GB2231110A

GB2231110A - Control arrangement for pressure control in anti-locking brake systems

Info

Publication number: GB2231110A
Application number: GB9008135A
Authority: GB
Inventors: Hans-Juergen Beilfuss; Michael Vogt
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co OHG
Priority date: 1989-04-29
Filing date: 1990-04-10
Publication date: 1990-11-07
Anticipated expiration: 2010-04-10
Also published as: GB9008135D0; GB2231110B; DE3914401A1; FR2646390B1; JPH02296567A; FR2646390A1

Description

H.J.Beilfuss-9-4 1 11 :2:2 _:3 -1-:L X (2) CONTROL ARRANGEMENT FOR

PRESSURE CONTROL IN ANTI-LOCKING BRAKE SYSTEMS The present invention is concerned with a control arrangement for pressure control in an anti-locking brake system of the type comprising a master brake cylinder connected to brake wheels through initially open multi-way valves which are switchable to a- closed or blocking condition and a brake pressure modulator coupled upstream of the master brake cylinder, and being controllable in accordance with a multiplex process, with the multi-way valves leading to the wheel brakes, upon commencement of the anti-locking control, being reswitchable to the blocking position and with the pressure in the master brake cylinder being reducible.

In known brake systems of the afore-mentioned type, the pressure modulator comprises an assembly operated by hydraulic auxiliary pressure or vacuum and serving both for brake force boosting and for generating an auxiliary force counter-acting the pedal force whilst being capable, in the event of anti-locking control, to reduce the pressure in the working chambers of the master brake cylinder. Brake systems of this type are disclosed in published German Patent Applications Nos. DE-OS 3117629 and DE-OS 3641105. Such brake systems are operated in the multiplex process for which reason they need but a relatively small number of brake pressure control valves. Provided in a pressure fluid conduit leading from the master brake cylinder to one or to 2 two wheel brakes is a multiway inlet valve open in the initial position and switchable to a blocking position. Upon commencement of an anti- locking control operation all valves leading to the wheel brakes are first switched to blocking position and, subsequently, when the brake pressure in the master cylinder is decreased only that valve which leads to the unstable wheel is re-opened. Consequently, the brake pressure in the wheel brake of the unstable wheel will decrease whereas the pressure in the 'rest of the wheel brakes will remain constant. The brake pressure in the other wheel brakes will then be successively modulated, i.e. decreased, kept constant or further increased.

During blocking of the multiway inlet valves in the initial phase of the anti-locking control and in conjunction with the development of the auxiliary force counter-acting the pedal force and, in some cases, with a blocking or decoupling of the pedal the pressure in the master brake cylinder may in some unfavourable conditions rise further or increase excessively. This is disadvantageous because the pressure decrease required in the wheel brake of the wheel tending to lock is thereby delayed thus affecting the effectiveness of the control.

It is, therefore, an object of the present invention to overcome the above disadvantage without substantial additional components and avoiding other disadvantages.

According to the present invention there is provided a circuit configuration or control arrangement for pressure control in an antilocking brake system, comprising a master brake cylinder connected to wheel brakes through multi-way valves which are open in the initial position and switchable to a blocking condition and a brake pressure modulator coupled to the master brake cylinder, the said control arrangement providing control of the system according to a multiplex process by which the multi-way valves leading to the wheel brakes on commencement of an anti-locking control operation are reswitchable to blocking condition and the pressure in the master brake cylinder is reduced, 4 -1 3 characterised in that the control arrangement controls the operation of the valves so that in the initial control phase of the operation, once the first wheel to show a locking tendency is a front wheel, reswitching of the wheel valves leading to the rear wheel brakes is delayed by a predetermined period of time by time delay means of the arrangement.

The invention is based on the principle that in the majority of cases (and in the most hazardous cases) the first wheel of a vehicle to become unstable during a braking operation is a front wheel. In such situations further relatively small increases in pressure of a temporary nature in the rear wheel brakes have no notable influence on the running stability of the wheels and can even be advantageous for the braking operation. However, preventing the pressure from rising excessively and the particularly rapid pressure decrease of the brake pressure in the unstable front wheel attainable thereby, will lead to a substantial improvement of the control because the risk that the wheel slip will become excessively high due to an excessively slow brake pressure decrease is avoided.

According to one preferred embodiment of the circuit configuration or control arrangement of the invention, the predetermined period of time by which the response of the rear wheel valves is delayed, is between 4 and 20 milliseconds and preferably between 5 and 10 milliseconds. The duration of that period of time is adjusted to the respective brake system, in particular, to the brake pressure generator and its dead times. The optimal value can best be determined empirically.

By way of example the present invention will now be described with reference to the accompanying drawing in which:

Figure 1 shows the essential components of a brake system of the type hereinbefore defined and to which the invention is applied; and, Figure 2 is a diagram indicating the brake pressure 4 pattern in the initial phase of an anti-locking control operation of the system according to Figure 1.

Referring to the drawings, Figure 1 shows a brake system of the type to which the circuit arrangement of the invention is applied. The system comprises a brake pressure generator 1, wheel valves 2 to 4, a modulator pressure control valve 5, wheel sensors 6 to 9, and an electronic controller 10 of which the circuit arrangement of the present invention forms a part.

The brake pressure generator 1 comprises a tandem master brake cylinder 11 having coupled thereto a servo arrangement 12 serving both as a brake force booster and a generator of an auxiliary force H counteracting the pedal force F. The brake force is applied to the brake force generator 1 and the servo arrangement 12 through a brake pedal 13.

The servo-arrangement 12 in the present embodiment of the invention corresponds generally to a conventional vacuum pressure brake force booster. The interior chamber space of the arrangement 12 is subdivided into two chambers 15,16 by a piston 14. In the resting position of the brake system, as shown, vacuum prevails in both chambers from a connection "Vac" and through the modulator pressure control valve 5 to the working chamber 16, and then through a valve_17, shown only schematically, which is open in the resting position of the brake to provide vacuum in the pedal-sided chamber 15. The "Vac" connection may correspond to the connection of the brake system to the intake system of an Otto engine serving as an auxiliary energy source for brake force boosting and brake pressure modulation.

The brake force which is boosted by the arrangement 12 -in known manner is transmitted to the working pistons 18 and 19 of the tandem master brake cylinder 11, and from the working chambers thereof through brake circuits I,II and valves 2 to 4 in the open position, to the wheel brakes 20 to 23.

Information relating to the rotating pattern of the c individual wheels of the vehicle is obtained from the wheel sensors.6 to 9 as electrical signals and fed to the controller 10 which generates corresponding control signals for the wheel valves 2 to 4 and for the control valve 5. 5 The mode of operation of the brake system is as follows: As long as there is no locking tendency of the vehicle wheels as indicated by the wheel sensors to the controller 10 all valves 2 to 5 will maintain their open positions as shown in Figure 1. The servo arrangement 12 serves as a brake force booster.

once a locking tendency is sensed on a wheel such as the left-hand front wheel VI, an anti-locking control operation will commence. First, all the wheel valves 2 to 4 are switched to closed position and atmospheric pressure is admitted to the working chamber 16 of the booster through switching of the modulator pressure control valve 5, thereby causing the auxiliary force H counteracting the pedal force F to develop. If the brake pressure generator 1 is furnished with a means for locking or decoupling the pedal.13 from the piston 14, the pedal 13 upon commencement of the anti-locking control, is blocked and decoupled, respectively. Since means of this type are known in the art, for the sake of clarity they have not been shown in the drawing.

Once the pressure in the master brake cylinder 11 has decreased to or below the pressure level prevailing upon commencement of the brake pressure control, the wheel valve 2 leading to the wheel having instability - in the present instance the left front wheel VL - is reswitched to the open condition so that the brake pressure in the associated wheel brake 20 can drop. The brake pressure, in the other brakes 21 to 24, in view of the closed wheel valves 3 and 4, remains constant. Subsequently, the brake pressure in the remaining wheels VR, HL and HR can be lowered or further increased.

- Figure 2 shows the brake pressure pattern PHZ in the 1.11 6 master brake cylinder 11 during the aforedescribed antilocking control phase. AT the time to a braking operation will commence. At the time tl, one wheel - the lef t-hand f ront wheel VL in the present case - will become unstable causing the anti-locking control phase to commence. At the time tl, the modulator pressure control valve 5 is reswitched thereby causing a rise in the pressure in the chamber 16. The wheel valve 2 leading to the lefthand front wheel VI, having become unstable continues to be switched to open (or is switched back to open immediately upon commencement of the control). The wheel valve 3 leading to the second front wheel VR is reswitched to blocking. The multi-way valve 4 leading to both of the rear wheels, however, in accordance with the invention is reswitched to blocking only at time tV i.e. after a delay of, for example 5 to 10 milliseconds. Accordingly, pressure p, prevailing at the time t, is,,locked" in the wheel brake 21 of the right-hand front wheel VR, while the slightly higher brake pressure P2 (or a part thereof if a brake pressure reducer is provided) is "locked" in the rear wheel brakes 22,23. As shown in Figure 2, after commencement of the anti-locking control at the time tl, a brake pressure decrease in the wheel brake 20 of the wheel VL having become unstable is attained relatively rapidly.

Without the delay At = t2 - t, pending reswitching of the wheel valve 4 in the connection of the rear wheels HL, HR, the pressure pattern pi in the master brake cylinder 11 HZ shown in broken lines in Figure 2, and, hence, also in the wheel brake 20 would have resulted.

The chain line pressure curve shows a "non-interfered" brake pressure rise. A simultaneous reswitching of all valves 2 to 4 (at the time tl) would result in a sudden switch-off of all pressure fluid connections to the brake pressure generator. It has already been mentioned that minor changes in the brake pressure generator arising, for example, as a consequence of the insert masses, can lead to an increase or excessive rise in the pressure. Thus instead of the rapid pressure decrease desired at time t, as a t.

7 counter-measure against the wheel locking tendency, the anti-locking control phase as a result of the decoupling of all wheel brakes, initially, would commence upon a pressure rise. In that critical part of the control phase during which the attainable quality of the anti-locking control is dependent on the pressure decreasing the speed of the unstable wheel such an excessive rise in the pressure would be highly disadvantageous. A decrease of the bake pressure in the wheel brake 20 could commence at time t3 at the 10 earliest.

In carrying out the invention, hence, a substantial improvement of the anti-locking control is attained by a very simple alteration or modification of the control circuit which thereby provides a time delay At between the time ti at which the anti-locking control phase commences due to instability of a front wheel and the time t2 when the valve or valves associated with the rear wheels is/are reswitched from an open condition to a blocked condition.

I 8

Claims

CLAIMS:

1. A circuit configuration or control arrangement for pressure control in an anti-locking brake system, comprising a master brake cylinder connected to wheel brakes through multi-way valves which are opening the initial position and switchable to a blocking condition and a brake pressure modulator coupled to the master brake cylinder., the said control arrangement providing control of the system according to a multiplex process by which the multi-way valves leading tot eh wheel brakes on commencement of an anti-locking control operation are reswitchable to blocking condition and the pressure in the master brake cylinder is reduced, characterised in that the control arrangement controls the operation of the valves so that in the initial control phase of the operation, once the first wheel to show a locking tendency is a front wheel, reswitching of the wheel valves leading to the rear wheel brakes is delayed by a predetermined period of time (At) by time delay means of the arrangement. 20

2. A control arrangement according to claim 1, characterised in that the predetermined period of time (/\t) is between 4 and 20 milliseconds and preferabiy between 5 and 10 milliseconds.

3. A control arrangement as claimed in claim 1 or claim 2, in which the time delay means is embodied in an electronic controller of the arrangement.

4. A control arrangement in an anti-locking brake system substantially as hereinbefore described with reference to the accompanying drawing.

Published 1990 atThe Patent Office, State House, 6671 High Holborn, London WC1R 4TP. Further copies maybe obtainedfromThe PatentOtftce. Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd. St Mary Cray, Kent, Con. 1187 Q..