Hydraulic Four-Wheel-Drive Working Vehicle

A hydraulic four-wheel-drive working vehicle comprising main and sub driving wheels arranged on one and the other sides in a vehicle lengthwise direction, a main hydraulic motor outputting rotational power for driving the main driving wheel, a sub hydraulic motor outputting rotational power for driving the sub driving wheel, one or plural hydraulic pump operatively driven by a driving power source, a pair of main operation fluid lines fluidly connecting the hydraulic pump and the main hydraulic motor in such a manner that they form a main-driving-wheel HST, and a pair of sub operation fluid lines fluidly connecting the hydraulic pump and the sub hydraulic motor in such a manner that they form a sub-driving-wheel HST, the pair of sub operation fluid lines being independent from the pair of main operation fluid lines, the hydraulic four-wheel-drive working vehicle further comprising

• a front/rear differential-lock switch valve that fluidly connects forward-movement high-pressure lines of the pair of main operation fluid lines and the pair of sub operation fluid lines and also fluidly connects the forward-movement low-pressure lines of the pair of main operation fluid lines and the pair of sub operation fluid lines,
• wherein the front/rear differential-lock switch valve is configured so as to take a throttling fluid-connection state of fluidly connecting the corresponding lines in a state where a throttle is interposed therebetween and a full fluid-connection state of fluidly connecting the corresponding lines in a state where the throttle is not interposed therebetween.