1.1 Introduction
Safety feature of a car is that a percentage of the car can protect its driver and passenger when driving also when have a crash or accident. Not only that, It also about a probability for the car to avoid an accident in the first place.
The safety feature can be group into two:
Primary safety describes features designed to help you avoid a crash. Brakes and lights fall into this group as well as systems like electronic stability control or lane keeping support.
Secondary safety features come into play once you have an accident and are designed to reduce injuries to you and your passengers. This covers seat belts and airbags, head restraints and the design of the bodyshell and vehicle interior.
1.2 Discussion
1.2.1 Air Bag
1.2.1.1 History of air bag
The first steps towards today's airbag were taken by John W. Hetrick, a retired industrial engineering technician, in the early '50s. Following a car accident involving Mr. Hetrick and his wife and daughter, he thought of a device that would prevent passengers from hitting the inside of a car.
He received a patent in 1953 for something called "safety cushion assembly for automotive vehicles." At about the same time, German inventor Walter Linderer received a patent for a similar prototype. Mr. Linderer's product was using a compressed air system, which could be either released by bumper contact or by the driver.
Following the two patents, Ford and General Motors started tinkering with inflatable restraints, but they were faced with two big problems. One of them was related to the detection of a collision and the inflation of the airbag, which took too long to work properly. The second issue was that the airbags themselves would cause secondary injuries to passengers.
⌕ Airbag schemeIt wasn't until the late 1960's that the airbag development made some real progress. The man responsible for this? A New Jersey mechanical engineer by the name of Allen K. Breed. He invented what is considered the world's first electromechanical automotive airbag system in the form of a crash sensor.
Mr. Breed would later on come up with another important development in the field, namely the airbag that vents air as it inflates, reducing the risk of secondary injuries by reducing the inflated bag's rigidity.
Soon after that, Ford built an experimental airbag fleet (1971), while General Motors tested airbags on a 1973 model Chevrolet, albeit only sold for government use. The year 1973 brought the first passenger car fitted with an airbag for the general public, this breakthrough arriving as a 1973 Oldsmobile Toronado. One year later, Buick, Cadillac and Oldsmobile offered dual airbags as an option on several of their full-sized models. Mercedes-Benz was the first to offer the modern airbag as an option on their S-Klasse model.
The big difference between the US and German approach was that while Ford and GM marketed their airbags as an alternative to the seatbelt, Mercedes-Benz combined the two safety devices for more efficiency in preventing in injuries.
The first side and torso airbags became optional in 1995 on Volvo's 850 models. Three year later, the US federal government mandated dual frontal airbags on all passenger vehicles. The first airbag system for motorcycles came from Honda in 2006.
An air bag is an inflatable cushion created to protect passengers and drivers from serious injury in the case of a collision. The air bag is part of an inflatable restraint system, also called an air cushion restraint system (ACRS) or an air bag supplemental restraint system (SRS), because the air bag is designed to supplement the protection offered by seat belts. Seat belts are still needed to hold the occupant securely in place, especially in side impacts, rear impacts, and rollovers. Upon detecting a collision, air bags inflate instantly to cushion the exposed occupant with a big gas-filled pillow.
A typical air bag system consists of an air bag module (containing an inflator or gas generator and an air bag), crash sensors, a diagnostic monitoring unit, a steering wheel connecting coil, and an indicator lamp. These components are all interconnected by a wiring harness and powered by the vehicle's battery
The crash sensors are designed to prevent the air bag from inflating when the car goes over a bump or a pothole, or in the case of a minor collision. The inflator fits into a module consisting of a woven nylon bag and a break-away plastic horn pad cover. The module, in turn, fits into the steering wheel for driver's-side applications and above the glove compartment for front passenger applications.
In a frontal collision equivalent to hitting a solid barrier at nine miles per hour (14.48 kilometers per hour), the crash sensors located in the front of the car detect the sudden deceleration and send an electrical signal activating an initiator (sometimes called an igniter or squib). Like a light bulb, an initiator contains a thin wire that heats up and penetrates the propellant chamber. This causes the solid chemical propellant, principally sodium azide, sealed inside the inflator to undergo a rapid chemical reaction (commonly referred to as a pyrotechnic chain). This controlled reaction produces harmless nitrogen gas that fills the air bag. During deployment the expanding nitrogen gas undergoes a process that reduces the temperature and removes most of the combustion residue or ash.
The expanding nitrogen gas inflates the nylon bag in less than one-twentieth (1/20) of a second, splitting open its plastic module cover and inflating in front of the occupant. As the occupant contacts the bag, the nitrogen gas is vented through openings in the back of the bag. The bag is fully inflated for only one-tenth (1/10) of a second and is nearly deflated by three-tenths (3/10) of a second after impact. Talcum powder or corn starch is used to line the inside of the air bag and is released from the air bag as it is opened.
1.2.1.3 Component Of Air bag
The three major component which is important are sensor, inflator and air bag.
Sensor is important in order to determine when a collision has occured which will operate at the lower severity. It is basically function for detecting a collision when it is occur. In other word,it is a mechanism that tells the bag it's time to inflate, which generally requires the equivalent force of running into a brick wall at 10 - 15 mph. However, sensors in newer airbag systems are designed to determine whether or not there is a person in the front passenger seat and whether or not the passenger has enough weight for the bag to be safely deployed.
Inflator are designed to provide the gas to inflate the air bag after the sensor have determined that a collision has occured.
There are 3 main type of inflator:
1. The stored-gas generator : consist of gas stored at high pressure in a tank and supplied to the air bag through a fast adding valve and manifold.
2. Gas generation system : consist of propellant or fast-burning powder which generates the gas from burning.
3. The hybrid system : consist of a combined stored gas system and gas generation system.
Airbag are usually made of a coated nylon and must be strong enough to withstand the forces generated by the measure and the opening force.
1.2.1.4 Basic Operation
Ignition judgement and conditions
(1)Front collision
When both the deceleration sensor and safing sensor in the center airbag sensor assembly turnon, the driver airbag, front passenger airbag and seat belt pretensioners are ignited.The center airbag sensor assembly switches the threshold level that should be activatedaccording to the signal from the front airbag sensors (front satellite sensor).The safing sensor of the center airbag sensor assembly is designed to be turned on by asmaller deceleration rate than the deceleration sensor.There used to be a three sensor type in which the driver airbag, front passenger airbag and seatbelt pretensioners were ignited when the front airbag sensor turned on or the decelerationsensor in the center airbag sensor assembly turned on, and the safing sensor in the center airbag sensor assembly turned on.There also used to be a one sensor type that had no front airbag sensor and performed all thecontrol only with the airbag sensor assembly.
(2)Front side collision
The safing sensor of the center airbag sensor assembly is designed to be activated by a smaller deceleration rate than the deceleration sensor of the side airbag sensor. As illustrated, ignitionof the side airbag and curtain shield airbag is caused when current flows to the initiator, whichhappens when a safing sensor and the deceleration sensor go on simultaneously.Some model with E-type SRS airbags have a safing sensor in the side airbag sensor.Vehicle with side door sensor When the safing sensor in the center airbag sensor assembly turns on and the deceleration sensor in the side door sensor or in the side airbag sensor is on, the side airbag and curtainshield airbag are ignited.
(3)Rear side collision
When both the safing sensor and the deceleration sensor in the curtain shield airbag sensor turn on, the curtain shield airbag is deployed.Some models have a safing sensor outside the curtain shield airbag sensor and control with thesafing sensor in the center airbag sensor assembly.
1.2.2 Chrysler Air Bag System
Every Chrysler 200 Convertible is equipped with standard advanced airbag systems. Front multistage airbags and front seat-mounted side airbags.
This provide enhanced side protection for the driver and front passenger and also deploy with appropriate force based on the severity of the impact.
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