| 摘要 |
PROBLEM TO BE SOLVED: To solve several problems related to a relief valve and save energy by lowering impressed voltage to an electric motor when an electric pump discharge fluid pressure becomes the predetermined value or more so as to regulate a maximum discharge fluid pressure of the electric pump to a necessary maximum fluid pressure to a power cylinder. SOLUTION: A discharge fluid pressure P of an electric pump 18 is detected by means of a pressure sensor 31, and when the discharge fluid pressure P is the necessary maximum fluid pressure P0 set at the predetermined value or more, a duty ratio D/T, at which impressed voltage to an electric motor 14 is PWM (pulse width modulation) controlled in every sampling time when a computing process is executed, is lowered sequently from D/T0 (=100%), D/T1 ,... to D/T4 (=80%), so that the impression voltage is lowered from an ordinary impression voltage to the minimum impression voltage at which the maximum discharge fluid pressure P of the electric pump 18 is increased to the necessary maximum fluid pressure P0 at most. |
