All gear-driven, torque-biasing differentials work under the same principles, but the Wavetrac adds a couple of features that address one of the inherent weaknesses in this kind of a system.
First, let’s get through the basic function of a geardriven, torque-biasing differential. It works on the principle of worm gears and worm wheels.
What are those?
A worm gear’s teeth are axially wrapped around a cylinder–picture the tuning pegs on a guitar–and engage the driven component at an angle. That “driven component” is called the worm wheel.
Now let’s introduce some physics. When a turning force is applied to the worm gear, it rotates and drives its interfacing worm wheel.
However, when a twisting force is applied to the worm wheel, it cannot drive the worm gear.
As a result, the worm gear/worm wheel interface is sort of a one-way valve for rotational force.
In a torque-biasing diff, the worm wheels are placed on the ring gear, where they’re driven by the pinion gear. Instead of rotating the worm gears, however, those forces simply push the worm gears and drive the axle.
But when the axles need to move at different speeds, those worm gears can spin the worm wheels, which are connected across the two halves of the axle by spur gears. What happens, in effect, is that torque on the “fast side” of the axle assembly spins the worm gears, which drives the worm wheels on that side of the axle, which eventually drives the spur gears on the “slow side” of the axle. In the end, the forces are pushing the slow side of the axle backward relative to the fast side.
In other words, demon magic.
Here's a good video that shows you how a Torsen works, near the end:
This is an infinite torque bias ratio Torsen which means that it can drive a wheel with zero traction to the opposite wheel without anything like a Wavetrac mechanism, but also that it will easily send all of the power to the inside wheel in a corner, which is obviously not something you'd want in a real car.
This is great video showing how a Torsen works:
Here's their video on a clutch type lsd, for those interested:
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