All-wheel-drive systems work in many different ways. Well, they differ from ...
All-wheel-drive systems work in many different ways. Well, they differ from four-wheel-drive systems in that they don’t have the transfer case that typically provides low-range gearing.
They all can work full time (though many have the axle disconnect feature to preserve fuel), while 4WD systems may or may not be able to work full time.
Today, Jason of Engineering Explained is here to delve into how the AWD system of his Subaru Crosstrek works in the snow.
Jason’s car has the manual transmission, so that means it has the particular type of system within Subaru’s portfolio that differs from what the automaker uses on the automatic transmission versions.
The AWD system with the stick uses the 50/50 torque split front to rear through the viscous coupling. If one of the axles starts to spin, a viscous coupling will send more power to the other axle. Jason Fenske gives examples of 70/30 or even 80/20 torque splits to the axle with more grip.
Both the front and the rear axles have open differentials. There could be the scenario in which one tire on each axle slips. An unsophisticated traction control system would cut a power and use the brakes on both axles and the vehicle wouldn’t be able to move.
To remedy that, Subaru has the limited slip device (not differential) that uses the anti-lock brake system on individual wheels so if the tire on one side slips, the power can go to the other tire on the same axle. And this allows that tire or those tires to keep the car moving.
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