A central component in four-wheel drive (4WD) and all-wheel drive (AWD) vehicles, this unit is a gearbox-like assembly that connects the transmission to both the front and rear axles. Its primary function is to distribute power from the transmission to these axles. It allows the vehicle to operate in two-wheel drive for fuel efficiency on normal roads and switch to four-wheel drive for enhanced traction in challenging conditions such as snow, mud, or off-road terrain. An example of its operation involves shifting from two-high to four-high to engage both axles for increased grip.
The inclusion of this mechanism offers significant advantages. It improves vehicle handling and stability on slippery surfaces, increasing safety and control. It enables access to areas inaccessible to two-wheel drive vehicles, expanding the vehicle’s utility. Historically, these units were mechanically operated, requiring manual engagement. Modern systems often employ electronic controls, allowing for automatic or on-demand activation, improving ease of use and responsiveness.