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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.

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.

This paper is concerned with the energy saving analysis for the closed center gear steering system and its design and performance. After reviewing the recent efforts in developing steering system with high energetic efficiency, the new system using closed center steering gear is proposed to reduce power consumption while keeping the conventional steering feel. The mathematical model of the closed-center for steering gear is derived and its stability and performance are analyzed. If the steering feel introduced by the closed center valve is not satisfying, an impedance controlled haptic device (TRW developed, named Column Drive) may be used. The advantage of this system's energy saving will be evaluated for different duty cycles.

This paper is concerned with power consumption analysis for conventional steering system, the importance of duty cycle before choose appropriate pump drive system, and the energy saving potential of the proposed systems. After reviewing the recent efforts in developing energy-efficient steering system, two new on-demand pump drive systems are proposed to provide varying flow according to vehicle/engine speed: one is the combination of a sized pump without flow control valve and an Electrical Power Hydraulic Steering (EPHS) unit; the other is the combination of multiple EPHS units. The energy saving advantage of the combinations will be emphasized for different duty cycles.

A prototype active cab suspension has been built and evaluated. As the system uses low bandwidth valves and is powered by the existing power steering system, it is perhaps a good example of expected performance from a production active control system. System architecture is described. The control system is presented, and system performance is reported.

Commercial vehicles must transport an increasing volume of freight on a relatively fixed infrastructure. Some of these vehicles are highly specialized and customized to perform particular tasks. One way to increase freight hauling efficiency is to allow longer vehicles with more axles. These vehicles will have different handling properties and must be driven on existing infrastructure. Longer term, autonomous-like vehicles could be used to increase vehicle utilization. In both cases characterizations of multi-axle vehicle dynamics are required. A two-dimensional yaw plane model is used in practice to analyze handling performance of two-axle passenger cars. Commonly known as the "bicycle" model because it combines all tire forces associated with a given axle to act on the centerline of the vehicle, the yaw plane model allows lateral velocity and yaw rate degrees of freedom.

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.

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.

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.

The conventional rear tandem axle of a three-axle vehicle produces a yaw resisting moment that adversely impacts vehicle performance. This work examines the effect of steering the rear axle on tire wear. Using actual vehicle test data, a tire wear model is developed. This tire wear model is then used to predict tire wear savings over an actual commercial vehicle duty cycle when the rear axle is steered. The result of this projection is shown to be consistent with reported third party field experience.