Apparatus for converting rotational movement to linear movement

An apparatus for converting rotational movement into linear movement is disclosed. The apparatus comprises: a screw member having a threaded external surface and a sleeve member having a threaded interior surface for receiving the threaded external surface of the screw member, wherein the threaded surfaces are configured so that rotation of the screw member relative to the sleeve member, in use, causes the screw member to move axially relative to the sleeve member. The apparatus may also comprise a force applicator for applying pressure to the region between the screw member and sleeve member so as to urge the external surface of the screw member and the opposing interior surface of the sleeve member apart from each other.

FOREIGN PRIORITY

This application claims priority to European Patent Application No. 17461537.7 filed May 25, 2017, the entire contents of which is incorporated herein by reference.

FIELD

The present disclosure relates generally to assemblies for converting rotational movement into linear movement and in embodiments related to hydraulic valves and apparatus for controlling flow through such valves.

BACKGROUND

Proportioning valves using a linear motor are known and a schematic of such a valve is shown inFIG. 1A. However, current proportioning valves have good flow characteristics only in a certain operating range of the device.FIG. 1Bshows the fluid flow through such a proportioning valve as a function of the control signal applied to the valve. Initially, as the magnitude of the control signal is increased, the fluid flow through the valve does not significantly increase. This is known as a dead zone and is depicted as region “a” inFIG. 1B. In region “b”, the fluid flow increases substantially linearly as the magnitude of the control signal is increased. The valve therefore has good flow characteristics in this operating range. Region “c” is a zone of deformation characteristics due to the operating characteristics of the linear motor. Engines using such motors typically have a limited stroke length of approximately 5.2 mm.

It is known to use hydraulic screws and motors instead of a linear motor in order to eliminate the above inconvenience, as a hydraulic screw operates with the desired valve characteristics throughout its entire range of travel. It is also possible to increase the stroke of the valve spool. The external dimensions of a valve using this technology is also comparable to that using the linear motor.

U.S. Pat. No. 4,503,888 discloses a rotary to linear control for actuating an axially movable spool of a rotary input servo-valve.

SUMMARY

From a first aspect the present disclosure provides an apparatus for converting rotational movement into linear movement, said apparatus comprising: a screw member having a threaded external surface; a sleeve member having a threaded interior surface for receiving the threaded external surface of the screw member; wherein the threaded surfaces are configured so that rotation of the screw member relative to the sleeve member, in use, causes the screw member to move axially relative to the sleeve member; and a force applicator for applying pressure to a region between the screw member and sleeve member so as to urge an external surface of the screw member and an opposing interior surface of the sleeve member apart from each other.

For the avoidance of doubt, the axial movement described herein is movement in the longitudinal direction of the (elongated) screw member, i.e. in a direction through the sleeve member.

The sleeve member described herein may be a nut.

From a second aspect the present disclosure provides an apparatus for converting rotational movement into linear movement, said apparatus comprising: a screw member having a threaded external surface; a sleeve member having a threaded interior surface for receiving the threaded external surface of the screw member; wherein the threaded surfaces are configured so that rotation of the screw member relative to the sleeve member, in use, causes the screw member to move axially relative to the sleeve member; and at least one conduit extending through the sleeve member to the threaded interior surface for applying pressure to a region between the threaded interior surface of the sleeve member and the threaded exterior surface of the screw member.

Each of said at least one conduit may extend from an opening in a radially exterior surface of the sleeve member to at least one opening in a radially interior surface of the sleeve member.

The may comprise a plurality of said conduits having a plurality of said openings arranged circumferentially spaced around the interior surface of the sleeve member; and/or comprise a plurality of said conduits having a plurality of said openings arranged longitudinally spaced along the interior surface of the sleeve member.

The openings may be spaced substantially equidistantly around the circumference of the interior surface.

The threaded interior surface of the sleeve member may form a helical ridge on the interior surface; wherein each of the at least one conduit may extend radially inwards through the sleeve member and radially inwards through the ridge to one or more opening in the interior surface.

The one or more opening may be in one or more side wall of said ridge.

The threaded exterior surface of the screw member may form a helical ridge on the exterior surface, wherein said one or more conduit openings in the sleeve member may face one or more side wall of the ridge on the screw member.

The apparatus may comprise a force applicator arranged and configured to force a fluid into said at least one conduit and out of said one or more conduit openings in the sleeve member so as to exert a force on said one or more side wall of the ridge on the screw member, optionally so as to create a bearing force so that the screw member may carry a load in its radial and/or axial directions without the threads on the screw contacting the threads on the sleeve.

The apparatus may comprise a force applicator arranged and configured to apply a force into said at least one conduit for applying pressure to the region between the screw member and sleeve member so as to urge the external surface of the screw member and the opposing interior surface of the sleeve member apart from each other.

The force applicator described herein (e.g. described in relation to the first and/or second aspect of the disclosure) may comprise a pump or piston for pressurising the region between screw member and sleeve member.

The force applicator may be configured to urge a fluid into said region at a pressure above ambient pressure.

The apparatus may comprise a source of fluid for supplying said fluid to said force applicator; optionally wherein the fluid is a lubricating fluid, such as oil.

The apparatus may be configured such that the force applicator applies said pressure to the region between the threaded interior surface of the sleeve member and the threaded exterior surface of the screw member.

The region between the threaded interior surface of the sleeve member and the threaded exterior surface of the screw member is optionally an annular region between the screw member and the sleeve member.

The apparatus may be configured such that when the force applicator applies said pressure, in use, the threaded interior surface of the sleeve member does not contact the threaded exterior surface of the screw member. Alternatively, or additionally, the exterior surface of the screw member and the interior surface of the sleeve member may be substantially cylindrical, and the apparatus may be configured such that when the force applicator applies said pressure, in use, the screw member is radially centralised within the sleeve member.

The apparatus may comprise a fluid return line for receiving fluid flowing away from or out of the region between the sleeve member and screw member and returning the fluid to said source of fluid.

The present disclosure also provides a valve for controlling the flow of fluid, the valve comprising: a housing having a fluid inlet port, a fluid outlet port and a fluid channel therebetween; a valve closure member that is movable for varying an opening in the fluid channel so as to control the fluid flow between the inlet and outlet ports; and the apparatus for converting rotational movement into linear movement that is described herein; wherein the valve closure member is coupled to the screw member or sleeve member such that rotation of the screw member relative to the sleeve member, in use, causes the valve closure member to move so as to vary the opening in the fluid channel

The screw member may comprise a valve spool forming said valve closure member.

The valve may comprise a motor coupled to said screw member or sleeve member for rotating said screw member relative to the sleeve member.

The valve may be a proportional valve and/or a servo-valve.

The valve may be a hydraulic valve for controlling the flow of hydraulic fluid.

The present disclosure also provides a machine for controllably moving a work-piece, the machine comprising: the apparatus as described above; a mounting surface for receiving or mounting the work-piece thereto, wherein the mounting surface is coupled to said screw member or sleeve member such that rotation of the screw member relative to the sleeve member, in use, causes the mounting surface to move.

The present disclosure also provides a method of forming a conduit through a sleeve member comprising a threaded interior surface that forms a helical ridge on the interior surface; the method comprising drilling radially inwards through the sleeve member and radially inwards through the ridge so as to form one or more opening in the interior surface on one or more side wall of the ridge.

The method may be used to form one or more of the conduits in the sleeve members described herein, and or to form the assembly, valve or machine described herein.

DETAILED DESCRIPTION

FIG. 2shows a schematic of an embodiment of the present disclosure comprising a sleeve member2and a screw member4received within the sleeve member2. In the illustrated embodiment, the sleeve member2is a nut and the screw member4is a screw. The nut2and screw4may form part of a hydraulic valve (not shown), e.g. servo valve. Although the nut2circumferentially surrounds at least part of the screw4, the nut2is shown in cross-section inFIG. 2so that the features of the screw4that are within the nut2can be seen. The screw4is an elongated member having a helical thread around its external surface. The thread extends along at least a portion of the length of the screw4. The nut2comprises a helical thread on its interior surface for cooperation with the external thread on the nut2. The threads on the nut2and screw4are arranged and configured such that circumferential rotation of the nut2relative to the screw4causes the screw4to move in a direction along its longitudinal axis, relative to the nut2.

According to embodiments a lubricating fluid, such as oil, is provided between the radially inner surface of the nut2at which its thread is located and the radially outer surface of the screw4at which its thread is located, so as to lubricate the rotation of the nut2relative to the screw4.

According to at least some of the embodiments, the lubricating fluid is pressurised. The lubricating fluid may be pressurised such that the pressure of the fluid exerts a force between the nut2and screw4that may substantially radially centralise the screw4within the nut2(at least along the threaded portions of the nut and screw). In other words the pressurised fluid may push the threaded inner surface of the nut2away from the threaded outer surface of the screw4. The fluid may be pressurised in this manner such that there is substantially no physical contact between the screw4and nut2(at least along the threaded portions) since the fluid remains between them. This reduces wear, friction, energy consumption and the requirement to replace the components of the assembly.

FIG. 3shows a perspective view of the portion of the nut2circled inFIG. 2. It can be seen that the nut2may have one or more conduits6extending from the radially outer surface of the nut2to the radially inner surface of the nut2. In the embodiment shown, the nut2has a plurality of rows of such conduits6extending through the nut2from the external surface to the interior surface. These conduits6enable the lubricating fluid to be injected between the threads of the nut2and screw4. The conduits6also enable the lubricating fluid between the nut2and screw4to be pressurised.

FIG. 4shows a schematic of one embodiment for forming the conduits6in the nut2.FIG. 4shows a cross-sectional view through a portion of an upper wall of the nut2, i.e. such that the upper surface2aof the portion shown is the radially outer surface of the nut2and the lower surface2bof the portion shown is the threaded interior surface of the nut2. Each conduit6may be formed by drilling from the radially outer surface2aof the nut2, through the wall of the nut2to the radially interior surface2b. The threaded surface2bof the nut2forms a helical ridge8and a helical valley10around the nut interior surface1b. The diameter of the drill bit12used in the drilling may be selected to be smaller than width of the base of the ridge8(in the longitudinal direction of the screw4), but larger than the width of the tip of the ridge8. The drilling may be performed such that the drill bit12passes through the base of the ridge8and through the ridge towards its tip. As the drill bit12progresses towards the interior surface2bof the nut2, it breaks through the interior surface2bof the nut2at locations on either side wall14,16of the ridge8so as to form holes18,20on either side wall of the ridge. The drilling may halted at this stage, thereby forming a conduit6from the exterior surface2aof the nut2that is connected to both holes18,20on either side wall14,16of the ridge8, in a single drilling operation. In other words, the drilling may be performed such that the free end of the drill bit12does not entirely pass through the inner surface2bof the nut2. A plurality of such drilling operations may be performed, e.g. one for each of the conduits6shown inFIG. 3.

FIG. 5Ashows a schematic of a top-down view of the nut2after some of the conduits6have been drilled. The central portion of the nut2is illustrated as being translucent purely for illustrative purposes so that it is possible to see the arrangement of the threaded surface on the interior2bof the nut2. As can be seen fromFIG. 5A, each conduit6that is drilled through the exterior surface2aof the nut2breaks through the interior surface2bon opposing side walls of the ridge8of the thread so that the conduit6is in fluid communication with the two holes18,20through the interior surface1b.

FIG. 5Bshows a cross-sectional perspective view of the nut2, illustrating the conduits6formed through the wall of the nut2and some of the resulting holes18formed on either side wall of the ridge8. In the view ofFIG. 5Bonly the holes18on one side of the ridge8can be seen as the holes20on the other side are obscured from view by the ridge8itself.

FIG. 5Cshows another view of the interior threaded surface2bof the nut2in which the two holes18,20formed on either side of the ridge8by each drilling operation can be seen.

FIG. 6shows a schematic illustrating a threaded portion of the screw4. The nut2around the screw4is not illustrated, in order to enable the screw4to be viewed, although the conduits6through the nut2are illustrated. As described above, each drilling operation forms a conduit6that breaks through the interior surface2bof the nut2so as to form two holes18,20on either side wall of the ridge8. As described above, lubricating fluid may be forced into the nut2through each conduit6in its external surface2a. This fluid passes through the conduit6and out of the holes18,20on either side wall of the ridge8. As the screw4has a threaded exterior surface5that compliments the interior thread on the nut2, the pressurised fluid exiting the interior surface2bof the nut2acts on the opposing side walls22,24of the ridge of the screw thread, thereby urging the nut2radially outwards relative to the screw4. Multiple such conduits6and their associated holes18,20may be arranged circumferentially around the nut2so that the urging force created by the fluid radially centres the screw4relative to the nut2(e.g. at least three conduits6that may be equidistantly spaced around the circumference). The rotation of the nut2relative to the screw4may therefore be performed with minimal friction, backlash and wear.

Additionally, or alternatively, to the conduits6being arranged to radially centre the screw4relative to the nut2, the conduits6may be arranged such that the pressurised fluid exiting the interior surface2bof the nut2acts on the opposing side walls22,24of the ridge of the screw thread, thereby urging the screw4so as to move longitudinally through the nut2.

The number and/or area of the holes18,20in the interior surface2bof the nut2, and/or the pressure of the lubricating fluid may be selected so as to provide the desired force for radially or axially urging the screw4relative to the nut2.

Although a drilling operation has been described that forms two holes18,20on either side of the nut thread, it is contemplated that in the drilling operation the free end of the drill bit12may pass through the interior surface2bof the nut2so as to only form a single hole through the interior surface (e.g. the end of the drill bit may entirely pass through the interior surface of the nut).

The screw-nut assembly described herein may be used in a variety of applications to convert rotational movement of the screw4relative to the nut2into axial movement of the screw4relative to the nut2. For example, the assembly may be used in a valve such as a proportional valve or a servo-valve, e.g. in aircraft systems, automotive systems, or industrial machinery.

FIG. 7Aillustrates a schematic, perspective view of a hydraulic valve30according to an embodiment.FIG. 7Bshows a cross-sectional view of the embodiment ofFIG. 7A(except that five hydraulic fluid inlet/outlet ports are shown rather than two). The valve30comprises a housing32that houses a nut2and a screw4received within the nut2. The housing30circumferentially surrounds the screw2and nut4, although inFIG. 7Apart of the housing has30been cut away to show various interior features. Both the nut2and screw4have complementary threaded surfaces and the nut2has conduits6through it for supplying lubricating fluid between the threads of the nut2and screw4, as described hereinabove. The housing30has a lubricating fluid supply line34for supplying the lubricating fluid to the conduits6in the nut2. A force applicator35(e.g. a pump or piston) is provided for forcing the lubricating fluid into the lubricating fluid supply line34. The housing30may also have a lubricating fluid return line36at one or both longitudinal ends of the nut2for receiving lubricating fluid. The screw4is coupled at one of its ends via a coupling37to a motor38such that the motor may rotate the screw4about its longitudinal axis. The other end of the screw4is configured as a valve spool40and is arranged in slidable communication with a hydraulic fluid inlet port42and a hydraulic fluid outlet port44. A fluid channel45is arranged between the fluid inlet port42and the fluid outlet port44and the valve spool acts as a valve closure member40that is movable for varying the size of an opening47in the fluid channel (e.g. to open and close the opening) so as to control the fluid flow between the inlet and outlet ports42,44.

In operation, the force applicator35forces lubricating fluid through the lubricating fluid supply line34and into the conduits6in the nut2under pressure such that the lubricating fluid exits the inner surface2bof the nut2and urges against the outer surface of the screw4. As described above, the conduits6through the nut2may be arranged and configured such that the pressurised lubricating fluid causes the screw4to be maintained in a radial central position within the nut2and optionally such that the thread on the nut2does not contact the thread on the screw4. The motor38is operated so as to rotate the coupling37and hence rotate the screw4about its longitudinal axis. Due to the cooperating threads on the screw4and nut2, this causes the screw4to move along its longitudinal axis relative to the nut2and hence move relative to the housing30. It will be appreciated that even though the threads on the nut2and screw4may not be in physical contact due to the pressurised lubricating fluid radially centralising the screw4, the arrangement of the helical ridge8on the screw4within the helical valley on the nut2(and the arrangement of the helical ridge on the nut within the helical valley on the screw) will still result in axial movement of the screw4relative to the nut2when the screw is rotated relative to the nut. The motor38therefore moves the screw4and its valve spool40relative to the hydraulic fluid inlet and outlet ports42,44in the housing30. The motor38is therefore able to control the hydraulic fluid flow into the inlet port42and out of the outlet port44. The coupling37between the motor38and screw4may be configured to accommodate movement of the screw4relative to the motor38whilst the motor is driving the screw. Any lubricating fluid that leaves the nut2at one or both longitudinal ends of the nut may be received at the lubricating fluid return line(s)36. The return line(s)36may recycle the lubricating fluid back to the lubricating fluid supply line34for reinjection back into the nut2.

The stroke of the valve spool40may be, for example, ±0.2 mm (±0.0079 in) such as in typical servo valves.

The valve may be a direct screw servo valve.

FIGS. 7C and 7Dshow perspective and cross-sectional views of the nut2, respectively.

FIGS. 7E and 7Fshow perspective and cross-sectional views of the screw4, respectively.

For example, it is contemplated that the screw valve may be mounted in a housing and configured to be operable either as a servo-valve or a proportioning valve. The screw valve may be controlled such that it performs relatively fast and coarse movements in a proportional valve mode and relatively slow and accurate movements in a servo-valve mode. Such a screw-valve may be used in applications such as, for example, a space craft (e.g. a space shuttle) in order to connect one object with another object. A single screw-valve can be operated in the two modes so as to perform a quick coarse approach in a first mode and then a slower precise connection between the two objects in the second mode. Another exemplary application of such as screw-valve is in the rolling process of metal (e.g. to form sheet metal). The servo-valve can be used in a first mode to provide relatively coarse movements of the metal (e.g. into and/or out of the processing machine), whereas the screw-valve may be operated in the servo-valve mode for fine control of the movement of the metal within the machine. This is in contrast to conventional machinery, which currently require two hydraulic systems to perform these functions. Accordingly, embodiments provide a machine for controllably moving a work-piece.

Although embodiments have been described in which the screw and nut assembly are employed in a valve, the assembly may be applied in other systems. For example, the assembly may be a ball screw.

The apparatus described herein may be used in aircraft, automotive systems (e.g. in the steering gear for a vehicle), or industrial machinery, for example.