Torque motor assembly

Abstract

A torque motor assembly comprising two or more pole piece pairs, each pair comprising two opposing pole pieces each having an end facing an end of the opposite pole piece, the ends separated by a gap; and a magnetic plate extending between the pole piece pairs and located in the gap, the magnetic plate having surface portions facing the respective pole piece ends; wherein the surface portions of the magnetic plate and the respective pole piece ends are non-parallel with respect to each other.

Claims

1. A torque motor assembly comprising: two or more pole piece pairs, each pair comprising two opposing pole pieces each having an end facing a respective end of the opposite pole piece, the ends separated by a gap, each pole piece defining a pole piece surface; and a magnetic plate extending between the pole piece pairs and located in the gap, the magnetic plate having surface portions that define planes and that are facing the respective pole piece ends; wherein the planes defined by the surface portions of the magnetic plate are non-parallel to the pole piece surfaces; wherein each pole piece end has a triangular cross-section cut out such that opposing pole pieces define a diamond-shaped gap between them, and wherein the magnetic plate has a diamond-shaped cross-section defined by angles different from those defining the gap.

2. The torque motor assembly of claim 1, wherein the pole piece ends define one or more slopes and the surface portions of the magnetic plate define one or more slopes and the slopes of the pole piece ends have an angle different from that of the slopes of the magnetic plate surface portions.

3. A servo valve assembly comprising: a moveable member to control fluid flow; and a torque motor assembly as claimed in claim 1 configured to drive the moveable member in response to a control signal.

4. A torque motor assembly comprising: two or more pole piece pairs, each pair comprising two opposing pole pieces each having an end facing a respective end of the opposite pole piece, the ends separated by a gap, each pole piece defining a pole piece surface; and a magnetic plate extending between the pole piece pairs and located in the gap, the magnetic plate having surface portions that define planes and that are facing the respective pole piece ends; wherein the planes defined by the surface portions of the magnetic plate are non-parallel to the pole piece surfaces; wherein each pole piece end has a triangular cross-section cut out, and the ends are spaced apart such that opposing pole pieces define a hexagonal-shaped gap between them, and wherein the magnetic plate has a hexagonal-shaped cross-section defined by angles different from those defining the gap.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a conventional torque motor assembly in a servo valve;

(2) FIG. 2A is a cross-sectional view of a torque motor assembly according to an embodiment of the disclosure.

(3) FIG. 2B is a perspective view of the embodiment of FIG. 2A.

(4) FIG. 3A is a cross-sectional view of a torque motor assembly according to another embodiment of the disclosure.

(5) FIG. 3B is a perspective view of the embodiment of FIG. 3A.

DETAILED DESCRIPTION

(6) A torque motor assembly as described below can be used as a drive assembly of a servo valve to control a flow of fluid that is output to control the movement of an actuator. The actuator can control e.g. ailerons or elevator flaps of an aircraft.

(7) A typical flapper-nozzle type servo valve is shown in FIG. 1. The assembly shown comprises a single stage valve assembly.

(8) The toque motor 1 causes the flapper 6 to move to the right/left responsive to a control signal. The flapper 6 thus moves between two axially opposing nozzles 2, which, in turn, changes the flow output/pressure at the control part 3.

(9) The control signal is applied to the torque motor and armature which causes the flapper-type drive member 6 to deflect left or right. The single stage assembly can be used as a drive stage for a spool valve assembly. Therefore, when the control signal is such as to cause the drive stage to apply greater fluid pressure to one end of the spool, by diverting more fluid to that end, the spool will move away from that end and vice versa.

(10) In more detail, in the conventional assemblies, to open the servo valve, control current is provided to coils of the motor (e.g. a torque motor) creating electromagnetic torque opposing the sum of mechanical and magnetic torque already ‘present’ in the torque motor. The bigger the electromagnetic force from the coils, the more the jet pipe nozzle turns or the flapper pivots. A torque motor usually consists of coil windings, a ferromagnetic armature, permanent magnets and a mechanical spring (e.g. two torsional bridge shafts). This arrangement provides movement of the nozzle/flapper proportional to the input control current.

(11) The torque motor assembly comprises pairs of opposing pole plates 10 between which is located a magnetic plate 5 connected to the drive member (e.g. flapper 6). The faces 10a of the pole pieces 10 are flat to match the opposing face 5a of the magnetic plate 5 as this provides the most force efficient configuration.

(12) As mentioned above, though, this can give rise to latching.

(13) The torque motor assembly according to this disclosure operates in a manner similar to the above-described conventional assemblies, but the faces of the pole pieces and/or the magnetic plate are not flat or precisely form fitting—rather they are shaped such that there is a difference in the angle of the pole piece face and the angle of the corresponding magnetic plate surface—i.e. that the adjacent surfaces of the pole pieces and the magnetic plate are not exactly form-fitting.

(14) Examples are shown in FIGS. 2A, 2B, 3A and 3B.

(15) FIGS. 2A and 2B show, from different perspectives, an embodiment in which the surfaces 100a of the pole pieces 100 have a triangular shape. The magnetic plate 200 is also formed with a triangular cross section but having angles differing from the angles of the triangles of the pole pieces such that there is a small gap 300 between the pole pieces and the plate at some areas of the interface, rather than the magnetic plate directly contacting the pole pieces all along the interface when latching takes place.

(16) FIGS. 3A and 3B show an alternative configuration in which the magnetic plate has a conical cross-section with the pointed ends being received in a triangular indentation of the pole pieces but with the sloping surfaces of the magnetic plate having a different angle to the sloping surfaces of the pole pieces, again leaving a gap where the interfacing parts do not precisely match when latching takes place.

(17) Such a geometry at the interface between the pole pieces and the magnetic plate mean that there is an increased surface area over which the magnetic field flows, but that because the respective angles differ and the surfaces are not parallel to each other, efficiency is reduced. The higher efficiency provided by the greater surface area may balance out the reduction in efficiency due to the non-parallel surfaces, but this will depend on the selected angles and overall dimensions. Although there may be an overall drop in efficiency of the system, this is offset by the fact that the different angles means that the actual possible contact area is reduced which reduces the possibility of latching. Even if latching does occur, the force required to separate the pole pieces and the magnetic plate will be less than for parallel surfaces. This smaller force should be achieved by the torque motor without the need for additional external force.

(18) Latching may be avoided by adding a ‘hard stop’ to the design such as a screw protruding from the pole piece surface, although this will require further modification of the surface and, further, will reduce the efficiency of the torque motor. Another way to reduce the possibility of latching is to provide an increased gap between the pole pieces, although this requires the Permanent Magnets to be sized differently, and possibly even selection of a different, more powerful magnet material, which in turn requires a different coil design (number of coil windings, coil resistance, impedance etc.) not discussed further here.

(19) The rest of the operation of the servo valve and spool assembly is analogous to that of the flapper and jet-pipe arrangements and will not be described in detail.

(20) Although this disclosure has been described in terms of preferred examples, it should be understood that these examples are illustrative only and modifications and alterations are possible within the scope of the claims.