| 摘要 |
<p>A power assisted vehicle steering system has a pressure biased piston and cylinder (1) actuation of which effects in the power assistance. The piston (2) has axially opposed faces (5, 7) with different effective pressurized areas of which the face (5) with the smaller area communicates with a first chamber (6) and the face (7) with the larger effective area communicates with a second chamber (8). A valve (10) which is axially adjustable (but may be rotary) in response to a steering manoeuvre controls flow of pressure fluid from the pump (9) to the piston and cylinder (1) for providing power assistance. The valve (10) derives fluid pressure from the pump (9) through a restrictor (26) (which may be adjustable) and has a neutral condition in which the first and second chambers (6, 8) and the pump output communicate with the reservoir (23) by way of control ports (18, 19, 20) in the valve, the second chamber (8) communicates with the pump by way of the restrictor (26) and the control port (19) and the first chamber (6) communicates with the pump upstream of the restrictor (26) and the control port (19). The restrictor (26) is arranged so that with the valve (10) in its neutral condition the fluid pressure in the second chamber (8) provides an axial force on the piston face (7) which balances the opposing axial force on the smaller piston face (5).</p> |
