How SH-AWD works: Acura’s AWD system explained
Have you been wondering how the Acura SH-AWD system differs from other “Haldex style” AWD systems? In this video I explain how Super Handling All Wheel Drive differs from Audi’s Quattro, BMW’s x-Drive and the other transverse AWD systems on the market.
Aside from the fact that Honda/Acura doesn’t have a RWD drivetrain to borrow, the benefit main benefit to a transverse engine layout is improved interior packaging.
“Super Handling All Wheel Drive” may not have been the best name for the system, but it is arguably the best AWD system you can tack onto a transverse FWD platform. The systems used by Infiniti, Lexus, Volvo, Lincoln and just about everyone out there that had an AWD system tacked onto a transaxle has no center differential. Instead the power flows from the final gearset of the transmission to the front diff and the rear diff via gears at a fixed 1:1 ratio. Between this gear arrangement and the rear diff is a clutch pack that allows the car to connect, disconnect or have a varied connection between the transmission and rear axles. When fully connected the power is split 50/50 assuming all wheels have traction.
SH-AWD also uses the same arrangement but adds a unique differential unit in the rear that does two things. First, it has a gearset to “speed up” the rear wheels so that when they are connected, they spin 1.7% faster than the fronts. (The old RL used a variable ratio system but it is no longer used.) Next it has a torque vectoring unit that is capable of slitting power 100:0/0:100 left to right. In a straight line, “overdriving” the rear wheels gives the MDX a more RWD feel than otherwise possible and in corners the system is capable of sending up to 70% of the power to the outside rear wheel helping the MDX’s cornering manners and masking the “plowing” tendencies normal in a front heavy car. For 2014 Acura took this a step further and uses a system to brake wheels selectively to improve neutral handling. This is beyond stability control because the system is always active rather than active only when things are going pear-shaped.
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