MULTIPLE RANGE INDEPENDENTLY DISCONNECTING SMART AXLE

A forward rear drive axle of a vehicle having at least two rear drive axles has a multiple ratio gearbox and a power divider or inter-axle differential that can be connected to or disconnected from the rearward rear drive axle, so that the vehicle can be operated in 6×4 mode or in 6×2 mode. A control system is connected to the transmission and to the multiple ratio gearbox, and is configured to shift the gearbox sequentially through its ratios when the transmission is within a subset of its gear ratios chosen to maximize use of transmission gears exhibiting higher gear train efficiency. The control system is further configured to control the use of 6×4 mode or 6×2 mode independently from the shifting of the multiple ratio gearbox.