- 01 July 2008 -
PPA housing for car suspension unit

DUPONT’S ZYTEL® HTN polyphthalamide (PPA) with 35 wt. % glass fibres has been chosen by Woco Industrietechnik GmbH for the housing of a pneumatic switchover unit used in air suspension systems from Continental Automotive Systems.

The housing is 133 mm long, 83 mm wide and 70 mm high and is produced using precision injection moulding. Tolerances of ±0.05 mm are possible due to the high flowability of the Zytel HTN grade used and its very low tendency to warp.

Working temperatures range from -40°C to 80°C. Short-term temperature peaks can reach 120°C at a maximum operating pressure of 16 bar. In its new condition, the housing is required to withstand a burst pressure of 35 bar.

DuPont’s PPA also leads to lower manufacturing costs compared to die-cast magnesium housings traditionally used for such units, as no further refinishing work is required, and that the complex-shaped parts can be produced in a single manufacturing stage.

“We chose Zytel HTN PPA 51G35 due to the positive experience we have had with the material to date,” says Peter Henninger, development engineer at Woco. “It meets all our requirements in terms of mechanical strength and is highly-suited to this application. Moreover, the material maintains its very high dimensional stability and accuracy even at very high temperatures. This helps ensure that an air-tight seal is created between the switchover unit and the compressor unit for its entire lifetime, which is in turn critical for the reliable operation of the air suspension system.”

The switchover unit contains coils, electro- and pneumatic valves as well as several check valves. It connects directly to the compressor unit and manages the air supply to the suspension system. Depending on the car make, it is installed either under the front bumper, near the exhaust or in the car’s interior such as in the spare wheel cavity. The housing is therefore exposed to aggressive media such as cleaning and brake fluids, oils, lubricants and contaminants such as dust and sand during its entire lifetime.

DuPont; www.dupont.com

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