A radial piston hydraulic device distributed by pilot operated check valves includes a housing, a plurality of piston assemblies, a main shaft, the rotating shaft, first pilot operated check valves having a same number with the plurality of piston assemblies and one-to-one corresponding to the plurality of piston assemblies, and second pilot operated check valves having a same number with the plurality of piston assemblies and one-to-one corresponding to the plurality of piston assemblies. The housing includes a plurality of piston chambers, a rotating shaft chamber, a high-pressure oil passage, and a low-pressure oil passage. Each of the plurality of piston assemblies is slidable up and down in a corresponding piston chamber of the plurality of piston chambers. The main shaft is rotatably connected to the housing and is connected to the plurality of piston assemblies in a transmission way.

A hydraulic device having: a plurality of main piston-cylinder arrangements, each of the respective pistons having a fixed stroke length and configured for axial reciprocation within their respective cylinder; a plurality of flow control valves for switching between a lockdown state and an unlocked state of one or more of the plurality of main piston cylinder arrangements during operation of the hydraulic device; and one or more control valves for directing the plurality of flow control valves between their respective unlock and lock positions.

A hydraulic device having: a plurality of main piston-cylinder arrangements, each of the respective pistons having a fixed stroke length and configured for axial reciprocation within their respective cylinder; a plurality of flow control valves for switching between a lockdown state and an unlocked state of one or more of the plurality of main piston cylinder arrangements during operation of the hydraulic device; and one or more control valves for directing the plurality of flow control valves between their respective unlock and lock positions.

In accordance with at least one aspect of this disclosure, a variable displacement pump system can include, a variable displacement pump disposed in a main line and configured to supply pressure to receive a low pressure fluid and to output a high pressure fluid. The main line can connect a hydraulic fluid source to a plurality of system actuators, where the variable displacement pump is disposed in the main line between the hydraulic fluid source and the plurality of system actuators to pressurize the hydraulic fluid.

A hydraulic apparatus including an electronically commutated machine having a plurality of working chambers which are controlled on each cycle of working chamber volume to carry out active or inactive cycles of working chamber volume allows only a plurality of defined fractions of cycles to be active cycles to avoid generating frequencies of active cycles which cause low frequency resonances. The demand signal may be quantised into fractions m/n where n is an integer below a threshold selected to avoid repeating patterns of active cycles of more than a cut-off length.

A hydraulic apparatus including an electronically commutated machine having a plurality of working chambers which are controlled on each cycle of working chamber volume to carry out active or inactive cycles of working chamber volume allows only a plurality of defined fractions of cycles to be active cycles to avoid generating frequencies of active cycles which cause low frequency resonances. The demand signal may be quantised into fractions m/n where n is an integer below a threshold selected to avoid repeating patterns of active cycles of more than a cut-off length.

A hydraulic device having: a plurality of main piston-cylinder arrangements, each of the respective pistons having a fixed stroke length and configured for axial reciprocation within their respective cylinder; a plurality of flow control valves for switching between a lockdown state and an unlocked state of one or more of the plurality of main piston cylinder arrangements during operation of the hydraulic device; and one or more control valves for directing the plurality of flow control valves between their respective unlock and lock positions.

A hydraulic device having: a plurality of main piston-cylinder arrangements, each of the respective pistons having a fixed stroke length and configured for axial reciprocation within their respective cylinder; a plurality of flow control valves for switching between a lockdown state and an unlocked state of one or more of the plurality of main piston cylinder arrangements during operation of the hydraulic device; and one or more control valves for directing the plurality of flow control valves between their respective unlock and lock positions.

An electronically commutated hydraulic machine is coupled to a drivetrain. Working chambers of the hydraulic machine are connected to low and high pressure manifold through electronically controlled valves. The phase of opening and closing of the valves has a default. In order to avoid cycle failure due to acceleration events, for example due to backlash in the drivetrain, the phase of opening or closing of the electronically controlled valves is temporarily advanced or retarded from the default timing.

An electronically commutated hydraulic machine is coupled to a drivetrain. Working chambers of the hydraulic machine are connected to low and high pressure manifold through electronically controlled valves. The phase of opening and closing of the valves has a default. In order to avoid cycle failure due to acceleration events, for example due to backlash in the drivetrain, the phase of opening or closing of the electronically controlled valves is temporarily advanced or retarded from the default timing.