This paper introduces the structure and working principle of the auto cruise control system, and chooses the PID control strategy based on Atmega 8 microcontroller to realize the stable driving and acceleration and deceleration control process of the vehicle. The system can effectively reduce the working intensity of drivers in long-distance driving, improve comfort, and reduce fuel consumption, which is conducive to environmental protection.
According to the survey, 10% of traffic accidents are caused by fatigue driving and improper operation. The automatic cruise control system described in this paper can effectively reduce driver fatigue, avoid traffic accidents, and benefit the environment. When driving on the expressway for a long time, after opening the automatic control switch of the system, the cruise control system will automatically increase or decrease the throttle opening according to the driving resistance, so as to prevent the driver from frequently stepping on the accelerator pedal to keep the driving speed of the vehicle constant. The fatigue strength of the driver is greatly reduced. Since the cruise control system can automatically maintain the vehicle speed, unnecessary artificial changes of the accelerator pedal are avoided, thereby reducing fuel consumption of the automobile and exhaust gas emissions.
1 Composition of the car cruise control systemThe automotive electronic automatic cruise control system is mainly composed of a cruise control switch, a vehicle speed sensor, an electronic control unit (ECU), an automobile brake switch, an actuator and the like. The components of the electronic automatic cruise control system and the installation of each part in the car are shown in Figure 1.
The structural principles and functions of each part will be specifically described below.
(1) Cruise control switch. When the main switch is turned on, if the vehicle speed is within the range of cruise control (generally 40~200km/h), the “set/slide†switch will be turned off. At this time, the speed will be stored in the RAM, and the car will maintain this speed. Travel. When the driver wants to increase the speed of the cruise, the "recovery/acceleration" switch is turned on, and the cruise control ECU increases the opening of the throttle through the actuator to accelerate the vehicle. At this time, the RAM that stores the actual vehicle speed parameter is stored. The memory is in a dynamic refresh state, and the vehicle speed at the moment when the switch is turned off is stored in the memory, after which the car will drive at a constant speed; when the driver desires a stable vehicle speed to decrease, the "set/slide" switch is turned on, and the cruise control ECU The throttle opening is turned off by the actuator, and the car decelerates and slides. At this time, the RAM memory storing the actual vehicle speed parameter is in a dynamic refresh state, and the vehicle speed at the moment when the switch is turned off is stored in the memory, and then the car will travel at a constant speed.
(2) Cruise control ECU. It is used to receive the signal sent by each sensor, and after calculation and processing, it sends an instruction to the actuator to control the action of the actuator.
(3) Neutral start switch. Used to control whether the car immediately exits the cruise control state.
(4) Brake switch. Installed on the brake pedal for transmitting a brake signal to the cruise control ECU (ie, the driver's step on the brake pedal) to quickly exit the cruise control state.
(5) Vehicle speed sensor. The vehicle speed sensor collects the actual real-time vehicle speed signal as an input to the electronic control unit.
2 How the cruise control system worksFigure 2 is a block diagram of a typical double closed-loop automotive electronic cruise control system. As can be seen from Fig. 2, the input of the controller is the difference between the set fixed vehicle speed signal and the actual vehicle speed feedback signal. The ECU compares the two signals to obtain an error signal, which is amplified and processed to become a throttle control signal, sent to the throttle actuator, drives the throttle actuator to operate, and adjusts the engine throttle opening to correct the actual vehicle speed. Thus, the actual vehicle speed is quickly adjusted to the driver setting. The relationship between the vehicle speed and the throttle opening when the vehicle is traveling on a flat road is usually stored in the ROM of the cruise control system ECU. The cruise control system automatically maintains the car at a constant speed based on the target speed.
When the car is at a constant cruise speed, when the speed of the car decreases, the ECU increases the throttle opening to increase the engine power, increase the torque, and the vehicle speed reaches the set speed. Conversely, reduce the opening of the throttle. When the system performs cruise control, if the vehicle speed is v on a flat road surface, press the setting switch to enter the automatic driving state of the cruise control. When the climb is encountered, the driving resistance increases. If the adjustment control is not performed, the vehicle speed will decrease. At this time, the cruise controller will increase the throttle opening according to certain control rules, so that the vehicle speed is stabilized at v, and the power balance is regained. When encountering a downhill slope, the running resistance is reduced, and the cruise control system adjusts the opening of the throttle to become smaller, so that the vehicle speed is maintained at a balance. Therefore, even if the running resistance changes, the vehicle speed changes only in a small range, achieving the purpose of stable driving. When the vehicle speed exceeds the specified upper and lower limits, the cruise system does not work. The range of the upper and lower limits is not fixed slightly depending on the model.
When the sensor of the system fails or the control signal circuit is cut off, the sensor output is zero. At this time, the vehicle speed exceeds the specified upper and lower limits, and the cruise control system stops working.
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