Power steering system including a rotary control valve with multiple

Abstract

In a power steering apparatus comprising a pump, a reservior, a power cylinder having two opposite chambers, and a rotary control vale, the rotary control valve consists of a first control portion which communicates between the pump and the reservior, and a second control portion which communicates not only between the pump and the reservior but also with the power cylinder. In the first control portion, each of four underlapping variable orifices is so provided as to take the form of underlap in itself. In the second control portion, two underlapping variable orifices are provided on the side of the pump, and besides each of two overlapping variable orifices is so provided as to take the form of overlap in itself on the side of the reservior. In this manner, while a steering wheel is operated within a predetermined angle, an opening area of the overlapping variable orifice changes little. When the steering wheel is operated beyond the predetermined valve, the opening are increases sufficiently according to steering operation. As a result, a differential pressure between the chambers is prevented from originating at and around the neutral position of the steering wheel. Consequently, as for steering feeling, the rigidity of the steering operation at and around the neutral position is enhanced, and furthermore, a beginning point where the power assist is produced by operating the steering wheel from its neutral position is distinguished.