How does cruise control respond when a car reaches a hill?

Conventional cruise control aims to keep a vehicle near a selected speed. It receives a measurement of the vehicle’s current speed and compares it with the target. The difference helps determine a command to the powertrain.

When the vehicle reaches an uphill slope, gravity contributes a force opposing its forward travel. The drive force that was enough on level ground may no longer be enough. If speed begins to fall, the controller can request more driving force to reduce the difference from the target.

For an invented example, a target of 20 meters per second and a measured speed of 18 give an error of 2 meters per second. That number is information for a controller, not a force by itself. A control rule translates measurements and their history into an output command.

The loop repeats while the vehicle moves. Response delays, limited power and steep slopes can prevent exact speed holding. Reducing drive force may also be insufficient on a steep descent. Speed feedback is therefore one useful function with limits; sensing nearby traffic and choosing a following distance require additional systems.