Hydraulic control apparatus for a servomotor

Claim 1

A hydraulic steering control assembly, comprising, a bidirectional servomotor having two operating ports on opposite sides thereof, a pump and a tank, a steering wheel operated metering control unit having inlet and outlet ports and left and right control ports to which pressurized fluid may be selectively directed from said inlet port and returned from the other of said control ports to said outlet port, bidirectional valve means having inlet port means and outlet port means connected to said servomotor ports for selectively supplying and exhausting pressurized fluid therefrom, said bidirectional valve means having left turn inlet and outlet control ports and right turn inlet and outlet control ports, a two sided control circuit connected to said metering unit control ports and to said bidirectional valve means right and left turn inlet control ports, amplifier valve means having pressure regulating and control and power valve capabilities, said amplifier valve means having a slidable spool disposed in a valve housing having first and second inlet passage means and outlet passage means, said spool and said housing forming first and second chambers at opposite ends thereof, a regulating valve having an inlet connected to said pump and first and second outlets connected respectively to said metering control unit inlet port and said amplifier valve means first inlet passage means, a fixed metering throttle between said regulating valve and said metering control unit having the upstream and downstream sides thereof connected by pressure signal passages to opposite sides of said regulating valve for controlling said regulating valve in accordance with the pressure drop across said metering throttle to effect a substantially constant flow rate between said regulating valve and said metering control unit, a power circuit connected to said pump and to said amplifier valve means first input passage means, said spool having a first internal passage means having fluid communication with said first chamber and being in an adjustable throttling relationship with said first housing inlet passage means to regulate the pressure of said fluid thereat, said bidirectional valve means left and right turn outlet control ports being selectively connected via said metering control unit to said amplifier valve means second chamber and to said valve housing second inlet passage means, said spool having second internal passage means in constant fluid communication with said first internal passage means thereof and said housing second inlet passage means and said valve housing outlet passage means to combine pressure fluids from said control and power circuits, said valve housing outlet passage means being connected to said bidirectional valve means inlet port means to provide a common path for pressurized fluids from said power and control circuits.