The second action of active 4WS is same-phase steering angle input to the rear wheels. Turn the wheel right, and the rear wheels also turn slightly to the right. However, that rear angle is even shallower than the opposite-phase angles in the above scenario. This improves higher-speed stability, like when a driver changes lanes or corners rapidly through fun twisties or on a racetrack. Rear steering angles vary anywhere from 2.5 degrees to 10 degrees, depending on vehicle design and purpose.
Four-wheel steering, in hard parts
In real nuts, bolts, and notoriety, Honda first brought 4WS to modern production in the 1988 Prelude Si as an option. Nissan followed suit with its HICAS system, and Mazda had a system in with extremely limited production, but Honda made the biggest splash.
The Honda system was entirely mechanical. It used a shaft connecting the front steering rack to a planetary gear. That gear created the phase (direction) and degree of rear steering indexed to steering wheel input. This shaft led to a sliding rod that acted like the rack of a rack and pinion steering gear, carrying that input to the rear wheels.
At small steering angles, the rear wheels turned a maximum of 1.5 degrees in phase (in the same direction) as the fronts. At larger steering wheel angles above roughly 270 degrees from center, the rear wheels steered as much as 5.3 degrees out-of-phase with the fronts, tightening the turning circle about 10 percent.
Honda
The operating mechanism of the Honda’s rear steering box, connecting two different cranks (one is hidden), that results in different phases using a planetary gear.
Honda
Honda
An early Honda test mule, mating two Accords together.
Honda
The operating mechanism of the Honda’s rear steering box, connecting two different cranks (one is hidden), that results in different phases using a planetary gear.
Honda
An early Honda test mule, mating two Accords together.
Honda
The results in those 1980s and ’90s Preludes were impressive. Some auto critics, like that most cerebral of British scribes, L.J.K. Setright of Car Magazine, cited that the third and fourth-generation Honda Preludes with 4WS exuded the finest steering in the history of history. Weight, feel, accuracy, and telepathic information all sent the auto critic into automotive euphoria.
Four-wheel steering, digitally rendered
As Honda engineers toiled away on their system outside Tokyo, about 37 km away, Nissan worked on its HICAS (“High Capacity Actively Controlled Steering”) variants. Only active above roughly 90 km/h (55 mph) and below 200 km/h (125 mph), it used a computer-controlled hydraulic actuator to move the rear lower lateral links. A computer signaled a rear steering rack, allowing toe changes of plus or minus one degree, depending on speed and front steering angle.