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This paper reviews activities relating to understanding, and improving the on-center performance of heavy truck steering systems. Initially, the on-center steering performance characteristics for commercial vehicles were quantified. Steering wheel torque and angular position were the prime measurables. Graphical analyses of the on-center handling data were performed. To better understand the data, and to insure statistical significance, an algebraic model of the analyzed data was developed, with confidence intervals determined. The calculated system stiffness, as determined from the steering wheel data, was found to be a key discriminator between steering gears. System stiffness is a function of several component values, which were measured in the laboratory. Finally, to test the above findings, a correlation study of subjective driver impressions with measured steering gear characteristics and objective vehicle measures was performed.

Synthetic torque feedback (artificial feel) is valued in the market for enhancing steering performance as perceived by the driver. The possibility of using this same hardware, with minimal control modifications, to aid the driver in responding to tire failures, is discussed.

The classic two-degree-of-freedom yaw-plane or “bicycle” vehicle model is augmented with two additional states to describe lane-keeping behavior, and further augmented with an additional control input to steer the rear axle. A simple driver model is hypothesized where the driver closes a loop on a projected lateral lane position. A rear axle steer control law is found to be a function of front axle steering input and vehicle speed that exhibits high speed stability and improved low speed maneuverability. The theoretically derived control law bears similarity to practical embodiments allowing a deeper understanding of the functional value of steering a rear axle.

With the expectation that means of redundant steering will be necessary for highly autonomous vehicles, different methods of providing redundant steering can be considered. One potential for redundancy is to steer the rear axle for directional control of the vehicle in the event of a failure in the primary steered front axle. This paper will characterize the dynamics of directional control of a three-axle vehicle when steered at the rear, and compare it to a conventionally steered three-axle vehicle. Several compensators are suggested that allow similar vehicle dynamic behavior when steering the rear axle as a driver would expect when steering the front, giving hope that a steerable rear axle can provide acceptable redundancy for a failed primary steering system on the front axle.

A computer controlled steering system providing an artificial feel or synthetic torque feedback to the driver has recently been launched into production in the commercial vehicle market. This work compares the artificial feel control strategy with prior electric power steering control strategies and hydraulic power steering. Suitability for integration with other vehicle control systems such as lane sensing and electronic stability enhancement is explored.