This "unrealistic" fantasy may come true in the near future. At present, Toyota has applied to the United States Patent and Trademark Office for a brand-new four-wheel steering technology. As can be seen from the patent drawing, Toyota will allow four wheels to rotate freely at 0-90 degrees, and the vehicle can realize lateral translation, in-situ U-turn and other actions.
At present, the maximum steering angle of automobile wheels is 45, which is mainly designed for safety and chassis structure. If the wheel steering angle is allowed to be 90, the danger caused by misoperation at high speed will be greatly enhanced. In addition, 90-wheel steering has a great test on the layout of suspension, shock absorption, steering and transmission system.
Toyota's brand-new four-wheel steering technology is based on hub motor. In the new technology, Toyota will equip each wheel with an independent hub motor. The motor in the wheel drives the wheel to move back and forth, which reduces the space occupation of the transmission mechanism. At the same time, the hub motor will also integrate a vibration reduction system and some suspension structures, which will greatly save the chassis space and further ensure that the wheels have a larger steering angle.
According to the patent document, the vehicle with the new four-wheel steering system can move horizontally and obliquely, and can also rotate in situ. In order to ensure safety, vehicles need to remind drivers or pedestrians of the next vehicle movement through sound or optical signals.
Toyota's four-wheel steering technology not only solves the problem of side parking, but also solves the problem of turning around in a narrow space. Going up a flight of stairs will greatly increase the flexibility of the car. Such a beautiful technology actually has many technical difficulties. Firstly, the steering mechanism is redesigned. The steering rod of conventional vehicles is relatively straight, and Toyota's four-wheel steering technology may use hook steering rod to meet the steering angle of 90, so the strength of steering rod and chassis space need to be strengthened.
The second is how to realize the large-scale steering of the rear wheel. Taking Audi as an example, Audi's rear wheel steering is to calculate the vehicle speed and the input angle of the steering mechanism through the driving computer, and then control the rear wheel to slightly steer. Because Toyota's brand-new four-wheel steering technology involves many angles, it is likely to adopt several fixed modes. That is, when driving normally, the front wheels are the same as ordinary vehicles, and the rear wheels will rotate in the same direction as the front wheels, thus improving the tracking performance. At low speed, the rear wheel will rotate in the opposite direction, reducing the steering radius and improving the flexibility. After parking, you can choose lateral movement mode or in-situ U-turn mode.
Finally, the disadvantages brought by hub motor. Hub motor is the core of Toyota's brand-new four-wheel steering system, but the existence of hub motor increases the unsprung weight and makes the handling loss of the vehicle. For this reason, the models adopting Toyota's new four-wheel steering technology are likely to be small cars or mini-cars with urban traffic as the mainstay. It will take a long time for this technology to be applied to a larger model.