FR2646390A1 - CIRCUIT ARRANGEMENT FOR REGULATION OF PRESSURE REDUCTION IN AN ANTI-LOCK BRAKING SYSTEM - Google Patents

Abstract

This circuit arrangement includes a brake master cylinder 11, to which the wheel brakes 20, 21, 23 are connected via multi-way valves 2, 3, 4, which are open in the rest position and which can be switched to the locked position, and a brake pressure modulator 5 mounted upstream of the brake master cylinder 11, this circuit arrangement being controllable according to a multiplexing process, while, at the start of the anti-lock regulation, the multi-way valves 2, 3, 4, leading to the wheel brakes 20, 21, 22, 23 can be switched to the locked position and the pressure in the brake master cylinder 11 can be subjected to a discount. According to the invention, it is characterized in that, in the first phase of the regulation, if the first wheel having a tendency to block is a front wheel 20, 21, the switching, in the blocked position, of the wheel valves 4 leading to the rear wheel brakes 22, 23 may be delayed by a predetermined time interval.

Description

i

  The present invention relates to a circuit arrangement which enables

  both to control the pressure reduction and intended to be used with

  an anti-lock braking system which, on the one hand, includes a master

  brake cylinder, to which the wheel brakes are connected by means of

  number of multi-way valves, which are open in the position of

  idle and which can be switched to the locked position, and a modula-

  braking pressure, mounted upstream of the brake master cylinder,

  and which, on the other hand, can be controlled by a multiple-process

  when, at the beginning of the antilock regulation, the multi-way valves leading to the wheel brakes can be switched to the locking position and the pressure prevailing in the brake master cylinder

  can be reduced.

  In known braking systems of this type, the modulator

  is an assembly operated by hydraulic pressure

  or depression, which serves both to amplify the braking force and to produce an auxiliary force exerted against the force applied on the pedal and likely, in case of control, to reduce the pressure in the working chambers of the master brake cylinder (DE-A 3,117,629, DE-A 3,641,0105 and DE-A 3,822 26U). Braking systems of this type are operated according to the multiplexing method, so that they need only one

  relatively small number of brake pressure control valves.

  In each pressure agent line leading from the master brake cylinder to one or both of the wheel brakes there is provided a multi-way valve which is open in the home position and can be switched to the locked position. At the beginning of the anti-lock control, all the valves leading to the wheel brakes are first switched to the locked position, then the braking pressure in the master cylinder is reduced and only the wheel valve which drives at the unstable wheel is reopened. As a result, the brake pressure in the wheel brake of the unstable wheel decreases, while in the other wheel brakes it remains constant. In the same way, it is then in a successive manner that the brake pressure in the other wheel brakes is modulated, that is to say reduced, kept constant or even

increased.

  When blocking the inlet valves during this phase

  initial phase of the regulation of blocking, a block which goes hand in hand with the devel-

  the development of the auxiliary force acting against the force applied on the pedal and, in some cases, with a blockage or disengagement of the pedal: (DE-A 3 822 260), it occurs, at least in the

  cases, an additional increase, or an excessive fluctuation

  sive, pressure prevailing in the master brake cylinder. This has a disadvantage, since the reduction in pressure in the wheel tending to lock, reduction which is necessary in this phase, is thus delayed, which is detrimental to the regulation or more precisely to

the quality of it.

  This is why the present invention aims to overcome this disadvantage, and this by using the additional means the

  more reduced possible and without causing other disadvantages.

  To this end, the object of the invention is an arrangement zircuit of the type mentioned above, characterized in that, in the first phase of the regulation, if the first wheel having a tendency to lock is a front wheel, the switching in the locked position, wheel valves leading to the rear wheel brakes can be delayed by an interval of

time fixed in advance.

  The invention is based on the observation that in most cases, especially in critical cases, the first wheel to become unstable is a front wheel. In such a situation, any

  further persistent, low and short-term increase in

  in the rear wheel brakes has no significant influence on the rolling stability of the wheels or is even advantageous for the braking operation. However, preventing the pressure from being the subject of a

  excessive fluctuation, and the particularly rapid reduction of pressure

  braking force in the unstable front wheel which can thus be achieved, lead to a noticeable improvement in regulation, given that

  now eliminated the risk that wheel slip becomes excessive.

  high under the effect of an excessively slow reduction in the pressure

braking pressure.

  According to an advantageous embodiment of the circuit arrangement of the invention, the time interval set in advance which can be delayed the response of the rear wheel valves is between 4 and milliseconds, preferably between 5 and 1U milliseconds. Advantageously, the duration of this time interval is adapted to the particular braking system considered, in particular to the brake pressure generator and to its idle time. It is empirically that the optimal value

is determined most simply.

  Other objects and advantages of the invention will emerge from the

  description which follows, by way of non-limiting example and with regard to

  attached drawing in which: Figure 1 schematically shows the essential components of a braking system of the type considered here and Figure 2 is a graph of the variation of the braking pressure during the initial phase of an anti-lock control . As shown in Figure 1, a braking system, for which

  the circuit arrangement according to the invention is provided, comprises a gen-

  brake pressure regulator 1, wheel valves 2 to 4, a modul-

  pressure control unit 5, wheel sensors S6 to 9 and a regula-

  electronic circuit 10 which includes the circuit arrangement of the invention.

  tion. The brake pressure generator 1 itself comprises a brake master cylinder 11 and a servo assembly 12 mounted in

  upstream of the latter and serving both as a brake force

  swimming and producing an auxiliary force H acting against the force F applied to the pedal. The braking force is applied by means of a pedal 13 on the brake pressure generator 1 and on the assembly

of servitude 12.

  In the embodiment of the invention described here, the assembly

  The servo link 12 corresponds to a large extent to an amplifier

  braking force of a conventional type. The chamber

  of this assembly 12 is divided by a piston 14 into two chambers 15

  and 16. In the position of rest of the braking system, as

  In both rooms there is a depression which is created in the working chamber by means of an "empty" connection and the

  modulating valve of pressure control 5. A valve 17, which is not

  schematically and that is open in the rest position of the brake, allows a vacuum prevails in the chamber 15 located on the side of the pedal. "Empty" symbolizes the connection of the braking system to the intake system of an Otto engine which serves here as an auxiliary power source

  for the amplification of the braking force and the modulation of the

braking pressure.

  The braking force amplified in the assembly 12 is transmitted, in a known manner, to the working pistons 18 and 19 of a master cylinder

  type of brake 11 and from the working chambers thereof

  ci, to the wheel brakes 20 to 23 via braking circuits

  I and II and valves 2 to 4 switched to the passage position.

  Information on the rotational behavior of the different vehicle wheels is obtained using wheel sensors.

  to 9 and they are sent, in the form of electrical signals, to the

  which generates corresponding regulation signals for

  nation of wheel valves 2 to 4 and control valve 5.

  The mode of operation of the braking system of the type described above is as follows: As long as there is no tendency to block, all

  valves retain their switching position shown in Figure 1.

  The servo assembly 12 serves as a brake force amplifier.

  If a blocking tendency is detected on a wheel, for example on the front left wheel VL, the anti-lock control starts. the

  At the beginning, the wheel valves 2 to 4 are all closed and the air pressure is

  It is admitted into the working chamber 16 by a switching of the pressure control valve modulator 5, which shows the auxiliary force H acting against the force F applied to the pedal. If the brake pressure generator 1 is provided with means for locking the pedal 13 or uncoupling the piston 14, it is at the same time, that is to say at the beginning of the anti-lock regulation, that this pedal 13 is blocked or uncoupled. Means of this type are known in the art and for this reason and to facilitate

  understanding, they are not represented here.

  Once the pressure prevailing in the master cylinder of

  fi2in 11 decreased to the level of pressure at the beginning of the

  the pressure of the brake pressure or below this level, the wheel valve 2 leading to the wheel which has begun to become unstable, in this case to the left front wheel VL, is switched to the passage position, so that the braking pressure in the wheel brake 20 can not decrease. Due to the presence of the wheel valves 3 and 4, the braking pressure in the other brakes 21 to 24 remains constant. Subsequently, the

  brake pressure in other wheels may be reduced

  tion, or a further increase, in an identical manner.

  Figure 2 shows the variation of the braking pressure

  PHZ in the brake master cylinder 11 during the regulation phase

  described above. At instant to, the braking operation begins. At time t1, a wheel, the left front wheel VL, becomes unstable, which causes the anti-lock control to begin. At this time t1, the pressure control modulating valve 5 is switched, which causes an increase in the pressure in the chamber 16. The wheel valve 2 leading to the left front wheel VL become unstable continues to be switched into position crossing "or is recommenced in crossing position

  immediately after the start of regulation). The wheel valve 3 driving

  at the second front wheel VL is reset to the locked position. In

  However, in accordance with the invention, the multi-flight valve 4 conducts

  rear wheels, is only reset when

  moment t2, that is to say after a delay of, for example, 5 to 10 milliseconds.

  onds. As a result, it is the pressure Pi prevailing at time tl which is "locked" in the wheel brake 21 of the right front wheel, while it is the brake pressure P2 slightly higher (o part of the if it is provided a brake pressure reducer) -which is "locked" in the brakes of the wheelsarriâre 22 and 23. As shown in Figure 2, after the start of the anti-lock regulation at the moment '1 , a reduction of the brake pressure in the wheel brake 20 of the wheel VL

  become unstable is reached relat-time quickly.

  Without the delay t = t2 - ti until the switching of the wheel valve 4 connected to the rear wheels hL and HR, it would have been obtained, for the pressure prevailing in the master brake cylinder 11 and therefore also in the

  2U wheel, the variation plot PHZ shown in

i ipu in Figure 2.

  The mixed pressure curve represents an increase

  brake pressure "unmodified". Indeed, a simul-

  Tanning of all the valves 2 to 4 in the rest position (at time t1) corresponds to a sudden cut-off of all the pressure agent consuming members which are connected to the brake pressure generator. Therefore, it is already slight variations in stroke of the brake pressure generator, which occur for example because of the inert masses, which lead to an increase in pressure or an excessive fluctuation of the pressure. Due to the disconnection of all the brakes from driving the regulation cycle would first start with an increase in pressure instead of the rapid pressure reduction sought at time t1 as a countermeasure against the tendency to block. In this critical phase of regulation, during which the quality obtainable for anti-lock regulation depends on the speed of pressure reduction, such an excessive increase in pressure would be a great disadvantage. A reduction of the brake pressure in the 2U wheel brake could start at the earliest

the moment t3.

  Therefore, in accordance with the invention, a significant improvement in antilocking control is obtained by means of an adjunction

  or very simple modification of the control circuit.

Claims (2)

  1. Cirucit arrangement for controlling the pressure reduction and for use with an anti-lock braking system which, on the one hand, comprises a brake master cylinder (11), to which the wheel brakes (20, 21 , 23) are connected via multi-way valves (2, 3, 4), which are open in the home position and can be switched to the locked position, and a brake pressure modulator (5). mounted on the upstream side of the brake master cylinder (11) and which, on the other hand, can be controlled by a multiplexing method, whereas at the beginning of the anti-lock control the valves (2, 3, 4) , to a plurality of tracks, leading to the wheel brakes (20, 21, 22, 23) can be switched to the locking position and the pressure prevailing in the   brake master cylinder (11) can be reduced,   rised in that, in the first phase of the regulation, if the first   a wheel with a tendency to lock is a front wheel (20, 21), the   in the locked position, the wheel valves (4) leading to the rear wheel brakes (22, 23) can be delayed by a period of time. set in advance (At).   Circuit arrangement according to Claim 1, characterized in that the time interval set in advance (/ At) is between 4   and 2U milliseconds, preferably between 5 and 10 milliseconds.