Explain the technical architecture of automobile safety system from details

    With the rapid development of China's automobile industry and the substantial increase in the number of cars, the number of casualties and property losses caused by traffic accidents in my country has also increased significantly each year. The passive safety performance of automobiles has naturally attracted more and more attention from the Chinese people. Manufacturers are also increasingly focusing on the safety of their products. 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 field.

　　Automotive Active Safety Systems

　　Safety designs adopted to prevent car accidents and avoid injuries to people are called active safety designs, such as ABS, EBD, TCS, etc. They are characterized by improving the driving stability of the car and trying to prevent accidents. Other features such as high-mounted brake lights, front and rear fog lights, and rear window defogger lights are also active safety designs.

　　Actively avoiding and preventing accidents requires various sensing and detection systems, such as front and rear radars, night vision systems, infrared detection, ranging, CMOS/CCD image monitoring, and tire pressure monitoring systems (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 sends it to a specific control unit for analysis, and makes effective decisions and preventive measures.

　　

　　Figure 1 The trend of automobile safety systems from passive to active

　　1. Pre-collision system

　　AWS is the abbreviation of Advance Warning System. It is a driver assistance system for accident prevention and mitigation, providing timely sound and visual warnings to drivers before danger occurs. At present, highway traffic accidents have become an increasingly serious public safety issue worldwide. Statistics show that the rate of highway traffic accidents caused by human factors of drivers is the highest. Both the number of accidents and the number of casualties are as high as about 90% of the total. Moreover, among the human factors of drivers that lead to these highway traffic accidents, fatigue and distracted driving are one of the important reasons. The driver's lack of concentration within 3s caused 80% of the traffic accidents, mainly manifested as lane departure and rear-end collision. At present, both at home and abroad, a lot of beneficial explorations have been carried out in both preventing lane departure and maintaining safe vehicle distance, and 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 have gradually realized that the use of monocular vision technology, using only one camera, can achieve the functions of front road environment, vehicle detection and vehicle distance monitoring to a certain extent. According to the research of the car element, if the driver is warned 1.5 seconds before a highway traffic accident occurs, 90% of such accidents can be avoided. Therefore, by installing a car collision warning system on the car, using technical means to analyze the driving environment information such as the lane and the condition of surrounding vehicles, once the driver is tired and distracted, the car has an unconscious lane deviation, and the distance between cars is too close, there is a possibility of rear-end collision. Being able to give the driver active warning in time is an effective technical measure to reduce highway traffic accidents.

　　2. ACC Adaptive Cruise Control System

　　The so-called pre-collision system can only make a series of active preparations before a collision occurs, but it cannot "prevent" the occurrence of a collision. The rapidly developing ACC (Adaptive Cruise Control) can partially prevent collision accidents.

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

　　The key to ACC's speed and distance control is to lock onto the target vehicle in front and then calculate the vehicle's speed, acceleration and other driving information. The owner will set the reaction time for ACC in advance, and ACC will calculate the safe distance based on the relative speed and current distance of the vehicle while driving, and determine the next speed control; and when the vehicle is too close and beyond the control range of ACC, the system will switch to the pre-collision safety processing system.

　　3. Driving warning system

　　The driving warning system mainly uses sensors and imaging devices such as CCD/CMOS as monitoring means, and uses the built-in recognition system to determine whether the vehicle status and the driver's behavior are normal. If there is a problem, a warning signal will be issued in time to avoid accidents. Some driving warning systems can also detect the alcohol concentration in 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 spots and avoid common collision accidents when reversing.

　　The functions of the driving warning system mainly include Lane Departure Warning (LDW), driving hazard warning, visual blind spot warning (or blind spot detection), etc. Among them, the lane departure warning mainly warns the driver when driving into the wrong lane, or prompts the driver to turn on the turn signal 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 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 will not only be unhelpful to safe driving, but sometimes it will make the driver tired of dealing with various auxiliary information and lose concentration, which is easy to cause accidents.

　　In addition, how the auxiliary information is sent to the driver is also a question worth studying. Screen display, dashboard, voice, etc. are traditional means, and there is also a "body sensing warning" method, that is, the car sends information to the driver or attracts his attention by vibrating the pedals, seats, steering wheels, etc.

　　4. Electronic Stability Program

　　The Electronic Stability Program is a traction control system that controls not only the driving wheels but also the driven wheels. For example, in the case of oversteering, which often occurs in rear-wheel drive vehicles, the rear wheels will lose control and the vehicle will drift. ESP will stabilize the vehicle by moderately braking the outer front wheels. In the case of understeering, in order to correct the tracking direction, ESP will brake the inner rear wheel to correct the driving direction.

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

　　Sensor types and selection

　　Whether it is an auxiliary prompt system such as a driving warning system or a system control such as an electronic stability program, its 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 rapid response and reliable algorithm of the control system.

　　Vehicle sensors are located in different positions on the vehicle body according to their specific characteristics and uses. They mainly include radar, infrared, LIDAR (Light Detecting and Ranging), ultrasonic, acceleration sensor, CCD/CMOS imaging system, etc.

　　The main sensors used in the pre-collision system are millimeter-wave radar or laser radar. The millimeter-wave radar is more expensive and mainly targets the high-end car market; while the laser radar is cheaper, only about 1/3 of the millimeter-wave radar, and targets the low-priced car market. However, in terms of performance, the laser has a short wavelength, which limits its application range and is not conducive to use in harsh environments such as rain and snow.

　　Monitor technology based on infrared and image sensors is mainly used for obstacle recognition and auxiliary vision during 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 objects as images; NIR is mainly used in conditions with poor visibility such as nighttime, and can detect farther than the distance of car lights, but it is also easily affected by the lights on the opposite side, and is mainly used for auxiliary road condition display such as night vision.

　　If you need to detect the specific situation outside or even inside 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 widespread. With advanced visual recognition algorithms, moving objects, road conditions and friction coefficients, roadside traffic signals and signs, road lane dividers, etc. within the imaging range can be visually identified, which can completely become the eyes of the driver.

　　CCD/CMOS can also achieve greater dynamics to show image details in dim and high-contrast environments. This technology is achieved by capturing high-sensitivity and low-sensitivity images and synthesizing them. In addition, if CCD/CMOS is combined with infrared or radar as mentioned above, it can form a hybrid 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 identified regardless of day or night, providing the driver with powerful auxiliary vision.

    System architecture analysis

　　The principles of various warning and response systems such as pre-collision processing, safe speed/distance control, etc. in automobile safety systems are very similar, that is, after the ECU (central electronic control unit) receives relevant information from external sensors, it uses built-in algorithms to conduct real-time evaluation and determine the best response measures. Therefore, the design of automotive electronic systems is not much different from general system design, but hard real-time and reliability are the significant features that distinguish them from other electronic control systems.

　　First, let's take the airbag control system as an example. The system mainly consists of airbags in front of the driver and passengers, collision sensors (Satellite Sensor) located outside the car body, acceleration sensors (G-Sensor) placed in the doors, seats and roof, and ECU, which is usually a 16-bit or 32-bit MCU. When the car body is hit, the collision sensor will immediately send a signal to the ECU, which will collect parameters such as collision intensity, seat position, passenger weight, seat belt status, etc. for rapid evaluation, and open the airbag through the squib driver in a very short time to protect the safety of the people in the car.

　　

　　Figure 2 Airbag system architecture

　　As shown in Figure 3, the active suspension system is also a common safety system in cars, which can greatly improve the handling of the vehicle. The active suspension system is mainly composed of sensors, shock absorbers and computer control systems. The system can collect data such as the speed, acceleration, load, steering degree, left and right G-force of the car to adjust the suspension coefficient and the height of the chassis from the ground in real time through the program.

　　

　　Figure 3 Active suspension system architecture

　　The laws and regulations of more and more countries have put forward requirements for the performance of anti-lock brake systems (ABS). The higher requirements for its reliability have increased the complexity of ABS design and the difficulty of research and development. In the system shown in Figure 4, the main purpose of ABS is to prevent the dangerous situation of vehicle stalling and sliding. When the control link finds that the emergency brake causes the speed to be too low, it will quickly release the brake to give the tires enough rolling space and greater grip to prevent the vehicle from running off the track. The key to this system is the measurement of tire speed.

　　

　　Figure 4 ABS system architecture

　　The system shown in Figure 5 is an Electric Power Assisted Steering (EPAS) system, also known as power steering. Compared with the traditional hydraulic steering wheel, EPAS uses an electronic motor to provide the driver with auxiliary control of wheel steering. EPAS generally obtains the position and torque of the steering wheel through sensors, and then combines parameters such as vehicle speed, engine temperature, and battery power supply to achieve auxiliary control of the electronic motor. EPAS has gradually entered the market, which can not only reduce the engine load, but also further improve the efficiency of fuel use.

　　

　　Figure 5 Power steering system architecture

　　The pre-tensioned seat belt (Seat Belt Tensioner) is also an advanced driving safety protection system, which can be used as a subsystem in the collision system. When the vehicle is driving normally, the pre-tensioned seat belt gives the driver and passengers more shoulder space, allowing them to enjoy the comfort of driving and riding; but at the moment of an accident, in order to protect the safety of the personnel and avoid physical injuries caused by the forward impact, the pre-tensioned seat belt can be quickly tightened to make the personnel close to the seat and reduce the risk of collision with the object in front.

　　

　　Figure 6 Pre-tensioning seat belt system architecture

　　in conclusion

　　With the continuous progress of electronic technology and control science, automotive electronic systems have also undergone revolutionary changes. The vehicle's safety protection system has also gradually upgraded from traditional passive systems such as seat belts and airbags to active safety systems such as pre-collision control. All of this is achieved thanks to the support of a variety of sensors and their control systems for driving, braking, engine control, speed control, safety protection and other performance.

　　In future automotive electronic systems, the further development of advanced sensors such as accelerometers and gyroscopes, the trend of single-chip control links, and the formation of in-vehicle network systems will greatly improve performance in terms of real-time, processing speed, and data transmission capabilities. At that time, people will be able to enjoy the convenience of high-speed travel while also getting maximum safety guarantees.