Plastic Regulator Simplifies Car Door AssemblyPlastic Regulator Simplifies Car Door Assembly

Thermoplastic door modules have over the years triggered no small amount of parts consolidation within car doors. The latest effort comes from Faurecia Interior Systems, whose engineers have come up with a thermoplastic door module that for the first time integrates a cable-driven, rail-less window regulator.

The new regulator, currently found only on the rear doors of Daimler Chrysler's 2007 Dodge Nitro SUV, does away with much of the separate hardware that normally raises and lowers the windows. "There's usually a lot of assembly work associated with the window regulator," says Mike Twork, a development leader at Faurecia.

Typically, the window glass sits in a metal lift plate that rides up and down on one or two steel rails. The motor that does the lifting resides within a drum housing that bolts onto the door module substrate. Cables connecting the motor and lift plate typically have to be routed through Bowden sleeves.

The Dodge Nitro's new regulator system eliminates or integrates most of the components that normally have to be assembled. The system has no steel rails. Instead, the glass snaps into a molded acetal lift plate that rides directly on the carrier. The drum housing has also been molded into the carrier. And the cables no longer require Bowden sleeves.

Susan Yester, a senior manager for organic materials development in Chrysler's Advanced Materials Group, calls the window regulator a prime example of the parts consolidation possible with innovative plastics design, materials and processing. In this case, the new system resulted in a weight savings of about 25 percent compared to a single-rail regulator. Twork estimates that the time to assemble the system dropped by about half.

As for the materials and processing, Faurecia molds the carrier out of a polypropylene filled with Twintex long-glass-fibers and polypropylene filaments, blending the compound at the molding machine. Twork explains that the long-glass-fiber allows the part to be made from a low-cost, general purpose polypropylene while still meeting the loading requirements. "With the long glass, we were able to avoid the cost of a more expensive base resin," he says.

And those loads aren't all that easy to meet. The system has to withstand stall loads up to 334N. "Abuse loads" - think of a thief trying to push down the glass - extend up to 650N. Toughest of all to meet is a constant load creep test that involves 800 hours exposure at 90C and 80 percent relative humidity. "The window still has to cycle at regular intervals throughout the test," says Twork.

Faurecia began development on rail-less regulator designs about five years ago, and the Nitro represents the first commercial launch, according to Twork. Right now, the system is only on the Nitro's rear windows, which have a cycle test requirement of 15,000 cycles versus 25,000 cycles for the front windows. "The system does meet all the requirements for the front door too," Twork notes.

The new regulator recently won an Innovation Award from the Society of Plastics Engineers. And Twork says Faurecia plans to offer the system more widely in the future. "Every door is different," says Twork. "But we think a rail-less system could work wherever there's currently a single rail regulator."

--Joseph Ogando

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