WO2017098250A1

WO2017098250A1 - Radial pumps and motors

Info

Publication number: WO2017098250A1
Application number: PCT/GB2016/053866
Authority: WO
Inventors: Andrew John Collins
Original assignee: Domin Fluid Power Limited
Priority date: 2015-12-08
Filing date: 2016-12-08
Publication date: 2017-06-15
Also published as: GB201521634D0

Abstract

A radial pump or motor (100) comprising a plurality of reciprocal elements (102), for example pistons, balls or rollers, arranged in at least two layers (102 a -m) is disclosed. The reciprocal elements (102) of each of the at least two layers (102 a-m) are arranged to follow a different cam surface (105 a-m).

Description

Radial Pumps and Motors

Field of the Invention The present invention concerns radial reciprocating pumps and motors. More particularly, but not

exclusively, this invention concerns internally impinged radial reciprocating pumps and/or motors, for example radial piston pumps and motors and methods of operating such pumps and/or motors.

Background of the Invention

Radial reciprocating pumps (and/or motors) are used in a wide variety of applications including industrial, automotive and aerospace applications.

Typically a radial reciprocating pump (hereafter a pump) comprises a plurality of reciprocal elements, for example pistons, mounted for rotation relative to a cylindrical cam surface. Movement of the pistons, or other reciprocal elements, may be produced by rotating the pistons relative to the cam surface when the axis of rotation of the pistons is offset from the longitudinal axis of the cam surface. An inside (or internally) impinged pump may be defined as a pump in which the fluid flows into and out of the chambers in which the

reciprocal elements are located via the interior of the pump housing. An outside (or externally) impinged pump may be defined as a pump in which the fluid flows to and from chambers in which the reciprocal elements are located via structure located around the exterior of the piston housing.

Fig. 1 shows a schematic view of a prior art inside impinged radial piston pump 1. The pump 1 comprises a plurality of pistons 2 located in radially extending bores 4 formed in a rotor 6. The rotor 6 is surrounded by a cylindrical cam surface 5. The axis of rotation of the rotor 6 lies parallel to, but is offset from, the longitudinal axis of the cam surface 5 so that the radial distance between the centre of rotation of the rotor 6 and the cam surface 5 varies with distance around the circumference of the cam surface 5. The degree of offset (labelled ^λ0' in Fig 1) may be referred to as the offset displacement and determines the stroke length. The centre of the rotor 6 is hollow and divided into two semi-cylindrical chambers 8 and 9. In Fig. 1 the left- hand chamber 8 may be referred to as the discharge chamber; as the pistons 2 move radially inward fluid from the piston bores 4 is urged into this chamber and then out of the pump 1. Thus, in the pump of Fig. 1, the discharge side or half of the pump 1 is on the left. The right-hand chamber 9 may be referred to as the suction chamber; as the pistons 2 move radially outward fluid from this chamber 9 is pulled into the piston bores 4.

Thus, in the pump of Fig. 1, the suction side or half of the pump 1 is on the right. On the left-hand side of Fig. 1 the radial distance between the centre of rotation of the rotor 6 and the cam surface 5 decreases such that clockwise rotation of the rotor 6 causes the pistons 2 on the discharge side to be urged into the piston bores 4 by the contact between the cam surface 5 and a cam follower (not shown) attached to the piston 2. The reaction force experienced by the cam surface 5 when the piston 2 is being forced into the piston chamber 4 may be referred to as the offset load and is indicated by the dashed line and arrows labelled L in Fig. 1. The offset load acts on the left-hand side, and towards the left, in the pump of Fig. 1. In many systems the choice of pump is constrained by available space, cost, weight, and/or power.

Accordingly, it is generally desirable to increase the efficiency of a pump, in particular over a range of speeds and/or reduce the size of pump required for a given flow rate. It is also generally desirable to reduce pump noise where possible.

The volume of liquid moved through a radial piston pump for a single rotation of the rotor will depend on the number and diameter of the piston chambers, and the stroke length of the piston. Commercially available radial piston pumps typically have a limited number of pistons, for example eleven or less, as increasing the number pistons is seen as increasing costs, increasing complexity and/or rendering machining more difficult.

Accordingly the number of pistons in a pump is generally limited to 12 pistons or fewer. One way in which flow rate through a radial piston pump can be increased is by increasing the stroke length. However, this leads to a larger diameter cam surface thereby increasing the overall size of the pump. Another solution is to increase the diameter of the piston and piston chamber; however this can make maintaining a good seal between the piston and sides of the chamber more difficult. Larger pistons also have increased inertia which can limit the speed (and therefore power) of the pump and/or result in higher offset loads that necessitate increasing the strength (and therefore weight, cost and/or size) of the structure. Similar considerations will apply for pumps using other types of reciprocal elements.

The present invention seeks to mitigate the above- mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved radial pump or motor. Summary of the Invention

The present invention provides according to a first aspect, a radial pump (also known as a radial

reciprocating pump) comprising a plurality of reciprocal elements arranged in at least two layers, the reciprocal elements of each of the at least two layers being arranged to follow a different cam surface.

A reciprocal element may be a piston, and hence the pump may be a radial piston pump. Thus, there may be provided a radial piston pump comprising a plurality of pistons arranged in at least two layers, the pistons of each of the at least two layers being arranged to follow a different cam surface. Providing multiple layers of pistons may increase the flow through a pump for a given offset (and therefore stroke length) . Providing multiple layers of pistons may allow the diameter (and therefore inertia) of each piston to be reduced for a given flow rate.

One issue of importance in the design of reciprocal pumps and motors is the friction generated by the reciprocal element following the cam surface as the cam surface and the reciprocal element rotate past each other.

In the case that the reciprocal element is a piston, the pump may comprise a plurality of cam followers, a cam follower being associated with each piston. Thus, a cam follower may be used to reduce the friction loss.

Alternatively, it may be that the reciprocal element is a piston, but the pump (or motor) does not include any cam followers. In such a pump (or motor) the end of the piston may contact the cam surface. The distal end of the reciprocal element may be located immediately adjacent to the cam surface.

The reciprocal element may be a rollable element. That is to say, the reciprocal element itself may be

configured to roll along the cam surface. The reciprocal element may be a ball. The reciprocal element may be a roller. Using a rolling reciprocal element may allow the friction loss to be reduced in comparison to a pump that includes a piston. While a rolling element may offer less volumetric displacement for each stroke, there may be situations in which this is acceptable in order to reduce friction loss. Accordingly, a rolling reciprocal element such as a ball or roller may be used as an alternative to a piston.

A layer of reciprocal elements may comprise a plurality of reciprocal elements having a similar

longitudinal position on the axis of rotation of the pump. Reciprocal elements (or chambers therefor) may be defined as having a similar longitudinal position when they are cut through by the same plane. Thus, a layer of reciprocal elements may form a band at a given

longitudinal position on the axis of rotation of the ump. Each reciprocal element of a layer may have a different circumferential position to any other

reciprocal element in the layer. The reciprocal elements of a layer may have a different longitudinal position to the reciprocal elements of any other layer. The

reciprocal elements of a first layer may be located at a first position along the axis of rotation of the pump. The reciprocal elements of a second layer may be located at a second axial position, spaced apart from the first axial position. A layer of reciprocal elements may comprise more than five, for example more than twelve, reciprocal elements. The pump may be arranged such that the reciprocal elements of each layer can move

independently of the reciprocal elements of any other layer .

It will be appreciated that the pump may comprise more than two layers. For example the pump may comprise three or more layers, for example the pump may comprise more than five or more than ten layers.

Each layer of reciprocal elements may be arranged to follow a different cam surface, said cam surface having the same longitudinal position on the axis of rotation of the pump as the associated layer of reciprocal elements. The reciprocal elements of a layer may follow a different cam surface to the reciprocal elements of any other layer .

Alternatively, it may be that the pump is arranged such that two, three or more layers of reciprocal elements follow the same cam surface. Thus, a first one of the at least two layers may follow a first cam surface, a second one of the at least two layers may follow a second, different, cam surface and one or more further layers may follow the first and/or second cam surface .

The pump may comprise at least two cam surfaces, for example two separate cam surfaces. Each one of said at least two layers may be arranged to follow a different one of said at least two cam surfaces. Each different cam surface may be spaced apart from any other cam surface. The profile of a first cam surface may differ from the profile of any adjacent cam surface. Each different cam surface may be formed in a separate component to any other cam surface. Alternatively, a plurality of cam surfaces may be formed in the same component. In the case that a plurality of cam surfaces are formed in the same component, each cam surface may be separated from any other cam surface by an intermediate region. The pump may be arranged such that, in use, none of the plurality of reciprocal elements can follow an intermediate region.

The pump may be an inside-impinged pump.

According to a second aspect, the present invention provides a radial pump comprising a plurality of

reciprocal elements arranged in at least two layers, the reciprocal elements of each of the at least two layers being arranged to follow a different cam surface, and wherein the pump is arranged such that, in use, the offset load of a first layer acts in the opposite direction to the offset load of a second layer.

Arranging the pump such that the offset load of a first layer acts in the opposite direction to the offset load of a second layer may reduce the magnitude of the forces that the structure of the pump must withstand. That is to say, the offset load of a first layer can be used to balance (i.e. counteract) the offset load of a second layer.

The second layer may be adjacent to the first layer. It may be that the pump is arranged such that the offset load of each layer acts in the opposite direction to the offset load of an adjacent layer.

A first cam surface may be offset relative to the reciprocal elements of the first layer in a first direction. A second cam surface may be offset relative to the reciprocal elements of the second layer in a second, opposite, direction. It may be that the

magnitude of the offset displacement is the same for each layer, but the ^xsign' (i.e. the direction) is opposite for different, for example adjacent, layers. A discharge chamber associated with the reciprocal elements of the first layer may be located on the opposite side of the pump to a discharge chamber associated with reciprocal elements of the second layer. A suction chamber

associated with the reciprocal elements of the first layer may be located on the opposite side of the pump to a suction chamber associated with reciprocal elements of the second layer. The suction side of the first layer may be located on the opposite side of the pump to the suction side of the second layer. The discharge side of the first layer may be located on the opposite side of the pump to the discharge side of the second layer. That is to say, the discharge and suction sides may alternate position between different, for example adjacent,

reciprocal element layers. Thus, the offset loads of a first layer may act in the opposite direction to the offset load of a second layer. This pattern may be repeated along the length of the pump such that the direction in which the offset load acts alternates between layers.

The pump may comprise a rotor. The reciprocal elements of each layer may be received in radially extending chambers integrally formed in the rotor. That is to say, the reciprocal elements of different layers may be received in chambers formed in the same rotor. Providing chambers for multiple reciprocal element layers in the same rotor may facilitate the design of pumps with a reduced number of components.

The rotor may include a first layer (or series) of chambers in which a reciprocal elements may be received. The chambers of the first layer may be spaced apart around the circumference of the reciprocal element housing at a first axial location. The rotor may include a second layer (or series) of chambers. The chambers of the second layer may be spaced apart around the

circumference of the reciprocal element housing at a second axial location, spaced apart from the first axial location along the axis of the rotor. Thus, the chambers of the first and second layer (or series) may form two rings extending around the circumference of the rotor. The chambers of the second layer may be offset angularly with respect to the chambers of the first layer.

Providing two (or more) layers of chambers may allow the chambers to be accommodated in a more space-efficient manner than prior art pumps.

The pump may comprise a plurality of reciprocal elements (and accordingly the reciprocal element housing may comprise a plurality of chambers) . The pump may comprise more than 10, for example more than 20, for example more than 30 reciprocal elements. The pump may comprise an even number of reciprocal elements in each layer. Pumps in accordance with the present invention may have a large number of reciprocal elements, for example more than 10 reciprocal elements.

The pump may comprise a suction channel connected to a pump inlet. In use, fluid may flow from the suction channel into the chambers on the suction side of the pump. The reciprocal elements of each of the at least two layers may be connected to the same suction channel. The pump may comprise a discharge channel connected to a pump outlet. In use, fluid may flow from the discharge channel out of the chambers on the discharge side of the pump. The suction channel and/or discharge channel may extend along the axis of rotation of the pump between each of the at least two layers.

The chambers of each of the at least two layers may be connected to the same discharge channel. The position of the suction channel within the pump may vary along the length of the pump such that the portion of the suction channel associated with a first layer is on the opposite side of the pump to the portion of the suction channel associated with a second, or any adjacent, layer. The position of the discharge channel within the pump may vary along the length of the pump such that the portion of the suction channel associated with a first layer is on the opposite side of the pump to the portion of the suction channel associated with a second, or any

adjacent, layer.

The pump may comprise a stator. The rotor may be mounted on the stator for rotation relative thereto. The stator may comprise one or more ports associated with each layer of reciprocal elements (or chambers therefor) . The pump may be arranged such that, in use, fluid flows between the suction and/or discharge chambers and the chambers via the ports in the stator. The stator may comprise an integrally formed suction channel extending along a portion of the length, for example the majority of the length, of the stator. The stator may comprise an integrally formed discharge channel extending along a portion of the length, for example the majority of the length, of the stator. The suction and /or discharge channel may extend along the core of the stator. The suction and/or discharge channel may extend along the length of the stator from the first of the at least two layers to the last of the at least two layers. The position of the suction channel within the core of the stator may vary along the length of the stator such that the portion of the suction channel associated with a first layer is on the opposite side of the stator to the portion of the suction channel associated with a second, or any adjacent, layer. The position of the discharge channel within the core of the stator may vary along the length of the rotor such that the portion of the

discharge channel associated with a first layer is on the opposite side of the stator to the portion of the

discharge channel associated with a second, and/or adjacent, layer. Thus, the suction channel and discharge channel may intertwine along the core of the stator such that the discharge side and suction side alternate between layers. The portion of the suction channel associated with a layer may form the suction chamber for that layer. The portion of the discharge channel

associated with a layer may form the discharge chamber for that layer.

It may be that each port and/or chamber (i.e. discharge chamber and/or suction chamber) is associated with a different layer of reciprocal elements. Alternatively, it may be that a port and/or chamber is associated with more than one layer. In the case that two or more layers are associated with the same cam surface, it may be that said two or more layers are also associated with the same ports and/or chambers.

The pump may comprise an impeller and/or propeller arranged to promote the flow of fluid to or from a suction and/or discharge channel. It may be that the impeller and/or propeller is integrally formed with the rotor .

The pump may be arranged such that, in use, the reciprocal elements of a first layer switch between the suction and discharge phases at a different time to the reciprocal elements of a second (for example an adjacent) layer. It may be that the pump is arranged such that the circumferential positions of the reciprocal elements of a first layer are offset with respect to the

circumferential position of the reciprocal elements of a second layer. That is to say, the reciprocal elements of a first layer may be spaced apart around the

circumference of the rotor at a first set of positions. The reciprocal elements of a second (for example

adjacent) layer may be spaced apart around the

circumference of the rotor at a second, different, set of positions. The second layer may be adjacent to the first layer. Thus, in use, the reciprocal elements of a first layer may move between the discharge and suction side at a different time to the reciprocal elements of a second layer. It will be appreciated that where the arrangement of each layer is the same (i.e. the offset loads act in the same direction) varying the circumferential position of the reciprocal elements between layers will introduce a phase lag in the reciprocal-element motion of said layers. It will be appreciated that where the elements of alternate layers swap sides to produce offset loads that act in opposite directions, varying the

circumferential position of the reciprocal elements between layers will prevent the motion of the reciprocal elements of said layers being anti-phase. In either case, varying the relative circumferential position of the reciprocal elements between layers may reduce pump noise by preventing all the layers switching between the suction and discharge portions of the cycle at the same time .

According to a third aspect of the invention, there is provided a radial pump comprising a plurality of pistons arranged in at least two layers, and wherein the pump further comprises at least two resilient members, each piston of a layer being connected to the same resilient member such that inward movement of the pistons at one circumferential portion of the layer urges the pistons on the opposite circumferential portion of the layer outwards . Providing such a resilient member may facilitate an increase in the speed of the pump by reducing cavitation on the suction side.

It may be that the resilient member is a ring, for example a wire ring.

Each piston of a layer may comprise an integrally formed engagement portion, for example a hook or recess, arranged to connect the piston to the resilient member. The recess may comprise a channel extending through a portion of the piston and arranged to receive a portion, for example a circumferential portion, of the ring.

According to a fourth aspect of the invention, there is provided a radial pump comprising a plurality of

reciprocal elements arranged in at least two layers, the reciprocal elements of each of the at least two layers being arranged to follow a different cam surface, and wherein each of the cam surfaces is mounted for movement such that the offset displacement of each of the layers may be varied.

Providing a plurality of movable cam surfaces such that the offset displacement of each layer may be varied while the pump is in use may facilitate the design of variable displacement pumps having a relatively high number of reciprocal elements. Being able to vary the motion of the reciprocal element while the pump is in use may increase the efficiency of the pump by allowing the motion of the reciprocal element to be adjusted depending on the speed or desired flow rate.

It may be that a first one of said cam surfaces is mounted for radial movement relative to a second one of said cam surfaces. It may be that each of said cam surfaces is mounted for radial movement relative to any adjacent cam surfaces. Providing cam surfaces that move relative to each other may facilitate the design of variable displacement pumps in which the offset loads of a first layer are balanced by the offset loads of a second layer.

The pump may comprise a plurality of cam-surface mounts. Each cam-surface mount may be connected to a cam surface such that the cam surface moves with the mount. Each different cam surface may be connected to a

different cam-surface mount. Each cam-surface mount may be mounted for movement relative to the reciprocal elements of an associated layer such that the offset displacement of that layer can be varied.

The pump may comprise a camshaft. It may be that a cam surface is connected to the camshaft such that, in use, rotation of the camshaft causes movement of the cam surface. It may be that a plurality of cam surfaces are connected to a common camshaft. Thus, a rotation of the camshaft may allow the offset displacement of a plurality of cam surfaces to be varied simultaneously.

Providing a pump comprising a common camshaft via which the cam surfaces associated with different layers are moved may reduce the size and/or complexity of variable displacement pumps having a relatively high number of reciprocal elements.

A first and second cam surface may be connected to the camshaft such that movement of the first cam surface in the first direction causes a rotation of the camshaft that in turn causes movement of the second cam surface in the second cam surface, and vice versa.

In the case that the offset load of a first layer acts in the opposite direction to the offset load of a second layer, the cam surface of the first layer (the first cam surface) and the cam surface of the second layer (the second cam surface) may both be connected to the same camshaft. Further pairs of cam surfaces (e.g. two cam surfaces associated with layers having offset loads that act in opposite layers) may also be connected to the same camshaft. Alternatively, it may be that the pump

comprises multiple camshafts, each camshaft being

connected to a different pair of cam surfaces.

Providing a pump in which rotation of a common camshaft allows simultaneous movement of different cam surfaces in different directions may facilitate the design of

variable displacement pumps in which the offset loads are directed in different directions.

It may be that the radial pump comprises a plurality of reciprocal elements arranged in at least two layers, and at least two cam surfaces, the reciprocal elements of each of the at least two layers being arranged to follow a different cam surface. The pump may further be arranged such that, in use, the offset load of a first layer acts in the opposite direction to the offset load of a second layer and each cam surface is connected to the camshaft such that rotation of the camshaft causes a first one of said cam surfaces, the first cam surface being associated with said first layer, to move in a first direction and a second one of said cam surfaces, the second cam surface being associated with said second layer, to move in a second direction, opposite to the first direction.

Each cam surface may be connected to the camshaft via its associated cam-surface mount. A cam-surface mount may be connected to the camshaft such that a rotation of the camshaft causes the cam-surface mount, and thereby the cam surface, to move such that the offset

displacement may be varied.

It may be that each of the cam surfaces is connected to the camshaft via a rack and pinion arrangement. It may be that the cam shaft is the pinion (i.e. the circular gear) of the rack and pinion arrangement. It may be that each cam-surface mount comprises a rack (i.e. a linear gear) . It may be that a portion of each cam-surface mount comprises a series of teeth arranged to mesh with teeth formed on the outer surface of the camshaft.

According to a fifth aspect of the invention, there may be provided a method of varying the flow of fluid through a radial pump, the pump comprising a plurality of

reciprocal elements arranged in at least two layers, the reciprocal elements of each of the at least two layers being arranged to follow a different cam surface, the method comprising the step of moving each cam surface relative to the reciprocal elements of the associated layer to vary the offset displacement of each layer. It may be that the method includes the step of moving each of the cam surfaces simultaneously to vary the offset displacement of each layer. It may be that adjacent cam surfaces are moved in opposite directions.

According to a sixth aspect of the invention, there is provided a radial pump comprising a plurality of

reciprocal elements arranged in at least two layers, the pump being configured such that each of the at least two layers can be switched between a non-pumping state and a pumping state individually.

Multi-layer pumps in which the flow of fluid through layers may be switched 'on' and off individually may be more efficient than prior art pumps as the number of layers in operation can be varied according to operating requirements. This may increase the efficiency of a pump by minimising the number of layers in operation at any one time. Given that there is a ^xfixed' loss element associated with any layer that is in operation minimising the number of layers in operation may improve efficiency. Individual control of layers in multi-layer pumps may also increase efficiency by allowing those layers that are pumping to operate in a more efficient region of the performance envelope.

It will be appreciated that, typically, in order for a radial pump to output a supply of fluid (i.e. pump), a flow path that allows fluid to pass via the chambers must be provided and the offset displacement must be non-zero such that the reciprocal elements move in their

respective chambers as the pump rotates. Thus, it may be that by altering one or both of (i) the flowpath to or from a layer of reciprocal elements and (ii) the offset displacement associated with a layer of reciprocal elements, that layer may be switched between a pumping and a non-pumping state.

A layer may be said to be in a pumping state when the movement of the reciprocal elements of that layer is driving a significant flow of fluid through the chambers of that layer. A layer may be said to be in a non- pumping state when the flow of fluid via the chambers is negligible (for example, it may be that the reciprocal elements are stationary in their chambers or, it may be that the p reciprocal elements are moving but no fluid is being provided to the chambers) .

It will be appreciated that a layer that can be switched on and off (i.e. switched between the pumping and non-pumping state) individually is not necessarily a layer that can be switched on and off independently of any other layer. It may be that a second layer cannot be switched 'on' until a first layer is 'on' .

The pump may comprise at least two valves, each valve being arranged to control the flow of fluid to or from a different one of said at least two layers such that each of the at least two layers may be switched between a pumping and a non-pumping state by operating (for example opening or closing) the valve.

The pump may be arranged such that the offset

displacement of a layer can be varied individually. The pump may comprise at least two cam surfaces, the

reciprocal elements of each of the at least two layers being arranged to follow a different cam surface. Each cam surface may be mounted for movement relative to the associated reciprocal element layer between a centred position and an offset position such that the associated layer may be switched between a pumping and a non-pumping state by moving the cam surface. It may be that in the centred position rotation of the reciprocal elements relative to the cam surface results in substantially no movement of the reciprocal elements. It may be that in the offset position the layer has a non-zero offset such that rotation of the reciprocal elements relative to the cam surface results in reciprocation of the reciprocal elements in the chambers.

The pump may be arranged such that when a layer is in the pumping state, the flow rate through said layer can be varied individually. In the case that the pump comprises a valve associated with each layer, said valve may be arranged to vary the rate at which fluid is supplied to said layer, for example by varying the position of the valve with respect to the fully open position. In the case that the pump comprises a cam surface associated with each layer, the cam surface may be mounted for movement such that the offset displacement can be varied with respect to a centred position.

The pump may be arranged such that when the flow rate through a first layer reaches a threshold value, a second layer is switched from a non-pumping to a pumping state. It will be appreciated that, due to the fixed losses associated with the operation of a layer, switching on the layers of the pump sequentially once each previous layer reaches a particular threshold flow rate may increase the efficiency of the ump. The second layer may be automatically switched from the non-pumping to the pumping state once the first layer reaches the threshold value. The threshold value may be the maximum flow rate possible through that layer. For example, the increase in fluid pressure associated with a first layer reaching the maximum flow rate may cause a valve associated with a second layer to open.

The pump may be arranged such that the layers are switched from the non-pumping to a pumping state

sequentially (for example when an adjacent layer reaches a threshold flow rate) . The pump may comprise a control system arranged to control the supply of fluid to or from a layer and/or the offset displacement of a layer such that said layer can be switched ^λοη' and 'off

individually.

In the case that the pump comprises more than two layers of reciprocal elements, it may be that the pump is configured such that sets or groups of layers can be can be switched between a non-pumping state and a pumping state together. Thus, it may be that not every layer can be switched ^Λοη' and ^λοίί' individually with respect to every other layer.

According to a seventh aspect of the invention, there is provided a method of operating a radial pump, the radial pump comprising a plurality of reciprocal elements arranged in at least two layers, the method comprising the steps of pumping fluid through a first one of said at least two layers but not a second one of said at least two layers; and then pumping fluid thorough both the first and second of the at least two layers. The plurality of reciprocal elements may be arranged in more than two layers.

The method may comprise switching on the flow of fluid to each of the layers (or sets of layers) in sequence.

The method may comprise increasing the volume of fluid being pumped through the first one of said at least two layers until a maximum flow rate is reached before starting to pump fluid through the second one of said at least two layers. In the case that the pump comprises more than two layers, the method may comprise increasing the volume of fluid being pumped through a layer (or set of layers) until a maximum flow rate is reached before starting to pump fluid through a further (for example adjacent) layer (or set of layers).

The method may comprise pumping fluid through a first set of layers but not a second set of layers; and then pumping fluid thorough both the first and second set of layers. Providing pumps in which sets of layers can be switched On' and 'off together may allow for some of the efficiency gains associated with multi-layer pumps but with a simplified switching operation and/or

construction as compared to pumps in which every layer is switched at a different time to any other layer.

The first set of layers may include a first one of the at least two layers. The second set of layers may include a second one of the at least two layers. The first set of layers may comprise around a third of the layers. The second set of layers may comprise around two thirds of the layers.

In the case that the pump comprises a plurality of valves, each valve being associated with a different layer (or set of layers) the method may comprise opening a first valve to allow fluid to flow through the first layer (or set of layers) and then opening a second valve to allow fluid to flow through the second layer (of set of layers) . Thus, a layer (or set of layers) may be switched from a non-pumping to a pumping state by opening a valve.

In the case that each of the at least two layers of reciprocal elements is arranged to follow a different cam surface, the method may comprise moving a first cam surface to create an offset with respect to the first layer and then moving a second cam surface to create an offset with respect to the first layer. Thus, a layer may be switched from a non-pumping to a pumping state by creating an offset such that the reciprocal elements reciprocate in their respective chambers.

The steps of switching a layer between a pumping and a non-pumping state may be carried out while the reciprocal elements are rotating relative to a cam surface. Thus, it may be that pumps in accordance with the present invention allow layers to be switched between a pumping state and a non-pumping state while the pump is in operation.

According to an eighth aspect of the invention there is provided a method of manufacturing a radial pump in accordance with any other aspect of the invention. It may be that the method comprises the step of

manufacturing a radial pump in accordance with any other aspect of the invention using an additive manufacturing process. An additive manufacturing process may be defined as a process in which a component is built up, for example by building up layers of material. Additive manufacturing processes may be used instead of, or in combination with, traditional subtractive manufacturing processes .

The method of manufacturing the radial pump may comprise the step of using an additive manufacturing process to produce an integrally formed rotor including a plurality of chambers arranged to receive a plurality of reciprocal elements arranged in at least two layers.

The method may comprise the step of using an additive manufacturing process to produce an integrally formed stator including a suction and/or discharge channel extending along a portion of the length of the stator.

The method of manufacturing the radial pump may comprise the step of using an additive manufacturing process to produce the at least two cam surfaces. For example the method may include the step of manufacturing a plurality of cam-surface mounts each including at least one cam surface.

The method of manufacturing the radial pump may comprise the step of using an additive manufacturing process to produce a plurality of pistons, each piston comprising an integrally formed engagement portion arranged to connect the piston to a resilient member.

According to a ninth aspect of the invention there is provided a radial motor having the features described with reference to a radial pump in any other aspect. It will be apparent to the skilled man that a multi-layer motor having the features described above may be more efficient than other prior art motors. For example, a radial motor may comprise a plurality of reciprocal elements, for example pistons, arranged in at least two layers. Thus, where in the first to eighth aspects described above reference is made to a ^xpump' , this term can (in most cases as will be appreciated by the skilled man) be replaced with the term ^otor' .

In other aspects of the invention, discussed above, a multi-stage pump in which layers can be switched between a pumping and a non-pumping state individually is described. It will be appreciated that this teaching may also be applied to a motor. In connection with a motor the jumping' and ^,non-pumping^f states may be referred to as riving' and non-driving' states respectively. It will be appreciated that as the power required from the motor increases, additional layers may be switched to the driving state from the non-driving state.

According to a tenth aspect of the invention there is provided a method of operating and/or manufacturing a radial motor having the features described with reference to a radial pump in any other aspect.

It will of course be appreciated that features

described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa .

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: Figure 1 shows a cross-sectional view of a prior art radial pump;

Figure 2 shows a sectional view of a portion of a

radial pump according to a first example embodiment of the invention;

Figure 3 shows a sectional view of a portion of the radial pump of the first embodiment; and

Figure 4 shows a sectional view of a portion of the radial pump of the first embodiment; Figures 5 (a) and (b) show a close-up view of the rotor assembly of the first embodiment with and without pistons respectively; and

Figure 6 shows a cross-sectional view of a radial pump according to a second example embodiment of the invention.

Detailed Description Fig. 2 shows a cross-sectional perspective view of part of a pump 100 in accordance with a first example embodiment of the invention. Mounted on a stator 103 is a rotor 106 comprising a plurality of piston chambers 104, in the form of hollow cylinders, which when the rotor 106 is mounted on the stator 103 extend radially outward from the stator 103. The chambers 104 are arranged in thirteen layers (a-m) along the longitudinal axis of the pump 100, each layer a-m comprising nineteen chambers 104 equally spaced around the outer circumference of the rotor 106 at a given axial location. In use, a piston 102 is located in each of the chambers 104, thereby providing thirteen layers or bands of pistons 102 (a-m) spaced apart along the longitudinal axis of the shaft. Each piston 102 of a layer a-m comprises a through-hole 140 in which a circumferential portion of a ring 122 a-m is located. A different ring 122 a-m is associated with each layer. An inward facing cylindrical cam surface 105 a-m is positioned relative to each layer of piston chambers 104 a-m such that the distal end of a piston 102 a-m located in the chambers of that layer can follow the associated cam surface 105 a-m. Each cam surface 105 a-m is supported by a cam-surface mount 110 a-m. For the sake of clarity, only the cam-surface mounts 110a and 110b for the layers ^xa' and ^xb' are shown in Fig. 2. All thirteen mounts are shown in Fig. 3. Each cam-surface mount 110 a-m is in the form of an annular disk, with the cam surface 105 being located adjacent to, and extending along, the inside edge of the annulus . Each cam-surface mount 110 a-m also includes a pair of outwardly extending protrusions 111 - one at the top and one at the bottom of the ring. The lower protrusion 111 of each cam-surface mount 110 a-m has teeth along one side that together form a rack 118 a-m that engages with a common pinion shaft 120 (see Fig. 3) . The longitudinal axis of the pinion shaft 120 extends parallel to the longitudinal axis of the rotor 106/stator 103. The rack 118a of layer ^ya' is arranged to contact the right-hand side of the pinion shaft 120 and faces towards the left in Fig. 2. The rack 118b of layer ^Ab' is arranged to contact the left-hand side of the pinion shaft 120 and faces towards the right. This pattern is repeated in the remaining layers a-m so that the side on which the rack 118 contacts the pinion shaft 120 alternates between layers. A common guide shaft 121 is located on the opposite side of the rotor 106 to the pinion shaft 120. The upper protrusion 110 of each cam-surface mount 110 a- m contacts the guide shaft 121 on the same side as the pinion 120.

In Fig. 2, layer ^Aa' the cam surface 105a is offset upwards with respect to the rotor 106, in layer b' the cam surface 105b is offset downwards with respect to the rotor. This pattern is repeated in the remaining layers a-m so that the sign of the offset displacement

alternates between each layer.

The stator 103 is hollow and divided into two to provide a suction chamber 109 which is in fluid

communication with a pump inlet (not shown) and a discharge chamber 108 which is in fluid communication with a pump outlet (not shown) . The profile of the curved wall varies periodically with distance along the

longitudinal axis of the stator 103 such that the discharge 108 and suction 109 chambers alternate sides for each layer a-m. In layer a' the discharge chamber 108a is on the left hand side and the suction chamber 109a is on the right hand side. In layer b' the discharge chamber 108b is on the right hand side and the suction chamber 109b is on the left hand side and so on for the remaining layers. Thus, the two chambers 108, 109 form a pair of intertwined channels extending down the core of the stator 103.

Pumps in accordance with the present invention may allow a relatively large number of pistons to be

incorporated in a pump in a space-efficient manner.

Increasing the number of pistons in the pump may allow smaller diameter pistons to be used to produce a given flow rate thereby reducing the inertia of the pistons and/or magnitude of the offset loads.

In use, rotation of the rotor 106 causes the pistons

102 of each layer a-m to rotate relative to the

associated cam surface 105a-m. In layer a' , the upward offset of the cam surface 105a means that, on the right hand side, as a piston 102a rotates anti-clockwise from the bottom side of the pump 100 towards the top side of the pump 100 the radial distance between the axis of rotation of the rotor and the cam surface 105a increases and the piston 102a moves outward drawing fluid into the piston chamber 104 from the suction chamber 108. On the left hand side, as the piston 102a rotates anti-clockwise from the top side of the pump 100 towards the bottom side of the pump 100 the radial distance between the axis of rotation of the rotor and the cam surface 105a decreases and the piston 102a moves inwards. Accordingly, in layer a' , the offset force is generated on the left-hand side of the cam surface 105a/pump 100 (and the cam-surface mount 110a is strengthened on this side to compensate for the additional force) . In layer b' , the downward offset means that, with anti-clockwise rotation of the rotor, the offset force is generated on the right-hand side of the cam surface 105b. The offset force of each layer is reacted by the pinion shaft 120 and guide shaft 121 via the rack 118 and guide shaft 121. The

alternating layout of the layers a-m means that the offset force of one layer may be balanced, via the common pinion 120 and guide 121 shafts, by the offset force of the adjacent layer. For example, the offset force of layer a' may be balanced by the offset force of layer b' . In this way the common pinion 120 and guide 121 shafts are primarily under a shear rather than bending load which allows these structures to be reduced in size. Accordingly pumps in accordance with the present

embodiment may be smaller than equivalent prior art pumps with the same number of pistons.

In use, an actuator 132 is used to move each cam- surface mount 110 of a first set of layers (comprising layers a, c, e, g, i, k and m) upward. The upward movement of those layers causes the pinion 120 to rotate anticlockwise, which in turn causes each cam-surface mount 105 of a second set of opposing layers (comprising layers b, d, f, h, j , 1) to move downwards. In this way, the offset, and therefore the stroke length, of each layer a-m is increased simultaneously. Similarly, an actuator 132 is used to move each cam-surface mount 110 of the second set of layers upwards, turning the pinion 120 clockwise and consequently moving the first set of layers downwards to reduce the offset of both sets of layers a-m simultaneously. Consequently, pumps in accordance with the example embodiment may be variable displacement pumps. Using the rack and pinion system may provide a mechanically simple and compact means of controlling the variable

displacement.

As can be seen in Fig. 2 (and in more detail in Fig. 5) while the spacing between the pistons 102 is the same for all layers a-m, the circumferential position of the pistons 102 differs between adjacent layers. The pistons 102b of layer b' are offset in the clockwise direction with respect to the pistons 102a of layer a' . The pistons 102c of layer c' are offset a small amount in the clockwise direction with respect to the pistons 102b of layer b' and so on. This pattern continues in the remaining layers a-m. In use, because of this offset, the pistons of layer ^xb' will move from the suction side (which is on the left in layer b' ) to the discharge side (which is on the right in layer b' ) slightly before the pistons of layer ^xa' move from the discharge side (which is on the left in layer a' ) to the suction side (which is on the right in layer ^xa' ) on each cycle. As a result of this lag in switching, pumps in accordance with the present embodiment may be quieter than equivalent prior art pumps.

In other embodiments of the present invention having a structure similar to that described above a valve is associated with each suction chamber 109 a-m. In use the valve is used to control the flow of fluid into the pistons of the layer a-m associated with that chamber 109 a-m to switch that layer from a pumping state (in which a substantial volume of fluid is moved through the pistons of that layer) to a non-pumping state (in which

substantially no fluid flows via the pistons of that layer) . When the pump is switched on a control unit (not shown) causes the rotor 106 to rotate and the valves associated with layers ^xa' and ^xb' to open such that both those layers begin pumping fluid. The valves are opened gradually such that the output of the pump increases towards a desired flow rate. Once the layers a' and ^b' are operating at their maximum throughput, the control unit causes the valves associated with layers c' and ' to open such that both those layers begin pumping fluid. This pattern is repeated along the layers e-m of the pump until the desired output flow is achieved. Switching the layers of the pump on (or off) in turn allows pumps in accordance with the present embodiment to function more efficiently than prior art pumps because the number of layers operating at any one time (and therefore the fixed' loss associated with each layer) is reduced, while the layers that are pumping spend more time operating in the most efficient performance region (i.e. at or near their maximum flow rate) .

A second radial pump 100' that is an example embodiment of the invention (Fig. 6) is identical to the first, save that the balls 202 are used instead of pistons 102. The rotor 206 includes a plurality of chambers 204 (in this example nine chambers), arranged equidistantly around the circumference of the rotor 206. Each chamber 204 is open at the inner surface and the outer surface of the rotor 206. Each chamber 204 is cup- shaped, in that it has a wider opening at the outer surface of the rotor 206 than at the inner surface, and is a substantially constant bore diameter from the outer opening over the majority of its length along the radius of the rotor 206, before the bore diameter reduces to a narrower opening at the inner surface of the rotor 206, so that the walls of the chamber 204 curve towards the inner surface. A ball 202 is located in each of the chambers 204, thereby providing thirteen layers or bands of balls 202 (a-m, only one layer is visible in Fig. 6) spaced apart along the longitudinal axis of the shaft. An inward facing cylindrical cam surface 105 a-m is positioned relative to each layer of ball chambers 204 a-m such that the surface of the ball 202 can roll on the associated cam surface 105 a-m, whilst the ball 202 remains at least partially in the chamber 204.

In use, rotation of the rotor 206 causes the balls

202 of each layer a-m to rotate relative to the

associated cam surface 105a-m whilst also rolling on that surface 105a-m. In layer ^ya' , the upward offset of the cam surface 105a means that, on the right hand side, as a ball 202a rolls and rotates anti-clockwise from the bottom side of the pump 100' towards the top side of the pump 100' the radial distance between the axis of rotation of the rotor 206 and the cam surface 105a increases and the ball 202a moves outward, drawing fluid into the chamber 204 from the suction chamber 108. On the left hand side, as the ball 102a rolls and rotates anticlockwise from the top side of the pump 100' towards the bottom side of the pump 100' the radial distance between the axis of rotation of the rotor 206 and the cam surface 105a decreases and the ball 202a moves inwards, forcing fluid from the chamber 204 into the discharge chamber 109.

Using balls 202 rather than pistons 102 has the advantage that the rolling of the balls 202 as they rotate on the cam surface 105 produces less friction than when the pistons 102 rotate following the cam surface 105.

Pumps in accordance with the present embodiments may be produced, at least in part, using additive manufacturing processes. Integrally forming elements of the pump into a single component, for example the rotor 106 including the chambers 104, or the stator 103 including the discharge 108 and suction 109 chambers, using an additive manufacturing process may allow pumps in accordance with the present embodiment to be smaller than comparable prior art pumps.

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. For example while the above embodiment describes the

invention in terms of a pump, it will be appreciated that the device of the above embodiment may also be used as a motor. While the above embodiment describes a pump in which each layer is switched between a pumping and a non- pumping state using a valve associated with that layer, it will be appreciated that where each pair of cam surfaces is individually moveable, a layer may be switched between a pumping and a non-pumping state by moving a cam-surface associated with that layer to create an offset. While the above embodiment describes a pump in which the reciprocal elements of each layer follow a different cam surface, it will be appreciated that there may be two or more layers following each cam surface. Similarly, each inlet, outlet and/or valve may be associated with two or more layers.

As well as pistons in piston chambers and balls in ball chambers, other reciprocating elements will suggest themselves to the skilled person. For example, in another example embodiment of the invention, the

reciprocating elements are cylindrical rollers that roll in chambers in the rotor (in a similar manner to the balls in the ball chambers) as the rotor rotates, the chambers being elongate in the direction parallel to the axis of the rotor and holding the cylinders so that their axes extend in that direction.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable eguivalents, 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 radial pump comprising a plurality of reciprocal elements, for example pistons, balls or rollers, arranged in at least two layers, the reciprocal elements of each of the at least two layers being arranged to follow a different cam surface.

2. A radial pump according to claim 1, wherein the

plurality of reciprocal elements are arranged in more than two layers, each layer of reciprocal elements being arranged to follow a different cam surface.

3. A radial pump according to claim 1 or claim 2, wherein the pump is arranged such that, in use, the offset load of a first layer acts in the opposite direction to the offset load of a second layer.

4. A radial pump according to any previous claim, wherein the pump comprises a rotor and the reciprocal elements of each layer are received in chambers integrally formed in the rotor.

5. A radial pump according to any previous claim, wherein the pump is arranged such that, in use, the reciprocal elements of a first layer switch between the suction and discharge phases at a different time to the reciprocal elements of a second layer.

6. A radial pump according to any previous claim, wherein the rotor is mounted on a stator and the stator comprises an integrally formed suction channel and an integrally formed discharge channel, each of said channels extending along a portion of the length of the stator.

7. A radial pump according to any previous claim, wherein the reciprocal elements are pistons and the pump comprises at least two resilient members, each piston of a layer being connected to the same resilient member such that inward movement of the pistons at one circumferential portion of the layer urges the pistons on the opposite circumferential portion of the layer outwards .

A radial pump according to claim 7, wherein each piston of a layer may comprise an integrally formed engagement portion, arranged to connect the piston to the

resilient member.

A radial pump according to any previous claim, wherein each of said cam surfaces is mounted for movement such that the offset displacement of each of said layers may be varied.

A radial pump according to claim 9, wherein a first one of said cam surfaces is mounted for movement relative to a second one of said cam surfaces.

A radial pump according to claim 9 or claim 10, wherein the pump comprises a camshaft, and wherein each cam surface is connected to the camshaft such that, in use, rotation of the camshaft causes movement of the cam surface.

A radial pump according to claim 11, wherein

rotation of said camshaft causes a first one of said cam surfaces to move in a first direction and a second one of said cam surfaces to move in a second direction, opposite to the first direction.

A radial pump according to any previous claim, wherein each of the cam surfaces is connected to the camshaft via a rack and pinion arrangement, the camshaft being the pinion.

A radial pump according to any previous claim, the pump being configured such that each of the at least two layers can be switched between a non-pumping state and a pumping state individually.

15. A radial pump according to any previous claim, wherein the pump is an inside impinged radial pump.

16. A method of manufacturing a radial pump according to any previous claim, the method comprising the step of using an additive manufacturing process to produce a rotor comprising a plurality of integrally formed chambers arranged to receive a plurality of reciprocal elements, wherein said chambers are arranged in at least two layers.

17. A method of manufacturing a radial pump according to claim 16, wherein the method comprises the step of using an additive manufacturing process to produce a stator including an integrally formed suction channel and an integrally formed discharge channel extending along a portion of the length of the stator.

18. A radial motor comprising a plurality of reciprocal elements, for example pistons, balls or rollers, arranged in at least two layers, the reciprocal elements of each of the at least two layers being arranged to follow a different cam surface.

19. A radial motor according to claim 18, wherein the plurality of reciprocal elements are arranged in more than two layers, each layer of reciprocal elements being arranged to follow a different cam surface.

20. A radial motor according to claims 18 or 19, wherein the motor is arranged such that, in use, the offset load of a first layer acts in the opposite direction to the offset load of a second layer.

21. A radial motor according to any of claims 18 to 20, wherein the motor comprises a rotor and the reciprocal elements of each layer are received in chambers integrally formed in the rotor.

22. A radial motor according to any of claims 18 to 21, wherein the motor is arranged such that, in use, the reciprocal elements of a first layer switch between the suction and discharge phases at a different time to the reciprocal elements of a second layer.

23. A radial motor according to any of claims 18 to 22, wherein the rotor is mounted on a stator and the stator comprises an integrally formed suction channel and an integrally formed discharge channel, each of said channels extending along a portion of the length of the stator .

24. A radial motor according to any of claims 18 to 23, wherein the reciprocal elements are pistons and the motor comprises at least two resilient members, each piston of a layer being connected to the same resilient member such that inward movement of the pistons at one circumferential portion of the layer urges the pistons on the opposite circumferential portion of the layer outwards .

25. A radial motor according to claim 24, wherein each piston of a layer may comprise an integrally formed engagement portion, arranged to connect the piston to the resilient member.

26. A radial motor according to any of claims 18 to 25, wherein each of said cam surfaces is mounted for movement such that the offset displacement of each of said layers may be varied.

27. A radial motor according to claim 26, wherein a

first one of said cam surfaces is mounted for movement relative to a second one of said cam surfaces.

28. A radial motor according to claim 26 or claim 27, wherein the motor comprises a camshaft, and wherein each cam surface is connected to the camshaft such that, in use, rotation of the camshaft causes movement of the cam surface.

29. A radial motor according to claim 28, wherein rotation of said camshaft causes a first one of said cam surfaces to move in a first direction and a second one of said cam surfaces to move in a second direction, opposite to the first direction.

30. A radial motor according to any of claims 18 to 29, wherein each of the cam surfaces is connected to the camshaft via a rack and pinion arrangement, the camshaft being the pinion.

31. A radial motor according to any of claims 18 to 30, the motor being configured such that each of the at least two layers can be switched between a non-driving state and a driving state individually.

32. A method of manufacturing a radial motor according to any of claims 18 to 31, the method comprising the step of using an additive manufacturing process to produce a rotor comprising a plurality of integrally formed chambers arranged to receive a plurality of reciprocal elements, wherein said chambers are arranged in at least two layers.

33. A method of manufacturing a radial motor according to claim 32, wherein the method comprises the step of using an additive manufacturing process to produce a stator including an integrally formed suction channel and an integrally formed discharge channel extending along a portion of the length of the stator.

34. A radial pump comprising a plurality of pistons

arranged in at least two layers, and at least two resilient members, each piston of a layer being connected to the same resilient member such that inward movement of the pistons at one circumferential portion of the layer urges the pistons on the opposite

circumferential portion of the layer outwards.

35. A radial pump according to claim 34, wherein the pistons of each layer are arranged to follow a

different cam surface.

36. A radial pump according to claim 34 or claim 35,

wherein the resilient member comprises a wire ring.

37. A radial pump according to any of claims 34 to 36, wherein each piston of a layer comprises an integrally formed engagement portion arranged to connect the piston to the resilient member.

38. A radial pump according to claim 37, wherein the

engagement portion comprises a hook or a recess.

39. A radial pump according to any of claims 34 to 38, wherein the pump is an inside impinged radial piston pump .

40. A method of manufacturing a radial pump according to any of claims 34 to 39, the method comprising the step of using an additive manufacturing process to produce a plurality of pistons, each piston comprising an integrally formed engagement portion arranged to connect the piston to a resilient member.

41. A radial motor comprising a plurality of pistons arranged in at least two layers, and at least two resilient members, each piston of a layer being connected to the same resilient member such that inward movement of the pistons at one circumferential portion of the layer urges the pistons on the opposite

circumferential portion of the layer outwards.

42. A radial motor according to claim 41, wherein the pistons of each layer are arranged to follow a

different cam surface.

43. A radial motor according to claim 41 or claim 42, wherein the resilient member comprises a wire ring.

44. A radial motor according to any of claims 41 to 43, wherein each piston of a layer comprises an integrally formed engagement portion arranged to connect the piston to the resilient member.

45. A radial motor according to claim 44, wherein the engagement portion comprises a hook or a recess.

46. A radial motor according to any of claims 41 to 45, wherein the motor is an inside impinged radial piston motor .

47. A method of manufacturing a radial motor according to any of claims 41 to 46, the method comprising the step of using an additive manufacturing process to produce a plurality of pistons, each piston comprising an integrally formed engagement portion arranged to connect the piston to a resilient member.

48. A radial pump comprising a plurality of reciprocal elements, for example pistons, balls or rollers, arranged in at least two layers, the reciprocal elements of each of said at least two layers being arranged to follow a different cam surface and wherein each of said cam surfaces is mounted for movement such that the offset displacement of each of said at least two layers may be varied.

49. A radial pump according to claim 48, wherein the

plurality of reciprocal elements are arranged in more than two layers, each of said layers of reciprocal elements being arranged to follow a different cam surface .

50. A radial pump according to claim 48 or claim 49,

wherein a first one of said cam surfaces is mounted for movement relative to a second one of said cam surfaces.

51. A radial pump according to any of claims 48 to 50, wherein the pump comprises a camshaft, and wherein each cam surface is connected to the camshaft such that, in use, rotation of the camshaft causes movement of the cam surface.

52. A radial pump according to claim 51, wherein

53. A radial pump according to any of claims 48 to 52, wherein the each of the cam surfaces is connected to the camshaft via a rack and pinion arrangement, the camshaft being the pinion.

54. A radial pump according to any of claims 48 to 53, wherein the pump is an inside impinged radial pump.

55. A method of varying the flow of fluid through a

radial pump, the pump comprising a plurality of reciprocal elements, for example pistons, balls or rollers, arranged in at least two layers, the

reciprocal elements of each layer being arranged to follow a different cam surface, the method comprising the step of moving each cam surface relative to the reciprocal elements of the associated layer to vary the offset displacement of each layer.

56. A method of varying the flow of fluid through a

radial pump according to claim 55, wherein the method includes the step of moving each of the cam surfaces simultaneously to vary the offset displacement of each layer .

57. A method of varying the flow of fluid through a

radial pump according to claim 55 or claim 56, the method comprising the step of using an additive manufacturing process to produce a rotor comprising a plurality of chambers arranged to receive a plurality of reciprocal elements such that the reciprocal elements are arranged in least two layers.

58. A radial motor comprising a plurality of reciprocal elements, for example pistons, balls or rollers, arranged in at least two layers, each of said at least two layers of reciprocal elements being arranged to follow a different cam surface and wherein each of said cam surfaces is mounted for movement such that the offset displacement of each of said at least two layers may be varied.

59. A radial motor according to claim 58, wherein the plurality of reciprocal elements are arranged in more than two layers, each of said layers of reciprocal elements being arranged to follow a different cam surface .

60. A radial motor according to claim 58 or claim 59, wherein a first one of said cam surfaces is mounted for movement relative to a second one of said cam surfaces.

61. A radial motor according to any of claims 58 to 60, wherein the motor comprises a camshaft, and wherein each cam surface is connected to the camshaft such that, in use, rotation of the camshaft causes movement of the cam surface.

62. A radial motor according to claim 61, wherein

63. A radial motor according to any of claims 58 to 62, wherein the each of the cam surfaces is connected to the camshaft via a rack and pinion arrangement, the camshaft being the pinion.

64. A radial motor according to any of claims 58 to 63, wherein the motor is an inside impinged radial motor.

65. A method of varying the flow of fluid through a

radial motor, the motor comprising a plurality of reciprocal elements, for example pistons, balls or rollers, arranged in at least two layers, the

66. A method of varying the flow of fluid through a

radial motor according to claim 65, wherein the method includes the step of moving each of the cam surfaces simultaneously to vary the offset displacement of each layer .

67. A method of varying the flow of fluid through a

radial motor according to claim 65 or claim 66, the method comprising the step of using an additive manufacturing process to produce a rotor comprising a plurality of chambers arranged to receive a plurality of reciprocal elements such that the reciprocal elements are arranged in least two layers.

68. A radial pump comprising a plurality of reciprocal elements, for example pistons, balls or rollers, arranged in at least two layers, the pump being configured such that each of the at least two layers can be switched between a non-pumping state and a pumping state individually.

69. A radial pump according to claim 68, wherein the

pump further comprises at least two valves, each valve being arranged to control the flow of fluid to or from a different one of said at least two layers such that each layer may be switched between a non-pumping state and a pumping state by operating the valve.

70. A radial pump according to claim 68 or claim 69, the pump further comprising at least two cam surfaces, the reciprocal elements of each layer being arranged to follow a different one of said cam surfaces and wherein each cam surface is mounted for movement between a centred position and an offset position such that each layer may be switched between a non-pumping state and a pumping state by moving the cam surface.

71. A radial pump according to any of claims 68 to 70, wherein the pump is arranged such that when a layer is in the pumping state, the flow rate through said layer may be varied individually.

72. A radial pump according to claim 71, wherein the

pump is arranged such that when the flow rate through a first layer reaches a threshold value, a second layer is switched from a non-pumping to a pumping state.

73. A radial pump according to any of claims 68 to 72, wherein the pump comprises a control system arranged to control the supply of fluid to or from a layer and/or the offset displacement of a layer such that said layer may be switched between a non-pumping state and a pumping state individually.

74. A method of operating a radial pump, the radial pump comprising a plurality of reciprocal elements, for example pistons, balls or rollers, arranged in at least two layers, the method comprising the steps of:

- pumping fluid through a first one of said at least two layers but not a second one of said at least two layers; and then

- pumping fluid thorough the first and second of the at least two layers.

75. A method of operating a radial pump in accordance with claim 74, wherein the pump comprises more than two layers and the method comprising switching on the flow of fluid to each of the layers in sequence.

76. A method of operating a radial pump in accordance with claim 74 or claim 75, the method comprising the steps of increasing the volume of fluid flowing through the first one of said at least two layers until a maximum flow rate is reached before starting to pump fluid through the second one of said at least two layers .

7. A method of operating a radial pump in accordance with any of claims 74 to 76, the method comprising the step of increasing the volume of fluid flowing through the second one of said at least two layers until a maximum flow rate is reached and then allowing the flow of fluid thorough a further one of said at least two layers .

8. A method of operating a radial pump in accordance with any of claims 74 to 77, wherein the pump comprises at least two valves, each valve being associated with a different layer and the method comprises the step of opening a first valve to allow fluid to flow through the first layer and then opening a second valve to allow fluid to flow through the second layer.

9. A method of operating a radial pump in accordance with any of claims 74 to 78, wherein the reciprocal elements of each of the at least two layers are arranged to follow a different cam surface, and the method comprises the step of moving a first cam surface to create an offset with respect to the first layer such that fluid is pumped through said first layer, and then moving a second cam surface to create an offset with respect to a second layer such that fluid is pumped through said second layer.

0. A radial motor comprising a plurality of reciprocal elements, for example pistons, balls or rollers, arranged in at least two layers, the motor being configured such that each of the at least two layers can be switched between a non-driving state and a driving state individually.

81. A radial motor according to claim 80, wherein the motor further comprises at least two valves, each valve being arranged to control the flow of fluid to or from a different one of said at least two layers such that each layer may be switched between a driving state and a non-driving state by operating the valve.

82. A radial motor according to claim 80 or claim 81, the motor further comprising at least two cam surfaces, the reciprocal elements of each of said at least two layers being arranged to follow a different cam surface and wherein each cam surface is mounted for movement between a centred position and an offset position such that each layer may be switched between a driving state and a non-driving state by moving the cam surface.

83. A radial motor according to any of claims 80 to 82, wherein the motor is arranged such that when a layer is in the driving state, the flow rate through said layer may be varied individually.

84. A radial motor according to claim 83, wherein the motor is arranged such that when the flow rate through a first layer reaches a threshold value, a second layer is switched from a non-driving to a driving state.

85. A radial motor according to any of claims 80 to 84, wherein the motor comprises a control system arranged to control the supply of fluid to or from a layer and/or the offset displacement of a layer such that said layer may be switched between a non-driving state and a driving state individually.

86. A method of operating a radial motor, the radial

motor comprising a plurality of reciprocal elements, for example pistons, balls or rollers, arranged in at least two layers, the method comprising the steps of: - pumping fluid through a first one of said at least two layers but not a second one of said at least two layers; and then

- pumping fluid thorough the first and second of the at least two layers.

7. A method of operating a radial motor in accordance with claim 86, wherein the motor comprises more than two layers and the method comprising switching on the flow of fluid to each of the layers in sequence.

8. A method of operating a radial motor in accordance with claim 86 or 87, the method comprising the steps of increasing the volume of fluid flowing through the first one of said at least two layers until a maximum flow rate is reached before starting to pump fluid through the second one of said at least two layers.

9. A method of operating a radial motor in accordance with any of claims 86 to 88, the method comprising the step of increasing the volume of fluid flowing through the second one of said at least two layers until a maximum flow rate is reached and then allowing the flow of fluid thorough a further one of said at least two layers .

0. A method of operating a radial motor in accordance with any of claims 86 to 89, wherein the motor

comprises at least two valves, each valve being associated with a different layer and the method comprises the step of opening a first valve to allow fluid to flow through the first layer and then opening a second valve to allow fluid to flow through the second layer.

1. A method of operating a radial motor in accordance with any of claims 86 to 90, wherein the reciprocal elements of each of the at least two layers are arranged to follow a different cam surface, and the method comprises the step of moving a first cam surface to create an offset with respect to the first layer such that fluid is pumped through said first layer, and then moving a second cam surface to create an offset with respect to a second layer such that fluid is pumped through said second layer.

92. A radial pump or motor substantially as herein

described with reference to the accompanying drawings.

93. A method of manufacturing a radial pump or motor

substantially as herein described with reference to the accompanying drawings .