What is the difference between full-time four-wheel drive and on-demand four-wheel drive in sedans?

[VanSavannah]

The difference between full-time four-wheel drive and on-demand four-wheel drive in sedans lies in the driving method: the full-time four-wheel drive system uses four-wheel drive under all conditions; on-demand four-wheel drive is a more intelligent four-wheel drive system. Full-time four-wheel drive distributes driving force to all four tires through a flexibly connected central differential, along with independent front and rear axle differentials. Unlike purely mechanical differential locks, the differential in full-time four-wheel drive can be either a viscous coupling type or a multi-clutch type, but both allow for a speed difference between the front and rear wheels, as well as between the left and right wheels. On-demand four-wheel drive only switches to four-wheel drive when necessary and remains in two-wheel drive mode under other conditions. The system automatically switches between two-wheel drive and four-wheel drive modes based on the driving conditions, without requiring manual intervention.