New control algorithms for steering feel improvements of an electric powered steering system with belt drive

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New control algorithms for steering feel improvements of an electric powered steering system with belt drive

Bröcker, M.

In the past years, the acceptance in the automotive industry of electric power steering (EPS) systems grew based on the improvements with respect to driving comfort, driving safety and fuel consumption. However, EPS systems are more advantegeously positioned than hydraulic or electro-hydraulic powered steering systems. They offer a potential for cost reduction and a contribution to the environmental protection because of the saving of hydraulic oil and hoses. Further advantages of EPS systems can be summarized by the free relation between steering torque and assist and the standardized vehicle speed dependence of the assist. Added torque controller functions like active damping and active return lead to an improved vehicle behaviour. This contribution investigates an electric powered steering (EPS) system with belt drive of the company TRW Automotive GmbH, Düsseldorf (Germany), relating to new control algorithms for steering feel improvements. The EPS belt drive consists of an elektric motor that transforms the assist torque with a belt and ballnut mechanism to a power assist, which means to an assist force at the rack. The assist force at the rack is needed for the reduction of steering torques that are detected by the driver over the mechanical feedback of the assembling pinion, torsion bar and steering column. Steering feel improvements are obtained with new torque control functions for a vehicle fitted with an EPS belt drive. Additionally, a simulation analysis of the steering system shows the improvements of the controller design process regarding to some specific steering manoeuvres. On the basis of these simulation results, the vehicle measurements demonstrate the effectiveness of the new control algorithmus that are additionally in line with the subjective steering assessments of different professional drivers.