In a work vehicle equipped with a so-called Hydrostatic transmission (HST) circuit, a hydraulic pump is driven by an engine, and hydraulic fluid discharged from the hydraulic pump is supplied to a hydraulic motor. A drive wheel is then driven by the hydraulic motor, propelling the vehicle forward.
As an example of such a work vehicle, there is known a vehicle as disclosed in Japanese Laid-Open Patent Application Publication No. 2004-232469, in which the displacement of the hydraulic pump is controlled so that the pressure of hydraulic fluid circulating through a hydraulic drive circuit (hereafter referred to as “drive circuit hydraulic pressure”) does not surpass a predetermined cutoff pressure. In such a work vehicle, when the drive circuit hydraulic pressure reaches or exceeds the cutoff pressure, a cutoff valve reduces pilot pressure supplied to a pump displacement regulator. Because of this, the pump displacement regulator reduces the displacement of the hydraulic pump. As a result, the drive circuit hydraulic pressure is limited so as not to surpass the cutoff pressure. It is also possible to change the cutoff pressure to either of a high value and a low value in such a work vehicle by adjusting the pilot pressure supplied to the cutoff valve. Through this, the cutoff pressure can be easily set to a level appropriate to operating conditions. For example, when engaging in light work, the cutoff pressure of the cutoff valve can be adjusted so as not to generate high traction, preventing tire slippage from occurring.