WO1995025652A1

WO1995025652A1 - Circuit arrangement for an electronically controlled braking system

Info

Publication number: WO1995025652A1
Application number: PCT/EP1995/000909
Authority: WO
Inventors: Verena Alberg; Alexander Kolbe; Klaus Honus
Original assignee: Itt Automotive Europe Gmbh
Priority date: 1994-03-23
Filing date: 1995-03-11
Publication date: 1995-09-28
Also published as: DE4409909C2; DE4409909A1

Abstract

A circuit arrangement for an electronically controlled braking system, like an anti-lock or drive slip control, is fitted with sensors (S1 to S4) to detect the rotational behaviour of the wheels and with an electronic circuit to assess the sensor signals and generate braking pressure control signals used to control hydraulic valves. There are circuits (19, 20) detecting the reference braking pressure (Psoll) in the wheel brakes of the controlled wheels (HL, HR, VL, VR) depending on the rotational behaviour. There is also a second subsidiary control circuit (21, 22, 24) in which the reference braking pressure (Psoll) is compared with the actual braking pressure or a value (PMOD) close to it. The difference (ΔP) between the rated pressure (Psoll) and the approximate actual pressure (PMOD) is determined and the signals for controlling the hydraulic valves allocated to the controlled wheels are generated depending on the pressure difference (ΔP).

Description

Circuit arrangement for a brake system with electronic control

The invention relates to a circuit arrangement for a brake system with electronic control, in particular with anti-lock control, traction control or driving stability control, with sensors for determining the wheel turning behavior and with an electronic circuit for evaluating the sensor signals and for generating brake pressure Control signals, which are supplied to electrically actuatable actuators, in particular hydraulic valves, and with which the brake pressure in the wheel brakes is controlled as a function of the wheel turning behavior.

Electronically controlled brake systems are known in a variety of designs. Anti-lock braking systems (ABS) now belong to the standard version of medium and high class cars. Brake systems with traction control (ASR) through brake intervention (BASR) and driving stability control systems are becoming increasingly important.

In the known hydraulic brake systems with electronic control, the brake pressure in the wheel brakes of the controlled wheels is known to be controlled by means of hydraulic valves which are inserted in the brake pressure lines and electrically controlled, modulated in such a way that there is no excessive wheel slip when braking, starting or accelerating. The brake pressure control depends on the turning behavior of the respective wheel. With the help of the electronics of the controllers belonging to the brake systems, the valve actuation times are calculated by evaluating the sensor signals reflecting the wheel turning behavior, possibly including further information. From DE 38 09 100 AI it is also known to take into account a wheel pressure model which approximately reflects the pressure in the wheel brakes and which is formed by measuring and evaluating the variables determining the pressure, in particular the valve actuation times becomes. The pressure build-up and reduction characteristics of the wheel brakes or the entire brake system are also included in the pressure model. Numerous other influencing variables which determine the pressure in the wheel brake, for example valve dead times, hydraulic storage effects, pump speed, mutual hydraulic influence of the wheel brakes connected to the same brake circuit, etc., can also be taken into account when forming the pressure model.

The invention has for its object to achieve a more precise setting of the regulated pressure in the individual wheel brakes in a simple manner and thereby improve the control. The aim is to include the various influencing variables on the regulated pressure in the wheel brakes as far as possible without appreciably increasing the effort or the computing times. Hydraulic compensation processes, which can have a considerable influence on the regulated pressure in the wheel brakes in certain control phases, in particular in the case of traction control and in certain brake circuit divisions, should also be recorded. - 3 -

It has been shown that this object can be achieved with a circuit arrangement of the type mentioned at the outset, the special feature of which is that circuits are provided which determine the target brake pressure in the wheel brakes of the controlled wheels as a function of the wheel turning behavior, and that in In a second, subordinate control circuit, the setpoint brake pressure is compared with the actual brake pressure or a value approximated to the actual brake pressure, the difference between the setpoint and the actual brake pressure or the value approximated to the actual brake pressure is determined, and the signals for controlling the actuators assigned to the regulated wheels , e.g. of the hydraulic valves are generated as a function of the brake pressure difference.

According to the invention, the desired improvement in the pressure control in the wheel brakes is achieved in a very simple manner by inserting a subordinate control circuit which constantly includes the actual pressure in the wheel brakes or a value approximating the actual pressure in the control.

According to a particularly advantageous embodiment of the invention, the value approximating the actual pressure in the individual wheel brakes is determined by forming a wheel pressure model. This allows a good approximation to be achieved without measuring the pressure. The level of the actual pressure depends, among other things, on the valve actuation times of the respective wheel and also the valve actuation times of the other wheel brakes connected to the same brake circuit. As a result, the difficulties which arise in the case of traction control and black / white division of the brake circuits, caused by pressure equalization processes, which will be explained later with reference to the exemplary embodiment described in detail, can be overcome. Further pressure-determining variables that can additionally be used according to the invention to form the wheel pressure model are the brake pressure build-up and reduction characteristics of the wheel brakes and of the entire brake system, the initial pressure when the control system is started, brake actuation signals, control signals for a hydraulic pump in the auxiliary pressure supply system of the brake system etc.

Other advantageous exemplary embodiments of the invention are described in the attached subclaims.

Further details of the invention emerge from the following description of an exemplary embodiment with reference to the attached figures. Show it

1 shows a schematic representation of the essential hydraulic and electrical components of a brake system with anti-lock control and traction control, in which the invention is used,

2 shows a schematic representation of the second, subordinate control loop of the circuit arrangement according to the invention and

3 in the diagram, the valve control signals and the pressure profile in the wheel brakes during a traction control process.

1 relates to a brake system which is suitable for anti-lock control (ABS) and traction control by brake intervention (BASR) and belongs to a vehicle with rear-wheel drive. The braking system has two circuits. On one brake circuit I the two front wheels VL, VR, to the other brake circuit II the two rear wheels HL, HR an¬ connected. It is a so-called

"Black / white" brake circuit division, in which an undesirable mutual hydraulic influence of the controlled wheels can occur, particularly in the traction control mode; an example of this will be described later.

1 consists of a pedal-operated tandem master cylinder 1 with an upstream vacuum booster 2. Each wheel is assigned an inlet valve 3 to 6, which is switched to passage in the rest position, and an outlet valve 7 to 10, which blocks in the rest position. A double-circuit hydraulic pump 12, driven by a common electric motor 11, is provided for returning the pressure medium flowing through the outlet valves 7 to 10. In addition, there is a low-pressure accumulator 13, 14 in each brake circuit, which absorbs pressure medium in a known manner in the initial phase of an anti-lock control system.

For traction control, brake pressure control in the driven rear wheels HL, HR must also be possible when there is no pressure in the master cylinder 1. For this reason, a separating valve 15 which is open in the rest position and can be switched to locks is inserted into the pressure medium path leading from the master cylinder 1 to the rear wheel brakes. Via a hydraulically actuated 2/2-way valve 16, which interrupts the pressure medium path when pressure is applied and consequently when the brakes are applied, pressure medium is subsequently supplied from master cylinder 1 in ASR operation.

In the connection path of the front wheels VL, VR, there is no need to insert a isolating valve because the wheel brakes of the non-driven wheels in ASR operation remain depressurized.

The rotational behavior of the individual wheels is determined in the brake system according to FIG. 1 with the aid of wheel sensors S1 to S4 and evaluated in the electronics of an electronic controller 17. E designates the inputs of controller 17, and A designates the outputs of controller 17. The outputs A are connected via signal lines, not shown, to the coils of the individual electrically actuable hydraulic valves 3 to 10 and 15 and to a control of the electric pump motor 11, also not shown.

A pressure relief valve U is provided to limit the pressure in ASR operation to a predetermined maximum value.

During an ASR operation, the situation arises that initially only brake pressure in one of the two driven wheels has to be applied, for example via the inlet valve 3 into the wheel brake of the left rear wheel HL. The inlet valve 4 of the right rear wheel HR is closed in this phase. If subsequently a pressure build-up is also necessary in the wheel brake of the rear wheel HR, which is initially still depressurized, so that the inlet valve 4 has to be switched back to passage, an undesired pressure compensation takes place via the check valve 18. The drop in pressure in the wheel brake of the left rear wheel HL can be compensated for by actuating the inlet valve 3.

2 serves to illustrate the mode of operation of the control circuit according to the invention, which is part of the electronics contained in the controller 17 or of the controller program. The part of the controller logic or controller program with which the input information, above all The brake pressure control signals are obtained from the information obtained with the aid of sensors S1 to S4. According to the invention, the brake pressure P _{S is} calculated using the logic 19 and a subsequent circuit 20, which should prevail in the wheel brake of the respective wheel after evaluation of the input information. This target pressure Psoll is compared in a subtractor 21 with an actual pressure or a value _O D approximating the actual pressure. From the difference ΔP = Psoll ~ ^p MOD, the signals VS1 for controlling the inlet valve and the outlet valve of the associated regulated wheel are then calculated in a valve control 22. The associated inlet / outlet valve pair, for example 3.7 or 4.8; 5.9; 6.10 is symbolized with 23 in FIG. 2.

The actual brake pressure or the value PMOD approximated to the actual pressure is in the embodiment of the invention shown in FIG. 2 by forming a so-called. Wheel pressure model RDM derived using the circuit or the program part 24. The input control variables for forming the wheel pressure model RDM are primarily the valve control signals VS1 of the pair of intake / exhaust valves assigned to the respective wheel, but also the control signals (VS2) of other wheel valves and the isolating valve 15, via which pressure can also be reduced . For example, in a black / white division of the brake circuits, as in the exemplary embodiment according to FIG. 1, all the valves connected to a common brake circuit can make a contribution to the wheel pressure model RDM of a specific wheel. This becomes clear in the already mentioned example of a traction control system, in which a mutual hydraulic influence of the brake pressures on the controlled wheels can occur. 3 shows such an example.

When creating the wheel pressure model that corresponds to the actual pressure however, in addition to the valve control times, the pressure build-up and release curves of the wheel brakes, the characteristic curves of the entire brake system, the characteristics and switch-on times of the hydraulic pump, the initial pressure when the control is started, the control mode - ABS, TCS or stability control - and other influencing factors to be taken into account. In FIG. 2 the arrows VS1 (valve signal 1), VS2, pump signal HP etc. indicate that information or signals of the most varied types can be used to form the wheel pressure model.

3 shows, as an example, the course of an intake valve signal EVS1 and the associated wheel pressure PRADpowie the intake valve signal EVS2 and the associated wheel pressure PRAD2 during a traction control process. EVS1 is used to control valve 3 according to FIG. 1, EVS2 to control intake valve 4. In this example, RADI is the left rear wheel HL, RAD2 is the right rear wheel HR. At time ti, the inlet valve 3 is actuated for traction control for a certain period of time, and brake pressure is thereby built up in the rear wheel HL. The brake pressure is generated by the hydraulic pump 11, 12 which is switched on when the ASR operation is started, the isolating valve 15 interrupting the pressure medium path to the master cylinder 1. At time t2, the pressure at the rear wheel HL is increased by a further pressure build-up pulse or by renewed activation of the inlet valve 3. The right rear wheel HR is initially depressurized; At the beginning of the ASR operation, the inlet valve 4 was switched over.

At time t3, however, brake actuation on the right rear wheel HR is now also required. The inlet valve 4 is therefore open at time 3 for a predetermined period of time Passage switched back. Since the delivery rate of the hydraulic pump 12 is limited, the activation of the wheel brake of the right rear wheel at time t3 has the result that the brake pressure PRADI on the left rear wheel HL is reduced via the check valve 18 which is parallel to the inlet valve 3. This undesirable effect is recorded by the wheel pressure model RDM (24). By actuating the inlet valve 3 again at time t3, the brake pressure on the left rear wheel HL is built up again to the previous value.

A similar drop in brake pressure is repeated in the example shown in FIG. 3 at time tg, again triggered by a valve control signal EVS2 and the resulting increase in brake pressure PRAD2 on the right rear wheel HR.

The detection and correction of pressure drops which are a consequence of the mutual hydraulic influencing of the wheel brakes connected to a brake circuit, in particular in the case of traction control, is a typical example of the improvement of the control by the second, subordinate control circuit according to the invention. Recording the pressure drop via the reaction of the controlled wheel would be considerably more difficult and would involve delays.

3, the valve signals EVS1 and EVS2 can assume three levels. A valve switching state or a switching position corresponds to each level. These are the valve switching positions "K", ie pressure constant; "UP", ie pressure build-up, and "DOWN", ie pressure reduction. In the embodiment of the invention according to FIG. 1, the constant maintenance by the simultaneous closing of the inlet and the outlet valve, pressure build-up by the illustrated basic position of the valves Pressure build-up achieved by the illustrated basic position of the valves and pressure reduction by opening the exhaust valve while simultaneously closing the intake valve. With a known three-position valve instead of the 2/2-way valves according to FIG. 1, the desired brake pressure modulation could also be realized.

In the two diagrams in FIG. 3, which show the pressure curve PRADI PRAD2, the calculated pressure setpoint Psoll _/ roit with a solid line shows the actual value or the pressure value PMOD approximated to the actual value. The differences between Psoll and P OD are due, on the one hand, to the valve or system characteristics, which only permit changes at finite speed. On the other hand, the differences between P _so ll and PMOD ^AT times t3, tg and tg are noticeable, which are caused by the described hydraulic coupling of the brakes connected to a brake circuit. In the present case, a pressure medium flow from the wheel brake of the left rear wheel via the check valve 18 to the right front wheel takes place at times t3 and tg. At time _{δ, there} is a brief pressure equalization via the check valve 18 'which is parallel to the inlet valve 4.

Claims

claims

Circuit arrangement for a brake system with electronic control, in particular with anti-lock, drive slip or driving stability control, with sensors for determining the wheel turning behavior and with an electronic circuit for evaluating the sensor signals and for generating brake pressure control signals electrically actuated actuators are supplied and with which the brake pressure in the wheel brakes is controlled as a function of the wheel turning behavior, characterized in that circuits (20) are present which set the target brake pressure (Psoll) in the wheel brakes of the controlled wheels as a function of the Determine the wheel turning behavior and that in a second, subordinate control circuit (21, 22, 24) the setpoint brake pressure (Psoll) is compared with the actual brake pressure or a value (PMOD) approximating the actual brake pressure, the difference (ΔP) between the setpoint and the actual braking pressure or the value approximating the actual braking pressure b is determined and the signals for controlling the actuators assigned to the regulated wheels are generated as a function of the brake pressure difference (^ P).

Circuit arrangement according to Claim 1, characterized in that hydraulic actuators (3 - 10), in particular multi-way valves, are provided as actuators, which release or block the flow, depending on the switching position.

3. Circuit arrangement according to claim 1 or 2, characterized in that the approximate value of the actual brake pressure in the individual wheel brakes (PMOD) is determined by forming a wheel pressure model (RDM, 24).

4. Circuit arrangement according to claim 3, characterized ge ¬ indicates that the formation of the Rad¬ pressure model (RDM, 24) which determines the brake pressure in the respective wheel brake sizes, to which the control signals (VS1, VS2) of the actuators of the relevant and belong to the other wheel brakes connected to the same brake circuit are evaluated.

5. Circuit arrangement according to claim 4, characterized in that ¬ indicates that the pressure-determining variables, the brake pressure reduction and build-up characteristics of the wheel brakes and the entire brake system, the initial pressure when the control is used, brake actuation signals, control signals of a hydraulic pump in the auxiliary pressure supply system Brake system, namely all or some of the aforementioned sizes, are taken into account.

6. Circuit arrangement according to claim 5, characterized in that the initial pressure is determined when the control is used from the vehicle and / or from the wheel acceleration, taking into account the brake force or axle load distribution.

7. Circuit arrangement according to claim 6, characterized in that ¬ indicates that to determine the initial pressure, the time span between the actuation of the Brake and the onset of control is evaluated.

Circuit arrangement according to one or more of claims 1 to 7, characterized in that it is provided for a brake system with traction control by brake intervention (BASR), which has two hydraulically separate brake circuits (1, 11), each of which the wheel brakes of the two wheels of one axle (VL, VR; HR, HL) are connected.