The electric hub motor has been around for a long time. Ferdinand Porsche’s first automobile in 1898 was the Lohner-Porsche with two electric motors in the front wheel hubs. Initially, electricity was supplied from batteries and later by batteries and a gasoline engine-driven generator, in what is considered the first hybrid electric vehicle. While there has been on-and-off interest in hub drive systems, there are currently two programs underway that could lead to production vehicles within a couple of years.
One of the big challenges has been the substantial unsprung weight that can degrade ride quality and handling. This can be overcome by lighter weight motors and other components that are now available. For example, Ford has shown its Fiesta eWheelDrive prototype developed with Schaeffler Technologies in Germany. The two Schaeffler eWheelDrives are housed within the 16-inch rear wheel rims. Each highly-integrated wheel hub drive contains an electric motor, power electronics, controller, brake system, and liquid cooling system.
Each motor supplies a peak 54 horsepower or 44 horsepower continuous output to a rear wheel. The motor produces 516 lb-ft of torque. The highly-integrated wheel hub drive has a total weight of 117 pounds, only 17.6 pounds more than a conventional wheel including its wheel bearing and brake components.
The Fiesta eWheelDrive installation is just a technology demonstrator. Ford and Schaeffler feel the ideal application is in city cars for use in crowded urban areas with limited parking. Everything, with the exception of batteries, needed to propel and brake the car is located in the wheel. Thus, the space now needed for the engine and transmission or electric motor in an EV can be used for passengers and luggage. Indeed, it could mean a four-person car that takes up no more parking space than a current two-person car. The eWheel- Drive steering system could even allow moving sideways into parking spaces.
Despite its somewhat higher wheel-sprung masses, extensive testing has shown the Fiesta eWheelDrive exhibiting driving behavior equal to a conventional Fiesta in terms of comfort and safety. The two wheel hub drive motors also allow torque vectoring for enhanced maneuverability in tight spaces. Ford, Schaeffler, and other partners plan on producing two more drivable vehicles by 2015.
Protean Electric, based in Britain, has been developing hub drive motors for years and plans volume production of its Protean Drive system in China this year. It showed its in-wheel electric drive system on a BRABUS hybrid vehicle at Auto Shanghai 2013. The BRABUS Hybrid, based on the Mercedes-Benz E-Class, is powered by an internal combustion engine driving a generator and two Protean electric drive motors, one in each of the rear wheels. Protean had also demonstrated Protean Drive in a Vauxhall Vivaro cargo van, Guangzhou Trumpchi sedan, Ford F150 pick-up, and a BRABUS full electric vehicle also based on the Mercedes-Benz E-Class.
The Protean PD18, designed to fit inside an 18 x 18 inch wheel rim, provides 735 lb-ft torque and 100 horsepower. This is a 25 percent increase in peak torque compared with the previous generation design. Thus, it is powerful enough to be the only source of traction drive in electric vehicles. The unit only weighs 68 pounds per motor.
Each Protean Drive has a built-in inverter, control electronics, and software. The design can be used in small- to full-size vehicles including application in current vehicle platforms, retrofits to existing vehicles, or in all new vehicles. Protean says it recoups up to 85 percent of the available kinetic energy during regenerative braking. Compared to other electric vehicle drive systems, in-wheel motors apply regenerative braking directly at each wheel independently, similar to standard friction brakes.