Electric motors are round. Wheels are round. It’s a pretty natural impulse to combine the two. No lesser automotive luminary than Dr. Ferdinand Porsche did it first, inventing the wheel-hub motor in 1897. He mounted two of them to his front-driven battery-electric prototype “Lohner-Porsche.” Three years later he invented the gas-electric hybrid by fitting four hub motors to his elaborate four-ton “Mixte” coach. The one tiny rub: Those 14-hp motors weighed around 320 pounds. Each.
Modern materials and engineering have enabled dramatic improvements. For about seven years, Protean Electric has been selling a 100-hp hub motor that weighs just 68 pounds. So why do all volume-produced EVs still mount their motors inboard? To minimize unsprung weight for optimal ride quality.
Enter Silicon Valley inventor and serial startup founder Marcus Hays and co-inventor Scott Streeter. They wondered if it might be possible to develop a wheel and motor system that weighed no more than a conventional aluminum wheel. As folks in their neighborhood so often do, Hays, Streeter, and the Orbis Wheels team looked to disrupt as many paradigms as possible. Without the gear reduction of a body-mounted motor, a hub motor needs high torque to act through the 1-foot lever arm from the hub to the contact patch. Wheels then need hefty structure to transmit these acceleration, braking,
and cornering forces between the hub and the rim.
Hays’ radical solution: do away with the hub entirely and power the rim.
Mass, cost, and rotational inertia instantly plunge with this approach. Mounting the motor so that it drives a rim-mounted ring gear (via a small pinion shaft) lowers the required torque to get the wheel spinning. It also greatly increases the electric motor’s top speed. And guess what? Motors wound for high rpm instead of high torque, like those on a drone copter, can deliver the same power as high-torque motors using vastly less copper and hence weighing one-twentieth as much. Bam—a cost- and weight-savings twofer.
How does a hubless wheel connect to the car? Traditional suspension links attach to a carrier that supports the motor, brake caliper, and a triangular wheel-bearing system. The car’s weight bears on two pairs of rollers located at the 5 and 7 o’clock positions on the rim; a third set at 12 o’clock keeps the wheel from tilting. The inner and outer bearing race surfaces on the rim are angled to transmit side forces when cornering, and PTFE anodizing of the aluminum rim and Delrin rollers negates the need for lubrication. Hays says his 9.5-by-20-inch prototype Civic Type R rear wheels (below) exhibit one-fifth the dynamic friction and 13 percent less rotational inertia than Honda’s wheel. Covers and seals are expected to exclude debris, and typical air-cooled automotive-grade DC motors are tolerant of occasional, temporary submersion in water. I worry about those bearings and am eager to study the durability-testing results once Orbis fits motors to the Civic wheels.
Another ring-wheel benefit is that a large-diameter brake rotor positioned out nearer the tire contact patch greatly reduces the required brake force. That means less heat is generated and thus brake components can be smaller and lighter. Between this and the friction reduction, Orbis thinks this tech makes nondriven Orbis wheels ideal for F1 and Formula E.
Orbis installed small ring wheels powered by skateboard motors on a Chinese Dongfang electric scooter. Each weighs 20.6 pounds versus the stock wheel/motor’s 42.1 pounds. Performance and energy consumption were nearly identical, but Orbis’ gear drive is a tad noisier—64 dB versus 61. With batteries downsized for equivalent range and performance, the 2WD scooter weighs 100 pounds less than the original.
Cake icing: Hays reckons the cost of a ring-wheel-driven powertrain could be 25 percent less than that of a conventional EV. Orbis seeks to license the technology, assisting with prototype design and development. It has civilian and military projects ongoing—and if we’re lucky, a kit to add 140 hp and 232 lb-ft of electric drift inducement to the rear of a Civic Type R.
Read more by Frank Markus here:
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- Nissan Researches Mind-Over-Motor Technology
- Is the Era of the Camless Valvetrain Finally Upon us?
- Proactiv for Road Acne: A New Cure for Autonomous Car Sickness?
- Borla’s Pipe-Organ Tech Gets Your Car Riffing Like AC/DC
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