PURPOSE: To attain boom driving with no influence by fluctuating an engine speed by supplying pressure oil to a boom driving hydraulic cylinder through a solenoid proportional valve, and controlling this valve in accordance with an output of a DA converter of changing a proportional constant in accordance with the engine speed.
CONSTITUTION: When a push button 1 is pressed, since a pulse is generated from an acceleration pulse oscillator 3, a number of the pulses is counted by an up counter 5, and a count value is output as a binary code. This binary code is converted into a hexadecimal digital signal in a decoder circuit 6A, next in a DA convert 7, into an analog value by a prescribed transfer characteristic curve, and after amplification by an amplifier 8, the value is applied to a solenoid 14 of a solenoid proportional valve 9. In this way, a pressure oil flow of the solenoid proportional valve 9 is gradually increased in the beginning to drive a hydraulic cylinder 18 of a boom 17 gradually started and actuated at a fixed speed after a fixed time. Based on an actual rotational speed signal by a rotational speed detector 11A, a proportional constant of the DA converter 7 is adjusted.
MORIYA MASAKI
MURAKAMI HIROYUKI
TANAKA HIROBUMI
TAIHO BUSSAN KK