Active Yaw Control (AYC) is an automobile feature that uses an active differential to transfer torque to the wheels that have the best grip on the road (torque vectoring). Unlike traditional mechanical limited-slip differentials, an AYC is electronically controlled.
AYC was designed by Mitsubishi Motors, first introduced in the Mitsubishi Lancer Evolution IV. It has been included in certain models of every subsequent generation, and was also used in the VR-4 variant of the eighth generation Mitsubishi Galant sedan and Legnum wagon. Later developments led to S-AYC (Super-Active Yaw Control), first introduced on the Evolution VIII, utilizing a planetary gearset which could support an even greater torque bias than the previous system. AYC and S-AYC have also been seen in several Mitsubishi concept cars based on the underpinnings of the Lancer Evo, such as the CZ3 Tarmac and Tarmac Spyder, the Montero Evolution, the RPM 7000, and the Concept-X.
Active yaw control is based on a computer-controlled rear differential which can actively split torque based on input from various accelerometers in the vehicle measuring longitudinal and lateral g forces, steering, brakes and throttle position. Where ABS brakes are fitted they too are included in the input parameters. It accomplishes this via two hydraulic clutches which can limit torque on individual axles. This system should not be confused with stability control systems which utilize the braking system of a vehicle by individually braking certain wheels to rotate and slow the car (such as Electronic brakeforce distribution). AYC is a performance-oriented system which aims to increase cornering speeds.
The BMW Active Yaw Control is called Dynamic Performance Control.