CONTROLLER AND METHOD FOR HYDRAULIC APPARATUS

Abstract

The present invention provides a controller for a hydraulic apparatus. The controller is configured to determine (410) that a mode change criteria has been met for the hydraulic apparatus. In response to the determination, the controller is configured to control (420) a valve arrangement to change a first actuator chamber of a hydraulic actuator between being fluidly connected to a hydraulic machine and fluidly isolated from a second chamber of the hydraulic actuator, and being fluidly connected to both the second actuator chamber and the hydraulic machine. Further in response to the determination, the controller is configured to control (430) the hydraulic machine to change a flow rate of hydraulic fluid flowing through the hydraulic machine to regulate a movement of the hydraulic actuator during the control of the valve arrangement.

Claims

1. A controller for a hydraulic apparatus, the hydraulic apparatus comprising: a prime mover; a hydraulic circuit through which hydraulic fluid can flow; a hydraulic machine in the hydraulic circuit and having a rotatable shaft in driven engagement with the prime mover, the hydraulic machine configured such that, in operation, the hydraulic machine exchanges energy with the hydraulic circuit and the prime mover by flow of hydraulic fluid between the hydraulic machine and the hydraulic circuit and via movement of the rotatable shaft; at least one hydraulic actuator having at least a first actuator chamber and a second actuator chamber, each actuator chamber in the hydraulic circuit, the at least one hydraulic actuator to be used in a hydraulic work function of the hydraulic apparatus, wherein the first actuator chamber is partially defined by a first actuator working surface and the second actuator chamber is partially defined by a second actuator working surface, the second actuator working surface arranged to act at least partially in opposition to the first actuator working surface; and a valve arrangement in the hydraulic circuit for selectively routing the hydraulic fluid between the first actuator chamber and one or more of: the hydraulic machine; and the second actuator chamber, and for selectively routing the hydraulic fluid between the second actuator chamber and one or more of: the first actuator chamber; and a low pressure fluid reservoir, the controller configured to: determine that a mode change criteria has been met for the hydraulic apparatus; and in response to said determination: control the valve arrangement to change the first actuator chamber between being fluidly connected to the hydraulic machine and fluidly isolated from the second actuator chamber, and being fluidly connected to both the second actuator chamber and the hydraulic machine; and control the hydraulic machine to change a flow rate of hydraulic fluid flowing through the hydraulic machine and a portion of the hydraulic circuit in fluid communication with the first actuator chamber, to thereby regulate a movement of the at least one hydraulic actuator during the control of the valve arrangement.

2. The controller of claim 1, wherein the valve arrangement and the hydraulic machine are controlled during a lowering movement of the hydraulic work function in which the at least one hydraulic actuator is used, or wherein the valve arrangement and the hydraulic machine are controlled during a raising movement of the hydraulic work function in which the at least one hydraulic actuator is used.

3. The controller of claim 1, wherein a surface area of the first actuator working surface is greater than a surface area of the second actuator working surface.

4. The controller of claim 1, wherein the determination that the mode change criteria has been met for the hydraulic apparatus is in response to a speed demand for the hydraulic work function crossing a predetermined threshold.

5. The controller of claim 1, wherein, in response to the determination, the valve arrangement is controlled to change the first actuator chamber from being fluidly connected to the hydraulic machine and fluidly isolated from the second actuator chamber, to being fluidly connected to both the second actuator chamber and the hydraulic machine, and wherein the hydraulic machine is controlled to reduce a flow rate of hydraulic fluid flowing through the hydraulic machine and the portion of the hydraulic circuit in fluid communication with the first actuator chamber.

6. The controller of claim 1, wherein, in response to the determination, the valve arrangement is controlled to change the first actuator chamber from being fluidly connected to both the second actuator chamber and the hydraulic machine, to being fluidly connected to the hydraulic machine and fluidly isolated from the second actuator chamber and wherein the hydraulic machine is controlled to increase a flow rate of hydraulic fluid flowing through the hydraulic machine and the portion of the hydraulic circuit in fluid communication with the first actuator chamber.

7. The controller of claim 1, wherein the hydraulic machine comprises a plurality of chamber groups, each comprising at least one working chamber in the hydraulic circuit, wherein the hydraulic apparatus comprises at least one further hydraulic fluid consumer in the hydraulic circuit and selectively fluidly connected to the hydraulic machine, wherein the at least one further hydraulic fluid consumer is to be used in a further hydraulic work function, wherein the determination that the mode change criteria has been met for the hydraulic apparatus is in response to an increase in demand for the further hydraulic work function, and wherein, in response to the determination, the hydraulic apparatus is controlled to isolate at least one chamber group of the hydraulic machine from the first actuator chamber of the at least one hydraulic actuator, the at least one chamber group among at least two of the plurality of chamber groups previously together in fluid communication with the first actuator chamber of the at least one hydraulic actuator.

8. The controller of claim 1, wherein the valve arrangement comprises an actuator chamber connection valve, provided in the hydraulic circuit between the first actuator chamber and the second actuator chamber, and being a non-proportional valve.

9. The controller of claim 1, wherein the hydraulic machine is an electronically commutated hydraulic machine.

10. The controller of claim 1, wherein there is a time offset between the change of the valve arrangement and the change in the flow rate of the hydraulic fluid flowing through the hydraulic machine and the portion of the hydraulic circuit in fluid communication with the first actuator chamber, optionally wherein the time offset is less than 0.5 seconds.

11. The controller of claim 1, wherein, to control the hydraulic machine to change the flow rate in response to the determination, the hydraulic machine is controlled to implement an intermediate flow rate of the hydraulic fluid flowing through the hydraulic machine and to subsequently implement a further flow rate of the hydraulic fluid flowing through the hydraulic machine.

12. The controller of claim 11, wherein the intermediate flow rate is in an opposite sense to the further flow rate, such that the hydraulic machine pumps hydraulic fluid towards the second actuator chamber to cause pressurisation of the second actuator chamber.

13. The controller of claim 1, wherein the change in the flow rate of the hydraulic fluid flowing through the hydraulic machine is implemented depending on a predetermined rate limit of the change of the displacement value.

14. A hydraulic apparatus comprising: a prime mover; a hydraulic circuit through which hydraulic fluid can flow; a hydraulic machine in the hydraulic circuit and having a rotatable shaft in driven engagement with the prime mover, the hydraulic machine configured such that, in operation, the hydraulic machine exchanges energy with the hydraulic circuit and the prime mover by movement of the hydraulic fluid between the hydraulic machine and the hydraulic circuit and via movement of the rotatable shaft; at least one hydraulic actuator having at least a first actuator chamber and a second actuator chamber, each actuator chamber in the hydraulic circuit, the at least one hydraulic actuator to be used in a hydraulic work function of the hydraulic apparatus, wherein the first actuator chamber is partially defined by a first actuator working surface and the second actuator chamber is partially defined by a second actuator working surface, the second actuator working surface arranged to act at least partially in opposition to the first actuator working surface; a valve arrangement in the hydraulic circuit for selectively routing the hydraulic fluid between the first actuator chamber and one or more of: the hydraulic machine; and the second actuator chamber, and for selectively routing the hydraulic fluid between the second actuator chamber and one or more of: the first actuator chamber; and a low pressure fluid reservoir; and a controller according to claim 1.

15. A method of controlling a hydraulic apparatus comprising: determining that a mode change criteria has been met for the hydraulic apparatus, wherein the hydraulic apparatus comprises: a prime mover; a hydraulic circuit through which hydraulic fluid can flow; a hydraulic machine in the hydraulic circuit and having a rotatable shaft in driven engagement with the prime mover, the hydraulic machine configured such that, in operation, the hydraulic machine exchanges energy with the hydraulic circuit and the prime mover by flow of hydraulic fluid between the hydraulic machine and the hydraulic circuit and via movement of the rotatable shaft; at least one hydraulic actuator having at least a first actuator chamber and a second actuator chamber, each actuator chamber in the hydraulic circuit, the at least one hydraulic actuator to be used in a hydraulic work function of the hydraulic apparatus, wherein the first actuator chamber is partially defined by a first actuator working surface and the second actuator chamber is partially defined by a second actuator working surface, the second actuator working surface arranged to act at least partially in opposition to the first actuator working surface; and a valve arrangement in the hydraulic circuit for selectively routing the hydraulic fluid between the first actuator chamber and one or more of: the hydraulic machine; and the second actuator chamber, and for selectively routing the hydraulic fluid between the second actuator chamber and one or more of: the first actuator chamber; and a low pressure fluid reservoir; and in response to said determination, controlling the valve arrangement to change the first actuator chamber between being fluidly connected to the hydraulic machine and fluidly isolated from the second actuator chamber, and being fluidly connected to both the second actuator chamber and the hydraulic machine; and further in response to said determination, controlling the hydraulic machine to change a flow rate of hydraulic fluid flowing through the hydraulic machine and a portion of the hydraulic circuit in fluid communication with the first actuator chamber, to thereby regulate a movement of the at least one hydraulic actuator during the control of the valve arrangement.

Description

DESCRIPTION OF THE DRAWINGS

[0062] An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

[0063] FIG. 1 is a schematic illustration of an example of hydraulic apparatus as described herein;

[0064] FIG. 2 is a schematic illustration of a portion of hydraulic apparatus as described herein;

[0065] FIG. 3 is a schematic illustration of systems of a vehicle according to an example of the present disclosure;

[0066] FIG. 4 is a flowchart illustrating a method of controlling a hydraulic machine as described herein; and

[0067] FIG. 5 is a schematic diagram of an example of a hydraulic machine.

DETAILED DESCRIPTION OF AN EXAMPLE EMBODIMENT

[0068] FIG. 1 is a schematic illustration of an example of hydraulic apparatus as described herein. The hydraulic apparatus 100 comprises a prime mover 102 and a hydraulic machine 104. The hydraulic machine 104 has a rotatable shaft 106 in driven engagement with the prime mover 102. In this example, the hydraulic machine 104 defines a plurality of groups of working chambers, specifically five groups of working chambers, sometimes referred to as chamber groups 108a, 108b, 108c, 108d, 108e. The detailed operation of the hydraulic machine 104, and in particular the groups of working chambers 108a, 108b, 108c, 108d, 108e will be explained further with reference to FIG. 5 hereinafter. Although not shown in FIG. 1, it will be understood that each group of working chambers 108a, 108b, 108c, 108d, 108e typically comprises a plurality of working chambers in a hydraulic circuit, each working chamber being defined partially by a movable working surface mechanically coupled to the rotatable shaft 106 such that, in operation, the hydraulic machine 104 exchanges energy with the hydraulic circuit and the prime mover 102 by movement of the working surfaces and the rotatable shaft 106.

[0069] It will be understood that the hydraulic circuit is defined by any portions of the hydraulic apparatus 100 through which hydraulic fluid can flow and which are in or can be brought into fluid communication with any of the working chambers of the hydraulic machine 104.

[0070] The hydraulic apparatus 100 comprises a first hydraulic work function, in this example a boom lifting work function 110. The boom lifting work function 110 uses a first hydraulic actuator 112a and a second hydraulic actuator 112b, each in the form of a cylinder ram, mounted between two mutually movable components of a boom of the vehicle to be moved by operation of the boom lifting work function. The first hydraulic actuator 112a comprises a first actuator chamber 114a and a second actuator chamber 116a. Similarly, the second hydraulic actuator 112b also comprises a first actuator chamber 114b and a second actuator chamber 116b. Each of the actuator chambers 114a, 114b, 116a, 116b are in the hydraulic circuit. The first hydraulic actuator 112a further comprises a piston 118a having a rod 120a extending therefrom through the second actuator chamber 116a of the first hydraulic actuator 112a. Similarly, the second hydraulic actuator 112b also comprises a piston 118b having a rod 120b extending therefrom through the second actuator chamber 116b of the second hydraulic actuator 112b. The rod 120a of the first hydraulic actuator 112a is mechanically connected to the rod 120b of the second hydraulic actuator 112b and to the boom 122, such that movement of one of the hydraulic actuators 112a, 112b and the boom 122 causes movement of the other of the hydraulic actuators 112a, 112b and the boom 122.

[0071] An actuator valve arrangement 124 is provided in the hydraulic circuit between the first and second hydraulic actuators 112a, 112b and the hydraulic machine 104, and further in fluid communication with a low pressure fluid reservoir 126. Although not shown in FIG. 1, the actuator valve arrangement 124 typically comprises a plurality of valves, each for restricting flow of fluid in at least one direction therethrough. At least one of the plurality of valves is selectively controllable to change between at least two operating states. The actuator valve arrangement 124 is in fluid communication with both of the first actuator chambers 114a, 114b of the first and second hydraulic actuators 112a, 112b, and separately in fluid communication with both of the second actuator chambers 116a, 116b of the first and second hydraulic actuators 112a, 112b. The actuator valve arrangement 124 can be controlled to selectively route hydraulic fluid via part of the hydraulic circuit between the first actuator chambers 114a, 114b (located at the bottom of each of the cylinder rams) and one or more of: the hydraulic machine 104; and the second actuator chambers 116a, 116b (located at the top of each of the cylinder rams), and controlled to selectively route hydraulic fluid via the hydraulic circuit between the second actuator chambers 116a, 116b and one or more of: the first actuator chambers 114a, 114b; and the low pressure fluid reservoir 126. In other words, the actuator valve arrangement 124 is configured to, in a first configuration, bring the first actuator chambers 114a, 114b into fluid communication with the hydraulic machine 104, and isolate the first actuator chambers 114a, 114b from the second actuator chambers 116a, 116b, instead bringing the second actuator chambers 116a, 116b into fluid communication with the low pressure fluid reservoir 126. The actuator valve arrangement 124 is further configured to, in a second configuration, bring the first actuator chambers 114a, 114b (located at the bottom of the cylinder ram) into fluid communication with the hydraulic machine 104 and with the second actuator chambers 116a, 116b, and isolate the low pressure fluid reservoir 126 from the second actuator chambers 116a, 116b. An example configuration of the actuator valve arrangement 124 and its operation is shown and described in more detail with reference to FIG. 2 hereinafter.

[0072] The hydraulic apparatus 100 further comprises a hydraulic machine valve arrangement 128 in the form of a ganging arrangement 128. The ganging arrangement 128 comprises a plurality of valves for selectively bringing the working chambers of the hydraulic machine 104 into fluid communication with other components of the hydraulic apparatus 100 via the hydraulic circuit.

[0073] The other components comprise an energy storage component 130 in the form of a hydraulic accumulator 130 and one or more further hydraulic services, in this example six further hydraulic services 132, 134, 136, 138, 140, 142. Three of the six further hydraulic services 132, 134, 136 are controllably fluidly connected to the ganging arrangement 128 via a first conduit 144. A further three of the six further hydraulic services 138, 140, 142 are controllably fluidly connected to the ganging arrangement 128 via a second conduit 146, separate to the first conduit 144. It will be understood that a further valve (not shown in FIG. 1) may be fluidly connected between the ganging arrangement 128 and each of the further hydraulic services 132, 134, 136, 138, 140, 142. Each of the further hydraulic services may also be selectively connected to other hydraulic circuit components, such as the low-pressure fluid reservoir 126, though these connections are omitted for simplicity.

[0074] FIG. 1 also includes double-headed broken-line arrows, showing the routing of hydraulic fluid based on the illustrated settings of the valves shown in the ganging arrangement 128.

[0075] The hydraulic apparatus 100 further comprises a controller (not shown in FIG. 1) configured to control at least the hydraulic machine 104, the actuator valve arrangement 124, and the ganging arrangement 128 of the hydraulic apparatus 100. The operation of the controller will be explained further with reference to FIG. 4 hereinafter. It will be understood that in some examples, the hydraulic apparatus can be connected to a separate controller for controlling one or more components of the hydraulic apparatus, but can still nevertheless be considered to be hydraulic apparatus.

[0076] FIG. 2 is a schematic illustration of a portion of hydraulic apparatus as described herein. Specifically, the portion 200 of the hydraulic apparatus comprises a first hydraulic actuator 212a and a second hydraulic actuator 212b each in the form of a cylinder ram, together being used in a hydraulic work function 210. The first hydraulic actuator 212a comprises a first actuator chamber 214a and a second actuator chamber 216a. Similarly, the second hydraulic actuator 212b also comprises a first actuator chamber 214b and a second actuator chamber 216b. Each of the actuator chambers 214a, 214b, 216a, 216b are in a hydraulic circuit 250. The first hydraulic actuator 212a further comprises a piston 218a having a rod 220a extending therefrom through the second actuator chamber 216a of the first hydraulic actuator 212a. Similarly, the second hydraulic actuator 212b also comprises a piston 218b having a rod 220b extending therefrom through the second actuator chamber 216b of the second hydraulic actuator 212b. Although not shown in FIG. 2, typically, the rod 220a of the first hydraulic actuator 212a is mechanically connected to the rod 220b of the second hydraulic actuator 212b, such that the pistons move together.

[0077] An actuator valve arrangement 224, in the form of an H-bridge 224, is provided in the hydraulic circuit 250 between the first and second hydraulic actuators 212a, 212b and a hydraulic machine 204, and further in fluid communication with a low pressure fluid reservoir 226.

[0078] The actuator valve arrangement 224 comprises a plurality of valves, controllable to cause the hydraulic apparatus to function as described herein. The hydraulic circuit 250 is formed of a plurality of conduits. The plurality of conduits comprises a first chamber conduit 252, connecting both of the first actuator chambers 214a, 214b with the actuator valve arrangement 224. The plurality of conduits further comprises a second chamber conduit 254, connecting both of the second actuator chamber 216a, 216b with the actuator valve arrangement 224. The plurality of conduits further comprises a hydraulic machine conduit 256, connecting the hydraulic machine 204 to the actuator valve arrangement 224, and a low-pressure reservoir conduit 258, connecting the low-pressure fluid reservoir 226 to the actuator valve arrangement 224. The actuator valve arrangement 224 comprises a first valve 260, a second valve 262, a third valve 264 and a fourth valve 266.

[0079] The first valve 260 controls flow between the second chamber conduit 254 and the low-pressure reservoir conduit 258. In the first position, the first valve 260 is configured to permit flow of hydraulic fluid only from the low-pressure reservoir conduit 258 towards the second chamber conduit 254, whilst substantially preventing flow of hydraulic fluid from the second chamber conduit 254 towards the low-pressure reservoir conduit 258. In the second position, the first valve 260 is configured to permit flow of hydraulic fluid from the second chamber conduit 254 towards the low-pressure reservoir conduit 258. The first valve 260 can be controlled proportionally to implement a plurality of different fluid flow rates in the second position.

[0080] The second valve 262 controls flow between the second chamber conduit 254 and the hydraulic machine conduit 256. In the first position, the second valve 262 is configured to permit flow of hydraulic fluid only from the second chamber conduit 254 towards the hydraulic machine conduit 256, whilst substantially preventing flow of hydraulic fluid from the hydraulic machine conduit 256 towards the second chamber conduit 254. In the second position, the second valve 262 is configured to permit flow of hydraulic fluid in either direction between the hydraulic machine conduit 256 and the second chamber conduit 254. The second valve 262 is solenoid-operated.

[0081] The third valve 264 controls flow between the first chamber conduit 252 and the hydraulic machine conduit 256. In the first position, the third valve 264 is configured to permit flow of hydraulic fluid only from the first chamber conduit 252 towards the hydraulic machine conduit 256, whilst substantially preventing flow of hydraulic fluid from the hydraulic machine conduit 256 towards the first chamber conduit 252. In the second position, the third valve 264 is configured to permit flow of hydraulic fluid in either direction between the hydraulic machine conduit 256 and the first chamber conduit 252. The third valve 264 is solenoid-operated.

[0082] The fourth valve 266 controls flow between the first chamber conduit 252 and the low-pressure reservoir conduit 258. In the first position, the fourth valve 266 is configured to permit flow of hydraulic fluid only from the low-pressure reservoir conduit 258 towards the first chamber conduit 252, whilst substantially preventing flow of hydraulic fluid from the first chamber conduit 252 towards the low-pressure reservoir conduit 258. In the second position, the fourth valve 266 is configured to permit flow of hydraulic fluid in either direction between the low-pressure reservoir conduit 258 and the first chamber conduit 252. The fourth valve 266 can be controlled proportionally to implement a plurality of different fluid flow rates in the second position.

[0083] Each of the first, second, third, and fourth valves (260, 262, 264, 266) is an electronically controllable valve movable between a first position (as shown in FIG. 2) and a second position.

[0084] The actuator valve arrangement 224 further includes a safety valve 268 allowing the hydraulic machine conduit 256 to be connected directly to the low-pressure reservoir conduit 258 in the event of a dangerous pressure build-up in the hydraulic machine conduit 256.

[0085] The apparatus is further provided with a first actuator safety valve 270 and a second actuator safety valve 272, which each operate to prevent uncontrolled lowering of the first actuator 212a and the second actuator 212b respectively should there be a failure of the electronic control system of the apparatus.

[0086] FIG. 3 is a schematic illustration of systems of a vehicle according to an example of the present disclosure. The vehicle 300 comprises hydraulic apparatus 310 as described herein, including a hydraulic machine 320, and a controller 330. The controller 330 is configured to exchange signals 325 with the hydraulic machine 320 to control the hydraulic apparatus 310 in accordance with input signals received by the controller 330, for example from user inputs by an operator of the vehicle 300. The controller 330 in this example is realised by one or more processors 340 and a computer-readable memory 350. The memory 350 stores instructions which, when executed by the one or more processors 340, cause the hydraulic apparatus 310 to operate as described herein.

[0087] Although the controller 330 is shown as being part of the vehicle 300, it will be understood that one or more components of the controller 330, or even the whole controller 330 can be provided separate from the vehicle 300, for example remotely from the vehicle 300, to exchange signals with the vehicle 300 by wireless communication.

[0088] FIG. 4 is a flowchart illustrating a method of controlling a hydraulic machine as described herein. The method 400 is a method of controlling hydraulic apparatus, including a hydraulic machine, during transition of at least one hydraulic actuator, between a normal mode of operation and a differential mode of operation. Specifically, the method 400 comprises determining 410 that a mode change criteria has been met for the hydraulic apparatus. In other words, the method comprises determining, based on one or more parameters, that the operating mode of the at least one hydraulic actuator should be transitioned from the current operating mode, to a different operating mode (i.e. from normal mode to differential mode or vice versa). As described hereinbefore, the determination that the operating mode of the at least one hydraulic actuator should be changed may depend on one or more of 1) the requested speed of the hydraulic actuator, 2) operating demands in place for further hydraulic work functions connected to the hydraulic machine, and 3) a change in the shaft speed of the prime mover.

[0089] The method 400 further comprises, in response to the determination, controlling 420 the valve arrangement to change the operating mode of the at least one hydraulic actuator between modes. Specifically, to operate the at least one hydraulic actuator in normal mode, the first chamber of the hydraulic actuator is fluidly isolated from the second chamber of the hydraulic actuator, and fluidly connected with the hydraulic machine. Typically the second chamber is fluidly connected with a low-pressure fluid reservoir. To operate the at least one hydraulic actuator in differential mode, the first chamber of the hydraulic actuator is fluidly connected to both the second chamber of the hydraulic actuator and the hydraulic machine, at the same time.

[0090] Also in response to the determination, the method 400 further comprises controlling 430 the hydraulic machine to change a flow-rate of hydraulic fluid (e.g. a displacement fraction of a hydraulic machine) flowing through the hydraulic machine and the portion of the hydraulic circuit in fluid communication with the at least one hydraulic actuator. As described hereinbefore, where the operating mode of the actuator is changed from normal to differential or from differential to normal, during movement of the hydraulic actuator, the proportion of hydraulic fluid being exchanged between the first chamber of the hydraulic actuator and the hydraulic machine will change significantly in a very short space of time. Therefore, the flow-rate of the hydraulic fluid through the hydraulic machine also needs to change to ensure smooth movement of the hydraulic actuator during the transition. Specifically, the flow-rate needs to be reduced during a transition from normal operating mode of the hydraulic actuator to differential operating mode of the hydraulic actuator. Conversely, the flow-rate needs to be increased during a transition from differential operating mode of the hydraulic actuator to normal operating mode of the hydraulic actuator.

[0091] FIG. 5 is a schematic diagram of part of the hydraulic apparatus shown in FIGS. 1 and 2, and shows a single group of working chambers currently connected to one or more hydraulic components (e.g. an actuator) through a high pressure manifold 554. FIG. 5 provides detail on the first group 500, said group comprises a plurality of working chambers (8 are shown) having cylinders 524 which have working volumes 526 defined by the interior surfaces of the cylinders and pistons 528 (providing working surfaces 528) which are driven from a rotatable shaft 530 by an eccentric cam 532 and which reciprocate within the cylinders to cyclically vary the working volume of the cylinders. The rotatable shaft is firmly connected to and rotates with a drive shaft. A shaft position and speed sensor 534 sends electrical signals through a signal line 536 to a controller 550, which thus enables the controller to determine the instantaneous angular position and speed of rotation of the shaft, and to determine the instantaneous phase of the cycles of each cylinder.

[0092] The working chambers are each associated with Low Pressure Valves (LPVs) in the form of electronically actuated face-sealing poppet valves 552, which have an associated working chamber and are operable to selectively seal off a channel extending from the working chamber to a low-pressure hydraulic fluid manifold 554, which may connect one or several working chambers, or indeed all as is shown here, to the low-pressure hydraulic fluid manifold hydraulic circuit. The LPVs are normally open solenoid actuated valves which open passively when the pressure within the working chamber is less than or equal to the pressure within the low-pressure hydraulic fluid manifold, i.e. during an intake stroke, to bring the working chamber into fluid communication with the low-pressure hydraulic fluid manifold but are selectively closable under the active control of the controller via LPV control lines 556 to bring the working chamber out of fluid communication with the low-pressure hydraulic fluid manifold. The valves may alternatively be normally closed valves. As well as force arising from the pressure difference across the valve, flow forces from the passage of fluid across the valve, also influence the net force on the moving valve member.

[0093] The working chambers are each further associated with a respective High-Pressure Valve (HPV) 564 each in the form of a pressure actuated delivery valve. The HPVs open outwards from their respective working chambers and are each operable to seal off a respective channel extending from the working chamber through a valve block to a high-pressure hydraulic fluid manifold 558, which may connect one or several working chambers, or indeed all as is shown in FIG. 5. The HPVs function as normally-closed pressure-opening check valves which open passively when the pressure within the working chamber exceeds the pressure within the high-pressure hydraulic fluid manifold. The HPVs also function as normally-closed solenoid actuated check valves which the controller may selectively hold open via HPV control lines 562 once that HPV is opened by pressure within the associated working chamber. Typically, the HPV is not openable by the controller against pressure in the high-pressure hydraulic fluid manifold. The HPV may additionally be openable under the control of the controller when there is pressure in the high-pressure hydraulic fluid manifold but not in the working chamber, or may be partially openable.

[0094] In a pumping mode, the controller selects the net rate of displacement of hydraulic fluid from the working chamber to the high-pressure hydraulic fluid manifold by the hydraulic motor by actively closing one or more of the LPVs typically near the point of maximum volume in the associated working chamber's cycle, closing the path to the low-pressure hydraulic fluid manifold and thereby directing hydraulic fluid out through the associated HPV on the subsequent contraction stroke (but does not actively hold open the HPV). The controller selects the number and sequence of LPV closures and HPV openings to produce a flow or create a shaft torque or power to satisfy a selected net rate of displacement.

[0095] In a motoring mode of operation, the controller selects the net rate of displacement of hydraulic fluid, displaced via the high-pressure hydraulic fluid manifold, actively closing one or more of the LPVs shortly before the point of minimum volume in the associated working chamber's cycle, closing the path to the low-pressure hydraulic fluid manifold which causes the hydraulic fluid in the working chamber to be compressed by the remainder of the contraction stroke. The associated HPV opens when the pressure across it equalises and a small amount of hydraulic fluid is directed out through the associated HPV, which is held open by the controller. The controller then actively holds open the associated HPV, typically until near the maximum volume in the associated working chamber's cycle, admitting hydraulic fluid from the high-pressure hydraulic fluid manifold to the working chamber and applying a torque to the rotatable shaft.

[0096] As well as determining whether or not to close or hold open the LPVs on a cycle by cycle basis, the controller is operable to vary the precise phasing of the closure of the HPVs with respect to the varying working chamber volume and thereby to select the net rate of displacement of hydraulic fluid from the high-pressure to the low-pressure hydraulic fluid manifold or vice versa.

[0097] Arrows on the low pressure fluid connection 506, and the high-pressure fluid connection 521 indicate hydraulic fluid flow in the motoring mode; in the pumping mode the flow is reversed. A pressure relief valve 566 may protect the first group from damage.

[0098] In normal operation, the active and inactive cycles of working chamber volume are interspersed to meet the demand indicated by the hydraulic machine control signal.

[0099] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to and do not exclude other components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0100] Features, integers, characteristics or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.