Method of manufacturing a servo valve manifold

Abstract

A method of manufacturing a servo valve manifold by casting molten metal around a single piece core 102 which comprises a spool cavity portion 104 and a plurality of flow gallery portions 106-114. Aft

Description

Field of the Invention The present invention concerns a method of manufacturing a servo valve manifold. More particularly, but not exclusively, this invention concerns a method of manufacturing a servo valve manifold by casting the servo valve manifold around a core having a shape which corresponds to the internal shape of the servo valve manifold. The invention also concerns a servo valve manifold formed by the method, and a servo valve comprising the servo valve manifold. Background of the Invention Figure 1 shows a schematic representation of a prior art servo valve 1. The servo valve 1 comprises a manifold 3 comprising a spool cavity 5 housing a spool 7. The servo valve 1 comprises a control interface 9 comprising five ports, including a high pressure supply port P, two low pressure return ports T, Tl, a first service port A, and a second service port B. A plurality of flow galleries 11 in the servo valve manifold connect each of the ports to the spool cavity 5. A further U-shaped flow gallery 13 connects two regions of the spool cavity 5 and provides for fluid communication between the low-pressure return ports T, Tl. The position of the spool 7 in the spool cavity 5 defines the fluid flow path between the ports. The spool 7 is actuated by motor M. Servo valve manifolds can be manufactured by casting. To form the spool cavity and the flow galleries, the servo valve manifold is cast around a core which has a shape corresponding to the shape of the spool cavity and the flow galleries. It is known to form the core from a frangible material such as sand, although other materials can be used. The servo valve manifold is cast by pouring molten manifold material, which is typically a metal, around the core. Once the servo valve manifold material has set, the core is removed. The core may be removed by shaking the manifold, which breaks up the core and causes it to be expelled from the manifold. After the servo valve manifold has been cast, certain areas of the servo valve manifold may be machined in order to improve the surface quality and / or form features in the servo valve manifold. Figure 2 shows a prior art servo valve manifold 15. The servo valve manifold 15 has been manufactured by casting. The servo valve manifold 15 is shown with a core 17 still in place and prior to machining. The core 17 comprises a spool cavity portion 19, a plurality of flow gallery portions 21, 23, 25, 27, 29 and a further U-shaped flow gallery portion 31. The servo valve manifold 15 comprises a spool cavity 33 and a plurality of flow galleries 35 which correspond to the shape of the core 17. A control interface 37 is provided on the underside of the servo valve manifold 15. The control interface 37 comprises five ports T, A, P, B and T1 distributed in a pattern according to international standard ISO 4401-05. Each port is connected to the spool cavity 33 via a different one of the flow galleries 35. Each of the flow galleries 35 opens into the spool cavity 33 via a circumferential opening which extends all the way around the spool cavity 33. A further U-shaped flow gallery 39 places the two outer ports T and T1 in fluid communication. Figure 3 shows a view of the core 17 from underneath. As can be seen, the core 17 is shaped such that the ports formed in the servo valve manifold 15 are distributed in a triangular arrangement according to the above standard. Figure 4 shows an enlarged view of the three middle flow gallery portions 23, 25, 27 of the core 17. As can be seen, the central flow gallery portion 25 of the core 17 overlaps the two adjacent flow gallery portions 23 and 27 of the core 17 in a longitudinal direction L by a distance D. In the cast servo valve manifold 15, the central flow gallery and the central port P therefore overlaps the two adjacent flow galleries and ports A and B in the longitudinal direction. In consequence of the flow gallery portions 23, 25, 27 of the core 17 overlapping each other, the core 17 cannot be moulded as a single piece using a conventional two-part mould. The overlapping parts of the core 17 would prevent the two mould parts being separated whilst maintaining the desired shape of the core 17. The core 17 is therefore manufactured in two pieces using two different moulds. The two pieces of the core 17 are then assembled together. A first piece of the core 17 comprises the central flow gallery portion 25 and a correspondingly wide section of the spool cavity portion 19. A second piece of the core 17 comprises the other flow gallery portions 21, 23, 27, 29, 31 and the remainer of the spool cavity portion 19. The assembling together of the two pieces of the core 17 adds complexity to the manufacturing process. In practice, it is difficult to align the two pieces of the core 17 in exactly the same position each time. l-2mm deviations in the alignment of the two pieces are typical. This leads to variations in the servo valve manifolds 15 made according to this method. The variations are particularly found in the region of the central port P. Problems associated with these variations can include poorer sealing and lower fatigue life. Solving these problems by redistributing the flow galleries and the ports in a different pattern would jeopardise compliance with above international standard. An example of a servo valve having a port pattern according to ISO 4401-05 is the S10 Pro manufactured by Dornin Fluid Power Limited (UK). The present invention seeks to solve the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved method of manufacturing a servo valve manifold, an improved servo valve manifold and / or an improved servo valve. Summary of the Invention The present invention provides, according to a first aspect, a method of manufacturing a servo valve manifold. The servo valve manifold comprises: a spool cavity configured to receive a spool such that the spool can reciprocate in the spool cavity in a longitudinal direction; a control interface comprising a plurality of ports for connection to an external hydraulic system, each of the ports comprising a port opening in an external surface of the servo valve manifold; and a plurality of flow galleries, each of the flow galleries extending between the spool cavity and a different one of the ports, each of the ports thereby being connected to the spool cavity by one of the flow galleries. It will be understood that the flow galleries are arranged such that, when the servo valve manifold is in use, the position of the spool in the spool cavity determines the fluid flow path between the ports. The method comprises the following steps: forming a core from a core material, the core comprising a spool cavity portion corresponding to the shape of the spool cavity, and a plurality of flow gallery portions corresponding to the shape of the flow galleries, the core being integrally formed as a single piece; casting the servo valve manifold by introducing molten material around the core and allowing the molten material to solidify; and then removing the core material from the servo valve manifold; and machining the servo valve manifold. The plurality of flow gallery portions of the core are spaced apart in the longitudinal direction such that, after the step of casting the servo valve manifold and before the step of machining the servo valve manifold, the plurality of flow galleries are spaced apart from each other in the longitudinal direction (and thus the port openings are spaced apart from each other in the longitudinal direction). The step of machining comprises increasing the cross-sectional area of one or more of the flow galleries and the corresponding port openings such that at least some of the flow galleries overlap each other (and thus at least some of the port openings overlap each other) in the longitudinal direction. According to the present method, one or more flow gallery portions of the core are narrower (in the longitudinal direction) than the flow galleries in the final manufactured servo valve to such an extent that the flow gallery portions do not overlap each other in the longitudinal direction. The core can thereby be made as a single piece using a conventional two-part mould. A single piece core avoids the need to assemble together a core formed of multiple pieces. The method may thereby be easier to perform and result in a more consistent final product. The desired size of the flow galleries and port openings is achieved by machining after the servo valve manifold has been cast. The step of forming the core may use a mould (e.g. a two-part mould) comprising a first core moulding element and a second core moulding element. The first and second core moulding elements may be arranged to be brought together to form a core moulding cavity having a shape corresponding to the shape of the core. The step of forming the core may comprise bringing together the first and second core moulding elements. The step of forming the core may comprise moulding the core material in the core moulding cavity. The step of moulding the core material in the core moulding cavity may comprise filling the core moulding cavity with the core material. The core moulding cavity may be filled by blowing core material into the core moulding cavity via one or more openings which open into the core moulding cavity. The step of moulding the core material in the core moulding cavity may comprise heating the core material within the core moulding cavity, for example to harden the core material. The step of forming the core may comprise separating the first and second core moulding elements and removing the core from the mould. When the first and second core moulding elements are brought together, (at least part of) a face of the first moulding element may meet (at least part of) a face of the second moulding element at a plane which extends parallel to the longitudinal direction. When the first and second core moulding elements are separated, they may be moved apart in a separation direction. The separation direction may lie in a plane which is perpendicular to the longitudinal direction. Preferably, the core is free of portions which overhang and / or undercut other portions of the core in the separation direction. The core material may be or may comprise a frangible material, for example sand, although other materials may be used. The step of casting may comprise sand casting. The step of casting may comprise providing the moulten material in a mould cavity having a shape corresponding to an external shape of the servo valve manifold, the core being provided within the mould cavity. The moulten material may be or may comprise a metal, for example steel or aluminium. The step of removing the core material from the servo valve manifold may comprise shaking the servo valve manifold. The shaking may break up the core. The shaking may partly or fully expel the core material from the servo valve manifold. The step of removing the core material may alternatively or additionally involve supplying an airflow through the servo valve manifold to remove the core material. The step of machining will be understood to comprise the mechanical removal of material from the cast servo valve manifold. The step of machining may comprise drilling, reaming, routing, cutting, filing and / or boring. The step of machining may comprise drilling into one or more of (optionally each of) the port openings. The step of drilling may increase the diameter of one or more of the port openings. The step of drilling may increase the diameter of at least part of one or more of flow gallery / galleries. The step of machining may comprises increasing the cross-sectional area of one or more of (optionally each of) the flow galleries along at least 10%, 20%, 30%, 40%, 50% (half), 60%, 70%, 80%, or 90% of the distance from the port opening to the spool cavity. After the step of machining, the one or more of (optionally each of) the port openings may be circular. It may be that, prior to machining, one or more of the port openings are non-circular. For example, one or more of the port openings may have a truncated circular shape prior to machining. After the step of machining, the one or more of (optionally each of) the flow galleries may comprise a cylindrical section extending from the port opening towards the spool cavity. The cylindrical section may have a circular cross-section. The cylindrical section may extend along at least 10%, 20%, 30%, 40%, 50% (half), 60%, 70%, 80%, or 90% of the distance from the port opening to the spool cavity. The extent of the cylindrical section may correspond to the distance to which a drill penetrates the flow gallery during the step of machining. After the step of casting and prior to the step of machining, the one or more of (optionally each of) the flow galleries may have a first width in the longitudinal direction. After the step of machining, the one or more of (optionally each of) the flow galleries may have a second width in the longitudinal direction. The second width is greater than the first width. After the step of machining, the one or more of (optionally each of) the flow galleries may comprise a first section extending from the port opening towards the spool cavity having the second width, and a second section which is relatively closer to the spool cavity (compared to the first section) having the first width. The first section may be the cylindrical section. The second section may taper outwards towards the spool cavity. The one or more of (optionally each of) the flow galleries may comprise a step change in width as between the first section and second section. The one or more of (optionally each of) the flow galleries may comprise a tapered section between the first section and second section. The tapered section may have a profile corresponding to a profile of a tapered end of a drill used to increase the cross-sectional area of the flow gallery / galleries. It has been found that by machining the one or more flow galleries after casting, at least part of the machined flow galleries may be straighter, wider and / or smoother. This may reduce the flow resistance in the flow galleries, which may increase the maximum flow rate through the servo valve manifold. The control interface may comprise two, three, four or five ports. Accordingly, the plurality of ports may comprise one or more of a first port comprising a first port opening, a second port comprising a second port opening, a third port comprising a third port opening, a fourth port comprising a fourth port opening, and / or a fifth port comprising a fifth port opening. Similarly, the plurality of flow galleries may comprise two, three, four or five flow galleries. Accordingly, the plurality of flow galleries may comprise one or more of a first flow gallery associated with the first port, a second flow gallery associated with the second port, a third flow gallery associated with the third port, a fourth flow gallery associated with the fourth port, and / or a fifth flow gallery associated with the fifth port. It will be understood that each of the plurality of flow galleries provides a fluid flow path between the spool cavity and a different one of the ports. Each of the flow galleries may extend between the spool cavity and only one of the ports. Similarly, each of the ports may be associated with only one of the flow galleries. Each of the flow galleries may provide a fluid flow path which extends in a substantially straight line between the spool cavity and one of the ports. Each of the flow galleries may comprise a section which extends circumferentially around the spool cavity. The spool cavity may be in fluid communication with each of the flow gallies via a plurality of openings distributed around the circumference of the spool cavity, or via a single circumferential opening extending fully around the circumference of the spool cavity. Each of the flow galleries may extend directly between the spool cavity and a different one of the ports. Each of the ports may thereby be directly connected to the spool cavity by one of the flow galleries. Each of the flow galleries may comprise a first end defined by the port opening, and a second end at which the flow gallery opens into the spool cavity. The step of machining may comprise increasing the cross-sectional area of one or more of the first flow gallery, second flow gallery, third flow gallery, fourth flow gallery and / or fifth flow gallery; for example, by drilling into the respective first port opening, second port opening, third port opening, fourth port opening and / or fifth port opening. The step of machining may comprise increasing the cross-sectional area of each of the plurality of flow galleries. After the step of machining, the first port opening may overlap with the second port opening in the longitudinal direction. After the step of machining, the first port opening may overlap with the third port opening in the longitudinal direction. It may be that, after the step of machining, the fourth port opening and / or the fifth port opening are still spaced apart from the other port openings in the longitudinal direction. The first port opening may be a central port opening. The second port opening may be adjacent the first port opening and to a first side thereof (in the longitudinal direction). The third port opening may be adjacent the central port opening and to a second side thereof (in the longitudinal direction). The fourth port opening may be adjacent the second port opening and disposed on the opposite side to the first port opening (in the longitudinal direction). The fifth port opening may be adjacent the third port opening and disposed on the opposite side to the first port opening (in the longitudinal direction). The fourth and fifth port opening may thereby be outer port openings disposed on opposing outer sides of the group comprising the first, second and third port openings (in the longitudinal direction). The control interface may comprise a flat portion of an external surface of the servo valve manifold. The control interface may be configured such that the port openings are located in the same plane. In use, the plurality of port openings may be surrounded by a gasket. The gasket may be provided at a perimeter of the control interface. After the step of casting and prior to the step of machining, the plurality of port openings may be spaced apart in a direction perpendicular to the longitudinal direction. Said perpendicular direction may be defined in the plane of the flat external surface of the control interface. After the step of machining, at least some of the plurality of port openings may overlap with each other in the direction perpendicular to the longitudinal direction. After the step of machining, the second port opening may overlap with the fourth port opening in the direction perpendicular to the longitudinal direction. After the step of machining, the third port opening may overlap with the fifth port opening in the direction perpendicular to the longitudinal direction. After the step of machining, the first port opening may still be spaced apart from the other port openings in the direction perpendicular to the longitudinal direction. The first port (or the fourth and fifth ports) may be for connection to a hydraulic fluid supply line, e.g. a high-pressure supply. The second and third ports may be service ports for controlling an external hydraulic device such as a hydraulic actuator. The fourth port (or the first port) may be for connection to a hydraulic fluid return line, e.g. a low-pressure return. The fourth and fifth ports (or the first port) may be for connection to a hydraulic fluid return line, e.g. a low-pressure return. The ports may be disposed in a triangular arrangement. The ports may be arranged in ISO standard port pattern. For example, a port pattern according to ISO 4401 (e.g. ISO 4401-05). The ports may be arranged in an NG10 port pattern. The port openings may comprise a first set of port openings (e.g. the second and fourth port openings) disposed on (e.g. overlaying) a first straight line, and a second set of port openings (e.g. the third and fifth port openings) disposed on (e.g. overlaying) a second straight line. The first and the second lines may be oriented at an angle to each other such that the lines cross at a location occupied by a central port opening (e.g. the first port opening). The first port opening may be disposed on a first axis extending parallel to the longitudinal direction. The second and third port openings may be disposed on a second axis extending parallel to the longitudinal direction. The fourth and fifth port openings may be disposed on a third axis extending parallel to the longitudinal direction. The first axis, second axis and third axis being spaced apart in the direction perpendicular to the longitudinal direction. The centre point of the port openings may lie on the respective axes. After the step of machining, the first axis may be separated from the second axis by between 10mm and 20mm, or between 12.5mm and 17.5mm, for example, the separation may be 15.1mm. After the step of machining, the first axis may be separated from the third axis by between 20mm and 30mm, or between 22.5mm and 27.5mm, for example, the separation may be 26.2mm. After the step of machining, the second axis may be separated from the third axis by between 5mm and 15mm, or between 7.5mm and 12.5mm, for example, the separation may be 11.1mm. After the step of machining, the centre point of the first port opening may be disposed centrally in the longitudinal direction between the second and third ports and / or the fourth and fifth ports. After the step of machining, the centre point of the second and third port openings may be separated in the longitudinal direction by between 15mm and 25mm, or between 17.5mm and 22.5mm, for example, the separation may be 20.6mm. After the step of machining, the centre point of the fourth and fifth port openings may be separated in the longitudinal direction by between 42.5mm and 52.5mm, or between 45mm and 50mm, for example, the separation may be 47.6mm. After the step of machining, the one or more of (optionally each of) the port openings may have a diameter greater than 5mm, 6mm, 7mm, 8mm, 9mm, 10mm or 11mm. After the step of machining, the one or more of (optionally each of) the port openings may have a diameter less than 20mm, 19mm, 18mm, 17mm, 16mm, 15mm, 14mm, 13mm or 12mm. In embodiments, the machined port openings (optionally each of the port openings) may have a diameter of 11.2mm. The plurality of flow gallery portions of the core may comprise one or more of: a first flow gallery portion corresponding to the shape of the first flow gallery, a second flow gallery portion corresponding to the shape of the second flow gallery, a third flow gallery portion corresponding to the shape of the third flow gallery, a fourth flow gallery portion corresponding to the shape of the fourth flow gallery, and / or a fifth flow gallery portion corresponding to the shape of the fifth flow gallery. The servo valve manifold may comprise one or more further flow galleries. The one or more further flow galleries may form a fluid flow path between two regions of the spool cavity which are spaced apart in the longitudinal direction. The one or more further flow galleries may comprise a further flow gallery providing a fluid flow path between two of the ports, for example the fourth and fifth ports. The fluid flow path between two of the ports may be via the spool cavity. The further flow gallery providing the fluid flow path between two of the ports may be substantially U-shaped. The further flow gallery providing the fluid flow path between two of the ports may be disposed on an opposite side of the spool cavity to the plurality of ports. The plurality of flow galleries which provide a flow path between the spool cavity and one of the ports may be referred to as input / output (or intemal-to-external, or spool cavity-to-port) flow galleries. The one or more further flow galleries which provide a flow path between two of the ports, e.g. via the spool cavity, may be referred to as internal (or spool cavity-to-spool cavity) flow galleries. The core may comprise one or more further flow gallery portions for forming the one or more further flow galleries in the servo valve manifold. The one or more further flow gallery portions may comprise a further flow gallery portion which extends between two regions of the spool cavity portion which are spaced apart in the longitudinal direction. The one or more further flow gallery portions may comprise a further flow gallery portion which extends between two of the plurality of flow gallery portions, for example the two outer flow gallery portions (in the longitudinal direction). The further flow gallery portion which extends between two of the plurality of flow gallery portions may be substantially U-shaped. The servo valve manifold may comprise an actuator housing configured to house (at least part of, optionally all of) an actuator for moving the spool within the spool cavity. The actuator may be an electric motor. The actuator housing may be a motor housing. The electric motor may have a rotor having a rotational axis which is oriented transverse to the longitudinal direction. The actuator housing may further house components which convert the rotational movement of the electric motor into longitudinal movement of the spool. The components may comprise a crank mechanism. The components may comprise a gearbox. The core may comprise an actuator housing (e.g. motor housing) portion having a shape which corresponds to the shape of the actuator housing (e.g. motor housing). Each port may comprise an O-ring seat around the port opening. The step of machining may comprise forming the O-ring seat around each port opening. The O-ring seat may be configured to receive an O-ring to improve, in use, sealing between the port and an external hydraulic system connected to the servo valve manifold via the control interface. The servo valve manifold may comprise a controller housing for a controller for controlling the actuator for the spool. For example, the controller may control the actuator based on feedback from a spool position sensor. The core may comprise a controller housing portion having a shape which corresponds to the shape of the controller housing. It will be appreciated that the portions of the core have a shape which correspond to the shape of the respective parts of the servo valve manifold after the step of casting but before the step of machining. The present invention provides, according to a second aspect, a method of manufacturing a servo valve. The method comprises manufacturing a servo valve 08 01 25 manifold by performing a method according to the first aspect, and providing a spool into the spool cavity, wherein the position of the spool in the spool cavity determines the fluid flow path between the plurality of ports. The method may comprise providing an actuator in the actuator housing. The method may comprise 5 mechanically linking the actuator to the spool such that movement of the actuator controls movement of the spool in the spool cavity. The method may comprise closing open ends of the spool cavity. The method may comprise sealing the spool cavity. The method may comprise a step of forming the spool, for example by additive manufacturing. The method may comprise a step of providing a controller in the 10 controller housing. The method may comprise a step of electrically connecting the controller to the actuator and / or to an external electrical connector. The present invention provides, according to a third aspect, a servo valve manifold. The servo valve manifold comprises: a spool cavity configured to receive a spool such that the spool can reciprocate in the spool cavity in a longitudinal 15 direction; a control interface comprising a plurality of ports for connection to an external hydraulic system, each of the ports comprising a port opening in an external surface of the servo valve manifold; and a plurality of flow galleries, each of the flow galleries extending between the spool cavity and a different one of the ports, each of the ports thereby being connected to the spool cavity by one of the flow galleries. The 20 servo valve manifold is formed by: casting around a core, the core comprising a spool cavity portion corresponding to the shape of the spool cavity, and a plurality of flow gallery portions corresponding to the shape of the flow galleries, wherein the plurality of flow gallery portions are spaced apart in the longitudinal direction such that the plurality of flow galleries are spaced apart from each other in the longitudinal 25 direction; and then removing the core material from the servo valve manifold; and machining to increase the cross-sectional area of one or more of the flow galleries and the corresponding port openings such that at least some of the flow galleries overlap each other in the longitudinal direction. The servo valve manifold may be formed by performing the method according 30 to the first aspect. Accordingly, the servo valve manifold according to the third aspect may have any features set out above in relation to the first aspect. In particular, the one or more flow galleries (whose cross-sectional area has been increased by machining, e.g. drilling) each comprise a first section extending 08 01 25 from their port opening towards the cavity. The first section is a cylindrical section formed by machining (e.g. drilling). The cylindrical section may have a circular crosssection. The cylindrical section may extend along at least 10%, 20%, 30%, 40%, 50% (half), 60%, 70%, 80%, or 90% of the distance from the port opening to the spool 5 cavity. The cylindrical section has a side wall formed by machining (e.g. drilling) away material from the cast servo valve manifold. The one or more flow galleries each comprise a circumferential section extending circumferentially around the spool cavity, and a second section which extends from the first section to the circumferential section. The second section is 10 formed by casting and has a side wall which is cast and has not been machined. Surfaces of the servo valve manifold formed by machining may have a first surface finish, and surfaces of the servo valve manifold formed by casting (and not having been machined) may have a second surface finish. Accordingly, the side wall of the first section (the cylindrical section) has the first surface finish, and the side 15 wall of the second section has the second surface finish. The first surface finish is smoother than the second surface finish. The first section of at least one of the one or more flow galleries overlaps another of the flow galleries in the longitudinal direction, and the second section of said at least one of the one or more flow galleries is spaced apart from said another of 20 the flow galleries in the longitudinal direction. The present invention provides, according to a fourth aspect, a servo valve comprising a servo valve manifold, the servo valve comprising a spool provided in the spool cavity, wherein the position of the spool in the spool cavity determines the fluid flow path between the plurality of ports. The servo valve manifold may be a servo 25 valve manifold according to the third aspect. The servo valve may be formed by performing the method according to the second aspect. Accordingly, the servo valve according to the fourth aspect may have any features set out above in relation to the second aspect. The servo valve may comprise an actuator housed within the actuator housing, 30 the actuator being configured to move the spool within the spool cavity. The actuator may be configured to move in response to control signals. The servo valve may comprise a controller configured to control the actuator in response to control signals. LO CXI i— 00 The controller may be configured to control the actuator in response to feedback from a position sensor configured to sense the position of the spool. The controller may be housed within the controller housing. The servo valve may comprise an electrical connector providing an electrical connection to the actuator and / or controller from an 5 external source. Figure 8A shows an underside view of the core used to form the servo valve manifold according to the first embodiment of the invention; Figure 8B shows a perspective view of the core used to form the servo valve manifold according to the first embodiment of the invention; Figure 9 shows an underside view of the servo valve manifold according to the first embodiment of the invention, prior to machining; Figure 10 shows an underside view of the servo valve manifold according to the first embodiment of the invention, after machining; Figure 11 shows a cross-sectional side view of the servo valve manifold according to the first embodiment of the invention, after machining; Figure 12 shows a schematic representation of a hydraulic system comprising a servo valve according to the invention; Figure 13 shows a method according to a second embodiment of the invention; and Figure 14 shows a method according to a third embodiment of the invention. Detailed Description Figure 5 shows a servo valve manifold 100 according to a first embodiment of the invention. The servo valve manifold 100 has been cast around a sand core 102, which is shown still in place inside the servo valve manifold 100. The servo valve manifold 100 is yet to be machined. The core 102 comprises a spool cavity portion 104, a first flow gallery portion 110, a second flow gallery portion 108, a third flow gallery portion 112, a fourth flow gallery portion 106, a fifth flow gallery portion 114, a U-shaped further flow gallery portion 116 and a motor housing portion 118. The servo valve manifold 100 comprises a spool cavity 120, a first flow gallery 126, a second flow gallery 124, a third flow gallery 128, a fourth flow gallery 122, a fifth flow gallery 130, a U-shaped further flow gallery 132, and a motor housing 134, which each have a shape corresponding to the shape of the respective part of the core 102. In use, the servo valve manifold 100 is provided with a spool within the spool cavity 120. The spool cavity 120 is cylindrical and is configured to receive the spool such that the spool can reciprocate within the spool cavity 120 in a longitudinal direction L. In the orientation shown, the underside of the servo valve manifold 100 comprises a control interface 136 comprising five ports 138, 140, 142, 144, 146. Each of the five flow galleries 122-130 extends between the spool cavity 120 and a different one of the ports 138-146 such that each of the ports 138-146 is served by one of the flow galleries 122-130. Each of the five ports 138-146 comprises a port opening. The control interface 136 comprises a flat external surface of the servo valve manifold 100 in which the port openings are located. The port openings are thereby all located in the same plane. At the port opening end of each of the flow galleries 122-130 (the end distal from the spool cavity 120), the flow galleries 122-130 comprise a cylindrical or truncated cylindrical section having a constant cross-sectional area. Moving away from the port opening, and towards the spool cavity 120, the cross-sectional area of each of the flow galleries increases in a step-wise manner at a distance X from the control interface 136. The flow galleries 122-130 thereafter taper outwards and increase in cross-sectional area as they approach the spool cavity 120. Each of the flow galleries 122-130 comprises a section which extends circumferentially around the spool cavity 120. The circumferential sections are each in fluid communication with the spool cavity 120 via a respective circumferential opening which extends fully around the spool cavity 120. The five flow gallery portions 106-114 of the core 102 are spaced apart from each other in the longitudinal direction. Accordingly, in the cast servo valve manifold 100, the five flow galleries 122-130 are spaced apart from each other in the longitudinal direction and the five port openings are spaced apart from each other the longitudinal direction. Figures 6 shows the servo valve manifold 100 and core 102 looking in a direction from the ports 138-146 towards the spool cavity 120. The spacing between the five flow gallery portions 106-114 and the absence of any overlap in the longitudinal direction is easily seen. The spacing between the central (first) flow gallery portion 110 and the two adjacent (second and third) flow gallery portions 108, 112 is indicated as spacing S. The truncated cylindrical sections of the second and third flow gallery portions 124, 128 on either side of the central flow gallery portion 126 have a cross-section having a truncated circular shape, that is, a circular shape with a segment removed. A section of the central flow gallery portion 126 also has a cross-section comprising a truncated circular shape, with segments removed on two opposing sides. The cross sections are truncated in this manner to avoid overlap between the flow gallery portions 122-130 in the longitudinal direction. The absence of any overlap between the flow gallery portions 122-130 in the longitudinal direction, and the absence of any other portions of the core 102 which overhang or undercut other portions of the core 102 in a separation direction (discussed below), allows the core 102 to be formed in a two-part mould. The port openings of the ports 138-146 are also spaced apart from each other in a direction perpendicular to the longitudinal direction, said direction being defined in the plane of the flat external surface of the control interface 136. The motor housing 134 in the servo valve manifold 100 is configured to house at least part of an electric motor in an orientation in which the rotational axis R of the rotor is perpendicular to the longitudinal direction L, i.e. perpendicular to the direction of travel of the spool. In use, the motor housing 143 also houses a crank mechanism which transfers the rotational motion of the electric motor to the linear motion of the spool. The servo valve manifold 100 according to the present embodiment comprises only one further flow gallery 116. The further flow gallery 116 provides a flow path between the two (longitudinal) regions of the spool cavity 120 where the spool cavity 120 connects to the outer (fourth and fifth) flow galleries 122, 130. The outer flow galleries 122, 130 may thereby be in fluid communication with each other, similarly the outer ports 138, 146 may thereby be in fluid communication with each other, via the further flow gallery 116 and the spool cavity 120. Figures 7, 8 A and 8B show the core 102 in the absence of the servo valve manifold. The two-part mould which forms the core 102 comprises a moulding cavity having a shape which corresponds to the shape of the core 102. In Figure 8 A, line A-A indicates a plane in which a face of a first moulding element and a face of a second moulding element of a two-part mould meet when forming the core 102. Not all parts of the two moulding elements will meet on this plane. Figure 8B shows the split line 164 where the moulding elements meet at various regions along the core 102. The solid white regions, e.g. region 164A, indicate parts of the core 102 where the split line 164 can follow a path anywhere within that region. Arrows B indicate a separation direction in which the moulding elements may be separated after core 102 has been moulded. The separation direction is perpendicular to the longitudinal direction L. Figure 9 shows the control interface 136 of the servo valve manifold 100 after the core 102 has been removed and prior to machining. The port openings of the ports 138-146 are spaced apart in the longitudinal direction. The port openings of the two ports 140, 144 on either side of the central port 142 have a truncated circular shape corresponding to the truncated circular shape of the truncated cylindrical sections of the corresponding flow gallery portions 108, 112 of the core 102. As can be seen, the ports 138-144 are provided in a generally triangular / arrow shaped distribution. Ports 138, 142 and 146 define the vertices of the triangular shape. Port 140 is disposed on a side of the triangle extending between the ports 138 and 142, and port 144 is disposed along on a side of the triangle extending between ports 142 and 146. Figure 10 shows the control interface 136 after machining. Figure 11 shows the servo valve manifold in cross-section after machining. The machining comprises drilling into each of the port openings a distance Y, which is approximately half the distance from the port opening to the spool cavity 120. The distance Y indicates the depth to which the flow galleries 122-130 are drilled out to the full width of the drill bit. As can be seen in Figure 10, the cross-sectional area of each of the port openings is increased to such an extent that the port opening of the central port 142 overlaps with the port openings of the two ports 140, 144 adjacent to the central port 142 in the longitudinal direction. The port openings of the two outermost ports 138, 146 are still spaced apart from the other port openings in the longitudinal direction. Similarly, the cross-sectional area of each of the port openings is increased to such an extent that the port opening of the two ports 140, 144 on either side of the central port 142 overlap with the port openings of the two outermost ports 138, 146 in the direction perpendicular to the longitudinal direction. The port opening of the central port 142 is still spaced apart from the other port openings in the direction perpendicular to the longitudinal direction. As a result of the machining, the truncated sections of the three middle flow galleries 124-128 have been drilled out. Each of the five port openings is circular and the port pattern conforms with ISO 4401-05. Approximately the first half of each of the five flow galleries 122-130, when taken in a direction going away from the port openings, is in the form of a cylindrical section with a circular cross-section. It has been found that, in comparison to the prior art servo valve manifold shown in Figure 2, the servo valve according to the present embodiment is capable of handling a higher flow rate through the five flow galleries 122-130. This may be due to the machining providing a flow gallery which is at least partly straighter, wider and smoother, and thus provides less resistance to fluid flow. Whilst it might not be strictly necessary for the outer (fourth and fifth) flow gallery portions 106, 114 to be narrower than the flow galleries in the final machined servo valve manifold, as the outer flow gallery portions are already spaced apart sufficiently to avoid any overlap, it has been found that the port opening size can be controlled more accurately via machining than via casting. Therefore, it has been found to be beneficial to make all of the plurality of flow gallery portions narrower, and thus to make all of the cast port openings smaller, and to then to use machining to create the final port opening size in all of the ports. As can be seen in Figure 11, other areas of the servo valve manifold 100 are also machined. For example, the spool cavity 120 and the motor housing 134 are both widened by machining. The machining of the spool cavity 120 also has the effect of improving surface quality in the spool cavity 120 to improve sealing between the spool and the surface of the spool cavity 120. Interface features are also machined into the servo valve manifold 100. The interface features include O-ring grooves 148 around each of the port openings, and features for receiving parts to close the ends of the spool cavity 120. Figure 12 shows a schematic representation of a hydraulic system 150 comprising a servo valve 152. The servo valve 152 comprises the machined servo valve manifold 100, a spool 154 provided within the spool cavity 120, and an electric motor 156 housed within the motor housing 134. The electric motor 156 is configured to control the position of the spool 154 in the spool cavity 120 via a cam mechanism, and thereby control the fluid flow path between the ports 138-146, in response to control signals. The control signals are sent from an external controller 158, which is connected to the electric motor 156 via an electrical connector 160. The servo valve 152 is in fluid communication with a high pressure hydraulic fluid supply P via the central port 142, and a low pressure hydraulic fluid return T, T1 via the two outer ports 138, 146. The two ports 140, 144 on either side of the central port are in fluid communication with a hydraulic actuator 162. The servo valve 152 thus controls the movement of the hydraulic actuator 162 in response to the control signals. Figure 13 shows the steps of a method 200 according to a second embodiment of the invention, the method being a method of manufacturing the servo valve manifold 100 according to the first embodiment. At step 202, a first core moulding element and a second core moulding element are provided and used to form the core 102. The core moulding elements together form a two-part mould. The core is formed by bringing the core moulding elements are together and providing a core material inside a core moulding cavity which is formed between the moulding elements. The core moulding cavity has a shape which corresponds to the shape of the core 102. In this embodiment, the core material is sand. The sand is blown inside the core moulding cavity through an opening in the mould. The core moulding elements are then heated to heat the sand, which causes the sand to chemically bond and solidify. At step 204, the core moulding elements are separated by moving the core moulding elements apart in a separation direction. The separation direction lies in a plane perpendicular to the longitudinal direction. The spacing of the flow gallery portions and the absence of any overlapping or undercutting portions of the core in the separation direction allows the core 102 to retain its moulded shape as the core moulding elements are separated. At step 206, the servo valve manifold 100 is cast by introducing molten material around the core 102. The core 102 and the molten material are provided in a cavity formed by further moulding elements, the cavity having a shape which corresponds to the external shape of the servo valve manifold 100. The molten material is allowed to solidify. At step 208, the core material is removed from the servo valve manifold 100 by shaking the servo valve manifold 100. The shaking is sufficiently vigorous that the core 102 is broken up and expelled from the openings in the servo valve manifold 100. The heat imparted to the core 102 during the casting step helps to weaken the core 102 and make it easier to remove. At step 210, the servo valve manifold 100 is machined. The machining comprises drilling into the port openings to a distance approximately half way from the port opening to the spool cavity 120. The drilling increases the cross-sectional area of the plurality of flow galleries 122-130 and port openings to such an extent that the central flow gallery 142 (and the associated port opening) overlaps with the adjacent flow galleries 140, 144 (and associated port openings) in the longitudinal direction. Similarly, the outermost flow galleries 138, 146 overlap with their adjacent flow galleries 140, 144 in a direction transverse to the longitudinal direction. The machining also comprises boring into the spool cavity 120, forming O-ring grooves 148 around the port openings, and forming other interface features, such as features for receiving parts to close the ends of the spool cavity 120. Figure 14 shows the steps of a method 300 according to a second embodiment of the invention, the method being a method of manufacturing a servo valve. At step 200, the method according to the second embodiment is performed to manufacture a servo valve manifold. At step 302, a spool is provided in the spool cavity 120. At step 304, an actuator in the form of an electric motor is housed in the motor housing 134 and is mechanically linked to the spool via a crank mechanism such that rotational movement of the electric motor causes linear moment of the spool in the spool cavity 120. Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described. In alternative embodiments, the motor housing portion 118 is omitted from the core 102 and the motor housing 134 is formed by machining. In alternative embodiments, the servo valve manifold 100 comprises fewer or more than five flow galleries and ports, and the core 102 comprises fewer or more than five corresponding flow gallery portions. For example, the servo valve manifold may comprise four flow galleries and four ports, with the core comprising four corresponding flow gallery portions. In embodiments, the fifth flow gallery 130 and port 146 are omitted. Additionally, the U-shaped further flow gallery 132 may be omitted. In alternative embodiments, they hydraulic system 150 is arranged such that the high pressure hydraulic fluid supply P is connected via the two outer ports 138, 146 and the low pressure hydraulic fluid return T, T1 is connected via the central port 142. Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

1. A method of manufacturing a servo valve manifold, the servo valve manifold comprising:a spool cavity configured to receive a spool such that the spool can reciprocate in the spool cavity in a longitudinal direction;a control interface comprising a plurality of ports for connection to an external hydraulic system, each of the ports comprising a port opening in an external surface of the servo valve manifold;a plurality of flow galleries, each of the flow galleries extending between the spool cavity and a different one of the ports, each of the ports thereby being connected to the spool cavity by one of the flow galleries;wherein the method comprises the following steps:forming a core from a core material, the core comprising a spool cavity portion corresponding to the shape of the spool cavity, and a plurality of flow gallery portions corresponding to the shape of the flow galleries, the core being integrally formed as a single piece;casting the servo valve manifold by introducing molten material around the core and allowing the molten material to solidify; and thenremoving the core material from the servo valve manifold; andmachining the servo valve manifold;wherein the plurality of flow gallery portions of the core are spaced apart in the longitudinal direction such that, after the step of casting the servo valve manifold and before the step of machining the servo valve manifold, the plurality of flow galleries are spaced apart from each other in the longitudinal direction;wherein the step of machining comprises increasing the cross-sectional area of one or more of the flow galleries and the corresponding port openings such that at least some of the flow galleries overlap each other in the longitudinal direction.

2. A method according to claim 1, wherein the step of forming the core uses a mould comprising a first core moulding element and a second core moulding element arranged to be brought together to form a core moulding cavity having a shape corresponding to the shape of the core;wherein the step of forming the core comprises:moulding the core material in the core moulding cavity; and separating the first and second core moulding elements and removing the core from the mould.

3. A method according to claim 2, wherein when the first and second core moulding elements are brought together, a face of the first moulding element meets a face of the second moulding element at a plane which extends parallel to the longitudinal direction.

4. A method according to claim 2 or 3, wherein when the first and second core moulding elements are separated, they are moved apart in a separation direction which lies in a plane perpendicular to the longitudinal direction.

5. A method according to claim 4, wherein the core is free of portions which overhang and / or undercut other portions of the core in the separation direction.

6. A method according to any preceding claim, wherein the core material comprises sand.

7. A method according to any preceding claim, wherein the step of casting comprises sand casting.

8. A method according to any preceding claim, wherein the step of machining comprises drilling into the port openings.

9. A method according to any preceding claim, wherein the step of machining comprises increasing the cross-sectional area of one or more of the flow galleries along at least half the distance from the port opening to the spool cavity.

10. A method according to any preceding claim, wherein the plurality of ports comprises a first port comprising a first port opening, a second port comprising a second port opening, and a third port comprising a third port opening,wherein after the step of machining, the first port opening overlaps with the second port opening and the third port opening in the longitudinal direction.

11. A method according to any preceding claim, wherein the servo valve manifold comprises a motor housing configured to at least partly house an electric motor for moving the spool within the spool cavity, the electric motor having a rotor having a rotational axis which is oriented transverse to the longitudinal direction.

12. A method according to claim 11, wherein the core comprises a motor housing portion having a shape which corresponds to the shape of the motor housing.

13. A method according to any preceding claim, wherein the step of machining comprises forming an O-ring seat around each port opening.

14. A method according to any preceding claim, wherein the control interface comprises a flat portion of an external surface of the servo valve manifold such that the port openings are located in the same plane.

15. A method according to any preceding claim, wherein the control interface comprises five ports.

16. A method according to any preceding claim, wherein after the step of casting and prior to the step of machining, the plurality of port openings are spaced apart in a direction perpendicular to the longitudinal direction; and after the step of machining, at least some of the plurality of port openings overlap with each other in the direction perpendicular to the longitudinal direction.

17. A method of manufacturing a servo valve, the method comprising: manufacturing a servo valve manifold by performing a method according to any preceding claim, andproviding a spool into the spool cavity, wherein the position of the spool in the spool cavity determines the fluid flow path between the plurality of ports.

18. A servo valve manifold comprising:a spool cavity configured to receive a spool such that the spool can reciprocate in the spool cavity in a longitudinal direction;08 01 25a control interface comprising a plurality of ports for connection to an external hydraulic system, each of the ports comprising a port opening in an external surface of the servo valve manifold;a plurality of flow galleries, each of the flow galleries extending between the5 spool cavity and a different one of the ports, each of the ports thereby being connected to the spool cavity by one of the flow galleries;the servo valve manifold being formed by:casting around a core, the core comprising a spool cavity portion corresponding to the shape of the spool cavity, and a plurality of flow gallery portions10 corresponding to the shape of the flow galleries, wherein the plurality of flow gallery portions are spaced apart in the longitudinal direction such that the plurality of flow galleries are spaced apart from each other in the longitudinal direction; and then removing the core material from the servo valve manifold; and machining to increase the cross-sectional area of one or more of the flow15 galleries and the corresponding port openings such that at least some of the flow galleries overlap each other in the longitudinal direction;wherein the one or more flow galleries each comprise:- a first section extending from their port opening towards the cavity,- a circumferential section extending circumferentially around the spool20 cavity; and- a second section extending from the first section to the circumferential section;wherein the first section is a cylindrical section being formed by the machining and having a side wall formed by machining away material from the cast25 servo valve manifold, and the second section is formed by the casting and has a side wall which is cast and has not been machined;wherein the side wall of the first section has a first surface finish, and the side wall of the second section has a second surface finish, the first surface finish being smoother than the second surface finish; and30 wherein the first section of at least one of the one or more flow galleriesoverlaps another of the flow galleries in the longitudinal direction, and the second section of said at least one of the one or more flow galleries is spaced apart from said another of the flow galleries in the longitudinal direction.08 01 2519. A servo valve manifold according claim 18, wherein cylindrical section extends along at least 30%, optionally at least half, of the distance from the port opening to the spool cavity.

520. A servo valve manifold according to claim 18 or 19, wherein the plurality of ports comprise five ports disposed in a triangular arrangement.

21. A servo valve comprising a servo valve manifold according to any of claims 10 18 to 20, the servo valve comprising a spool provided in the spool cavity, wherein theposition of the spool in the spool cavity determines the fluid flow path between the plurality of ports.

22. A servo valve according claim 21, wherein the servo valve manifold 15 comprises a motor housing and the servo valve comprises an electric motor housed within the motor housing, the electric motor being configured to move the spool within the spool cavity, the electric motor having a rotor having a rotational axis which is oriented transverse to the longitudinal direction.20 23. A hydraulic system comprising: a servo valve according to claim 21 or 22, ahydraulic actuator, a hydraulic fluid supply line, a hydraulic fluid return line, and two service lines supplying hydraulic fluid to the actuator;wherein the hydraulic fluid supply line, hydraulic fluid return line and the two service lines are connected to the servo valve via the control interface such that the25 servo valve can control the hydraulic actuator.

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