How to boost fuel economy in AWD systems

The American Axle & Manufacturing (AAM) Eco Trac system is billed as a way to get the fuel economy of a front-wheel-drive vehicle in an AWD system. Seen here is a cutaway of a Gen1 rear-drive module as might be found on a Jeep Cherokee. When AWD is engaged, the clutch pump generates pressure on the clutch pack which has a torque capacity of about 2,500 Nm. This lets the rear wheels drive a hypoid ring gear and pinion. This action makes the propeller shaft (non-automotive engineers might call this the drive shaft) rotate. This rotates gears within a power transfer unit in the vehicle’s transaxle (not shown). At this point the input gear couples to the input shaft where torque to the rear axle can be modulated based on driver commands. The recently developed Gen 2 module, below, is smaller than Gen 1 and is said to reduce the parasitic losses involved by about 90%
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