Mahle Uses DuPont Bushings to Optimize Work of Electrical Wastegate Actuators

Exhaust gases account for the lion’s share of greenhouse emissions that take a heavy toll on the environment. Hence, it is important to keep them to the minimum possible level by using devices that can make engines more efficient. Mahle makes electrical wastegate actuators which regulate the volume of exhaust gas which is lead past the turbo charger for boost pressure control. In its current actuator series, Mahle uses bushings made of DuPont Vespel TP injection grade to help the associated connecting rod work precisely and smoothly so that the actuator works with minimal friction and experiences low levels of wear. In view of the high ambient temperatures and the aggressive nature of the substances present in exhaust gases, it is important to use bushings made of the best material.

The electrical wastegate actuators from Mahle facilitate an optimized interaction between engine and turbocharger, specifically in downsized engines and the connecting rod guide bushing made that is made from Vespel helps the actuator to achieve high speeds and precise boost pressure control, thus enhancing the responsiveness of the engine and economizing the use of fuel in stopped traffic. The bushing is positioned on the output side of the actuator, and provides linear guidance for the lever that actuates the wastegate on the turbocharger, while absorbing varying lateral forces that are created when the toggle mechanism is used.

The bushing is very close to the engine and just a few centimeters away from a turbocharger the temperature of which can be as high as 1000 degrees C. The bushing should be durable enough to withstand these extremely high ambient temperatures of up to 140 degrees C. As it is in a position that is so close to the compressor, it is constantly exposed to vibration. It must also be able to resist corrosion in spite of repeated exposure to splashes and jets of water that are likely to be contaminated with grease, salt, oil and dirt particules.

Bernd van Eickels, Actuator Development Manager at MAHLE Filtersysteme GmbH explained that the guide bushing faces really tough challenges on a daily basis. Mahle worked together with DuPont to develop the special Vespel TP grade material which meets all these requirements. One distinctive feature of the material was that unlike other plastics they tested, it has no tendency to incorporate dirt particles or chips. In fact, the guide bushings ensure a virtually constant actuator force over the entire service life.

Peter Bergmann, European Transportation Market Segment Leader, DuPont Vespel & DuPont Kalrez, added that the specified Vespel grade is part of a wide range of Vespel TP thermoplastic injection moulding materials that are suitable for mass producing components with a complex geometry. He said DuPont recommended it to MAHLE as it was tailored for use at high temperatures and to withstand exposure to aggressive chemicals. Optimised with various fillers, this polyimide combines good mechanical properties and excellent dimensional stability with very good friction and wear behavior.

An electrical wastegate actuator is a key component when turbochargers are used as it controls boost pressure in modern spark-ignition engines and perts some of the exhaust gas past the turbocharger via a bypass valve (wastegate) to ensure that the desired boost pressure is not exceeded. This limits maximum turbine speed. If actuators are not used, the turbocharger keep spinning at faster rates as the engine speeds rise and the throttle valve opens until an excessive boost pressure would result in knocking damage or the turbine shattering at above 230,000 to 300,000 min1 (depending on turbocharger size) and at 1000 °C or more. Either one of these can cause tremendous engine damage.

Mahle was the first firm to design actuators that are independent of intake manifold pressures and bring them into mass production in 2009. This design combines various advantages, such as faster pressure build-up in the event of abrupt load changes, quicker heating of the catalyst, gentler operation of the turbocharger in the cold start phase and reduced fuel consumption under partial load when no boost pressure is required.