| 摘要 |
PURPOSE:To prevent the overrotation of a hydraulic motor at the time of changeover, when the two-stage speed-change transmission for a construction vehicle is changed over from a high-speed stage to a low-speed stage, by operating a clutch changeover solenoid valve when the output rotating speed reaches a permissible changeover rotating speed. CONSTITUTION:When a changeover switch 46 is closed in order to change over from a high-speed clutch 13 to a low-speed clutch 3, since a centrifugal type hydraulic control valve 22 as a rotating speed detecting means does not operate as long as the clutch 13 is kept in a high rotating speed, an oil passage 33 is maintained in a high-pressure output not to operate a pressure detecting switch 23, and accordingly an a-contact switch 45 is maintained in an opened condition. With the lapse of time, when the throttle of the drain port 39 of a control valve 22 begins to open, the oil pressure in the oil passage 33 decreases. And, when the oil pressure reaches a preadjusted pressure, the pressure detecting switch 23 is closed to magnitize a relay 44, and the a-contact switch 45 is closed. In this case, since the switch 46 is already closed, a solenoid valve 24 is magnetized to communicate an oil passage 58 with an oil passage 29. |
