Active and passive rear-wheel steering technology is one of the most striking innovations in the automotive sector, influencing the handling and driving feel of a vehicle in different ways. Let's dive into the principles of these two technologies, their applications, and their evolution in the world.
At the heart of active rear-wheel steering is a sophisticated steering motor on the rear axle of the vehicle. This motor is similar to the steering system of the front wheels through a lead screw nut mechanism, but its role is to push the steering tie rod, which changes the angle of the rear wheels. The original intention of this design was to improve the vehicle's agility and U-turn performance by turning the rear and front wheels in the opposite direction at low speeds. At high speeds, the rear wheels rotate in the same direction as the front wheels, which improves the stability of the body when changing lanes.
The implementation of this active rear-wheel steering is not straightforward and requires a complex software calibration process. Because rear-wheel steering affects the dynamic geometry of the suspension, and there is no hard link between the rear wheels and the steering wheel, the software needs to be fine-tuned to ensure the smooth operation of the system. In the case of the Mercedes-Benz S series, its active rear-wheel steering system allows the rear wheels to reach a large angle under conditions of large steering at low speeds.
At speeds above 60 km/h, the rear wheels rotate in the same direction as the front wheels, creating a shifting line feel similar to translation. This driving feedback varies from person to person, so manufacturers often design active rear-wheel steering as an optional configuration to meet the preferences of different drivers.
In addition to the complexity of hardware and software, active rear-wheel steering is also limited by the model. This technology is mainly used in five-link rear suspension systems, which are often found on high-end brand models, giving active rear-wheel steering a certain "expensive" label.
In contrast, passive rear-wheel steering, also known as "rear-wheel follower steering", takes a different design concept. The characteristic feature of this technology is that the rear and front wheels are reversed when entering a corner, and the rear wheels are steered in the same direction as the front wheels again after the corner.
PSA (Peugeot Citroen) has PSS rear-wheel steering technology. This technology takes advantage of the "roll steering" feature to achieve rear-wheel steering through the unique design of the side-view swingarm angle and swingarm length, as well as the use of multiple self-deflecting rubber bushings.
When the roll is small, the jump on the outboard wheels causes the curved outer wheels to move backwards, causing the rear wheels to show a deflection angle that is opposite to the front wheels, thus reducing the turning radius and providing a more responsive driving experience. When the vehicle goes deep into a corner, the body roll becomes larger, and the rear wheels show a reverse deflection angle to the front wheels, making the vehicle more stable and improving the driver's sense of control and confidence.
Although PSA's passive rear-wheel steering technology excels in performance, it requires a high level of upfront design. High-end brands may opt for more advanced and expensive active steering technology, while lower-end brands may lack design experience, and the current automotive industry's emphasis on vehicle stability and safety has made this passive technology fade out of the market.
The design ingenuity of the PSA is that only a few self-deflecting rubber bushings are used to achieve even more unique properties. This simple yet sophisticated design demonstrates innovative thinking in the development of automotive technology, making PSA leave a strong mark in the history of automotive technology development.
As automotive technology continues to evolve, so does rear-wheel steering. In the future, we may see more advanced and intelligent rear-wheel steering. More models are likely to feature active rear-wheel steering, offering a more agile and customized driving experience through finer software calibration and more advanced hardware design. At the same time, it is also possible to see some unique passive rear-wheel steering technology, which brings a new level of handling to the driver through innovative design concepts.
The development of rear-wheel steering technology has not only provided drivers with more options, but has also pushed the entire automotive industry to a higher level. The R&D and application of these technologies not only affect vehicle performance, but also lead the direction of future automotive technology. With the emergence of more and more advanced technologies, we can expect the driving experience to continue to evolve in the future, bringing even more exciting driving experiences to the driver.