GB2345119A

GB2345119A - Solenoid-operated control valve for hydraulic braking systems

Info

Publication number: GB2345119A
Application number: GB9828449A
Authority: GB
Inventors: Robert Alan Anderson
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1998-12-24
Filing date: 1998-12-24
Publication date: 2000-06-28
Anticipated expiration: 2018-12-24
Also published as: GB2345119B; GB9828449D0

Abstract

A solenoid-operated valve for an hydraulic braking system comprises a longitudinally extending hollow member (9) movable with an armature (10) with respect to a valve body (1) in opposition to the force in a return spring (11). The exterior of the hollow member is sealed, preferably by rings (12,17) at spaced locations with respect to the valve body. The interior of member (9) is in permanent communication with inlet port (6) with both ends of the hollow member being exposed to pressure at the inlet port. A radial port (7) provides communication between the interior of member (9) and the outlet port (7) when the armature moves in a first direction against the return spring but otherwise is closed by a sealing ring (17). The ring (17) may be carried by the hollow member a limited distance defined between spaced shoulders on the valve body.

Description

IMPROVEMENTS IN SOLENOID-OPERATED CONTROL VALVE ASSEMBLIES FOR HYDRAULIC SYSTEMS This invention relates to solenoid-operated control valve assemblies for hydraulic systems of the kind in which a valve is adapted to control communication between an inlet port and an outlet port in a valve body, and operation of the valve is controlled by an armature responsive to energisation of a solenoid coil.

In known solenoid-operated control valve assemblies of the kind set forth the valve comprises a valve member movable against a relatively large pressure in order to place the ports in communication. Thus the force generated by the solenoid must be of similar magnitude with consequent generation of the large forces involved in conjunction with large pressure differentials.

When the valve assembly is used in a vehicle electro-hydraulic braking (EHB) system and the valve is cycled to modulate the supply of fluid from the inlet port to the outlet port during a braking cycle, the large pressure differentials have the effect of causing the valve to overshoot thereby affecting accuracy of brake-pressure reapplication.

According to our invention in a solenoid-operated control valve assembly of the kind set forth for an hydraulic system, the valve comprises a longitudinally extending hollow member movable with the armature with respect to the valve body in opposition to the force in a return spring, and the exterior of the hollow member is sealed at spaced locations with respect to the valve body, the interior of the hollow member being in permanent communication with the inlet port with both ends of the hollow member being exposed to pressure at the inlet port, and a radial port in the hollow member providing communication between the interior of the hollow member and the outlet port when the armature moves in first direction against the force in the return spring but otherwise being closed by a sealing ring normally sealing that region of the hollow member from the valve body.

Since the hollow member is normally exposed at opposite ends to equal pressures, when it is moved longitudinally to open the valve the force exerted by the solenoid has only to be sufficiently strong to overcome the force in the return spring and the friction between the seals and the hollow member. This achieves accurate and substantially instantaneous response time, and substantially eliminates any tendency for the valve to overshoot.

Preferably the two seals each comprises a sealing ring of elastomeric material which can be carried by the hollow member through a limited distance defined between spaced shoulders on the valve body.

The hollow member preferably comprises a tube of which the end remote from the inlet port abuts against the return spring which is housed in a chamber in the valve body and which is exposed to pressure at the inlet port but which is otherwise sealed from the valve body by the respective seal.

Our construction is simple and cheap to produce with a minimum of machined components. The provision of spaced sealing rings eliminates tolerance variations and concentricity problems which may otherwise arise between concentric components.

One embodiment of our invention is illustrated in the accompanying drawings in which: Figure 1 is a longitudinal section through a solenoid-operated control valve assembly for a vehicle hydraulic braking system; Figure 2 is a view on an enlarged scale of the valve of Figure 1 ; and

Figure 3 is a schematic layout of a typical electro-hydraulic braking (EHB) system incorporating the solenoid-operated control valve assembly of Figures 1 and 2.

The solenoid-operated control valve assembly illustrated in Figures 1 and 2 of the accompanying drawings comprises a valve body 1 comprising spaced end fittings 2 and 3 which are interconnected by a rigid sleeve 4 having a cylindrical internal bore 5.

Communication between an axial inlet port 6 and a radial outlet port 7 in the end fitting is controlled by a valve 8 illustrated in greater detail in Figure 2 of the drawings. The valve 8 comprises a longitudinally extending hollow member in the form of a tube 9 which extends from the inlet port into a blind bore 10 defining a chamber for a helical return spring 11. The return spring 11 acts on that end of the tube 9. That end of the tube 9 is sealed in the end fitting 3 by means of a first sealing ring 12 disposed between spaced shoulders 13, 14 in the end fitting 3, the shoulders being spaced by a distance greater than the diameter of the sealing ring 12. The opposite end of the tube 9 is provided with a radial supply port 16 which provides communication between the inlet port 6 and the outlet port 7 but which is normally closed by a second sealing ring 17 of elastomeric material. The sealing ring 17 provides a seal between the wall of the inlet port 6 and the tube 9, and is disposed between radial shoulders 18,19 which are spaced by a distance greater than the diameter of the ring 17.

An armature 20 fixed on the tube 9 is guided to slide in the bore of the sleeve 4 and is movable in the bore in response to energisation of a solenoid core 21 which encircles the end fitting 3 and an adjacent portion of the sleeve 4.

When the valve assembly is installed in a hydraulic system, for example an hydraulic braking system, high pressure fluid at the inlet port 6 acts on and communicates with both ends of the tube 9, through the tube itself.

The tube 9 is therefore"pressure-balanced"and is held in the position shown in the drawings by the spring 11 in which the radial supply port 16 is closed by the sealing ring 17. The valve is therefore in a closed position and is usually designated as a so called"normally closed"valve.

When the solenoid coil 21 is energised the armature 20 and the tube 9 are both moved towards the end fitting 3 to withdraw the tube through the sealing ring 17 so that high pressure fluid can flow to the outlet port 7 through the radial supply port 16 and through an annular gap 23 which is formed intermediate the end fitting 2 and the exterior of the tube 9. During this operation the force in the solenoid needs to be sufficient only to overcome the force in the return spring 11 and friction between the tube 9 and the sealing rings 12 and 17.

Two such solenoid-operated valve assemblies 30,31, each as described above, are incorporated in the electro-hydraulic (EHB) braking system illustrated in Figure 3 of the accompanying drawings.

The valve assembly 30 controls the supply of fluid from an hydraulic accumulator 32 to a wheel brake 33, and the valve assembly 31 controls a return from the brake 33 to a reservoir 34 for fluid.

In a"brake-off"position the valve assembly 30 is closed and the valve assembly 31 is open.

To apply the brake the valve assembly 31 is closed and the valve assembly 30 is opened to supply hydraulic pressure to the brake. This supply can be modulated by pulsing the solenoid coil of that valve as necessary, in conjunction with pulsing the solenoid coil of the valve assembly 31.

The behaviour of a wheel braked by the brake, e. g. during anti-lock control (ABS), can therefore be controlled in accordance with signals sent to the solenoids under control of an electronic control module or computer.

Claims

CLAIMS 1. A solenoid-operated control valve assembly of the kind set forth for an hydraulic system, in which the valve comprises a longitudinally extending hollow member movable with the armature with respect to the valve body in opposition to the force in a return spring, and the exterior of the hollow member is sealed at spaced locations with respect to the valve body, the interior of the hollow member being in permanent communication with the inlet port with both ends of the hollow member being exposed to pressure at the inlet port, and a radial port in the hollow member providing communication between the interior of the hollow member and the outlet port when the armature moves in first direction against the force in the return spring but otherwise being closed by a sealing ring normally sealing that region of the hollow member from the valve body.
2. A control valve assembly according to claim 1, in which the two seals each comprises a sealing ring of elastomeric material which is adapted to be carried by the hollow member through a limited distance defined between spaced shoulders on the valve body.
3. A control valve assembly according to claim 1 or claim 2, in which the hollow member comprises a tube of which the end remote from the inlet port abuts against the return spring which is housed in a chamber in the valve body and which is exposed to pressure at the inlet port but which is otherwise sealed from the valve body by the respective seal.
4. An hydraulic braking system for a vehicle incorporating a first solenoid-operated control valve assembly according to any preceding claim in which the inlet port is connected to a high pressure source and the outlet port is connected to a brake.
5. A system according to claim 4, indicating a second solenoidoperated valve assembly according to any of claims 1 to 3, in which the inlet port is connected between the outlet port of the first valve assembly, and the outlet port is connected to a reservoir for fluid.
6. A solenoid-operated control valve assembly substantially as described herein with reference to and as illustrated in Figure 1 and 2 of the accompanying drawings.
7. An hydraulic anti-lock braking system substantially as described herein with reference to and as illustrated in Figure 3 of the accompanying drawings.