Safety Airbag System (SRS for short)\x0d\The airbag is a striking new technology device on modern cars. In order to reduce the damage to the driver and passengers caused by the huge inertial force when the car is in a frontal collision, modern cars are generally equipped with an airbag system in the center of the steering wheel in front of the driver. Some cars have a toolbox in front of the driver's passenger seat. The upper end is also equipped with an airbag system. Experiments and practice have proven that after a car is equipped with an airbag system, the degree of harm to the driver and passengers in a frontal collision is greatly reduced. Some cars are not only equipped with front airbags, but also side airbags. When the car is in a side collision, the side airbags can also be inflated to reduce the damage during a side collision. A car steering wheel equipped with an airbag device is no different from an ordinary steering wheel. However, once a strong collision occurs at the front of the car, the airbag will "jump" out of the steering wheel instantly and place a cushion between the steering wheel and the driver. This wonderful device prevents 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 its introduction. An American research institute analyzed more than 7,000 car traffic accidents in the United States from 1985 to 1993 and found that when a car with an air bag device crashed into the front, the driver's mortality rate was reduced by 30% for large cars, 11% for medium-sized cars, and 11% for small cars. 14. \x0d\\x0d\In fact, the airbag was invented 40 years ago. On August 18, 1953, American John Herritt obtained a U.S. patent for the "automobile buffer safety device". Herritt, a self-taught Pennsylvania engineer, came up with the idea for a crash safety device after an accident in 1952. In this accident, he swerved to brake to avoid an obstacle, and both he and his wife instinctively used their arms to protect their daughter, who was sitting in the middle of the front seat. After this accident, he realized that there must be a better way to protect the occupants. Two weeks later, he drew a design drawing and gave it to the agent. This drawing determined the prototype of today's airbag. \x0d\\x0d\Of course, the development of things is not smooth sailing. From the patent to the application and promotion of airbags, it took more than 30 years and experienced several twists and turns, because the automobile manufacturers cited cost reasons. Refusal to accept airbag devices. Only a few years ago, the U.S. Senate passed the Highway Death and Injury Reduction Ordinance, which confirmed the role of airbags and stipulated that all cars manufactured after September 1, 1995 should be equipped with airbags in the front seats. The U.S. government also requires that cars manufactured after 1998 should be equipped with airbags. New cars are equipped with driver and passenger airbags. At present, most of the mid- to high-end cars produced in various countries have airbags, and some cars have included airbags as required equipment. \x0d\\x0d\ (1) Working principle of the airbag system: \x0d\\x0d\ When a frontal collision occurs in a car, the airbag control system detects that the impact force (deceleration) exceeds the set value, the airbag computer Immediately turn on the electric squib circuit in the inflatable component, ignite the ignition medium in the electric squib, the flame ignites the ignition powder and gas generating agent, generates a large amount of gas, and inflates the air bag within 0.03 seconds, causing the air bag to rapidly It expands, breaks through the decorative cover on the steering wheel, and bulges toward the driver and passengers, causing the driver and passengers' heads and chests to press against the gas-filled airbag, cushioning the impact on the driver and passengers, and then releasing the gas in the airbag. . \x0d\\x0d\ (2) Composition of the airbag \x0d\\x0d\ The airbag system is mainly composed of four parts: collision sensor, airbag computer, SRS indicator light and airbag assembly. \x0d\\x0d\1. Collision sensor \x0d\\x0d\The collision sensor is the main control signal input device in the airbag system. Its function is that when the car collides, the collision sensor detects the intensity signal of the car collision and inputs the signal into the airbag computer. The airbag computer determines whether to detonate the inflatable element to inflate the airbag based on the signal from the collision sensor.
The airbag system is generally equipped with 2 to 4 collision sensors, one on each of the front left and right fenders. Some are also equipped with one in the middle of the front bumper, and some are also equipped with one in the car. Most collision sensors now use inertial mechanical switch structures. \x0d\\x0d\The collision sensor is composed of a housing, an eccentric rotor, an eccentric weight, a fixed contact, a rotating contact and other parts. There is also a resistor R fixed outside the sensor. The function of the resistor R is to detect whether the connecting wire between the airbag computer and the front airbag collision sensor is open or short-circuited during self-test of the system. \x0d\\x0d\ Under normal circumstances, the eccentric rotor and the eccentric weight press against the stop block connected to the housing under the action of the elastic force of the coil spring. At this time, the rotating contact and the fixed contact do not contact, Switch "OFF". When a car collides, the eccentric weight will drive the eccentric rotor to deflect due to the inertial force against the spring force. When the collision intensity reaches the set value, the deflection angle of the eccentric rotor will cause the rotating contact to contact the fixed contact and close. At this time, the collision sensor inputs an "ON" signal to the airbag computer. The airbag computer will detonate the inflatable component only when it receives the "ON" signal input from the collision sensor. Some cars are also equipped with side airbags. When the car collides sideways, the airbags will also inflate. Therefore, systems equipped with side airbags also have collision sensors on the left and right sides of the car. \x0d\\x0d\2. Airbag computer\x0d\\x0d\ The airbag computer is the control center of the airbag system. Its function is to receive signals input from the collision sensor and other sensors, determine whether to ignite the airbag and inflate it, and Self-diagnosis of system faults. \x0d\\x0d\The airbag computer also needs to continuously perform diagnostic tests on the circuits of key components in the control assembly (such as sensor circuits, backup power circuits, ignition circuits, SRS indicator lights and their drive circuits), and pass the SRS indicator light and Fault codes stored in memory to display test results. The SRS indicator light on the instrument panel provides airbag system status information directly to the driver. The status information and fault codes in the computer memory can be retrieved from the serial communication interface with special instruments or through specific methods for assembly inspection. \x0d\\x0d\ (1) Signal processing circuit \x0d\\x0d\ The signal processing circuit is mainly composed of amplifiers and filters. Its function is to shape, amplify and filter the signals detected by the sensor so that the SRS computer can receive, identify and process them. \x0d\\x0d\ (2) Backup power circuit \x0d\\x0d\ The airbag system has two power sources: one is the vehicle power supply (battery and alternator); the other is the backup power supply (BACK UP POWER). Backup power is also called backup power or emergency backup power. The backup power circuit consists of a power control circuit and several capacitors. In the control component of the single airbag system, there is a computer backup power supply and an ignition backup power supply. In the control module of the dual airbag system, there is a computer backup power supply and two ignition backup power supplies, that is, one backup power supply for each of the two ignition circuits. 10 seconds after the ignition switch is turned on, if the vehicle power supply voltage is higher than the minimum operating voltage of the SRS computer, then the computer backup power supply and ignition backup power supply can complete the energy storage task. \x0d\\x0d\The function of the backup power supply is: when the circuit between the car power supply and the SRS computer is cut off, within a certain period of time (usually 6s), the airbag system maintains power supply and maintains the normal function of the airbag system. When the car suffers a collision and the circuit between the battery and alternator and the SRS computer is cut off, the computer backup power supply can supply power to the computer within 6 seconds to maintain the normal functions of the computer such as detecting collisions and issuing ignition commands; the ignition backup power supply can Within 6 seconds, sufficient ignition energy is supplied to the igniter to detonate the ignition agent, causing the inflator to thermally decompose and inflate the airbag. After the time exceeds 6 seconds, the power supply capacity of the backup power supply decreases, and the computer backup power supply cannot ensure that the computer detects a collision and issues an ignition command; the ignition backup power supply cannot supply the minimum ignition energy, and the SRS air bag cannot be inflated.
\x0d\\x0d\ (3) Protection circuit and voltage stabilizing circuit \x0d\\x0d\In the automotive electrical system, many electrical components have inductive coils, there are a dazzling array of electrical switches, and the electrical load changes frequently. When the coil current is turned on or off, the switch is turned on or off, or the load current suddenly changes, instantaneous pulse voltages or overvoltages will be generated. If these overvoltages are added to the airbag system circuit, the electronic components in the system may be damaged due to Excessive voltage may cause damage. In order to prevent damage to the airbag system components, a protection circuit must be installed in the SRS control module. At the same time, in order to ensure that the airbag system can operate normally when the vehicle power supply voltage changes, a voltage stabilizing circuit must be set up. \x0d\\x0d\3. SRS indicator light \x0d\\x0d\SRS indicator light is the abbreviation of airbag system indicator light. The SRS indicator light is also called the SRS warning light or SRS warning light. The SRS indicator light is installed under the mask on the dashboard of the cab, and graphics or the words SRS, AIR BAG, etc. are made at the corresponding positions on the surface of the mask. \x0d\\x0d\The function of the SRS indicator light is to indicate whether the airbag system function is in a normal state. When the ignition switch is turned to the "ON" or "ACC" position, if the SRS indicator light illuminates or flashes for about 6 seconds (flashes 6 times) and then goes out automatically, it means that the airbag system is functioning normally. If the SRS indicator light does not light up, stays on, or suddenly lights up or flashes while the car is driving, it means that the self-diagnosis system has discovered that the airbag system is faulty and should be eliminated in time. While the self-diagnosis system controls the SRS indicator light to light up or flash, it will also encode the discovered faults into codes and store them in the memory. When checking or troubleshooting airbag system faults, first use special testing instruments or call out fault codes (commonly called fault codes) from diagnostic sockets or communication interfaces in a specific way to quickly find and troubleshoot faults. Practice has proven that when a car suffers a collision, , after the air bag has been deployed, it is generally difficult to retrieve the fault code. The purpose of this design is to require that the SRS computer must be replaced after the SRS air bag is detonated. \x0d\\x0d\4. The air bag assembly\x0d\\x0d\ The inflatable element and the air bag are both installed in the steering wheel or on the upper end of the tool box and cannot be disassembled. The inflatable element is composed of an electric blast tube, ignition powder and gas generating agent. The function of the inflatable element is to inflate the air bag. The inner surface is coated with resin. \x0d\\x0d\When the vehicle collides, the impact force of the collision turns on the collision sensor and trigger sensor, and the SRS computer turns on the detonation circuit, causing the current to flow through the electric explosion tube, causing it to heat up and explode. The ignition medium in the tube ignites, and the flame then spreads to the ignition powder and gas generating agent, producing a large amount of gas. After being cooled by the filter, the gas enters the air bag, and the air bag expands rapidly, breaking through the steering wheel and cushioning the impact on the driver and passenger. The airbag is installed on the steering wheel and rotates together with the steering wheel. The wire connection between the electric squib and the SRS computer is connected by a spiral wire