| 摘要 |
<p>A power steering system (10) incorporating a valve assembly (16) having a rotary input member (40) and a valve sleeve (42). The valve assembly (16) includes a pair of closed center input valves (46) and a normally closed by-pass valve (50) with a variable orifice having their inlets fluidly connected to a pair of output valves (24) which are fluidly connected to the hydraulic pump (12). The hydraulic pump (12) is controlled so as to maintain a constant pressure drop between the inlets and outlets of the closed center input valve (46) and the by-pass valve (50) whereby initial fluid flow through the control valve is proportional to the area of the variable orifice of by-pass valve (50). When sufficient torque is applied to the rotary input member (40), one of the closed center valves (46) begin to open whereby total flow through the valve assembly (16) is proportional to the combined area of orifices within the opening of closed center valves (46) and the by-pass valve (50).</p> |
