| 摘要 |
PURPOSE: To prevent abrupt start of a vehicle by judging a failure in opening a proportional valve which adjusts pressure of hydraulic oil to be supplied to a hydraulic main clutch, setting power transmission of a first hydraulic change gear device to off condition when a failure occurs in opening the proportional valve, and making it impossible to transmit engine power to a running device when a second change gear device is on a high speed side. CONSTITUTION: In a tractor for agriculture of four wheel drive type, power from an engine 1 is transmitted to a running device D through a main clutch A, a first change gear device B, and a second change gear device C. In a hydraulic circuit on a pump discharge side, an electronic proportional valve which corresponds to forward and reverse clutches 5, 6 in the main clutch A, a selector valve of pilot operation type, and a selector valve of pilot operation type for the first speed to the fourth speed clutches 21 to 24 of a main change gear device 10 are provided. In this case, in a controller, a failure in opening the electronic proportional valve is judged, power transmission of the first change gear device B is set to off condition when the failure occurs in opening the electronic proportional valve, and the transmission of engine power to the running device D is impossible when the second change gear device C is on a high speed side. |
