The operating principle and usage precautions of cruise control

Car Encyclopedia Trivia

Cruise Control

Cruise Control_The originator of L0-level automatic driving configuration, how to automatically stabilize the vehicle speed? Standard answer: ECU&ESP! The former is the overall control, and the latter is the foundation. "ECU_electronic control unit" means electronic control unit, generally called "driving computer" or "core controller". Its function is to integrate information feedback from various sensors (including sensors of manual control equipment), analyze and judge the results, and control the engine. A popular description is that all the configurations of the car are just "trigger switches" and "sensors", and the ECU is the brain of the car.

Sensor

The key word of vehicle speed sensor for cruise control is: speed. The control program sets the vehicle speed at a certain node, and the ECU will maintain the current vehicle speed by default. The ECU will combine the vehicle speed sensor to determine the power output of the engine. For example, cruising at 100km/h requires 80PS of horsepower. At this time, the forward gear of the transmission is 6th gear, and the engine will calculate the "speed demand" based on the relationship between "torque and speed". . Assuming that the engine has a maximum torque of 300N·m, the speed can be controlled at around 1900rpm.

Disabled scenes

Automatic restoration of constant speed after deceleration on roads with very low friction coefficients such as icy gravel roads on rainy days will cause a very strong acceleration state. If you are in a hurry on a slippery road, When accelerating, the vehicle may slip and lose control. Although the ESP system can correct the body after a skid, the intervention speed and braking efficiency are not so timely. Therefore, on this kind of road surface where the sliding friction coefficient is only 0.1~0.3, the cruise control function is disabled.

Knowledge Points

The sliding friction coefficient of ordinary paved roads (commercial concrete/asphalt) is 0.9~1.0, and the tamped dirt road will be between 0.6~0.7. On such smooth roads, fixed-speed cruise can be used, and even adaptive cruise can be used. You can also try other ESP-derived functions, such as steep hill descent, electronic handbrake forced braking, and uphill assist functions. However, even smart cars must rely on manual driving in special weather conditions for reference.