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A large percentage of commercial vehicles transport freight on our interstate highway system. These vehicles spend the vast majority of their duty cycle at high speed maintaining a lane. As steering is integrated into ADAS, objective performance measures of this most common mode of commercial vehicle operation will be required. Unfortunately in the past this predominant portion of the commercial vehicle duty cycle was overlooked in evaluating vehicle handling. This lanekeeping mode of operation is also an important, although less significant portion of the light vehicle duty cycle. Historically on-center handling was compromised to achieve acceptable low speed efforts. With the advent of advanced active steering systems, this compromise can be relaxed. Objective measures of lanekeeping are developed and performance of various advanced steering systems is quantified in this important operating mode.

Electrically Powered Hydraulic Steering (EPHS) has provided value in passenger car applications by reducing power consumption at engine idle, providing only the required power during high speed lane-keeping, and allowing engine-off operation of vehicles with alternative power sources. This work discusses the design modifications made to use EPHS for medium duty commercial vehicle applications. Configuration options along with communication and diagnostic interface are discussed. Bench tests show the steady-state performance of the system. Experiments are done on a medium duty truck with the EPHS as the sole source of steering power to determine the speed of steer at various vehicle speeds. Finally, the power consumption for the EPHS system is compared to a conventional engine driven pump.

The conventional rear tandem axle of a three-axle vehicle produces a yaw resisting moment that adversely impacts vehicle performance. This work examines the steady-state handling effect of steering the rear axle of a three-axle vehicle in terms of equivalent wheelbase and understeer. It is found that a very simple rear axle steer control strategy improves both the equivalent wheelbase and understeer. The equivalent wheelbase of the rear axle steered vehicle calculated from vehicle performance data equals the intuitively expected kinematic result. Finally, improvement in tire wear by steering the third axle is reported.

Hydraulic power steering systems traditionally are sized in a straightforward manner with easily verifiable results. The source of power in conventional systems is an engine driven pump that is effectively a source of hydraulic flow. As energy consumption of auxiliary functions becomes significant, on-demand power sources are considered. Best typified by hydraulic pumps driven by electric motors, these on-demand sources are often power limited, and established sizing practices should be re-visited.

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.

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.

The effect of an artificial feel steering device providing a synthetic torque feedback to the driver is studied for a transit bus operating in an urban drive cycle. Driver workload is greatly reduced and the results are shown to be statistically valid for a wide range of transit bus routes.