As every engineer knows, thicker and heavier means stronger.
In the automotive world there are a myriad of problems with this, most of them related to that word “heavier.” Weight has become the biggest single issue facing everyone involved in the design, development, manufacture and sale of passenger vehicles today.
It takes power to move an object. The heavier the object, the more power required.
Developing power requires the consumption of energy – more power, more energy whether from fossil fuel or electricity. Thus the battle against weight begins – meeting ever-stricter fuel consumption and exhaust emission regulations. The powertrain folks plug away at squeezing more kilometres from every drop of fuel through a variety of advances from high-pressure direct injection and variable valve timing to turbocharging and hybrids.
Meanwhile, the scientists and engineers over in the body and chassis departments are engaged in a struggle of their own – diets.
Reducing the weight of the vehicle pays dividends for everyone involved. A lighter car can not only be motivated by a smaller and more efficient engine, which itself requires a smaller fuel tank and cooling system, but also a lighter transmission. It can use smaller and lighter brakes, etc.
But there’s also the requirement to protect occupants. It is one thing to make a vehicle lighter, but quite another to also make it stronger.
Using materials like carbon-fibre, aluminum and magnesium is one route to reduce weight – but all are more expensive, some very much so.
Steel suppliers – and all but a very few car companies buy steel from outside suppliers – are working feverishly on a wide range of new steels that offer increased strength with less weight. The new ultra high-strength steels are up to four times harder and stronger than high-strength steel. They can also be formed in pieces that are 10-15 per cent thinner than normal steel without sacrificing strength. They can also be formed into complex shapes.
Put yourself in the development department. The plans for the new vehicle call for it to offer a whole new range of features, things that will add weight. It must have more interior space but be smaller on the outside. It must be lighter for improved fuel efficiency but stronger for more occupant protection and to give the suspension engineers a rigid platform upon which to bolt their stuff.
The seemingly opposite requirements for weight reduction and improved strength have led to some pretty interesting developments.
Mazda has established a goal of cutting 100 kilograms from every new vehicle it develops. This commitment has motivated the R&D department to go back to the drawing board and design bodies that set new standards in lightweight construction while simultaneously meeting the highest internationally-recognized current and proposed safety standards.
I use Mazda as an example because it is a small company with limited resources producing affordable mass-market vehicles where every dollar of additional cost puts it at a competitive disadvantage. The first example of this new push for lower weight and higher strength is the CX-5, the replacement for the Tribute coming in 2012.
The chassis is 30 per cent more rigid yet weighs 8 per cent less. Instead of making various structural components thicker and stronger to provide a new level of occupant protection, engineers used new generations of steel in a structure formed to not only “crumple” but also to distribute the forces of a crash around and past the occupant cell. This has been standard industry practice for several decades, but what is new is the need to do it while cutting weight.
In addition to a greater use of high-tensile steel (60 per cent of the body versus 40 per cent previously), computer-aided design and crash simulation, Mazda engineers established numerous new paths to divert energy. A process called weld-bonding results in a more thorough joining of body parts.
Smaller, lighter, stronger and safer – that’s the new mantra for the auto industry.
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