How does BMW vanos work?

This model shows how BMWs VVT system works, commonly known as VANOS. There is a helical spline cut on the end of the camshaft (green) and an intermediate gear between the camshaft and cam gear grey). This intermediate gear (yellow) has a helical spline on the inside to match that of the cam, and straight cut spline on the outside. When plunger moves it back and forth, the cam angle relative to the crank is phased.