| 摘要 |
<p>A hydraulic circuit structure for a tractor with a stepless hydraulic transmission, which is constructed to transmit the output of an engine (1) through a main clutch (23) to a transmission (25), transmit the output of the transmission to a travelling gear transmission (34), and also transmit the output of the engine through the main clutch (23) to a PTO shaft (15) to drive an attached work unit by-passing the transmission (25), and supply hydraulic oil from a hydraulic pump (36) driven directly by the engine (1) to a hydraulic circuit of a lifting arm cylinder (9) lifting the work unit. A return oil passage of a hydraulic circuit driving the lifting arm cylinder is connected to a charging oil passage of the transmission so that oil is supplied to the charging oil passage irrespective of the engagement or disengagement of the main clutch. When the cylinder (9) only is moved, the oil from the pump (36) which is coupled directly to the engine branches at a flow priority valve (38), the excess flow is supplied to the hydraulic circuit driving the lifting arm cylinder, the control flow of the valve (38) is joined to the return oil passage from the circuit, at least a predetermined quantity of the control flow is supplied to the charging oil passage even if the oil is not flowing to the return passage when the oil is being supplied to the lifting arm cylinder, thereby eliminating the complete interruption of the charging oil supply.</p> |
