Credit: Protean/ Motor Authority
Between a motor & the road, there are several causes of inefficiency: clutch, torque converter, gearbox, differential. Some of these are not necessary in an electric car (EV), e.g. torque converter & (usually) clutch. By eliminating these components & their inefficiencies, an EV becomes more efficient. Of course, weight savings achieved by eliminating these components further improves efficiency.
Including a separate electric motor for each driven wheel removes the mechanical losses & weight inherent in a differential. Traction control & torque vectoring can also be added without additional mechanical complexity.
Drive shafts can be eliminated along with the inherent weight & mechanical losses by moving the electric motors into the wheel hubs.
http://www.greencarreports.com/news/1083562_protean-launches-production-in-wheel-electric-motor#100425040
http://www.motorauthority.com/news/1083563_protean-in-wheel-electric-motor-to-enter-production-in-2014 / in-wheel electrification unsprung weight power sources source wheel driveshaft efficiency transfer control controlled independently control performance vehicle dynamics drive system traction control launch control torque vectoring implemented software technology concept phase production 2013 Society of Automotive Engineers World Congress volume production plant Liyang China factory 75 kilowatts 100 horsepower 735 pound-feet of torque superior regenerative braking kinetic energy recovered during braking hybrid powertrain system internal combustion engine retrofitted retrofit reduce fuel consumption traction drive /
