With the rapid development of China's automobile industry and the substantial increase in car ownership, the number of casualties and property losses caused by traffic accidents in China has also increased significantly each year. The passive safety performance of the car is naturally more and more concerned by the people of the country. More and more manufacturers regard the safety of their products as the focus of publicity. More and more of the world's latest safety technology research results have been introduced to China, and more and more Chinese engineers and R&D personnel have begun to focus on this. A field.
Automotive active safety system
In order to prevent accidents in cars and avoid safety, the safety design, called active safety design, such as ABS, EBD, TCS, etc. are active safety design. They are characterized by improving the driving stability of the car and trying to prevent car accidents. Others like high-position brake lights, front and rear fog lights, rear window defogging lights are also active safety design.
Achieving active prevention and prevention of accidents requires various sensing and detection systems such as front-rear radar, night vision systems, infrared detection, ranging, CMOS/CCD image monitoring, and tire pressure automatic monitoring systems (TPMS). The main working principle is that the sensor obtains the required physical analog signal value from the outside, converts it into a digital signal and then analyzes it by a specific control unit, and makes effective decision-making and preventive measures.
Figure 1. Trend chart of car safety system from passive to active mode
AWS is an acronym for Advance Warning System. It is an accident prevention and mitigation driver assistance system that provides timely sound and visual warning to the driver before the danger occurs. At present, road traffic accidents have become an increasingly serious public safety issue worldwide. Statistics show that the driver's human factors lead to the highest rate of road traffic accidents. No matter the number of accidents. The number of casualties is about 90% of the total. and. Among the human factors that cause drivers of these road traffic accidents, fatigue and mentally dispersed driving are one of the important reasons. The driver's attention during the 3s period was not concentrated, causing 80% of the traffic accidents, mainly in the lane departure and rear-end collision. Currently. At home and abroad, there have been quite a lot of useful explorations in preventing lane departure and maintaining safe distance. Some breakthroughs have been made in radar, laser, ultrasonic, infrared, machine vision and other sensor technologies. After a long period of research and practice, people gradually realized that the use of monocular vision technology, using only one camera, can achieve the function of road environment, vehicle detection and distance monitoring to a certain extent. Vehicle element studies have shown that 90% of such accidents can be avoided if an early warning is given to the driver 1.5s before the road traffic accident. Therefore, by installing a car collision warning system on a car, using technical means to analyze driving environment information such as the condition of the lane and surrounding vehicles, once the driver is fatigued and mentally dispersed, the car is unconsciously deviated, and the distance between the cars is too close. . There is a possibility of a rear-end collision. Being able to give active driving warnings in a timely manner is an effective technical measure to reduce road traffic accidents.
2. ACC adaptive cruise control system
The so-called pre-crash system can only make a series of positive preparations before the collision occurs, instead of "preventing" the collision. The current rapid development of ACC (AdapTIve Cruise Control), that is, adaptive cruise control, can partially achieve collision prevention.
ACC is a speed control system for forward driving. Its main function is to control the safety distance between the vehicle and surrounding vehicles. It provides drivers with auxiliary information and advice for safe driving by means of multiple sensors and in-vehicle control systems arranged around the body, and promptly sends alerts to the driver when potential hazards are detected, even directly intervening in vehicle handling The system intervenes. However, in any case, the ACC only has partial intervention on the brakes, and the driver is still the core of the drive.
The key to ACC's speed and distance control is to lock the target vehicle in front and then calculate the speed and acceleration of the vehicle. The owner will set the reaction time for the ACC in advance. When the ACC is driving, the safety distance will be calculated according to the relative speed of the vehicle and the current distance, and the speed control in the next step will be judged; The control range of the ACC, the system switches to the pre-crash safety processing system.
3. Driving warning system
The driving warning system mainly uses sensors and imaging equipment such as CCD/CMOS as monitoring means. The built-in identification system determines whether the vehicle status and the driver's behavior are normal. If there is a problem, a warning signal is issued in time to avoid an accident. There are also driving warning systems that detect the alcohol concentration of the driver's exhaled gas and give appropriate warnings. In addition, the rear and side monitors can also be part of a driving warning system that eliminates the driver's visual dead angle and avoids common crashes when reversing.
The functions of the driving warning system mainly include Lane Departure Warning (LDW), driving danger warning, visual blind warning (or blind spot detection). Among them, the lane departure warning mainly warns the driver to enter the wrong lane, or prompts him to strike the direction light when changing lanes.
The driving warning system can provide effective auxiliary information for the driver's safe driving, but if the auxiliary information is not comprehensive enough, it will not play its due role. On the other hand, everything has its two sides. If the auxiliary information is too much or too complicated, it will not only be beneficial to safe driving, but sometimes it will make the driver tired of handling various auxiliary information and lack of concentration, which is easy to cause an accident.
In addition, the means by which auxiliary information is sent to the driver is also one of the issues worth studying. Screen display, instrument panel, voice, etc. are traditional means. At present, there is also a "body sense warning" mode, that is, the car sends information to the driver through the vibration pedal, seat, steering wheel, etc., or draws its attention.
4. Electronic stability program
The Electronic Stalbity Program is a traction control system that controls not only the drive wheels but also the driven wheels. For example, in the case of rear-wheel drive vehicles, the over-steering situation often occurs. At this time, the rear wheels will be out of control and the tail will be tailed. The ESP will stabilize the vehicle by moderate braking of the outer front wheels. In case of understeer, in order to correct the tracking direction, the ESP will brake the inner rear wheel to correct the direction of travel.
With the development of electronic technology in recent years, various automotive intelligent security systems have also begun to develop, mainly through the "predictive sensors" composed of radars and cameras to judge the danger of driving and help the driver to handle. This system automatically intervenes to ensure safety before the car collides with other objects.
Sensor type and selection
Whether it is an auxiliary warning system such as a driving warning system or a system control system for electronic stability programs, its effective work is based on sufficient and reliable information and correct and rapid judgment in the background. The key to obtaining reliable information is the sensor and its reasonable distribution; the correct judgment comes from the fast response and reliable algorithm of the control system.
Vehicle sensors are located at different positions of the vehicle body according to their specific characteristics and applications, including radar, infrared, LIDAR (Light DetecTIng and Ranging), ultrasonic, acceleration sensor, CCD/CMOS imaging system.
The main sensors used in the pre-crash system are millimeter wave radar or laser radar. Among them, the price of millimeter wave radar is relatively high, mainly for the high-end car market; while the cost of laser radar is lower, only about 1/3 of the millimeter wave radar, targeting the low-priced car market. However, in terms of performance, the wavelength of the laser is short, which limits its application range, and is not conducive to the use of harsh environments such as rain and snow.
Infrared and image sensor-based monitor technology is mainly used for obstacle recognition and auxiliary field of view during driving. Infrared imaging can be further divided into far-infrared (FIR) technology for temperature detection and near-infrared (NIR) technology for night vision. FIR can detect organisms with temperature, which can display the heat radiated by the object as an image; NIR is mainly used for night vision and other poor line of sight, which can detect farther than the illumination of the lamp, but is also susceptible to the opposite light. The impact is mainly used for auxiliary road conditions such as night vision.
If you need to detect the outside of the car or even the inside of the car, you can use CCD or CMOS components as visual image sensors. At present, the application of CCD/CMOS is becoming more and more extensive. With advanced visual recognition algorithms, moving objects, road conditions and friction coefficients in the imaging range, traffic signals and signs on the roadside, and road lane separation lines can all be distinguished. Can become the driver's eyes.
CCD/CMOS also enables large dynamics to represent image detail in dim and high contrast environments by capturing high-sensitivity and low-sensitivity images and synthesizing them. In addition, the CCD/CMOS can be combined with the infrared or radar described above to form a hybrid sensor (Sensor Fusion). After the infrared generator illuminates the target object, the reflected infrared rays are absorbed by the CCD/CMOS, so that the road conditions can be recognized both day and night, providing the driver with powerful auxiliary vision.
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