| 摘要 |
PROBLEM TO BE SOLVED: To obtain proper characteristics of steering torque both at low speed running and at high speed running. SOLUTION: A servo valve V has a first control part Va and a second control part Vb, each composed of a fluid bridge circuit prepared by connecting two pairs of variable throttle parts in a loop form. Operation fluid is supplied from a fluid supply device 30 whose supplying amount is larger under a low engine speed than under a high engine speed. A pair of variable throttle parts T1, T2 of the second control part Vb are valves closed at the neutral position. Other variable throttle parts U1, U2, N1 to N4 are valves opened at the neutral position. The fluid supply device, the first control part, the second control part and a power cylinder 16 are connected to each other a through first changeover valve Wa, second changeover valves Wb1, Wb2, and third changeover valves Wc1, Wc2. A power cylinder is controlled by the first control part under low speed running condition, while it is controlled by the second control part under high speed running condition. |
