Wikipedia
Super Handling-All Wheel Drive or SH-AWD is a full-time, fully automatic all-wheel drive traction and handling system designed and engineered by Honda Motor Company. The company describes SH-AWD as a system "... that provides cornering performance that responds faithfully to driver input, and outstanding vehicle stability. A world's second (after Mitsubishi AWC), the SH-AWD system combines front-rear torque distribution control with independently regulated torque distribution to the left and right rear wheels to freely distribute the optimum amount of torque to all four wheels in accordance with driving conditions." The system was announced in April 2004, and first introduced in the North American market in the second generation 2005 model year Acura RL, and in Japan as the fourth generation Honda Legend.
As first implemented in the Acura RL, SH-AWD allows torque to be continuously distributed between front and rear wheels from 70% front/30% rear to 30% front/70% rear, with up to 100% of the rear power being distributed to the outer left or right wheel to assist in cornering and dramatically reducing understeer. For example, in straight line full throttle acceleration, the RL is capable of distributing 40% of torque to the rear wheels and 60% to the front wheels. In a hard turn, of percentage of power distributed to the rear wheels, up to 100% of the rear wheel power can be distributed to the single, outer rear wheel. This action will push the rear around the corner, and helping with steering, reducing understeer and keeping the car balanced and controlled. The effect can be likened to steering in a row boat where applying more power to one oar can turn the boat.
The SH-AWD all-wheel-drive system was lauded by Popular Science as one of the best automotive innovations of 2004, and as part of an already tech-filled vehicle helped to earn the 2005 "Tech car of the year" from CNET.com.
Honda has since announced an evolution of SH-AWD using hybrid electric technology. In a 2012 announcement, Sport Hybrid SH-AWD (Super Handling All Wheel Drive), replaces the engine powered mechanical drive shaft and clutch packs by two 27 hp electric motors, one on each wheel not driven by the gasoline engine. The first two announced applications of the Sport Hybrid SH-AWD will be on the rear wheels of the 2014 Acura RLX, and on the front wheels of the new Acura NSX Concept.