Airbag system (SRS)\x0d\ Airbag is a remarkable new technical device in modern automobiles. In order to reduce the damage caused by the huge inertial force in frontal collision, modern cars are generally equipped with an airbag system in the center of the driver's front steering wheel, and some cars are also equipped with an airbag system at the upper end of the toolbox in front of the driver's passenger seat. Experiments and practice have proved that the degree of injury to drivers and passengers in frontal collision accidents is greatly reduced after the automobile is equipped with airbag system. Some cars are equipped not only with front airbags, but also with side airbags, which can also be inflated when the car collides side to reduce the injury during side collision. The steering wheel of an automobile equipped with airbag device is no different from the ordinary steering wheel, but once the front end of the automobile collides strongly, the airbag will "jump out" of the steering wheel in an instant and pad it between the steering wheel and the driver to prevent the driver's head and chest from hitting hard objects such as the steering wheel or dashboard. This wonderful device has saved many lives since it came out. An American research institute analyzed more than 7,000 automobile traffic accidents in the United States from 1.985 to 1.993. The results showed that the death rate of drivers in large cars decreased by 30%, that of medium-sized cars by 1% and that of small cars by 1%. In fact, airbags were invented as early as 40 years ago. 1953 August 18, an American, john hart Ritter, obtained an American patent for "automobile buffer safety device". Hartritt is a self-taught Pennsylvania engineer. 1952 after an accident, he came up with the idea of designing an anti-collision safety device. In this accident, he slammed on the steering wheel to avoid obstacles. He and his wife instinctively protected their daughter sitting in the middle of the front seat with their arms. After the accident, he realized that there must be a better way to protect passengers. Two weeks later, he drew a design and gave it to the agent, which confirmed the prototype of today's airbag. \ x0d \ x0d \ Of course, things didn't go smoothly. It has been more than 30 years since the airbag was patented and popularized, and it has experienced many twists and turns because the automobile manufacturers refused to accept the airbag device for cost reasons. Only a few years ago, the US Senate passed the expressway Casualty Reduction Ordinance, which confirmed the role of airbags and stipulated that all cars manufactured after 1 September 19951should be equipped with airbags in front of the front seats. The US government also requires all new cars after 1998 to be equipped with airbags for drivers and passengers. At present, most middle and high-end cars produced in various countries have airbags, and some cars have included airbags as compulsory parts. \x0d\\x0d\ (1) Working principle of airbag system: \x0d\\x0d\ When the car has a frontal collision accident, when the airbag control system detects that the impact force (deceleration) exceeds the set value, the airbag computer immediately connects the electric detonator circuit in the inflatable element, igniting the ignition medium in the electric detonator, and the flame ignites the gunpowder and gas generator. Within 0.3 seconds, the airbag will expand rapidly, break through the decorative cover on the steering wheel, and bulge to the driver and passenger, so that the driver and passenger's head and chest will be pressed against the airbag filled with gas to cushion the impact on the driver and passenger, and then the gas in the airbag will be released. \x0d\\x0d\ (II) Composition of airbag \ x0d \ x0d \ The airbag system is mainly composed of four parts: collision sensor, airbag computer, SRS indicator light and airbag module. \ x0d \ x0d \ 1 and collision sensor \ x0d \ x0d \ collision sensor are the main control signal input devices in the airbag system. Its function is to detect the intensity signal of automobile collision by the collision sensor when the automobile collides, and input the signal into the airbag computer, and the airbag computer judges whether to detonate the inflation element to inflate the airbag according to the signal of the collision sensor. Airbag systems are generally equipped with 2~4 collision sensors, one for the front and left fenders, one for the middle of the front bumper, and one for some cars. At present, most collision sensors adopt inertial mechanical switch structure. \ x0d \ x0d \ The collision sensor consists of a shell, an eccentric rotor, an eccentric weight, a fixed contact and a rotating contact. The resistor r is also fixed outside the sensor. The function of the resistor R is to detect whether the connecting line between the airbag computer and the front airbag collision sensor is open or short-circuited during the system self-test. \ x0d \ x0d \ Under normal circumstances, the eccentric rotor and eccentric weight are pressed against the stop connected with the housing under the elastic force of the coil spring. At this time, the rotating contact is not in contact with the fixed contact, and the switch is in the "off" state. When a car collides, due to the inertia force, the eccentric weight will drive the eccentric rotor to deflect against the spring force. When the collision intensity reaches the set value, the deflection angle of the eccentric rotor will make the rotating contact contact with the fixed contact and close. At this time, the collision sensor inputs an "on" signal to the airbag computer. Only when the airbag computer receives the "ON" signal input from the collision sensor will the inflatable element be detonated. Some cars are also equipped with side airbags, which will also inflate when the car collides laterally, so the system equipped with side airbags is also equipped with collision sensors on the left and right sides of the car. \x0d\\x0d\2。 Airbag computer \ x0d \ x0d \ Airbag computer is the control center of airbag system, and its function is to receive the signals input by collision sensors and other sensors, judge whether the airbag is ignited, and self-diagnose the system failure. \ x0d \ x0d \ airbag computer will also continuously diagnose and test the key component circuits in the control module (such as sensor circuit, standby power supply circuit, ignition circuit, SRS indicator lamp and its driving circuit), and display the test results through SRS indicator lamp and fault code stored in memory. The SRS indicator light on the dashboard can directly provide the driver with the status information of the airbag system. The status information and fault codes in the computer memory can be transmitted from the serial communication interface through special instruments or in a specific way for assembly inspection. \x0d\\x0d\( 1) signal processing circuit \x0d\\x0d\ signal processing circuit is mainly composed of amplifier and filter. Its function is to shape, amplify and filter the signal detected by the sensor, so that SRS computer can receive, identify and process it. \x0d\\x0d\(2) Standby power supply circuit \ x0d \ x0d \ The airbag system has two power supplies: one is the automobile power supply (battery and alternator); The other is the backup power supply. Standby power supply is also called standby power supply or emergency standby power supply. The standby power supply circuit consists of a power supply control circuit and several capacitors. In the control module of the single airbag system, there is a computer standby power supply and an ignition standby power supply. In the control module of the double airbag system, there is a computer standby power supply and two ignition standby power supplies, that is, two ignition circuits each have a standby power supply. After 10s ignition switch is turned on, if the vehicle power supply voltage is higher than the minimum working voltage of SRS computer, then the computer standby power supply and ignition standby power supply can complete the energy storage task. \ x0d \ x0d \ The function of the standby power supply is: after the circuit between the automobile power supply and the SRS computer is cut off, the power supply of the airbag system will be maintained for a certain time (generally 6 seconds) and the normal function of the airbag system will be maintained. When the car is collided, the circuit between the battery, alternator and SRS computer is cut off, and the standby power supply of the computer can provide power for the computer within 6s, so as to keep the normal functions of the computer such as collision detection and ignition instruction. The ignition standby power supply can provide enough ignition energy for the igniter to detonate the igniter within 6s, so that the inflator can be decomposed by heat and the airbag can be inflated. After the time exceeds 6s, the power supply capacity of the standby power supply decreases, and the computer standby power supply cannot ensure that the computer detects the collision and sends out the ignition instruction; The ignition standby power supply can't provide the minimum ignition energy, and the SRS airbag can't inflate. \x0d\\x0d\(3) Protection circuit and voltage stabilizing circuit \x0d\\x0d\ In the automobile electrical system, many electrical components are equipped with inductance coils, and the electrical switches are dazzling, and the electrical load changes frequently. When the coil current is turned on or off, the switch is turned on or off, and the load current suddenly changes, instantaneous pulse voltage, that is, overvoltage, will be generated. If these overvoltage are added to the airbag system circuit, the electronic components in the system may be damaged due to overvoltage. In order to prevent the airbag system components from being damaged, a protection circuit must be set in the SRS control module. At the same time, in order to ensure that the airbag system can work normally when the power supply voltage of the automobile changes, a voltage stabilizing circuit must be set up. \x0d\\x0d\3, SRS indicator \x0d\\x0d\SRS indicator is the abbreviation of airbag system indicator. SRS indicator light is also called SRS warning light or SRS warning light. The SRS indicator light is installed under the mask on the dashboard of the cab, and the words such as graphics or SRS and airbag are written on the corresponding position of the mask surface. \ x0d \ x0d \ SRS indicator light is used to indicate whether the airbag system function is in normal state. When the ignition switch is turned to the "on" or "ACC" position, if the SRS indicator lights up or flashes for about 6 seconds, it will automatically go out, indicating that the airbag system is functioning normally. If the SRS indicator goes out, stays on, or suddenly lights up or flashes when the car is driving, it means that the self-diagnosis system finds that the airbag system is faulty and should be eliminated in time. When the self-diagnosis system controls the SRS indicator to light up or flash, it will also encode the faults found and store them in the memory. When checking or troubleshooting the airbag system, the fault code (usually called fault code) should be called from the diagnostic socket or communication interface in a specific way, so as to find and troubleshoot the fault quickly. Practice has proved that it is generally difficult to call out the fault code after the car is hit and the airbag is inflated. The purpose of this design is to require that the SRS computer must be replaced after the SRS airbag is detonated. \x0d\\x0d\4。 Airbag assembly \ x0d \ x0d \ Airbag assembly consists of inflatable components and airbags, which are installed in the steering wheel or at the upper end of the toolbox and cannot be disassembled. The inflatable element consists of electric detonator, ignition powder and gas generant. The function of the inflatable element is to inflate the airbag. The airbag is made of nylon cloth and its inner surface is coated with resin. \ x0d \ x0d \ When a vehicle collides, the collision impact force turns on the collision sensor and the trigger sensor, and the SRS computer turns on the detonating circuit, so that current flows through the nonel tube to heat and ignite the ignition medium in the nonel tube, and then the flame spreads to the ignition powder and gas generant, producing a large amount of gas. The gas enters the airbag after being cooled by the filter screen, and the airbag expands rapidly, breaking through the steering wheel and buffering the impact on the drivers and passengers. The inflatable element and airbag are installed on the steering wheel and rotate together with the steering wheel. The wiring between the explosion tube and the SRS computer is connected by a helix.