Fluid working machine with valve actuator and method for controlling the same

Abstract

A fluid working machine has at least one working chamber of cyclically varying volume and low and high pressure valves to regulate the flow of working fluid into and out of the working chamber, from low and high pressure manifolds. The low and high pressure valves are actuated by electronically controlled valve actuation means which, when actuated, applies forces to the low and high pressure valve members to open and/or close the respective valves. The low and high pressure valve members are independently moveable and, although the low pressure valve member typically begins to move quickly in response to a shared valve control signal, the high pressure valve member typically moves only after a change in the pressure within the working chamber. The electronically controlled valve actuation means may be a shared electronically controlled valve actuator, such as a solenoid within a magnetic circuit which directs magnetic flux through both low pressure and high pressure valve armatures which are connected to the respective valve members.

Claims

1. A fluid working machine comprising at least one working chamber of cyclically varying volume, a low pressure fluid line, a high pressure fluid line, a low pressure valve for regulating a flow of fluid between the working chamber and the low pressure fluid line, a high pressure valve for regulating the flow of fluid between the working chamber and the high pressure fluid line, the low and high pressure valves being selectively actuatable on each cycle of working chamber volume to determine a net displacement of working fluid by the working chamber, the low pressure valve comprising a low pressure valve member, the high pressure valve comprising a high pressure valve member, the low pressure valve member and the high pressure valve member, being independently movable between open and closed positions, wherein the fluid working machine further comprises an electronically controlled valve actuation unit configured to both cause an opening or closing force to be applied to the low pressure valve member and to cause an opening or closing force to be applied to the high pressure valve member responsive to a shared valve actuation signal so that the movement of one of the low pressure valve member and the high pressure valve member to the closed position begins before the movement of the other of the low pressure valve member and the high pressure valve member to the open position, wherein the electronically controlled valve actuation unit comprises a shared electronically controlled valve actuator coupled to both the low pressure valve member and the high pressure valve member and configured to cause both the opening or closing force to be applied to the low pressure valve member and to cause the opening or closing force to be applied to the high pressure valve member responsive to the shared valve actuation signal, wherein the shared electronically controlled valve actuator comprises a solenoid coil, wherein the low pressure valve member and the high pressure valve member are each mechanically coupled to a respective armature, and wherein both the armatures are electronically driven by the same solenoid coil.

2. A fluid working machine according to claim 1, wherein the electronically controlled valve actuation unit causes said opening or closing forces to be applied to the low pressure valve member and the high pressure valve member concurrently but the low pressure valve member and the high pressure valve member open or close at different times in dependence on changes in the pressure in the working chamber and the low and high pressure fluid lines respectively.

3. A fluid working machine according to claim 1, wherein the low pressure valve comprises a low pressure valve biasing member which biases the low pressure valve member to the open position, the high pressure valve comprises a high pressure valve biasing member which biases the high pressure valve member to the closed position, and the forces caused by the electronically controlled valve actuation unit oppose the biasing forces of the low pressure and high pressure valve biasing members.

4. A fluid working machine according to claim 1, wherein the low pressure valve member is biased either to the open position or the closed position by one or more low pressure valve biasing members and the high pressure valve member is biased either to the open position or the closed position by one or more high pressure valve biasing members and said opening or closing forces caused by the electronically controlled valve actuation unit oppose and exceed the net biasing forces applied to the low pressure and high pressure valve members by the one or more low pressure and high pressure valve biasing members.

5. A fluid working machine according to claim 1, wherein the electronically controlled valve actuator comprises an armature which is moved when the electronically controlled valve actuator is actuated and the forces applied to the low pressure valve member and the high pressure valve member are coupled to movement of the armature.

6. A fluid working machine according to claim 1, further comprising a magnetic circuit extending through the solenoid coil and configured to direct magnetic flux through both armatures.

7. A fluid working machine, comprising at least one working chamber of cyclically varying volume, a low pressure fluid line, a high pressure fluid line, a low pressure valve for regulating a flow of fluid between the working chamber and the low pressure fluid line, a high pressure valve for regulating the flow of fluid between the working chamber and the high pressure fluid line, the low and high pressure valves being selectively actuatable on each cycle of working chamber volume to determine a net displacement of working fluid by the working chamber, the low pressure valve comprising a low pressure valve member, the high pressure valve comprising a high pressure valve member, the low pressure valve member and the high pressure valve member being independently movable between open and closed positions, wherein the fluid working machine further comprises an electronically controlled valve actuation unit configured to both cause an opening or closing force to be applied to the low pressure valve member and to cause an opening or closing force to be applied to the high pressure valve member responsive to a shared value actuation signal, wherein the electronically controlled valve actuation unit comprises a shared electronically controlled valve actuator coupled to both the low pressure valve member and the high pressure valve member and configured to cause both the opening or closing force to be applied to the low pressure valve member and to cause the opening or closing force to be applied to the high pressure valve member responsive to the shared valve actuation signal, wherein the shared electronically controlled valve actuator comprises a solenoid coil, wherein the low pressure valve member and the high pressure valve member are each mechanically coupled to a respective armature, wherein both the armatures are electronically driven by the same solenoid coil, wherein the fluid working machine comprises a magnetic circuit extending through the solenoid coil, and wherein the magnetic circuit is configured to direct magnetic flux through both armatures in series.

8. A fluid working machine according to claim 1, wherein said opening or closing forces are variable responsive to a valve actuation signal and the fluid working machine is configured to vary the valve actuation signal while said opening or closing forces are applied to thereby vary said opening or closing forces with the low pressure valve member and the high pressure valve member maintained in the open position or the closed position, during at least some operations of said valves.

9. A fluid working machine according to claim 8, wherein the fluid working machine is configured to make a step change in the valve actuation signal with the low pressure valve member and the high pressure valve member maintained in the open position or the closed position whilst said opening or closing forces are applied to the low and high pressure valve members.

10. A fluid working machine according to claim 1, wherein the low pressure valve is a face seating valve.

11. A fluid working machine according to claim 1, wherein the high pressure valve is a face seating valve.

12. A fluid working machine according to claim 1, wherein the low pressure valve or the high pressure valve further comprises a pilot valve having a pilot valve seat, wherein the electronically controlled valve actuation unit is also coupled to the pilot valve member to apply an opening or closing force to the pilot valve responsive to actuation of the electronically controlled valve actuator.

13. A fluid working machine according to claim 1, wherein the low pressure valve and high pressure valve are integrated into a single unit.

14. A method of controlling a fluid working machine according to claim 1, wherein the electronically controlled valve actuation unit causes the opening or closing force to be applied concurrently to both the low pressure valve member and the high pressure valve member responsive to the shared value actuation signal and the low pressure valve member and the high pressure valve member move, as a result of the applied forces, at different times.

15. A fluid working machine, comprising at least one working chamber of cyclically varying volume, a low pressure fluid line, a high pressure fluid line, a low pressure valve for regulating a flow of fluid between the working chamber and the low pressure fluid line, a high pressure valve for regulating the flow of fluid between the working chamber and the high pressure fluid line, the low and high pressure valves being selectively actuatable on each cycle of working chamber volume to determine a net displacement of working fluid by the working chamber, the low pressure valve comprising a low pressure valve member, the high pressure valve comprising a high pressure valve member, the low pressure valve member and the high pressure valve member being independently movable between open and closed positions, wherein the fluid working machine further comprises an electronically controlled valve actuation unit configured to both cause an opening or closing force to be applied to the low pressure valve member and to cause an opening or closing force to be applied to the high pressure valve member responsive to a shared value actuation signal, wherein the electronically controlled valve actuation unit comprises a shared electronically controlled valve actuator coupled to both the low pressure valve member and the high pressure valve member and configured to cause both the opening or closing force to be applied to the low pressure valve member and to cause the opening or closing force to be applied to the high pressure valve member responsive to the shared valve actuation signal, wherein the shared electronically controlled valve actuator comprises a solenoid coil, wherein the low pressure valve member and the high pressure valve member are each mechanically coupled to a respective armature, wherein both the armatures are electronically driven by the same solenoid coil, wherein the fluid working machine comprises a magnetic circuit extending through the solenoid coil and configured to direct magnetic flux through both armatures, and wherein the fluid working machine further comprises a magnetic connecting portion disposed adjacent both the low pressure and high pressure valve armatures, the magnetic connecting portion including tapered bridging pieces at both sides in a travel direction of the low pressure and high pressure valve armatures.

16. A fluid working machine according to claim 15, further comprising a non-magnetic support member supporting the magnetic connecting portion.

17. A fluid working machine, comprising at least one working chamber of cyclically varying volume, a low pressure fluid line, a high pressure fluid line, a low pressure valve for regulating a flow of fluid between the working chamber and the low pressure fluid line, a high pressure valve for regulating the flow of fluid between the working chamber and the high pressure fluid line, the low and high pressure valves being selectively actuatable on each cycle of working chamber volume to determine a net displacement of working fluid by the working chamber, the low pressure valve comprising a low pressure valve member, the high pressure valve comprising a high pressure valve member, the low pressure valve member and the high pressure valve member being independently movable between open and closed positions, wherein the fluid working machine further comprises an electronically controlled valve actuation unit configured to both cause an opening or closing force to be applied to the low pressure valve member and to cause an opening or closing force to be applied to the high pressure valve member responsive to a shared value actuation signal, wherein the electronically controlled valve actuation unit comprises a shared electronically controlled valve actuator coupled to both the low pressure valve member and the high pressure valve member and configured to cause both the opening or closing force to be applied to the low pressure valve member and to cause the opening or closing force to be applied to the high pressure valve member responsive to the shared valve actuation signal, wherein the shared electronically controlled valve actuator comprises a solenoid coil, wherein the low pressure valve member and the high pressure valve member are each mechanically coupled to a respective armature, wherein both the armatures are electronically driven by the same solenoid coil, wherein the fluid working machine comprises a magnetic circuit extending through the solenoid coil and configured to direct magnetic flux through both armatures, and wherein the fluid working machine further comprises an end stop which defines a maximal axial travel of the low pressure or high pressure valve armatures, and a tapered bridging piece disposed adjacent the end stop.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) An example embodiment of the invention will now be illustrated with reference to the following Figures:

(2) FIG. 1 is a schematic diagram of a prior art fluid working machine;

(3) FIG. 2 is a schematic diagram of an embodiment of the invention employing a separate actuator for each valve;

(4) FIG. 3 is a schematic diagram of a circuit for actuating the valves in the embodiment of FIG. 2;

(5) FIG. 4 is a schematic diagram of an embodiment of the invention employing a shared electronically controlled valve actuator;

(6) FIG. 5 is a schematic diagram of an embodiment of the invention using coupled pistons;

(7) FIG. 6A is a schematic radial cross section of an embodiment of the invention in which both valve members are driven directly by a single solenoid;

(8) FIG. 6B is a schematic radial cross section of an embodiment of the invention in which both valve members are driven directly by a single solenoid;

(9) FIG. 6C is a schematic radial cross section of an embodiment of the invention in which both valve members are driven directly by a single solenoid;

(10) FIG. 7 is a schematic radial cross section through an alternative example embodiment in which both valve members are driven directly by a single solenoid;

(11) FIG. 8 is a cross-section through an example embodiment in which both valve members are driven directly by a single solenoid;

(12) FIG. 9A is a detail of FIG. 8;

(13) FIG. 9B is a corresponding detail after opening of the high pressure valve;

(14) FIG. 10 illustrates low pressure valve position, a high-pressure valve position, working chamber pressure and the common actuator control signal for both pumping (upper traces) and motoring (lower traces);

(15) FIG. 11A is a schematic radial cross section through an example embodiment in which magnetic flux from a single solenoid is directed through armatures associated with each valve member, either in parallel or in series.

(16) FIG. 11B is a schematic radial cross section through an example embodiment in which magnetic flux from a single solenoid is directed through armatures associated with each valve member, either in parallel or in series.

DESCRIPTION OF EMBODIMENTS

(17) FIG. 1 is a schematic diagram of an individual working chamber 2 in a fluid-working machine 1. The net throughput of fluid is determined by the active control of electronically controllable valves, in phased relationship to cycles of working chamber volume, to regulate fluid communication between individual working chambers of the machine and fluid manifolds. Individual chambers are selectable by a controller, on a cycle by cycle basis, to either displace a predetermined fixed volume of fluid or to undergo an idle cycle with no net displacement of fluid, thereby enabling the net throughput of the pump to be matched dynamically to demand.

(18) An individual working chamber 2 has a volume defined by the interior surface of a cylinder 4 and a piston 6, which is driven from a crankshaft 8 by a crank mechanism 9 and which reciprocates within the cylinder to cyclically vary the volume of the working chamber. A shaft position and speed sensor 10 determines the instantaneous angular position and speed of rotation of the shaft, and transmits shaft position and speed signals to a controller 12, which enables the controller to determine the instantaneous phase of the cycles of each individual working chamber. The controller typically comprises a microprocessor or microcontroller which executes a stored program in use.

(19) The working chamber comprises an actively controlled low pressure valve in the form of an electronically controllable face-sealing poppet valve 14, which faces inwards toward the working chamber and is operable to selectively seal off a channel extending from the working chamber to a low pressure manifold 16. The working chamber further comprises a high pressure valve 18. The high pressure valve faces outwards from the working chamber and is operable to seal off a channel extending from the working chamber to a high pressure manifold 20.

(20) At least the low pressure valve is actively controlled so that the controller can select whether the low pressure valve is actively closed, or in some embodiments, actively held open, during each cycle of working chamber volume. In some embodiments, the high pressure valve is actively controlled and in some embodiments, the high pressure valve is a passively controlled valve, for example, a pressure delivery check valve.

(21) The fluid-working machine may be a pump, which carries out pumping cycles, or a motor which carries out motoring cycles, or a pump-motor which can operate as a pump or a motor in alternative operating modes and can thereby carry out pumping or motoring cycles.

(22) A full stroke pumping cycle is described in EP 0 361 927. During an expansion stoke of a working chamber, the low pressure valve is open and hydraulic fluid is received from the low pressure manifold. At or around bottom dead centre, the controller determines whether or not the low pressure valve should be closed. If the low pressure valve is closed, fluid within the working chamber is pressurized and vented to the high pressure valve during the subsequent contraction phase of working chamber volume, so that a pumping cycle occurs and a volume of fluid is displaced to the high pressure manifold. The low pressure valve then opens again at or shortly after top dead centre. If the low pressure valve remains open, fluid within the working chamber is vented back to the low pressure manifold and an idle cycle occurs, in which there is no net displacement of fluid to the high pressure manifold.

(23) In some embodiments, the low pressure valve will be biased open and will need to be actively closed by the controller if a pumping cycle is selected. In other embodiments, the low pressure valve will be biased closed and will need to be actively held open by the controller if an idle cycle is selected. The high pressure valve may be actively controlled, or may be a passively opening check valve.

(24) A full stroke motoring cycle is described in EP 0 494 236. During a contraction stroke, fluid is vented to the low pressure manifold through the low pressure valve. An idle cycle can be selected by the controller in which case the low pressure valve remains open. However, if a full stroke motoring cycle is selected, the low pressure valve is closed before top dead centre, causing pressure to build up within the working chamber as it continues to reduce in volume. Once sufficient pressure has been built up, the high pressure valve can be opened, typically just after top dead centre, and fluid flows into the working chamber from the high pressure manifold. Shortly before bottom dead centre, the high pressure valve is actively closed, whereupon pressure within the working chamber falls, enabling the low pressure valve to open around or shortly after bottom dead centre.

(25) In some embodiments, the low pressure valve will be biased open and will need to be actively closed by the controller if a motoring cycle is selected. In other embodiments, the low pressure valve will be biased closed and will need to be actively held open by the controller if an idle cycle is selected. The low pressure valve typically opens passively, but it may open under active control to enable the timing of opening to be carefully controlled. Thus, the low pressure valve may be actively opened, or, if it has been actively held open this active holding open may be stopped. The high pressure valve may be actively or passively opened. Typically, the high pressure valve will be actively opened.

(26) In some embodiments, instead of selecting only between idle cycles and full stroke pumping and/or motoring cycles, the fluid-working controller is also operable to vary the precise phasing of valve timings to create partial stroke pumping and/or partial stroke motoring cycles.

(27) In a partial stroke pumping cycle, the low pressure valve is closed later in the exhaust stroke so that only a part of the maximum stroke volume of the working chamber is displaced into the high pressure manifold. Typically, closure of the low pressure valve is delayed until just before top dead centre.

(28) In a partial stroke motoring cycle, the high pressure valve is closed and the low pressure valve opened part way through the expansion stroke so that the volume of fluid received from the high pressure manifold and thus the net displacement of fluid is less than would otherwise be possible.

(29) With reference to FIG. 2, in a first example embodiment, the controller transmits a shared valve actuation signal through a signal output wire 30. The shared valve actuation signal may be a current which is applied to the solenoid of the low and high pressure valves or, for example, a digital signal used to control a circuit which applies a current to the solenoid of the low and high pressure valves responsive to the digital signal. In response to the shared valve actuation signal, current is applied to the solenoids of both the low pressure and high pressure valves, so that they are both energized at the same time, and so the low pressure valve solenoid applies a closing force to the low pressure valve member, and the high pressure valve applies an opening force to the high pressure valve member at the same time. However, because the low and high pressure valve members can move independently, although the low pressure valve member will typically begin to move almost immediately that current is applied to the solenoids, the high pressure valve member will typically not begin to move until the pressure differential across the high pressure valve member, between the working chamber and the high pressure manifold, drops below a threshold.

(30) FIG. 3 illustrates an example of how the low and high pressure valve solenoids 38A, 38B may be driven by the controller. In this example, the controller generates shared valve actuation signals, in digital form, which are processed by an FPGA 32. The FPGA generates a signal which is routed in parallel to a separate FET driver 34A, 34B for each valve. The respective FET drivers each drive an FET 36A, 36B associated with the respective valve, which in turn generate a current which is applied to the respective solenoids. However, one skilled in the art will appreciate that where the control of the low pressure valve and high pressure valve solenoids is split is a matter of design choice. For example a single FET driver might drive two FETs, a single FET might provide a current passed through both the low pressure valve and high pressure valve solenoids, in series or in parallel, and so forth. The control circuit of FIG. 3 and the low and high pressure valve solenoids together function as the electronically controlled valve actuation means.

(31) FIG. 4 is a schematic diagram of a working chamber of a second fluid working machine according to the invention. A shared electronically controlled valve actuator 50 is coupled to the valve members (not shown in FIG. 4) of both the high and low pressure valves. A shared valve actuation signal is transmitted by the controller through control line 52. When the shared valve actuator is actuated, forces are applied to the valve members of the high and low pressure valves to urge the low pressure valve to close and the high pressure valve to open. However, the high and low pressure valve members are able to move independently and, although the low pressure valve member will typically start to move shortly after the shared actuator is actuated, there will be a delay before the high pressure valve member can move, while the pressure in the working chamber increases to a level which enables the high pressure valve to open.

(32) A first example of a shared valve actuator arrangement is illustrated in FIG. 5. A piston 100 is slidably mounted in a master cylinder 102 and driven by a solenoid operated actuator 104. When the solenoid operated actuator is actuated by a shared control signal received through the control line 52, hydraulic fluid is displaced through hydraulic connections 106 to slave cylinders 108, 110 which comprise pistons 112 and 114, which are coupled through valve stems 116, 118 to a low pressure valve member 120 and a high pressure valve member 122 to urge the low pressure valve member towards low pressure valve seat 124 and the high-pressure valve member away from high-pressure valve seat 126. Thus, although actuation of the solenoid operated actuator causes a force to be applied to the low pressure valve member to urge the low pressure valve member towards the low pressure valve seat, and thereby close the low pressure valve, and at the same time causes a force to be applied to the high-pressure valve member to urge the high-pressure valve member away from the high-pressure valve seat, and thereby open the high-pressure valve, the high-pressure valve member can, and in practice does, move at a different time to the low pressure valve member.

(33) With reference to FIG. 6A, in an alternative embodiment a solenoid coil 200 functions as the electronically controlled valve actuator. The solenoid coil is coupled to the low pressure valve member and high pressure valve member (not shown) through a magnetic circuit formed of a first magnetic circuit member 202 (functioning as part of the major portion of the magnetic circuit), and a second magnetic circuit member 204 (functioning as the minor portion of the magnetic circuit) which directs magnetic flux through a low pressure valve armature 206 which is connected to the low pressure valve member (not shown) via a low pressure valve stem 208, and a high pressure valve armature 210 which is connected to the high pressure valve member (not shown) via a high pressure valve stem 212. The low pressure and high pressure valves are configured so that the low pressure valve is closed by axial movement of the low pressure valve armature and valve stem towards the solenoid and the high pressure valve is opened by axial movement of the high pressure valve armature and valve stem towards the solenoid. Although the items labelled 206 in the Figures are the low pressure valve armature and the items labelled 210 are the high pressure valve armature in this example embodiment, the low and high pressure valve armatures could be interchanged in alternative embodiments.

(34) Magnetic circuit members are typically made from steel, and in particular suitable materials include a silicon steel, a silicon core iron, or 430FR which is a ferritic stainless steel.

(35) When current is passed through the solenoid (functioning as the shared valve actuation signal) magnetic flux are directed around the magnetic circuit member and through the low and high pressure valve armatures, in series. As a result, a force acts on both armatures, urging them in an axial direction, towards the solenoid (upwards in FIG. 6A). This applies an opening force to the low pressure valve member and a closing force to the high pressure valve member.

(36) FIGS. 6B and 6C illustrate alternative embodiments which work on a corresponding principle. In the arrangement of FIG. 6C the armatures are urged towards each other. The range of movement of each valve member is governed in one direction by the respective valve seat, and a respective end stop in the other direction. The end stop may engage the valve member, or part of the armature connected to the valve member.

(37) FIG. 7 illustrates a further embodiment which corresponds in general terms to the embodiment of FIG. 6A but the magnetic circuit includes a magnetic connecting portion (functioning as the minor portion of the magnetic circuit) 204, supported by a non-magnetic support member 214 which is adjacent both the low pressure and high pressure valve armatures and includes tapered bridging pieces 216, 217 which have an axial first surface 220 and an angled opposed surface 222. A further bridging piece 218 extends from the magnetic circuit portion adjacent an end stop 224 which defines the maximum axial travel of the high pressure valve armatures towards the solenoid.

(38) The armatures move parallel to the axial first surfaces and as a result of the tapered shape of the bridging pieces, the axial force acting on the valve armatures increases as the armatures move towards their ‘activated’ positions (the positions towards which they are urged responsive to actuation of the electronically controlled valve actuator). This means that a lower current is required to latch (retain) the valve members in a displaced position when they have completed their movement towards the solenoid and the respective valves are open or closed, than is required to start movement of the valve members. The tapered bridge piece 216 does not change the magnetic force with axial displacement of either armature. Its functions are to help to axially align the HPV armature, to provide additional metal within the magnetic circuit flow path (helping to avoid magnetic saturation), and also to reduce the distance the magnetic flux needs to travel (reduced reluctance).

(39) The taper bridging piece 217 and the further bridging piece 218 provide the proportional control aspect of the magnetic circuit. The ‘tip’ part of these bridging pieces becomes saturated once the solenoid is activated. Once saturated, flux cannot flow through this portion, and thus flows around the saturated region. Magnetically, the saturated portion equates to an air gap, therefore increasing the tendency for flux to find another path around the saturated portion.

(40) The total length of the bridging pieces, in part determined by the point of truncation, determines the stroke length of each respective armature. The angle of taper of the bridging pieces determines the time to saturation, which can thus be selected. Generally speaking the greater the internal angle between the axial first surface 220 and the angled opposed surface, the longer the time to saturation. The angle of taper of each of the bridging pieces can be manipulated relative to one another in order to change the forces applied to each armature, and thus both the start time, and initial movement characteristics of each armature relative to each other.

(41) FIG. 8 illustrates an integrated valve arrangement 225 based on the general principle of FIGS. 6A and 6B. The integrated valve arrangement comprises both the low pressure and high pressure valves, and a cylinder 226 which slidably receives a piston (not shown) to define a working chamber 227 of cyclically varying volume. Corresponding features have corresponding labelling.

(42) It can be seen that the low pressure valve armature and valve stem 208 are formed integrally with the low pressure valve member 228 and that the low pressure valve moves axially towards the solenoid to close the low pressure valve by bringing the low pressure valve member into sealing contact with the low pressure valve seat 230. The low pressure valve member is biased to the open position by spring 232 and the force from the solenoid reverses the sense of overall biasing.

(43) The high pressure valve member 234 is biased towards high pressure valve seat 236 by spring 237 and actuation of the solenoid reverses the sense of the overall biasing. The integrated high and low pressure valves are held in place in a chassis 238 by an interference fit with oil seals 239 dividing connections to the low and high pressure manifolds 240, 242. A tube of a non-magnetic material 244 (e.g. plastics material, non-magnetic stainless steel, or brass) is also provided around a central core 246 which is part of the magnetic circuit and a further tube of non-magnetic material 248 is provided outside the cylinder to define the magnetic flux path and guide flux through the high pressure valve armature.

(44) FIGS. 9A and 9B illustrate a detail of FIG. 8. The high pressure valve armature is located adjacent a protrusion 250 in a magnetic circuit member such that when the high pressure valve member moves axially, towards the solenoid, from the valve closed position, in which the high pressure valve member has the position illustrated in FIG. 9A to the valve open position, in which the high pressure valve member has the position illustrated in FIG. 9B, the reluctance of a magnetic circuit path 252 through the protrusion and the high pressure valve member is increased, to maximise the passage of flux through magnetic circuit path 254, reducing the total current and therefore power consumption required to hold the high pressure valve member open against a given pressure differential.

(45) Layout 7A initially allows lots of flux to enter and exit the HPV armature in a radial direction with low reluctance so that good force can be generated on the LPV. When the LPV shuts and a partial stroke pumping cycle occurs to equalise pressure, this pressure pulse helps HPV armature move upwards (alternatively the radial flux path can be made thin enough to start saturating after which some flux is forced to enter or leave axially generating an axial up force). After it has started to move, the flux path radially across the HPV armature, gets cut off (due to the ‘protrusion’ 250, the radial flux path reduces in area as armature moves upwards) and flux is forced to flow axially and generates an axial upforce. Once it is in the latching position the flux flow enters and or exits the armature in an axial direction generating a strong latching force and current can then be dropped to give efficient latching.

(46) FIG. 10 shows the variation in low pressure valve position 300A, high pressure valve position 302A, the value of a shared control signal (e.g. the current through a solenoid) 304A and working chamber pressure 306A (which is illustrated relative to the low pressure manifold pressure 308) during a pumping cycle, as well as the variation in low pressure valve position 300B, high pressure valve position 302B the value of a shared control signal (e.g. the current through a solenoid) 304B and working chamber pressure 306B during a motoring cycle. The timing of events is shown relative to cycles of working chamber volume 310 between the point of maximum volume, bottom dead centre (BDC) and point of minimum volume, top dead centre (TDC) and is applicable to the valves illustrated in FIGS. 6A, 6B, 6C, 7 and 8.

(47) During a pumping cycle, shortly before bottom dead centre a current (functioning as the shared control signal) is passed through the solenoid (functioning as the shared actuator). As a result, a closing force is applied to the low pressure valve member and an opening force is applied to the high pressure valve member. In each case, the force from the armature exceeds the biasing force from the respective spring, changing the sense of the net biasing on the respective valve members. The low pressure valve begins to open straight away, leading to an active pumping cycle (if in the alternative no signal is sent, the low pressure valve remains open and an idle cycle takes place). Pressure in the working chamber rises as the working chamber contracts whilst sealed and the high pressure valve opens once the pressure differential between the working chamber and the high pressure manifold is sufficiently low that the net force urging the high pressure valve open exceeds the forces urging the high pressure valve closed arising from the pressure differential across the high pressure valve member. Once the high pressure valve has opened, the force from the solenoid is generally not further required and the current can be switched off.

(48) The high pressure valve closes passively when the piston reaches top dead centre and the working chamber begins to expand again. The low pressure valve then opens once the pressure within the working chamber is sufficiently close to the low pressure manifold that the spring biasing the low pressure valve can overcome the force due to the pressure differential across the low pressure valve member.

(49) During a motoring cycle, a current is applied to the solenoid shortly before top dead centre. This causes the low pressure valve to immediately close, however, the high pressure valve cannot immediately open due to the pressure differential between the working chamber and the high pressure manifold. However, once the working chamber is sealed, the pressure rises rapidly until the high pressure valve opens. Once the high pressure valve has opened, the average solenoid current which is required to maintain the low pressure valve in the closed position and high pressure valve in the open position is reduced, and so the average current through the solenoid is reduced, by using pulse wave modulation, and reducing the mark to space ratio of the current pulses as far as possible. This reduces overall energy consumption. Thus, there is a step change decrease 312 in the mean current through the solenoid, once the low pressure valve is closed and the high pressure valve has opened.

(50) As well as an arrangement in which magnetic flux are directed through the low pressure and high pressure valve armature is in the series, it is also possible for a single solenoid to apply forces to both armatures by directing magnetic flux through them in parallel. This is illustrated in FIGS. 11A and 11B, where magnetic circuit member 202 directs flux through both low pressure valve armature 206 and high pressure valve armature 210 at the same time. The arrangement illustrated in FIG. 11B, in which there is a significant gap 260 between the magnetic circuit members and each armature is preferable as this reduces the extent to which the movement of one of the armatures until it has seated against the core 246 decreases the reluctance of the magnetic circuit path through the armature which has moved, reducing the force applied to the armature which has not yet moved.

(51) Thus, the invention has provided a mechanism which is compact and which requires only a single control signal to enable both the low and high pressure valves to be actively controlled, to enable the hydraulic machine to select between active and inactive cycles. This reduces wiring requirements and simplifies control.

(52) In some embodiments, the timing of the single shared control signal relative to cycles of working chamber volume enables the controller to select between active pumping and motoring cycles. The timing of the single shared control signal relative to cycles of working chamber volume (the phasing) can be varied to determine the precise fraction of maximum working chamber volume which his displaced during each active cycle.

(53) Once the low and high pressure valve members have moved, the force which is required to hold them (in the closed position in the case of the low pressure valve and the open position in the case of the high pressure valve member) is reduced and, particularly during motoring cycles, power consumption can be reduced, for example, by reducing the average current through the solenoid, thereby increasing overall efficiency of the machine.

(54) Further variations and modifications may be made within the scope of the invention herein disclosed.

REFERENCE SIGNS LIST

(55) 1 Fluid-working machine 2 Working chamber 4 Cylinder 6 Piston 8 Crankshaft 9 Crank mechanism 10 Shaft position and speed sensor 12 Controller 14 Low pressure valve 16 Low pressure manifold 18 High pressure valve 20 High pressure manifold 30 Signal output wire 32 FPGA 34A, 34B FET drivers 36A, 36B FETs 30A, 30B High pressure valve solenoids 50 Shared electronically controlled valve actuator 52 Control line 100 Piston 102 Master cylinder 104 Solenoid operated actuator 105 Hydraulic connections 108, 110 Slave cylinders 112, 114 Pistons 116, 118 Valve Stems 120 Low pressure valve member 122 High pressure valve member 124 Low pressure valve seat 126 High pressure valve seat 200 Solenoid coil 202 Major portion of magnetic circuit (first magnetic circuit portion) 204 Minor portion of magnetic circuit (second magnetic circuit portion) 206 Low pressure valve armature 208 Low pressure valve stem 210 High pressure valve armature 212 High pressure valve stem 214 Non-magnetic support 216, 217 Tapered bridging pieces 218 Further bridging piece 220 First surface 222 Opposed surface 224 End stop 225 Integrated valve arrangement 226 Cylinder 227 Working chamber 228 Low pressure valve member 230 Low pressure valve seat 232 Spring 234 High pressure valve member 236 High pressure valve seat 237 Spring 238 Chassis 239 Oil seals 240 Low pressure manifold 242 High pressure manifold 244 Tube of non-magnetic material 246 Central core 248 Tube of non-magnetic material 250 Protrusion 252 Magnetic circuit path 254 Magnetic circuit path 260 Gap 300A Low pressure valve position during pumping cycle 300B Low pressure valve position during motoring cycle 302A High pressure valve position during pumping cycle 302B High pressure valve position during motoring cycle 304A Shared control signal during pumping cycle 304B Shared control signal during motoring cycle 306A Working chamber pressure during pumping cycle 306B Working chamber pressure during motoring cycle 308 Low pressure manifold pressure 310 Working chamber volume