GB2345107A

GB2345107A - Motor vehicle hydraulic braking systems

Info

Publication number: GB2345107A
Application number: GB0006511A
Authority: GB
Inventors: Christopher Garth Williams
Original assignee: Dura Automotive Ltd
Current assignee: Dura Automotive Ltd
Priority date: 2000-03-18
Filing date: 2000-03-18
Publication date: 2000-06-28
Anticipated expiration: 2020-03-18
Also published as: GB2345107B; GB0006511D0

Abstract

A hydraulic braking system for a motor vehicle permits complete pedal depression to take place following a front-end impact, thereby increasing the available space in the foot well of the driving cockpit so as to reduce the risk of driver injury. At the same time braking effort is continued, either at a constant level or under computer control such as ABS control. To achieve this, an impact sensor 30 actuates an isolation valve means 26 which diverts the pressure in the brake master cylinder 10 to drain while isolating the or each hydraulic braking circuit 22,32,34,12,14 or 24,16,18 from the reducing hydraulic pressure in the master cylinder 10. The impact sensor may also activate an air bag.

Description

TITLE Motor Vehicle Hydraulic Braking Systems DESCRIPTION Field of the Invention The invention relates to motor vehicle hydraulic braking systems, and in particular to systems for enhancing driver, and passenger safety in the event of a vehicle frontal impact.

Background Art Brake pedal boxes have been proposed which collapse on application of an excessive load such as that applied by the forward momentum of a driver when the vehicle is in a front-end collision. A collapse of the brake pedal box in such a situation permits it to move forward and away from the driver's feet, providing important extra leg-room to reduce the risk of the driver's feet becoming trapped in the accident. Even a few centimetres of extra leg-room in such circumstances can be a significant safety advantage.

The collapse of a pedal box in such circumstances has always been accompanied by a loss of brake pressure in the hydraulic braking system, as the brake pedal and pedal box move together forwardly and away from the pressure of the driver's foot. The result is that the vehicle brakes are released or partially released after an impact. This invention is based on the observation that such brake release can seriously increase the chance of driver and passenger injury if the first front-end impact is followed by a subsequent rear-end impact, which can propel the unbraked vehicle forward and thus generate a second front-end impact.

It is an object of the invention to provide a hydraulic braking system which enhances the safety of the driver and passengers in a frontal impact road accident.

The Invention The invention provides a hydraulic braking system for a motor vehicle, comprising a pedal-operated master cylinder for controlling the hydraulic braking pressure in one or more hydraulic braking circuits, characterized in that isolation valve means are provided between the master cylinder and the or each hydraulic braking circuit and are actuable in response to triggering of an impact sensor by a front-end collision of the vehicle, and when so actuated have the effect of diverting to drain the hydraulic pressure in the master cylinder while isolating the or each hydraulic braking circuit from the reducing hydraulic pressure in the master cylinder.

In its simplest form, the isolation valve means is no more than a spool valve which on actuation simultaneously isolates the master cylinder from the hydraulic braking circuits and dumps to drain the hydraulic pressure generated in the master cylinder. When the master cylinder controls dual or multiple hydraulic braking circuits then either a single spool valve can be provided, serving all hydraulic braking circuits simultaneously, or one spool valve can be provided per hydraulic braking circuit. In the latter case all spool valves are preferably actuated by the same single impactor sensor.

The impact sensor may be the same general type as that used for triggering air-bag inflation in a road accident, but dedicated to actuating the spool valve or valves. The impact sensor may even be the same sensor that is used for triggering air-bag inflation, so that'when the sensor senses an impact it simultaneously causes inflation of the vehicle's air-bag and actuation of the isolation valve means.

Many vehicles provided with driver and/or passenger air-bags are provided with dual or multiple impact sensors. For example impact sensors may be provided in the passenger cabin and in the two front wing areas of the vehicle, so that triggering of any one of those three sensors is sufficient to inflate the air-bags. In an entirely analogous way there may be dual or multiple impact sensors for actuating the isolation valve means in the braking system of the invention. Or the existing set of sensors may serve both the air-bag actuators and the isolation valve means. Actuation of any one of the impact sensors is sufficient to actuate the isolation valve means, thereby providing fail-safe protection.

The dumping of the hydraulic pressure in the master cylinder to drain may be a rapid pressure dump, resulting in a rapid reduction in the hydraulic pressure in the or each working chamber of the master cylinder, or it may be a gradual or throttled pressure dump, resulting in a controlled pressure reduction. In either case, the reduction in the master cylinder pressure permits pedal movement in the brake-applying direction, without that pedal movement being responsible for any change in the hydraulic braking pressure in the hydraulic brake circuit or circuits. One possible reason for controlling or throttling the pressure dump would be to avoid too sudden a movement of the brake pedal after a front-end impact, which may itself cause driver injury as the driver's foot follows the moving pedal.

The invention also preferably provides means, effective after the above isolation of the or each hydraulic brake circuit from the master cylinder, for controlling the pressure in the hydraulic brake circuit or circuits. For example, the brake pressure may be maintained at the pressure that existed in the hydraulic brake circuits at the time of the front-end impact, or it may be driven to a predetermined maximum braking pressure by connecting each brake circuit to a high pressure source. Or it may be driven in a predetermined and desirable pressure variation cycle, such as rising rapidly to a maximum braking pressure followed by a controlled rate of release. If té vehicle is provided with ABS braking (Antiskid Brake System) then advantageously the control of the hydraulic brake pressure after a front-end impact is handed over to the ABS pressure modulator, so as to achieve maximum braking effect without causing the vehicle to skid.

The response time of the isolation valve means is crucial to the viability of the system. Preferably the response time should be better than 60 milliseconds. A solenoid-actuated isolating valve with a linear or rotary valve spool is capable of response times of better than 20 milliseconds, which is well within the target range.

Drawings Figure 1 is a schematic circuit diagram of a hydraulic braking circuit according to the invention; and Figure 2 is a schematic diagram of an isolating valve for use in the circuit of Figure 1.

In the braking system illustrated in the drawings, a tandem master cylinder 10 controls the braking pressure at four vehicle wheels 12,14,16 and 18. The master cylinder 10 is operated by a pedal 20 and generates hydraulic braking pressure at two output ports 22 and 24.

One output port 22 serves vehicle front wheels 12 and 14, whereas the other output port serves the vehicle rear wheels 16 and 18. Between the output ports 22 and 24 and the vehicle wheels 12,14,16 and 18 there are provided, in series, an isolating valve means 26 and an antiskid brake control (ABS) unit 28. An impact sensor 30 is electrically connected to the isolating valve means 26.

In use, depression of the brake pedal 20 causes generation of a hydraulic braking pressure in the master cylinder 10 which is transmitted through parallel brake lines to the isolation valve means 26, the ABS control unit 28 to the vehicle brakes 12 to 18. Consider the front wheel brake circuit. Fluid at the master cylinder output port 22 passes into the isolation valve means 26 at an input port 32 and out through an output port 34. The isolation valve means 26 may comprise a pair of solenoid-actuated spool valves as illustrated in Figure 2. In the non-actuated condition, fluid flows from the input port 32 to the output port 34 without interruption, and there is no fluid supply to a drain port 36. When the solenoid is actuated, however, the input fluid is discharged through the drain port 36 and the output port 34 is isolated. The sensing at 30 of a vehicle front-end impact is sufficient to trigger the actuation of the solenoid valve (s) 26', which after actuation are held in the actuated condition.

The discharge of master cylinder brake fluid to drain causes the brake pedal to move without effort or with only limited'damping'control to a fully depressed condition.

That creates valuable additional space in the vehicle driver's foot well, reducing the potential for driver injury as a result of the impact.

The braking pressure at the vehicle wheels 12 and 14 is not lost on actuation of the spool valve 26', because the dumping of master cylinder output pressure to drain is accompanied by the simultaneous isolation of the brake circuits from the master cylinder. The ABS control has the potential to increase or decrease the braking pressure at the wheel cylinders, and controls the braking pressure in a manner to minimize the risk of the vehicle skidding after the impact. That is particularly important if the vehicle is thrown free of the collision'area at a later phase of the crash.

Claims

CLAIMS 1. A hydraulic braking system for a motor vehicle comprising a pedal-operated master cylinder for controlling the hydraulic braking pressure in one or more hydraulic braking circuits, characterized in that isolation valve means are provided between the master cylinder and the or each hydraulic braking circuit and are actuable in response to triggering of an impact sensor by a front-end collision of the vehicle, and when so actuated have the effect of diverting to drain the hydraulic pressure in the master cylinder while isolating the or each hydraulic braking circuit from the reducing hydraulic pressure in the master cylinder.

2. A braking system according to claim 1, wherein the master cylinder controls the hydraulic braking pressure in dual or multiple braking circuits, and the isolation valve means comprises a single spool valve serving all hydraulic braking circuits simultaneously.

3. A braking system according to claim 1, wherein the master cylinder controls the hydraulic braking pressure in dual or multiple braking circuits, and the isolation valve means comprises a separate spool valve for each hydraulic braking circuit, and means for actuating all the spool valves simultaneously.

4. A braking system according to any preceding claim, further comprising means for controlling or throttling the dumping to drain of the pressure in the master cylinder on actuation of the isolating valve means.

5. A braking system according to any preceding claim, further comprising means for controlling the hydraulic pressure in the or each hydraulic braking circuit after actuation of the isolating valve means.

6. A braking system according to claim 5, wherein the pressure controlling means comprises means for maintaining the hydraulic pressure in the or each hydraulic braking circuit at the pressure which existed at the time of actuation of the isolation valve means.

7. A braking system according to claim 5, wherein the pressure controlling means comprises means for driving the hydraulic pressure in the or each hydraulic braking circuit to a predetermined maximum braking pressure.

8. A braking system according to claim 5, wherein the pressure controlling means comprises means for driving the hydraulic pressure in the or each hydraulic braking circuit through a predetermined pressure variation cycle.

9. A braking system according to claim 5, wherein the pressure controlling means is an anti-skid braking system.

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

Amendments to the claims have been fled as follows CLAIMS 1. A hydraulic braking system for a motor vehicle which incorporates at least one impact sensor, which braking system comprises a pedal-operated master cylinder for controlling the hydraulic braking pressure in one or more hydraulic braking circuits, and isolation valve means provided between the master cylinder and the or each hydraulic braking circuit, the isolation valve means being actuable in response to triggering of the impact sensor or one of the impact sensor of the vehicle by a front-end collision of the vehicle, and when so actuated have the effect of diverting to drain the hydraulic pressure in the master cylinder while isolating the or each hydraulic braking circuit from the reducing hydraulic pressure in the master cylinder.
2. A hydraulic braking system for a motor vehicle comprising a pedal-operated master cylinder for controlling the hydraulic braking pressure in one or more hydraulic braking circuits, one or more impact sensors for sensing a front end collision of the vehicle, and isolation valve means between the master cylinder and the or each hydraulic braking circuit, the isolation valve means being actuable in response to triggering of the impact sensor or one of the impact sensors by a front-end collision of the vehicle, and when so actuated have the effect of diverting to drain the hydraulic pressure in the master cylinder while isolating the or each hydraulic braking circuit from the reducing hydraulic pressure in the master cylinder.
3. A braking system according to claim 1 or claim 2, wherein the master cylinder controls the hydraulic braking pressure in dual or multiple braking circuits, and the isolation valve means comprises a single spool valve serving all hydraulic braking circuits simultaneously.
4. A braking system according to claim 1 or claim 2, wherein the master cylinder controls the hydraulic braking pressure in dual or multiple braking circuits, and the isolation valve means comprises a separate spool valve for each hydraulic braking circuit, and means for actuating all the spool valves simultaneously.
5. A braking system according to any preceding claim, further comprising means for controlling or throttling the dumping to drain of the pressure in the master cylinder on actuation of the isolating valve means.
6. A braking system according to any preceding claim, further comprising means for controlling the hydraulic pressure in the or each hydraulic braking circuit after actuation of the isolating valve means.
7. A braking system according to claim 6, wherein the pressure controlling means comprises means for maintaining the hydraulic pressure in the or each hydraulic braking circuit at the pressure which existed at the time of actuation of the isolation valve means.
8. A braking system according to claim 6, wherein the pressure controlling means comprises means for driving the hydraulic pressure in the or each hydraulic braking circuit to a predetermined maximum braking pressure.
9. A braking system according to claim 6, wherein the pressure controlling means comprises means for driving the hydraulic pressure in the or each hydraulic braking circuit through a predetermined pressure variation cycle.
10. A braking system according to claim 6, wherein the pressure controlling means is an anti-skid braking system.
11. A hydraulic braking system substantially as described herein with reference to the drawings.