TOKYO — Lost in a sea of oddities at the Tokyo Motor Show is a proposal from Nissan Motor Co. Ltd. for a neat and efficient all-wheel-drive system. The company dubs it E4WD and unveiled it in the mm concept (see p.48), which in production will serve as the basis for Nissan's next-generation Micra.
Display in the subcompact mm showcases E4WD's greatest benefit: small size and weight, resulting in easy “packagability.”
E4WD is an on-demand system: When the front wheels slip, only then is a signal transferred to an electronic control unit. The ECU then activates a generator, which produces current for an electric motor. The motor torque drives through a multiplate clutch pack to the rear wheels. The amount of front-wheel slippage is converted to an electric current for the generator, meaning the amount of juice supplied to the rear wheels correlates to the amount of slippage at the front.
Nissan engineers say a big advantage — apart from the fuel-economy savings that comes when all-wheel drive is supplied only when necessary — is that the system requires no expensive, heavy and bulky torque transfer differential, such as a viscous coupling, and also means the elimination of a propshaft running to the rear axle, allowing for better interior space.
Nissan officials say, however, that it has not been decided that E4WD will bow on the next-generation Micra, and they will not commit to when the system may be fitted to a production vehicle.
