Valve for fluid working machine, fluid working machine and method of operation

1. A fluid working machine comprising

a rotatable shaft and a plurality of working chambers having working volumes which vary cyclically with rotation of the rotatable shaft, each working chamber having a valve unit comprising a low pressure valve which regulates the flow of working fluid between the working chamber and a low pressure manifold, and each working chamber having a high pressure valve which regulates the flow of working fluid between the working chamber and a high pressure manifold, wherein each valve unit of the corresponding working chamber includes a valve having a valve member, a valve actuator coupled to the valve member, and an electronic actuator controller which is integral to the valve unit and configured to actively control the valve actuator to thereby control the valve member, and the actuator controller is configured to receive commands and to determine the timing of changes to the active control of the valve actuator taking into account the received commands; and

a machine controller configured to determine, for each cycle of working chamber volume, whether the respective working chamber should carry out an active cycle in which the working chamber makes a net displacement of working fluid or an inactive cycle in which the working chamber makes no net displacement of working fluid and to transmit command signals to the electronic actuator controllers, wherein the actuator controllers receive the command signals and control the respective valve actuators responsive thereto to thereby determine the net displacement of working fluid by the working chambers.

2. The fluid working machine according to claim 1 , wherein the actuator controller of the valve unit of at least one of the working chambers is configured to determine a valve actuator control sequence from the commands.

3. The fluid working machine according to claim 1 , wherein the actuator controller of the valve unit of at least one of the working chambers is configured to receive data specifying one or more of the timing, duration or amplitude of active control of the corresponding valve actuator from one or more of the received commands.

4. The fluid working machine according to claim 3 , wherein the valve actuator of the valve unit of at least one of the working chambers is a solenoid and determining the timing of changes to the control of the corresponding valve actuator comprises changing a current through or a voltage across the solenoid at specific times.

5. The fluid working machine according to claim 1 , wherein the actuator controller of the valve unit of at least one of the working chambers is configured to start a valve actuator control sequence responsive to one or more of the received commands.

6. The fluid working machine according to claim 1 , wherein the actuator controller of the valve unit of at least one of the working chambers comprises a memory storing one or more sequences of changes to the control of the corresponding valve actuator, the actuator controller of the valve unit of the at least one of the working chambers being configured to select one of valve opening and/or closing sequences from the memory responsive to the received commands.

7. The fluid working machine according to claim 1 , wherein the commands include a phase or frequency signal and wherein the actuator controller of the valve unit of at least one of the working chambers takes into account the phase or frequency signal when determining the timing of changes to the control of the corresponding valve actuator.

8. The fluid working machine according to claim 1 , wherein the valve unit of at least one of the working chambers further comprises a power line configured or configurable to deliver electrical power to the corresponding valve from a power supply, and

wherein the actuator controller of the valve unit of the at least one of the working chambers is configured to receive the commands from an external controller through the power line.

9. The fluid working machine according to claim 1 , wherein the valve unit of at least one of the working chambers further comprises one or more sensors, and

wherein the actuator controller of the valve unit of the at least one of the working chambers is configured to receive sensor measurements from the one or more sensors and to determine the timing of changes to the control of the corresponding valve actuator taking into account the received sensor measurements.

10. The fluid working machine according to claim 1 , wherein the actuator controller of the valve unit of at least one of the working chambers is configured to cause the corresponding valve member to remain in an open position or in a closed position by applying a pulse width modulated signal to the corresponding valve actuator, and optionally to determine a frequency and/or mark to space ratio of the pulse width modulated signal.

11. The fluid working machine according to claim 1 , wherein the actuator controller of the valve unit of at least one of the working chambers further comprises a closed electrical current control loop configured to maintain a consistent actuating force to the corresponding valve actuator.

12. The fluid working machine according to claim 1 , wherein the valve unit of at least one of the working chambers further comprises a stored identifier of the corresponding valve or is configured to generate or receive and then to store an identifier of the corresponding valve, and

wherein the actuator controller of the valve unit of the at least one of the working chambers is configured to receive commands comprising identifiers and to process the commands if the received commands comprise the stored identifier of the corresponding valve.

13. The fluid working machine according to claim 1 , wherein the actuator controller of the valve unit of at least one of the working chambers is configured to, in response to a command signal being indicative, pause for a period of time before carrying out a sequence of changes to the actuation of the corresponding valve actuator.

14. The fluid working machine according to claim 1 , wherein the actuator controller of the valve unit of at least one of the working chambers is configured to transmit data to the machine controller.

15. The fluid working machine according to claim 1 , wherein the valve unit of at least one of the working chambers further comprises

a further valve having a further valve member, and

a further valve actuator coupled to the further valve member,

wherein the electronic actuator controller of the valve unit of the at least one of the working chambers is also configured to actively control the further valve actuator to thereby control the further valve member, and

wherein in the valve unit of the at least one of the working chambers, the valve member and the further valve member are configured to regulate the flow of hydraulic working fluid into or out of the same working chamber of the fluid working machine.

16. The fluid working machine according to claim 1 , wherein the machine controller and the actuator controller of the valve unit of at least one of the working chambers comprise synchronised clocks, and the machine controller is configured to transmit the time at which an event should occur to the actuator controller of the valve unit of the at least one of the working chambers.

17. The fluid working machine according to claim 1 , configured such that the valve units transmit data to the machine controller, or wherein the machine controller is configured to transmit to the valve units identifiers of valve units which individual commands concern.

18. The fluid working machine according to claim 1 , wherein the machine controller is configured to command one or more valve units to cause their respective working chamber to undergo an active cycle, wherein the fluid working machine further comprises means to determine which working chamber carries out an active cycle as a result and thereby determine which working chamber a valve unit is associated with.

19. A method of operating the fluid working machine according to claim 1 , comprising the actuator controller of the valve unit of at least one of the working chambers receiving a command and, responsive thereto, to carrying out one or more changes to the control of the corresponding valve actuator.