WO1988000542A2

WO1988000542A2 - Motor vehicle brake pressure regulating system

Info

Publication number: WO1988000542A2
Application number: PCT/EP1987/000375
Authority: WO
Inventors: Anton Van Zanten; Uwe Hartmann; Friedrich Kost; Wolf-Dieter Ruf
Original assignee: Robert Bosch Gmbh
Priority date: 1986-07-16
Filing date: 1987-07-13
Publication date: 1988-01-28
Also published as: DE3624007A1; WO1988000542A3

Abstract

An antiblocking control system with single-channel regulation uses as regulating criterion the derivative of vehicle deceleration, a slippage regulation being superimposed thereon.

Description

Brake pressure control system for vehicles

In the known methods of brake pressure control to improve the braking distance and the vehicle stability and controllability during the braking process, only the behavior of the individual wheels is generally taken into account without directly measuring the movements of the vehicle and the steering influences of the driver and attributing it to the brake pressure control . As a result, the control behavior is not always optimally adapted to the situation.

Depending on the number of brake pressures on the individual wheels which can be modulated differently and independently of one another, a distinction can be made in motor vehicles with four wheels between one, two, three and four-channel solutions.

According to the present invention with the features of claim 1, a simple but good control behavior brake pressure control system is created, which is improved in various respects by the design and developments of the subclaims.

The vehicle deceleration (measured directly or by differentiation from the vehicle speed) is a suitable measure for optimizing the braking distance by regulating the braking pressure or the braking pressures in such a way that a maximum deceleration occurs. Measures to ensure vehicle stability and controllability are superimposed on this maximization. The yaw acceleration or speed mentioned in claim 3 is to be regarded as a measure of vehicle stability. If the driver is not steering, a deviation of these variables from zero indicates unstable vehicle behavior, ie the vehicle begins to turn.

If the steering angle or the steering angle speed is taken into account according to claim 2, yaw acceleration and yaw rate can be used to assess the controllability of the vehicle, since in the ideal case a relationship between these variables which is dependent on the vehicle speed and geometry can be derived. Larger deviations from this indicate inadequate controllability, i. H. the vehicle does not react to steering movements in the manner desired by the driver.

If a lack of stability or manageability is found, these quantities can be improved in various ways depending on the system configuration, generally by an appropriate reduction in braking pressure on one, several or all wheels. As a result, the wheels affected adjust to lower slip values and the transferable cornering force is increased.

If the yaw acceleration or speed is not measured, an improvement in controllability can also be achieved without this feedback by reducing the brake pressure in a controlled manner at larger steering angles and steering angle speeds in the manner described in the previous section.

By measuring one or more lateral accelerations or transverse speeds (e.g. in front and rear of the vehicle), similar improvements are possible as by measuring the yaw acceleration or speed.

The wheel speeds and accelerations can be used to combine already known or new methods of wheel control ("ABS") with methods of the present vehicle control or they can be used as auxiliary measuring devices to support the vehicle control. For this, z. T. already the existing speedometer signal, with the z. B. can be determined whether the wheels lock on the sensed axle. In the following description, exemplary embodiments of the invention are explained:

Show it

1 shows a basic structure of the brake pressure control system,

2 diagrams for explanation,

3 shows diagrams for explaining a first exemplary embodiment,

4 diagrams for explaining a second embodiment,

5 diagrams for explaining a third embodiment,

Fig. 6 is a block diagram of the third embodiment.

1, a single-channel configuration with sensors for the steering angle 1, the vehicle acceleration in the longitudinal direction 2 and the yaw acceleration of the vehicle 3 is described as the simplest implementation. In a microprocessor-based switching device 4, control signals for a pressure modulator 5 are calculated by a link. The pressure modulator, e.g. B. a modulatable brake booster can change the pressure in both brake circuits synchronously. Depending on the standard equipment of the vehicle, devices may be present which set a suitable brake pressure ratio between the front and rear axles. That can e.g. B. be one or two load-dependent brake pressure reducer 6. An advantage of this arrangement is that the complete system, apart from the sensor for the steering angle, can be combined in one block, which can replace an existing brake booster, without further changes to the vehicle's brake system being necessary.

Since the measurements z. B. are disturbed by pitching movements of the vehicle and uneven roadways, they must first be prepared by suitable filter algorithms.

According to a first controller concept, the controller tries with a small steering angle, a small steering angle speed and, on average, a small yaw acceleration optimize the longitudinal deceleration. The change in the delay is constantly monitored. If the slope of the deceleration approaches zero when the pressure builds up, then it can be assumed that the wheels are approaching the maximum of the slip curve at which the force which can be transmitted to the road is greatest in the longitudinal direction.

Fig. 2 shows the curves of the vehicle deceleration and the slip of a front and a rear wheel when the brake pressure and thus the braking torque is gradually increased. The braking torque ratio between front and rear wheels is constant 2: 1 in this example (vehicle deceleration v = - vehicle acceleration a)

A typical control process on a homogeneous roadway is shown in FIG. 3. The controller initially increases the brake pressure until the gradient of the vehicle deceleration falls below a predetermined value (t ₁ ). The pressure is then held until the vehicle deceleration decreases (t ₂ ). Then pressure is built up again.

If the vehicle deceleration has not increased after a predetermined minimum pressure build-up time, it can be assumed that the wheels are in the area of the maximum of the slip curve or have already exceeded it. The controller then builds (t ₃ ) the brake pressure by a z. B. pulsed depending on the vehicle deceleration and then checks through a pressure build-up phase (t ₄ ) whether the deceleration increases when pressure builds up again, ie whether wheels move in the stable area to the left of the maximum of the slip curve. This process is repeated until the measured vehicle deceleration has increased again after the pressure build-up test phase.

In order to recognize when the control must intervene for the first time, the brake pressure should be measured continuously as an auxiliary measurement. This is the only way to recognize whether changes in the vehicle deceleration are not caused by changes in the pedal pressure of the driver. It must also be known whether pressure build-up commands cause a significant change in pressure at all or whether the brake pressure has not already reached the level of the pre-pressure specified by the driver. In the case of a slow stationary circular drive, the relationship between the steering angle and yaw rate is approximately as follows:

Vehicle speed

Yaw rate = * steering angle

Wheelbase

The relationship and its time derivation can be used to assess

Stability and controllability are used.

In the event of larger deviations, the regulator can be reduced by additional pressure

Improve stability and manageability of the vehicle by using the

Pressure reduction of the wheel slip is reduced and the cornering force is increased.

For this purpose, the deviations (yaw acceleration) are added up and if the total exceeds a predetermined value, pressure is forcibly reduced and the total value is reset to zero.

A second possibility of regulating the brake pressure when the need for this has been recognized is described with reference to FIG. 4.

The controller initially allows pressure to build up quickly until the gradient of the vehicle deceleration falls below a predetermined value (tg). Then the pressure is held until the delay changes little. A pressure build-up pulse of predetermined length then follows (tg). This change from pressure build-up and pressure maintenance is repeated until the vehicle deceleration after the pressure build-up pulse has increased only slightly (t ₇ ). It can now be assumed that several wheels are moving in the area of the maximum of the slip curve or have already exceeded it.

In order to increase the cornering force, the controller now (from t ₇ ) relieves pressure until it is largely ensured that wheels move again in the stable area to the left of the maximum of the slip curve. This is recognized by a sudden, sharp decrease in vehicle deceleration (t ₈ ). In order to avoid excessive loss of braking force, the controller immediately builds up pressure again until the deceleration is approximately constant again. This process is repeated continuously. To ensure vehicle stability and manageability, a criterion is continuously formed from yaw rate and steering angle. Unless it is measured directly, the yaw rate can be calculated by integrating the yaw acceleration. Depending on this criterion, two switching thresholds are now changed so that the pressure level is more or less reduced during the regulation, so that the cornering force is improved, wheels are prevented from locking or braking force differences between the left and right side of the vehicle are reduced.

A typical control process on a homogeneous roadway is described with reference to FIG. 5 with a third control concept. There is the pressure curve with p, the vehicle deceleration with a, the derivative and two limits for

da / dt shown.

In the block diagram of FIG. Β, 10 denotes the sensor for obtaining the vehicle longitudinal deceleration, 11 a differentiator for obtaining the derivative of this deceleration, and 12 and 13 two comparators. Of the

Comparator 12 compares the derivative da / dt with a lower threshold

S _u , which is determined anew in each case on the basis of the level of the pressure jump (measurement by sensor 14 and calculation by computer 15) and the comparator 13 compares the derivative da / dt with the fixed upper threshold S _o . For the pressure modulator 16 to be controlled, it is assumed here that the pressure remains constant without a control signal, 17 builds up pressure at a control signal at the output of an OR gate, and 18 reduces pressure at a control signal at the output of an OR gate. With 19 a pulse generator is designated. Its output is also connected to a timing element 20, the output of which, together with other lines, is connected to an AND gate 21. The output of this AND gate in turn turns on a pulse generator 22.

After a pressure build-up pulse, not shown, of fixed or variable length (via a terminal 23), the system waits until the derivative of the filtered vehicle acceleration (da / dt) assumes a minimum value. Now the threshold S _{u is} calculated from the amount of the pressure jump (measured by 14) in the computer 15, which must be undercut by da / dt so that a further pressure build-up and pressure build-up pulse can follow. This is generated by the pulse generator 19 at time t ₁₀ . This change from pressure build-up and pressure maintenance is repeated until the vehicle deceleration increases only slightly after the pressure build-up pulse. It can now be assumed that several wheels are moving in the area of the maximum of the slip curve or have already exceeded it.

By choosing the limit, it can be determined to a certain extent whether the blocking of one or more wheels is accepted. If the threshold S _u for da / dt was not undershot after a pressure build-up pulse (t ₁₁ ), that is to say that the comparator 12 does not generate a signal, then the controller reduces the pressure in order to increase the cornering force until it is largely ensured that again Move the wheels in the stable area to the left of the maximum of the slip curve. This is achieved in that the pressure build-up pulse activates the timing element 20, which drives the AND gate 21 for a certain time after a predetermined time (t ₁₁ -t ₁₀ ) and controls the pulse generator 22 without output signals from the comparator, the breakdown pulses from t ₁₁ delivers. The fact that wheels are again in the stable range is recognized by a sudden sharp decrease in vehicle deceleration: da / dt exceeds the upper threshold S _o of comparator 13 at t _12. Pressure is then immediately built up again and the whole process is repeated.

The control behavior can be significantly improved if, in addition to the vehicle deceleration, the average front wheel speed e.g. at the differential (tachometer speed) is used for control. The electronic recording of the tachometer speed causes only little additional costs in comparison to the measurement of the wheel speeds, however, as an additional parameter for single-channel systems, it provides a number of valuable information about the wheel behavior on the sensed axle (in general, the front wheels are also known).

A reference speed v _ref is continuously calculated from the tachometer speed T (from sensor 24) and the measured vehicle deceleration a (in FIG. 25), by means of which the real vehicle speed is approximated. The reference speed is increased when the filtered tachometer speed becomes greater than v _ref . Otherwise, v _{ref is} reduced using the measured vehicle deceleration. From v _ref and T, an average slip S on the front wheels can now be determined (in a comparator 26). This slip also serves to lower the pressure. However, it is important to ensure that the slip control only intervenes in the event of relatively large deviations, so that the deceleration signal is generally regulated.

If the stability control is used to identify cases in which it is advantageous to have a front wheel blocked in single-channel systems, e.g. in the case of very different friction coefficients of the road on the left and right wheels, then the misalignment must! be dispensed with, since S then becomes greater than 0.5. In such cases, e.g. be monitored whether both front wheels lock at the same time, which should generally be excluded.

A weighting of the two control variables S and derivation of the vehicle acceleration da / dt can be made dependent on the level of the coefficient of friction of the road (which can be estimated from the measured vehicle deceleration that can be achieved). With a small coefficient of friction, the changes in the vehicle deceleration when the pressure changes are small and can be lost in the measurement noise. S should therefore be weighted more strongly here. If the coefficient of friction is high, the deceleration controller works more reliably and you can restrict yourself to monitoring S for fast and large slip changes and e.g. Abort pressure reduction phases earlier than is possible with the delay control by monitoring an upper limit for da / dt. If you switch back from pressure reduction to pressure build-up as soon as S falls below a minimum value, phases that are too braked can generally be avoided in the cycle. This weighting is indicated in FIG. 6 by the supply of the vehicle acceleration a to the comparator 26 for the purpose of variation in mistake.

Here too, a criterion of yaw rate and steering angle is constantly formed to ensure vehicle stability and controllability. Unless it is measured directly, the yaw rate can be calculated by integrating the yaw acceleration. The novelty of this arrangement is that it is not the behavior of the individual wheels that is observed and regulated, but the behavior of the entire vehicle. It is accepted that individual wheels lock. On a homogeneous road surface when driving straight ahead, these can occasionally be the front wheels, when cornering, they are the wheels on the inside of the curve, with different coefficients of friction on the sides of the vehicle, it is the wheels with the low coefficient of friction. However, since the locking wheels could only transmit smaller cornering forces when cornering and with different coefficients of friction, even if they would also roll, locking does not result in a major disadvantage. In many cases there is a significant improvement in manageability if the wheels that are still rolling are regulated not at the optimum braking force but at lower slip values. The controller is simple and inexpensive compared to 3- or 4-channel controllers.

A further improvement in braking behavior can be achieved by adding additional sensors or actuators, e.g. by reducing the brake pressure on individual wheels.

INTERNATIONAL PATENT COOPERATION (PCT)

(51) International Patent Classification ⁴ (11) International publication number: WO 88/00 B60T 8/00 A3 (43) Internationales

RELEASE DATE: January 28, 1988 (Jan 28

(21) International file number: PCT / EP87 / 00375 (74) Lawyer: KAMMER, Arno; PO Box 10 56 08, Gr Höfer Weg 36, D-6900 Heidelberg 1 (DE).

(22) International filing date: July 13, 1987 (July 13, 1987)

(81) Destination countries: AT (European patent), BE

(31) Priority reference number: P 36 24 007.9 European patent), CH (European patent), (European patent), FR (European patent),

(32) Priority date: July 16, 1986 (July 16, 1986) (European patent), IT (European patent), LU (European patent), NL (European pat

(33) Priority country: DE SE (European patent), US.

(71) Applicant (for all destinations except US): ROVublished

BERT BOSCH GMBH [DE / DE]; Central department with international search report. Patents, PO Box 50, D-7000 Stuttgart 1 (DE). Approved for changes to claims before expiry

Deadline. Publication will be repeated if change

(72) inventor; and

(75) Inventor / Applicant (for US only): VAN ZANTEN, Arriving. ton [DE / DE]; Waldstrasse 15/2, D-7257 Ditzingen 4 (DE). HARTMANN, Uwe [DE / DE]; Olgastraße 79, (88) Date of publication of the international search D-7000 Stuttgart 1 (DE). KOST, Friedrich [DE / DE]; ^{Judge: '} April 7, 1988 (April 7, Heinrich-Ebner-Strasse 24, D-7000 Stuttgart 50 (DE). RUF, Wolf-Dieter [DE / DE]; Schlatthölzlesweg 17, D-7076 Waldstetten (DE).

(54) Title: ENGINE VEHICLE BRAKE PRESSURE REGULATING SYSTEM

(54) Description: BRAKE PRESSURE CONTROL SYSTEM FOR VEHICLES

(57) Abstract

(57) Summary

An anti-lock control system with single-channel control, in which the derivation of the vehicle deceleration is used as a control criterion, and over which a slip control is superimposed.

Claims

1. Brake pressure control system for vehicles in particular single-channel control system in which the brake pressure is controlled using a vehicle decelerator, characterized in that the brake pressure build-up is stopped when the slope of the vehicle deceleration (-da / dt) reaches a predetermined small value.

2. Brake pressure control system according to claim 1, characterized in that this value is increased when cornering (steering angle, steering angle speed).

3. Brake pressure control system according to claim 1 or 2, characterized in that this value is increased when the vehicle behavior is unstable (yaw rate, yaw acceleration, lateral acceleration).

4. Brake pressure control system according to one of claims 1-3, characterized in that the brake pressure is kept constant after reaching the predetermined value.

5. Brake pressure control system according to one of claims 1-4, characterized in that pressure is reduced when the vehicle deceleration (negative slope) decreases.

6. Brake pressure control system according to claim 5, characterized in that degradation takes place over a predetermined time.

7. Brake pressure control system according to claim 6, characterized in that it is then checked whether the vehicle deceleration increases again when pressure builds up and otherwise further pressure is reduced.

8. brake pressure control system according to one of claims 6 or 7, characterized in that after increasing the vehicle deceleration pressure build-up pulses are generated and it is checked whether the vehicle deceleration increases.

9. Brake pressure control system according to claim 4, characterized in that the pressure after the constant phase is increased in stages until the vehicle deceleration increases only slightly, that pressure is then reduced until the vehicle deceleration decreases sharply, and that pressure is then built up again becomes.

10. Brake pressure control system according to one of claims 1-3, characterized in that it is checked in the case of pulsed brake pressure build-up after each pressure pulse whether a predetermined lower limit for da / dt is reached and that only if this is the case further pressure is built up.

11. Brake pressure control system according to claim 10, characterized in that this limit is variable and preferably depends on the level of the pressure pulse.

12. Brake pressure control system according to claim 10 or 11, characterized in that, if the lower limit is not reached, pressure is reduced until a predetermined upper limit for da / dt is exceeded and that pressure is then built up again.

13. Brake pressure control system according to one of claims 1-12, characterized in that the brake pressure is measured as an auxiliary measurement variable.

14. Brake pressure control system according to one of claims 1-13, characterized in that the control after the derivation of the vehicle deceleration is superimposed on a slip control which triggers pressure reduction at high slip values.

15. Brake pressure control system according to claim 14, characterized in that the speedometer signal is used for slip control.

16. Brake pressure control system according to claim 15, characterized in that the reference variable for slip formation is obtained from the speedometer speed and the vehicle deceleration.

17. Brake pressure control system according to one of claims 14 - 16, characterized in that a weighting is provided which varies the ratio of the influences of the two superimposed regulations.