Machine Design

Fabrico and Alfmeier team for more reliable automotive lumbar support

Engineers in the Seating Comfort business unit of Alfmeier Präzision AG, Treuchtlingen, Germany, ran into a problem with lumbar-support devices they supply luxury automakers like BMW. The modular subsystems give the driver electropneumatic control over the seat contour with massage and memory functions, but the units were failing prematurely and damaging adjacent seat foam.

The electropneumatic, valve-driven unit lets the driver determine the amount of air that inflates a rubber-bladder assembly, controlling softness and back support. The entire lumbar support is composed of three 18-gage-thick bladders welded into a 414 × 54-mm assembly. It must perform reliably for 10,000 inflation-deflation cycles with a normal operating pressure of approximately 4.4 psi and hold 12 psi without bursting.

Alfmeier engineers discovered bladders rubbing against the foam of the seat cushion caused premature wear to both the foam and the bladder, noise, and problems adjusting the back support. They needed to isolate the bladder from the foam without affecting the inflating and deflating process and still meet customer flammability standards.

Alfmeier took the problem and a sample of a high-performance, high-cost material that met their needs to Fabrico, Kennesaw, Ga. Ultimately, Fabrico engineers recommended encasing the existing bladders in a “bag” of polypropylene felt.

The durable, silky material is commonly used as a filter in pharmaceutical, beverage, and fuel applications. In addition to withstanding inflation-deflation cycles of the bladders, the felt meets U.S. and international supply specifications for flame retardancy of interior trim materials in passenger cars, multipurpose passenger cars, commercial vehicles, and buses.
Fabrico engineers proposed four die-cut felt pieces be wrapped around and between the lumbar bladders and sewn into a bag that would glide over the seat-cushion foam instead of abrading it.

Currently, Fabrico procures the material, die-cuts and orients the parts, and ships kits from its plant in Ontario, Calif., to one in Monterey, Mexico, near the Alfmeier assembly facility in Apodaca where the final wrapping and sewing is done.

The arrangement gave Alfmeier a local supplier, and polypropylene felt cut the cost of protecting the lumbar support bladders while extending bladder life. Lower costs made the system more attractive to customers, including Mercedes. MD

TAGS: Materials
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