Protean 'Inside-Out' Wheel Motor Design: A Company To Watch?

By John Voelcker

John Voelcker

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Brabus Hybrid Mercedes-Benz with Protean Electric wheel motors, EVS-26, Los Angeles, May 2012

Starting a company to build electric cars is tough, as Tesla, Fisker, and others have found out.

Building electric motors is tough, too. It's tougher yet if you intend to turn the traditional design inside out, and build big, powerful, slim wheel motors to be used in large sedans, full-size pickup trucks, and other heavy vehicles.

But Protean Electric is doing just that, and today the company announced it has received $84 million in venture funding from GSR Ventures and the New Times Group, a Chinese industrial conglomerate.

Protean's original venture investor, Oak Investment Partners, is also participating in the new round.

590 lb-ft of torque

Protean's wheel motors weigh 68 pounds apiece, and each one puts out 81 kilowatts (110 hp) and a whopping 590 lb-ft of torque.

This makes them particularly well adapted to both heavy load-carrying vehicles and high-performance cars, those weighing 4,000 to 7,500 pounds.

Those vehicles will be the hardest ones to make efficient enough to meet upcoming fuel-economy standards, and Protean sees a big market opening there.

Its motor is designed to fit inside wheels of 18 to 24 inches in diameter, and is said to allow up to 85 percent of the kinetic energy to be recaptured under regenerative braking.

It also integrates a traditional friction disk brake as well.

Protean in-wheel motor - exploded diagram

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Depending on the size of the battery pack, Protean says its motors can increase fuel efficiency up to 30 percent when an electric powertrain is added to a conventionally-driven vehicle.

Multiple small motors, inside out

But Protean's "secret sauce" is to turn the electric motor inside out and partition it into a series of sub-motors, arranged in a circle, each with its own power electronics.

The stator is on the inside, mounted to the vehicle's suspension and the rear face of the wheel hub, along with the coils, power electronics, and heat sinks.

Individually wound copper coils are mounted to the heat sink on the stator, each one with its own micro inverter.

The rotor is on the outside, fastened to the wheel and the wheel bearing, resembling nothing so much as an old-fashioned brake drum (albeit depicted in bright green in the diagrams and on some prototypes).

Road shocks are carried through the wheel into the wheel hub and absorbed by the suspension, rather than by the wheel motor.

Protean Electric converted Ford F-150 pickup truck, Detroit, October 2010

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Electric F-150

We first encountered Protean at an October 2010 electric-car conference, where their bright green Ford F-150 full-size pickup truck seemed better suited to promoting an energy drink than demonstrating innovative electric motor technology.

But the F-150 was running solely on plug-in power, and we got a few loops around the same drive course where we'd previously driven "Amp'd Equinox" electric crossover conversion from AMP Electric Vehicles.

The big truck was relatively smooth, for a prototype development vehicle, and somehow the smooth silence of electric drive is eerier when you're in a gigantic pickup truck usually powered by a large V-8 engine that struggles to reach 18 or 20 mpg.