What is the basic working principle of automobile cruise control system?

The input of the controller is the difference between the following two speed signals: one is the speed signal set by the driver according to the required speed; The other is the feedback signal of the actual vehicle speed. The ECU compares these two signals to obtain an error signal, which becomes a throttle control signal after amplification, and sends it to the throttle actuator to drive the throttle actuator to work, adjust the engine throttle opening and correct the actual vehicle speed, so as to quickly adjust the actual vehicle speed to the vehicle speed set by the driver and keep it constant.

Generally, the relationship between the vehicle speed and the throttle opening is stored in the ROM of the cruise control system ECU. The cruise control system automatically keeps the car at a constant speed according to the target speed. When the car is cruising at a constant speed and the speed drops, the ECU increases the throttle opening, so that the engine power and torque increase and the speed reaches the set speed. Conversely, reduce the throttle opening. When the vehicle speed is lower than 40km/h and higher than 160km/h, the cruise system will not work. Of course, the upper and lower limits are slightly different according to different models.

If the control line is vertical, the fluctuation of vehicle speed (control error) will be reduced to zero. In this way, the slight change of driving resistance will cause the change of throttle opening, and because of the over-sensitive response, it is easy to cause the car to run off. Therefore, it is necessary to comprehensively consider the control error and driving problems and choose the appropriate slope of the control line. Once the sensor of the system fails, or the control signal circuit is cut off, because there is no vehicle speed signal, the low speed limit circuit will think that the vehicle speed is zero and the cruise control system will stop working.