| 摘要 |
PROBLEM TO BE SOLVED: To provide a speed control device of a crane easily changable to three kinds of speed modes of a crawling speed, a high speed and a constant speed. SOLUTION: A regulator 21a for controlling a tilt angle qp of a hydraulic pump 21 and a regulator 22a for controlling a tilt angle qm of a hydraulic motor 22 are respectively connected to a pilot oil pressure source 25 via hydraulic directional control valves 31, 33 and solenoid proportional pressure reducing valves 32, 34, and a mode changeover switch 15a and a speed setting dial 15b are connected to a computing element 36. The mode changeover switch 15a can be switched to three positions in response to speed modes, and the computing element 36 performs a prescribed operation according to a position of the switch 15a and a preset value (a) of the dial 15b to output a control signal to the solenoid proportional pressure reducing valves 32, 34 to thereby control a pressure reducing degree of the solenoid proportional pressure reducing valves 32, 34 in response to the speed modes so as to change the upper limit value of the tilt angle qp of the pump and the lower limit value of the tilt angle qm of the motor.
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