Mazda2 drops weight to deliver driving dynamics
To make the body structure lighter and stronger, the 2011 Mazda2 features extensive use of high-tensile strength steel, with the highest strength steel (dark blue) in the crash-critical areas.
Originally launched in Europe, Japan, and Australia in 2007 to worldwide acclaim—including a 2008 World Car of the Year award at the New York International Auto Show—the Mazda2 subcompact finally comes to the U.S. showrooms this summer.
While powered by a 100-hp (75-kW), 1.5-L four-cylinder engine, the four-door Mazda2 was designed to deliver the same maneuverability and driving dynamics that the automaker has come to be known for, without adversely affecting fuel economy—29/35 mpg manual, 27/33 mpg automatic—or safety. To achieve this, the development team employed a rigorous weight-reduction strategy.
“Fun to drive in a Mazda is all about having a real connection between a driver and the car—how that car responds to every input and every desire that the driver has, making it feel natural and intuitive,” Dave Coleman, Product Development Engineer, Mazda North American Operations, said at the car’s Montreal media introduction. “Turns out, you don’t need a lot of power to do that, you just need the car to sort of read the driver’s mind.”
The development team shaved 10% off the weight of the previous-generation model, making it the lightest vehicle among its competitors. Weight reduction was achieved in two ways: application of new materials and methods to make body structure lighter and stronger, and examining parts and subassemblies to find reductions wherever possible, similar to the gram strategy used on the MX-5 sportscar program.
“We went through piece by piece and analyzed in detail every little gram that we could shave off of each piece, and when you add those up you actually have a pretty big difference,” Coleman said.
Compared to the previous model, extended use of high-tensile-strength steel in the body shell shaved 50 lb (23 kg), and reviewing the structure of the total suspension system saved an additional 28 lb (13 kg).
“Fifty-three percent of the body weight is some grade of high-strength steel,” Coleman said. “The highest strength steel is in the crash-critical areas where the side impact would happen or in the back to transfer load onto both frame rails.”
Another method to reduce weight and improve the structure was used in the bonding techniques.
“The door openings and rear hatch are some of the highest stress areas in the car, so around the rear hatch opening, we used a heat-activated structural adhesive. We put the adhesive between the two panels and when you spot weld it, that activates the adhesive and creates a continuous bond,” Coleman said. “And then around the door openings, we used more spot welds than we had before. Combined with those two techniques, if we had gotten the same structural benefit from simply adding more material, it would have added 6 kg.”
Rigorous examination of even the most standard vehicle parts uncovered additional opportunities to save weight. Major changes included optimizing the wiring harness layout (-6.4 lb [-2.9 kg]) and redesigning the hood latch and hinges, door latches, and window regulator motors (-5.55 lb [-2.52 kg]). Even the door speakers were examined, cutting the weight in half from the previous generation.
“We changed the driver magnets from a conventional ferrite magnet to a neodymium magnet, which is the magnetic equivalent of high-tensile-strength steel, more magnetism per weight, so we can put a smaller magnet in there, and because the magnet was lighter, we could optimize the frame of the speaker, which added up to another 2.2 lb,” Coleman said.
For the suspension system, the front control arms, which were previously made from two separate stampings welded together, are now made from a single stamping that is easier to produce and 3.4 lb (1.5 kg) lighter. The torsion beam axle at the rear was also changed, with the trailing arm shorter and lighter.
“In total, weight savings of all of the suspension changes that we made added up to 13 kg of unsprung weight we took out of the car,” Coleman said. “That makes an incredible difference in how we can make the car ride and handle at the same time.”
Matt Monaghan
Original article: http://www.sae.org/mags/AEI/8599