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Rear wheels get in on the action for steering

When changing direction, most vehicles have an inherent limitation:their front wheels can move, but their rear wheels always pointstraight ahead.

When changing direction, most vehicles have an inherent limitation: their front wheels can move, but their rear wheels always point straight ahead. This means that when moving sideways, especially at higher speeds, the rear tires tend to slide as they try to follow the front wheels.


Infiniti counters this with its 4-Wheel Active Steer, available on the all-new Infiniti M
Four-wheel steering has been available in the past, including a version on Chevrolet’s pickup trucks, but that system turned the rear wheels at low speeds, in a direction opposite to the front ones, to make it easier to back up. Infiniti’s system moves the rear wheels one degree in the same direction as the front wheels, producing better stability and handling at higher speeds. The system also adjusts the steering ratio of the front wheels for better and more stable response at different speed


“The system looks at what you’re doing,” says Ian Forsyth, Director of Corporate Planning for Nissan Canada. “It’s an active system. It’s using the Vehicle Dynamic Control controller, so it’s looking at steering angle input, acceleration, brake input and throttle sensing.”


There are two actuators, one for each set of wheels, including a high-response motor mounted on the steering column that adjusts the ratio between the steering wheel and the steering rack.


This affects how much steering input is needed to change direction. This results in easier turning at low speeds, such as when manoeuvring around a parking lot, and more control at higher speeds.


With both front and rear wheels turning into a curve, the car moves more smoothly around it, and with increased stability. Since sharp steering inputs can be hazardous at higher speeds, the turning angle of the front wheels decreases above 80 km/h. This, along with the slight change in direction at the rear wheels, means the car will move smoothly and under control when moving between lanes.


“The technology isn’t designed to take control of the vehicle, but to enhance what you’re trying to do,” Forsyth says. “The systems know what the driver is doing because of the input, and they assist with it. If you want better response, the system can give it to you.”

 
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