With electric powered steering systems reducing fuel consumption and offering increased functionality, one of Europe’s leading industry publications, ‘Automotive Engineer’ talked to TRW’s global engineering director for EPS, Alastair McQueen, about steering feel and what TRW is doing to further develop it.
Fast facts
| Automotive Engineer Magazine |
Leading monthly magazine for engineers in the automotive industry |
| Focus |
Business & technology |
| Established |
1975 |
| Circulation |
31,000 |
| Readership |
24 countries |
“Steering feel is the relationship between the steering wheel and the front wheels; capturing the feeling of control, responsiveness, linearity, precision and feedback from the road,” explained Alastair. “It tells us what the car is about to do and where it is going.”
Early EPAS systems used old-fashioned brush motor technology, but the big motor increased inertia. Low friction, brush-less motors have greatly reduced inertia due to their high power density. As the basic mechanical controls, friction and inertia need to be managed according to power level, so are sized exactly for each vehicle.
Development
To develop steering feel, TRW looks at the whole steering package, including speed and the motor’s smoothness (amount of torque ripple).
“We also look at steering system architecture,” he continued. “It’s all about eliminating lost motion-feel, through the system. Our system in the Ford Fiesta has proved that you CAN get good feel from a column drive car, regardless of the sensor and actuator being further from the wheels. Indeed, for us, the only demarcation about whether we would use a column-drive or a rack-drive product is the absolute power of the system and how the OEM wants to manage crash.”
The quality of the software and control of the motor also play a big part and affect the outcome and performance of the system; and with TRW making huge progress in sensor quality and in the microprocessing speeds, the technology is under continuous development.
“Ultimately it comes back to test drivers and the feelings they have in their hands,” Alastair commented. “We design tuning parameters in an outer area of the software, so that they are more robust. And with determined upper and lower thresholds, we can keep on adjusting the tuning. With these systems, even after a press launch, there is still a chance to make slight modifications to the damping or boost curvers.”
Future
The next step is controlled EPAS, where the OEM lets his chassis sensors decide how the steering will react – that’s the next wave of feature content. “There is lots of interest from the market for this technology for the next generation of models coming around 2014. Watch this space!” concluded Alastair.