Virtually all electric traction motors currently used in such applications employ permanent magnets made from materials such as neodymium-iron-boron and samarium-cobalt. Since switched reluctance motors (SRM) do not use permanent magnets, they could provide an ideal replacement technology.

Basic mechanism of a SRM. Source: Nidec. Click to enlarge.

In a switched reluctance motor, torque is produced by the magnetic attraction of a steel rotor to stator electromagnets; there are no permanent magnets, and the rotor carries no windings. A controller energizes each stator winding only when it can produce useful torque. With suitable timing of the stator excitation, the machine can operate as a motor or generator. Switched reluctance motors are simple, robust and can offer very good efficiency over a wide load range.

However, one of the main challenges of the project will be to produce a torque-dense motor that is also quiet enough for use in luxury vehicles. While SRMs can have very high power density at low cost, they have had issues with high torque ripple when operated at low speed, and the acoustic noise caused by torque ripple.

As part of its work in the project, Cobham will develop multi-physics software and capture the other partners’ methodology in order to design, simulate and analyze the performance of high efficiency, lightweight switched reluctance traction motors. Using these new software tools JLR and Ricardo will design and manufacture a prototype SRM that addresses the requirements of luxury hybrid vehicles.

Design software for switched reluctance motors is at about the same level as diesel engine design software when it was first introduced. Cobham will develop its existing SRM capabilities to provide the consortium with enhanced tools based on the widely used Opera suite for design, finite element simulation and analysis. In addition to expanding various facets of Opera’s electromagnetic capabilities, we will investigate advanced integration with our other multi-physics software, to obtain more accurate evaluation of model related performance parameters such as vibration. Design throughput will also be enhanced via more extensive parallelization of code and developing an environment which captures the workflow of the design process.

—Kevin Ward, Director of Cobham Technical Services - Vector Fields Software

The project has a three-year timetable, at the end of which improved design tools and processes will be in place to support rapid design, helping to accelerate the uptake of this technology into production.

The project is one of 16 collaborative R&D programs to have won funding from the UK government-backed Technology Strategy Board and the Department for Business, Innovation and Skills (BIS), which have agreed to invest £10 million aimed at achieving significant cuts in CO₂ emissions for vehicle-centric technologies. (Earlier post.)