Understanding Vehicle Safety Systems: Airbags, Capacitors, and Control Modules, Lecture notes of Physics

Download Understanding Vehicle Safety Systems: Airbags, Capacitors, and Control Modules and more Lecture notes Physics in PDF only on Docsity! MCFRS Driver Certification Program Page 1 Rescue Squad - Module 12 Vehicle Safety Introduction Airbags were first introduced in the early 1970’s and since then, vehicles, as well as their safety features, have developed rapidly. Since model year 1998, all new cars have been required to have air bags on both driver and passenger sides (light trucks came under the rule in 1999). There are many safety features located within the vehicles found on the road today and many more advancements can be expected. However, while these “safety” features are great for protecting the passenger upon impact they can be very hazardous to rescuers, and possibly the passengers, while working to extricate the patients from the vehicle. The dangerous possibilities of airbags were demonstrated by the injuries sustained by two firefighters from Ohio during an extrication. Both rescuers were injured when the multiple airbags deployed during extrication, seriously injuring one of the rescuers. The following information is current as of late fall 2004. The automobile manufacturing industry has made great strides in the safety features of today’s automobiles and will continue to make advancements in this field. All firefighter/rescuers must make every attempt to stay current with the technology of today and tomorrow. Batteries Batteries used to be located under the hood either on the passenger side of the driver’s side, however with modern day vehicles this is no longer the case. In today’s vehicles batteries can be found under the hood, in the trunk, under the rear passenger seat, and just about anywhere else the manufacturer can find a place to put the battery. MCFRS Driver Certification Program Page 2 Rescue Squad - Module 12 Car batteries are lead-acid batteries. A car's battery is designed to provide a very large amount of current for a short period of time. This surge of current is needed to turn the engine over during starting. Once the engine starts, the alternator provides all the power that the car needs. A car battery may go through its entire life without ever being drained more than 20 percent of its total capacity. Used in this way, a car battery can last a number of years. To achieve a large amount of current, a car battery uses thin plates in order to increase its surface area. A car battery typically has two ratings: CCA (Cold Cranking Amps) - The number of amps that the battery can produce at 32 degrees F (0 degrees C) for 30 seconds RC (Reserve Capacity) - The number of minutes that the battery can deliver 25 amps while keeping its voltage above 10.5 volts If you look at any battery, you'll notice that it has two terminals. One terminal is marked (+) or positive (usually red), while the other is marked (-) or negative (usually black). In an AA, C or D cell (normal flashlight batteries), the ends of the battery are the terminals. In a large car battery, there are two heavy lead posts that act as the terminals. Electrons collect on the negative terminal of the battery. If you connect a wire between the negative and positive terminals, the electrons will flow from the negative to the positive terminal as fast as they can (and wear out the battery very quickly). This can be dangerous, especially with large batteries. Normally, some type of load would be connected to the battery using the wire. In automobiles the load is the motor. Inside the battery itself, a chemical reaction produces the electrons. The speed of electron production by this chemical reaction (the battery's internal resistance) controls how many electrons can flow between the terminals. Electrons flow from the battery into a wire and must MCFRS Driver Certification Program Page 5 Rescue Squad - Module 12 When you connect a capacitor to a battery, here’s what happens: The plate on the capacitor that attaches to the negative terminal of the battery accepts electrons that the battery is producing. The plate on the capacitor that attaches to the positive terminal of the battery loses electrons to the battery. Once it's charged, the capacitor has the same voltage as the battery (1.5 volts on the battery means 1.5 volts on the capacitor). For a small capacitor, the capacity is small. But large capacitors can hold quite a bit of charge (think METRO). You can find capacitors as big as soda cans, for example, that hold enough charge to light a flashlight bulb for a minute or more. When you see lightning in the sky, what you are seeing is a huge capacitor where one plate is the cloud and the other plate is the ground, and the lightning is the charge releasing between these two "plates." Obviously, in a capacitor that large, you can hold a huge amount of charge! MCFRS Driver Certification Program Page 6 Rescue Squad - Module 12 Control Module The control module is where the capacitor is typically housed and will frequently have a master sensor for the supplemental restraint system (this may be the only sensor in the vehicle). The control module is also known as the Diagnostic Energy Reserve Module (DERM), Central Processing Unit (CPU), Electronic Control Unit (ECU), the computer or the “Brain.” The control module may be found in several locations; under the center console, in the dashboard, in the passenger footwell area, etc. GM 'black box' SDM air bag module. Mounted under center console. 2001 Cadillac DTS shown. MCFRS Driver Certification Program Page 7 Rescue Squad - Module 12 In addition to housing the capacitor this “black box” records the following information: Vehicle speed (in five one-second intervals preceding impact) Engine speed (in five one-second intervals preceding impact) Brake status (in five one-second intervals preceding impact) Throttle position (in five one-second intervals preceding impact) Driver's seat belt state (On/Off) Passenger's airbag enabled or disabled state (On/Off) Airbag Warning Lamp status (On/Off) Time from vehicle impact to airbag deployment Maximum Delta-V ( DV ) for near-deployment event Delta-V ( DV ) vs. time for frontal airbag deployment event Time from vehicle impact to time of maximum Delta-V ( DV ) Time between near-deploy and deploy event (if within 5 seconds) Sensors Sensors are used to send a signal to the control module in a crash. Some vehicles have a single sensor located in the control module while other vehicles have a number of sensors located throughout the vehicle. The sensor is the device that tells the bag to inflate. Inflation happens when there is a collision force equal to running into a brick wall at 10 to 15 miles per hour (16 to 24 km per hour). A mechanical switch is flipped when there is a mass shift that closes an electrical contact, telling the sensors that a crash has occurred. The sensors receive information from an accelerometer built into a microchip. Front Airbags What an air bag wants to do is to slow the passenger's speed to zero with little or no damage. The constraints that it has to work within are huge. The air bag has the space between the passenger and the steering wheel or dash board and a fraction of a second to work with. Even that tiny amount of space and time is valuable, however, if the system can slow the passenger evenly rather than forcing an abrupt halt to his or her motion. There are three parts to an air bag that help to accomplish this feat: The bag itself is made of a thin, nylon fabric, which is folded into the steering wheel or dashboard The sensor MCFRS Driver Certification Program Page 10 Rescue Squad - Module 12 Even though the whole process happens in only one-twenty-fifth of a second, the additional time is enough to help prevent serious injury. The powdery substance released from the air bag, by the way, is regular cornstarch or talcum powder, which is used by the air bag manufacturers to keep the bags pliable and lubricated while they're in storage. AT NO TIME SHOULD ANY POST MANUFACTURED DEVICE BE PLACED OVER ANY AIRBAG. A view of the rear of this frontal airbag clearly shows the two separate inflator modules. This airbag is designed to fire only one inflator in a low-speed collision, leaving responders faced with a “dead” airbag with a “live” charge remaining. MCFRS Driver Certification Program Page 11 Rescue Squad - Module 12 Passenger Side Airbag In September of 1997, a mandate was issued for vehicle manufacturers to provide a front impact air bag for the passenger side of the vehicle. Several manufacturers had already introduced this passenger protection system beginning in 1990. By 1995 passenger side airbags were a common vehicle addition. The passenger bag is mounted in the top of the dash on the passenger side of the vehicle. Below is a Photographic cross section of a Passenger Side Airbag Module Some vehicles are equipped with an airbag switch allowing them to deactivate the passenger airbag. If during an extrication a vehicle is found to be equipped with this switch an attempt should be made to switch it to “off.” While this does not guarantee that the bag will not deploy it is an extra step that should be taken to protect the patient, your crew, and yourself. While some vehicles are manufactured with a switch as pictured above, other vehicles may contain after market switches pictured below. MCFRS Driver Certification Program Page 12 Rescue Squad - Module 12 Side Airbags Side impact bags were first introduced by Volvo in 1995 and have rapidly increased in popularity. At the same time side impact airbags have had a lot of bad publicity because of multiple injuries and deaths related to side impact airbags. There are several different types of side impact airbags, included are: The Head-Thorax Bag MCFRS Driver Certification Program Page 15 Rescue Squad - Module 12 Be Aware, not all airbags deploy together. Treat ALL airbags as live airbags! Rollover Protection To maintain the clearance between the occupant's head and the roof of the vehicle, the vehicle can be equipped with a Belt-in-Seat system where the shoulder belt is attached to the backrest of the seat instead of to the pillar between the doors. The rollover also uses a new and very advanced micro- processed sensor which will trigger the seat belt pretensioners (to further increase the clearance between the roof and the occupant's head) and the Inflatable Curtains to help prevent the occupant's head from hitting that side of the vehicle or the ground. The Inflatable Curtain will also help prevent occupants from being ejected from the vehicle, which is very common in rollovers, especially among unbelted occupants. Deployed Airbags Non-Deployed Airbags MCFRS Driver Certification Program Page 16 Rescue Squad - Module 12 Micro processed sensor A roll-over protection system, fitted as standard, which extends to a height of 265 millimeters within 0.25 seconds if a sensor detects an impending rollover or crash. Pretensioners Pretensioners are incorporated into the belt assemblies to remove slack from the seat belt during a collision. Within milliseconds of a crash, the pretensioner is activated and increases the tension of the seat belt system around the occupant. This is what keeps you from bouncing around and keeps you in the proper position to benefit from the airbag if the crash is severe enough to trigger them. It contains an inertial reel with a pendulum device that senses sudden deceleration and automatically locks the belt in a crash. Currently there are three types of pretensioners in use today. Mechanical Mechanical pretensioners use an inertial wheel with a pendulum device that moves under the rapid deceleration of the crash to lock the belt into place. Such mechanisms can often be detected by giving a sudden tug on the belt. A mechanical pretensioner will automatically lock the belt into place, with the intent of limiting occupant travel in the event of a crash. MCFRS Driver Certification Program Page 17 Rescue Squad - Module 12 Electrical Electrical pretensioners replace the mechanical means of sensing deceleration (the pendulum) with an electrical device that may or may not be tied into the airbag ignition circuits. Pyrotechnic Pyrotechnic pretensioners use electrically triggered pyrotechnics that tighten the seatbelt a prescribed amount upon sensing a crash event. These devices can operate on either the buckle or ratchet side of the seatbelt mechanism. These are the most highly technical type of pretensioner, and also the most expensive. These will be the focus of this report. MCFRS Driver Certification Program Page 20 Rescue Squad - Module 12 as many hours of hands-on training and experience will a rescuer be able to perform competent and efficient extrication. A great place to keep up on the advances in new car construction and safety systems is automotive manufacturer’s web sites, the mechanics at area new car sales offices, and yearly auto shows. The information you learn at these locations could help save the life of a patient or even your own. The following are some of the changes that have occurred in new model vehicles, however, between the time of this being written and you reading this there have probably been additional improvements and modifications. Increased amount and types of metals used in posts as well as the number of bends Boron rod reinforced dashboard area Reinforced wheel and engine deflection systems that deflect the wheels and motor under the car and away from the passenger compartment area Crumple zones that absorb the energy of the impact (more damage, less injuries) Micro alloys and boron steel being used to improve the strength to weight ratio High Strength Low-Alloy or Ultra High Strength Low-Alloy steel being used to reinforce roof and pillar structures Side and rear glass – may have two panes of tempered glass, be laminated glass, bulletproof glass, or lexan Body materials consists of high impact plastic, carbon fiber, aluminum and other composite materials. These changes lead to more crumpling and shattering of material rather than bending. At times it may be easier to remove exterior panels to access purchase points. Carbon fiber is very difficult to cut/shatter and its dust particles and combustion by-products are hazardous This picture demonstrates double panes of tempered glass. MCFRS Driver Certification Program Page 21 Rescue Squad - Module 12 The above picture shows the improvements in passenger safety through stronger materials that absorb the impact. The above picture shows high impact plastic exterior panels as well as a deep door that will hamper rescuers accessing the U bolt. MCFRS Driver Certification Program Page 22 Rescue Squad - Module 12 The above picture shows new car construction that has eliminated the upper portion of the “B” post. MCFRS Driver Certification Program Page 25 Rescue Squad - Module 12 Electric Power from Hydrogen Fuel 1. Fuel cells create electricity through an electrochemical process that combines hydrogen and oxygen. 2. Hydrogen fuel is fed into the anode of the fuel cell. Helped by a catalyst, hydrogen atoms are split into electrons and protons. 3. Electrons are channeled through a circuit to produce electricity. 4. Protons pass through the polymer electrolyte membrane. 5. Oxygen (from the air) enters the cathode and combines with the electrons and protons to form water. Water vapor and heat are released as byproducts of this reaction. MCFRS Driver Certification Program Page 26 Rescue Squad - Module 12 Natural Gas Vehicle Above is a picture of the tank that holds the compressed natural gas. This tank is located between the rear passenger seat and the trunk and can be accessed easily from the trunk.