GB2124799A - Electro-hydraulic servo valve - Google Patents

Abstract

The torque motor of an electro- hydraulic servo valve includes a permanent magnet 8, pole-pieces 5, 6 and 7 and an electrical coil 10 having a part within the air gap between pole-pieces 5 and 6 and another part within the air gap between pole-pieces 6 and 7. The coil is connected to a saddle 13 and then to a flexure tube 15 mounted on the nozzle block 1. When an electrical current is applied to the coil, the flexure tube 15 permits limited tilting of the coil 10. Tilting movement of the coil 10 causes movement of a flapper 14, associated with the flexure tube, to control the flow of liquid from opposed nozzles 3 and 4 in the nozzle block. <IMAGE>

Description

SPECIFICATION Electro-hydraulic servo valve This invention relates to electro-hydraulic servo valves.

An electro-hydraulic servo valve usually has a torque motor. The torque motor comprises a permanent magnet, or magnets, opposed pole-pieces associated with the magnet, or magnets, an electrical coil associated with the pole-pieces, and an armature of soft iron mounted for tilting with parts in the air gaps between the opposed pole-pieces.

In the absence of an electrical current in the electrical coil, the armature will be in a socalled "null-position" with respect to the air gaps. When an electrical input signal is applied to the electrical coil, the magnetic flux in the armature and the air gaps will change and the armature will tilt, from the null-position, by an amount which is determined by the value of the input signal.

The tilting movement of the armature is transferred to a flapper which controls the flow of liquid from a nozzle or nozzles and determines the position of the spool of a spool-type hydraulic control valve.

The armature may be supported on part of the valve body, for tilting movement, by a socalled flexure tube to which the flapper is connected. Such a flexure tube not only permits small angular movements of the armature but also seals the torque motor from that part of the valve which, in use, contains liquid.

All commercially-available magnetic materials exhibit, in use, some magnetic hysteresis and this can affect the movement of the armature and, thus, the performance of the servo valve.

It is an object of this invention to provide an electro-hydraulic servo valve with reduced hysteresis.

According to this invention, an electro-hydraulic servo valve includes permanent magnet means, opposed pole-pieces providing a pair of air gaps, an electrical coil mounted for tilting movement and having a part disposed within one air gap and a part disposed within the other air gap and a flapper associated with the electrical coil.

When an electrical input signal is applied to the electrical coil, the coil will tilt and will cause the flapper also to tilt with respect to the nozzle or the pair of opposed nozzles whose output flow of liquid is controlled by the flapper.

The coil may be roughly rectangular in shape part of one side being disposed within one air gap and part of an opposite side being disposed within the other air gap. The two remaining sides may be connected to a saddle-shaped bracket which is supported on a part of the valve by a flexure tube. The flapper may be connected to the flexure tube.

An electro-hydraulic servo valve in accordance with one embodiment of the invention is illustrated in the accompanying drawings of which Figure 1 is a sectional view of the valve, and Figure 2 is another sectional view of the valve, taken along the line ll-ll of Fig. 1.

Referring to the drawings, the "hydraulic" part of the valve is shown in the lower part of the drawings and is a spool-type hydraulic control valve. The "electro" part of the valve is shown in the upper part of the drawings.

The interface between the "electro" part and the "hydraulic" part is a nozzle block 1 which is supported on the body 2 of the spool-type hydraulic control valve. The nozzle block 1 includes two opposed nozzles 3 and 4.

Supported on the nozzle block 1 are polepieces 5, 6 and 7. A permanent magnet 8 is connected to the pole-pieces 5 and 7.

A coil of insulated copper wire which is substantially rectangular in shape has sides 9, 10, 11 and 12.

The side 9 is disposed between pole-pieces 5 and 6 and the side 10 is disposed between pole-pieces 7 and 6.

The sides 11 and 1 2 are connected to opposite end portions of a saddle-shaped bracket 1 3 which is connected to the upper end portion of a flapper 14. A control portion of the flapper is carried within a flexure tube 1 5 which is supported on the nozzle block 1.

The lower end portion of the flapper is located between the opposed nozzles 3 and 4.

The electrical coil is suitably connected to a source of electrical current which will provide electric input signals to the valve when in use.

Prior to operation of the valve, the coil will be in a null position within the air gaps and the flapper and, as a consequence, will permit equal flows of liquid from the two nozzles.

When an electrical input signal is applied to the coil, equal and opposite forces will be generated on sides 9 and 10, so producing a torque proportional to the electrical current.

The coil will tilt with respect to the pole-pieces and the flapper will also be caused to tilt against the action of the flexure tube.

In a servo valve in accordance with the invention, the magnetic field in the air gaps remains practically constant, and thus the valve is less affected by hysteresis in the magnetic materials than previously-known valves.

To provide a positional feed-back signal, the flapper may be connected to the spool by means of a feed-back wire 1 6.

The nozzles 3 and 4 are hydraulically-connected to the ends of the spool valve as shown in Fig. 1 and are also connected through fixed orifices (not shown) to a fluid pressure supply.

Claims (4)

1. An electro-hydraulic servo valve including permanent magnet means, opposed polepieces providing a pair of air gaps, an electrical coil mounted for tilting movement and having a part disposed within one air gap and a part disposed within the other air gap, and a flapper associated with the moving coil.

2. An electro-hydraulic servo valve as claimed in Claim 1 in which the electrical coil is mounted for tilting movement by a flexure tube.

3. An electro-hydraulic servo valve as claimed in Claim 2 in which the coil is substantially rectangular in shape, part of one side being disposed within one air gap and part of the opposite side being disposed within the other air gap, the two remaining sides being connected by way of a saddleshaped member to the flexure tube.

4. An electro-hydraulic servo valve substantially as hereinbefore described and with reference to the accompanying drawings.

4. An electro-hydraulic servo valve substantially as hereinbefore described and with reference to the accompanying drawings.

CLAIMS (1 Mar 1983)

1. An electro-hydraulic servo valve including permanent magnet means, opposed polepieces providing a pair of air gaps in which the magnetic fields produced by the permanent magnet means are directionally polarised in the same direction, an electrical coil having a part disposed within one air gap and a part disposed within the other air gap and mounted for tilting movement about an axis between the two said parts, and a flapper associated with the moving coil.

2. An electro-hydraulic servo valve as claimed in Claim 1 in which the electrical coil is mounted for tilting movement by a flexure tube.

3. An electro-hydraulic servo valve as claimed in Claim 2 in which the coil is substantially rectangular in shape, part of one side being disposed within one air gap and part of the opposite side being disposed within the other air gap, the two remaining sides being connected by way of a saddleshaped member to the flexure tube.