Cruise control is a feedback control system that helps a car maintain a chosen speed without the driver holding the accelerator pedal. It matters because it reduces driver fatigue, improves speed consistency, and shows how sensors, computers, and actuators work together in modern engineering. A basic cruise control system measures vehicle speed, compares it with a set speed, and adjusts engine power or braking to reduce the difference.
Key Facts
- Speed error = set speed - actual speed
- If actual speed is below the set speed, the controller increases throttle or motor torque.
- If actual speed is above the set speed, the controller reduces throttle and may apply braking in adaptive systems.
- Wheel speed can be found from v = 2πrN, where r is wheel radius and N is wheel rotations per second.
- A feedback loop uses sensor data to continuously correct the car's motion.
- Control response must be smooth because too much correction can cause speed oscillations.
Vocabulary
- Feedback loop
- A process in which a system measures its output and uses that information to adjust its next action.
- Set speed
- The target speed chosen by the driver for the cruise control system to maintain.
- Speed sensor
- A device that measures how fast the vehicle is moving, often using wheel rotation or transmission data.
- Actuator
- A device that turns an electronic control signal into physical action, such as opening the throttle or applying brakes.
- Controller
- The onboard computer or circuit that compares actual speed with set speed and decides what correction to make.
Common Mistakes to Avoid
- Thinking cruise control keeps the accelerator pedal fixed is wrong because the system changes throttle or torque as hills, wind, and road conditions change.
- Ignoring feedback delay is wrong because sensors, computers, and actuators take time to respond, which can cause overshoot if the controller reacts too strongly.
- Confusing basic cruise control with adaptive cruise control is wrong because basic systems hold speed, while adaptive systems also use radar or cameras to adjust distance from vehicles ahead.
- Assuming cruise control replaces safe driving is wrong because the driver must still steer, watch traffic, brake when needed, and respond to hazards.
Practice Questions
- 1 A car is set to 27 m/s but is currently moving at 24 m/s. What is the speed error, and should the controller increase or decrease throttle?
- 2 A wheel has a radius of 0.32 m and rotates 13 times per second. Using v = 2πrN, estimate the car's speed in m/s.
- 3 A car using cruise control reaches a hill and begins to slow down. Explain how the sensor, controller, and actuator work together to bring the car back to the set speed.