Scooter Throttle Control

I have to analyze how an electric scooter controls the speed of a motor. When I took the throttle handle apart, there were three wires, green red, and black that were insulated against each other. The throttle handle has a magnet so that when you turn the throttle handle the magnet sweeps across the wires (but not directily touching them), and depending where the magnet is close to the wires, the motor runs at different speed. I was just wondering what type of circuit this is.

Thx.

I have also some chinese scooter, and i've made reverse engineering it and draw sematic. The part is a linear hall-sensor from Allegro, type UGN3503.

You have exactly what I wanted to know. Thank you.