GB2318621A

GB2318621A - Hydraulic braking systems

Info

Publication number: GB2318621A
Application number: GB9720424A
Authority: GB
Inventors: Matthew John Nightingale; Stephen Philip Wise
Original assignee: WILLIAMS GRAND PRIX ENG
Current assignee: WILLIAMS GRAND PRIX ENG
Priority date: 1993-12-14
Filing date: 1993-12-14
Publication date: 1998-04-29
Anticipated expiration: 2013-12-14
Also published as: GB2318621B; GB9720424D0; GB2284871A; GB2284871B; GB9325495D0

Abstract

A vehicle hydraulic braking system includes electromagnetically operated servo valve(s) 23 in the line(s) connecting a pump P to pressure transmitter(s) for pressurising the slave cylinders of the brakes 20 of the individual wheels of the vehicle. A pressure sensor 27 transmits a braking demand signal, representing the pressure generated in the master cylinder by the driver, to a computer 31 which, in response to signals from pressure sensors 27 and 29, controls the servo valve(s) 23 to determine the braking pressure(s) to be applied to the pressure transmitter(s). The pressurised fluid from the pump P may be different from that in the master cylinder. Isolation valve 10 adopts the illustrated condition on starting the engine or on the driver closing switch C. Electrical failure results in the brakes being operated manually.

Description

HYDRAULIC BRAKING SYSTEMS The present invention relates to hydraulic braking systems, for example for vehicles, of the kind comprising at least one hydraulic master actuator for generating therein a hydraulic pressure proportional to a force exerted on the master actuator by an operator of the system, at least one slave actuator for applying a brake and conduit means hydraulically connecting the or each master actuator to the slave actuator or actuators to be operated thereby.

This application is a divisional application from UK Patent Application No.9325495.1 (publication No. GB 2,284,871).

According to the present invention, there is provided a hydraulic braking system as set out in claim 1 to which reference should now be made.

Preferably, the brake pressure control means comprises a slave pressure sensor for each slave actuator or interconnected group of slave actuators and a computer connected to receive the signals output by the master and slave sensors and arranged to compute and output control signals to valve means for controlling the brake operating pressure or pressures.

Particularly where the fluid in the said source of fluid under pressure differs from the brake fluid in the master and slave actuators, the brake control means includes, for each slave actuator group of interconnected slave actuators, a pressure transmitter, the movable element within which has opposing surfaces in contact respectively with the fluid from the source of fluid under pressure and with the brake fluid, communication between the supply of pressure under fluid and the pressure transmitter being controlled by an electrically operated valve under the control of the computer.

Such a system is particularly suitable for incorporating anti-lock features and/or anti-wheelspin "traction control" features. In such anti-lock braking systems ("ABS") or traction control systems, each braked wheel, or differential unit interconnecting a pair of wheels has a speed sensor connected to the computer which analyses each speed signal for excessive deceleration in the case of an ABS system (or excessive acceleration in the case of traction control) and instructs an appropriate reduction or increase in braking pressure in the respective slave actuator.

For this purpose, the movable element in the or each pressure transmitter has an additional surface bounding a space communicating with the conduit leading to the master actuator.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: FIGURE 1 is a schematic diagram of a vehicle braking system, and FIGURE 2 is a flow chart of one cycle of the operations carried out by the computer of the system shown in figure 1 to prevent locking of a wheel during braking.

The simplified braking system shown in figure 1 has a conventional hydraulic brake master cylinder 1, the piston 2 of which carried a cup washer 3 and has a piston rod 4 connected to a conventional brake pedal 5. In the "off" position of the piston 2 and brake pedal 5, a reservoir 6 communicates with the space 7 within the cylinder 1 in which is closed off by the piston 2 at a location 8 just ahead of the cup washer 8.

A conduit 9 connects a space 7 within the master cylinder 1 to a solenoid operated two-position valve 10 which in the deenergised state connects the conduit 9 to a further conduit 11. In its energised state, the valve 10 closes off the conduit 9 and connects the conduit 11 to the reservoir 6 through a conduit 12.

The conduit 11 is connected to a port 13 of a pressure transmitter 14 in the form of a cylinder having a spool type valve member 15 slidable therein. One end of the pressure transmitter 14, the right hand end as seen in figure 1, is of similar construction to the master cylinder in that the spool valve member 15 carries a cup washer 16 immediately adjacent which is a return line 17 to the reservoir 6 in the "off" position of the spool valve member 15. The space 18 between the cup washer 16 and the end of the cylinder of the pressure transmitter 14 is connected by a pipe 19 to a disk brake calliper 20 acting on a brake disc 21.

When the solenoid valve 10 is in its closed position isolating the conduit 11 from the master cylinder 1, braking is effected by applying fluid pressure to the left hand end 22 of the pressure transmitter spool 15. This fluid under pressure is obtained from a source comprising a pump P driven by the engine or transmission of the vehicle which draws oil from a sump S and supplies it to an electromagnetically operated valve 23 which controls the pressure applied to the spool 15. For this purpose, the valve 23 is a servo valve for supplying oil from the pump P or returning it to the sump S at a flow rate proportional to electrical current supplied to it by a computer 24. Such valves are available from Moog Controls Limited, Ashchurch, Tewkesbury, Gloucestershire.

A braking demand signal is generated by a pressure sensor 27 which sends a signal representative of the pressure within the master cylinder space 7 along a line 28 to the computer. Further pressure sensors 29 generate signals representing the pressures in the spaces 18 and pipe work 19, the signals being transmitted to the computer along respective lines 30. The computer sends control current signals to the valves 23 along lines 31.

To provide the system with ABS capability, each wheel of the vehicle has a speed sensor, for example of the kind having a rotating part 33 connected to the brake disc 21 and a stationary pick up 34 connected by a line 35 to the computer.

In operation, the system shown in Figure 1 is activated either when the driver starts the engine of the vehicle or when he operates a control switch C. The solenoid of the valve 10 is then energised, thereby isolating the master cylinder space 7 from the remainder of the braking circuits.

Whenever the driver's foot presses on the brake pedal 5 the brake fluid within the space 7 will prevent any substantial movement of the piston 2. The signal from the pressure sensor 27 provides a direct representation of the force exerted by the driver on the pedal 5 and thus the intensity of braking which he intends to achieve. Thus, with the system enabled, the computer is supplied continuously with data representing the demand pressure required by the driver.

The computer differentiates the signal from the wheel sensor 34 three times with respect to time so as to produce data representing the angular speed of the wheel, the deceleration or acceleration of the wheel and the rate and sense of change of such deceleration or acceleration. On the basis of this information, the computer carries out the steps shown in Figure 2 for each wheel I in turn. In step 41, the deceleration of the wheel is assessed, for example by comparison with the deceleration of the other wheels. If the deceleration is acceptable, the wheel speed itself is assessed in step 42 and if the wheel speed is not to low, the computer instructs the servo valve 23 to achieve a brake calliper pressure equal to the demand pressure generated by the driver in the master cylinder space 7 (Steps 43 and 44). This series of steps then repeated in turn for the other wheels (Steps 45, 46). If, however, for any wheel the computer determines in Step. 41 that the wheel deceleration is to high, the computer determines in Step 47 whether or not the wheel deceleration is increasing. If it is not increasing, the wheel will not lock and the target pressure can accordingly still equal the demand pressure. If, however, the wheel deceleration is increasing or if in Step 42 the wheel speed is found to be slow even though the wheel deceleration is not too high, the computer in Step 48 calculates the excess pressure, that is the amount by which the pressure in the brake pipes 19 must be reduced to stop the tendency of the wheel to lock. In Step 49 a revised target pressure is calculated by subtracting the excess pressure determined in Step 48 from the demand pressure and in Step 50 the necessary instruction is given so that in Step 44 the servo valve 23 is instructed to reduce the pressure in the pressure transmitter 14 and the brake pipe 19 associated with the wheel in question. Similarly, in the case of traction control, where excessive acceleration or excessive wheel speed are sensed in steps similar to Steps 41 and 42, the servo valve 23 can be instructed to apply pressure through the pressure transmitter 14 to apply the brake associated with a wheel which is slipping.

During the operation of the ABS system in preventing a wheel from locking, there is no change of pressure in the space 7 or line 9 and no movement of the brake pedal 5 which could otherwise cause the driver inadvertently to change the demand pressure.

In the event of electrical failure or the driver deciding that there is a fault in the electronic control system and deciding to de-energise the latter, the solenoid valve 10 places the conduit 9 in communication with conduit 11 so that the pressure generated by the driver in space 7 is applied to an annular space 51 in each pressure transmitter, this space being defined between a land 52 on the valve spool 15 and a reduced bore portion 53 of the pressure transmitter casing. The land 52 and bore portion 53 each have sliding seals 54, 55 compatible with the brake fluid. The pressure in the space 21 urges the spool 15 to the right in Figure 1 to apply brakes.

Where the source of fluid under pressure supplied by the pump P supplies a different fluid from that used as brake fluid, an additional seal 56 is provided in the bore 53.

Claims

CLAIMS:

1. A hydraulic braking system comprising at least one hydraulic master actuator for generating therein a hydraulic pressure proportional to a force exerted on the or each master actuator by an operator of the system, at least one slave actuator for applying a brake and conduit means hydraulically connecting the or each master actuator to the slave actuator or actuators to be operated thereby, the hydraulic braking system including valve means in the conduit means operable to isolate the or each master actuator from its associated slave actuator or actuators, master actuator pressure sensor means for generating a signal representing the pressure obtaining at any instant in the master actuator or actuators, a source of fluid under pressure, and brake pressure control means responsive to the signal from the master actuator pressure sensor means to apply to the or each slave actuator an appropriate brake operating pressure generated by fluid under pressure from the said source thereof, wherein the brake pressure control means comprises a servo valve for supplying fluid from the said source at a flow rate proportional to the signal from the master actuator pressure sensor means.

2. A hydraulic braking system according to claim 1 wherein the fluid in the said source of fluid under pressure differs from the brake fluid in the master and slave actuators, the brake control means includes, for each slave actuator, or group of interconnected slave actuators, a pressure transmitter which separates the brake fluid in the master actuator or actuators, brake fluid in the slave actuator or actuators, and fluid in the said source of fluid under pressure from each other, and conduit means hydraulically connecting the or each master actuator to the pressure transmitter or transmitters to be operated thereby, and including isolation valve means in the conduit means operable to isolate the or each master actuator from its associated pressure transmitter or transmitters, and corresponding slave actuator or actuators.

3. A hydraulic braking system according to claim 1 or claim 2 wherein the brake pressure control means comprises a slave pressure sensor for each slave actuator or interconnected group of slave actuators and a computer connected to receive the signals output by the master and slave sensors and arranged to compute and output control signals to valve means for controlling the brake operating pressure or pressures.

4. A hydraulic braking system according to any preceding claim, wherein the pressure transmitter includes a movable elemnet which has opposing surfaces in contact respectively with the fluid from the source of fluid under pressure and with the brake fluid.

5. A hydraulic braking system according to claim 4, wherein the movable element in the or each pressure transmitter has an additional surface bounding a space communicating with the conduit means leading to the master actuator via the valve means.

6. A vehicle having a braking system according to any of the preceding claims, in which each braked wheel, or differential unit interconnecting a pair of wheels has a speed sensor connected to the computer which analyses each speed signal for excessive deceleration in the case of an ABS system and/or excessive acceleration in the case of traction control and instructs an appropriate reduction or increase in braking pressure in the respective slave actuator.

7. A vehicle according to claim 6, wherein the computer is arranged also to be responsive to the wheel speed when the acceleration or deceleration is not excessive.

8. A hydraulic braking system substantially as described with reference to the drawings.

Amendments to the claims have been filed as follows Claims 1. A hydraulic braking system comprising a hydraulic master actuator for generating therein a hydraulic pressure proportional to a force exerted on the master actuator by an operator of the system, a slave actuator for applying a brake and tconduit means hydraulically connecting the master actuator to the slave actuator to be operated thereby, including isolation valve means in the conduit means operable to isolate the master actuator from its associated slave actuator, master actuator pressure sensor means for generating a signal representing the pressure obtaining at any instant in the master actuator, a pump for;supplying fluid under pressure, and brake pressure control means responsive to the signal from the master actuator pressure sensor to apply to the slave actuator an appropriate brake operating pressure generated by fluid under pressure from the said pump, wherein the brake pressure control means comprises an electromagnetically operable servo valve for supplying fluid from the pump, or returning fluid to a sump, at a flow rate proportional to the electrical current supplied to it by a computer.

2. A hydraulic braking system according to claim 1 wherein the fluid supplied from said pump differs from the brake fluid in the master and slave actuators, the brake pressure control means includes a pressure transmitter which separates the brake fluid in the master actuator, brake fluid in the slave actuator, and fluid supplied from said pump from each other, the conduit means hydraulically connecting the master actuator to the pressure transmitter to be operated thereby, anc . Sc includingAisolation valve means in the conduit means operable to isolate the master actuator from its associated pressure transmitter, and corresponding slave actuator.

3. A hydraulic braking system according to claim 1 or claim 2 wherein the brake pressure control means comprises a slave actuator pressure sensor and the computer is connected to receive the signals output by the master and slave sensors and arranged to compute and output control signals to the servo valve for controlling the brake operating pressure.

4. A hydraulic braking system according to claim 2, wherein the pressure transmitter includes a movable element which has opposing surfaces in contact respectively with the fluid supplied from the pump and with the brake fluid in the slave actuator.

5. A hydraulic braking system according to claim 4, wherein the movable element in the pressure transmitter has an additional surface bounding a space communicating with the conduit means leading to the master actuator via the isolation valve means.

d < ontla' unlt lnterc^nnsstlng a pair of xthools hac a sFood sensor co ed to the computer which analyses each speed signal for excessive de ation in the case of an ABS system and/or excessive acceleration in t se of traction control and instructs an appropriate reduction or re in braking precEurc in tho respective sla=e a-tuator. ~ 7. A vehicle according to claim 6, wherein the computer is arranged also to be responsive to the wheel speed when the acceleration or deceleration is not excessive.