Hydrostatic apparatus and method of operating the same

An apparatus comprising a prime mover and a plurality of hydraulic actuators, a hydraulic machine having a rotatable shaft in driven engagement with the prime mover and comprising a plurality of working chambers having a volume which varies cyclically with rotation of the rotatable shaft, a hydraulic circuit extending between a group of one or more working chambers of the plurality of working chambers of the hydraulic machine and one or more hydraulic actuators of the plurality of hydraulic actuators,

• each working chamber of the plurality of working chambers of the hydraulic machine comprising a low-pressure valve which regulates a flow of hydraulic fluid between the working chamber and a low-pressure manifold and a high-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a high-pressure manifold,
• the hydraulic machine being configured to actively control at least the low-pressure valves of the group of one or more working chambers to select a net displacement of hydraulic fluid by each working chamber on each cycle of working chamber volume, and thereby the net displacement of hydraulic fluid by the group of one or more working chambers, responsive to a demand signal,
• wherein the apparatus comprises a machine controller which is operable to apply a torque limit to the hydraulic machine, the hydraulic machine torque limit being selected to be below a prime mover torque limit, wherein the hydraulic machine torque limit is selected in dependence on a current prime mover speed, and
• wherein the hydraulic machine controller is further operable to cause the hydraulic machine to implement one or more rates of change of torque.