SEAT BELTS AND AIRBAGS Mercedes-Benz
Competence in Safety. Safety is indivisible. Mercedes-Benz has been passionate about making cars each one even better than the last from day one. Since the first model invented by Gottlieb Daimler and Karl Benz, cars have become not only faster but also more comfortable and considerably safer. And even though the traffic volume on our roads has increased several-fold, the risk of accidents remains relatively low thanks to the enormous progress made in the areas of active safety (accident prevention) and passive safety (minimisation of the risk of injury during accidents). Mercedes-Benz has made key contributions in these fields with a programme of development spanning several decades. Safetyconscious design has always been and remains a vital aspect of the Mercedes-Benz passenger car development. A pioneer in automotive safety. Many new developments in automotive safety first saw the light of day in a Mercedes, often long before they appeared in competitor vehicles. As a result the Mercedes-Benz brand has become synonymous with automotive safety around the world. Seat belts and airbags are perhaps two of the most well known and still most effective passive safety systems. Mercedes-Benz first offered its customers 3-point seat belts in 1968 and, in 1980, was the world's first automotive manufacturer to install front airbags in standard-production vehicles. The protective capabilities of these systems can only be fully realised if seat belts are used on every trip: buckle up and then drive. Wearing a seat belt alone can prevent many injuries or lessen the severity of injuries, whereas an airbag alone cannot provide the same degree of protection, since it is designed only to supplement the protective effect of the seat belt. Understanding safety. In order to understand how seat belts and airbags provide protection, it is important to know about occupant movement in the event of an accident. Upon impact, a vehicle is either decelerated rapidly (when colliding with another vehicle or object) or accelerated when hit by a moving object such as another vehicle. When a vehicle is decelerated or accelerated, inertia always causes the occupants to move in the opposite direction to the applied impact force. Restraint systems are intended to reduce the risk of contact between the occupants and the vehicle interior caused by this occupant movement. Such systems primarily include seat belts, and if necessary supplemented by seat belt emergency tensioning devices (ETDs), seat belt force limiters and airbags. However, seat belts and front airbags cannot generally prevent the risk of injuries caused by objects entering the vehicle from the outside. Seat belts are vital. The seat belt is the most important restraint system in the vehicle. When worn correctly, it most effectively reduces occupant movement during a collision. All occupants must therefore properly fasten their
seat belts before every trip. Only then can seat belts and supplemental restraint systems such as airbags provide the best possible protection potential. ETDs and seat belt force limiters. The front seat belts and some of the outer rear seat belts are equipped with ETDs. In addition, in some seat belt systems, belt force force limiter is tuned to the front airbag which, in turn, takes on some of the seat belt induced forces, thus providing a more even load distribution. When the ignition is on, the ETDs are deployed during a frontal or rear-end collision of sufficient severity, that is, accidents with high longitudinal deceleration or acceleration sensed over a significant period of time in an early phase of an impact. In vehicles equipped with rollover sensors ETDs are activated during a lateral rollover, if an additional protection potential is anticipated. Seat belt force limiters will come into action during a severe frontal collision. Other deployment events are described in detail in the operator's manual. In vehicles equipped with an occupancy sensor for the front passenger seat, the front passenger s ETD is only in operation when the sensor detects an occupant in the front passenger seat or - in current vehicles - if the seat belt is fastened. After pyrotechnic deployment of an ETD which may cause some smoke release the SRS indicator lamp illuminates. limiters are included. If deployed in the event of an accident, an ETD reduces the seat belt slack. The occupant is restrained earlier and thus participates sooner in the vehicle s deceleration, decreasing the occupant loads during the collision. However, an ETD cannot correct improper seating positions, nor can it correct improperly fastened seat belts or pull an occupant back into the seat backrest. If the seat belt is also equipped with a force limiter, it reduces upon activation the peak seat belt force exerted on the occupant. The belt Seat belt height adjustment ETD in installation position
Effective co-operation. Available restraint systems for the E-class (W211) Airbags can do a lot, but not everything. An airbag increases the protection potential for a vehicle occupant properly wearing a seat belt and is thus referred to as a Supplemental Restraint System (SRS). However, even if the vehicle is equipped with airbags, occupants must still fasten their seat belts properly before every trip. On the one hand, a front airbag is only deployed in the event of an accident, if the protection potential offered by the seat belt needs to be supplemented. On the other hand, airbags only provide additional protection potential, if the seat belt is worn correctly, since: - the seat belt helps to keep the occupant in a more favourable position to the airbag and - for example, in the event of a frontal collision the seat belt restricts the movement of the occupant (in the opposite direction to the impact force) thus reducing the risk of injury. What happens when an airbag deploys? During deployment an airbag inflates within fractions of a second during the actual collision in order to provide the occupant with additional protection. Airbag inflation is accompanied by a loud noise which usually does not affect hearing. Contact between the properly belted occupant and the inflated airbag reduces the movement of the occupant, compresses the airbag, and thus enables the hot gas to escape through the airbag's vent holes. The hot gas of a front airbag or sidebag flows out under pressure, in order to minimise the load to the occupant's head or thorax. After an accident, the front airbag or sidebag is deflated. Generally, the advantage of the supplemental protection potential provided by a deploying airbag reduces the risk of injuries, providing that the occupants are wearing their seat belts properly and are seated in a proper position in relation to an airbag. The proper seating position is as far away as possible from an airbag with the back against the seat backrest which should be in a nearly upright position. ETD and front airbag deployment logic. If the seat belt is fastened, only the ETD for that seat belt is deployed when a first deployment threshold is reached. The respective front airbag is only deployed in addition to the ETD once a higher deployment threshold is reached. Front sensors Two-stage front-passenger airbag Trigger device with roll-over sensor Front passeneger recognition with weight classification and automatic child seat recognition Additional sensor for sidebag Sidebag in seat, front Belt tensioner with adaptive force limiter Windowbag Rear sidebag Rear belt tensioner with force limiter Two-stage driver s airbag
Criteria for an ETD / airbag deployment. In order to determine the necessity to deploy an ETD and/or airbag, the electronic control unit evaluates the direction and intensity of the vehicle deceleration or acceleration over time during the early phase of an impact. The ETD / airbag deployment thresholds are variable and are adapted in response to the intensity of the sensed impact. This process is anticipatory, because the deployment of an ETD / airbag has to happen during the impact rather than at the end of or after the impact. Vehicle deceleration or acceleration and the impact force direction are determined based on the force distribution, the impact angle, the vehicle deformation characteristics and the characteristics of the object with which the vehicle collides (for example, the other vehicle). Vehicle deformation is neither a determinative factor for an ETD / airbag deployment, nor an indication that an ETD / airbag should have been deployed. This means that, even if a vehicle is severely deformed in an accident, an ETD / airbag did not necessarily have to deploy, because the impact only affected soft structures and the necessary impact severity for the deployment of an ETD / airbag was not reached. Conversely, ETD / airbags could deploy, even if the vehicle is only slightly deformed in an accident. For example, in an impact involving rigid vehicle structures alone (for example, a longitudinal member) the necessary impact severity for deploying an ETD / airbag might be reached. Furthermore, vehicle speed at the beginning of a collision or injuries suffered during a collision do not indicate whether an ETD / airbag should have deployed. In addition to the impact severity, the injury severity also depends on the type of the collision, the deformation characteristics of the object involved in the collision, and the individual physical resilience of the occupant. Special features of dual-stage front airbags. If the vehicle is equipped with adaptive, dual-stage front airbags, the front airbag is initially inflated with sufficient gas to reduce the risk of injury when a certain deployment threshold is reached. If a higher threshold is reached, based on the further evaluation of the impact severity by the electronic control unit within a few milliseconds, the front airbag is inflated with the full quantity of gas. If the vehicle is equipped with a front passenger weight classification system, the body weight class of the front passenger is taken into account along with the impact severity and seat belt usage status when determining the rate of airbag inflation.
Intelligent systems. Driver and front passenger airbags. The driver s front airbag is installed in the steering wheel housing, whereas the front passenger airbag is housed above the glove compartment (or in older models instead of the glove compartment). They can be recognised by the "SRS, "SRS-AIRBAG" or "AIRBAG" lettering. Upon deployment, a front airbag has the function to eliminate or reduce the risk of contact between the driver's head and chest and the steering wheel or the front passenger's head and chest and the dashboard. The driver front airbag inflates in front of the steering wheel. The front passenger airbag is deployed in front and above of the glove compartment. Driver and/or front passenger airbags are deployed: - during a collision with high longitudinal deceleration or acceleration sensed over a significant period of time in an early phase of an impact, - differently depending on seat belt usage, - independently of other airbags installed in the vehicle. A front airbag is not deployed in the event of a rollover unless a high longitudinal vehicle deceleration is sensed over a significant period of time during the accident. In vehicles equipped with an airbag deactivation system (AKSE) the front passenger airbag is only enabled, if the PASSENGER AIRBAG OFF indicator lamp is not lit, that is, if the system does not recognise a special Mercedes-Benz child seat (with AKSE transponders) on the front passenger seat. In vehicles equipped with an occupancy sensor for the front passenger seat, the front passenger airbag is enabled, if the sensor detects that the front passenger is heavier than a certain minimum weight. Sidebags. Upon deployment, a sidebag has the function to increase the protection potential for the thorax (but not for the head, neck or arms) of the occupant sitting on the side of the vehicle sustaining an impact which generates a high rate of lateral vehicle deceleration or acceleration over a significant period of time. The sidebag deploys in the area of the door below the side window (door installation position) or directly next to the affected seat (seat backrest installation position). Sidebag installation positions vary depending on the vehicle model. See the operator's manual for further details. The basic principles for the evaluation of the necessity of a sidebag deployment are similar to those for the deployment of a front airbag in the event of a frontal collision. However, the accident situation must be detected much earlier in the event of a side-impact collision, as the distance between the occupant and the object involved in the collision is much smaller in a side collision than in a frontal collision. Sidebags are deployed: - during a collision with high lateral deceleration or acceleration sensed over a significant period of time in an early phase of an impact, - in general, only on the side of the vehicle receiving the impact; in vehicles equipped with an occupancy sensor for the front passenger seat, the front passenger sidebag is only enabled, if the sensor detects that the front passenger is heavier than a certain minimum weight or in some vehicles also if the seat belt buckle is fastened, - independently of the deployment of the front airbags - independently of the deployment of ETDs (if activated), - generally not in the event of a rollover, unless a high lateral vehicle deceleration is reached over a significant period of time in an early phase of an impact,
- in vehicles with an airbag deactivation system (AKSE) on the front passenger side, even if the PASSENGER AIRBAG-OFF- indicator lamp is lit, that is, if the system recognises a special Mercedes-Benz child seat (with AKSE transponders) on the front passenger seat. Head protection systems. Depending on the vehicle model (sedan or convertible), a Mercedes- Benz may be either equipped with windowbags (installed in the roof frame) or head-thorax bags (installed in the door or seat with a larger airbag for the head area than the sidebag). The following section describes in principle the deployment events of head protection systems. Refer to the operator's manual for further details about the deployment of head protection systems, since Mercedes-Benz vehicles feature different restraint system designs depending on the model vehicle. Windowbags. Your Mercedes-Benz vehicle may be equipped with windowbags (as an option or standard, typically in sedans or coupes but not in convertibles), which have the function to increase the head protection potential for the occupant sitting on the side of the vehicle receiving the impact. Upon deployment, the windowbag enfolds in the area of the side windows. Windowbags are deployed: - during a collision with high lateral deceleration or acceleration sensed over a significant period of time in an early phase of an impact, - in general, on the side of the vehicle receiving the impact, - generally not in the event of a rollover, unless a high lateral vehicle deceleration is reached over a significant period of time in an early phase of an impact or if a rollover sensor is installed, and if an additional occupant protection potential is anticipated. In the latter case windowbags will be deployed on both sides of the vehicle; - independently of the deployment of the front airbags, - in vehicles with an airbag deactivation system (AKSE) on the front passenger side, even if the PASSENGER AIRBAG-OFF- indicator lamp is lit, that is, if the system recognises a special Mercedes-Benz child seat (with AKSE transponders) on the front passenger seat. Head-thorax bags. If the vehicle is equipped with head-thorax bags (instead of windowbags and front sidebags ), the deployment of such a bag has the function to increase the head and thorax protection potential for the occupant sitting on the side of the vehicle receiving the impact. Depending on the installation position the head-thorax bag inflates either in the area forward of the front seat back or in the area of the door and side window of the affected side of the vehicle. Head-thorax bags are deployed: - during a collision with high lateral deceleration or acceleration sensed over a significant period of time in an early phase of an impact, - on the side of the vehicle receiving the impact, - independently of the deployment of the front airbags, - in vehicles with an airbag deactivation system (AKSE) on the front passenger side, even if the PASSENGER AIRBAG-OFF- indicator lamp is lit, that is, if the system recognises a special Mercedes-Benz child seat (with AKSE transponders) on the front passenger seat. We hope we have given you a helpful insight into this complex safety topic and wish you many more hours of safe driving in your Mercedes-Benz.
Not all of the systems described in this brochure are available for all Mercedes-Benz models. In addition, some of the safety systems described in this brochure are not available as standard equipment for certain Mercedes-Benz vehicles. Detailed information showing which of the systems described are standard, optional equipment, or are available for your particular Mercedes-Benz passenger car model in your country can be obtained from current model series brochures. The purpose of this brochure is to provide an understanding of the principal functionality of restraint systems. Restraint system designs may vary depending on the model vehicle. This publication went to print on 19.01.2004. We reserve the right to make modifications in vehicle and system design and brochure content even without updating this brochure. DaimlerChrysler AG, Stuttgart MKP/K 7259. 0001. 02-00/0204 Printed in Federal Republic of Germany/Imprimé en République fédérale d Allemagne www.mercedes-benz.com