Apparatus with hydraulic machine controller

A method of operating an apparatus, the 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 hydraulic machine and one or more of the hydraulic actuators,

• each working chamber of the hydraulic machine comprising a low-pressure valve which regulates the 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 a net displacement of hydraulic fluid by the group of one or more working chambers, responsive to a demand signal,
• the method comprising calculating the demand signal in response to a measured property of the hydraulic circuit or one or more actuators,
• the method further comprising selectively regulating the demand signal to implement a hydraulic machine torque limit, where the hydraulic machine torque limit is calculated in dependence on a prime mover speed error, and
• the method further comprising reducing the hydraulic machine torque limit at low speed and increasing the hydraulic machine torque limit at high speed.

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 hydraulic machine and one or more of the hydraulic actuators,

• each working chamber of the hydraulic machine comprising a low-pressure valve configured to regulate a flow of hydraulic fluid between the working chamber and a low-pressure manifold and a high-pressure valve configured to regulate 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 a net displacement of hydraulic fluid by the group of one or more working chambers, responsive to a demand signal,
• the apparatus comprising a controller configured to calculate the demand signal in response to a measured property of the hydraulic circuit or one or more actuators, wherein the controller is configured to receive a measured pressure and to compare the measured pressure to a pressure limit and to limit displacement by one or more of the plurality of working chambers when the measured pressure is within a margin of the pressure limit, wherein the margin is a margin within a range of the pressure limit and is below the pressure limit.

A method of operating an apparatus, the 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 hydraulic machine and one or more of the hydraulic actuators,

• each working chamber of the hydraulic machine comprising a low-pressure valve which regulates the 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 a net displacement of hydraulic fluid by the group of one or more working chambers, responsive to a demand signal,
• the method comprising calculating the demand signal in response to a measured property of the hydraulic circuit or one or more actuators,
• the method further comprising receiving a measured pressure and comparing the measured pressure to a pressure limit and limiting displacement by one or more of the plurality of working chambers when the measured pressure is within a margin of the pressure limit, wherein the margin is a margin within a range of the pressure limit and is below the pressure limit.