EP0876270A1

EP0876270A1 - Method and brake system for control of brake pressure build-up during a control process

Info

Publication number: EP0876270A1
Application number: EP97901044A
Authority: EP
Inventors: Ralph Gronau; Utz Lambert; Gunther Buschmann; Norbert Ehmer
Original assignee: ITT Manufacturing Enterprises LLC
Current assignee: ITT Manufacturing Enterprises LLC
Priority date: 1996-01-23
Filing date: 1997-01-16
Publication date: 1998-11-11
Also published as: DE19602244A1; JP3880625B2; US6238020B1; JP2000503929A; DE19602244B4; WO1997027090A1

Abstract

A method is proposed for vehicles for an electronically-controlled brake system (e.g. ABS) where the rotational characteristics of the individual wheels is measured for the control of the brake pressure (re-) build-up during a control process, evaluated for the determination of the brake pressure control signals. According to this method, during the brake pressure control process, the brake pressure reduction in the preceding cycle (26) is taken into account, for control of the brake pressure re-build-up (27). According to the invention, a brake pressure rising gradient (G) is calculated on the basis of a brake pressure build-up in the preceding brake pressure build-up phase (25) and the brake pressure build-up or the process of the brake pressure build-up is calculated and given on the basis of this rising gradient (G) and of the calculated wheel brake cylinder pressure at the beginning of the current brake pressure build-up phase (27) and on the basis of the current, calculated blocking pressure level (N3) of the brake pressure build-up or the progress of the brake pressure build-up.

Description

Method and brake system for controlling the brake pressure build-up during a regulation process

The invention relates to a method which is provided for a motor vehicle brake system with electronic brake pressure control and is used to control the brake pressure build-up or brake pressure build-up during a control process, the rotational behavior of the individual vehicle wheels being measured and evaluated to determine brake pressure control signals and wherein the brake pressure reduction in the previous cycle is taken into account in the control of the brake pressure restoration during a brake pressure control process. Brake systems for performing the method are also part of the invention. Brake pressure control processes of this type occur in particular during anti-lock control, but also in the context of driving stability controls and the like.

Brake systems with electronic anti-lock control (ABS) are known in numerous variants and on the market. In the common systems, the rotational behavior of the individual vehicle wheels is known to be measured with wheel speed sensors, or wheel sensors for short, and is evaluated as the only or as the most important input variable of the brake pressure control system. In order to achieve a satisfactory control despite the very different road conditions and driving situations, which guarantees the maintainability of the steering ability and driving stability and in which the vehicle requires only a short braking distance, a very sophisticated control philosophy is necessary, which can only be achieved with a complex control algorithm ¬ men can be achieved.

CONFIRMATION COPY A special design problem of the control philosophy ^" represents the brake pressure build-up or rebuild after a previous, control-related brake pressure decrease. The brake pressure should approach the blocking pressure level very quickly and with high accuracy, so that the wheel runs stably and is braked effectively at the same time. The control frequency, ie the lowering and re-building of the pressure during an anti-lock control process, should be as low as possible for physical and comfort reasons.

From DE 39 03 180 AI (P 6632) a circuit arrangement for a brake system with anti-lock control is already known, with which the brake pressure is controlled in each case with a steep, then with a flatter gradient into the wheel brake after pressure reduction after a regulation-related pressure reduction. This is achieved by means of a variable pulse and short fixed pulses which follow one another at a large distance. The dimensioning of the pressure rebuilding also depends on the duration of the pressure build-up during the steep increase phase in the previous cycle, on the duration of the total pressure build-up in the previous cycle and on the duration of the previous pressure reduction.

The present invention is also based on the object of developing a method with which a precisely metered pressure build-up which is adapted to the respective situation can be set after a previous pressure reduction due to the regulation. The blocking pressure level of the regulated wheel, which runs again after the previous pressure reduction and is braked again, should be raised to the blocking pressure level as quickly as possible, in order to keep the control frequency low, avoiding the application of an excessively high braking pressure or the blocking pressure level should not be exceeded again immediately. Moreover fast and precise adaptation to the constant changes in the controlled variables or influencing variables is required.

It has been found that this object can be achieved by the method described in claim 1, the special feature of which is that in the method of the type mentioned at the beginning, a brake pressure increase gradient is calculated on the basis of the brake pressure build-up in the previous brake pressure build-up phase that on the basis of this brake pressure rise gradient and the wheel cylinder pressure at the beginning of the current brake pressure build-up phase and on the basis of the current blocking pressure level, the brake pressure build-up and the brake pressure build-up curve are calculated and specified.

Some particularly advantageous exemplary embodiments of the method according to the invention and brake systems for carrying out the method are described in the subclaims.

According to the invention, the brake pressure build-up gradient in the previous build-up phase is used as a basis for determining or dimensioning the brake pressure restoration during a control process. The starting point of the brake pressure reconstruction is the current wheel cylinder pressure, which was determined from the immediately preceding brake pressure reduction phase. The brake pressure build-up continues until the blocking pressure level is reached again, a change in this blocking pressure level which has occurred in the meantime being incorporated immediately into the dimensioning of the brake pressure build-up.

The brake pressure increase gradient in a brake pressure build-up phase is dependent on the admission pressure or master cylinder pressure and thus ^" on the force with which the driver operates the brake. According to the invention, the information about the admission pressure is therefore included in the calculation of the brake pressure restoration. In this way, the pre-pressure prevailing in the immediately preceding cycle or in the immediately preceding brake pressure build-up phase is used as the basis for the calculation of the current brake pressure build-up.

Further details of the invention will become apparent from the following description of an embodiment with reference to the accompanying figures.

Show it:

Fig. 1 in a schematically simplified manner, the essential components of a motor vehicle brake system, for which the inventive method is useful, and

2 shows the idealized representation of the course of the brake pressure in the wheel cylinder of a controlled wheel during an anti-lock control process using the method according to the invention.

In Fig. 1, 1 denotes a pedal-operated master cylinder which is connected to a wheel brake 3 via a brake line 2. In the brake line 2, an inlet valve 4 is inserted, which is actuated electromagnetically and is switched to passage in its basic position or rest position. If this valve 4 is activated, it switches to a state in which the brake line 2 is closed. A return line 5 runs parallel to the brake line 2 and connects the wheel brake 3 to the master cylinder 1. A hydraulic pump 6 is inserted into this line, the wheel brake 3 and the suction side of the pump 6 being hydraulically connected via an outlet valve 7.

The outlet valve 7 is also actuated electromagnetically. The outlet valve 7 is in the basic or rest position closed. When the valve 7 is actuated, a return line from the wheel brake 3 to the hydraulic pump 6 is opened.

A low-pressure accumulator 8 is connected to the suction side of the pump 6 and temporarily absorbs the pressure medium discharged from the wheel brake 3 for pressure medium reduction.

The rotational behavior of the wheel 9, which is braked by the wheel brake 3, is measured with the aid of a wheel sensor 10. An electronic evaluation circuit 11 detects the signals from the wheel sensor 10 and the signals from the other wheel sensors (not shown here) of the other vehicle wheels, evaluates these signals and finally generates brake pressure control signals for actuating the inlet and outlet valves 4 and 7.

The exemplary embodiment of a brake system shown is a so-called closed system. The method according to the invention is of course equally suitable for open hydraulic systems and for completely differently designed controlled brake systems.

The special feature of the invention can be seen in the evaluation of the sensor signals and in the calculation of the brake pressure build-up with the aid of the evaluation circuit 11. Such evaluation circuits are nowadays preferably implemented on a digital basis using program-controlled circuits, in particular microcomputers or microcontrollers.

FIG. 2 shows a brief section of the brake pressure curve in the wheel brake of a controlled wheel, for example in the wheel brake 3 of the brake system according to FIG. 1. The typical course of the brake pressure p in the wheel brake is shown during a brake pressure control cycle. During one Control process generally takes place several pressure fluctuations or control cycles of the type shown.

The blocking pressure level N for the vehicle wheel considered here is shown by a dashed line. In a system of the type shown, this blocking pressure level N is calculated on the basis of the wheel deceleration and / or the vehicle deceleration, the suitable, meaningful values being obtained by logically linking the deceleration signals and / or from the vehicle reference speed in be ¬ can be derived and calculated in a known manner.

For the wheel in question, N symbolizes the relevant, continuously updated blocking pressure level. In the illustrated section of a control process, a brake pressure reduction due to the control begins at time t ₀ , at which the brake pressure or the blocking pressure level NO prevails in the wheel under consideration. Within a period of time 24, the pressure in the wheel cylinder is reduced from the blocking pressure or blocking pressure level NO to a pressure Pl. In the example according to FIG. 2, this takes place within the time span 24 and is brought about by three pressure reduction pulses T _A1 , T _A2 , T _A3 , which are separated by pulse pauses (characterized by the horizontal pressure curve). The pressure reduction time is thus composed of the time period 24, reduced by the pulse pauses (horizontal areas of the pressure curve).

The blocking pressure NO is calculated from the wheel or vehicle deceleration. The brake pressure reduction characteristic curve of the system is known because it is always reduced against a defined counter pressure. Consequently, the pressure reduction times T _A can be based | T + _A2 "'" T _A3 determine the prevailing at the end of the reduction phase brake pressure Pl. In the time period 25, the pressure is restored until the blocking pressure level N2 is reached. The inlet valve opening times or actuation times which are required to raise the pressure from level P1 to the blocking pressure level N2 are designated in FIG. 2 by T _E1 , T _E2 , T _E3 . The

Brake pressure increase gradient G can thus be determined from the pressure difference N2 -Pl divided by the sum of the intake valve actuation times T _{E1 +} T _{E2 +} T _E3 .

After the end of the first control cycle, the wheel under consideration becomes unstable again, so that the wheel cylinder pressure is reduced again at time t ₂ . From the blocking pressure level N2 at the beginning of the pressure reduction and the valve actuation times T _A4 + T _A5 - taking into account the brake reduction characteristics of the system - the pressure P2 can be calculated as previously explained.

All data for the calculation of the current pressure build-up in the current build-up phase 27 are now available. Starting from the wheel cylinder pressure P2 at the time t ₃ , based on the

Pressure increase gradient G of the previous pressure build-up phase, which results from the quotient

G = (N2 - Pl) / (T _E1 + T _E2 + T _E3 )

results, the inlet valve opening times T _{E4 (} T _E5f T _E6 ; T _E6 can be determined in this current pressure build-up _phase , however, depending on the current blocking pressure level N3, N4.

The total opening time T _E4 + T _E5 + T _{E6 of} the intake valve in the

Pressure build-up phase - apart from the adaptation to the last determined blocking pressure level N4 - is derived from the before determined data, namely from the immediately preceding pressure reduction 26 and from the pressure increase gradient G in the previous cycle 25. The following applies:

T _E total = T _E4 + T _E5 + T _E6 = (N ₃ - P ₂ ) / G

The distribution over an initial pulse (T _E4 ), which is about the

Half of the total valve actuation time, and on the further, shorter periods or pulses T _E5 , T _E6 takes place in the present embodiment of the invention according to a predetermined scheme. The "careful" pressure control in the area of the locking pressure level prevents a premature occurrence of a renewed locking tendency of the controlled wheel (without braking the wheel).

In the exemplary embodiment shown, a new control cycle begins at time t4.

According to the method according to the invention, the relevant parameters for dimensioning the pressure reconstruction are derived from the most current data. The immediately preceding pressure reduction and the pressure build-up previously carried out are evaluated. The decisive factor is initially the blocking pressure level N3 at the time of the pressure build-up calculation, but, as in the example according to FIG. 2, a subsequent, significant change in the blocking pressure level (to the value N4) can be taken into account, for example, by one or more additional short build-up pulses become. If the change in the blocking pressure level is greater than a certain, predetermined limit value (for example greater than 20%), it will be at time t ₃

(FIG. 2) the calculated total valve actuation time is corrected accordingly and the pressure build-up is thus adapted to the current conditions.

Claims

claims

1. Method for a motor vehicle brake system with electronic brake pressure control, for controlling the brake pressure build-up during a control process, for example an anti-lock control or driving stability control process, in which the rotational behavior of the individual vehicle wheels is measured and evaluated to determine brake pressure control signals and in which during a brake pressure control process the brake pressure reduction in the previous cycle is taken into account when controlling the brake pressure build-up or build-up, characterized in that a brake pressure increase gradient (G) is calculated on the basis of the brake pressure build-up in the previous brake pressure build-up phase (25) that on the basis of the brake pressure increase gradient (G), the wheel cylinder pressure (P2) at the beginning (t ₃ ) of the current brake pressure build-up phase (27) and the current blocking pressure level (N3) the brake pressure build-up and the course of the brake pressure build-up are calculated and specified.

2. The method according to claim 1, characterized in that the wheel cylinder pressure (P2) at the beginning of the current brake pressure build-up phase (27) from the blocking pressure level (N2) and the brake pressure reduction (26) is determined, the measured values being immediate previous brake pressure reduction phase (26) are used as a basis.

3. The method according to claim 2, characterized in that to determine the brake pressure reduction, the Ansteu¬ erzeit (T _A ) of the brake pressure reduction valves or So-called exhaust valves (7) can be evaluated taking into account the blocking pressure level (N) or the wheel brake pressure at the beginning of the reduction phase and taking into account the brake pressure reduction characteristic of the system.

4. The method according to one or more of claims 1 to 3, characterized in that the Blockier¬ pressure level (Nx; x = 0, 1,2,3,4) from the wheel deceleration and / or from the vehicle deceleration when the brake pressure control or the brake pressure reduction is calculated.

5. The method according to one or more of claims 1 to 4, characterized in that the current brake pressure build-up takes place according to a predetermined brake pressure build-up scheme.

6. The method according to claim 5, characterized in that the brake pressure build-up is brought about by actuating an inlet valve (4), the calculated total opening time of the inlet valve (T _{E total} ) being _{split up} according to the predetermined brake pressure build-up scheme.

7. The method according to claim 6, characterized in that the total opening time (T _{E total} ) of the inlet valve (4) in a first brake pressure build-up time period (T _E4 ), which is approximately half of the total opening time

(T _E4 + T _E5 + T _E6 ) corresponds, and is divided into further, approximately equally long brake pressure build-up periods (T _{E5 /} T _E6 ) which are interrupted by approximately equally long pauses. Brake system with electronic brake pressure control, for performing the method according to one or more of claims 1 to 7, with wheel sensors for determining the rotational behavior of the individual wheels and with an electronic evaluation circuit for evaluating the sensor signals and for generating brake pressure control signals, with a master cylinder and wheel brakes which are connected via brake lines into which electrically actuable brake pressure control valves are inserted, the pressure medium inflow to the wheel brakes and thus the pressure build-up and thus the pressure reduction with outlet valves being controllable with inlet valves, characterized in that the electronic evaluation circuit ( 11) Means for calculating the wheel deceleration and the vehicle deceleration on the basis of the wheel sensor signals contains that the current blocking pressure level (N) is calculated from the current wheel and / or vehicle deceleration, that the exhaust valve control is based on the total time iten (T _A ) of a wheel during a

Brake pressure reduction phase (26) taking into account the current blocking pressure level (N) and the brake pressure reduction characteristic curve of the system, the current wheel brake pressure and the totality of the intake valve actuation times (T _E ) during a brake pressure build-up phase (25, 27) taking into account the wheel cylinder pressure (P ) at the beginning of the build-up phase and the current blocking pressure level (N) the brake pressure increase gradient (G) is calculated.

Brake system according to claim 8, characterized in that the brake pressure increase gradient (G) of the preceding brake pressure build-up phase (25) is evaluated to calculate the current brake pressure build-up.