| 摘要 |
<p>In a hydraulic drive system, first and second flow control valves means (8, 9; 100,101; 170,171; 200,201) comprise each; a main valve (11,70; 102,103; 160; 271) of seat valve type having a valve body (21; 162; 276) for controlling communication between an inlet port (17; 273) and an outlet port (18; 274) both connected to a main circuit (2-5), a variable restrictor (22; 163; 277) capable of changing an opening degree thereof in response to displacements of the valve body, and a back pressure chamber (24; 278) communicating with the inlet port through the variable restrictor and producing a control pressure to urge the valve body in the valve-closing direction; a pilot valve (15,74; 120,121; 290) connected to a pilot circuit (12-14, 71-73; 116, 117; 289) which is connected between the back pressure chamber and the outlet port of the main valve; and an auxilary valve (16,75; 124,125; 150; 172, 173; 190-196; 202,203; 242,243; 272) connected to the pilot circuit for controlling a differential pressure between the inlet pressure and the outlet pressure of the pilot valve. The auxiliary valve is controlled (by 43-49,51; 131-137; 151-154; 175-180; 202A, 203A, 213; 244-247, 254; 282-286) such that the differential pressure between the inlet pressure and the outlet pressure of the pilot valve has a relationship expressed by a certain equation including constants alpha , beta and gamma , with respect to a differential pressure between the delivery pressure of a hydraulic pump (1; 385; 390) and the maximum load pressure of first and second hydraulic actuators (6,7; 87-90), a differential pressure between that maximum load pressure and the self-load pressure of each of the hydraulic actuators, and the self-load pressure, the constants alpha , beta and gamma being set to respective predetermined values.</p> |
