Flow volume control device for power steering system

Abstract

A flow volume control device for use in a power steering system, which comprises: a casing having an inlet port, a reflux port and a delivery port; a fluid passage formed in the casing in communication with the inlet, reflux and delivery ports; fixed orifice means provided in the fluid passage to restrict the flow or pressurized fluid from the inlet port to the reflux and delivery ports; and throttle means provided in the fluid passage between the fixed orifice means and delivery port. The control device further includes a main spool movable in response to pressure differential across the throttle means for controlling the flow rate of the pressurized fluid from the fixed orifice means to the reflux port of maintain a predetermined flow rate of the fluid to be fed to the delivery port through the throttle means; an auxiliary spool movable in response to the pressure differential across the fixed orifice means for reducing the open area of the throttle means according to increases of fluid pressure supplied to the inlet port; and a branch passage formed in the casing by-passing the fixed orifice to connect said inlet port directly to the throttle means, the branch passage being opened when the auxiliary spool is shifted to reduce the open area of the throttle means to slow down the speed of movement of the auxiliary spool.