Unit07Four-wheelDrive.pptVIP

Unit 7 Four-wheel Drive;Unit 7 Four-wheel Drive;Unit 7 Four-wheel Drive; Four-wheel drive—Usually, when carmakers say that a car has four-wheel drive, they are referring to a part-time system. These systems are meant only for use in low-traction conditions, such as off-road or on snow or ice[2]. All-wheel drive—These systems are sometimes called full-time four-wheel drive. All-wheel-drive systems are designed to function on all types of surfaces, both on- and off-road, and most of them cannot be switched off. ;Torque, Traction and Wheel Slip Torque is the twisting force that the engine produces. The torque from the engine is what moves your car. More torque can be sent to the wheels in first gear than in fifth gear because first gear has a larger gear-ratio by which to multiply the torque[3]. The interesting thing about torque is that in low-traction situations, the maximum amount of torque that can be created is determined by the amount of traction, not by the engine. ; Well define traction as the maximum amount of force the tire can apply against the ground (or that the ground can apply against the tire—theyre the same thing). These are the factors that affect traction: (1)??The weight on the tire—The more weight on a tire, the more traction it has. Weight can shift as a car drives. For instance, when a car makes a turn, weight shifts to the outside wheels. When it accelerates, weight shifts to the rear wheels. ;(2)??The coefficient of friction—This factor relates the amount of friction force between two surfaces to the force holding the two surfaces together. In our case, it relates the amount of traction between the tires and the road to the weight resting on each tire. (3)??Wheel slip—There are two kinds of contact that tires can make with the road: static and dynamic. ;(4)??Static contact—The tire and the road (or ground) are not slipping relative to each other. The coefficient of friction for static contact is higher than for dynamic contact,