| 摘要 |
PURPOSE:To make the operation sensations of travel levers equal and improve the travel operability of a first/second-speed construction machine by controlling the outlets of center bypass oil paths in response to the first/second-speed switching signal and the operation shift signal of the travel levers. CONSTITUTION:The switched position of a first/second-speed switching solenoid selector valve and the operation shift quantities of travel levers 1L, 1R are detected and inputted to a controller 29, and the outlets of center bypass oil paths 18, 19 where part of the main pump pressure oil tends to flow out are squeezed in response to the first/second-speed switching signal and the operation quantities of the travel levers 1L, 1R. At the time of a second-speed start, the outlets of the pump pressure oil are squeezed by pilot opening/closing valves 20, 21 more sufficiently than at the time of a first-speed start via the closing direction command signal from the controller 29 and solenoid proportional pressure reducing valves 31, 32, and the operation angle quantities of the travel levers 1L, 1R at the time of the second-speed start are reduced to nearly equal to the operation angle quantities at the time of the first-speed start. |
