Automobile safety design automatic fail-safe function

Airbags play a key role in the SRS. At present, the installation of airbags in passenger cars has become a standard. Everyone knows that in the event of a car collision, airbags and seat belts can reduce the chances of the head and upper body of the passengers hitting the components in the car. They can also reduce the risk of personal injury by making the impact force more evenly distributed. But now, many people have realized that the auxiliary restraint system that can bring safety to people may also endanger the lives of people in the car. Therefore, when developing a safety system, the various characteristics of the system must be fully considered to ensure that the required safety level is achieved. In order to solve this problem, Infineon has developed an airbag trigger chip with rich features, which can help the system realize automatic fault protection.

The automotive airbag system market in Asia is expected to continue to grow, mainly due to the growth of the Chinese market. In the next five years, the market will increase by 25%. In addition, South Korean cars exported to Europe and America are equipped with more and more airbags, mainly because of the new safety regulations implemented in Europe and the United States. At present, passenger cars in South Korea are 100% equipped with front airbags, and the increase in head airbags is expected to reach 44% by 2013. The current positive airbag installation rate in the Chinese market is only 62%, so we expect that this field will usher in rapid growth. In addition, with the continuous growth of China's vehicle exports, safety issues are also getting more and more attention. Therefore, we expect that side and head airbags will continue to grow in the next four years.

At present, with the implementation of new regulations in Europe and America, the airbag system is expected to become more complete. High-end equipment manufacturers will face price pressure and need to meet the challenges of balancing costs, innovation and reliability. Related research shows that the current positive airbags with an average price of 105 US dollars are expected to reduce costs by 15% after 4 years. The industry believes that reliable application is the most important issue for automotive airbag systems. Therefore, this article will discuss how to balance safety elements and system costs under poor execution conditions (such as leakage and low pressure).

Over the past 30 years, the number of vehicles on European roads has tripled, but roads have only doubled. With the increasing traffic volume, Hyundai Motors has shown a trend of providing drivers and passengers with higher and higher safety and comfort.

Electronic technology and other chemical and mechanical technologies have played an important role in improving the safety and comfort of automobiles. Today, GPS systems, automatic mirrors, automatic lights, power seats, electronic injection devices and hundreds of other functions have become an indispensable part of automobiles. But in addition to comfort, users also want to buy cars with higher safety for themselves and their families.

Therefore, the security system comes into play. Currently, automobiles provide active and passive safety systems such as ABS, ESC, ASR, airbags, and pedestrian protection. In the future, the market is expected to continue to grow as roads are far from 100% safe.

The security system from the highland has adopted separate components to provide the required functions, but in recent years, all systems have adopted an integrated approach. At present, most RCU (safety protection control unit) is composed of MCU (main control unit), communication interface, power supply, sensor interface and ignition circuit. This article covers the explosion-proof circuit part of RCU. The following will discuss the safety of the airbag system and the relevant safety features of the application IC.

Figure 1: ECU diagram of airbag.

Figure 1: ECU diagram of airbag.

Airbag safety

When developing a safety system, the various characteristics of the system must be fully considered to ensure that the required safety level is achieved. From the perspective of the system, the airbag controller must have two safety features: 1. Trigger under accident conditions; 2. Prevent accidental trigger.

Both of the above characteristics must comply with the specific requirements of the relevant standards (ie IEC 61508) to ensure that the corresponding safety level is achieved.

The relevant safety standards of the safety system put forward the concept of "automatic failure prevention". When a safety system fails, its design should ensure that the failure will not damage adjacent systems or cause injury to personnel.

At first glance, someone may think that the first feature is more important than the second feature. However, it is not. When the safety system detects an accident, if the trigger of the airbag cannot be completed due to a certain failure, it will cause casualties, although most car owners still want to never need to trigger the airbag. On the other hand, after the RCU is installed on the car, the airbag may be triggered accidentally at any time from the test period of the car to the end of the use period. If this happens, it will cause harm to the relevant personnel (factory worker, car driver or car mechanic).

Overall, it is necessary to ensure that the correct triggering of the airbag is achieved when an accident occurs, and at the same time, efforts must be made to prevent the accidental triggering of the airbag.

In order to enable everyone to better understand the airbag system and how to implement the fault protection function, it is necessary to introduce the implementation of the entire system (see Figure 2).

Normally, the car satellite sensor interface acquires and analyzes the data sent by an external sensor (acceleration or pressure sensor). These sensors are distributed in the front of the car, in the door, or on the B-pillar, depending on the function or type (front impact acceleration sensor, side impact pressure sensor, or side impact acceleration sensor). In the event of a collision, the absolute acceleration or pressure on the sensor will increase significantly, so that the main microcontroller will know that a collision has occurred. At this time, the main microcontroller must decide whether to trigger the airbag based on the data of the sensor, the data of the onboard sensor, the position of the seat, and other parameters.

If it is decided to trigger the airbag, the main microcontroller will send a command to the explosive interface. At the same time, the backup system (usually a backup 8-bit microcontroller) must also make a decision based on more basic data (that is, only onboard sensor data) to allow the designated hardware circuit to allow the IC to trigger the airbag.

Triggering is achieved by causing current to flow through the blast tube (usually between 1.2A and 1.75A). The blast tube is used as a resistor with a resistance of only a few ohms, so the current must be controlled to save energy. If the current flows through the detonator for a certain period of time (usually 0.5ms to 2ms), the airbag will complete the trigger.

From generating sensor information, sending sensor information, analyzing all parameters, making decisions, and transmitting decisions to the trigger IC to finally ensure that the current only passes through the blast tube when needed, in this entire process must ensure that there is a reliable Automatic fail-safe performance.

The following will analyze the last two steps that trigger the airbag process.

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