HYDRAULIC APPARATUS AND METHOD FOR A VEHICLE

Abstract

A vehicle includes: a prime mover; a hydraulic fluid manifold; a hydraulic machine; a hydraulic accumulator; one or more hydraulic actuators; a valve arrangement; and a controller. The controller is configured to receive an actuator demand signal indicative of a demand to move the one or more hydraulic actuators; and to control the hydraulic machine and the valve arrangement to cause movement of the one or more actuators in accordance with the actuator demand signal by bringing the hydraulic accumulator into fluid communication with a first actuator chamber of the one or more hydraulic actuators, and to synchronise therewith changing a pressure in a second actuator chamber of the one or more hydraulic actuators. The second actuator chamber is in fluid communication with the hydraulic machine.

Claims

1. A vehicle having a hydraulic work function, the vehicle comprising: a prime mover; a hydraulic fluid manifold; a hydraulic machine in fluid communication with the hydraulic fluid manifold, having a rotatable shaft in driven engagement with the prime mover, and configured such that, in operation, the hydraulic machine exchanges hydraulic fluid with the hydraulic fluid manifold by movement of the rotatable shaft, a hydraulic accumulator in fluid communication with the hydraulic fluid manifold and for exchanging hydraulic fluid with the hydraulic fluid manifold; one or more hydraulic actuator, the one or more hydraulic actuators together having at least two actuator chambers in fluid communication with the hydraulic fluid manifold, the one or more hydraulic actuators to be used in the hydraulic work function; a valve arrangement configured to selectively control fluid communication between at least one of the at least two actuator chambers and the hydraulic accumulator, via the hydraulic fluid manifold, and between at least one of the at least two actuator chambers and the hydraulic machine, via the hydraulic fluid manifold; and a controller configured to: receive an actuator demand signal indicative of a demand to move the one or more hydraulic actuators; and control the hydraulic machine and the valve arrangement to cause movement of the one or more hydraulic actuators in accordance with the actuator demand signal, wherein, to cause the movement of the one or more hydraulic actuators in accordance with the actuator demand signal, the hydraulic machine and the valve arrangement are controlled to bring the hydraulic accumulator into fluid communication with a first actuator chamber of the at least two actuator chambers, via a first portion of the hydraulic fluid manifold and the valve arrangement, and to synchronise therewith, a change in pressure in a second actuator chamber of the at least two actuator chambers, the second actuator chamber in fluid communication with the hydraulic machine via a second portion of the hydraulic fluid manifold and the valve arrangement, and wherein the hydraulic machine comprises a plurality of pump groups, each comprising a plurality of working chambers in fluid communication with the hydraulic fluid manifold, each working chamber defined partially by a movable working surface mechanically coupled to the rotatable shaft, and wherein the controller is configured to control at least one of the pump groups differently to at least one other of the pump groups.

2. A controller for a vehicle having a hydraulic work function, the controller configured to: receive an actuator demand signal indicative of a demand to move one or more hydraulic actuators to be used in the hydraulic work function; and control a hydraulic machine of the vehicle and a valve arrangement to cause movement of the one or more hydraulic actuators in accordance with the actuator demand signal, wherein, to cause the movement of the one or more hydraulic actuators in accordance with the actuator demand signal, the hydraulic machine and the valve arrangement are controlled to bring a hydraulic accumulator of the vehicle into fluid communication with a first actuator chamber of the at least two actuator chambers, via a first portion of a hydraulic fluid manifold of the vehicle and the valve arrangement, and to synchronise therewith, a change in pressure of a second actuator chamber of the at least two actuator chambers, the second actuator chamber in fluid communication with the hydraulic machine via a second portion of the hydraulic fluid manifold and the valve arrangement, and wherein the hydraulic machine comprises a plurality of pump groups, each comprising a plurality of working chambers in fluid communication with the hydraulic fluid manifold, each working chamber defined partially by a movable working surface mechanically coupled to the rotatable shaft, and wherein the controller is configured to control at least one of the pump groups differently to at least one other of the pump groups.

3. The vehicle of claim 1, wherein the valve arrangement comprises: one or more actuator chamber valves each associated with, of the at least two actuator chambers, only a respective one actuator chamber; and a manifold valve group, in a fluid communication pathway within the hydraulic manifold, between the one or more actuator chamber valves and the hydraulic machine.

4. The vehicle of claim 1, wherein the controller is configured to control the valve arrangement to bring at least one of the pump groups into fluid communication with the first portion of the hydraulic fluid manifold in a first configuration, and with the second portion of the hydraulic fluid manifold in a second configuration.

5. The vehicle of claim 1, wherein the vehicle is for performing a plurality of hydraulic work functions, optionally wherein at least one of the hydraulic work functions is performed using a further hydraulic actuator having at least one actuator chamber configured to be always in fluid communication with the hydraulic machine.

6. The vehicle of claim 1, wherein the hydraulic machine is configured to be always in fluid communication with the hydraulic actuator or a given hydraulic actuator of the one or more hydraulic actuators, optionally wherein the hydraulic machine is configured to be always in fluid communication with a given actuator chamber of the given hydraulic actuator.

7. The vehicle of claim 1, wherein the actuator demand signal is indicative of a flow demand or a velocity demand in relation to the hydraulic work function.

8. The vehicle of claim 1, wherein the controller is configured to control the hydraulic machine and the valve arrangement depending on an error between a measured parameter of the one or more hydraulic actuators and a demanded value for the parameter of the one or more hydraulic actuators.

9. The vehicle of claim 1, wherein the controller is configured to determine a demanded force parameter of the one or more hydraulic actuators depending on a demand to move the one or more hydraulic actuators with a given velocity, and to control the hydraulic machine and the valve arrangement to cause movement of the one or more hydraulic actuators depending on the demanded force parameter.

10. The vehicle of claim 1, wherein the demand to move the one or more hydraulic actuators is determined from a user input.

11. The vehicle of claim 1, wherein the hydraulic work function includes at least one of a boom and a bucket.

12. The vehicle of claim 1, wherein the one or more hydraulic actuators are arranged such that an expansion in a volume of the first actuator chamber corresponds to a reduction in a volume of the second actuator chamber.

13. The vehicle of claim 1, wherein the hydraulic machine is a variable displacement hydraulic machine.

14. The vehicle of claim 1, wherein the hydraulic machine is a pump-motor, optionally an electronically commutated pump-motor.

15. A method for controlling a vehicle having a hydraulic work function, the method comprising: receiving a demand to move one or more hydraulic actuators to be used in the hydraulic work function; and controlling a hydraulic machine and a valve arrangement to bring a hydraulic accumulator of the vehicle into fluid communication with a first actuator chamber of the one or more hydraulic actuators, via a hydraulic fluid manifold of the vehicle and the valve arrangement, and synchronised therewith, changing a pressure in a second actuator chamber of the one or more hydraulic actuators, the second actuator chamber in fluid communication with the hydraulic machine via the hydraulic fluid manifold and the valve arrangement, to thereby cause movement of the one or more hydraulic actuators in accordance with the demand, wherein the hydraulic machine comprises a plurality of pump groups, each comprising a plurality of working chambers in fluid communication with the hydraulic fluid manifold, each working chamber defined partially by a movable working surface mechanically coupled to the rotatable shaft, and the method comprises controlling at least one of the pump groups differently to at least one other of the pump groups.

16. The controller of claim 2, wherein the valve arrangement comprises: one or more actuator chamber valves each associated with, of the at least two actuator chambers, only a respective one actuator chamber; and a manifold valve group, in a fluid communication pathway within the hydraulic manifold, between the one or more actuator chamber valves and the hydraulic machine.

17. The controller of claim 2, wherein the hydraulic machine is configured to be always in fluid communication with the hydraulic actuator or a given hydraulic actuator of the one or more hydraulic actuators, optionally wherein the hydraulic machine is configured to be always in fluid communication with a given actuator chamber of the given hydraulic actuator.

18. The controller of claim 2, wherein the actuator demand signal is indicative of a flow demand or a velocity demand in relation to the hydraulic work function.

19. The controller of claim 2, wherein the controller is configured to control the hydraulic machine and the valve arrangement depending on an error between a measured parameter of the one or more hydraulic actuators and a demanded value for the parameter of the one or more hydraulic actuators.

20. The controller of claim 2, wherein the controller is configured to determine a demanded force parameter of the one or more hydraulic actuators depending on a demand to move the one or more hydraulic actuators with a given velocity, and to control the hydraulic machine and the valve arrangement to cause movement of the one or more hydraulic actuators depending on the demanded force parameter.

Description

DESCRIPTION OF THE DRAWINGS

[0055] An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

[0056] FIG. 1 is a schematic illustration of an example of hydraulic apparatus as described herein;

[0057] FIG. 2 is a schematic illustration of systems of a vehicle according to an example of the present disclosure;

[0058] FIG. 3 is a flowchart illustrating a method of controlling a hydraulic machine as described herein; and

[0059] FIG. 4 is a schematic diagram of an example of a hydraulic machine.

DETAILED DESCRIPTION OF AN EXAMPLE EMBODIMENT

[0060] FIG. 1 is a schematic illustration of an example of hydraulic apparatus for use in a vehicle, as described herein. The vehicle is a loader, such as an excavator. 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 eight groups of working chambers, sometimes referred to as chamber groups 108a, 108b, 108c, 108d, 108e, 108f, 108g, 108h. The detailed operation of the hydraulic machine 104, and in particular the groups of working chambers 108a, 108b, 108c, 108d, 108e, 108f, 108g, 108h will be explained further with reference to FIG. 4 hereinafter. Although not shown in FIG. 1, it will be understood that each group of working chambers 108a, 108b, 108c, 108d, 108e, 108f, 108g, 108h 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. The hydraulic machine 104 exchanges energy with the hydraulic circuit by exchange of hydraulic fluid between the hydraulic circuit and the hydraulic machine 104, and exchanges energy between the prime mover 102 and the hydraulic machine 104 by movement of the rotatable shaft 106.

[0061] 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. The one or more components of the hydraulic apparatus 100 forming the hydraulic circuit are referred to as a hydraulic fluid manifold 109.

[0062] The hydraulic apparatus 100 comprises a first hydraulic work function 110, in this example a boom lifting work function 110. The boom lifting work function 110 uses at least one hydraulic actuator 112, the (or each) hydraulic actuator 112 in the form of a double-acting cylinder ram to raise or lower a boom of an excavator arm of the loader vehicle. The hydraulic actuator 112 comprises a first actuator chamber 114 and a second actuator chamber 116. Each of the first actuator chamber 114 and the second actuator chamber 116 are in fluid communication with at least a portion of the hydraulic fluid manifold 109. The first actuator chamber 114 and the second actuator chamber 116 are separated by a piston 118 having a rod 120 extending therefrom through the second actuator chamber 116 of the hydraulic actuator 112. The rod 120 is mechanically connected to a boom (not shown in FIG. 1), such that movement of one of the rod 120 of the hydraulic actuator 112 and the boom causes movement of the other of the rod 120 of the hydraulic actuator 112 and the boom. The effective working area of the first actuator chamber 114 is less than the effective working area of the second actuator chamber 116.

[0063] In this example, the hydraulic apparatus 100 comprises further hydraulic work functions 122, 124, specifically a second hydraulic work function 122 in the form of a stick work function 122 for moving a stick portion of the excavator arm of the loader vehicle, and a third hydraulic work function 124 in the form of a bucket work function 124 to move a bucket of the excavator arm of the loader vehicle. Each of the further hydraulic work functions 122, 124 includes one or more further hydraulic actuators, as illustrated in FIG. 1. In this example, the second hydraulic work function 122 comprises a second hydraulic actuator 123 having a rod 123a extending through both sides of the second hydraulic actuator 123. The third hydraulic work function 124 comprises a third hydraulic actuator 125, similar in configuration to the hydraulic actuator 112 of the first hydraulic work function 110, but of a smaller size in this example.

[0064] The hydraulic apparatus 100 further comprises three energy storage components in the form of three hydraulic accumulators 140, 142, 144. The hydraulic accumulators 140, 142, 144 are each separately in fluid communication with the hydraulic fluid manifold 109, and are configured to exchange hydraulic fluid therewith. A first hydraulic accumulator 140 is a low-pressure hydraulic accumulator 140, for example configured to store hydraulic fluid at a pressure of approximately 300 kilopascals. A second hydraulic accumulator 142 is a medium-pressure hydraulic accumulator 142, for example configured to store hydraulic fluid at a pressure of approximately 15 megapascals. A third hydraulic accumulator 144 is a high-pressure hydraulic accumulator 144, for example configured to store hydraulic fluid at a pressure of approximately 30 megapascals. In this example, the low-pressure hydraulic accumulator 140 is in fluid communication with a low-pressure side of the hydraulic machine 104, specifically a low-pressure side of each of the groups of working chambers 108a, 108b, 108c, 108d, 108e, 108f, 108g, 108h of the hydraulic machine 104.

[0065] The hydraulic apparatus 100 further comprises a further hydraulic work function 150, in this example for performing a rotational swing operation of an excavator arm to rotate the excavator arm about a vertical axis, typically near a cab of the vehicle. The further hydraulic work function 150 is performed using a hydraulic motor 152 for converting hydraulic fluid pressure and flow into rotational movement of a shaft (not shown in FIG. 1). A directional control valve 154 is provided in fluid communication with both sides of the hydraulic motor 152 to control a direction of rotation of the hydraulic motor 152, to thereby control a direction of swing of the excavator arm. The directional control valve 154 is also in fluid communication with the low-pressure hydraulic accumulator 140.

[0066] The hydraulic apparatus 100 further comprises a valve arrangement made up of a plurality of actuator chamber valves 126, 128, 130, 132, 134, 136 and a manifold valve group 138, in the form of a ganging arrangement 138. The valves of the valve arrangement are together configured to selectively control fluid communication between any one or more of the actuator chambers of the hydraulic actuators and one or more of the hydraulic accumulators 140, 142, 144, via the hydraulic fluid manifold 109. The valves of the valve arrangement are also together configured to selectively control fluid communication between one or more of the actuator chambers of the hydraulic actuators and the hydraulic machine 104, via the hydraulic fluid manifold 109.

[0067] The actuator chamber valves 126, 128, 130, 132, 134, 136 are each arranged at an outlet of a respective one of the hydraulic chambers of the hydraulic actuators in the hydraulic work functions 110, 122, 124. The actuator chamber valves 126, 128, 130, 132, 134, 136 are sometimes referred to as switching valves. Each actuator chamber valve 126, 128, 130, 132, 134, 136 comprises a single port at a first side, in fluid communication with a hydraulic chamber of a hydraulic actuator of a hydraulic work function, and a plurality of ports, in this example four ports, at a second side. A first port of the plurality of ports is in fluid communication with the first hydraulic accumulator 140. A second port of the plurality of ports is in fluid communication with the second hydraulic accumulator 142. A third port of the plurality of ports is in fluid communication with the third hydraulic accumulator 144. A fourth port of the plurality of ports is in fluid communication with the manifold valve group and typically with at least one of the groups of working chambers 108a, 108b, 108c, 108d, 108e, 108f, 108g, 108h of the hydraulic machine 104. Each actuator chamber valve 126, 128, 130, 132, 134, 136 can be independently controlled to bring the respective hydraulic chamber of the hydraulic actuators 112, 123, 125 into fluid communication with typically exactly one of the first hydraulic accumulator 140, the second hydraulic accumulator 142, the third hydraulic accumulator 144 and the hydraulic machine 104. The actuator chamber valves 126, 128, 130, 132, 134, 136 are provided in pairs, one pair for each of the hydraulic actuators 112, 123, 125. Specifically, a first pair of actuator chamber valves is provided by a first actuator chamber valve 126 fluidly connected to the first actuator chamber 114 of the hydraulic actuator 112 and a second actuator chamber valve 128 fluidly connected to the second actuator chamber 116 of the same hydraulic actuator 112. Similarly, a second pair of actuator chamber valves is provided by a third actuator chamber valve 130 and a fourth actuator chamber valve 132, respectively connected to first and second actuator chambers of the second hydraulic actuator 123. A third pair of actuator chamber valves is provided by a fifth actuator chamber valve 134 and a sixth actuator chamber valve 136, respectively connected to first and second actuator chambers of the third hydraulic actuator 125. In each pair of actuator chamber valves, typically only one of the actuator chamber valves can connect the actuator chambers to a given hydraulic component, via the hydraulic fluid manifold.

[0068] The ganging arrangement 138 is shown as a conceptual portion of the hydraulic apparatus 100 in FIG. 1. In practice, the ganging arrangement 138 comprises a plurality of valves to control fluid communication routing between a plurality of ports. The ganging arrangement 138 is independently fluidly connected to each of the groups of working chambers 108a, 108b, 108c, 108d, 108e, 108f, 108g, 108h of the hydraulic machine 104, each pair of actuator chamber valves 126, 128, 130, 132, 134, 136 associated with each hydraulic actuator 112, 123, 125, the medium-pressure hydraulic accumulator 142 and the high-pressure hydraulic accumulator 144, and the directional control valve 154. Thus, in this example, any one or more of the plurality of groups of working chambers 108a, 108b, 108c, 108d, 108e, 108f, 108g, 108h of the hydraulic machine 104 can be fluidly connected to one of the medium-pressure hydraulic accumulator 142, the high-pressure hydraulic accumulator 144, any one pair of actuator chamber valves 126, 128, 130, 132, 134, 136 associated with each hydraulic actuator 112, 123, 125, and the directional control valve 154. A further one or more of the plurality of groups of working chambers 108a, 108b, 108c, 108d, 108e, 108f, 108g, 108h of the hydraulic machine 104 can be fluidly connected to a different one of the medium-pressure hydraulic accumulator 142, the high-pressure hydraulic accumulator 144, any one pair of actuator chamber valves 126, 128, 130, 132, 134, 136 associated with each hydraulic actuator 112, 123, 125, and the directional control valve 154. In this way, the ganging arrangement 138 can be controlled to bring the groups of working chambers 108a, 108b, 108c, 108d, 108e, 108f, 108g, 108h of the hydraulic machine 104 into fluid communication with other hydraulic components of the hydraulic apparatus 100 via the hydraulic fluid manifold 109.

[0069] The hydraulic apparatus 100 further comprises a controller (not shown in FIG. 1) configured to control at least the hydraulic machine 104, the actuator chamber valves 126, 128, 130, 132, 134, 136, the ganging arrangement 138, and the directional control valve 154 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 100 can be connected to a separate controller for controlling one or more components of the hydraulic apparatus 100, but can still nevertheless be considered to be hydraulic apparatus 100.

[0070] Although not shown in FIG. 1, the hydraulic apparatus 100 also typically includes one or more sensors for measuring flow rate and/or pressure of hydraulic fluid at different points in the hydraulic fluid manifold 109. The hydraulic apparatus 100 further includes one or more sensors for measuring a force exerted by or a movement speed of any of the hydraulic work functions.

[0071] In an example, to cause a raising movement of the boom, the ganging arrangement 138 is configured to fluidly connect the first and second groups of working chambers 108a, 108b to the first pair of actuator chamber valves, including the first actuator chamber valve 126 and the second actuator chamber valve 128, via the ganging arrangement 138. Furthermore, the first actuator chamber valve 126 is configured to bring the first actuator chamber 114 into fluid communication with the portion of the hydraulic fluid manifold 109 in fluid communication with the first and second groups of working chambers 108a, 108b via the ganging arrangement 138. At the same time, the second actuator chamber valve 128 is configured to bring the second actuator chamber 116 into fluid communication with the high-pressure hydraulic accumulator 144. It will be understood that the high-pressure hydraulic accumulator 144 will supply hydraulic fluid into the second actuator chamber 116 at a pressure substantially corresponding to the pressure of the hydraulic fluid within the high-pressure hydraulic accumulator 144. By controlling a flow rate of hydraulic fluid pumped by the hydraulic machine 104, specifically the first and second groups of working chambers 108a, 108b of the hydraulic machine 104, towards the first actuator chamber 114, the exact desired lifting force and movement speed of the first hydraulic work function 110 can be achieved. A small change in lifting force and/or movement speed can be easily achieved by modifying the flow rate of the hydraulic fluid pumped by the first and second groups of working chambers 108a, 108b. Larger changes can be achieved by using a different number of groups of working chambers 108a, 108b, 108c, 108d, 108e, 108f, 108g, 108h in fluid communication with the first actuator chamber 114, and/or by bringing the second actuator chamber 116 instead into fluid communication with the medium-pressure hydraulic accumulator 142 or even the low-pressure hydraulic accumulator.

[0072] In some examples, where the boom is to be lowered, and energy is to be recovered, one or more of the groups of working chambers 108a, 108b, 108c, 108d, 108e, 108f, 108g, 108h of the hydraulic machine 104 can be brought into fluid communication with the second actuator chamber 116, via the second actuator chamber valve 128, the one or more groups of working chambers configured to operate in a motoring configuration. As described elsewhere herein, the recovered energy can be used to contribute rotational torque to the rotatable shaft 106, which can, for example, be used to pump hydraulic fluid, using one or more other of the groups of working chambers 108a, 108b, 108c, 108d, 108e, 108f, 108g, 108h, towards at least one of the medium-pressure hydraulic accumulator 142, the high-pressure hydraulic accumulator 144 and any one or more further hydraulic work functions 122, 124, 150; the ganging arrangement 138 is configured to route the hydraulic fluid accordingly. Alternatively, the recovered energy can instead be stored directly in the hydraulic accumulators 142, 144, or used in the further hydraulic work functions 122, 124, 150, without passing via the hydraulic machine 104.

[0073] FIG. 2 is a schematic illustration of systems of a vehicle according to an example of the present disclosure. The vehicle 200 comprises hydraulic apparatus 300 as described herein, including a hydraulic machine 310, and a controller 320. The controller 320 is configured to exchange signals 315 with the hydraulic machine 310 to control the hydraulic apparatus 300 in accordance with input signals received by the controller 320, for example from user inputs by an operator of the vehicle 200. The controller 320 in this example is realised by one or more processors 330 and a computer-readable memory 340. The memory 340 stores instructions which, when executed by the one or more processors 330, cause the hydraulic apparatus 300 to operate as described herein.

[0074] Although the controller 320 is shown as being part of the vehicle 200, it will be understood that one or more components of the controller 320, or even the whole controller 320 can be provided separate from the vehicle 200, for example remotely from the vehicle 200, to exchange signals with the vehicle 200 by wireless communication.

[0075] FIG. 3 is a flowchart illustrating a method of controlling a vehicle as described herein. The method 400 is a method of controlling a vehicle having a hydraulic work function, including a hydraulic machine, to cause movement of hydraulic actuator(s) used in the hydraulic work function. Specifically, the method 400 comprises receiving 410 a demand to move a plurality of hydraulic actuators to be used in the hydraulic work function. The hydraulic work function is typically a main hydraulic work function of the vehicle, such as a boom lifting work function. The demand is typically in a form of a demand signal receiver from a user input apparatus, such as a control device, for example a joystick.

[0076] The method 400 further comprises bringing 420 a hydraulic accumulator of the vehicle into fluid communication with a first actuator chamber of the plurality of hydraulic actuators, via a hydraulic fluid manifold of the vehicle and a valve arrangement. Typically, the valve arrangement is controlled to bring the hydraulic accumulator into fluid communication with the first actuator chamber.

[0077] The method 400 further comprises, synchronised therewith, changing 430 a pressure in a second actuator chamber of the hydraulic actuator. The second actuator chamber is in fluid communication with the hydraulic machine via the hydraulic fluid manifold and the valve arrangement. Typically, the hydraulic machine is controlled to change the pressure in the second actuator chamber. If necessary, the valve arrangement can be controlled to bring the second actuator chamber into fluid communication with the hydraulic machine via the hydraulic fluid manifold and the valve arrangement.

[0078] As a result of bringing 420 the hydraulic accumulator into fluid communication with the first actuator chamber, and of changing 430 the pressure in the second actuator chamber, the hydraulic actuators are caused to move in accordance with the demand.

[0079] FIG. 4 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.