DELPHI AIR VALVE, POWER PISTON INNOVATION BOOSTS BRAKE SYSTEM RELIABILITY
20 March 2002 - DuPont Engineering Polymers

Delphi Automotive Systems' vacuum brake boosters benefit from a thermoplastic air valve and tandem power piston that is lighter, stronger and more durable than previous generation components. Mass production of the air valve is already underway and a new power piston component for Delphi's next generation vacuum booster will soon be featured on vehicles produced in North America.

Tandem power piston handles the pressure
A central part of the vacuum booster, the tandem power piston converts and multiplies atmospheric air intake into hydraulic pressure that activates the brakes. Switching from thermoset to high performance polyamides enabled engineers to significantly reduce the power piston's wall thickness and achieve a 60 percent weight reduction, while still meeting the criteria of withstanding more than 3,000 pounds of force, according to Delphi. "We worked with our suppliers to push the envelope on geometric tolerances," said Michel Vermoesen of Delphi Dayton Technical Center. "With support from DuPont, Delphi was able to achieve tolerances unknown in this industry."

The strength capability and dimensional stability of DuPont Zytel HTN high performance polyamide make it possible to reduce the thickness of the piston's walls. This enables the piston to have larger air passages, which contribute to better air-flow and allow for improved packaging and assembly of mating components.

Air valve is light and tough
The air valve, a component at the heart of the firm's Generation II vacuum boosters, delivers a weight reduction of 19 percent while increasing strength by more than 15 percent to improve function and reliability, according to Delphi. The old valve, made of PPS, was replaced with DuPont Zytel HTN high performance polyamide as a running change this year in Delphi's current brake systems on more than 4.5 million vehicles.

The air valve regulates airflow in the vacuum booster, defines reaction ratio and provides feedback to the driver under braking conditions. The application required a high strength material able to withstand high forces. Also, the material was required to be dimensionally stable and hold tight tolerances in an intricate design. The air valve specifications also demanded exceptionally low warpage to ensure proper sealing performance under extreme braking conditions and temperatures.

"Today's brake systems are required to handle more weight as content is increasing on a greater number of vehicles. This is particularly true for all truck and SUV platforms," said Vermoesen. "Moving to different materials allow us to increase strength without negatively impacting cost or performance, which adds significant value for our customers and the end consumer."

In addition to supplying Zytel HTN, DuPont provided advance support from the origin of the concept in the form of computer-based simulation studies to predict warpage and mold flow. DuPont also provided technical support to the component molders, DynaPlas Ltd. and Pixley Richards, Inc.

http://plastics.dupont.com

More News:
  • For March 2002
  • From DuPont Engineering Polymers
  • For Engineering Plastics