GB2134201A - Hydraulic anti-skid braking systems for vehicles - Google Patents

Abstract

An X-split anti-skid hydraulic braking system comprises first and second brake applying circuits of which each circuit comprises a supply of fluid under pressure (10, 11), and a modulator (12, 16) including first and second modulating means (12a, 12b; 16a, 16b) for modulating fluid from a supply to brakes on two different wheels (1 and 4, or 2 and 3) independently of each other and pump means for reapplying the brakes. A drive connection (15, 19) is provided between each modulator (12, 16) and a part of the transmission of the vehicle, a skid sensor (25, 26, 27, 28) senses the behaviour of each respective wheel (1, 2, 3, 4), and a control module (29) operates each modulating means (12a, 12b; 16a, 16b) in accordance with a skid signal from a sensor (25, 26, 27, 28) of a respective wheel. In Fig 1 individual front wheel drive shafts drive the modulator pumps and in Figs 2 and 3 the pumps are driven by belts or gears from a rear axle drive shaft. <IMAGE>

Description

SPECIFICATION Improvements in hydraulic anti-skid braking systems for vehicles This invention relates to hydraulic anti-skid braking systems for vehicles ofthe kind in which a supply of hydraulicfluid under pressure, for example from an hydraulic master cylinder, is adapted to be supplied to the actuatorofa wheel brake through a modulator which is adapted to modulate the pressure applied to the actuator in accordance with a skid signal from skid sensing means.

Known hydraulic anti-skid braking systems ofthe kind set forth normally include an hydraulic power system for re-applying the brake following the release of brake fluid upon skid correction. The power is required to make up the loss of energy as a consequence of having dumped fluid from the brake to affect brake release. The power may be provided by a pump driven by the prime mover ofthe vehicle or by a pump driven by an electric motor. When the pump is driven from the prime mover, the brake cannot be re-applied following correction of a skid if, in the mean time, the prime mover has stalled. Similarly, upon failure of the electric motor, the brake cannot be re-applied since the pump is unable to meterfluid back to the master cylinder as is required for brake re-application.

In our G.B. Patent Application No. 8230101 we have described an anti-skid system in which a pump for affecting brake re-application following correction of a skid can be driven from a wheel of a vehicle. Thus, energyfor re-applying the brake is always available when the vehicle is rolling in a forwards direction.

The system described in G.B. Patent Application No.

8230101 is concerned with controlling the braking effect in response to a signal from a wheel from which the pump is driven and it is not possible with that system to modulate independently the relative braking pressures applied to all fourwheels ofthe vehicle in accordance with skid signals from the individual wheels.

According to our invention in an anti-skid braking system for a four wheel vehicle having brakes on front and rearwheels, the system comprises first and second brake applying circuits, the first circuit comprising a supply offluid under pressure, a first modulator including first and second modulating means and pump means for modulating fluid fro the supplyto brakes on two different wheels independently of each other, the second circuit comprising a second supply offluid under pressure, a second modulator including third and fourth modulating means and pump means for modulating fluid from the second supply to brakes on the two remaining wheels independently of each other, a drive connection between each modulator and a partofthetransmis- sion ofthe vehicle for operating both pump means simultaneously, four skid sensors, each for providing a skid signal dependent upon the behaviour of a respective wheel, and a control module for operating each modulating means in accordance with a skid signal from a skid sensor for sensing the behaviour of a respective wheel.

By the use of two modulators driven from the transmission ofthevehiclewhich provides the energy for brake re-application following skid correction, we are able to control the behaviour of thefourwheels in accordance with the skid signals, and independently of each other.

When the vehicle is ofthe front wheel drive type each modulator may be driven from a respective front wheel. However, when the vehicle is of the rearwheel drive type both modulators are driven from the output shaft of the gear box.

Each modulator may control the brakes on one front wheel and a diagonally opposite rearwheel, in the case of an "X" split.

In such a layout each supply may comprise a different pressure space of a tandem master cylinder.

When the system has a fronfrearsplitone pressure space is connected to one modulating means of each modulator, and the other pressure space is connected to the other modulating means of each modulator.

In such a construction upon failure of one ofthe pressure spaces under normal braking conditions eitherthe front or rear brakes can still be applied.

However, upon failure of one ofthe modulators under anti-skid conditions, the system may act as an "X" split, although the control module may be operative to shutthe system down when such a condition is sensed.

Three embodiments of our invention are illustrated in the accompanying drawings in which: Figure lisa layout of an hydraulic anti-skid braking system for a four wheel vehicle; Figure 2 is a layout similarto Figure 1 but showing a modification; and Figure 3 is a layout similarto Figure 2 but showing a modification.

The braking system illustrated in the layout of Figure 1 comprises two separate hydraulic brakeapplying circuits for a vehicle of a front wheel drive type having two front wheels 1,2 and two rear wheels 3,4.

The wheels 1 and 2 are adapted to be braked by respective brakes 5 and 6, and the wheels 3 and 4 by respective brakes 7 and 8.

A pedal-operated master cylinder 9 has two pressurespacesl0andll.Thepressurespacel0is connected to a brake-pressure modulator 12 through a pipe-line 13. The modulator 12 is driven by a shaft 14, which, in turn, is driven through a drive 1 5 from the front wheel 1. The pressure space 11 is connected to a brake-pressure modulator 16th rough a pipe-line 17.

The modulator 16 is driven by a shaft 18 which, in turn, is driven through a drive 19from the wheel 2. Each modulator 12,16 is conveniently ofthetwin kind forming the subject of our G.B. PatentApplication No.

8302460 of even date and need not be further described herein exceptto explain that each modulator 12,16 incorporates two separate modulating means and pump means 1 2a, 1 2b; 16a, 16b respec tivelyfor modulating the pressure from a respective pressure space to the brake on one front wheel and to the brake on a diagonally opposite rear wheel respectively. As illustrated the two modulating means ofthe modulator 12 are connected to the brake 5 and the brake 8 through separate pipe-lines 30 and 31, and thetwo modulating meansofthe modulator 16 are connected to the brake 6 and the brake 7 through separate pipe-lines 32 and 33.

A brake-pressure apportioning valve may be positioned in the pipe-line 31 between the modulator 12 and the brake 8, and a brake-pressure apportioning valve may be positioned in the pipe-line 33 between the modulator 16 and the brake 7.

The behaviour of each wheel 1,2,3,4, namely deceleration and/or slip is sensed by respective sensors 25,26,27,28 which emit skid signals, and the skid signals are supplied to an electronic control module 29 which, in turn, is operative to emit an electric current to operate the solenoid-operated dump valve of one ofthe modulating means in order to relieve the pressure of fluid supplied to the respective brake.

Should the apportioning valves be omitted, then the rearwheel brakes must be taken-off at lower thresholds, with the brake-applying pressure relieved at relatively lower pressures.

The control module 29 is ofthefour-channel type and is adapted to operate a respective modulating means to relieve the pressure applied to brake in response to a skid signal from asensoron a corresponding wheel.

If a vehicle is aqua-planing at high speed on a very wet surfacethe further re-application of a brake on a rear wheel will be delayed until the respective front wheel 1 or 2 has passed onto a good surface so that rotation of the front wheel 1 or 2, and consequent rotation ofthe respective shaft 14or 18, can start again.

The control module 29 is arranged to shut down the anti-skid system in the event of failure of a drive 15 or 19 to one ofthe modulators. This is achieved by arranging for the sensors 25 and 26 to sense the rotation ofthe shafts 14 or 18, rather than the direct behaviourofthe wheels 1 and 2. Upon failure of one of the drives 15 or 19, the respective sensor, say the sensor 25, will emit a skid signal which is monitored by the control module 29. When the difference between that signal and any signal emitted bythe sensor 26 has lasted for a predetermined interval the control module 29 will shut down the system, and may be adapted to actuate a warning device.

In the layout of Figure 2 for a rearwheel drive vehicle the modulators 12 and 16 are driven from the output shaft ofthe gear box 40through belts 41 and 42. Thus the modulators 12 and 16 are both driven at substantially constant speeds.

The construction and operation of the system of Figure 2 is otherwise the same as Figure 1 and corresponding reference numerals have been applied to corresponding parts.

In this construction failure of one ofthe belts 41 or42 is sensed bythe control module 29 which may be operable immediately to shut down the system and actuate the warning device.

In this construction the sensors 27 and 28 sense the mean of speed of the rear wheels 3 and 4 since both rearwheels 3 and 4 are driven from the same output shaft.

In a modification, the modulators 12 and 16 can be driven from the differential forthe back axle. This is not preferred due to the increased number of and substantial length ofpipeswhich would be required.

In the layout of Figure 3 the two modulators 12 and 16 are driven from the output shaft 49 from the gearbox 40 through drive gearing 50.

The system has a front/rear split so thatthe pressure space 10 is connected to corresponding modulating means 12a, 16a of both modulators 12 and through the pipe-line 13 and thesetwo modulating means 1 2a, 1 6a are in turn connected through pipe-lines 51 and 52 to the brakes 5 and 6 respectively ofthe front wheels.

The pressure space 11 is connected to corresponding modulating means 12b, 16bofboth modulators 12 and 1 6through the pipe-line 17, and these modulators are connected through the pipe-lines 31 and 33 to the brakes 8 and 7 ofthe diagonally opposite rearwheels 4 and 3 respectively.

In the event offailure of one ofthe pressure spaces during normal braking the brakes on eitherthefront or rear pair of wheels can still be applied from the remaining, still operative, pressure space.

Should one ofthe modulators 12 or 16 fail then the system acts as an "X" split with the remaining modulatoroperativeto operate the brake on one front wheel, and the brake on the diagonally opposite rear wheel.

Failure of a modulator is more likelyto occurwhen the modulator is driven by a belt as in the construction of Figure 2 when the belt snaps. In such a situation of differential between the signals sensed by the sensors 27 and 28 will be recognised by the control module 29 which maythen shut down the system and actuate a warning device to indicate to the driverthat failure has occurred.

The construction and operation ofthe system of Figure 3 is otherwise the same as that of Figure 2 and corresponding reference numerals have been applied to corresponding parts.

Claims (10)

1. An anti-skid braking system forafourwheel vehicle having brakes on front and rearwheels, in which the system comprises first and second brake applying circuits, the first circuit comprising a supply offluid under pressure, a first modulator including first and second modulating means and pump means for modulating fluid from the supply to brakes on two different wheels independently of each other, the second circuitcomprising a second supply of fluid under pressure, a second modulator including third and fourth modulating means and pump means for modulating fluid from the second supply to brakes on the two remaining wheels independently of each other, a drive connection between each modulator and a part of the transmission of the vehicle for operating both pump means simultaneously, fourskid sensors, each for providing a skid signal dependent upon the behaviourofa respective wheel, and a control moduleforoperating each modulating means in accordance with a skid signal from a skid sensorfor sensing the behaviour of a respective wheel.

2. Asystem as claimed in claim 1, in which the vehicle is ofthe front wheel drive type, and each modulator is driven from a respective front wheel.

3. A system as claimed in claim 1, in which the vehicle is ofthe rear wheel drivetype, and both modulators are driven from the output shaft of the gear box.

4. A system as claimed in any preceding claim, in which each modulator is adapted to control the brakes on onefrontwheel and a diagonally opposite rear wheel

5. A system as claimed in any preceding claim, in which each supply comprises a different pressure space of a tandem master cylinder.

6. A system as claimed in claim 5, in which one pressure space is connected to one modulating means of each modulator, and the other pressure space is connected to the other modulating means of each modulaton

7. A system as claimed in any preceding claim in which each modulator is of the twin type forming the subject of our G.B. Patent Application No. 8302460.

8. An hydraulic anti-skid braking system for a four wheel vehicle substantially as described herein with reference to and as illustrated in Figure 1 ofthe accompanying drawings.

9. An hydraulic anti-skid braking system for a four wheel vehicle substantially as described herein with reference to and as illustrated in Figure 2 ofthe accompanying drawings.

10. An hydraulic anti-skid braking system for a four wheel vehicle substantially as described herein with reference to and as illustrated in Figure3 of the accompanying drawings.