Virtual Mechanical Load Setup For Steer-by-Wire - a Case Study

Abstract

In the electric drives scenario, the automotive is one of the most active and promising application fields. So far, electric steer eliminated many elements of a hydraulic system, with fair fuel economy in the process. The next step, the electronic steering, is in progress. It will definitively substitute any mechanical connection with the steering wheel by wire-transmitted digital signals to one or more remote electric motors. Obviously, the design of any control strategy has to pass through hardware verification. At the early stages, or when a real car prototype is not easily available, the design could greatly benefit of a hardware-in- the-loop (HIL) emulator, to enable the fast control prototyping. In the paper, a reduced-order model, implemented with a high-dynamic electric drive, substitutes the real mechanical load. The model details, the system architecture and the experimental results are presented in the paper. I. INTRODUCTION The conventional steering systems include different forms of mechanical and hydraulic connections between the steering wheel and the steering valve. In simplest terms, the steering wheel rotation is proportionally amplified by the steering valve to obtain a proportional articulation angle. Since the two systems (steering wheel and steering power system) are mechanically coupled, there is a built-in inherent force feedback to the operator at the steering wheel proportional to the steering conditions. Electric steering (E-Steer) represents a substantial improvement (1,2). It uses a small but powerful electric motor to increase the mechanical forces created when the driver moves the steering wheel. E- Steer and other electric systems eliminate many elements of a hydraulic system: pumps, fluid reservoirs, hoses and the rubber-belt-and-pulley system. Consequently, there are engine power and fuel savings in the process. Steer- by-wire also provides benefits in terms of noise, vibration and crashworthiness, due to the loss of the steering column, as well as opening up the tremendous possibilities of vehicle stability control.