Continuously Variable Transmissions for Torque Vectoring in Automobiles

Tyler Chilson

Torque vectoring technology applied to automobiles allocates torque from the transmission to a specific wheel or set of wheels in order to achieve various dynamic goals such as improving handling, stability, or driver feel. This concept is typically achieved through an advanced differential or with independent wheel brakes. While these mechanisms perform adequately, they all utilize some type of brake or slipping clutch that fundamentally dissipates energy. This paper introduces the novel concept of using continuously variable transmissions (CVT) in series with an open differential to control wheel-torque without relying on a resistive element.  

A model reference vehicle with idealized road conditions is used to generate a target yaw rate for the “real” vehicle so that a Youla controller can act on the two CVTs to match the desired yaw rate. Bond graphs are used to model the vehicle and drivetrains, and produce equations of motion to simulate through MATLAB and Simulink. The CVT model is tested against two different drivetrains–a standard open differential (SOD), and a clutch based torque vectoring differential (TVD). The SOD model is used as a baseline for performance while the TVD is used for comparison to the current industry standard. An additional model, CVT*, which adds in clutch activated reverse gears to apply negative torques to a given wheel when desirable, is also tested. It is shown that the CVT models can improve handling, stabilize in non-ideal road conditions, and help reject wind gusts while using less energy than the TVD model.

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