AWD
All Wheel Drive
This is a type of driving which drives all four wheels to propel vehicle. Griping force between road surface and tire is much better than two wheel driving system, therefore a driver can keep the vehicle stance very stable during conering, slippery road surface or on the snowy road. As seen in the picture, there is one more differential (Center Differential) in the drive train to keep the torque balance even between front and rear wheels. The torque from the engine will reach directly to the center differential through transmission.
Of course there is a slight sacrifice in terms of fuel economy. Some type of car has a shift lever which can select 2WD or 4WD. Vehicle manufacturers have their own term of AWD, such as, Quattro of Audi, 4Matic of Daimler, X-Drive of BMW.
