To prevent cavitation which is expected to occur when a working vehicle decelerates or goes downhill and when it is switched from forward to reverse or vice versa.
This driving unit has a variable displacement type hydraulic pump for travel, driven by engine power, a hydraulic motor driving a vehicle at a predetermined speed or less in response to oil delivered from the variable displacement type hydraulic pump for travel, and a travel switching valve which receives the oil delivered from the variable displacement type hydraulic pump for travel to supply the oil to the hydraulic motor or to discharge the oil therefrom. In this case, the driving unit has a horse power control mechanism 80 connected to the variable displacement type hydraulic pump 2 for travel and operating on receiving the pressure driving the hydraulic motor 6 at one end and receiving a signal proportional to the speed of the engine 1 at the other, outputting a command to deliver a discharge at which the pressure driving the hydraulic motor 6 attains a predetermined value or higher, when the speed of the engine 1 is not more than a predetermined value with the hydraulic motor 6 driven reversely from the vehicle.
SUMI HIDEKI
NUNOTANI SADAO
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