, wheel speed, wheel sizing, etc.

In the event of a failure of the electronic steering, for example in the event of a loss of the supply voltage, in the event of disturbances in the electronic control unit 10, etc., the hydraulic emergency braking system is activated so that the driver can brake the vehicle by directly acting on the wheel brakes. If there is too much undissolved gas in the hydraulic emergency brake circuit, the driver cannot build up sufficient braking force in the wheel brakes by means of foot power in the event of a failure of the electronic steering system. This can lead to undesirable operating situations.

According to the invention, it is therefore proposed to detect undissolved gas in the hydraulic fluid of the brake system in a timely manner by means of a monitoring.

This monitoring is performed in certain operating situations, for example when the vehicle is stationary before the start of a journey, during a vehicle standstill when the brake is not affected (for example at a traffic light), etc. The pressure boost valves can be opened by a defined pulse, possibly individually for each wheel. so that pressure builds up in the associated wheel brake. If the built-up pressure is in a stationary operating state, it is possible to infer due to the pressure level reached to possible undissolved gas in the hydraulic fluid.

Due to the magnitude of the compression capacity of gases compared to liquids, in the case of a liquid-air / gas mixture, the gas will first be compressed at a pressure increase before a clear pressure increase takes place in the system.

Therefore, the pressure increase triggered by the test build-up pulse at an impermissibly large amount of undissolved gas in the hydraulic fluid does not reach the intended end value. 10 15 20 25 30 509 576 6 A preferred embodiment of the solution according to the invention is shown with the aid of the fate diagram in Fig. 2. After starting the program part when the corresponding operating condition is present (vehicle stopping before starting a journey, after parking the vehicle or during operation in the case of unaffected brake) a pressure defined in a first stage 100 is built up in the wheel brake. This is done in the preferred embodiment by sending a pressure-building pulse of a predetermined length, for example 10 milliseconds, to the corresponding valve. After transmitting the pressure build-up pulse, a counter T is started in step 102, which is counted up in the subsequent step 104. Then, in a question step 106, it is checked whether the counter has reached its maximum value. This maximum value is so dimensioned that the pressure build-up carried out by the pressure build-up pulse has reached a stationary pressure level. In the preferred embodiment, this is the case after 200 milliseconds. If the maximum value is not reached, the counter is calculated according to step 104 until the maximum value is reached. Then, in step 108, the brake pressure Phjm of it is read. or the corresponding wheels and is compared in step 110 with a predetermined pressure level Pnørm, which is to be achieved. This pressure value is through experiments known in advance for the braking system used. If the measured stationary pressure value PhJ-ul falls below the standard pressure, it is assumed according to step 112 that a certain amount of undissolved gas is in the brake fluid brake fluid and possibly a corresponding warning is issued to the driver and / or emergency braking measures are initiated. If the measured wheel pressure essentially corresponds to the standard pressure, it is assumed that there is a functional emergency braking system and, as after step 112, the test is terminated according to step 114 by pressure reduction.

The pressure reduction takes place by short-term opening of the pressure reduction valve by a corresponding pulse. After step 114, the tesh phase is completed so that the program part ends.

In the preferred exemplary embodiment, a renewed test is carried out only in one of the next operating cycles of the vehicle, according to another advantageous exemplary embodiment only after a certain operating time has elapsed. 10 15 20 25 30 1 509 576 When determining the maximum time (see step 106), the system's oscillation time must be taken into account during pressure build-up. The pressure build-up pulse within the framework of the test shown in Fig. 2 shall then be selected so that a sufficiently high pressure is built up to sense the pressure drop caused by the undissolved gas in the hydraulic fluid, but on the other hand so that the system swings in as quickly as possible. a constant pressure value. With regard to the test time, the controllable parameters must be determined so that this time period is kept as short as possible. In this case, the test is interrupted and the built-up pressure is lowered when the test operating condition is abandoned, for example by gas supply. The test is repeated on one of the following occasions when the vehicle is stationary.

As an alternative to specifying a maximum time, after which comparison of the stationary pressure value with a standard value is carried out, the pressure is constantly sensed during the pressure build-up and the ironing for sensing undissolved gas in the hydraulic fluid is carried out when the pressure has turned within a tolerance band, e.g. %.

The function of the solution according to the invention is illustrated by means of the timing diagrams in Fig. 3. Fig. 3a shows the time course of the pressure in a wheel brake when no undissolved gas is present in the hydraulic fluid (200) and when undissolved gas is present in the hydraulic fluid (202). . Fig. 3b shows the pressure build-up (204) and the pressure drop pulse (206). At a time t = 0, the pressure build-up pulse according to Fig. 3b was transmitted.

This leads to an increase in pressure, which slowly swings into a stationary pressure level.

After the predetermined maximum time has elapsed, in the example according to Fig. 3 200 milliseconds, the achieved pressure level is compared with the standard pressure (here P1). At the end of the comparison, a pressure drop pulse is emitted, which leads to a pressure drop to the value zero. In the diagram according to Fig. 3 it appears that in a case in which the stationary pressure value the value P2 is reached, undissolved gas is present in the hydraulic fluid.

From the difference between the achieved pressure level and the predetermined standard value, according to a preferred exemplary embodiment, by comparison with predetermined, experimentally determined values, a measure of the amount resp. the volume of the hydraulic fluid gas content.

If an unauthorized amount of undissolved gas is sensed in the hydraulic fluid, the driver is informed of the emergency brake circuit only limited, and in some preferred embodiments he is forced by power limitation, speed limits, etc., alternatively or in addition to visit a workshop to bleed the brake system.

The test can be performed individually for one wheel, one axle or simultaneously for all wheel brakes by controlling the corresponding valves. Thereby, individual areas of the braking system can be selectively examined with respect to undissolved gas.

In the preferred embodiment, a pressure measured value is used for evaluation. In other advantageous embodiments, the control described is carried out on the basis of other quantities representing the force exerted by the brake, such as, for example, the hiring force, and is evaluated for control in accordance with the solution according to the invention.

Claims (9)

10 15 20 25 9 509 576 Patent claims Method for controlling the braking system of a vehicle, in which pressure is built up or lowered in at least one wheel brake via an electrically manoeuvrable valve device, characterized in that in at least one predetermined operating condition a defined pressure is built up in at least one wheel brake, which pressure is lowered again after a stationary pressure or force level has been reached. Method according to Claim 1, characterized in that the stationary pressure or force value obtained is evaluated for detecting undissolved gas in the brake fluid of the brake system. Method according to Claim 1 or 2, characterized in that a stationary pressure or force level is assumed to be reached when a predetermined time has elapsed after the beginning of the pressure build-up. Method according to one of Claims 1 to 3, characterized in that the stationary pressure (force) level is assumed to be reached when the pressure or force value turns within a predetermined tolerance band. Method according to one of Claims 1 to 4, characterized in that undissolved gases in the brake fluid of the braking system are sensed when the stationary pressure or force value is less than a predetermined value. Method according to one of Claims 1 to 5, characterized in that from the difference between the stationary pressure resp. the force value and a predetermined value are determined by the quantity resp. the volume of the gas content in the brake fluid. Method according to one of Claims 1 to 6, characterized in that the at least one operating condition is a vehicle standstill before the start of a journey, after parking of the vehicle and / or in the event of an unaffected brake. 5Û9 576 10 Method according to one of Claims 1 to 7, characterized in that the braking system is an electro-hydraulic braking system. Device for controlling the braking system of a vehicle, with an electric control unit, which via valve devices builds up or lowers pressure in at least one wheel brake, characterized in that the electronic control unit in at least one operating state for defined purposes builds up pressure in at least one wheel brake and after reaching a stationary pressure or force level, the built-up pressure decreases again.