Patent Description:
Torque motors are commonly used to control hydraulic actuators and other, e.g., pneumatic systems, for example as part of a servovalve. The design of a torque motor has become fairly standardised, and many examples of such standard construction may be found in the art. In particular, the magnetic components of a torque motor are typically designed so that they can provide a relatively compact assembly and fit well with the other components of the torque motor such as described in, for example, Patent Application Numbers <CIT>, <CIT> and <CIT>.

<FIG> shows an example of a cross-section of a conventional torque motor <NUM>, with a view of a lower pole piece <NUM> in isolation. As is evident from <FIG>, the lower pole piece <NUM> comprises a substantially annular piece, having vertical extensions <NUM> that are configured to sit either side of an armature <NUM> of the torque motor <NUM>, and opposite an upper pole piece <NUM> that is essentially a mirror of the lower pole piece <NUM>.

The magnetic elements of a torque motor, such as the pole pieces and armature are typically designed to provide mechanical integrity of the overall torque motor structure whilst providing the required transfer of magnetic flux. The shape of the magnetic elements are designed as a compromise between these structural and magnetic functions.

Additionally, the shape and layout of the magnetic elements is usually optimised for conventional machining processes. This may be evident from the lower pole piece <NUM> of <FIG>, from which it can be seen that a simple annular is used, with various drill holes <NUM> being formed in the lower pole piece <NUM> insertion of it, e.g., fasteners to secure the torque motor <NUM> together.

<FIG> shows the results of a finite element model analysis as shaded portions of the torque motor <NUM>, during which it was observed that saturation effects can occur at various locations in the conventional magnetic elements. For example, a local saturation effect can be visible at arrow <NUM> due to the drill holes <NUM> in the lower pole piece <NUM>. The local saturation has been found to degrade and limit torque motor performance and complicate the magnetic flux throughout the torque motor <NUM>.

It is desired to improve the structure of a torque motor so that magnetic flux distribution is improved.

In accordance with an aspect of the disclosure, there is provided a torque motor according to claim <NUM>, wherein a pole piece is formed at least partially by two separate arcuate members, each extending in opposite directions and following a generally circular path defining a perimeter of the pole piece, wherein the arcuate members meet each other at diametrically opposed attachment portions of the pole piece.

Use of arcuate members in this manner has been found to improve the magnetic flux distribution and other magnetic properties of the pole piece, for example reduction of saturation effects and/or higher magnetic torque than conventional arrangements.

The arcuate members may have a substantially constant cross-sectional area along a longitudinal axis thereof. For example, the cross-sectional area of the arcuate member(s) may not vary by more than +/- <NUM>% along the length thereof. This may further reduce saturation effects. The cross-sectional area in this regard may be a cross-section perpendicular to a longitudinal axis of the arcuate member(s).

The arcuate members may be or comprise generally cuboid projections following the generally circular path.

The arcuate members may be symmetrically opposed to each other, meaning that the magnetic flux through each arcuate member is substantially the same.

The pole piece is a single piece of material that is devoid of any holes or apertures.

An outer circumferential surface of the pole piece may have a generally cylindrical profile.

The apparatus may further comprise one or more permanent magnets extending between the lower pole piece and the upper pole piece, wherein the permanent magnets are configured to support the upper pole piece in use. The upper pole piece may be supported solely by the permanent magnets in use.

The armature may extend along a longitudinal axis, and may comprise opposed surfaces located at opposed ends of the armature along the longitudinal axis thereof, wherein the opposed surfaces follow a curved profile corresponding to a curved profile of the lower pole piece and the upper pole piece.

In accordance with an aspect of the disclosure, there is provided a servovalve comprising a torque motor as described above.

In accordance with an aspect of the disclosure, there is provided a method of constructing a torque motor as described above, comprising:
providing at least one pole piece formed at least partially by two arcuate members extending in opposite directions and following a generally circular path defining a perimeter of the pole piece, wherein the arcuate members meet each other at diametrically opposed attachment portions of the pole piece.

The arcuate members may have a substantially constant cross-sectional area along a longitudinal axis thereof.

Herewith will be described various embodiments of a in servovalve and torque motor, wherein the magnetic elements thereof have a structure designed to improve the magnetic flux through the various components, and in particular the magnetic elements of the servovalve and torque motor thereof.

<FIG> shows a servovalve <NUM> that may be used in any suitable hydraulic and pneumatic application in order to, for example, control an actuator using a flow of hydraulic or pneumatic fluid. The operation of such a servovalve is well known in the art and will not be described in detail herein.

The servovalve <NUM> comprises a torque motor <NUM> that is configured to sit on a base <NUM> of the servovalve <NUM>. The base <NUM> of the servovalve <NUM> contains the various hydraulic, pneumatic or other fluid ports, and as is known in the art the torque motor <NUM> controls the flow of fluid through the various ports. It should be noted that the torque motor <NUM> disclosed herein, and various components thereof are considered to be advantageous in their own right, and the broadest aspects of the present disclosure are not limited to the use of the torque motor <NUM> within the servovalve <NUM> as shown in <FIG>.

<FIG> shows the torque motor <NUM> in isolation.

The torque motor <NUM> comprises a lower pole piece <NUM> and an upper pole piece <NUM>. The lower pole piece <NUM> and the upper pole piece <NUM> are substantially identical, although mirror images of each other. The lower pole piece <NUM> and the upper pole piece <NUM> have a substantially circular shape when viewed from above or below (see, e.g., <FIG>). The lower pole piece <NUM> and the upper pole piece <NUM> have a unique shape, in that they are formed by two arcuate or U-members <NUM>, <NUM> that are attached to one another at diametrically opposed attachment portions <NUM>, <NUM>.

The arcuate members <NUM>, <NUM> extend from a first of the attachment portions <NUM>, <NUM> in opposite directions, then follow a substantially circular path such that they meet at a second of the attachment portions <NUM>, <NUM>, which is diametrically opposed to the first attachment portion <NUM>, <NUM>.

Each arcuate member <NUM>, <NUM> is be formed by three sections 122A-C, 132A-C, wherein a first section 122A, 132A connects to an attachment portion <NUM>, <NUM> and extends vertically and circumferentially away from the attachment portion <NUM>, <NUM> to the second section 122B, 132B, which extends circumferentially around the circular path, wherein the second section 122B, 132B then extends into a third section 122C, 132C that extends vertically and circumferentially towards the diametrically opposed attachment portion <NUM>, <NUM>.

An outer circumferential surface <NUM>,<NUM> of each pole piece <NUM>, <NUM> has a generally cylindrical profile. For example, when viewed from above (see <FIG>) the outer cylindrical surface <NUM>, <NUM> follows a substantially circular path.

The torque motor <NUM> further comprises an armature <NUM> that is located between the lower pole piece <NUM> and the upper pole piece <NUM>. The armature <NUM> extends along a longitudinal axis A thereof between one of the diametrically opposed locations and the other of the diametrically opposed locations.

The torque motor <NUM> comprises a central, longitudinal axis X that is perpendicular to the longitudinal axis A of the armature <NUM>.

As discussed above and generally, each arcuate member <NUM>, <NUM> of the pole pieces <NUM>, <NUM> extends from a respective attachment portion <NUM>, <NUM> at least partially in a vertical direction away from the armature <NUM> and around a circumferential path formed by the general shape of the pole piece <NUM>, <NUM>.

In various embodiments, a cross-section of each arcuate member <NUM>, <NUM> may be substantially constant along a longitudinal axis (Y) (see <FIG>) thereof. As will be appreciated from <FIG>, this cross-section will be substantially square or rectangular, but in various embodiments the cross-section may also be circular or another shape. Use of a constant cross-section in this regard has been found to reduce magnetic losses that can be caused by locally decreased cross-sectional areas, such as those formed by the drill holes <NUM> in the conventional pole piece described above.

Similar effects may be achieved by reducing the variation in cross-sectional area, as opposed to keeping it exactly constant. As such, in various embodiments the cross section of the arcuate members <NUM>, <NUM> along their longitudinal axis Y may not change by more than +/- <NUM>%, +/- <NUM>% or +/- <NUM>%.

The torque motor <NUM> further comprises permanent magnets <NUM> located on opposed sides of the torque motor <NUM> and extending between respective arcuate members <NUM>, <NUM> of the upper pole piece <NUM> and the lower pole piece <NUM>. The permanent magnets <NUM> may be arcuate such that they follow the general profile of each arcuate member <NUM>, <NUM> that they extend between.

In various embodiments, the cross-section of each arcuate member <NUM>, <NUM> may be substantially constant along its longitudinal axis Y and between its respective attachment portion <NUM>, <NUM> and the point at which it meets a respective one of the permanent magnets <NUM>, at which point the magnetic flux can dissipate into the permanent magnet <NUM>.

In the illustrated embodiment, a small undercut <NUM> is present at the point at which the arcuate member <NUM>, <NUM> meets the permanent magnet <NUM>. This is provided to facilitate positioning of the elements, but may not be present.

As shown in <FIG>, the armature <NUM> of the torque motor <NUM> comprises a substantially solid block of material, which comprises first and second opposed arm portions <NUM>, <NUM>. A central portion <NUM> of the armature <NUM> comprises an aperture <NUM> and notches <NUM> on opposed sides of the aperture <NUM>. The notches <NUM> are configured to maintain a constant cross-section of the armature <NUM> along its longitudinal axis A, taking into account the aperture <NUM>. The volume of the notches <NUM> may substantially correspond to the volume of the void formed by the aperture <NUM>.

The armature <NUM> may terminate at end surfaces <NUM>, which end surfaces <NUM> are perpendicular to the longitudinal axis A of the armature <NUM>. The end surfaces <NUM> may be curved, and may follow the outer circular or cylindrical contour of the torque motor <NUM>, and specifically the contour of the upper and lower pole pieces <NUM>, <NUM> as shown in <FIG>.

The various features described in respect of the armature <NUM>, for example the substantially constant cross-section along its longitudinal axis A, and the curved nature of the end surfaces <NUM> have been found to reduce magnetic flux losses in accordance with the overall aims of the present disclosure.

The torque motor <NUM> further comprises one or more electromagnetic coils <NUM>, which extend around a respective arm portion <NUM>, <NUM> of the armature <NUM>. As is known in the art, application of an electrical current to the electromagnetic coils <NUM> causes the armature <NUM> move. This, in turn, causes one or more components of the servovalve <NUM> to move and fluid within the base portion <NUM> of the servovalve <NUM> to be displaced, for example to actuate a component.

Various embodiments of the present disclosure are aimed at providing a smooth magnetic circuit for the torque motor <NUM>, which is designed to provide various technical effects due to the shape and construction of the various components of the torque motor <NUM>.

As shown in various finite element simulations (see, e.g., <FIG>) the torque motor <NUM> described herein reduces saturation effects of magnetic flux throughout the magnetic circuit of the torque motor <NUM>. This means that the magnetic torque achieved by the torque motor <NUM> can be higher for a particular application, for example over and above the conventional torque motor shown in <FIG>.

Use of constant cross-section pieces, or sections of pieces as discussed above can lead to reduced saturation of magnetic flux, and increased magnetic torque. These technical effects mean that the angular stroke for the torque motor <NUM> may be higher compared to the conventional arrangements.

The manufacturing cost of the components, in particular the upper and lower pole pieces <NUM>, <NUM> may be decreased, due to the reduced need to, for example, drill through them, and the ability to injection mould the pieces.

As will be appreciated from <FIG>, the lower pole piece <NUM>, permanent magnets <NUM> and upper pole piece <NUM> are constructed such that the upper pole piece <NUM> is supported (e.g., solely) by the permanent magnets <NUM> and the lower pole piece <NUM>. This means that there is no need to provide any additional supporting structure for the upper pole piece <NUM>, and it will be held in place on top of the permanent magnets <NUM>. This eliminates the need to drill through the upper and/or lower pole pieces <NUM>, <NUM> and, in turn, the complications caused by drill holes as discussed above. This has an additional benefit in that the operating temperature range for the torque motor <NUM> can be increased, due to the elimination of the fasteners that would otherwise extend through the upper and/or lower pole pieces of a conventional torque motor. Furthermore, the mass of the torque motor <NUM> can be reduced.

Claim 1:
A torque motor comprising:
a lower pole piece (<NUM>) and an upper pole piece (<NUM>) with respect to a vertical axis (X) of the torque motor; and
an armature (<NUM>) that is located between the lower pole piece (<NUM>) and the upper pole piece (<NUM>), the armature comprising first and second opposed arm portions (<NUM>, <NUM>), each arm portion (<NUM>, <NUM>) being positioned between the lower pole piece (<NUM>) and the upper pole piece (<NUM>);
wherein at least one of the lower pole piece (<NUM>) and the upper pole piece (<NUM>) are formed by two respective arcuate members (<NUM>, <NUM>) that are attached to one another at diametrically opposed attachment portions (<NUM>, <NUM>), wherein each arcuate member extends in opposite directions and follows a generally circular path defining a perimeter of said pole piece (<NUM>,<NUM>); characterised in that
each diametrically opposed attachment portion (<NUM>,<NUM>) is configured as a block of material extending vertically away from a respective one of the first and second opposed arm portions (<NUM>, <NUM>), the respective arcuate members (<NUM>,<NUM>) extending from the block of material, wherein each arcuate member (<NUM>, <NUM>) is formed by three sections (122A-C, 132A-C), wherein a first section (122A, 132A) connects to one of the diametrically opposed attachment portions (<NUM>, <NUM>) and extends vertically and circumferentially away from the diametrically opposed attachment portion (<NUM>, <NUM>) to the second section (122B, 132B), which extends circumferentially around the circular path, wherein the second section (122B, 132B) then extends into a third section (122C, 132C) that extends vertically and circumferentially towards the other of the diametrically opposed attachment portions (<NUM>, <NUM>).