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Old 08-17-2012, 10:37 AM   #67
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Member#: 299286
Join Date: Oct 2011
Chapter/Region: NESIC
Location: Upstate NY
2017 Legacy Limited


Originally Posted by sgoldste01 View Post
Can someone please explain the difference in Subaru's AWD implementation in CVT-equipped cars vs. 5MT-equipped cars. I know there is a difference (I think my salesperson said that the CVT implementation is more sophisticated/smarter), but I don't recall the details.
Subaru Automatic and CVT use an electronically controlled AWD system that has clutches to engage and transfer power from front to rear. Depending upon who you ask and which car (outback, impreza, etc) the split is 90/10 - 60/40 FWD/RWD power in normal driving.

When the computer senses or predicts wheel slip it sends more power to the rear tires as needed, and this happens quickly.

The 5spd Impreza uses viscous coupling, a hydraulic transfer system. It is normally 50/50 split power distribution, but if the wheels start to slip the fluid in the viscous coupling case heats up, thickens, and transfers more power between the front and rear to be distributed as needed (wheels that are slipping are stopped by the ABS system so wheels with grip take on the extra power).

That's the essence. Some systems like that in the STI are even more advanced and add differentials between the two rear tires to adjust traction and are much more adjustable over all.

I like the simplicity of the viscous coupling system, the electronic clutch system can respond quicker to slippage because it can more efficiently transfer power.

But if you want to irritate CVT Impreza drivers, just remind them their car is mostly FWD most of the time...
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