GB2096283A - Electro-fluid control device - Google Patents

Abstract

An electrically-operable fluid pressure control device (10) in which the valve elements are magnetically susceptible discs (51, 52) operable by pot-coil electromagnets (63, 64) to close or not close at separate or simultaneous times respective ports (41, 44). When not closing these ports the discs can close other ports (42, 43) but not both at one time by the opposition of a link member (7) which is also effective to aid the unseating of one disc from the respective port of 42 and 43 when the other disc approaches. The speed and reliability of operation are obtained from this construction by relatively simple and non-critical manufacture. The fluid can be gas or liquid as no close-tolerance sliding surfaces exist. <IMAGE>

Description

SPECIFICATION Electro-fluid control device This invention relates to a control device responsive to an electrical input to control pressure or flow of fluid. The fluid may be a liquid or a gas.

In one form the device is an electro-hydraulic valve electrically energisable to control flow of a liquid under pressure from a supply for selective application to individual outputs.

Control devices are known in which a fluid pressure from a supply can be selectively applied to one or other of two distinct outlets by the operation of a valve element e.g. by an electric field acting on a magnetically susceptible body on or forming the valve element. However devices available hitherto have been expensive to make in view of the close tolerances for long-term reliable action. Despite care in manufacture contamination or wear can occur shortening service life and causing breakdowns with further increase in costs.

Also to achieve the operating speeds now required the electrical power that has to be applied in the region of the valve element creates problems in terms of heating and insulation.

It is an object of the invention to provide a control device which has an improved performance while mitigating the manufacturing and operational problems.

According to the invention there is provided an electrically-operable fluid pressure control device including in a housing a valve chamber and fluid pressure conduits between said chamber and fluid pressure connections of the housing, the valve chamber having fluid flow parts of said conduits and in the chamber a magnetically susceptible valve arrangement movable by electromagnetic force to cooperate with one or more of said ports to selectively control fluid flow through the chamber, means to selectively apply an electromagnetic force to move the valve arrangement, the valve arrangement having two spaced-apart, magnetically susceptible, individually movable portions and link member to transmit movement of each valve portion to the other over a section only of the range of movement of each valve portion and not transmit movement over another section of said range of movement.

Conveniently the link member is a rigid thrust rod too short to be in movement-transmitting contact with both valve portions throughout all their ranges of movement.

Advantageously each valve portion is a disc positioned between respective opposed fluid flow ports with a range of movement to seal one or other of the respective ports by the action of a respective face of the disc. The link member may be in a fluid pressure conduit joining a port for one valve member with a port for the other.

In one torm of the device the valve chamber has two parts spaced along a fluid pressure conduit with a disc valve portion in each chamber part positioned transversely of the conduit, and dividing it into a central part and outer parts, a central part of the conduit joining the valve chamber parts and housing a link member free of the valve discs, ports being formed where the central and outer parts of the conduit emerge into each chamber part, the outer parts of the conduit forming individual supply conduits from supply connections and the central part a common conduit to a drain outlet connection, the chambers also having respective fluid pressure load connections for fluid pressure flow to and from the control device in dependence on the valve portion positions, the electromagnetic means being positioned around each outer conduit for action on the adjacent valve disc.

Embodiments of the invention will now be described with reference to the accompanying drawing which shows a cross-section through an electro-hydraulic control device according to the invention.

In the drawing a valve housing is indicated at 1 0. This can be of any suitable shape and constructional form. Conveniently it is of three parts to ease assembly of the components. O-ring seals are used as appropriate. A conduit 2 extends through the housing from end to end between fluid pressure supply connections 21,22. Two valve chamber parts 31, 32 are formed in the housing and the line of conduit 2 extends through both, a central part 25 of the conduit connects the valve chamber parts and outer conduit parts 23, 24 extend from chamber parts 31, 32 respectively to the supply connections 21, 22. A common drain conduit 26 extends from central conduit part 25 to a drain outlet connection 29. Load connections 27, 28 are provided for each valve chamber part. The conduit 2 forms ports where it emerges into each valve chamber part.

Conveniently each port projects into the chamber as a nozzle. These nozzles are indicated at 41, 42, 43, 44. A valve portion is provided in each valve chamber part, 51 in part 31 and 52 and part 32.

The valve portions are discs, conveniently circular in plan, formed partly or wholly of magnetically susceptible material, such as Swedish (soft) iron annealed after fabrication to produce the magnetic properties appropriate to the duty. Each disc face may have a non-magnetic layer such as plastic film of MYLAR (RTM), to improve release from a port on removal of an applied magnetic field. The discs are free to "float" in the valve chamber in the axial sense but are conveniently a loose fit in the radiai sense to provide some location of the disc.

A clearance of 0.001 inch to 0.002 inch is suitable. There must be a clearance for fluid flow around or through the disc, apart from the central port-closing portion.

In one embodiment the valve portions 51, 52 are circular in plan with a number of small projections from each circular face spaced around the edge of the face. The projections are conveniently three or four in number and form stops arranged to limit the approach of the valve element to the end walls of the valve chamber.

When a valve element about 0.15 inch (4 mm) thick is used the stops are some 0.003 inch to 0.005 inch (0.1 mm) thick.

Electromagnetic means 61,62 are provided for each valve portion at the outer side of each valve chamber. The means 61, 62 are each coils 63, 64 wound on iron cores 65, 66. For the above reasons these also may be of annealed Swedish (soft) iron. The cores may have central bores to form some of the conduit 2. These central bores may be provided with brass or other non-magnetic liners to define the outer conduits 23, 24. The liners may also provide the nozzles 41 and 44.

These nozzles may be arranged to deform slightly in contact with the valve portions to provide a fluid-tight contact. For a pneumatic device the nozzle may be of rubber or like flexible material to achieve a similar result. The projection of nozzles 41,44 is some 0.003 inch to 0.005 inch while that of nozzles 42, 43 is greater to reduce hydrostatic effects between the valve portion face and the adjacent wall around the nozzle. The valve discs and electro-magnetic means are arranged so that when a coil is energised the discs are attracted to the respective nozzle and port to close the port against fluid flow, as is shown for disc 52.

A link member in the form of rigid rod 7 is provided in conduit portion 25. This member permits fluid flow in the conduit. The member is made to be long enough to project from both of nozzles 42 and 43 but not so long as to be able to touch both discs when one is on a nozzle of the central conduit portion and the other on an outer conduit portion. The clearance that exists, 71, is very important for the effective operation of the valve and is some 0.002 inch (0.05 mm) in measurement. The link member is not joined to either disc in this embodiment. The link member must be free to move easily in conduit portion 22.

Other forms of rigid link member may be used, for example a tube, while the rigid link member may be replaced by a link member able to collapse by a small amount under axial loading so that the clearance can be reduced or omitted. Other possible forms include a tube able to deform slightly by central expansion with length reduction under axial load. A row of ball-bearings if necessary with a cage to allow fluid flow, may also be used or a spring loaded telescopic tube arrangement.

The operation of the device is as follows.

Hydraulic fluid pressure is supplied to connections 21 and 22 from a suitable source, not shown.

Load connections 27 and 28 are connected to utilisation means (not shown) such as a hydraulic power amplifier coupled to an actuator. Drain connection 29 may be arranged to return hydraulic fluid to the source. Electrical supplies are made available to the coils 63, 64 of the electromagnetic means 61, 62. Switches, not shown, are provided to permit one or other or both of the coils 63, 64 to be energised. As shown in the figure coil 63 is energised and coil 64 deenergised. The disc 51 is attracted by coil 63 to close offthe port in nozzle 41 against the pressure of the hydraulic fluid from conduit 23. Disc 52 is free to move in the absence of any electromagnetic field from coil 64 so the disc is pushed away from nozzle 44 by the fluid pressure in conduit 24 to seat on nozzle 43 and close it.

Rod 7 is pushed along conduit 25 by the disc movement but does not reach to disc 51. Fluid from conduit 24 flows to connection 28 for use.

Connection 27 connunicates with nozzle 42 past the disc 51 seated on nozzle 41 so fluid returning from the utilisation means can flow through connection 27, chamber port 31, nozzle 42 and conduit portion 25 to drain connection 26.

On energising coil 64 and de-energising coil 63 disc 51 is pushed off the nozzle 41 by the pressure of the fluid supply as it is no longer held by the .electromagnetic field of coil 63. The moving disc 51 makes contact with rod 7 and pushes on disc 52 through the rigid rod. This push combines with the electromagnetic pull of the energised coil 64 to move disc 52 to seat on and close nozzle 44 against the flow of fluid from conduit 24.

Load connection 27 is now in communication with supply connection 21 and load connection 28 in communication with drain connection 26.

The sense of the application of fluid pressure to the utilization means has thus been reversed providing a drive to bring about a required action there.

Reference has been made above to the energisation of one or other or both of the coils 63, 64. When neither coil is energised then the valve arrangement can be designed to "centre" under the fluid pressures from the fluid supply. In some applications the coils can be energised with an intermittent current rather than a steady value or a shaped current waveform. It is also possible to energise the coils at different fixed or varying steady levels. Using these techniques a chosen set-point or a graduable action may be achieved.

The current applied to the coils may be shaped, on a time basis, to provide a high initial value, to produce "pull-in" of the valve, followed by a lower value to "hold" the valve in place. Suitable electronic current control means can readily be devised to achieve this and associated with the valve if required.

An important factor in control devices is the speed with which such reversal occurs. In devices according to the invention this reversal is made fast and reliable by the arrangement of valve portions and link member. Because of clearance 71 when a coil is de-energised the respective disc moves without restriction under the fluid pressure from the supply acting initially on one face. This is because the flow from the nozzle is initially radially producing a positive pressure gradient over one face of the disc during the initial movement rather than acting on the nozzle area alone. The thrust on the released disc is therefore augmented and the augmented thrust can act through the link member on the other disc to unseat it and move it towards its supply nozzle against the pressure of fluid from the nozzle. The two discs and the rod thus accelerate as one element. The energised coil also attracts the nearer disc towards it completing the movement of the disc after the further disc has sealed off the conduit portion 25 and ceased to push on rod 7. Thus the thrust from the initial radial flow on the released disc transmitted through the link member followed by the action of the electromagnetic field produces a rapid reliable switching action. The design of the nozzles and their spacing and the disc-rod clearance clearly affect this action and the design of a device for any specific use must take account of these.

Also the nozzles are arranged to project into the valve chamber. Firstly this allows for as much pressure balancing as possible between the disc face areas during the steady-state condition of the device and secondly limits the adherence of the disc to the coil face on de-energisation of the coil.

The nozzle seat areas are therefore also significant for any design.

The illustrated embodiment has valve discs above 1 inch (25 mm) in diameter and 0.15 inch (4 mm) thick, excluding the projections. The conduit parts 23, 24 are about 0.06 inch (1.5 mm) diameter and the central part 25 is sized to produce an equivalent cross-section around link member 7. The coil power is some 30 to 40 watts, typically 20 to 30 volts at 1 to 12 amps in a 20 ohm coil. This produces a pull of some 20 to 50 Ibs on the valve disc. The device can operate with fluid pressures of 100 bar (1500 psi) at flow rates of 25 litres per minute.

Embodiments of the'invention as described above have been successfully operated at switching rates of 100 Hz using air as the fluid and 50 Hz using hydraulic oil. This fast action is obtained without resort to a complex construction with many close tolerances and therefore high cost. The essentially ON/OFF nature of the control signals required makes the valve most suitable for use with the electronic, two-condition signals used by modern digital electronic equipment and simplifies the interface with such equipment. The switching action may be of pulse width modulated form, that is the ON and OFF energisation conditions can be of adjustable duration to achieve a particular flow balance between the load connections 27 and 28. The high rate, or frequency, of switching possible is also useful in avoiding the excitation of mechanical resonances in the valve.

The device does not have any small orifices and this is an advantage for hydraulic systems as the device is thereby relatively insensitive to contamination. As there are no close-tolerance sliding surfaces the working fluids need not be lubricants, e.g. water/hydraulic oil matures are usable.

The device described has 4 ports (supply, drain, two load) and two positions and is a 4-way, 2position valve in fluid control technology terms.

More complex or different valve actions can be obtained from modifications of the illustrated device and by other electrical control actions. Thus a 4-way, 3-position valve can be provided, for example, as the two valve discs are not rigidly linked.

The device described is thus capable of highspeed reliable operation, without being subject to high construction costs and close tolerance, and can cope with a wide range of working fluids, gas or liquid.

It is also possible to produce compound valves using the above techniques. For example a pair of devices as described above but each with valve elements of two sizes could be arranged with the supply connections for the smaller valve elements connected together and to a common supply. The load connections from the valve chamber parts for these adjacent elements then provide the load connections for the arrangement while both the existing drain connections are used. This provides a valve arrangement which has a remotely operable centre section. This section can be selected to form a closed centre, a fully open centre or a centre open on one side or the other.

These are the four possible configurations of a 3 position, 4-way valve.

A single device, with valve elements of different sizes if required, can be arranged as an on/off 3way valve by closing one load connection.

Claims (7)

1. An electrically-operable fluid pressure control device including in a housing a valve chamber and fluid pressure conduits between said chamber and fluid pressure connections of the housing, the valve chamber having fluid flow ports of said conduits and in the chamber a magnetically susceptible valve arrangement movable by electromagnetic force to cooperate with one or more of said ports to selectively control fluid flow through the chamber, means to selectively apply an electromagnetic force to move the valve arrangement, the valve arrangement having two spaced-apart, magnetically susceptible, individually movable portions and a link member to transmit movement of each valve portion to the other over a section only of the range of movement of each valve portion and not transmit movement over another section of said range of movement.

2. A device according to Claim 1 in which the link member is a rigid thrust rod too short to be in movement-transmitting contact with both valve portions throughout all their ranges of movement.

3. A device according to Claim 1 or Claim 2 in which each valve portion is a disc positioned between respective opposed fluid flow ports with a range of movement to seal one or other of the respective ports by the action of a respective face of the disc.

4. A device according to Claim 1 or Claim 2 or Claim 3 in which the link member is in a fluid pressure conduit joining a port for one valve member with a port for the other.

5. A device according to Claim 1 in which the link member is an element spring-biassed to reduce in length under load before being able to transmit movement.

6. An electrically-operable fluid pressure control device including in a housing a valve chamber and fluid pressure conduits between said chamber and fluid pressure connections of the housing, in which the valve chamber has two parts spaced along a fluid pressure conduit with a disc valve portion in each chamber part positioned transversely of the conduit, and dividing it into a central part and outer parts, said central part of the conduit joining the valve chamber parts and housing a link member free of the valve discs, ports being formed where the central and outer parts of the conduit emerge into each chamber part, said outer parts of the conduit forming individual supply conduits from supply connections and said central part a common conduit to a drain outlet connection, the chambers also having respective fluid pressure load connections for fluid pressure flow to and from the control device in dependence on the valve portion positions, the electromagnetic means being positioned around each outer conduit for action on the adjacent valve disc.

7. An electrically-operable fluid pressure control device substantially as herein described with reference to the accompanying drawing.