FR2745254A1 - METHOD AND DEVICE FOR TESTING THE BRAKING SYSTEM OF A VEHICLE - Google Patents

Abstract

Method for controlling the braking circuit of a vehicle in which the printing in at least one of the wheel brakes is established or suppressed by an electrically controlled valve device, characterized in that in at least one predetermined state of use , a pressure for control is established in at least one wheel brake, this pressure being released after reaching a pressure or stationary force value.

Description

STATE OF THE ART The present invention relates to a method and a

  device for controlling the braking circuit of a vehicle according to which the pressure in at least one of the wheel brakes is established or removed by a valve device controlling

electrically dice.

  According to document DE-A-41 12 137, there is known a

  positive braking for a vehicle in which the brake pressure in the brakes of the vehicle wheels is fixed as desired by the driver by actuation of the brake pedal by the control of a valve device. This electric braking system provides for activating a hydraulic brake control according to the actuation of the pedal in the event of

  electrical control failure. When the com-

  electric control, the driver can therefore slow down and stop

  the vehicle by actuation of the brake pedal. For this-

  there, it must transmit the necessary brake pressure to the

  wheel brake by pedal and brake cylinder of the device

  hydraulic braking system. To ensure the security of this

  hydroelectric braking system, one must perform a con-

  role of this backup system, even during normal use, because a failure of this backup system in the event of a failure of the electrical control can lead to failure of the entire installation. It is particularly problematic,

  in this context, that too much gas not available

  under is in the brake fluid of the closed circuit of the

emergency brake.

  The object of the invention is to provide means for controlling the braking device of a vehicle making it possible to

  check the emergency brake system of a hydroelectric brake

  stick, in particular for gas not dissolved in the hydraulic circuit. To this end, the invention relates to a braking installation characterized in that in at least one predetermined state of use, a pressure is established for control in at least one wheel brake, this pressure being

  released after reaching a stationary pressure or force value.

  Advantages of the invention The method according to the invention guarantees the operational safety of an electro-hydraulic braking system with a hydraulic emergency braking system. It is particularly advantageous for this control to be carried out during

  normal use of the brake system.

  For this, an unacceptable quantity of gas not dissolved in the brake fluid of the braking system is advantageously detected. The method according to the invention makes it possible to detect

very small amounts of gas.

  It is particularly advantageous under these conditions

  gas control can be carried out in an in-

  very short time interval of the order of 250 msec.

  It is particularly advantageous that, due to the exploitation of the stationary pressure value, it is not necessary to take account of the dynamic behavior

pressure increase.

  It is particularly advantageous to be able to

  terminate the quantity or volume of gas contained in the brake fluid since the stationary pressure value

  is a direct measure of the gas content. Advantageously, surveillance does not require

  site no additional sensors and is based only

  on already mounted sensor signals.

  It is particularly advantageous that an optimization

  control time is possible taking into account the influence of temperatures, if we take the final value of stationary pressure when the pressure has stabilized in

  a predetermined tolerance band.

  It is also particularly advantageous for gas detection to be carried out by establishing a pressure

  target in each of the wheel brakes and in this way it is possible to search for the unacceptable amounts of gas35 in the different areas of the brake fluid circuit, independently of one another.

  According to other advantageous characteristics of the invention: - the value of pressure or stationary force reached is used to detect gas not dissolved in the brake fluid of the brake installation, - it is considered to have reached a pressure or a stationary force level when a predetermined time has elapsed after the start of pressurization,

  - it is considered to have reached the pressure value (force) sta-

  when the pressure or force value has stabilized within a predetermined tolerance band, - it is estimated that there is undissolved gas in the brake fluid of the braking device when the pressure value

  or stationary force is smaller than a predefined value

over,

  - the quantity or volume of gas contained is determined, from

  deriving from the difference between the pressure or stationary force value and a predetermined value, - one of the situations of use is: the vehicle stopped before starting, after the vehicle has stopped, and / or when the brake is not applied, - the braking system is a hydroelectric braking system.

  The invention also relates to an installation for implementing the method defined above, this installation

  tallation being characterized in that the electronic control unit establishes a defined pressure for control in at least one situation of use and in at least one brake

  wheel and removes this pressure after reaching a

  their pressure or stationary force.

Drawings

  The present inventions will be described below in more detail with the aid of several exemplary embodiments.

  tion shown in the accompanying drawings in which: - Figure 1 is a block diagram of a hydroelectric braking installation, - Figure 2 is a flowchart representing the process according to

  the invention in the context of an exemplary embodiment before-

  geux, - Figure 3 shows how the process works

  the invention using chronograms.

  Description of the exemplary embodiments

  Figure 1 shows a block diagram of an ins-

  hydroelectric braking system for a vehicle. Reference 10 represents an electronic control unit which controls the braking device 12 equipped with the

  corresponding valve. For this, the electronic control unit

  that 10 receives input lines 14 to 16 from the instal-

  measuring lations 18 to 20 to determine the pressure, the

  torques or forces in the wheel brakes, it also receives

  Lely an input line 22 coming from at least one measuring installation 24 to determine the amplitude of the actuation of the brake pedal as well as the input lines 26 to 28 coming from measuring installations 30 to 32 for detect others

  operating variables of the braking device or vehicle

  hicle, like the speed of rotation of the wheels, the speed of the

  vehicle. The electronic control unit 10 controls the van-

  nes of the hydraulic braking system 12 through the output lines. For readability reasons, only the

  output lines 34 and 36 are shown; these lines com-

  command the decompression valve 38 and the compression valve associated with a wheel brake. A hydraulic line 42, shown in dotted lines, connects a reservoir 44 to the brake cylinder 46 of a wheel 48 in the decompression valve 38 which

  in the embodiment is in the closed position when

  that it is not controlled and in the open position when it

  is ordered. Correspondingly, the compression valve

  sion 40, in the preferred embodiment, is connected

  in a hydraulic line 50 which leads from a pump

  increasing the pressure 52 at the wheel brake 46, the control valve

  pressure 40, is closed in an uncontrolled state and open in a controlled state. On the suction side, the pump 52 is connected by a hydraulic line 54 to a tank 56 which may be the same as the tank 44. A high pressure accumulator 58 is connected to the hydraulic line 50. In addition, the pressure in

  the wheel brake cylinders 46 can be influenced directly-

  by the driver actuating the pedal via the hydraulic line 60 connected on one side to the wheel brake

  46 and the other to the master cylinder not shown. This liiai-

  sound is only active during a breakdown of the electrical system

  which is symbolized in FIG. 1 by a switching element

  tion 62. For reasons of clarity, the hydraulic part of the braking system has only been shown for a wheel brake. Similar devices require at least the wheel brake on the same axle or for all wheel brakes

of the vehicle.

  In normal use, the electric control unit

  Tronic 10 determines the driver's braking setpoint from the degree of actuation of the brake pedal, transmitted by line 22. This braking setpoint is transformed into a setpoint for the pressure to be established at each of the wheel brakes . In the context of a pressure regulation circuit, this pressure is established as a function of the pressure measured by the control of valves 38 and 40. When the pressure is established, the brake fluid then passes through line 50 and the compression valve 40 open, in the wheel brake 46, from the reservoir, through the pump 52 and / or the accumulator 58. During decompression, the compression valve 40 is closed, the decompression valve 38 is open, so that the brake fluid returns to the reservoir via line 42. In addition, the electronic control unit 10 includes an anti-blocking regulator and / or an anti-skid regulator which can establish the pressure or decompression to the corresponding wheel brake, depending on the

  monitoring of the wheel speed when locking or slipping

swim.

  In addition to regulating the pressure in the wheel brakes, in other advantageous exemplary embodiments, the braking setpoint of the driver is achieved by regulating the braking torque, the braking force, the speed.

wheel, wheel slip.

  In the event of a failure of the electronic control, for example during a cut in the supply voltage, a failure of the electronic control unit 10, or the like, the hydraulic emergency brake system is activated by so that the driver of the vehicle can brake the vehicle by

  directly applying the brakes. If too much

  aunt of undissolved gas is in the emergency brake hydraulic circuit, the driver cannot, during a failure of the electronic control system, deliver sufficient braking force to the wheel brakes using pressure of his foot, which can result in

  undesirable operating conditions.

  According to the invention, as part of a control, it is intended to detect in time, undissolved gases which may be

  find in the hydraulic circuit. This monitoring is effective

  carried out under predetermined operating conditions,

  for example when the vehicle is stationary before starting-

  rage, during a vehicle stop when the brakes are not applied (for example at a fire) or the like. In that case,

  individually for each wheel, the compression valve

  sion is opened by a predetermined pulse so as to establish a pressure in the brake concerned. If the established pressure is stationary, we conclude that there is the possibility of gas not dissolved in the liquid as a function of

the pressure value reached.

  Due to the higher order of magnitude of the compressibility of gases compared to that of liquids, in the case of a liquid / gas mixture, during an increase in pressure, the gas is compressed first before n 'there appears a significant increase in pressure in the system. As a result, the increase in pressure triggered by the compression pulse does not reach the final value expected during

  the presence of too much undissolved gas.

  An advantageous exemplary embodiment of the invention will be described in more detail using the flowchart 2. After starting the program part in the presence of the corresponding state of use (stop before start, after cut-off contact or during use when the brake is not applied), in a first step 100, a defined pressure is established in the wheel brake. For this, according to the advantageous exemplary embodiment, a pressurizing pulse of a predetermined duration, for example msec, is sent to the corresponding valve. After sending the pressurizing pulse, a counter T is started at

  step 102. This counter is incremented in the next step 104. Next, in interrogation step 106, it is checked whether the comp-

  tor has reached its maximum value. This maximum time is defined so that the compression produced by the pressurizing pulse reaches a stationary pressure value. In the exemplary embodiment, this is the case after 200 msec. If the

  maximum value is not reached, the counter is incremented by step 104 until it reaches the maximum value.

  After that, the brake pressure Prow of the corresponding wheel or wheels taken independently is recorded in step 108 and in step 110 a comparison is made with a predetermined pressure value born to reach PNorm. This pressure value is known by experimentation for the braking device used. If the measured stationary pressure value Prow is lower than the normal pressure, then according to step 112, it is deduced therefrom that a certain quantity of gas in suspension is in the liquid of the braking installation and if necessary it is - see a warning signal to the driver and / or take

  security measures. If the measured wheel pressure corresponds essentially to the normalized pressure, it is concluded that the emergency braking system is in working condition and the control ends, as after step 112, by a decompression according to the step 114. The decompression is done by one or

  short-term release of the pressure relief valve by a corresponding pulse. After step 114, the control phase is completed and the program part ends. 30 A new control is not carried out, in the example

  that during the next cycle of use of the

  hicule, and in another exemplary embodiment, after a time

of predetermined use.

  When determining the maximum time (see not

  106), the bone attenuation time must be taken into account

  cillations of the system for establishing the pressure.

  The pressurizing pulse as part of the control

  shown in Figure 2, should be chosen to obtain sufficient pressure to recognize the pressure drop due to undissolved gas in the liquid and to bring the system to a constant pressure value as quickly as possible. In

  taking into account the duration of the control, the pa-

  variable rameters so as to keep this duration as short as possible. The control is cut and the pressure released

  when leaving the control state, for example in accelerated

  rant. We resume control at the next stop of the vehicle.

  According to another alternative to preset a maximum time, after the stationary pressure value has

  was compared to the normalized value, during power-up

  pressure is constantly determined and the comparison is carried out to detect the gas not dissolved in the liquid when the pressure has stabilized, for example in a band

5% tolerance.

  How the solution works

  the invention is represented using a timing diagram at the end

gure 3.

  Figure 3a shows the pressure as a function of

  time in a wheel brake when there is no gas not available

  under in the liquid (200) and when there is undissolved gas

in the liquid (202).

  FIG. 3b represents the compression pulse (204) and the decompression pulse (206). At time t = 0 the compression pulse according to FIG. 3b is sent; it leads to an increase in pressure which slowly stabilizes at a stationary pressure value. At the end of the predetermined maximum time (in the example in Figure 3,

  msec) the pressure value reached is compared to the pressure

  normalized sion (here P1). After the comparison, a decompression pulse is sent which lowers the pressure to the

  zero value. In the representation according to FIG. 3, it appears

  Note that if P2 is reached as the pressure value

  stationary ion, there is gas suspended in the liquid

hydraulic braking.

  In an advantageous embodiment, it is eva-

  read a measurement for the quantity or volume of gas contained

  in the fluid of the hydraulic circuit by comparing the different

  The difference between the pressure value reached and the level of com-

  pressure normalized with predetermined values experiment-

  really. If an unacceptable amount of gas is detected in the hydraulic fluid, the driver is informed that the emergency brake system is only available from

  in a limited manner, in this exemplary embodiment, by a power limitation, a speed limitation, or alternatively or forcibly, he is forced to seek a workshop10 to bleed the braking device.

  The test can be carried out wheel by wheel, by

  or for all wheel brakes simultaneously by the com-

  requires corresponding valves. We can thus control the

  gas not dissolved in the different separate zones of the device

braking.

  In the preferred embodiment, a pressure measurement is used for the evaluation. In other advantageous embodiments, checks are made in the direction of the solution according to the invention on the basis of other values re-20 presenting the force applied by the brake, such as for example the clamping force and / or using in the direction of control

according to the invention.

Claims (7)

R E V E N D I C A T IONS   1) Method for controlling the braking circuit of a vehicle according to which the pressure in or out is established   at least one of the wheel brakes by a valve device controlled   electrically, characterized in that in at least one predetermined state of use, a pressure is established for control in at least one brake   wheel, this pressure being released after reaching a   their pressure or force, stationary.   ) Method according to claim 1, characterized in that the value of pressure or stationary force reached is used to detect gas not dissolved in the liquid   brake of the brake system.   3) Method according to one of the preceding claims,   characterized in that a stationary pressure or force level is considered to have reached when a predetermined time has elapsed after the start of pressurization.   4) Method according to one of the preceding claims, characterized in that   we consider to have reached the pressure value (force)   when the value of pressure or force has stabilized   biliated into a predetermined tolerance band.   5) Method according to one of the preceding claims,   characterized in that it is estimated that there is undissolved gas in the brake fluid of the braking device when the pressure or   stationary force is smaller than a predetermined value.   6) Method according to one of the preceding claims,   characterized in that the quantity or volume of gas contained is determined from the difference between the pressure value or the force   stationary and a predetermined value.   7) Method according to one of the preceding claims,   characterized in that one of the situations of use is: the vehicle stopped before starting, after stopping the vehicle, and / or when the brake is not applied.   8) Method according to one of the preceding claims, characterized in that   the braking system is a hy- braking system   droelectric. 9) Device for controlling a brake installation of a vehicle with an electrical control unit which establishes the pressure or suppresses it in at least one wheel brake by means   a valve device for implementing the se-   according to one of the preceding claims,   characterized in that the electronic control unit establishes a pressure defined for control in at least one operating situation and in at least one wheel brake and removes this pressure after   have reached a pressure or stationary force value.