Patent Description:
Servo valves are well-known in the art and can be used to control how much fluid is ported to an actuator. A single stage flapper type servovalve includes a valve housing having a cavity which receives a pair of opposed nozzles, between which is arranged a flapper which is coupled to a flapper actuator such as a torque motor. The servovalve housing further comprises three ports which allow communication of the working fluid of the servovalve to the nozzles. One of the ports is typically called a control port and its function is to communicate fluid to the actuator (not shown). Deflection of the flapper by means of the flapper actuator changes the amount of fluid that is communicated to the actuator.

Typically the valve housing is formed of aluminium, and the nozzles are formed of stainless steel. The nozzles must be located with very high precision relative to the valve housing in order to assure proper functioning of the valve. This can be challenging in certain operational conditions.

A prior art servovalve having the features of the preamble to claim <NUM> is disclosed in <CIT>. Other prior art servovalves are disclosed in <CIT>, <CIT>, <CIT> and <CIT>.

According to a first aspect of the present invention, there is provided a single stage flapper type servovalve housing as set forth in claim <NUM>.

In some embodiments, the mounting bores are at the housing periphery.

The servovalve housing may be formed by an additive manufacturing technique.

According to a further aspect of the present invention, there is provided a method of manufacturing a single stage flapper type servovalve housing as set forth in claim <NUM>.

The method may further comprise brazing or welding one end of a stainless steel connecting tube to the valve housing for attachment to a torque motor.

According to a further aspect of the present invention, there is provided a single stage flapper type servovalve as set forth in claim <NUM>.

The valve housing and the nozzles may be made from stainless steels having the same or a similar coefficient of thermal expansion. By similar in this context may be meant within +/- <NUM>%, optionally within +/- <NUM>%.

In some embodiments, the valve housing and the nozzles may be made from the same stainless steel.

The servovalve may further comprise a torque motor mounted to the valve housing.

In embodiments, a stainless steel connecting tube may be brazed or welded between the valve housing and the torque motor, the flapper element extending through the connecting tube.

The servovalve may further comprise respective plugs closing the ends of the valve housing bore. The plugs may also be formed of a stainless steel, optionally having the same or a similar coefficient of thermal expansion to that of the valve housing.

According to a further aspect of the present invention, there is provided a method of assembling a single stage flapper type servovalve as set forth in claim <NUM>.

Some embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:.

With reference to <FIG>, a single stage flapper type servovalve <NUM> is illustrated.

The servovalve <NUM> comprises a valve housing <NUM> to which is mounted a flapper actuator <NUM>, in particular a torque motor <NUM>.

As can be seen from <FIG> and <FIG>, the valve housing <NUM> comprises a bore <NUM> in which are fitted, in particular press fitted a pair of opposed nozzles <NUM>. A flapper element <NUM> which is coupled to the torque motor <NUM> is arranged between the pair of nozzles <NUM>. The valve housing <NUM> further comprises a plurality of fluid ports <NUM>, <NUM>, <NUM> for communicating a working fluid to and from the nozzles <NUM>. The ports <NUM>, <NUM>, <NUM> are in fluid communication with the housing bore <NUM>. The central port <NUM> is typically called a control port and its function is to communicate working fluid to an actuator (not shown).

The bore <NUM> is closed at its opposed ends by plugs <NUM> which may be press fitted into the ends of the bore <NUM>.

This general type of servovalve is well known in the art, being used in a wide variety of aircraft control systems, for example in fuel and air management systems for operating engine fuel metering valves, active clearance control valves, bleed valves and so on.

However, the servovalve <NUM> of the disclosure departs from known servovalves in a number of significant respects which will be described further below.

As mentioned earlier, in prior art single stage flapper type servovalves, the valve housing <NUM> is typically made from aluminium. This is because the servovalve will typically be used in aircraft systems, where weight is of concern, and for ease of manufacture. However, the nozzles <NUM> are formed of stainless steel and must be positioned very accurately in the in valve housing.

The use of aluminium as a valve housing material, while being advantageous in many respects has been recognised as being not ideal in others. For example, Aluminium may lose its physical properties at elevated temperatures. Aluminium alloy <NUM> T651 which is a material typically used for servovalve housings may lose up to <NUM>% of its Ultimate Tensile Stress and may suffer fatigue after as little as <NUM> hours exposure to temperatures of <NUM>. Moreover, the nozzles <NUM> have to be very accurately positioned in the bore <NUM> to ensure proper operation of the servovalve <NUM> without any degradation in performance over time. As the nozzles <NUM> are generally press fitted within the bore <NUM>, due to the difference in the coefficient of thermal expansion of the nozzle and housing materials, the interference fit may relax too much at higher temperatures resulting in movement of the nozzles <NUM>.

To overcome or at least mitigate these potential drawbacks, the servovalve housing <NUM> and the nozzles <NUM> are both made from a stainless steel material. Thus embodiments of the invention have the advantage that the servovalve <NUM> may be used in higher temperature environments without weakening the valve housing <NUM>. Moreover, as the coefficients of thermal expansion of the valve housing <NUM> and the nozzles <NUM> will be much closer to one another, an improved interference fit will be formed between the valve body <NUM> and the nozzles <NUM> which will not significantly loosen during use, even at elevated temperatures.

In embodiments of the invention the valve housing <NUM> and the nozzles <NUM> are made from stainless steels having the same or similar coefficients of thermal expansion. By similar in this context may be meant within +/- <NUM>%, or, more narrowly within +/-<NUM>%. This will have the advantage of eliminating or substantially reducing any loss in press fit at high temperatures and will allow looser tolerances in the internal diameter of the bore <NUM> and the external diameter of the nozzles <NUM>, where previously very tight tolerances had to be met due to the very different coefficients of thermal expansion of the bore and nozzle materials. In some embodiments, the valve housing <NUM> and the nozzles <NUM> may be made from the same stainless steel material, for example from A <NUM>.

In embodiments of the invention, the plugs <NUM> sealing the bore <NUM> may also be made from a stainless steel material, for example one having a coefficient of thermal expansion similar to (as discussed above) or equal to that of the valve housing <NUM>. The plugs <NUM> may be therefore be made from made from the same stainless steel material as the valve housing <NUM>, for example from A286.

The valve housing <NUM> comprises a mounting <NUM> for the torque motor <NUM>. As can be seen from <FIG>, in this embodiment, the mounting <NUM> comprises a mounting boss <NUM> upstanding from a top plate <NUM> of the valve housing <NUM>. A chimney <NUM> is formed integrally with and extends upwardly from the valve housing <NUM>. As can be seen from <FIG>, the flapper element <NUM> of the servovalve extends through the chimney <NUM>. The chimney <NUM> is formed with a recess <NUM> at its upper end for receiving a seal, for example an O-ring seal <NUM> which seals against the upper end of the flapper <NUM> to seal the torque motor <NUM> from the fluid in the valve housing <NUM>.

The torque motor <NUM> is attached to the valve housing <NUM> by means of fasteners <NUM> which extend into receiving bores <NUM> formed in the upper surface of the mounting boss <NUM>.

The servovalve <NUM> is mounted to a support surface <NUM> (<FIG>) by means of fasteners <NUM>, for example screw fasteners which are received in mounting bores <NUM> formed at the periphery of the valve housing <NUM>. According to the invention, the mounting bores <NUM> are formed in tubular elements <NUM>. The tubular elements <NUM> are attached at their upper end to the top plate <NUM> of the valve housing <NUM> by webs <NUM>. The tubular elements <NUM> are attached to a central portion <NUM> of the valve housing <NUM> in which is formed the valve bore <NUM> and the ports <NUM>, <NUM>, <NUM> by a network of connecting elements <NUM>, in this embodiment a plurality of connecting arms <NUM>. This creates a lattice-like structure for the valve body <NUM>, with voids <NUM> being formed within the structure between the peripheral connecting tubes <NUM> and the central portion <NUM> of the valve housing <NUM>. This acts significantly reduce the weight of the valve housing <NUM>, which is of particular importance when using stainless steel as the housing material. The central portion <NUM> itself has a generally tubular construction, with the valve bore <NUM> being formed by a tubular wall structure <NUM> and the ports <NUM>, <NUM>, <NUM> being formed by spaced apart tubular elements <NUM>, <NUM>, <NUM> extending from the valve bore wall <NUM>.

In the embodiment of <FIG>, the connecting arms <NUM> are arranged in a rectangular lattice arrangement joining the connecting tubes to each other and to a lower portion <NUM> of the central portion <NUM> of the valve housing <NUM>, surrounding the valve ports <NUM>, <NUM>, <NUM>. Vertical connecting arms <NUM> extend upwardly on either side of the valve housing <NUM> from the nodes <NUM> formed between the connecting arms <NUM> which extend generally parallel to the axis A of the bore <NUM> to connect to the top plate <NUM> of the valve housing <NUM>. This provides a stiff, yet light valve housing construction.

It will be appreciated that other forms of lattice structure may be employed. A further embodiment in accordance with the invention, which incorporates such a structure, is illustrated in <FIG>. The structure of the valve housing <NUM> is generally the same as that of the valve housing <NUM> of the first described embodiment, apart from the lattice structure. Only the lattice structure will therefore be described in detail below.

In this embodiment, the peripheral tubular elements <NUM> arranged on either side of the central portion <NUM> of the valve housing <NUM> are connected together by first connecting arms 150a which extend generally parallel to the axis of the bore <NUM> of the valve housing <NUM>. Those connecting tubular elements <NUM> are then connected to an end mid-height portion 154a of the central portion <NUM> of the valve housing, generally in line with the axis A of the valve housing bore <NUM>, by second, shorter connecting arms 150b. The tubular elements <NUM> are further connected to a central mid-height portion 154b by diagonally extending arms 150c. Relatively short vertical connecting arms <NUM> connect the first connecting arms 150a to the top plate <NUM> of the valve housing <NUM>. The top ends of the connecting elements <NUM> are also attached to the top plate <NUM> by webs <NUM>.

This structure therefore also defines large voids <NUM> in the valve housing <NUM>, thereby significantly reducing its weight.

The valve housing <NUM>, <NUM> of the above described embodiments may be made by any suitable manufacturing technique. However, a particularly advantageous method of manufacturing for use in the present disclosure is additive manufacturing. Additive manufacturing is a technique in which successive layers of material are deposited one upon the other to create a desired shape. An example of such a process which may be usefully employed in producing servovalve housings in accordance with the disclosure is laser powder bed fusion. Additive manufacturing has the advantage that it allows relatively complicated shapes to be produced. Stainless steel is a material which is capable of use in such a process.

The additively manufactured housing <NUM>, <NUM> may be produced to a near-net shape and then finish machined to provide various features such as the bore <NUM>.

The use of stainless steel as a valve housing material may also allow modification and simplification of other aspects of the servovalve.

As described briefly above, in a traditional servovalve construction, a chimney <NUM> is integrally formed with the servovalve housing <NUM> and the chimney <NUM> is sealed to the flapper element <NUM> by a seal to avoid leakage of fluids from the servovalve housing <NUM> into the torque motor <NUM>. In the embodiment of <FIG>, however, the valve housing <NUM> is provided with a much shorter chimney <NUM> and a separate tube <NUM> is attached to the top of the chimney <NUM>. The tube <NUM> may be relatively thin, for example between <NUM> and <NUM> thick. The wall thickness will be determined to a large extent by the operating pressure of the servovalve, so for an air servovalve the thickness may be about <NUM>, but for a fuel application where pressures would be higher, the thickness may be greater, for example about <NUM> to about <NUM>. The thickness may also be dependent to some extent on the total armature stiffness of the torque motor. The precise thickness can be determined as necessary for any particular application. The tube <NUM> may, for example be received in a groove <NUM> in the top of the chimney <NUM>. The tube <NUM> is secured to the chimney <NUM> by a braze or weld <NUM>.

The upper end of the tube <NUM> is similarly attached to the torque motor <NUM>. In this embodiment the tube <NUM> is attached to a torque bridge <NUM> of the torque motor <NUM>, to which the flapper element <NUM> is attached. The tube <NUM> may be received in a groove <NUM> in the bottom surface of the torque bridge <NUM> and secured by a braze or weld <NUM>. While fluid from the servovalve housing <NUM> will be able to enter the lower end of the tube <NUM>, it will not be able to exit the upper end of the tube <NUM> due to the close fit between the flapper element <NUM> and the torque bridge and the braze or weld <NUM>.

It will be seen from the above that various embodiments of the disclosure have distinct advantages over prior art servovalves. By using stainless steel as the material of the servovalve housing <NUM>, the servovalve may potentially be used at higher operating temperatures, thereby potentially expanding the range of applications for such valves. The improved strength of the housing <NUM> due to its manufacture from stainless steel also means that the servovalve may be used not only at higher temperatures, but also at higher pressures.

By making the nozzles <NUM> and valve housing <NUM> of stainless steel, optionally the same material, the problem of potential loss of press fit at elevated temperatures is prevented. It also means that it may be possible to increase the tolerance on the bore and nozzle diameters, thereby facilitating manufacture and assembly of the servovalve <NUM>. This also applies to the plugs <NUM> closing the bore <NUM> of the housing <NUM>.

By designing the valve housing <NUM> with a lattice type construction, a significant reduction of weight may be achieved. In fact, it may be possible to produce housings which are lighter that hitherto known aluminium based housings, for example by as much as <NUM>% lighter.

The use of an additive manufacturing process will also be advantageous as it will all allow intricate shapes of housing to be produced. Moreover, in embodiments, the valve housing <NUM> may comprise internal voids which may further reduce the weight of the housing. For example, the individual tubular structures and connecting arms of the valve housing <NUM> may comprise voids. Such structures may be created using additive manufacturing, but not by conventional techniques such as casting or machining.

Claim 1:
A single stage flapper type servovalve housing (<NUM>; <NUM>; <NUM>) comprising:
a bore (<NUM>; <NUM>) for receiving a pair of opposed nozzles (<NUM>) therein; and
a plurality of fluid ports (<NUM>, <NUM>, <NUM>) in fluid communication with the housing bore (<NUM>; <NUM>);
a plurality of mounting bores (<NUM>) for receiving fasteners (<NUM>) for mounting the valve housing to a surface (<NUM>), the mounting bores (<NUM>) formed as tubular elements (<NUM>; <NUM>),
characterised in that:
the mounting bores are attached to a central portion (<NUM>; <NUM>) of the valve housing (<NUM>; <NUM>; <NUM>) in which is formed the valve bore (<NUM>; <NUM>) and the plurality of fluid ports (<NUM>, <NUM>, <NUM>) by means of a plurality of connecting arms (<NUM>; 150a; 150b; 150c), wherein the connecting arms form a lattice structure with voids (<NUM>; <NUM>) formed between the connecting arms (<NUM>; 150a; 150b; 150c) and the central portion (<NUM>; <NUM>) of the valve housing (<NUM>; <NUM>; <NUM>), and wherein the valve housing (<NUM>; <NUM>; <NUM>) is made from stainless steel.