Electronics architecture for electric power steering systems

July 20, 2012 // By Betram Möller, Nexteer Automotive
Functional safety systems, such as steering and braking, provide particular challenges for electronics platform designers. Demand for added functions, compliance with new safety standards and compatibility with new communications protocols are increasing the pressure on existing architectures, like FlexRay for example. To future-proof its systems, Tier One electric power steering (EPS) supplier Nexteer Automotive has developed a flexible but cost-effective architecture that addresses the many challenges.

The introduction of new safety standard ISO 26262 (“Road vehicles – Functional safety”) increases the emphasis on the demonstration of robustness, with compliance made more important in an environment where zero defect is standard. Starting in 2011, all developments of new cars have to be aligned to this standard. This, along with sharp increases in the number of electronic functions, new communications protocols and the introduction of standardized Autosar software, increases the amount of memory and processing speed that steering systems require.

The conventional approach to cost-effective manufacture is to increase the volumes of standardized units, increasing component purchasing power and supporting investment in the most efficient production processes. Minimal component variation also drives up quality throughout the supply chain and makes control of stock levels more robust.

However, the increasing diversity of the automotive market inevitably means that, in many applications, a standardized system will carry features required only by certain customers, resulting in over-specification of the product and making cost-effective design more difficult. The alternative strategy, developed by Nexteer, is a modular approach based on building block architecture.

The ECU is divided into a series of separate elements, such as the CPU section, power section, sensor section and relay section. The block architecture eliminates the repetition of basic design work for each new application, building up the system instead with proven, optimized elements. This approach results in detailed knowledge and high levels of expertise in the individual blocks, their capabilities, limitations and how best to optimize them. Design effort can instead focus on cost reduction, system performance increases and design improvement.

Nexteer uses common circuits, configured in a custom board layout for each application. Its components are standard, commercially available and automotive-grade. The printed circuit board can be built on almost any electronics assembly line with appropriate fixturing and controls. Packaging and final assembly takes place in-house at a Nexteer plant.

In application, the building block strategy means

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