Four-Wheel-Drive：四轮驱动.pptVIP

Full-time 4WD Newer computer-controlled designs allow for different operational modes. Ford Automatic Four-wheel-drive (A4WD) Navigator and Expedition 4WD AUTO - full power to the rear wheels. The front wheels receive power as required. 4WD High - Full power to both wheels, no center gear-reduction. 4WD Low - Low gear ratio in center differential for (2:1 ratio) for slow, high torque driving On-demand four-wheel drive - Automatically controlled 4WD. One axle is driven until slip is detected or anticipated. Computer controlled uses wheel speed sensors and/or axle speed sensors to detect slippage. When slippage is detected, torque is sent to the opposite axle. The amount sent depends on the amount of slippage. 4WD Definitions On-demand four-wheel drive 4WD Definitions Viscous coupling in a center differential 4WD Definitions Viscous coupling in a center differential 4WD Definitions On-demand four-wheel drive Ford’s control-trac system normal operation - 96% of torque is sent to the rear wheels. Upon slippage a computer energizes an electro-magnetic clutch in the transfer case. Up to 96% of torque can be sent to the front wheels. 4WD Systems Four-wheel drive systems without a center differential. Tire sizes must all be the same (this holds true for any 4WD application) Tread wear must be similar Tire changes on an all-wheel drive must be done in sets of four Gear ratios should be the same in the front and rear differentials. Front Axle and Hub Service Guidelines Most front axles are serviced like those in 2WD systems Follow the recommended procedure for servicing 4WD hubs Some hubs are not serviceable and must be replaced Effects of Vehicle Modifications Installing larger tires and lift kits Alters vehicle handling by changing unsprung weight Increases steering effort Causes a rough ride May cause vehicle to wander and vibrate Possible driveshaft working angle issues Possible Vehicle Speed sensor issues May necessitate computer programming Maintenance Tips Che