Actuator

Abstract

With variable airgap reluctance actuators problems arise due to the relationship between actuator mass and displacement range. By providing opposed surfaces in the actuator stator core and armature which have undulations typically in the form of grooves, slots and projections, a greater displacement range can be achieved whilst maintaining performance above a rated displacement force characteristic. In such circumstances by establishing a necessary rated displacement force characteristic, an actuator can be tailored and designed to meet that characteristic over a desired displacement range which has significantly less mass in comparison with a prior actuator arrangement having flat surfaces.

Description

Embodiments of certain aspects of the present invention will now be described by way of example only and with reference to the accompanying drawings in which:—

FIG. 3 is a schematic cross section of an actuator;

FIG. 4 is a graphic illustration of axial force relative to airgap for an actuator in accordance with aspects of the present invention;

FIG. 5 provides schematic illustrations of alternate undulations in opposed surfaces in accordance with aspects of the present invention;

FIG. 6 is a schematic cross section enlargement of part of the actuator of FIG. 3;

FIGS. 7 a and 7b are schematic cross section enlargements of alternative undulation arrangements wherein the undulations are disengaged; and

FIG. 7 c is a schematic cross section enlargement of the undulation arrangement of FIG. 7b wherein the undulations are partially overlapped.

Claims

1. An actuator comprising an armature, a stator and electrical coils; the electrical coils being arranged, when energised, to cause relative displacement between the armature and the stator, the stator and the armature having opposed surfaces with an airgap between them, the opposed surfaces having undulations, the undulations comprising projections from one opposed surface and recesses in the other opposed surface whereby in use the projections and recesses move between a first position in which the projections are unenclosed by the recesses and a second position which the projections are within the recesses.

2. An actuator as claimed in claim 1 wherein the undulations are reciprocal in the respective opposed surfaces of the armature and the stator.

3. An actuator as claimed in claim 1 wherein the undulations are provided by slots in the opposed surfaces.

4. An actuator as claimed in claim 3 wherein the cross-sectional shape of the slots is at least one of the group comprising rectangular, mortice, truncated tapered and point tapered.

5. An actuator as claimed in claim 1 wherein the undulations vary in depth.

6. An actuator as claimed in claim 1 wherein the undulations have a consistent depth across the shared gap between the opposed surfaces.

7. An actuator as claimed in claim 1 wherein the actuator is general cylindrical.

8. An actuator as claimed in claim 1 wherein the actuator is a generally polyhedral prism.

9. A gas turbine engine incorporating an actuator as claimed in claim 1.