| 摘要 |
PURPOSE:To vary the vertical moving speeds of the boom of a working machine by selectively opening an electromagnetic valve in a fully opening or half way opening manner by a switcher by a method in which switching elements are each connected to solenoids for raising and lowering the electromagnetic valve and the switcher is operated by drive signals given to each switching element. CONSTITUTION:A control circuit consists of solenoids 13, 14, 16, and 17 to control an electromagnetic valve, switchers 2-23, switching elements 26-29, a pulse generating circuit 31, and a switcher 35. When a boom is lowered for example, since the element 26 is on ON side when the switcher 35 is on the contact (b) side, the solenoid 14 is excited when the lowering switcher 21 is turned On and the electromagnetic valve is fully opened to the lowering side. When the switcher 35 is set to the contact(a) side, an intermittent pulse signal is sent out of the circuit 31, and on-off operations of the element 26 are repeated. When the lowering switcher 21 is turned ON, since the excitation and demagnetization of the solenoid 14 are repeated, the electromagnetic valve becomes to a halfway opened state on the lowering side, and the lowering of the boom is delayed. |
