SAAB'S 'BALANCED FORCES' SAFETY CONCEPT IS ENGINEERED FOR REAL-LIFE
NORCROSS, Ga. - In a frontal collision, often it's not the other vehicle or object in the crash that results in your most severe injuries. Even though you've been expertly protected by airbags, seatbelts and crumple zones up front, it's could be the cargo you're carrying behind you that deals the critical blow. Unless you're driving a Saab, of course.
The Saab 9-5 has been engineered to withstand a load of up to 175 lbs. shifting during a frontal collision without the back seat fracturing. "It's one of our important real-life safety tests," commented Annika Kindberg from Saab's Crash Safety Center.
"Say a family has been out on a ski weekend, and despite the tie hooks in the back of the wagon, much of the load hasn't been secured - it's loose. OK, say they're involved in a crash, which accelerates the load in the rear the equivalent of 30g. This turns their 175-lb. load into 5,300 lbs. If the back seats weren't designed to take this force, the load would intrude forcibly into the passenger compartment."
If these figures mean little to you, then imagine a small truck; it's roughly the same weight. "It's no good having excellent frontal protection if you're going to be hurt by your luggage," Kindberg said.
Engineered solutions to real-life situations are fundamental to Saab's build integrity. The new 9-5 continues to build on its reputation as a car with state-of-the-art safety. For 2002, there are many significant enhancements, including adaptive airbags; further developments of Saab's advanced airbag sensing system; seatbelts that offer improved collision protection; better knee protection for driver and passenger; an improved deformable steering column; new, more absorbing headlining; an upgraded interior that meets new Free Motion Head regulations; ISOFIX child-restraint fittings are now standard; and the occupant safety zone has been repackaged around the engine and new five-speed automatic transmission.
Building on a safety platform
"What we've done with the new 9-5 is to improve on many areas. New technologies that weren't available to us when the car was first launched have now been incorporated," Kindberg commented. "There's been a continuous program of improvement."
Last year, the Saab 9-5 was given a top, four-star crashworthiness rating by EuroNCAP after the inclusion of a new pole impact test. Following the tests, the EuroNCAP consortium stated that the Saab 9-5 was the safest car they had ever tested. The EuroNCAP consortium is comprised of the Swedish Road Administration, the British and Dutch Ministries of Transport, the EU Commission, Fˇdˇration Internationale de l'Automobile (FIA), Allgemeiner Deutscher Automobil-Club e V (ADAC), Alliance Internationale de Tourisme (AIT) and International Consumer Research and Testing (ICRT).
While acknowledging the accolade, Saab engineers have always tried to build high levels of safety into their cars by studying what happens in real-life crashes - more than 6,000 actual accidents have been analyzed - and then incorporating those findings into making safer Saab cars. Real-life accident investigations have led to such laboratory simulations as the moose test, which makes sure the A-pillars and roof structure can withstand impact with Sweden's natural - but often hazardous - wildlife.
The front structure incorporates three load paths that are designed to distribute crash forces. These are linked to an energy-absorbing system that collapses progressively depending on the collision speed. The 9-5 is designed to exhibit robust crash behavior virtually regardless of what the car crashes into. At the back of the car, similar controlled-deformation zones help to protect occupants from rear-end crash forces.
A safety cage surrounds the passenger compartment. It's made from high-tensile steel members with specially manufactured joints that are designed to resist tearing. To help protect from side impacts, the door-post B-pillar acts as a pendulum, "hinging" at the top and swinging in from the base. This assists in deflecting crash forces away from passengers' head and torso areas towards less sensitive areas of the body. To make this arrangement work more effectively, the center section of the B-pillar is very rigid, which helps resist deformation and intrusion into the interior. The door also overlaps the sill sufficiently to prevent it from sliding over and into the passenger compartment.
Three-point seatbelt harnesses restrain all five passengers, while the seats are designed to occupant from sliding under the belts (anti-submarining protection). The front seatbelts are further equipped with pretensioners and load limiters, as well as semi-automatic height adjustment to both front seatbelts and the two outer rear seatbelts.
Further head and chest protection is provided by a full-size 65-liter driver's airbag, supplemented by a 145-liter airbag for the front passenger. Standard equipment also includes front side airbags, of the head-torso type. The side airbags have a volume of 20 liters, and each consists of a lower section and an upper section. When the airbag is activated, the lower section is inflated first to protect the occupant's rib cage - it is this part of the body that is first subjected to impact forces in a side collision. As the rib cage presses into the lower section, gas is displaced upwards. This fills the upper section to help protect the head which, at the instant of impact, is furthest away from the side structure of the car and is therefore subjected to the crash forces after a slight delay.
Yet further occupant protection is provided by the Saab Active Head Restraint (SAHR) system, which is standard equipment on all new Saabs. Designed to reduce the risk of whiplash injuries, the SAHR system limits the movement of the head in a rear-end crash.
The head restraint is connected to a pressure plate in the backrest. When the car is thrown forward in a rear-end crash, the occupant will be pressed into the backrest. This pressure pushes the plate in the backrest, which moves the head restraint upwards and forward, so that it meets the head and limits its movement towards the rear before a whiplash motion can occur. To spread the load more uniformly over the occupant's back, the seat is designed to spread and distribute the crash forces over a large backrest area.
So how have Kindberg and other members of the Saab Crash Safety Center team improved upon the 9-5's already impressive credentials?
Adaptive airbag deployment forms part of 'balanced forces' safety strategy
New adaptive technology allows a less aggressive airbag deployment depending on the severity of the crash. Within milliseconds, two sensors fitted in the front bumper measure the force of deceleration exerted on the front of the car.
These sensors are fitted on the beam that supports the bumper. The bumper beam is connected to the two chassis rails, which now feature new crash boxes that are designed to deform in a controlled manner. The sensors detect the speed of crash-box deformation and feed this information to a third sensor placed in the middle of the car between the front seats. This middle sensor - or trigger - then decides the level of airbag deployment required: level 1 or level 2, depending on the impact's severity.
However, the trigger is also designed to take into account the seating position of the occupants. A switch in the seat track lets the trigger sensor know how close - or how far back - the driver or passenger is sitting in relation to the steering wheel or dashboard. Another switch in the buckle also tells the trigger sensor whether the front-seat occupants are wearing seatbelts. Having assessed all this information, the trigger will calculate at what pressure to deploy the airbags.
The ability to decide the level of pressure required for airbag deployment means protection is optimized for the individual situation. In a collision with a high level of violence, more airbag pressure is produced to protect the occupant than in a less severe impact. Or, an airbag may be triggered with less pressure for a person who drives sitting close to the wheel, so they are less likely to be injured by an airbag that deploys with too much power.
Having incorporated this adaptive technology, the crash test department then set about re-tuning the seatbelts to meet the more progressive airbag action. During the course of these changes, it was possible to reconfigure the steering-column compression force to further improve occupant protection. In addition, better protection for the knees has been incorporated into the lower dashboard. "I think we've been quite successful in balancing crash forces and directing loads to those areas of the body that can better accommodate them, while deflecting loads away from sensitive areas of the body," Kindberg noted.
Testing was carried out on both an average (50-percentile) dummy as well as a five-percentile dummy (representing the female form) to meet regulations that don't come into force for another two years. Further testing was carried out on a 95-percentile dummy, which is ahead of any legal requirements, but common practice for Saab. "It's difficult achieving consistent results for people of different sizes who sit in different positions, but this is a true reflection of real-life safety," Kindberg commented. "I believe we are one of the first manufacturers to meet new standards with the new car."
Free Motion Head tests meet new requirements
The new Saab 9-5 also meets new US requirements for head protection. Using a new test - called Free Motion Head - you measure the impact of a head form at different areas in the car's interior. The measured force must not exceed a set value.
To meet these requirements, the headlining has been bolstered with new, more absorbent lining and the A-, B- and C-pillar surrounds have been softened, too. "It shows the importance of engineering a solution for different conditions," explains Kindberg. "In a rollover collision, for example, a head will hit different surfaces in the car's interior. And once an airbag deflates, you can still have the head rebounding, so it's important to provide as much protection as possible to accommodate the collision's aftershocks." Even the mounting points for the sunvisor shades are fully deformable.
ISOFIX rear-seat mountings are also incorporated on the new 9-5 range. This provides easier and more reliable installation of child restraints. For older children, a child booster seat that pulls out from the rear seatback is available as a dealer-installed accessory.
The safety test program for the new Saab 9-5 range has been continuous for the last two years. The team has been working on a complex matrix of tests to ensure that the car meets or exceeds current legislation, as well as meeting Saab's own extensive real-life safety requirements.
"I'm pleased with the results," Kindberg said. "After all, the 9-5 was already a car with a high level of safety, but I think we've made important changes that make it even safer now. And it hasn't just been by adding airbags, which is sometimes the easy way to appear 'safer.' Our new 9-5 is built on robust design principles."