Rack-assist EPS from Nexteer finds favor in larger vehicles

  • 03-Aug-2011 10:13 EDT
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Nexteer’s rack-assist on-demand EPS can now provide forces exceeding 15 kN (3370 lb), some 2 kN (450 lb) more than the threshold that some systems experience.

Electric power steering (EPS) is growing up; its applications are spreading beyond small cars and starting to find design and engineering favor for large models as the problem of achieving sufficient force to the rack is overcome.

Nexteer’s rack-assist on-demand EPS can now provide forces exceeding 15 kN (3370 lb), some 2 kN (450 lb) more than the approximately 13-kN (2920-lb) threshold that some systems experience. It positions the motor, drive assembly, and control electronics directly on the steering rack.

The company is also focusing on technologies to improve steering feel, keeping power assistance more precisely in phase with vehicle response. The number of interfaces are being reduced to help lower friction and inertia.

“Our system’s low-friction, low-inertia design means that the steering responds as swiftly as hydraulic systems,” said Laurent Bresson, the company’s Executive Director, Europe. He added that the technology would help larger cars and light commercial vehicles achieve reduced CO2 emissions while providing required brand differentiation with regard to performance, feel, and practicality characteristics.

The 2011 Ford Mustang is being fitted with Nexteer EPS, a significant element of a program to enhance the car’s fuel economy and dynamic signature.

As part of its philosophy of continuous improvement, Nexteer has a number of further innovations in the pipeline that reduce mass and increase systems’ functionality. Much of the mass reduction will come from greater functional integration of key components within the system, explained Paul Poirel, Nexteer Chief Engineer, Europe: “For example, incorporating the assist mechanism into the motor housing will make the system around 9% lighter. The more compact unit that will result will also be easier to package.”

A major plank of Nexteer’s future development concerns further exploitation of its in-house-designed software engineering capability. EPS’s torque overlay functions, created via electronic control of the motor to apply torque to the steering system independent of driver input, are regarded as crucial to the introduction of more advanced steering functions.

“They also present significant opportunities for vehicle manufacturers to create additional value for customers and to differentiate their brands,” explained Bresson.

Advances in Nexteer’s control software and the company’s proprietary tuning tools will facilitate greater precision and speed for individual marques in fine-tuning systems. This will allow more freedom to achieve not only brand-specific characteristics but also more flexibility during vehicle development.

Nexteer will be building on considerable, established experience of on-demand column EPS technology. Its first-generation system was selected for the 1999 Fiat Punto and its application spread to other small cars. It also met criteria for higher performance variants, including the Fiat 500 Abarth, Opel Corsa OPC/Vauxhall Corsa VX-R, and Citroën DS3.

“The superior efficiency of EPS compared to hydraulic systems can improve a vehicle’s economy by up to 6%, which typically reduces emissions by up to 8 g/km,” said Poirel, adding that it is also an enabling technology for a host of advanced driver-assistance systems to improve both safety and convenience.

With this aim, Nexteer is now working to develop algorithms in support of functions such as lane pull compensation, lane-keeping assistance, and torque-steer compensation. The company is also examining ways for the steering to work more closely with electronic stability control systems to enhance vehicle controllability and reduce braking distances, particularly on split friction coefficient (split mu) surfaces.

Also looking to the future, the company’s present EPS system has been designed to meet the requirements of hybrid-electric and pure electric vehicles that use high-voltage architecture. Depending on the voltage range involved, Nexteer has stated that it can provide optimized controller designs for the specific requirements of various vehicles.

Nexteer is increasing manufacturing capacity at its Polish facilities at Tychy and Gliwice to support global programs slated for 2013-2014. Tychy, home of the company’s single-pinion EPS manufacturing, is ramping up production to meet requirements for the Lancia Ypsilon supermini. “Precision manufacturing and quality controls are vital in the delivery of systems with consistently good steering feel and low road noise,” said Rafal Wyszomirski, President, Nexteer Automotive Poland.

More than 50 million euros will be spent on the plants to support three substantial programs. At Tychy, the spend is in addition to 40 million euros worth of investment over the past two years and indicates its confidence in the continuing trend within the auto industry of shifting from hydraulic to EPS as part of achieving its targets of lowering fuel consumption and emissions, and moving toward alternative motive systems.

In 2009, Nexteer introduced RFID tagging to increase the traceability of errors and to focus on potential areas of risk in production. The company also uses Centers of Analysis to maintain manufacturing quality standards; mechanical and electronic teams scrutinize any defect and communicate findings to production line teams. The Centers decide whether the solution is the simple application of common sense or if it requires what it designates a Six Sigma or Fast-X application to eliminate sources of variation.

Established in 2010, the Centers work with Innovation and Continuous Improvement Methodologies teams. Said Wyszomirski: “It is too soon to disclose definitive figures, but productivity has so far increased by more than 15%, the number of defects has reduced by over 30%, and the waste has reduced enormously.”

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