Designing Safer Bodies The Volvo Way

Soon after the car division of Volvo was bought by Ford in 1999, Volvo engineers were overwhelmed. Not by fresh development demands from their new American owner, but by a deluge of more informal inquiries from engineers in Ford's various divisions eager to tap into Volvo's prodigious knowledge base for designing safe vehicles. "We had to limit access so our engineers could get their own work done," says Thomas Broberg, deputy director of the Volvo Cars Safety Centre in Gothenburg, Sweden. A lot of that interest centered around body engineering, and it has only intensified as Ford has charged Volvo with helping to devise global safety engineering strategies. Simply put: Volvo designs some of the safest car bodies in the industry and has for decades, so who better to get the job done for all of the Ford marques?

 

Inside Out. Mattias Bergwall, body structure engineer, explains that the first step he and his team take in designing a body is not to create an initial body shell model and fit an interior within its parameters, but to situate the vehicle's occupants and work their way out. "We don't take a car and say how can we design this to be safe?" says Bergwall. "Rather we look at the occupants in many different situations, and try to determine what type of restraint systems we will have in the future. Then we set up body and packaging targets based on that." This approach leads to design decisions that most automakers would find pretty foreign to their ways of thinking. For example, powertrains are generally considered sacrosanct packages with given dimensions that body engineers are forced to work around and forbidden to tinker with. But at Volvo, nothing is more sacred than human occupants, so powertrains are freely modified to add crush space or reduce cabin intrusion. Two recent development projects illustrate this. In creating the new S40 compact sedan, Volvo conducted virtual crash tests on prototypes without engines and then rearranged auxiliary components like batteries and brake boosters to fit the crushed engine room space, rather than designing the space to fit the existing engine configuration. By taking this unconventional approach the S40 gained 200 mm of crush space for occupants even though the vehicle's overall length was reduced by 48 mm compared with the previous model. And Broberg says of the forthcoming XC90 V8: "We went so far in demanding that a transverse-mounted V8 meet our crush requirements that we could not find an appropriate engine in the entire Ford Motor Company group that would not require us to change the packaging." So they designed a new compact 60º unit that measures only 25 in. wide to fit inside the crush envelope. Bergwall sums up the body engineering philosophy: "You have to start with the blue-sky thinking of what you need to do to keep the passengers safe, otherwise you start thinking, ‘Ah, that can't work because we don't have that powertrain.'"

 

Weight vs. Safety. Bergwall sees the biggest challenge to his body design team as striking the right balance between safety and weight. In the past, Volvo added body features like its SIPS (side impact protection system) which uses steel tubes under the seats to transmit side impact forces to crush boxes in the center of the car, but this sort of safety item adds a weight penalty that Volvo can ill afford to have proliferate. So its engineers have gotten more clever about re-designing existing structures to absorb more crash force without having to add new parts. A good example of this is the complete re-thinking of the front body structure on the XC90. The S80 had been Volvo's gold standard for safety, but engineers found that a radically different design would allow the XC90 to absorb as much impact as an S80 at a lower overall weight. Bergwall explains: "With the S80, we ran the side member beams around the wheel arch to take the impact forces there. The concept relied on the bending capacity of the beams and joints. With the XC90 concept, there is a framework where you're working compression and tension instead of bending. And we use the IP beam as the final structural member of the front structure. In the S80 it is just a carrier of the steering rack, now we are using it as a structural part of the crash system. It is a much more weight-efficient system."

 

Volvo has also put an increasing amount of emphasis on materials to maintain safety standards while reducing weight. The smorgasbord of steel grades designed into the new S40 points to where the company is headed. The basic idea is to use higher strength steels on the outer parts of the body that bear the brunt of an impact and incur the most deformation, and then manage the impact forces by graduating to grades that deform less and less until the rigid passenger compartment cage is reached. To add more strength to the body, this material strategy is coupled with a design practice that is so fundamental to Volvo that it is often overlooked by others: Volvo bodies use fewer and bigger parts. Why? Bergwall's answer sounds like an excerpt from "All I Really Need to Know about Body Engineering I Learned in Kindergarten": "If you make two parts you must put them together and you will always have a weak joint." That idea recurs when Bergwall is asked about what the future holds for body engineering: "One future dream would be to get away from spot welding, since you could have stronger, more efficient bodies without it." Don't expect that any time soon, but as with just about any other idea to make bodies safer, Volvo is working on it.