Describe the technical architecture of automobile safety system from the details

With the rapid development of China's auto industry and the substantial increase in car ownership, the number of casualties and property losses caused by traffic accidents in China has also increased substantially every year. Naturally, the passive safety performance of cars is increasingly concerned by the Chinese people. Manufacturers are increasingly taking 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 into China. More and more Chinese engineers and R & D personnel have begun to focus on this One area.

Automotive Active Safety System

The safety design adopted to prevent accidents in automobiles and avoid injury to people is called active safety design, such as ABS, EBD, TCS, etc. are all active safety designs. Their characteristic is to improve the driving stability of the car, and try their best to prevent car accidents. Others like high-level brake lights, front and rear fog lights, and rear window defog lights are also active safety designs.

Achieving active avoidance and prevention of accidents requires various sensing and detection systems, such as front and rear vision radar, night vision system, infrared detection, ranging, CMOS / CCD image monitoring, and automatic tire pressure monitoring system (TPMS). The main working principle is that the sensor obtains the required physical analog signal value from the outside world, converts it into a digital signal and then passes it to a specific control unit for analysis, and carries out effective decision-making and preventive measures.

Figure 1 The trend of automobile safety system from passive to active mode

1. Pre-collision system

AWS is the abbreviation of Advance Warning System. It is a driver assistance system for accident prevention and mitigation, which provides drivers with timely sound and visual alarms before dangers occur. At present, road traffic accidents have become an increasingly serious public safety problem worldwide. Statistics show that the driver's human factors have the highest road traffic accident rate. Regardless of the number of accidents. The number of casualties was as high as 90% of their respective totals. and. Among the human factors that cause drivers of these road traffic accidents, fatigue and distracted driving are one of the important reasons. The driver's lack of concentration in 3 seconds caused 80% of the traffic accidents, mainly manifested as lane departure and rear-end collisions. Currently. There are quite a lot of useful explorations both at home and abroad in preventing lane departures and maintaining safe vehicle distances. Some breakthroughs have been made in sensor technologies such as radar, laser, ultrasonic, infrared, and machine vision. After a long period of extensive research and practice, people gradually realized that using monocular vision technology, using only one camera, can achieve the function of the road environment, vehicle detection and distance monitoring to a certain extent. Car element research shows that if a warning is given to the driver 1.5s before the road traffic accident, 90% of such accidents can be avoided. Therefore, by installing a car collision warning system on the car, and using technical means to analyze the driving environment information such as the lane and the surrounding vehicles, once the driver is fatigued and mentally distracted, the car has an unconscious lane departure and the car is too close . When there is a possibility of rear-end collision. Being able to give active early warning to drivers in a timely manner is an effective technical measure to reduce road traffic accidents.

2. ACC adaptive cruise control system

The so-called pre-collision system can only make a series of active preparations before the collision occurs, rather than "prevent" the collision. The rapidly developing ACC (AdapTIve Cruise Control), that is, adaptive cruise control, can partially prevent collision accidents.

ACC belongs to the speed control system for forward driving, and its main function is to control the safe distance between the vehicle and surrounding vehicles. It provides drivers with auxiliary information and suggestions for safe driving through multiple sensors arranged around the body and advanced algorithms of the in-vehicle control system, and sends timely alerts to the driver when a potential danger is detected, or even directly intervenes in the control of the vehicle System to intervene. However, in any case, ACC has only a partial degree of intervention on the brakes, and the driver is still the core of driving.

The key to ACC's speed and distance control is to lock the target vehicle ahead, and then calculate the vehicle's speed, acceleration and other driving information. The owner will set the reaction time for ACC in advance. When ACC is driving, it will calculate the safe distance based on the relative speed of the vehicle and the current distance, and judge the next speed control; and when the distance of the vehicle is too close ACC control range, the system switches to the pre-collision safety handling system.

3. Driving warning system

The driving warning system mainly uses CCD / CMOS and other sensors and imaging devices as monitoring methods, and uses the built-in identification system to determine whether the vehicle status and driver's behavior are normal. If there is a problem, a warning signal is issued in time to avoid accidents. Some driving warning systems can detect the alcohol concentration of the driver's exhaled gas and give appropriate warnings. In addition, the rear and side monitors can also belong to the driving warning system, which can eliminate the driver's visual blind spot and avoid the common collision accidents when reversing.

The functions of the driving warning system mainly include lane departure warning (LDW), driving danger warning, visual blind spot warning (or blind spot detection), etc. The lane departure warning mainly warns the driver when he enters the wrong lane, or prompts him to turn on the turn signal when he changes 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 cannot play its due role. On the other hand, everything has its two sides. If the auxiliary information is too much or too complicated, it is not only not conducive to safe driving, but sometimes it will make the driver tired of handling all kinds of auxiliary information and not concentrate on it, which is easy to cause accidents.

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 are also "sense warning" methods, that is, the car sends information to the driver through the vibration pedal, seat, steering wheel, etc., or attracts its attention.

4. Electronic stability program

The Electronic Stabilization Program (ElectronicStablityProgram) is a traction control system that not only controls the drive wheels, but also the driven wheels. If the rear-wheel drive car often oversteers, the rear wheels will lose control and flick, and ESP will stabilize the vehicle by moderately braking the outer front wheels. In order to correct the tracking direction when the steering is insufficient, ESP will brake the inner rear wheels to correct the driving direction.

With the development of electronic technology in recent years, various automotive intelligent safety systems have also begun to develop, mainly through "predictive sensors" composed of radars and cameras, to judge driving hazards and help drivers deal with them. This system can automatically intervene to ensure safety immediately before the car collides with other objects.

Sensor type and selection

Whether it is an auxiliary prompt system such as a driving warning system or a system control of an electronic stability program, the effective working basis is sufficient and reliable information and the correct and rapid judgment ability of 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 locations on the body of the car according to their specific characteristics and uses, including radar, infrared, LIDAR (Light DetecTIng and Ranging), ultrasound, acceleration sensors, and CCD / CMOS imaging systems.

The main sensors used in the pre-collision system are millimeter wave radar or lidar. 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 relatively low, only about 1/3 of the millimeter wave radar, targeting the low-cost car market. However, in terms of performance, the short wavelength of the laser limits its application range, which is not conducive to the use in harsh environments such as rain and snow.

The infrared and image sensor-based monitor technology is mainly used for obstacle recognition and auxiliary visual field when driving. Infrared imaging can be divided into far infrared (FIR) technology for temperature detection and near infrared (NIR) technology for night vision. FIR can detect organisms with temperature, and it can display the heat radiated by the object as an image; NIR is mainly used for poor sight at night, etc. It can be detected farther than the car light, but it is also susceptible to opposite lights It is mainly used for auxiliary road condition display such as night vision.

If you need to detect the specific conditions outside or even inside the car, you can use CCD or CMOS components as a visual image sensor. At present, the application of CCD / CMOS is becoming more and more extensive. With the advanced visual recognition algorithm, the moving objects in the imaging range, the road surface condition and the friction coefficient, the roadside traffic signals and signs, and the road lane separation line can be distinguished, completely Can become the driver's eyes.

CCD / CMOS can also achieve greater dynamics to express image details in dim and high-contrast environments. This technology is achieved by capturing and synthesizing two high-sensitivity and low-sensitivity images. In addition, if CCD / CMOS is combined with infrared or radar as described above, it can form a sensor (Sensor Fusion). After the infrared generator illuminates the target object, the reflected infrared light is absorbed by the CCD / CMOS, so the road conditions can be recognized no matter the day or night, providing a powerful auxiliary vision for the driver.