As the market for electric vehicles grows globally, there is an imperative to explore alternatives to permanent magnet traction motors which require the use of expensive and increasingly difficult to source rare earth elements. The Ricardo prototype that we have announced today demonstrates what can be achieved by using the latest electric machine design processes in the creation of a high performing, compact, lightweight, and rare earth element free concept.

—Paul Rivera, MD of the Ricardo hybrid and electric vehicle systems business

CAD model of Ricardo RapidSR motor. Click to enlarge.

Electric traction motors commonly employ permanent magnets made from materials such as neodymium-iron-boron and samarium-cobalt, although there are numerous efforts underway to reduce or to eliminate the use of rare earth elements in these applications (e.g., earlier post, earlier post, earlier post, earlier post). Since switched reluctance motors (SRM) do not use permanent magnets, they could provide an ideal replacement technology.

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, 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.

Ricardo’s prototype has a rotor made from cut steel laminations, which are used to direct and focus the flux across the air gap. By maximizing this flux linkage between the stator and rotor, performance can be optimized within a tightly packaged, low weight and rare earth element free design.

Since its launch in 2012, the RapidSR project has been researching the design of next-generation economic electric motors that avoid expensive and potentially difficult to source rare earth elements typically used in permanent magnets.

By developing effective CAE-led design processes as well as prototype designs, the team has created a framework for the future design and manufacture of electric vehicle motors that offer the performance, compact packaging and light weight required for EV applications, but at a significantly reduced cost compared to permanent magnet machines.

Ricardo’s partners in this research include project leader Cobham Technical Services —which is developing its multi-physics CAE design software, Opera, as a part of the project—and Jaguar Land Rover. The research is being co-funded by the UK’s innovation agency, Innovate UK.

Electromagnetic design in three dimensions. Cobham developed specialist simulation software and a design environment for electric motors to provide a virtual test bench for rapid design and optimization. Source: Cobham. Click to enlarge.

By bringing together state-of-the-art simulation technology with advanced electric machine design we have created a highly credible next generation EV motor concept that shows considerable promise. The Ricardo prototype is now built and will be rigorously tested over the coming weeks in order to validate the extremely positive results that it has shown in simulation, as a concept that provides an exceptional balance of performance, compact package, light weight and low cost.

—Dr. Will Drury, Ricardo team leader for electric machines and power electronics