Abstract: A system comprising a secondary mover such as an hydraulic pump driven by a prime mover such as a motor powered, in use, by an alternating current (AC) electrical supply, whereby the operation of the secondary mover is affected by any frequency variation in a substantially constant voltage AC supply. The system further comprises adjustment means in use powered by the same AC supply as the prime mover, having inherently substantially the same operating characteristics as the prime mover, being coupled to the secondary mover and operable to adjust the operating range thereof in accordance with variations in the frequency of the AC supply.

Abstract: Control method and apparatus for a moveable control member with n>3 observed states. The apparatus incorporates a sliding mode control system operable to maintain the state point of the moveable member on a predetermined non-linear hyperplane having n-1 dimensions. The hyperplane is such that, if the state point is maintained thereon, the maximum rate of change of the highest order observed state does not exceed that of which the control apparatus is capable. The sliding mode control system include sa digital processor operable to reference n-1 low order observed states to the predetermined hyperplane to establish a desired value of the highest order observed state. The control system compares such desired value with the observed highest order state, and implements the control action necessary to maintain the state point on the predetermined hyperplane.

Abstract: Control method and apparatus for a moveable control member with n observed states, the apparatus incorporating a sliding mode control system, operable to maintain the state point of the moveable member on a predetermined hyperplane having n-1 dimensions, and comprising digital processor means operable to reference, at a first frequency, n-1 low order observed states to the predetermined hyperplane to establish a desired value of the highest order observed state, the control system further comprising comparator means operable to compare, at a second frequency, said desired value with the observed highest order state, the first frequency being less than the second frequency, and means responsive to the comparator means and operable to implement the control action necessary to maintain the state point on the predetermined hyperplane.

Abstract: The circuit provides digital control of current in an inductive load. A switching circuit generates a square wave PWM voltage drive to the load, and the current is sensed by sensor. This current is fed back as signal, which is compared with two zone boundary signals. The switching state is changed between ON and OFF accordingly.The boundary signals are generated by adding and subtracting (by adder/subtractor) a half-zone-width signal (stored as digital data) in a zone width store with the signal. The zone position may be moved slightly up and down, under control of a counter driven by the ON/OFF signal, to produce dither. The zone width may be selected in dependence on the input signal to reduce ripple at low signal, and to adjust the frequency. The switching circuitry may have multiple power supplies, and/or means for changing the connection of the load to the power supply to modify the rate of change of current and the direction of current in the load.

Abstract: A lockable adjustment mechanism (1) for an adjustable component (2), the adjustment mechanism (1) comprising a first rotatable body portion (3) adapted in use to receive and be attached to a threaded elongated adjustment member (4) of the adjustable component (2), a second non-rotatable body portion (5) attachable to the adjustable component (2) and through which the threaded adjustment member in use passes, means (7, 9) for retaining a selected relative position between the first and second body portions, a third body portion (13) rotatably mounted on the first body portion (3) and lock means (17) operable to lock the third body portion (13) to the first body portion (3), rotation of the third body (13) effecting rotation of the first body portion (3) when locked thereto and thus effecting longitudinal movement of the adjustment member (4) of the adjustable component (2), the third body portion (13) being freely rotatable when not locked to the frist body portion (3) so as not to have any effect on the setti

Abstract: A rotary, variable-displacement hydraulic pump (1) in use driven by a prime mover (4), the pump (1) comprising control means (5) for varying the displacement of the pump and means (17) responsive to a signal related to the rotational speed of the pump and operable to override the control means so as, in use, to prevent stalling of the prime mover (4) within a predetermined operational range of the prime mover.

Abstract: The invention provides a spool for a spool valve, the spool (1) comprising at least one annular land (2) having at least one notch (3) therein which is part conical (4). The invention also provides a method of producing such a spool.

Abstract: An hydraulic latch device comprises a housing having an inlet (14) for hydraulic fluid, an outlet (17) for hydraulic fluid, and first and second spool means (63,67; 62) slidably mounted in the housing and operable to control the flow of hydraulic fluid from the inlet to the outlet, each of the first and second spool means having resilient means (68;69) associated therewith and being operable to bias the spool means in one direction of sliding movement, the resilient means being arranged such that that associated with the first spool means determines the inlet pressure which places the device in a latched mode in which a first relationship is established between the inlet and outlet, and the resilient means associated with the second spool means determines the inlet pressure at which the device is placed in the unlatched mode in which mode a second relationship is established between the inlet and the outlet, with the latch pressure being higher than the unlatched pressure, and means provided to assist in main

Abstract: A flow sensor comprises a body (4) formed with a through bore (5), at least one fluid inlet (6, 7) and one fluid outlet (7,6) for permitting ingress and egress of fluid to and from the sensor, and a spool (8) slidably mounted within the bore and having at least one shaped end (38) past which fluid flows from the inlet to the outlet, characterized in that the spool (8) also has resilient means (26) mounted internally thereof and acting against and between two spaced abutments (27, 28) which are connected to the interior of the spool in such a way that they move with the spool in one direction of movement thereof and slide relative to the spool in the opposite direction of movement thereof, the spool being arranged to close the outlet in the null position of the spool when no fluid takes place, and being movable against the action of the resilient means when fluid flow is present, to open the outlet, the extent of movement being representative of the rate of flow of the fluid and being sensed by sensor means (3

Abstract: A pilot valve for a two-stage hydraulic device, the pilot wave comprising a spool slidably mounted in a housing for movement in opposite directions from a normal null position in order to deliver fluid under pressure from an inlet port through one or other of two service ports to a second stage of the device to actuate the latter in one direction or an opposite direction from a normal null position, and an electrically-actuated spool control device, associated with one end of the spool. The pilot valve spool is movable beyond its normal operating range to an offset zero flow position in the event of a failure of a control device. A spring is disposed at one end of the pilot valve spool and is operable, in the event of failure of a control device, to move the spool to a predetermined position. A stop for the spring prevents further movement of the spool beyond the predetermined position.

Abstract: A pilot valve for a two-stage hydraulic device, the pilot valve comprising a spool slidably mounted in a housing for movement in opposite directions from a normal null position in order to deliver fluid under pressure from an inlet port through one or other of two service ports to a second stage of the device to actuate the latter in one direction or an opposite direction from a normal null position, and an electrically-actuated spool control device, associated with one end of the spool. The pilot valve spool is movable beyond its normal operating range to an offset zero flow position in the event of a failure of a control device. A spring is disposed at one end of the pilot valve spool and is operable, in the event of failure of a control device, to move the spool to a predetermined position. A stop for the spring prevents further movement of the spool beyond the predetermined position.