This technical information has been contributed by
Mahle
Click here to find suppliers

Polyimide Bushings Precisely Guide Connecting Rods in Electrical Wastegate Actuators

GENEVA – Mahle's electrical wastegate actuators control the volume of exhaust gas that is led past the turbo charger for boost pressure control. In its current actuator series, this tier-1 supplier uses bushings made from DuPont^TM Vespel^® TP injection molding grade to constantly guide the associated connecting rod smoothly and precisely over the engine’s service life. Unlubricated and exposed to high temperatures and aggressive substances present in engine exhaust gases, the bushings operate virtually without wear and with minimal friction, according to the manufacturer.

Mahle’s electrical wastegate actuators are used for controlling boost pressure in modern spark-ignition engines. They enable an optimized interaction between engine and turbocharger, in downsized engines specifically. The connecting rod guide bushing made from Vespel^® is reported to help achieve rapid actuating speeds and precise boost pressure control, enabling a very high responsiveness and low fuel consumption in stopped traffic. Positioned on the output side of the actuator, the bushing provides linear guidance for the lever that actuates the wastegate on the turbocharger, absorbing varying lateral forces arising from a toggle mechanism.

"The challenges placed on the guide bushing are extremely severe," said Bernd van Eickels, actuator development manager at Mahle Filtersysteme GmbH, in a press release. "In working together with DuPont, we found a special Vespel^® TP grade which meets all these requirements. One particularly positive feature was that this grade, unlike other plastics we tested, has no tendency to incorporate dirt particles or chips. The bottom line is that the guide bushings ensure a virtually constant actuator force over the entire service life."

Mahle is a prominent international development partner and supplier to the automotive industry. With its products for combustion engines and their peripherals, as well as products for electric vehicles, the group addresses crucial issues related to the powertrain and air conditioning technology–from engine systems and components to filtration to thermal management. DuPont Performance Materials (DPM) is a developer of thermoplastics, elastomers, renewably-sourced polymers, and high-performance parts and shapes, as well as resins that act as adhesives, sealants, and modifiers.

In the immediate vicinity of the engine, just a few centimeters away from a turbocharger that can be as hot as 1000°C, this bushing must be able to withstand ambient temperatures of up to 140°C. Being so close to the compressor, it is permanently exposed to vibration. It must not corrode when exposed to splashes and jets of water contaminated with dirt particles, oil, grease, and salt.

"The specified Vespel® grade is part of the wide range of Vespel® TP thermoplastic injection molding materials which are particularly suitable for mass producing components with a complex geometry," added Peter Bergmann, European transportation market segment leader, DuPont^TM Vespel® and DuPont^TM Kalrez®. "We recommended it to Mahle because it was specifically designed for use at high temperatures and with exposure to aggressive chemicals. Optimized with various fillers, this polyimide combines good mechanical properties and excellent dimensional stability with very good friction and wear behavior."

Mahles electrical wastegate actuators use bushings made from DuPont^TM Vespel® TP injection molding grade to constantly guide the associated connecting rod smoothly and precisely over the engine's service life. Image courtesy of Mahle and DuPont."