New modelling tool simplifies development of next-generation automotive power steering

A new magnetic solver for electric motor and design has been released by Vector Fields, a business unit of Cobham plc. The tool’s ability to accurately characterise effects provides a powerful means to optimise the performance and fidelity of new-generation electrically-assisted automotive power steering systems, and other high-performance actuators.

An automotive power steering motor must meet demanding specifications including the minimization of torque required to turn a motor’s rotors when the coils are not energized – an effect known as ‘drag-torque’. Employing specialty electrical steels in the motor laminations provides one means of minimising drag torque, and the new design tool from Vector Fields provides the means to quickly and accurately design and characterise this aspect of performance before prototype products are built.

The technology behind the new solver was developed as part of the recent ‘Advanced Electric Machines through Materials’ project sponsored by the UK’s Technology Strategy Board. During this project, the automotive component supplier TRW – known for pushing the boundaries of technology for electrically-assisted power steering systems – provided Vector Fields with real-world measurement data to verify the accuracy of the new model.

The modelling of hysteresis effects in soft magnetic materials is a complex problem that design tool suppliers have largely ignored, with the result that machine designers are forced to neglect remanent magnetic fields that are created by the pulsing or rotating actions of dynamic machinery. If hysteresis effects are considered, it’s usually done by means of some post-processing prediction based on a simplistic model.

In the drive towards higher efficiencies, many motor designers are now employing more efficient ferromagnetic alloy materials for laminations. Vector Fields’ new hysteresis solver provides the means to accurately simulate the dynamic performance of these materials. In conjunction with the sophisticated design-simulate-optimize capability offered by Opera’s finite element analysis toolchain, developers can accurately understand the improvements that electrical steels can make, as well as explore design ideas that minimize hysteresis effects. This approach speeds time to market and reduces costs, and allows optimum design decisions to be made to meet a developer’s particular performance, cost and manufacturability criteria.

The hysteresis solver is available as part of Vector Fields’ general-purpose Opera simulation toolsuite for static and transient electromagnetic design, or can be used in conjunction with Vector Fields’ application-specific tool for motor and generator design — Opera Electrical Machines . Among the product sectors that can be enhanced using the tool are dynamic electrical machinery such as motors and generators, as well as actuators and transformers.

“Future improvements to products such as power steering motors will undoubtedly rely heavily on design optimisation, and in today’s competitive business , sophisticated design automation support is becoming the practical way to achieve it,” says Alex Michaelides, Business Development Manager at Vector Fields.

Vector Fields’ new hysteresis solver is based on actual measured magnetic induction, and applied field characteristics. The turning points of the trajectory are used to predict the behaviour of arbitrary minor hysteresis loops, providing a good approximation of true physical behaviour without requiring extensive computation, and additionally making only realistic demands for materials data. The tool is provided with ready-to-use characteristics for some common silicon steel materials. This library can be expanded easily using data from a manufacturer’s datasheet, or from measurements using an Epstein Frame – the standardised device for measuring the magnetic properties of electrical steels. Magnetic test services are available commercially from a number of companies including .

The new hysteresis solver complements Vector Fields’ long-standing DEMAG electromagnetic modelling software for simulating the characteristics of permanent or hard magnet materials. This solver allows designers to optimize equipment designs by accurately simulating both the magnetization process, and the subsequent demagnetization effects that might be encountered, and is widely used by magnet suppliers and producers.

In March 2009, Vector Fields will start to market itself as Cobham Technical Services, as part of a Cobham programme to align all business units under one brand.