This paper introduces hydraulic 4WS system developed for the solar vehicles that participated in the 2017 and 2019 Bridgestone World Solar Challenges. This is the world's first solar powered vehicle to demonstrate hydraulic 4WS. The reverse phase 4WS allows the layout of steered tires are in a limited vehicle body space. Furthermore, in order to convert the crosswind into propulsion when the vehicle receives a crosswind, same phase 4WS was developed. The 2017 vehicle introduced a hydraulic 4WS system with multi-link and rigid suspension. In 2019 vehicles, 4WS was introduced to the trailing arm suspension. The same phase steering angle can be controlled from the driver's seat. The hydraulic circuit uses three cylinders. There is a cylinder mounted on the front steering mechanism, a cylinder that steers the rear wheels, and a centering cylinder that is responsible for adjusting and restoring the center position in the middle. When a load is input to the front cylinder, the centering cylinder and the rear cylinder operate. The steering unit consists of a rack and pinion gear that changes the steering wheel into linear motion, a front cylinder and a stopper which starts the operation of the 4WS. Normally, only the front wheels are steered by rack and pinion gears. When the steering is turned beyond a certain turning angle, the 4WS is driven for the first time by the stopper. The centering cylinder is loaded with an initial load by a spring. When the load on the front cylinder is stopped, all cylinders return to the initial position. In addition, the centering cylinder mechanism was designed so that the set length of the spring could be adjusted. The initial positions of the three cylinders can be adjusted by adjusting the spring set length. That is, same phase 4WS can be realized by this adjustment. This papers that hydraulic 4WS can be introduced for two different suspensions. The proposed systems were successfully tested on 3000 km of public roads in Australia. This paper introduces Reverse and Same Phase Hydraulic 4WS system.

Mr. Yuta Hayakawa, Kogakuin University, JAPAN Prof. Hiroto Hamane, Kogakuin University, JAPAN Mr. Akihiko Nakamura, Kogakuin University Solar Vehicle Research Center, JAPAN