Better electric motors can boost electric-car efficiency


Electric motor, shown in 'How Does an Electric Car Work?' video by Learn Engineering

Electric motor, shown in 'How Does an Electric Car Work?' video by Learn Engineering

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One of the greatest challenges faced by modern electric cars is the vehicle's range, which is largely proportional to the energy capacity of the battery. 

Range anxiety often keeps buyers out of electric cars and in their fossil-fuel powered counterparts.

Most of the attention given to solving the range dilemma has focused on the battery, but one key to more efficient electric cars may sit with the electric motor.

DON'T MISS: Video explains how electric cars work, battery and motor technology included

IEEE Spectrum detailed a conceptual electric motor that may unlock the potential for greater efficiency.

In fact, the motor design could even extend the range of electric cars currently on sale.

The basic idea is to tweak the magnetic fields in a "hybrid" design of sorts.

Tour of Tesla battery gigafactory for invited owners, Reno, Nevada, July 2016

Tour of Tesla battery gigafactory for invited owners, Reno, Nevada, July 2016

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The innovation is to combine the technology found in a traditional permanent-magnet synchronous machine—which uses permanent magnets embedded in the rotor—with that of a salient-pole synchronous machine.

The latter uses electromagnets inside the rotor, rather than permanent ones.

By combining the best of both motors, the design increases the efficiency of the motor significantly.

READ THIS: Plug-in hybrid problem: buyers don't understand them at all

The PMSM and SPSM motors reach peak efficiency at different times, which means the overall benefit isn't found simply by combining them.

Instead, the new conceptual motor has been reengineered so each type of motor peaks in efficiency at the same time.

However, this is no easy task, and the downside is reduced torque output when the motor works as a generator to slow the vehicle and turn otherwise wasted momentum back into battery energy.

Battery storage system electrified by BMW i

Battery storage system electrified by BMW i

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The conceptual motor uses wires and permanent magnets to create the necessary magnetic field.

But, the design issue rests in finding a rotor construction capable of shaping the fields appropriately.

It must also be sturdy enough to run at high speeds and not come apart.

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The concept motor uses rotor lamination, which carries the copper winding on an iron core.

The permanent magnets are glued to the shoulders of the poles and "additional nibs on the poles prevent them from ... flying away."

To overcome the loss of torque, the direction of the field can be altered to allow for more powerful regenerative braking that matches regular motor operation.

Charging Chevy Bolt EV before trip across Maryland [image: Brian Ro]

Charging Chevy Bolt EV before trip across Maryland [image: Brian Ro]

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Over its operating range, the motor requires 4.4. percent less energy—meaning roughly a 5-percent boost in the miles that could be delivered by any given battery capacity.

So, when will these new motors start showing up in production electric cars? Not for some time yet.

The new design has garnered interest, but mass deployment is likely years away.

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