GB2252140A - Solenoid-operated fluid-flow control valve assemblies - Google Patents

Abstract

A fluid-flow control valve assembly in an anti-lock braking system comprises a first, solenoid-operated normally open valve (23), and a second, pressure-responsive valve (24), which are arranged between an inlet (25) and an outlet (26). The first valve has a valve head (27) and a seating (29), and the second valve (24) comprises a differential piston (32) movable between an open position in which valve head (34) is spaced from seating (25) and a closed position (as illustrated) in response to changes in master cylinder (1) and return line (43) pressures acting on the piston. In the open position the second valve (24) defines a first unrestricted flow path between the inlet and the outlet, and in the closed position second valve (24) defines a second smaller restricted flow path (36) between the inlet and the outlet. When the pressures in the master cylinder and the return line are substantially equal the valve (24) will assume the open position, but when wheel lock is sensed the pressure in return line (43) will be reduced by energisation of solenoid-operated valve (3), thus causing valve (24) to close, and the valve (23) will also be closed. Thereafter, pressure is restored at the brake (2) during anti-lock control by pulsing solenoid (7) to permit flow from the master cylinder to the brake via the restricted flow path (36). <IMAGE>

Description

SOLENOID-OPERATED FLUID-FLOW CONTROL VALVE ASSEMBLIES This invention relates to improvements in solenoid-operated fluid-flow control valve assemblies of the kind adapted to control the supply of fluid under pressure from a source, for example a master cylinder of an hydraulic braking system, to a slave device, for example an hydraulically-operable brake.

When incorporated in hydraulic anti-lock braking systems, generally known as ABS, solenoid-operated valve assemblies of the kind set forth are used to control fluid pressure rate rises and are responsive to signals from skid sensors which monitor rates of change in the speed of a braked wheel. When the braking system is inactive, that is to say when the system is being operated for normal braking in a non-anti-lock mode, a large flow path for fluid is required through the solenoid-operated valve to achieve effective braking whereas, in an anti-lock mode, this is reduced to a smaller flow path.

Known solenoid-operated valve assemblies of the kind set forth are constructed with valve seats which are of an equivalent large size in order to achieve the desired large flow path. The flow has to be controlled to a fine degree by the co-operation with the seating of a complementary valve member in the anti-lock mode.

This is difficult to achieve in practice due to tolerance variations, and the like. In fact, unless the solenoid is increased in size to unacceptable proportions, when used in heavy duty braking systems in which the valve seat must be of sufficiently large size to achieve the required massive proportions of the flow path, the solenoid is unable to generate the sufficiently large force necessary to cause the valve to close against the flow and isolate the source from the brake, in an anti-lock mode.

According to our invention, in a solenoid-operated valve assembly comprising a first solenoid-operated valve, and a second pressure-responsive valve in series with the first valve between an inlet and an outlet, the second valve is movable between an open position and a closed position, in the open position the second valve defining a first unrestricted flow path between the inlet and the outlet, and in the closed position the second valve defining a second smaller restricted flow path between the inlet and the outlet.

Providing the pressure-responsive second valve enables us to arrange accurately the two rates of flow without any regard to the size, configuration, or accuracy of the first valve.

The second valve may be located upstream or downstream of the first valve.

Preferably the second valve comprises a valve member which is movable with respect to a seating between the open or closed position. In the open position an unrestricted passage is operative, and in the closed position the unrestricted passage is closed by the co-operation of the valve member with the seating which has the effect of introducing a restrictor between the inlet and the outlet.

The second valve may comprise a piston working in a bore in a housing with the piston provided at one end with a valve head for engagement with the seating, and a return spring normally urging the head relatively away from the seating, the piston being subjected to a differential pressure which is adapted to urge the piston towards the seating.

Preferably the piston is of differential outline so arranged that pressure from the source, and the pressure applied to the brake, which are both substantially equal, act over opposed effective areas, which are also substantially equal. Thus, in a normal brake-applying mode, forces generated by substantially equal pressures acting over substantially equal areas balance each other and the valve is held in an open position by the force in the return spring. In an anti-lock mode in which the pressure applied to the brake reduces substantially, the force generated by the pressure from the source is greater than the force in the spring and acts in a direction to oppose and overcome the force in the spring with the result that the piston is moved into engagement with the seating.

When the solenoid-operated fluid-flow control valve assembly is incorporated in a vehicle anti-lock braking system as a first normally-open brake application/re-application valve, in series with a second solenoid-operated dump valve assembly, for normal brake application the first valve assembly is normally open, and the second valve assembly is normally closed.In response to an anti-lock signal, both solenoids are energised with the first solenoid-operated valve of the first assembly closing against a relatively small seating which defines the restricted flow path, the second assembly opens to connect the brake to a dump chamber, and the reduction in brake pressure enables the piston to close against its substantially larger valve seating due to the force generated by the pressure from the source, substantially opposed by the force previously generated by the pressure applied to the brake. In a brake re-application mode the dump valve closes and the solenoid of the first valve is pulsed to re-apply the brake at a controlled rate determined by flow through the relatively'small seating.

We therefore provide a solenoid-operated control valve assembly which is adapted to act as a normally-open brake application/re-application valve in a vehicle anti-lock braking system in which the valve is adapted to control flow to the brake by using a relatively small solenoid operable to cause a valve member to seat over a similarly small seating and is also adapted to establish a large flow path to the brake for normal brake application.

Two embodiments of our invention are illustrated in the accompanying drawings in which: Figure 1 is a layout of a anti-lock (ABS) hydraulic braking system for a heavy duty vehicle; and Figure 2 is a modified version of the normally open solenoid-operated brake application/re-application valve.

The anti-lock hydraulic braking system illustrated in Figure 1 of the accompanying drawings comprises an hydraulic master cylinder 1 for applying a wheel brake 2 through a first normally-open solenoid-operated valve assembly 3, and a second normally closed solenoid-operated valve assembly 4.

Signals from a wheel speed sensor 5 are fed to an electronic control module 6. When the control module 6 recognises that an excessive rate of deceleration is present, it is operative to energise the solenoids 7, 8 of the two valve assemblies 3, 4 in a manner to be described, in order to isolate the supply from the master cylinder 1 to the brake 2, and dump fluid from the brake 2 to an expander chamber 9 from which fluid is adapted to be withdrawn by pump 10 driven by an electric motor 11 under the control of the control module 6.

The first solenoid-operated fluid-flow control valve assembly 2 comprises a housing 21 containing a valve block 22 providing a mounting for a first solenoid-operated valve 23, and a second pressure-responsive valve 24. The two valves 23, 24 are located in series between an inlet port 25 and an outlet port 26 with the second valve 24 located upstream of the first valve 23.

The solenoid-operated valve 23 comprises a valve head 27 which is carried by an armature 28 and is normally urged away from a seating 29 surrounding a passage 30 by means of a compression spring 31 to define an open position for the valve. Energisation of the solenoid 7 acts on the armature 28 to urge the head 27 towards the seating 29 to define the closed position for the valve.

The second valve 24 comprises a piston 32 of stepped outline which works in a complementary stepped bore 33 in the valve block 22, and has an axial through bore. The inner end of the piston 32 which is of smallest area carries a valve head 34 for engagement with a seating 35 comprising a face on the block at the opposite end of the passage 30 from the seating 29. A restricted passage 36 of relatively small area and surrounded by the head 14 interconnects opposite ends of the piston 32. A compression spring 38 acts on the piston 32 normally to urge it relatively away from the seating 35 to 'define an open position for the valve 24 in which the port 25 communicates with the port 26 through large ports 39.The inlet port 25 communicates with a first space in the bore 33 between the head 34 and a portion 40 of piston 32 which is of intermediate diameter, and through the piston 32 to the end of the bore 33 which is of greatest diameter. The piston 32 is also provided with a radial ports 41 leading to the passage 30. A return port 42 connected to a return line 43 from the second valve assembly 3 communicates with the bore 33 between the intermediate portion 40, and a portion 44 of the piston 32 which is of greatest diameter.

The second solenoid-operated valve assembly 3 in a first normally closed position connects the outlet port 26 to both the brake 2 and the return line 43, and isolates the brake 2 from the expander chamber 9. In a second position the brake assembly 3 isolates the return line 43 from the brake 2, and connects the brake 2 to the expander chamber 9, with the rate of release of fluid being controlled by an orifice 50.

The orifice 50 is variable in size, or is interchangeable with a number of similar orifices, whereby the rate of release of fluid can be controlled according to the capacity of the braking system.

In a normal brake operation both solenoids 8 and 7 are de-energised. The valve assembly 3 is in its first position. The valve assembly 2 is in a brake-applying position with the valve head 34 spaced from the seating 35 so that fluid from the master cylinder 1 is supplied to the brake 2 through an unrestricted flow path through the ports 39. The valve head 34 is held away from the seating 35 by the force in the spring 38 with forces comprising the pressures from the master cylinder 1 and from the brake 2, which are substantially equal, acting over effective areas of the piston, which are substantially equal. Specifically the pressure from the master cylinder 1 acts over an effective area comprising the larger end of the piston 32 minus the area at the intermediate portion 40, in order to bias the piston 32 towards the seating 35.The pressure from the brake 2 acts over an area comprising the largest area minus the area of the intermediate portion 40, in order to bias the piston 32 away from the seating 35. In such a situation the piston 32 is pressure balanced.

When an incipient skid signal is sensed by the sensor 5 the control module 6 acts to energise both solenoids 7 and 8. The head 27 closes the seating 29, and the valve assembly moves into the second position to dump fluid from the brake 2 and the line 43 into the expander chamber 9. This reduction in pressure relieves the force acting on the piston 32 in a direction to augment the force in the spring 38. The force acting on the piston 32 due to the pressure from the master cylinder 1 is able to overcome the force in the spring 38 and close the second valve by causing the valve head 34 to engage with the seating 35. The master cylinder 1 is isolated from the brake 2.

During this operation the pump 10 withdraws fluid from the chamber 9 and returns it to the master cylinder 1.

When the wheel has recovered, the valve assembly 3 returns to its first position to isolate the brake 2 from the expander chamber 9. The solenoid 7 is pulsed to enable fluid supplied to the master cylinder 1 from the pump to be supplied to the brake 2 at a rate determined by f low through the restricted passage 36, and the head 34 is held against the seating 35 in the absence of a balance force from the pressure applied to the brake 2.

Release of the master cylinder 1 at the termination of a brake operation relieves the pressure acting on the piston 32. The piston 32 is therefore retracted by the spring 38 to open the second pressure-responsive valve 24.

In the modification to the valve assembly 2 which is illustrated in Figure 2 of the drawings, the pressure from the master cylinder 1 is applied to opposite ends of the piston 32, and a restrictor 51 is located in the axial through bore in the piston 32.

The construction and operation of the vale assembly of Figure 2 is otherwise the same as that of Figure 1.

Claims (10)

1. A solenoid-operated valve assembly comprising a first solenoid-operated valve, and a second pressure-responsive valve in series with the first valve between an inlet and an outlet, in which the second valve is movable between an open position and a closed position, in the open position the second valve defining a first unrestricted flow path between the inlet and the outlet, and in the closed position the second valve defining a second smaller restricted flow path between the inlet and the outlet.

2. A valve assembly as claimed in claim 1, in which the second valve is located upstream of the first valve.

3. A valve assembly as claimed in claim 1, in which the second valve is located downstream of the first valve.

4. A valve assembly as claimed in any preceding claim, in which the second valve comprises a valve member which is movable with respect to a seating between the open or closed position, and in which, in the open position an unrestricted passage is operative, and in the closed position the unrestricted passage is closed by the co-operation of the valve member with the seating which has the effect of introducing a restrictor between the inlet and the outlet.

5. A valve assembly as claimed in claim 4, in which the second valve comprises a piston working in a bore in a housing with the piston provided at one end with a valve head for engagement with the seating, and a return spring normally urging the head relatively away from the seating, the piston being subjected to a differential pressure which is adapted to urge the piston towards the seating.

6. A valve assembly as claimed in claim 5, in which the piston is of differential outline so arranged that pressure from the source, and the pressure applied to the brake, which are both substantially equal, act over opposed effective areas, which are also substantially equal, whereby, in a normal brake-applying mode, forces generated by substantially equal pressures acting over substantially equal areas balance each other and the valve is held in an open position by the force in the return spring, and in an anti-lock mode in which the pressure applied to the brake reduces substantially, the force generated by the pressure from the source is greater than the force in the spring and acts in a direction to oppose and overcome the force in the spring with the result that the piston is moved into engagement with the seating.

7. A vehicle anti-lock braking system incorporating a solenoid-operated valve assembly as claimed in any preceding claim, in which the solenoid-operated valve assembly comprises a first normally-open brake application/re-application valve, in series with a second solenoid-operated dump valve assembly.

8. A solenoid-operated valve assembly substantially as described herein with reference to and as illustrated in Figure 1 of the accompanying drawings.

9. A solenoid-operated valve assembly substantially as described herein with reference to and as illustrated in Figure 2 of the accompanying drawings.

10. A vehicle anti-lock braking system substantially as described herein and incorporating a solenoid-operated valve as claimed in claim 8 or claim 9.