Biography
Biography: Ganesh Kondiboyina
Abstract
To understand the advantages of four-wheel steering, it is wise to review thedynamics of typical steering maneuvers with a conventional front -steered vehicle. The tires are subject to the forces of grip, momentum, and steering input when making a movementother than straight-ahead driving. These forces compete with each other during steeringmaneuvers. With a front-steered vehicle, the rear end is always trying to catch up to the di-rectional changes of the front wheels. This causes the vehicle to sway. As a normal part of operating a vehicle, the driver learns to adjust to these forces without thinking about them.When turning, the driver is putting into motion a complex series of forces. Each of these must be balanced against the others. The tires are subjected to road grip and slip angle.Grip holds the car's wheels to the road, and momentum moves the car straight ahead.Steering input causes the front wheels to turn. The car momentarily resists the turningmotion, causing a tire slip angle to form. Once the vehicle begins to respond to the steeringinput, cornering forces are generated. The vehicle sways as the rear wheels attempt to keepup with the cornering forces already generated by the front tires. This is referred to as rear-end lag, because there is a time delay between steering input and vehicle reaction. When thefront wheels are turned back to a straight -ahead position, the vehicle must again try toadjust by reversing the same forces developed by the turn. As the steering is turned, thevehicle body sways as the rear wheels again try to keep up with the cornering forcesgenerated by the front wheels.The idea behind four-wheel steering is that a vehicle requires less driver inputfor any steering maneuver if all four wheels are steering the vehicle. As with two-wheelsteer vehicles, tire grip holds the four wheels on the road. However, when the driver turnsthe wheel slightly, all four wheels react to the steering input, causing slip angles to form atall four wheels. The entire vehicle moves in one direction rather than the rear half attempting to catch up to the front. There is also less sway when the wheels are turned back to a straightahead position. The vehicle responds more quickly to steering input because rear wheel lag is eliminated.