Vickers Systems Limited

Trinova Limited

Kenneth G Cleasby

Jack T D'Aeth

An electrically operated, two-stage hydraulic spool valve comprising a maid stage (2) having a main spool (4), centering springs (9) acting on the main spool, a pilot stage (1) having a pilot spool (12), and two solenoids (39) acting on respective ends of the pilot spool to control the operating position of the latter the solenoid being opposed by return springs (18) also acting on respective ends of the pilot spool, the pilot stage comprising tank port means (23,24), supply port means (26), and two service ports (27,28), and the pilot spool comprising two portions (13,14), a spring (15) interposed between the two portions and operable to urge the two portions apart in a direction axially of the pilot spool so that on de-energization of the solenoids, the portions of the pilot spool separate under the action of the spring to provide an interconnection between the pilot service ports and the tank port means. The tank port means comprise two tank ports (23,24) between which the two service ports (27,28) are disposed, and the supply port means (26) comprises two supply ports (26a,26b) disposed between the service ports (27,28) and spaced apart by an amount such that, in normal operation of the pilot valve, neither supply port sees the ends of the two portions of the pilot spool which are maintained in contact by the operation of the solenoids (39).

Two-stage hydraulic valves

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. A separate analogue input may be summed with the feedback signal or the D/A output to modify the current magnitude or replace the input signal as the main input signal.

Digital pulse-width-modulation generator for current control

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.

Spool for a spool valve and method of producing same

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 maintaining the device in the latch mode by way of the first spool means (63,67) being stepped so as to provide first and second surfaces against which the inlet pressure can act, the effective surface area to which the inlet pressure is applied in the latched mode being greater than that to which the inlet pressure is applied in the unlatched mode.

Hydraulic latch device

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. The pilot valve is constructed to allow pressure fluid to react on the pilot valve spool so that when the spring engages the stop, this reaction results in movement of the spool to move the spool fully to the dump position in which both service ports are connected to tank, flow of fluid under pressure is metered from the inlet port through the service port, which would otherwise be subjected to such flow in such offset position of the pilot spool.

Pilot valves for two-stage hydraulic devices

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. The pilot valve is constructed to allow pressure fluid to react on the pilot valve spool so that when the spring engages the stop, this reaction results in movement of the spool to move the spool fully to the dump position in which both service ports are connected to tank, flow of fluid under pressure is metered from the inlet port through the service port, which would otherwise be subjected to such flow in such offset position of the pilot spool.

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Chichester, United Kingdom

Kenneth G Cleasby