Tier 1 electric power steering (EPS) specialist Nexteer has developed a flexible electronic architecture designed to allow OEMs to adapt and upgrade vehicle platforms throughout their production life cycle.
It uses a building-block principle so that it can be scaled to suit different vehicle types, mechanical layouts, and levels of functionality. Equipped with what the company describes as a simplified control platform, it can support a low-cost system for economy cars and emerging markets but has the flexibility to add advanced features for premium vehicles.
“The benefits for a vehicle’s CO2 emissions and fuel economy are driving the adoption of EPS,” said Laurent Bresson, Nexteer Automotive’s Senior Vice President Global Sales and Marketing and Chief Operating Officer International Division. “Developments in EPS electronics and software will provide functions that not only improve safety but also the driving experience and the user’s perception of the vehicle characteristics. Having customizable electronic architectures that can adapt to different customers and market requirements will be critical.”
He added that EPS suppliers usually provide standardized electronic architectures, which can reduce application engineering costs but are often over-specified.
The development of electronic architectures for EPS takes place in a changing environment, driven by a number of related factors plus the introduction of new safety standard ISO 26262, which places additional emphasis on the demonstration of robustness. Compliance is important to vehicle manufacturers who have to demonstrate the thoroughness of their approach to development.
Bresson explained that at one time, only two or three functions were required from an EPS system, whereas today it is normal to expect up to 20, which increases the communication requirements on the system.
Compatibility with dual CAN bus and FlexRay allows the integration of real-time control of the steering with input from other sources around the vehicle, making a number of complex control functions possible such as lane-keeping assistance, pull compensation (to counteract road camber effects), and wheel imbalance rejection (to filter wheel vibrations).
Nexteer’s architecture contains an ECU (electronic control unit) that is divided into a series of separate elements, such as the CPU (central processing unit) section, power section, sensor section, and relay section. Built up from proven, cost-effective standard components, each block is future-proofed against anticipated hardware changes from suppliers.
Developments are progressing that will allow EPS to play an even greater role in the dynamic control of the vehicle, believes Bresson. Braking on split-mu surfaces, where tire adhesion fluctuates, can be improved by integrating the steering control with wheel brake control, reducing both path deviation and braking distance, he says.
Yaw stability control can enhance vehicle safety during aggressive maneuvers that would otherwise risk extreme oversteer. “An algorithm in the Nexteer software can apply a suitably timed torque overlay to the steering, restoring yaw stability before the driver exceeds the limits of the vehicle. Though lower in authority than brake intervention, the steering intervenes much quicker, adding an extra layer to the safety performance,” said Bresson.
Nexteer has also developed a torque-steer compensation algorithm for high-powered, front-wheel-drive cars that corrects deviations from the driver’s intended path during hard acceleration, without the cost or mechanical constraints imposed by engineering equal-length driveshafts.
First full implementation of the new electrical architecture enters production in 2013.