GB2263954A - A valve for cadence braking - Google Patents

Abstract

A valve 10 for cadence braking comprises an inlet 16 connected to an engine vacuum, an outlet 25 connected to a brake servo unit in a vacuum servo-assisted brake system, a housing portion 11, two end caps 12, 13, a spool 14 spring biassed to its illustrated position, and an end plate 15. The end plate 15 incorporates a control tract 28 connecting spaces 19 and 37, and in operation generation of a vacuum in space 19 and in the servo unit will result in a gradual reduction of pressure in space 37 until the spool moves against its spring bias to open spaces 19 and 37 (and its servo unit) to atmosphere via openings 35. When the spaces 19 and 37 are at atmospheric pressure the spool will return to its illustrated position to recommence the cycle. Thus, when the brakes are applied the valve will produce a "pumping" action in the brakes. When there is insufficient vacuum, spring biassed ball 33 blocks tract 28 and prevents the valve operating. The valve may only be operated when the brakes are applied e.g. by utilizing a 'G' switch and/or a solenoid activated by the brake light circuit to open the control tract 28. Also the 'G' switch may only cause the tract to open on harsh braking. <IMAGE>

Description

Valve Devices This invention relates to valve devices for use in servo-assisted brake systems.

One of the systems added to top of the range motor cars as a safety selling feature is anti-lock brakes. These systems are typically complex and expensive, usually interrupting the hydraulic action of the braking circuit. This precludes them as options on smaller or lower specification models. The complexity of the systems also restricts or prevents them being fitted to existing vehicles.

As a result a massive percentage of car owners are not able to achieve the most efficient braking performance from their vehicle especially in an emergency situation.

Skilled drivers are able to reduce the speed of their vehicles quickly, safely and retaining full steering control by using a technique known as cadence braking. This requires the brake pedal to be fully applied, momentarily released and then fully applied in quick succession. This 'pumping' action prevents the wheels from locking which is also the effect of an anti-lock braking system. However, it is a very difficult technique to use, because releasing the pressure on the brake pedal when you want to stop quickly is against natural instinct.

According to the present invention there is provided a valve device for insertion in the fluid line between an engine and a servo unit in a vacuum servo-assisted brake system which valve device is operable to alternately interrupt and resume the flow of negative pressure fluid from the engine to the servo unit. In preferred arrangements the valve is operable only when the brake is applied.

Such arrangements implement cadence braking automatically and therefore offer a form of anti-lock braking system. Such devices may be designed to be suitable for fitting to both new and existing vehicles.

Any device which interrupts the hydraulic action in a motor car braking circuit must have a worst case failure resulting in a total loss of braking to at least one wheel. However, should the level of vacuum supplied to the brake servo unit be modulated the worst case failure would be loss of servo assistance, but a braking force could still be generated proportional to the force applied at the brake pedal.

Preferably the pattern of alternate interruptions and resumptions can be readily varied.

In one preferred embodiment the valve device comprises a valve housing a valve member arranged for reciprocal sliding motion in a chamber, a fluid inlet to the chamber on one side of the valve member, a fluid outlet to the servo from the chamber at said one side of the valve member, the outlet also communicating with the other side of the valve member, said communication incorporating a restriction, the arrangement being such that periodically the forces acting on either side of the valve member are such that the valve member moves and both sides of the valve member are vented to the pressure external of the device and the valve member returns to its original position.

A preferred feature is that the valve member is biassed in said one direction by biassing means.

The biassing means may comprise spring means and this may be formed integrally with the valve member. A convenient material for this may be plastic.

A further feature is that the chamber is stepped and said valve member is disposed in the area of larger cross section and is biassed into engagement with the step. Preferably the valve member shuts external vent means when abutting the step and periodically moves out of abutment against the biassing means to open the vent means to the chamber at both sides of the valve member. The vent means may comprise a number of holes formed in the valve housing. In one arrangement eight holes are provided at equiangular spacings around the housing.

With another preferred embodiment the valve member is constituted by one flange of a spool valve, the other flange being remote from said other side of the valve member and the side of the other flange remote from said first flange is vented permanently.

Preferably the spool valve closes the inlet when the spool valve moves against the biassing means.

Conveniently it is the remote flange which closes the inlet.

The housing may comprise a central portion and two end caps, one of which incorporates the inlet.

The central portion of the housing may have an annular recess communicating with the fluid inlet and cross slots to effect communication with the chamber.

In one arrangement the communication from the outlet is through a tapping in part of the central portion of the valve housing and said part of the housing extends sealingly through said valve member and into the other end cap.

Preferably the restriction comprises a flow control tract formed in a flow control plate which is removably attached to the said other end cap. Ideally the valve is generally of a cylindrical nature and the tract extends from a radially outerpoint in a generally coiled fashion towards the central axis of the valve device where it communicates with a bore extending through said other end cap.

In addition the central portion may also incorporate a second tapping which communicates with the inlet at one end and the flow control tract at the other end and incorporates an element biassed so as to block the tract, in use said bias being overcome by the pressure differential between the inlet and the tract when there is sufficient negative pressure in the inlet.

An embodiment of the invention will now be described in more detail. The description makes reference to the accompanying drawings in which: Figure 1 is an end view of the valve Figure 2 is a lengthwise sectioned view of the valve taken through the centre line and Figure 3 is a further sectioned view of the valve showing an integral biassing means.

In the figures there is shown a valve device 10 for connection to a conventional vacuum servoassisted brake system in the pipe between the engine and the servo unit. This pipe incorporates a nonreturn valve (not shown) and this non-return valve is removed, or not included, when the valve device 10 is provided.

The device 10 comprises five main parts, a central housing portion 11, first and second end caps 12, 13, a spool 14 and an end plate 15. The first end cap 12 is an interference fit on the central portion 11 and end cap 13 is a snap-fit on central portion 11.

The first end cap 12 incorporates an inlet port 16 which in use is connected to the negative pressure outlet of the engine. The central portion 11 has an annular recess 17 and cross slots 18 so as to allow fluid flow into a central chamber 19.

The spool 14 has first and second flanges 20, 21 interconnected by a central member 22. The spool 14 is made from plastics material with an integral biassing means 23 which acts against the second end cap 13 to urge the first flange 20 of the spool 14 into engagement with an outwardly stepped portion 24 of the central portion 11. In this position the second flange 21 is disposed behind the cross slots 18 thus allowing passage of fluid into chamber 19.

The central portion 11 also has an outlet port 25 which opens to the central chamber 19 and is connected to the servo unit. A cross tapping 26 is also provided in the central portion 11. The tapping 26 communicates with the outlet port 25 and extends through a cylindrical extension 27 of the central portion 11. The extension 27 passes through the first flange 20 of the spool 14 and through the second end cap 13.

The second end cap 13 has attached to it the removable end plate 15 which has on its inner face a restriction in the form of a flow control tract 28.

One end of the tract communicates with the end of the tapping 26 and the tract extends in a curved path until it reaches the central axis of the valve where it communicates with a bore 29 which extends through the second end cap 13.

There is also a second extension 30 to the central portion 11 extending through the first flange 20 and into the second end cap 13. A tapping 31 extends through this extension and terminates in one of the cross slots 18 at the inlet ends. A ball 32 is disposed in a bore 33 in the end plate and is urged into the flow control tract 28 by a spring 34, the force of which is overcome by sufficient negative pressure in the inlet 16.

The stepped portion 24 is formed with a number, in this case eight, of vent holes 35 which are closed by the first flange 20 of the spool 14 when said flange is biassed into abutment by the biassing means 23. The biassing of the flange 20 against the stepped portion 24 and the central portion 11 also seals around the extensions 27, 30.

It will also be clear that the first flange 20 of the spool 14 is not in sealing contact with the second end cap 13 at its radially outer periphery.

Also there is a vent 36 to atmosphere behind the second flange 21 of the spool 14.

The operation of the valve device will now be described in detail.

Negative fluid pressure generated by the engine passes through inlet port 16, annular recess 17, cross slots 18 and into central chamber 19. The negative pressure then passes through outlet port 25 to the servo unit. With the spool 14 in the position shown in the figures the servo unit receives the full negative pressure from the engine so that the servo unit generates its full servo assistance.

However, negative pressure also flows from the outlet port 25 through the tapping 26 to the flow control tract 28. The tract 28 is manufactured to close tolerances so that the rate of flow along the tract is carefully restricted.

The pressure in the end chamber 37 gradually reduces in a controlled manner and acts on the large face of the flange 20 of the spool 14. When the pressure in chamber 37 reduces sufficiently, the spool 14 moves to the left out of abutment with the stepped portion 24 of the central portion 11. This movement occurs when the forces acting to move the spool to the right as shown in figures 2 and 3, i.e. the fluid pressure in end chamber 37 and the force of the biassing means 23, are overcome by the forces acting to move the spool to the left, i.e. the fluid pressure in the central chamber 19 and the atmospheric pressure acting through the vent holes 35 on the flange 20 of the spool.

When the spool moves, both the end chamber 37 and the central chamber 19 are vented via holes 35 to atmosphere and also the second flange 21 of the spool prevents the flow of negative pressure through the inlet into the central chamber. Also the negative pressure in the servo unit vents through outlet port 26 and holes 35.

After venting the biassing means 23 returns the spool to the position shown in the drawings. The inlet is reopened and negative pressure again builds up in the device.

It will be appreciated that in this way negative pressure in the servo unit is built up and released in a cyclic fashion and the result of this is that the brakes are effectively being "pumped" as in cadence braking.

It is not uncommon in emergency braking for the engine to stall and when this happens negative pressure is no longer generated. If the servo unit has just been opened to atmosphere no further servo assistance will be possible. To prevent this problem the low negative pressure cut-off tapping 31 is provided. The spring 34 pushes the ball 32 into the flow control tract 28 thereby closing the tract. This prevents the build up of negative pressure in the end chamber 37 and hence the valve from operating.

However, when there is sufficient negative pressure at the inlet and thus in the low negative pressure cutoff tapping 31 to overcome the spring pressure and pull the ball 32 out of the tract 28 then the valve is able to operate. It can be seen, therefore, that when negative pressure from the engine is lost or is not at a level sufficient to overcome the spring 34 the valve will not operate.

It will be appreciated that different sizes and types of engine will deliver different flow rates of negative pressure and also cars will be fitted with different sizes of servo unit. Both of these factors require the valve to operate at different rates of cycling. The rate of cycling is primarily controlled by the size of the flow control tract 28 and this is easily changed by replacing the flow control plate 15 with one having different tract characteristics. This means that the valve can be used in many different cars simply by changing one component. Also different braking effects can be obtained on a single car by simple replacement of a plate.

The actual form of the valve device shown is simply an example of suitable configuration. It will be appreciated also that the characteristics of the valve device can also be altered by altering the biassing force, the areas of the spool flanges, the number and size of the vent holes. The above described communication from the outlet to the end chamber and the restriction are to be considered only as examples of suitable arrangements. Also the attachment of the end caps could be by any suitable means such as screw, interference, snap, adhesive. In addition the components can be made of any suitable material including plastics, metal, composites. The biassing means may be a separate spring member of any known type such as coil, leaf, disc.

The valve device described above will operate continuously whilst the engine is running and cadence braking will occur whenever the brake pedal is applied. However, it is possible to modify this operation so that the valve device operates only when the brakes are applied and this would increase the life of the device. Examples of such a modification would be to open the flow control tract in the end plate by utilising a 'G' switch mounted somewhere on the car and/or a solenoid activated by say the brake light circuit. It should of course be possible to tune the 'G' switch so that the cadence braking only operates when the brakes are applied quickly or harshly. Other control systems could be employed so that the valve operates only in certain circumstances when certain control parameters have been met.

In some cases it may be necessary to incorporate a vacuum reservoir between the engine and the valve device to ensure that there is always sufficient vacuum to render the valve device operable even during periods of continuous operation. The reservoir in its simplest form would comprise a chamber located in series in the vacuum line between the engine and the valve device.

Claims (22)

1. A valve device for insertion in the fluid line between an engine and a servo unit in a vacuum servo-assisted brake system which valve device is operable to alternately interrupt and resume the flow of negative pressure fluid from the engine to the servo unit.

2. A device as claimed in claim 1 wherein the valve is operable only when the brake is applied.

3. A device as claimed in claim 1 or 2 wherein the pattern of alternate interruptions and resumptions can be readily varied.

4. A device as claimed in any one of claims 1 to 3 wherein the valve device comprises a valve housing a valve member arranged for reciprocal sliding motion in a chamber, a fluid inlet to the chamber on one side of the valve member, a fluid outlet to the servo from the chamber at said one side of the valve member, the outlet also communicating with the other side of the valve member, said communication incorporating a restriction, the arrangement being such that periodically the forces acting on either side of the valve member are such that the valve member moves and both sides of the valve member are vented to the pressure external of the device and the valve member returns to its original position.

5. A device as claimed in claim 4 wherein the valve member is biassed in said one direction by biassing means.

6. A device as claimed in claim 5 wherein the biassing means comprises spring means.

7. A device as claimed in claim 6 wherein the spring means is formed integrally with the valve member.

8. A device as claimed in claim 7 wherein the valve member is made from a plastics material.

9. A device as claimed in any one of claims 1 to 8 wherein the chamber is stepped and said valve member is disposed in the area of larger cross section and is biassed into engagement with the step.

10. A device as claimed in claim 9 wherein the valve member shuts external vent means when abutting the step and periodically moves out of abutment against the biassing means to open the vent means to the chamber at both sides of the valve member.

11. A device as claimed in claim 10 wherein the vent means comprises a number of holes formed in the valve housing.

12. A device as claimed in claim 11 wherein eight holes are provided at equiangular spacings around the housing.

13. A device as claimed in any one of claims 9 to 12 wherein the valve member is constituted by one flange of a spool valve, the other flange being remote from said other side of the valve member and the side of the other flange remote from said first flange is vented permanently.

14. A device as claimed in claim 13 wherein the spool valve closes the inlet when the spool valve moves against the biassing means.

15. A device as claimed in claim 14 wherein the remote flange closes the inlet.

16. A device as claimed in claim 15 wherein the housing comprises a central portion and two end caps, one of which incorporates the inlet.

17. A device as claimed in claim 16 wherein the central portion of the housing has an annular recess communicating with the fluid inlet and cross slots to effect communication with the chamber.

18. A device as claimed in claim 17 wherein the communication from the outlet is through a tapping in part of the central portion of the valve housing and said part of the housing extends sealingly through said valve member and into the other end cap.

19. A device as claimed in any one of claims 1 to 18 wherein the restriction comprises a flow control tract formed in a flow control plate which is removably attached to the said other end cap.

20. A device as claimed in claim 19 wherein the valve is generally of a cylindrical nature and the tract extends from a radially outerpoint in a generally coiled fashion towards the central axis of the valve device where it communicates with a bore extending through said other end cap.

21. A device as claimed in claim 20 wherein the central portion may also incorporate a second tapping which communicates with the inlet at one end and the flow control tract at the other end and incorporates an element biassed so as to block the tract, in use said bias being overcome by the pressure differential between the inlet and the tract when there is sufficient negative pressure in the inlet.

22. A device described substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.