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How Marcel Ph. Mayer and Michael Frey want to revolutionize steering assistance systems on vehicles.

It could be an extremely comfortable situation: You get into your car, press a few buttons and then sit back and relax with the newspaper in your hand. The car then drives itself to its destination without any intervention from the vehicle's occupants. This is called "autonomous driving". A vision of the future or already an imminent reality?

"If you replace the human in the vehicle with an automatic system, the steering energy that the human exerts when driving must be completely substituted by technology. This is precisely where energy-efficient systems are desirable, and we want to develop them," explains Marcel Ph. Mayer. The mechanical engineer is an employee at Schaeffler, a leading global automotive and industrial supplier. However, his office is located directly on the KIT Campus East in Karlsruhe. Mayer heads the "Automated Driving" working group at the "Schaeffler Hub for Automotive Research in E-Mobility," which was established in July 2012 as part of the cooperation with Schaeffler and KIT.

Together with Michael Frey from the KIT Institute of Vehicle System Technology, he won over the German Federal Ministry of Education and Research (BMBF) with a project idea*. Now, the project partners Schaeffler and KIT are working together in a project team to develop a novel steering power assistance system using wheel-selective drives, a preliminary work for autonomous driving.

Steering force assistance systems in cars, trucks, or other vehicles reduce the steering torque applied to the steering wheel by the driver. Normally, energy must be provided for steering in addition to the drive energy of the vehicle. The progressive electrification of the drivetrain is opening up new possibilities for providing this energy, for example through wheel-selective drives.

The basic idea of the project is almost strikingly simple: imagine an old carriage. An electric drive is attached to the left and right of the wheel. These electric drives turn in different directions, so that the front carriage steering also turns. The project team now wants to integrate a modern interpretation of this principle into today's vehicles. The drives are to be used in such a way that a stronger torque is generated on one side than on the other.

In classic vehicles, steering always requires additional energy by power steering assistance, whether hydraulic or electromechanical. However, this energy is only there for steering; it has no effect on driving forward. "This should change in the future," Mayer explains, "because the traction drive, which is needed for the vehicle to move forward, is capable of providing steering power assistance through clever control and by using a suitable geometry of the wheel suspension. We want to use the difference in forces to distribute the energy directly, thus eliminating the need for additional actuators currently installed in the vehicle."

Current electric vehicles typically use conventional electromechanical drives for steering power assistance. "We want to use the drive forces of the electric motors to influence the lateral dynamics of the vehicle and thus the steering behavior," explains project team member Jürgen Römer, adding, "Steering power assistance is thus functionally integrated into the powertrain." By using wheel-selective traction drives, an intelligent control concept and suitable steering geometry, conventional steering power assistance can be dispensed with entirely. The wheels are steered without additional energy. Thus, the targeted shifting of drive power alone results in steering power assistance that is noticeable to the vehicle driver.

In the electromobility sector in particular, where questions of range are always viewed critically, this new type of steering power assistance not only offers opportunities for energy savings. There is also great potential in installation space and weight optimization through the potential substitution of a classic steering power assistance system. The more compact design of the vehicle results in significant savings in corresponding materials and manufacturing steps. "The major benefit of the novel steering power assistance to be researched and its integration into the drive system is the reduction of system components for electric vehicles and the energy optimization of the system. This results in potential cost savings on both the manufacturer and user side," explains Michael Frey.

Where is the journey heading: What will future research look like? "In the future, people will continue to take center stage and driving will remain their task for a long time to come. Only humans can take responsibility," says Frey. His team has yet to fathom whether classic steering-assist systems can be completely substituted, since steering while stationary is a challenge with conventional design. However, the potential is undoubtedly there, especially while driving. This is why the project team's aspirations for future systems remain correspondingly high: "We want to significantly improve the driving experience at the steering wheel," says Frey, "and thus increase driving quality. We are thinking of clear customer benefits such as increased comfort and safety, as well as high reliability of our systems. This will ensure that drivers continue to enjoy driving." An autonomously steering vehicle based on the new type of steering power assistance would be a further step that the research group is also already thinking about.

* The project "e²-Lenk Energy-optimal, intelligent steering power assistance for electric vehicles" is funded by the BMBF as part of the "ICT 2020 - Research for Innovation" program as part of the German government's high-tech strategy under the funding code 16EMO0073K.

Further links

Images: KIT


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