e²-Lenk – A novel concept for power steering using wheel individual electric drivetrain
IPG Apply and Innovate 2016
September 20th -21st 2016
Mayer, Marcel Ph.
The internal combustion engine of conventional vehicles not only accelerates the car but also supplies auxiliary systems with energy; such as the assisted steering system, which reduces the driver’s effort at the steering wheel. In electric vehicles, this energy is provided by battery and reduces the range as a result. However, is a dedicated power steering system needed in vehicles with wheel-individual electric drives? The joint research project "e²-Lenk" subsidized by the Federal Ministry for Education and Research (BMBF) focuses on a novel assisted steering concept for electric vehicles. If wheel torques on the steered axle are distributed in an intelligent way, this will evoke a resulting steering torque and have a positive effect to the driver's steering effort.
In this contribution, an investigation is presented that shows the influence of different wheel torques on the subject of reducing the steering wheel torque. To enable a profound statement, the possibility to depict realistic chassis geometries is necessary. In contrast to elementary two-track models, the use of IPG CarMaker as a vehicle dynamics simulation tool is proposed. This offers the possibility to consider energetic effects due to accurate description of suspension geometry. The study uses a maneuver normalized over distance, to investigate and compare the energy consumption of the novel assisted steering concept to state-of-the-art electric power steering systems at different speeds and lateral acceleration levels. The study clearly shows the energetic potential of wheel-individual drives as EPS-substitution by using a simple control approach to distribute driving torques depending on steering wheel torque. Compared to state-of-the-art power steering systems, both energetically better and poorer areas are pointed out. This reveals the need for more sophisticated control approaches and special chassis development. Furthermore, an analysis of different suspensions for the use with the innovative steering concept is presented. IPG’s MBS-Tool is used and allows extensive variation of suspension parameters. First investigations show the potential of conventional suspensions but reveal the limitations of standard chassis design. Optimized suspension parameters are needed to generate steering torque more efficiently. Additional requirements arise from emergency braking and electronic stability control. Hence, in lever arm design a trade-off between disturbing and utilizable forces occurs. A new design space for a novel chassis is discussed and a first design proposal is presented.