| 摘要 |
PURPOSE:To stabilize control of a servo piston, by a method wherein an electromagnetic value, which controls driving of a servo piston, forms a proportional electromagnetic valve which is increased in a passing flow rate as a driving current is increased, and the maximum speed of the servo piston is decreased depending upon a reaction force. CONSTITUTION:A proportional electromagnetic valve 21a, located adjacent to an electromagnetic valve 6b actuated in an ON-OFF system, has a solenoid 26a connected to an amplifier 14a. The proportional electromagnetic valve has characteristics in that, when a difference in pressure DELTAP between the upper stream side and the downstream side of the valve 21a is kept at constant value by means of a driving current ia, a passing flow rate Q is changed about rectilinearly. When the number Ne of revolutions of the input shaft of a pump is decreased and as a result of an increase in a load pressure PL, a reaction force F exerted on a servo piston 4 is increased, the valve 21a is brought into a condition in that oil is difficult to pass, and as a result, a positive maximum speed V1 can be decreased. This eliminates the need to widen a non-sensitive band set in comparators 13a and 13b, and enables stabilization of control of the servo piston. |
