Probably the only thing more important than escaping serious injury once in an automobile accident is avoiding one altogether. The newly redesigned Mercedes-Benz C-Class takes a major step toward that goal. Its electronic handling systems anticipate certain driver mistakes and intervene, often before trouble arises. When a collision can't be avoided, however, a suite of passive and active restraints and an improved impact-absorbing chassis help protect occupants from harm. The chassis is designed to also minimize damage to major structural components which lowers repair cost. Mercedes calls the approach the Real-Life Safety Concept.
The C-Class has four safety systems that act in concert as an electronic "copilot" to keep drivers out of trouble: the electronic stability program (ESP), antilock brakes (ABS), acceleration skid control (ASR), and brake assist (BAS). All modulate, for specific reasons, the brakes and engine power.
Although ABS can dramatically shorten stopping distances during hard braking, drivers often apply brakes too gingerly to take full advantage of its capabilities. In such cases, the BAS system instantly applies maximum braking effort. Tests show most drivers on dry road — without the benefit of BAS — consume 73 m to stop from a speed of 100 km/hr (63 mph). With BAS, the same car can halt in only 40 m, a 45% improvement.
The ABS sensor package also serves the acceleration-skid control (ASR) system. ASR keeps drive wheels from spinning when accelerating from rest or in motion by applying braking to the offending wheel and reducing engine torque.
The ESP system helps drivers recover from skids caused by extreme maneuvers or unfavorable road conditions such as ice, moisture, or gravel. Feedback from accelerometers and speed sensors get compared to calculated safe thresholds. ESP quickly and almost imperceptibly returns cars outside these limits to the correct "line" by pulsing brakes on one or more wheels and by cutting engine torque.
However, none of these systems can prevent another car from hitting yours. Some 80% of all collisions on Europe's roads happen at speeds of 15 km/hr or less, but other more serious categories are on the rise. For example, one study says side-impact collisions with injuries to occupants have more than doubled since 1985 accounting for nearly 44% of all automotive fatalities. To account for such a wide range of scenarios, Mercedes engineers designed into the C-Class features that help it better tolerate minor and major impacts — from any direction.
The basic idea is to dissipate collision energy in the body and outer sections of the chassis while the occupant cell, surrounded with high-strength steel panels, remains intact. The occupant cell and surrounding structure of the new C-Class contains twice as much high-strength steel as its predecessor. The greater strength allows certain panels to be thinner without compromising structural integrity. Some of the most highly stressed parts have been beefed up from 0.8 to 2.0 mm thick. The result is a stronger, stiffer, and lighter weight design.
Many of the injuries suffered during automobile accidents come from high deceleration and acceleration rates. Unfortunately, the design of many conventional seat belts and air bags can, in some cases, exacerbate the problem. For example, air bags that deploy too vigorously may injure occupants. Especially at risk are drivers of smaller stature sitting close to the steering wheel or children in car seats strapped in the front-passenger location facing forward.
Addressing these concerns are new adaptive front air bags. The system adjusts to conditions in two ways. First, the passenger-seat air bag is disabled when a child car seat carrying a special transponder is sensed by a seat-mounted antenna. Second, both front air bags are fitted with a two-stage gas generator. Detection of a relatively minor frontal impact — at speeds to about 35 km/hr — fires only one inflator unit per bag. The partially filled bags more gently decelerate occupants during minor collisions. More severe frontal impacts trig-ger the second stage within 5 to 15 msec of the first to give maximum protection.
The seat-belt system receives two upgrades: belt tensioners and force limiters. The belt tensioners instantly remove up to 13 cm of belt slack so occupants are held more firmly in place during a crash. Doing so takes better advantage of the protection afforded by the rigid occupant cell and also helps lower deceleration loads. Belt-force limiters built into the belt's inertia reels further quell loads. Here, a torsional member twists under load to allow belts to "give" which lessens chest impact forces.
With all these systems in place, the chances of surviving a crash unharmed improve greatly. But what if the car becomes disabled in the process? Or worse still, you or others are injured and rescue workers aren't informed in a timely manner. A study conducted by Munich Technical Institute in Germany says health consequences for one-fifth of severely injured victims would be greatly reduced if help were to arrive within 12 min.
Not to worry. An onboard automatic emergency calling system dubbed Teleaid, similar to Onstar in the U.S., uses a mobile phone to alert rescue personnel of a wreck and guides them to the site with GPS-derived coordinates. Also encoded in the message is the accident type (rollover, etc.) and severity so workers can arrive better prepared.
Perhaps the best way to avoid an accident in the first place, however, is to steer clear of heavy traffic whenever possible. A system called dynamic routing helps do just that.
Data from about 3,800 infrared and ultrasonic roadside sensors — that detect traffic density — feed to a traffic data provider. The provider transmits the information via the Short Messaging Service of the mobile phone network to the cars' onboard Comand navigation system. Comand uses the data to compute an alternative route: "This route has been computed on the basis of traffic news," an electronic voice alerts the driver, and the message "Congestion ahead" appears on the navigation system display. Dynamic routing is operational in Germany and is expected in other countries soon.
ALL-DIRECTION IMPACT PROTECTION
The new C-Class contains twice as much high-strength steel (painted red) in the bodyshell as the outgoing model. Frontal impacts to 15 km/hr are absorbed by an aluminum cross-member located behind the bumper and by two crash boxes (painted burgundy) made of a special, high-strength, dual-phase steel. The arrangement lessens impact forces imparted to occupants while protecting the more costly to repair structural members from damage. Rear impacts are mitigated via a rear steel crossmember fitted with impact absorbers at each end. This member is also modular and can be easily and inexpensively replaced.
High-strength steel tubes mounted directly behind the door skins help protect occupants during side impacts. The simple tube shape is easier and less expensive to make than complex extrusions. Special brackets on the tube ends direct impact energy to the door pillars.