Fluid working machines and methods

A method of supplying fluid to or receiving fluid from a fluid working machine working chamber of cyclically varying volume, during an expansion or contraction stroke of the working chamber respectively, comprising:

• opening an electronically controllable primary low pressure valve, in phased relation to cycles of working chamber volume, to bring the working chamber into fluid communication with a first low pressure manifold by a first path under the active control of a controller on a cycle by cycle basis,
• opening a secondary low pressure port, in phased relation to cycles of working chamber volume, to bring the working chamber into fluid communication with either the first low pressure manifold or a second low pressure manifold different from the first low pressure manifold by a second path, such that, during a portion of at least some cycles of working chamber volume, the primary low pressure valve and secondary low pressure port are open concurrently such that fluid flows into or out of the working chamber, as appropriate, through both the primary low pressure valve and the secondary low pressure port in parallel, wherein the primary low pressure valve and the secondary pressure port are open concurrently and in parallel at the point in the expansion or contraction stroke where the rate of change of volume of the working chamber is greatest.

A non-transitory computer readable storage medium comprising program code for a fluid working machine controller of a fluid working machine further comprising a working chamber of cyclically varying volume, the working chamber having an electronically controllable primary low pressure valve associated therewith to control the connection of the working chamber to a first low pressure manifold by a first path and a secondary low pressure port which is openable and closable in phased relationship to cycles of working chamber volume to connect the working chamber by a second path to either the first low pressure manifold or a second low pressure manifold different from the first low pressure manifold, to enable fluid to flow into or out of the working chamber concurrently and in parallel through both the primary low pressure valve and the secondary low pressure port during a portion of at least some cycles of working chamber volume at the point in an expansion or contraction stroke where the rate of change of volume of the working chamber is greatest, wherein the program code executed on the fluid working machine controller is configured to cause at least the primary low pressure valve to be actively controlled, in phased relationship to cycles of working chamber volume, to determine the net displacement of fluid by the working chamber on a cycle by cycle basis.