What is the function of a torque overlay system in an Electronic Power Steering (EPS) system?

The function of a torque overlay system in an Electronic Power Steering (EPS) system is to provide supplemental steering assist based on various factors, enhancing steering feel and vehicle stability beyond the basic speed-sensitive assist. EPS systems use an electric motor to provide steering assistance, and the amount of assist is typically varied based on vehicle speed, with more assist at low speeds and less at high speeds. A torque overlay system goes further by using inputs such as steering angle, steering rate (how quickly the steering wheel is turned), vehicle yaw rate (rotation around the vertical axis), and lateral acceleration to fine-tune the amount of steering assist. For example, during cornering, the torque overlay system may increase steering effort to provide the driver with better feedback and a more connected feel to the road. It might also reduce assist during emergency maneuvers to help prevent oversteering. The torque overlay system is designed to make the steering feel more natural and responsive, and to improve vehicle stability in various driving conditions, providing a more controlled and confident driving experience.