Geometry of a Four-Wheel-Steered Off-Road Vehicle

An off-road vehicle with a front- and rear-wheel steering capability (4WS) can move sideways, and can avoid obstacles easily, with the same steering phase of both front and rear wheels. With the different steering phase of front and rear wheels, its minimum turning radius is half of that of a vehicle of the same size with only front-wheel steering (2WS). Furthermore, it can make the inner radius difference zero regardless of the wheel base. However, the practical breadth of turning with a minimum radius of a 4WS vehicle is wider than that of an articulated- frame steered vehicle of the same size because the practical minimum inner turning radius of the 4WS is shorter than the inner radii of the inner wheels and the practical minimum outer turning radius is longer than the outer radii of the outer wheels, whereas the practical minimum outer and inner turning radii of the frame-steering whose body is narrower than the overall width equal the outer and inner turning radii of the wheels, respectively. The distance between obstacles in slalom running of a 4WS is 57–62% and 68–71% of that of the 2WS and the frame-steered vehicle of the same size, respectively. The 4WS we tested can efficiently pass through a 48–year-old plantation of hinoki which the same-sized 2WS can not penetrate.