GB2210438A - Improvements in solenoid-operated fluid-flow control valve assemblies - Google Patents

Abstract

A solenoid-operated flow control valve comprises an armature (6) which is spring urged in one direction normally to close one of two axially spaced valves (11, 12) in a body (1), and a single solenoid coil (13) which, when energised, urges the armature (6) in the opposite direction to open the valve (12) and close the valve (11). The two valves (11, 12) are in open communication only during the transitional movement of the armature (6) between extreme positions. Thus a finely controlled flow rate through the valve can be achieved by pulsing an energising current applied to the coil to cause oscillation of armature (6) in the body (1) between the extreme positions. This is of advantage when releasing fluid from, or applying fluid to, a brake in an hydraulic anti-lock braking system. <IMAGE>

Description

IMPROVEMENTS IN SOLENOID-OPERATED FLUID-FLOW CONTROL VALVE ASSEMBLIES This invention relates to solenoid-operated fluid-flow control valve assemblies of the kind in which an armature is movable in opposite directions in a chamber in a body to control operation of a pair of oppositely acting valves, each controlling a respective passage in the body, the armature normally being biassed by a spring in a first direction and into a first position in which one of the valves is closed and the other valve is open, and being movable in a second opposite direction and into a second position in which the said one valve is open and the other valve is closed in response to energisation of a solenoid coil in the body.

Solenoid-operated valve assemblies of the kind set forth are used in vehicle hydraulic anti-lock braking systems, primarily to control the release of fluid from a brake. For example to a de-boost chamber, in response to a coil energising anti-lock signal from a sensor for sensing the speed of rotation of a wheel braked by the brake.

Solenoid-operated valves used hitherto in vehicle hydraulic anti-lock braking systems are arranged to provide a rapid release of fluid from the brake. This is achieved by constructing the valve assembly to provide an open and substantially unrestricted communication between the brake and the de-boost chamber when the armature is displaced in the body in response to the energising signal in a direction to close the valve between a source of brake-applying pressure, suitably a master cylinder, and the brake, and open the other valve.In one known construction a lost-motion connection is provided between the armature and the said other valve to hold it open, or the act of opening the said other valve places a passage controlled by that valve in communication with a third passage in the body, for example as disclosed in GB-A-2 045 372, and with which the other valve normally communicates when the coil is de-energised.

When it is necessary to displace a large volume of fluid to effect release of a brake in response to an anti-lock signal, it is essential to ensure a rapid release of fluid as described above. However, when only a relatively smaller volume needs to be released in similar circumstances it would be advantageous if such a rate of release of fluid could be finely controlled since this would enable us to reduce the relative brake re-application response time and conserve the energy necessary to achieve brake re-application.

According to our invention in a solenoid-operated fluid-flow control valve assembly of the kind set forth the body is provided with two fluid-flow passages only, each controlled by a respective one of the oppositely acting valves, and both valves are controlled directly by the armature so that the two passages are in open communication only during the transition of the armature between its first and second positions.

This has the advantage that pressure modulation is allowed zznly during the transition of the armature between its first and second positions, and the valve assembly can therefore be referred to as a "transition time valve". Therefore, when a pressure differential exists between input to output, a finely controlled flow-rate through the valve assembly can be achieved by pulsing the energising voltage applied to the coil so that the armature oscillates in the chamber between two extreme positions.

When the solenoid-operated fluid-flow control valve assembly is incorporated in a vehicle hydraulic anti-lock braking system a finely controlled flow-rate can be achieved for releasing fluid from the brake, for example to a de-boost chamber, or for applying fluid to a brake.

The minimum pressure dumped from or applied to the brake is dependent on the transition time of the armature and not a solenoid reaction time in the case of convention solenoid-operated valve assemblies.

Preferably the armature carries a valve member at each of its opposite ends, and each valve member co-operates directly with a seating surrounding the inner end of the respective one of the two passages.

Each valve member may comprise a spherical ball which is trapped or otherwise retained in a recess in the armature against relative axial movement.

When installed in a vehicle hydraulic anti-lock braking system the valve assembly is arranged in such a way that the armature is normally biassed by the spring in a direction to close the valve controlling the passage on the output side. Thus no flow takes place through the valve assembly when the solenoid is de-energised since the corresponding output t valve seat is sealed. Similarly no flow takes place through the valve assembly after the armature has moved in the opposite direction to seal the input valve seat.

One embodiment of our invention is illustrated in the accompanying drawings in which: Figure 1 is a longitudinal section through a solenoid-operated fluid-flow control valve assembly; Figure 2 illustrates the comparison between the characteristics of the valve assembly of Figure 1 and a conventional solenoid-operated fluid-flow control valve assembly; and Figure 3 is a layout of an hydraulic braking braking system embodying valve assemblies similar to that of Figure 1.

The solenoid-operated fluid-flow control valve assembly illustrated in Figure 1 of the accompanying drawings comprises a body 1 which is provided in opposed end portions with axially aligned input and output passages 2 and 3 which lead into an armature chamber 4. The chamber 4 is of enlarged diameter and of stepped outline. The output passage 3 leads out from the portion 5 of the chamber which is of greater diameter.

An armature 6 located in the chamber 4 is guided for movement in opposite directions between opposite ends of the body 1. Valve members 7, 8 carried by opposite ends of the armature 6 are alternatively engageable with seatings 9, 10 in the body 1 at the inner ends of the passages 2, 3 and with which they constitute input and output valves 11, 12 respectively.

A single solenoid coil winding 13 is housed in the body 1 in an annular chamber 14 which encircles a major portion of the portion of the chamber 4 which is of smaller diameter.

A compression spring 15 acts between a shoulder 16 at the step in diameter of the chamber 54 and a shoulder 17 on the armature 6. When the solenoid coil 13 is de-energised, the spring 15 urges the armature 6 relatively away from the passage 2 to close the valve 12. The valve 11 is held open, but no flow through the assembly can take place since the valve 12 is shut.

When the solenoid coil 13 is energised the armature 6 moves relatively away from the passage 3 to open the valve 12 and close the valve 11. Fluid flow from the input passage 2 to the output passage 3 can take place during this transitional movement of the armature 6 only, since no flow can occur after the valve 11 has closed. The valve assembly can therefore be said to constitute a "transition time valve".

With a pressure differential across the transition time valve, from the input passage 2 to the output passage 3, a finely controlled flow rate can be achieved by pulsing the energising current to the coil 13. This causes the armature 6 to oscillate in the chamber 4 between extreme positions defined by the valve seatings 9, 10.

When the transition time valve is incorporated in an hydraulic anti-lock braking system the input passage 2 is connected to a brake and the output passage 3 to a de-boost chamber. By pulsing the energising current to the coil 13 as described above, in response to signals from a speed sensor on the braked wheel, a finely controlled release or re-application of brake pressure can be achieved Figure 2 shows a comparison between the characteristics of the transitional time valve (a) and a conventional solenoid-operated valve (b).

In the two constructions it will be observed that a given supply voltage effective for a given time "T" achieves a similar armature travel, but for the transitional time valve (a) the value of brake pressure release (Pp) is small in comparison with that (Pc) of the conventional valve (b) . This is because the minimum pressure dumped from the brake by the conventional valve (b) is dependent upon the solenoid reaction time rather than that upon the transitional time of the armature 6 in moving between its extreme positions.

The layout of Figure 3 illustrates a three-channel hydraulic anti-lock system for a four wheel vehicle having brakes 20, 21 on opposite front wheels 22, 23 and brakes 24,*25 on opposite rear wheels 26, 27. In this system the front wheel brakes are each controlled by separate channels, and the rear wheel brakes are both controlled by the third channel.

A booster-assisted pedal operated tandem master cylinder 28 having primary and secondary pressure spaces 27, 30 is adapted to apply all the brakes with the brakes 24, 25 on the rear wheels being applied from the primary pressure space 29, and those 20, 21 on the front wheels from the secondary pressure space 30.

The pressure space 30 is connected to both front brakes 20, 21 through a solenoid-operated cut-off valve 31, and the pressure space 29 is connected to the rear brakes 24, 25 through a similar cut-off valve 32.

A pump 33 including opposed plungers 34, 35 driven by a common shaft 36 is provided for re-applying the brakes at the end of an anti-lock cycle in a known manner.

The plunger 34 supplies the front brakes 20, 21 through a de-boost chamber 37, and the plunger 35 supplies the rear brakes 24, 25 through a de-boost chamber 38.

The system incorporates six transitional time valves (TTV) 40, 41, 42, 43, 44, 45, each as described above with reference to Figure 1 of the accompanying drawings. As illustrated the valves (TTV) are oppositely arranged in pairs (40, 42; 41, 43; 44, 45) in each channel. Thus the arrangement in one channel only need be described in detail.

The valve 41 is arranged with the valve 12 connected to the input from the pressure space 30 of the master cylinder 28 and the valve 11 leading to the brake 21. The other valve 42 of that pair is arranged with the valve 12 connected to the brake and the valve 11 leading to the de-boost chamber 37.

All the solenoids are responsive to signals from a 3-channel control module which receives wheel speeds signals from sensors on each wheel and is operative to energise the solenoids as necessary to control the behaviour of a braked wheel.

During normal braking all the solenoids are de-energised and the pump 33 is disabled. The cut-off valves 31 and 32 are open, and each valve (TTV) is in a position in which the respective valve 11 is closed and the valve 12 is open. Hydraulic fluid from the master cylinder is supplied to the brakes through the respective open cut-off valves 31, 32, but no flow takes place through the valves (TTV) in either direction.

When an anti-lock signal is emitted by the sensor on say the wheel 23, the control module is operative to energise the solenoid of the cut-off valve 31, thereby isolating the master cylinder 28 from both front wheel brakes 20, 21. The module is also operative to apply pulses of current to the solenoids of the valves (TTV) 40, 41, 42 and 43 in any desired sequence. For example the solenoid of the valve 43 will be pulsed to release fluid from the brake 21 to the de-boost chamber 37 to relieve the brake 21 as described above with reference to Figure 1. During this pressure relieving cycle the solenoid of the valve 41 remains de-energised.

When the wheel 23 has recovered from the anti-lock condition, the solenoid of the valve 41 is de-energised to isolate the brake 21 from the de-boost chamber 37, and the pump 33 operates in a known manner to re-apply the brake 21. This re-application takes place under the control of the valve 41 of which the solenoid is pulsed to provide a finely controlled flow rate.

The cut-off valve 31 remains closed during an anti-lock correction in a single braking cycle, but the solenoid of the valve (TTV) 40 may be pulsed by the control module to enable the pressure applied to the brake 20 to be increased at a rate determined by that valve. Of course during this time the valve (TTV) 42 remains de-energised to prevent pressure from the brake being released to the de-boost chamber 37.

Claims (7)

1. A solenoid-operated fluid-flow control valve assembly of the kind set forth in which the body is provided with two fluid-flow passages only, each controlled by a respective one of the oppositely acting valves, and both valves are controlled directly by the armature so that the two passages are in open communication only during the transition of the armature between its first and second positions.

2. A valve assembly as claimed in claim 1, in which the armature carries a valve member at each of its opposite ends, and each valve member co-operates directly with a seating surrounding the inner end of the respective one of the two passages.

3. A valve assembly as claimed in claim 2, in which each valve member comprises a spherical ball which is trapped or otherwise retained in a recess in the armature against relative axial movement.

4. A vehicle hydraulic anti-lock braking system incorporating at least one solenoid-operated fluid-flow control valve assembly as claimed in any of claims 1-3, in which the valve assembly is located between a brake and a de-boost chamber, and the armature is biassed by the spring in a direction to close the valve controlling the passage leading to the brake.

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

6. A vehicle hydraulic anti-lock braking system incorporating at least one control valve assembly as claimed in claim 5.

7. A vehicle hydraulic anti-lock braking system substantially as described herein with reference to and as illustrated in Figure 3 of the accompanying drawings-.