1、SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirelyvoluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefro
2、m, is the sole responsibility of the user.”SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions.QUESTIONS REGARDING THIS DOCUMENT: (724) 772-8512 FAX: (724) 776-0243TO PLACE A DOCUMENT
3、 ORDER; (724) 776-4970 FAX: (724) 776-0790SAE WEB ADDRESS http:/www.sae.orgCopyright 1997 Society of Automotive Engineers, Inc.All rights reserved. Printed in U.S.A.SURFACEVEHICLE400 Commonwealth Drive, Warrendale, PA 15096-0001INFORMATIONREPORTJ2431ISSUEDOCT1997Issued 1997-10The Effects of Front-mo
4、unted Accessories on Air Bag Sensors and Crashworthiness1. ScopeAlmost all light trucks now are being manufactured with at least a driver side air bag and all will havedual air bags by 1998. The driving forces behind this feature are occupant safety, federal regulations, andcompetition in the indust
5、ry. Along with the booming popularity of pickups and SUVs, they are commonlyaccessorized with a wide variety of products. Many accessories for four-wheel drives in particular aremounted on the front of the vehicle. These products include grille/brush guards, winches, snow plows,replacement bumpers,
6、bicycle carriers, etc. Concerns have arisen over the compatibility of these accessorieswith the vehicles air bag system.The vehicle manufacturers are concerned because of their huge investment in design and crash testverification of the complete vehicle system and keen awareness of the federal regul
7、ations. The crushability ofthe front bumper and supporting structure are key elements in the system, so alterations to that area becomelogical concerns.The accessory manufacturers, dealers, and installers are concerned because the very core of their businesscould be at risk. The unknowns can range f
8、rom fear of setting off an airbag while working on the vehicle toliability issues in an injury accident situation. In some cases, the installation of the product is contrary torecommendations from the vehicle manufacturer and may void the warranty.The ultimate customers (end users) are in a unique s
9、ituation and are not being well served in some situations.Their dilemma stems from the conflict between what a manufacturer is willing to certify for sale and what thecustomer needs and expectations are. Their needs in vehicle equipment can vary widely from making a livingto recreational lifestyle i
10、ssues to simplify the desire to individualize. The precedent for front-mountedaccessories is well established. The customers for both the vehicle and the equipment are there, so findingways for them to coexist safely is beneficial to all.2. References2.1 Related PublicationsThe following publication
11、s are provided for information purposes only and are not arequired part of this document.2.1.1 SAE PUBLICATIONAvailable from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001.SAE Seminar HandbookSensor Design for Automobile Air Bag SystemsSAE J2431 Issued OCT1997-2-2.1.2 OTHER PUBLICATION“Propo
12、sed Mandatory Standard for Vehicle Frontal Protection Bars” by Australian Automotive AftermarketAssociation, 23 April 1996.3. Definitions3.1 VehicleStructure that provides signals to sensor, support for inflator and bag, and interior integrity foroccupants.3.2 SensorBrain responsible for detection a
13、nd determination of crash severity.3.3 InflatorEnergy source that generates gas.3.4 BagCushion that interacts with occupant.4. Air Bag Systems OverviewIt is helpful at this point to have a basic understanding of air bag systemsoperation. The sensor seems to be the least understood component, but the
14、 operating principle is really quitesimple. There are several types in use, but they all are designed to sense deceleration. A very commondesign is the “ball-in-tube” type illustrated in Figure 1.FIGURE 1AIR BAG SENSORThe magnet normally holds the ball against the back of the tubular cavity. Under h
15、igh deceleration forces, i.e.,a crash, the balls momentum overcomes the magnets power and travels forward into the contacts, completingan electrical circuit which activates the inflator. Many systems use three sensors, two in the front near theradiator and one in the passenger compartment area. All
16、three must make contact and “agree” before theinflator is actually activated. The sensors can be calibrated by changing the magnetic force, clearance aroundthe ball, etc. They are calibrated or tuned to interface the specific vehicle with the following crash-sensingcriteria:a. No triggering for cras
17、hes that do not require air bag protectionEmergency braking, pot hole andrough road, impact with small objects, frontal impact below design threshold.b. Triggering in time for crashes that require air bag protectionFrontal and angular impacts beyonddesign threshold including vehicle-to-vehicle, barr
18、ier, pole, and other higher speed collisions.SAE J2431 Issued OCT1997-3-The graph in Figure 2, shows some triggering scenarios and approximates the results of real crash tests. Itshows that the performance of a vehicle with front-mounted accessory can fall within the same toleranceparameters as the
19、original vehicle.FIGURE 2CRASH-SENSING SCENARIOS5. CertificationIt is possible to certify front-mounted accessories for compliance with federal safety regulationsand full compatibility with air bag systems. In the known cases to date, this was accomplished with thecooperation of the vehicle manufact
20、urer. In some cases, it was done by actual crash testing and in others itwas done by safety engineers analysis. Products certified have included snow plows, replacement winch-mounting bumpers and grille guard/winch mount combinations which retain the original bumper. Interestingly,these products hav
21、e ranged from very rigid and stiff structures to very compliant and “crushable” designs. Thisindicates that the effects of these products may be quite minimal as shown in the previous graph.Crash simulation by computer is another avenue for certification, but requires the vehicle manufacturerscooper
22、ation to supply the base vehicle parameters. It is a very complicated and lengthy computer exercise andmay still require crash testing for final verification. Extensive work in this area has been performed in Australiawith good success. Some work is believed to be in progress also at a Japanese manu
23、facturer.Certification can also be done independent of the vehicle manufacturer by utilizing one of several companiesthat have crash test facilities and are familiar with the reporting requirements. However, this is cost prohibitivefor even the larger aftermarket suppliers. Not only is the test proc
24、edure expensive, but each product should betested for each vehicle model application. Also, for each certified application, 1 to 2 vehicles will be sacrificed.Most of these products do not have the sales volumes or profit margins to amortize such high-developmentcosts.In Australia, “bull bars” are c
25、ommonly fitted to vehicles including passenger cars for protection in impacts withkangaroos. Extensive research and testing was undertaken by the Australian Automotive AftermarketAssociation to determine the effects of these bars on the air bag systems. Their conclusions are that aproperly designed
26、bar will not have detrimental effects while still providing vehicle protection. A proposedstandard has been drafted.6. Legal ConsiderationsAny modification to a vehicle which could affect a safety devices or is contrary to thevehicle manufacturers recommendations should be carefully considered under
27、 the guidance of a qualifiedlegal advisor. Some type of policy statement or disclaimer may be required.SAE J2431 Issued OCT1997-4-7. RecommendationsSeveral factors should be considered in the design of front-mounted accessories tominimize their effect on the air bag system. The most important is not
28、 to move or modify the sensors. Theyshould be allowed to function as intended. This is common sense and has been easy to accomplish withcurrent attachments. There is a trend towards single-point sensing located near the center of the vehicle, sothis requirement should be even easier to meet.The meri
29、ts of “hard” verses “soft” structures are still being debated. A “hard” or stiff structure would tend to tripa sensor earlier, according to one point of view, and thus fire the bag and better protect the occupants. Theargument for a “soft” or compliant structure is that the forces to the occupant ar
30、e lower for a given impact andthe air bag will still deploy if the forces become high enough. As mentioned earlier, both types have beensuccessfully tested. There appears to be a tolerance window on either side of the original vehiclescrushability, but it is difficult to quantify. The best recommend
31、ation would be to try to approximate the crush ofthe original vehicle in the design of the accessory. In other words, not too soft and not too hard.The vehicle manufacturers are the real key to certification. They have the knowledge, vehicles, and facilities todo the best job at the least expense. S
32、ome have already stepped up and made the certification of theseaccessories part of their new model launches. Others have recommended against them because they haventtested them. The latter stance does not meet the customers expectations. It is highly recommended that allmanufacturers cooperate with
33、suppliers to certify these accessories.PREPARED BY THE SAFE AFTERMARKET SPECIALTY SYSTEM GROUPSAE J2431 Issued OCT1997RationaleNot applicable.Relationship of SAE Standard to ISO StandardNot applicable.ApplicationAlmost all light trucks now are being manufactured with at least a driver side air bag a
34、nd all willhave dual air bags by 1998. The driving forces behind this feature are occupant safety, federalregulations, and competition in the industry. Along with the booming popularity of pickups and SUVs,they are commonly accessorized with a wide variety of products. Many accessories for four-whee
35、l drivesin particular are mounted on the front of the vehicle. These products include grille/brush guards,winches, snow plows, replacement bumpers, bicycle carriers, etc. Concerns have arisen over thecompatibility of these accessories with the vehicles air bag system.The vehicle manufacturers are co
36、ncerned because of their huge investment in design and crash testverification of the complete vehicle system and keen awareness of the federal regulations. Thecrushability of the front bumper and supporting structure are key elements in the system, so alterationsto that area become logical concerns.
37、The accessory manufacturers, dealers, and installers are concerned because the very core of theirbusiness could be at risk. The unknowns can range from fear of setting off an airbag while working onthe vehicle to liability issues in an injury accident situation. In some cases, the installation of th
38、e productis contrary to recommendations from the vehicle manufacturer and may void the warranty.The ultimate customers (end users) are in a unique situation and are not being well served in somesituations. Their dilemma stems from the conflict between what a manufacturer is willing to certify forsal
39、e and what the customer needs and expectations are. Their needs in vehicle equipment can varywidely from making a living to recreational lifestyle issues to simplify the desire to individualize. Theprecedent for front-mounted accessories is well established. The customers for both the vehicle and th
40、eequipment are there, so finding ways for them to coexist safely is beneficial to all.Reference SectionSAE Seminar HandbookSensor Design for Automobile Air Bag Systems“Proposed Mandatory Standard for Vehicle Frontal Protection Bars” by Australian AutomotiveAftermarket Association, 23 April 1996.Developed by the SAE Aftermarket Specialty System Group
