Cars have always been committed to the technological transformation from passive to active. Four-wheel steering technology was proposed at the beginning of the last century and was also used by the United States in some military vehicles during World War II. and construction vehicles to improve low-speed agility. In subsequent developments, although four-wheel steering technology has made breakthroughs, it has not been popularized due to some problems that cannot be solved. Recently, Toyota applied for a four-wheel steering technology to the U.S. Patent and Trademark Office, which seems to have opened up a new idea for the popularization of this technology.
Two deflection laws of four-wheel steering technology
Generally speaking, four-wheel steering technology can produce different steering angles for the front and rear wheels according to differences in driving conditions, helping the vehicle to steer better. of turning or changing lanes.
In low-speed turns or when the steering wheel angle is large, the front and rear wheels turn in reverse phase and deflect in opposite directions. The angle of the rear wheels usually increases with the increase of the turning angle within a certain range (usually 5°), thus reducing the turning radius of the vehicle. In complex off-road roads, narrow paths, parking and other scenarios, reverse phase steering can effectively improve vehicle flexibility.
At high speeds, the four-wheel steering technology is changed to in-phase steering, with the same deflection angle. However, due to the increase in vehicle speed at this time, the deflection range of the rear wheels is much smaller than reverse-phase steering (generally 1°). Vehicles using in-phase steering can reduce the yaw angular velocity of the vehicle body when traveling at high speeds, effectively suppressing the tendency of the vehicle body to yaw dynamically and improving handling stability.
Early four-wheel steering technology only had a corner-following mechanical structure, and the front and rear wheels were constantly turning in reverse phase. Because this state was only suitable for low-speed scenarios and seriously affected high-speed stability, there were only some military vehicles and Engineering vehicle applications. With the development of later technology, vehicle speed-sensitive four-wheel steering technology was developed, which can realize two deflection rules of reverse-phase steering and in-phase steering according to the different vehicle speeds.
Why can’t four-wheel steering technology be popularized?
Compared with ordinary front-wheel steering cars, four-wheel steering technology can effectively improve low-speed flexibility and high-speed stability. It seems to be a perfect solution, but because it requires switching between two different deflection laws, To achieve this effect, it is necessary to accurately judge the road scene and driver's intentions.
Traditional four-wheel steering technology is mainly based on vehicle speed judgment, low-speed reverse-phase deflection, and high-speed deflection in-phase, but the method is still too rough and still has disadvantages.
This is also the biggest problem currently limiting the development of four-wheel steering technology. Therefore, the four-wheel steering systems currently used in passenger cars usually abandon reverse phase deflection and focus on improving high-speed stability. At low speeds, the car only relies on the front wheels for steering. After the vehicle speed exceeds a certain limit, the rear wheels participate in the same-phase deflection. However, due to the limited usage scenarios of this solution, the current mainstream electronically controlled hydraulic power system is still limited in flexibility and accuracy and has not been popularized.
Toyota’s four-wheel steering technology
According to Toyota’s patent information, this application for a four-wheel steering patent is to install an independent motor on each wheel to achieve the maximum turning angle of a single wheel. It can reach 90°, and can achieve two deflection patterns: same-phase steering and reverse-phase steering. The motor it uses also has better performance than the electronically controlled hydraulic power system in terms of control performance, system layout, energy saving, etc.
Unlike traditional four-wheel steering systems, Toyota's patent is no longer limited to assisting in improving low-speed agility and high-speed stability, but enables more flexible scene applications. The wheel angle range of this patent has been greatly increased, and both the front and rear wheels can achieve 90° deflection, which means that it can make a U-turn on the spot or move into a parking space. It has stronger applicability in some special road conditions and parking scenarios. In addition, Toyota's patent also supports four wheels deflecting at the same angle for diagonal driving.
In order to cooperate with the special functions of this four-wheel steering system, Toyota has also applied for a new type of sound and light prompt signal in the patent, which tells other traffic participants what is coming next through special regular light flashes or image information. direction of movement.
Conclusion
The most difficult thing about four-wheel steering technology is not the structural design and electronic system, but how to accurately judge the driver's intention. Different from traditional four-wheel steering technology, Toyota's new four-wheel steering technology not only retains the ability to optimize vehicle dynamic performance, but also provides more driving methods for vehicles and solves more practical needs. Of course, this method still has the same problems. If four-wheel steering technology is to be truly popular, we still need to wait for the arrival of the era of high-end autonomous driving.
This article comes from the author of Autohome Chejiahao and does not represent the views and positions of Autohome.