Ask Joe Mechanic - Getting Ready for Winter

The seasons are changing so it is time to start thinking about getting your vehicle ready for winter. There area number of things that sometimes get overlooked which are very important and can be very expensive to repair.  This is a good time of the year to have your car serviced. If you drive an average number of miles per year, about 12,000 or less, you need to have your car serviced at least twice a year.  Fall and Spring are excellent times to do this as it allows you to prep your car for winter’s cold and summer’s heat respectively. If you are not a “do-it-yourselfer,” and take your car to a reputable shop, they will most likely already be checking these things for you, but it never hurts to make sure.

            In addition to the normal oil and filter change, it is very important to check your tires. Check your tire pressure first of all. You should always inflate your tires to the vehicle manufacturer’s recommendations for your type of usage. Most vehicles have a label either on the driver’s door or doorjamb, if not, the information is in the owners’ manual. Do not just go by the maximum pressure marked on the tire sidewall, as this may not be suitable for your vehicle. A tire that is a few pounds low on air pressure can cost you 2 to 3 mpg.  At $3.50 per gallon, nobody wants to waste gasoline!

            When you are checking your air pressure, look for signs of abnormal tire wear. A tire that is worn on just the inside or outside edge is usually a sign of an alignment problem. If the tires are worn on both the inside and outside edges, this is usually a sign they have been run underinflated. If the center of the tire is worn down with good tread on the edges, this is a sign of either the tires being overinflated or having tires that are too wide for the wheels on the vehicle. This is seen most commonly on 4WDs.

            While your car is on the lift having its oil changed, your technician can give your tires a good professional lookover, and if necessary, do a tire rotation for you.  If he does a tire rotation, while each wheel is off, he can do a visual brake check to make sure your pads do not need replacement.

            When you get under the hood, there are quite a number of things that should be checked. Always check your antifreeze for fill level and condition. If your antifreeze is discolored, especially if it is rusty colored, you should have the system drained and flushed and refilled with new antifreeze. If you are not having the coolant changed, you should have it tested to make sure the level of protection is sufficient for your area. For our region, that should be at least -35 (F) degrees, because you never know when in your travels you could run into a cold pocket of air in a valley.

            Another item often overlooked until the first good freeze is your windshield washer solvent. Because people often add water over the summer, when the weather turns cold, I have seen many washer reservoirs frozen solid. It is important in the fall and winter to add full strength washer solvent to give maximum protection.  If the reservoir freezes and cracks, it can be expensive to replace because in most new vehicles it is not in a very easily accessible location and so may involve some significant labor to replace it.

Also, examine your belts and hoses. Check belts for proper tension and also for visible cracks. If your belts are older than 5 or 6 years old, it is a good idea to get them replaced.  It is not fun to get stuck on the side of the road with a broken belt on some cold morning.  As far as hoses, look for cracks or if they are bulging or have a spongy feeling near where they connect to the radiator or engine, if so, they should be replaced.

It’s also extremely important to know the status of your vehicle’s battery.  Make sure it doesn’t appear corrosive around the battery posts and cables.  If present, corrosion needs to be thoroughly cleaned off.  While cleaning, be careful not to get it on your skin, clothes or in your eyes. If your battery is not a sealed unit, the electrolyte level should be checked and add distilled water to bring it to the proper level if needed.

A few other items you may want to verify for proper operating condition are front and rear defrosters, your vehicle’s heater and if it has heated seats, making sure they’re in good working order.  If you check these items, your automobile should be pretty well prepared for winter.  However, do remember that problems can arise quickly, and without warning, so, if your vehicle suddenly starts acting differently, get it to the shop!  It may be nothing, but it is much better to be safe than sorry and sitting alongside the road in a disabled vehicle.

Ask Joe Mechanic - Electronic Stability Control

          Electronic stability control is known by quite a number of names including electronic stability program, dynamic stability control, Stabilitrak, Advance Trak, and more. No matter what name it has, this feature has one purpose, to aid the driver in recovering from an uncontrolled skid or wheel spin.

            As early as 1987, BMW and Mercedes Benz were working with and perfecting their first traction control systems for introduction. While traction control does not aid the driver in steering, it is an integral and very necessary part of the system.  Applying brakes to an individual wheel as needed and also modulating the throttle can control wheel spin. By 1992, BMW had made this feature standard across its entire model line.  The same year, Mercedes, with the help of Robert Bosch, co-developed a system that they called Elektronisches Stabilitatsprogrammen or Electronic Stability program, trademarked as ESP, designed to control lateral slippage. Mercedes introduced the system on its S Class models in 1995. BMW introduced their Robert Bosch manufactured version later that same year on their 7 Series models. At the same time, other manufacturers were working on their own systems; GM introduced Stabilitrak, a version of ESC, on certain Cadillac models in1997.  By 2007 it was standard equipment on all models except certain commercial vehicles. Meanwhile, Ford introduced Advance Trak on certain models in 2000, and by 2008 it was standard on most models.

In 1997, during a simulated moose avoidance test in Germany, a test driver rolled a small A Class Mercedes at a speed of only 47 mph. Mercedes, with their commitment to safety, recalled and retrofitted 130,000 A Class cars with ESP at no cost to their owners. This resulted in a significant reduction in the number of crashes and showed the importance of the feature. As a result, the European Union made ESC mandatory on all new cars built by January 1, 2011, and by January 1, 2014; any older model not equipped or retrofitted with ESC may not be re-sold by a licensed dealer in any European country.

In North America, Ford and GM announced all vehicles would be equipped with AdvanceTrak and Stabilitrak respectively by 2010 while Toyota offers it standard on all models in 2009. As of the 2012 model year the National Highway Traffic Safety Administration requires that all vehicles be equipped with ESC.  They are investigating placing the requirement on truck tractors and certain busses, but that is not finalized.

ESC combines a yaw rate control with anti-lock braking and traction control. Yaw is the rotation of an object around a vertical axis, in other words spinning to the right or left. To enable the system to recognize the problem, in other words the skid, requires a number of sophisticated sensors.  The first sensor is a steering wheel angle sensor. This sensor determines the rotation of the wheel and determines the direction that the driver was intending for the vehicle to travel.  The yaw rate sensor determines the rotation rate of the vehicle, or what direction the vehicle is actually turning.  A lateral acceleration sensor or accelerometer measures the speed of the skid. The ABS wheel speed sensors measure the speed of each individual wheel.  A hydraulic modulator measures and regulates the amount of braking pressure to an individual wheel, which differs from the ABS braking. This system can generate additional hydraulic and/or vacuum pressure as needed for just one or more wheels.

The electronic control unit (ECU) receives all the inputs from the sensors and systems and then analyzes and computes a course of action to counteract the uncontrolled state of the vehicle. Often this is incorporated into the same unit that controls the ABS and traction control, through a Controller Area Network. This is interfaced into the ABS, Traction Control and the engine ECU’s so as to not give any contradictory signals.

Many ECS systems have an override switch so that the driver can disable the ESC under certain conditions such as deep snow, driving on a beach or if a smaller spare tire had to be installed. Some systems also had a limited mode which raises thresholds so that drivers can performance drive their vehicle at or near its limits. Also, systems are designed to reset to turn on the next time the vehicle is started.  ESC only intervenes when it senses a possible loss of steering control, when the vehicle is not traveling in the direction that the driver is steering it. Examples of this are situations such as during an emergency evasive maneuver, hydroplaning, or an understeer or oversteer during poorly judged turns on slippery roads. The system could also activate in an unwanted way during high performance driving because the steering input may contradict the direction of travel such as during drifting.

The system can work on an surface from dry pavement to a frozen lake, often correcting a skid much faster and more effectively than the typical driver, sometimes even before the driver senses loss of control. This has led to some concerns about drivers becoming overly confident of their vehicle’s ability or their driving skills. Because of this, when the system activates, an indicator light illuminates on the dash to let the driver know that the vehicle’s handling limits have been approached. Some even offer an audible warning tone if the driver puts the vehicle into a dangerous situation.

ESC manufacturers emphasize that the system is not designed as a performance enhancement or a safe driving enhancement, but rather to help a driver recover from a bad situation. ESC does not increase traction or enable faster cornering, but it will enable better cornering. A reckless maneuver such as severe hydroplaning due to excess speed in deep water or trying to negotiate a turn at a speed the car is not capable of safely negotiating.

When the steering sensor and the yaw sensor send contradictory signals, the ECU pulls up the individual wheel speeds, the gradient and if equipped, the roll angle signals. The ECU quickly analyzes the signals and sends out the corrective signals, whether it being a separate braking application, throttle retarding or other corrective action. This is accomplished by the computer inputting the signals into a preloaded mathematical control algorithm and compensation signals being sent out depending on the severity of the departure from the baseline numbers.  

As far as cost and effectiveness, it is estimated that the cost of the ESC technology over and above a car equipped with ABS and TCS is about $125-250. This is a small price to pay for a system that can reduce crashes by about 35 percent and by 67 percent in SUVs. An IIHS study concluded that ESC reduces the likelihood of fatal crashes by 56 percent and single vehicle rollovers by 75-80 percent. This could translate into 3500 to 5500 lives saved each year.

Ask Joe Mechanic - Back Up Cameras and Blind Spot Monitors

Back up cameras have existed for quite a few years and have recently become more common on many types of vehicles.  A federal law will require that all new vehicles produced after 2015 are equipped with a back up camera.  Back up cameras were originally introduced for use on motorhomes where rear visibility is severely limited and also because the owner may be towing a car or trailer behind the motorhome with little to no visibility of the towed object.

            Adding a backup camera is a simple process for many manufacturers, since they already equip newer vehicles with a screen used for navigation or playing DVDs which can double as a backup monitor. They are now offered as standard or optional equipment on many SUVs, trucks and vans, and on many higher-end automobiles. On these vehicles, the camera is wired so that when reverse is selected, the display will show the camera view and switch back to GPS or DVD when the vehicle is taken out of reverse.

Most cameras use a wide angle or a fisheye lens to give a wider view of the entire rear of the vehicle. Blind spot alert cameras also use this type of lens. With a rear view camera, the display automatically does a horizontal mirror image flip so that you can get the correct side displayed on the viewer. With these lenses, you get an uninterrupted view of the entire rear of the vehicle.

I want to give you some simple information in easy to understand terms in case you are choosing to purchase a back up camera kit to install on your vehicle. One of the most important features to consider in the purchase of a camera is whether or not it has an automatic switching feature.  Meaning that the display comes on as soon as you put your vehicle into reverse. This is quite simply accomplished if the system is so equipped, by connecting a single wire into the back up light circuit. Additionally, this type can be turned on manually by pushing a power button or a wireless remote if so equipped. Some of the advanced systems can even operate multiple cameras.

The second important feature is the ability to provide the mirrored or reverse image. This means that the picture on the display will duplicate what you would see in the rear view mirror. Some high-end systems actually allow you to select between normal and mirror images. Many of the low priced systems, such as many of those offered on Ebay, do not have this feature. If it is not listed in the features, assume it is not there and do not consider buying it.

A wide-angle field of view is also very important. Low priced systems do not offer more than a 60 or 90-degree view.  While this may be okay for a small automobile, it is not nearly sufficient for a medium to large vehicle. Look for a system that offers 120 to 150 degree field of view with a 1/3-inch image sensor. A camera that offers 180 degrees or more is also not recommended, as it will give a distorted view.

There are two types of sensors, CCD (charge coupled device), and CMOS (complementary metal oxide semiconductor). The CCD image sensor is the preferred type as it offers greater clarity than CMOS. Sharp and Sony produce the highest quality CCD sensors, check to see who manufactures the sensors for the system you are considering.

Also, remember that the camera is mounted on the exterior of the vehicle and is therefore exposed to all sorts of weather conditions. The cameras are generally made to withstand it, but it is important to make sure that the cables and connectors are weather resistant. Many low-end systems use RCA type cable connectors similar to your TV or VCR; these connectors are not weather resistant.  Do not buy a system that will place these in exposed areas!  However, this type connector is okay, and is actually better for use in the interior of the vehicle.

Infrared night vision is also an important feature that can be easily misunderstood. Infrared gives the ability to see in very low or no light situations, which is quite important for night use. On a high quality system, the infrared LEDs turn on automatically when the unit measures the background light below a certain level.  Infrared light is not visible to the human eye as it is out of our vision spectrum, but the camera is designed to make use of it. A good camera will give at least 20 feet and ideally 30 to 50 feet of night vision range.  Don’t buy a system that gives less than 15 feet, as that is less than one car length.

One of the most serious questions to consider is not whether the system will work on your vehicle.  Most systems are designed to by universally compatible, but, how long and how well will they work? Many of the lower priced units do not come equipped with a voltage regulator. If a unit does not have one of these, it is at the mercy of a constantly varying voltage from the vehicle’s electrical system.  This factor will either cause eventual damage to the system, or at least cause serious variation in picture quality. Some high quality cameras are even designed to be adjustable for vehicles that have 24 or even 32-volt systems such as buses and heavy trucks.

If you are purchasing a system with an audible monitoring, make sure that the audible pickup is weatherproofed.  LCD monitors are the preferred type as they offer full color as opposed to the CRT screen’s gray or green screen. For best picture quality, always select a TFT-LCD type monitor. For larger vehicles, a five-inch or larger monitor is preferable, whereas in smaller vehicles or where space is limited, a three or four inch screen is sufficient.

There are four basic types of cameras; the type of mounting mostly determines the difference. Surface mounts are best suited for larger vehicles were it could be mounted on any flat or nearly flat surface.  The camera should be aimed downward at about a thirty-degree angle.  For pickups, cars and smaller SUVs the flush mounted camera is the preferred choice. This camera gets mounted through a hole in the back of the vehicle and should be set at a slightly downward angle. License mount cameras can be mounted on the license plate bracket as long as the camera can be adjusted to the proper angle. There are also side and forward facing cameras for those specific applications.

A hard-wired system will always offer a higher quality picture than a wireless system, as these are susceptible to interference from radio, TV, and cellular transmitters. Most of the wireless systems sold on Ebay will turn out to be a complete disappointment. Hopefully, armed with this information, if you go shopping for a camera, you will be able to find a system that suits your needs and budget, and gives you the kind of service that you deserve for your hard earned investment.

Ask Joe Mechanic - Rear Parking Assist

Rear parking assist is a feature that has been around for about ten to twelve years on select higher end vehicles and slowly became more popular on many SUVs and other vehicles.  However, back-up cameras are gradually replacing it. The system is designed to give warning of any object behind the vehicle while the car is backing up, and to give a more frequent warning as that object is being approached.  There are basically two types of systems in use. Both are considered proximity sensors, which will give off an audible and sometimes a visible warning while backing up. The two types are either electromagnetic or ultrasonic sensors.

            Ultrasonic proximity sensors are the more common of the two types and also the most recognizable. These systems usually have about four or five approximately one-inch diameter round sensors installed in the rear bumper cover. These sensors detect the distance between the object and the sensor by emitting acoustic pulses. A control unit measures the return interval of each reflected signal and calculates the distance. The system then warns the driver by emitting an audible tone inside the passenger cabin with the frequency of the tone signaling the distance. It emits a faster tone as the vehicle approaches the object until as it is very near it will emit a continuous tone.  Some vehicles have incorporated an LED or LCD indicator to provide a visible as well as the audible warning. A portion of the newer vehicles using this system even show the location and size of the object as a colored block on the vehicles’ infotainment system.

           

Generally, rear sensors are automatically activated when the vehicle is placed in reverse. One drawback of ultrasonic systems is that they rely on the reflection of sound waves, which may not be reflected off a flat object or a flat object that is set at an angle that prevents the return signal from reaching the sensor. The other drawback that I have personally witnessed is the pickup of false readings from heavy rainfall. A third, but minor drawback is that this type of sensor must be externally mounted, usually in the bumper fascia.

Mauro Del Signore patented electromagnetic parking sensor systems in 1992. These sensors rely on the vehicle moving slowly and smoothly toward the object to be detected. Once noticed, the signal will continue even if the vehicle stops moving. Once the vehicle resumes motion, the signal will become more frequent and intense until the vehicle stops moving and changes direction. The advantage to this system is that it can be mounted on the inside of the rear bumper without requiring any holes to be drilled or the cover to be defaced. It is also now possible to order a camera to work in conjunction with this system.

Next week we will cover backup cameras and blind spot monitors as these two systems utilize the same technology.  Some information for this article was sourced from Wikipedia.org.

Ask Joe Mechanic - Anti-Whiplash Head Restraints

Anti-whiplash head restraints were first introduced in 1999. Whiplash is the sudden jerking motion of the head in a rear end collision. This injury is often minor to mild and will go away after a few days or weeks. However, about 10-15 percent of whiplash incidents will cause long term or permanent injury and the pain and effects can be debilitating.

            Saab was the first manufacturer to introduce an active anti-whiplash headrest system as standard equipment across their entire product line. Although the company obtained patents for its system, they offered the technology to any other company that wanted to use it as they felt the importance of limiting these injuries was more important than the financial gain that they could obtain. A little later the same year, Volvo introduced their own system called WHIPS. These are the two basic systems that are in use, and while they are both doing the same job, they differ in design and operation.

            The Saab system is such a simple system that it is hard to believe that it took so long for someone to introduce it. The headrest consists of the outer headrest assembly, which is attached to an arm that is anchored in the upper part of the backrest. The lower end of the arm is attached to a flat plate that is located in the lower center of the backrest.

When the automobile is struck in the rear, the person’s body will be pressed into the seat by the impact. That pressure pivots the headrest forward to contact the back of the head, preventing the rearward snapping motion that causes the injury. As soon as the impact is over, the headrest returns to its original position and requires no repairs or resetting. The other plus to this system is that in the event of multiple impacts, it will activate upon each impact and be ready for the next.

            The Volvo system, WHIPS, is somewhat different. In the event of a rear-end collision, the seatback moves with the occupant while the headrest remains rigid. A WHIPS seat also has a plate in the backrest, but in this design, it actually absorbs some of the energy of the impact. This occurs while the bottom of the backrest pivots to allow movement of the hip joint, and moves rearward to absorb additional energy. The one major difference with this system is that it does require repairs to the seat to restore it to its correct operation and seating position.

            Studies of vehicles with anti-whiplash protection systems, sustaining rear impact collisions by various testing agencies have shown a reduction of short-term whiplash injuries by between 25-40 percent.  However, even more important is the effect on long-term whiplash injuries, a reduction of a staggering 54 percent. When you consider the high costs of rear impact injuries and the pain that the victims suffer, this is a very significant reduction in cost and in pain and suffering.

The most important thing to remember if you own a vehicle with an anti-whiplash protection system is to keep your headrest properly adjusted. When I was selling Saabs a number of years ago, we were instructed to share and demonstrate to the customer the proper alignment of the headrest. That positioning is to have the horizontal centerline of the headrest even with the person’s ears. In this position, the system will offer maximum protection.

           

The improvements in headrest technology have been impressive. In 1995, the National Institute for Highway Safety gave only 3 percent of vehicles a good rating at reducing head/neck injuries. By 2005, just ten years later, that number had grown to 51 percent.

            I can personally attest to the effectiveness of the Saab system.   About two months ago, my family and I were traveling to Atlantic City in our 2001 Saab 9-5SE. On Route 42, traffic was stopping in front of us. While at a complete stop, a young girl, talking on her cell phone, rear-ended us without apparently braking at all. Our Saab was totaled; we were pushed into two other cars immediately in front of us, and our vehicle was shortened about six to eight inches. The police and the insurance appraiser both estimated impact at about 50 MPH. The only injury suffered by the four people in our car was a sore left shoulder and arm by my wife. These systems do work, and if you are thinking about a new vehicle, it is something well worth factoring in to your buying decision.

Ask Joe Mechanic - Side, Curtain and other Air Bags

Side airbags utilize a different type of system for deployment. They are usually packaged into the backrest of the front seats and deploy by splitting the seam of the covering.  Though a few manufacturers place the bag into the center post between the doors. The system is set up with a pressure sensor in each door and each door has a sealed covering inside the inner door trim to maintain it as a sealed cavity. When the door gets hit, the change in pressure from the outer panel crushing sends the signal to the ACU, which then sends the trigger signal to the appropriate airbag(s).  The airbag will then deploy in a manner similar to how the front airbags do.

Some manufacturers, such as Saab, have developed a two-stage side airbag where the lower or torso section of the bag deploys first, and then a split second later the upper section deploys. This is intended to prevent the whipping motion that would cause the head to strike the side door.

            Certain vehicles use a head curtain airbag in place of or sometimes in conjunction with the seat-mounted side airbag. Head curtain airbags deploy from the same signal as a side airbag from the pressure sensor in the door.  They also deploy in a similar method, but deploy downward from the inside of the roof-rail. Head curtain airbags can offer an additional protection if the vehicle is equipped with a rollover sensing system. If so equipped, the head curtain airbag can deploy in the event of a rollover to prevent injury, and can possibly even prevent ejection from the vehicle.

Gyroscopes and accelerometers that determine the angle of inclination, the speed and direction of travel, and send their signals to the ACU actuate rollover systems.  This in turn, analyzes the signals and deploys the airbag or bags if needed. These sensors are the same ones, which actuate a fuel shutoff in the event of a rollover. Usually on four-wheel drive vehicles there is a manual switch to shut off the rollover system if the operator is going off-roading.

            There are also some vehicles that are equipped with either knee or torso frontal airbags. These systems work similar to and read the same signals as the front airbags.

            Seat-belt pretensioners are an important part of most airbag systems. When the trigger signal is sent to the airbag, the same signal goes to the seat-belt pretensioners for the front seat occupants. Each seatbelt unit has a small tube, usually about six inches long with an actuating charge at the lower end, attached to the recoil mechanism on the seat belt retractor. When the unit receives a trigger signal, the charge goes off, locking the belt and propelling the lock up the tube, which pulls in three to four inches of slack from the seatbelt and locking it in place to restrain the person occupying that seat.

When locked, the seat belt may be pulled so tight that it might have to be cut it if the latch cannot be released. While working as a Saab technician, I had to remove and replace a seat belt unit under warranty. The defective unit was to be returned after replacement, but we were not allowed to ship it charged, so I detonated it for shipment. I have to say that it was about as loud as setting off an M80 firecracker.  I also detonated an airbag for the same reason. 

To detonate an airbag, Saab supplied an actuator button which had two leads attached to it, one to connect to a car battery, and the other about fifteen feet long to connect to the airbag. We placed the airbag backside down on the pavement outside the building, attached the leads and detonated it. The bag actually jumped about four to five feet into the air and the sound was extremely loud. My only thought was, ‘did I really want something like that going off in my face?’  However, considering the possible alternatives in the event of a serious crash, I guess I would appreciate it after all.

            Next week we will review anti-whiplash head restraints. Some information for this article was obtained from www.wikipedia.org.

Ask Joe Mechanic - Air Bags Part 2

Many people do not understand the operation and inherent dangers of airbags. While airbags are one of the best safety features introduced in vehicles since the seatbelt, they do contain certain dangers due to their designing and operation.  This is especially true if the vehicle’s occupants are taking certain care as recommended.

            In design, the airbag system is fairly simple. An Airbag Control Unit (ACU) is a specifically designed Electronic Control Unit (ECU) or computer which receives signals from a number of sensors in the vehicle including impact sensors, side door pressure sensors, wheel speed sensors, brake pressure sensors, accelerometers, gyroscopes, and seat occupancy sensors. Upon receipt of the required signals (information) from the sensors, the ACU will send out an electronic signal to the trigger in the required airbag or airbags and other related items such as seat belt pretensioners.  The trigger then sets off a chemical reaction, which creates a gas that rapidly inflates the airbag.

            To explain this in a little more detail, after the ACU receives an electronic signal and sends out a trigger signal, it reaches a pyrotechnic device called an initiator or an electric match. An electric match is generally an electrical conductor wrapped in a combustible material, which will burn with just one to three amps of charge in less than two milliseconds. This ignites a gas generator, which in the case of an airbag is a mixture of a number of chemicals. In the most commonly used mixture, this sets off a series of three separate chemical reactions to create nitrogen gas. The time lapse from impact to receipt of the signal is normally 15 to 30 milliseconds, with a further 20 to 40 milliseconds to full inflation.

            The one chemical used in most airbags is sodium azide, which is highly reactive and gives off toxic byproducts, which are neutralized in the third step of the process. This is the reason many people complain of burning of their skin or in their throat after an airbag deployment.  Sometimes the byproducts do not get 100% neutralized, resulting in some irritation, but there are no known permanent effects.  There are replacement chemicals, which have been tested, and many manufacturers are using in the latest generation airbags. Though, many of the older airbags will be around for a long time. There is also testing on another chemical ongoing, which holds even more promise as a suitable replacement. The reason that many of the original chemicals were chosen is that the chemicals cannot be hygroscopic, in other words, they cannot absorb water, which would affect the operation of the airbag. The need to totally isolate the effects of water from the system is the reason for many of the connectors having a thin gold plating to prevent corrosion.

            After the third stage of the reaction is completed, the bags have fully inflated. There are small bleed holes in the bag to allow a controlled deflation as the body comes forward to contact the bag. This cushions the body and head and the controlled deflation allows a slowed forward movement rather than a sudden stop. Another advantage of the newer chemicals is that the operation temperature of the reaction is lower, so there is less chance of getting any burns from the airbag.

            Unlike crash tests into barriers, real world crashes occur at all sorts of angles, so a crash sensor must be designed to recognize this and to send the proper signals. The presently used sensors are called a MEMS accelerometer. It contains a small integrated circuit with microprocessors and a micro-mechanical element that moves quickly upon deceleration. This changes the built-in resistance of the unit, which triggers the electronics to send the signal to the ACU.

            At present, the federal requirement is that an airbag must deploy at a 14 miles per hour barrier collision or the equivalent deceleration. Another requirement is in the event of a fire in the vehicle, when a threshold temperature of 300 to 400 degrees F is reached, the airbags will automatically deploy. This is called auto ignition and is to prevent a total explosion of the entire airbag module.

            The newest airbag technologies are being designed to adjust to factors such as the severity of the crash: the size, seating position and posture of the occupants, seatbelt usage, and how close the person is seated to the airbag. They use multi-stage inflators with specific sensors to adjust the force of the deployment.

            The dust released during deployment has long been a source of complaint from people who experienced an airbag deployment. It is usually cornstarch, French chalk, or talcum powder, which is used to lubricate the bag while it deploys.  It is not harmful.

It may cause some minor irritation of the throat and eyes.  However, that usually occurs only if the person remains in the vehicle for a period of time after the crash, such as during an entrapment.

            Some automakers such as Mercedes Benz call for the replacement of any un-deployed airbags after a period of years in order to guarantee their effectiveness in the event of a crash in an older airbag equipped vehicle. Most manufacturers who do recommend replacement consider a lifespan to be about fourteen years. On the other hand, Volvo, a very safety-oriented company has said, “airbags do not require replacement during the lifetime of the vehicle except after deployment.”

Next week we’ll look at side airbags, seat belt pretensioners and other airbag systems. Some information for this article was obtained from Wikipedia.org.

Ask Joe Mechanic - Air Bags Part 1

Even though airbags have been around for quite a number of years, they have undergone a number of changes in recent years.  Some other safety systems are dependent on the airbag system for their operation.  Therefore it is important to understand how they operate. It is also imperative for your own safety to know how they operate and to possibly dispel some of the myths about airbags.

            American John Hetrick and German Walter Linderer first patented airbags in 1951. Linderer’s system was deemed ineffective as it depended on compressed air either released by bumper contact or by manual release by the driver, but it inflated too slowly to provide any margin of safety. Hetrick however, was an industrial engineer and had also worked with torpedoes in World War II.  He put this knowledge to use in designing and building an operable airbag. He actually worked for one of the “Big Three” automakers at the time.  Even though airbags are now required standard safety equipment on every car, when he showed his invention to each of the Big Three, there was no interest in purchasing or using it in their cars. At that time, the automakers could not see any way that it would make their cars more saleable or increase their profits. Saftety was not considered that important then as it is today. After his patent expired in 1971, Ford experimented with it in a few cars.

            The first major breakthrough in airbag technology came in 1967 when Allen Breed developed an electromechanical airbag crash sensor, which would detonate a small charge of sodium azide. Ford, Chrysler and an Italian company were soon experimenting with variations of this. In the early 1970s, both Ford and GM offered airbags on government fleet vehicles. Oldsmobile offered a drivers airbag on their Toronado model, but it was dropped in 1977 for lack of interest. Part of the problem of acceptance at that time was the fact that seatbelt usage was approximately ten percent of the driving public. During this era, airbag manufacturers required that the drivers use their seatbelt at all times, so this meant that most people wanted nothing to do with it.

            In 1981, Mercedes Benz introduced an airbag system that integrated a seatbelt with a pretensioner that would tighten the belt to limit forward movement in the event of a frontal collision. This essentially became the first supplemental restraint system (SRS). In 1987, Porsche became the first manufacturer to offer standard driver and passenger airbags on the 944 Turbo and as an option on the other 944 models. In 1988, Chrysler became the first US automaker to offer standard driver’s airbags on its most popular models, followed a year later by its availability across its entire product line.

During the 1990s, airbags became more common in many different vehicles; especially after the US Transportation Efficiency Act of 1991 mandated that all passenger cars and light trucks built after September 1, 1998 must have driver and passenger front airbags as standard equipment. During the 2000s, side impact airbags became commonplace, first on high-end luxury cars, later on many medium-priced cars and then even on some entry-level models. In recent years, head curtain, knee and torso airbags have been installed on some vehicles.

            The early 2000s brought some changes in the front airbag systems. The first change was the second-generation airbags, which deployed with less force than the earlier bags, especially in lower speed collisions. The next innovation was integrating a sensor into the system, which determined when there was no one occupying the passenger seat or someone who weigh less than a predetermined weight and deactivated the passenger bag. This also resulted in lower repair costs as the passenger airbag and the dashboard cover did not have to be replaced.  There are some inherent limitations to airbags. First is the fact that airbags will not protect someone in the event of multiple impacts. Once an airbag deploys, it deflates quickly and then is rendered useless.

            A second even more dangerous and more common situation is called an underride collision. This takes place when an auto strikes the rear of a large delivery truck or tractor-trailer. The ICC bumper which is standard on most North American tractor trailers, will often break away when struck from behind. This means that the vehicle will go under the back of the truck, sometimes as far as the windshield or on rare occasion even further, resulting in serious injuries or even death by decapitation. The problem here is that the impact is not sufficient enough to set off the airbag until the vehicle could potentially be way under the truck, without the airbag having deployed. European trucks require a much stronger rear bumper, and many newer North American trucks have a better-built reinforcement system.  However, there is no requirement to retrofit the thousands of trucks on the road that are not reinforced.

            A third problem has recently surfaced and received a lot of press coverage due to a major recall of GM vehicles and now some other automobiles too. This is due to if the power to the airbag system is interrupted because of defective ignition switch or other factors, the airbags will not deploy in the event of a crash.  This loss of ignition also affects many other systems such as power steering and brakes and there is a high likelihood of a crash if the switch cuts out while the car is in motion.

            The final limitation or hazard of airbags is the risk of injury from airbag deployment if the front seat occupants are not wearing seatbelts and move toward the airbag at time of impact. Also, children or adults of small stature have a risk if seated too close to the airbag.  The people who place a rear-facing child seat in the front place the child at high risk of serious injury or death if the airbag deploys.  However, when you consider that between 1990 and 2000, the US National Highway Traffic Safety Administration estimates that airbags are directly responsible for saving approximately 6,400 lives as opposed to 175 fatalities caused by airbags (104 of those being children).

            Next week, we will examine how airbags operate. Some information for this column was sourced from Wikipedia.org.