4 Wheel Steering Research

4 Wheel Steering

Also known as Quadra Steering, Rear Wheel Steering, or all Wheel Steering, this steering system allows the driver to turn the front and rear wheels at the same time.

There are three phases in 4-wheel steering, the negative, the neutral, and the positive.

· Wheels turn in opposite directions

· Leads to smaller turning radius and increased maneuverability

· Axles move in opposite directions

· Only the front wheels turn, and the rear wheels do not follow. This is seen in typical steering systems.

· Wheels turn in the same direction

· This is typically done at high speeds such as highway driving to allow for better stability during lane changes

There are three types of four-wheel steering systems: Mechanical, Hydraulic, and Electromechanical

Mechanical:

Two steering gears are used, one for the front and one for the rear. A shaft connects the two steering gearboxes.

The rotation of the steering wheel is carried through the front steering gear box to the center shaft and to an eccentric pin located in the rear steering gearbox.

During small turns, typically less than 130 degrees rotation of the steering wheel, the planetary gear rotates up to the 90-degree position within the annulus, causing the rear wheels to move in the same direction as the front wheels, i.e., the positive phase. When the steering wheel is turned further, the planetary gear continues to rotate within the annulus to the 180-degree position, returning the wheels to the neutral phase. When the steering wheel is turned even further, implying a need for greater turning capability, the planetary gear rotates up to the 270-degree position, turning the rear wheels in the opposite direction as the front, i.e., the negative phase.

Hydraulic:

In a hydraulic system controlled by electronic sensors which measure vehicle speed, the rear wheels are turned hydraulic ram cylinder. Below a set speed, the electronic control unit (ECU) feeds signals to the stepper motor which control the yoke angle. The steering phase control unit receives the position of the front wheels through the steering angle transfer shaft. Control valve controls the hydraulic pressure supplied to the ram cylinder which then controls the steering of the rear wheels.

Electromechanical:

Like the hydraulic system, electrical signals relayed to the ECU by sensors, allows the ECU to determine how much the wheels should rotate.

In this extremely simple diagram, the electric motor would be driven by the ECU and would move the rack and pinion by rotating the motor in the direction resulting in the required movement.

Another diagram showing how an electric motor powered steering rack would work at moving the rear wheels.

Sources:

https://www.slideshare.net/KhadeerKms/four-wheel-steering-system-77212582

https://www.theengineerspost.com/quadra-steering-system/

Active Rear Steering - 4 Wheel Steering - Explained

https://openscholarship.wustl.edu/cgi/viewcontent.cgi?article=1050&context=mems411

https://what-when-how.com/automobile/four-wheel-steering-4ws-automobile/