Actuator

A method of monitoring the pressurisation of a control valve for a hydraulic actuator, the control valve being movable between a neutral position, first actuation position and a second actuation position, the control valve comprising a spool movable along an axis (X), wherein the neutral position of the control valve comprises a mechanical neutral position and a hydraulic neutral position of the spool along the axis;

• the method comprising:
• controlling the flow of hydraulic fluid through the control valve using the spool so as to control the actuation of a component in a first direction when the spool is in the first actuation position and in a second direction when the spool is in the second actuation position, wherein the flow of hydraulic fluid through the control valve is based on the position of the spool along the axis (X), and wherein in an unpressurised state of the control valve the spool occupies the mechanical neutral position, in a pressurised state of the control valve the spool occupies the hydraulic neutral position and wherein a first two- position solenoid valve and a second two-position solenoid valve are configured to supply hydraulic fluid selectively to the control valve to move the pool from the hydraulic neutral position to one of the first actuation position or the second actuation position;
• monitoring the position of the spool within the control valve and detecting whether the spool occupies the mechanical neutral position or the hydraulic neutral position.

A hydraulic control system for an actuator, the system comprising:

• a first two-position solenoid valve and a second two-position solenoid valve;
• and
• an apparatus for monitoring the pressurisation of a control valve for a hydraulic actuator, comprising:
• a three-position control valve comprising a spool movable along an axis between a first axial position and a second axial position, wherein the spool is configured to control the flow of hydraulic fluid through the control valve based on its position along the axis so as to control the actuation of a component in a first direction when the spool is in a first actuation position, the first actuation position being a first position of the three-position control valve, and in a second direction when the spool is in a second actuation position, the second actuation position being a second position of the three-position control valve;
• and
• a position sensor configured to detect a slight variation in a neutral, resting position of the spool, the neutral, resting position of the spool being a third position of the three-position control valve,
• wherein in an unpressurised state of the control valve the neutral, resting position of the spool corresponds to the first axial position, and in a pressurised state of the control valve the neutral, resting position is modified such that it moves to the second axial position;
• and
• wherein the first two-position solenoid valve and the second two-position solenoid valve are configured to supply hydraulic fluid selectively to the control valve to move the spool from the second axial position to one of the first actuation position or the second actuation position.