General Motors is globally adopting a newly designedelectronic throttle control (ETC) actuator that reduces weight compared toprevious designs by 15 percent and improves performance.

"The new design also supports up to 5 mm lower hood lineover prior designs with associated fuel savings," says Jack Stockbridge, anelectrical technical specialist with GM Powertrain.

The improved aerodynamics and weight savings are achieved inpart through materials' innovations in seven components, including a newconcept in post-mold heat treating that improves moisture resistance.

GM has been a leader in applying electronic throttlecontrol, which removes the mechanical link between the accelerator pedal andthe throttle body. A sensor located at the gas pedal measures pedal angle andtransmits a signal to the engine control module (ECM), which directs anelectric motor to open the throttle at the appropriate rate and angle. Othersensors also provide data.

ETC is said to offer outstanding throttle response andgreater reliability than a mechanical connection, which typically uses a cablethat requires adjustment. The throttle can be moved irrespective of theposition of the driver's accelerator pedal and facilitates cruise, traction, andstability control.

The new electronic throttle control actuator was developedas a USCAR project, and noneof the technology is patented. Details of the new component were unveiled at thejudging of the Society of Plastics Engineers Automotive Division InnovationAwards. The actuator was a finalist in the competition. Winners were announcedNov. 9 (see sidebar below).

"This single actuator provides an optimal interface for theglobal range of engines with throttle bores spanning 40 mm to 85 mm," saysStockbridge. It combines the combined "worst case" limit specifications of GMFord, and Chrysler. USCAR, founded in 1992, is an umbrella organization forcollaborative research among the three largest US.-based car makers.

Some automotive engineers in Detroit are somewhat cynicalabout meaningful innovation coming from USCAR, but the electronic throttlecontrol actuator appears to have real substance.

The three primary technology developers on the project are GM, ContinentalAutomotive Systems, and DSM, a Dutch producerof engineering plastics that has U.S. headquarters in Evansville, IN.  

Interestingly, one of the key materials technologies in theproject is resistance to hydrolysis, a chemical reaction during which water  breaks down, affecting polymer stability.Moisture absorption issues with polymers were one of the problems citedby Toyota in gas pedal failures.

Heat Treatment

DSM application development engineers, led by Tony Padden,developed a new post-mold heat treatment process that improves moistureresistance of engineering plastics and also improves wear properties.

"The heat treatment reduces the lattice structure of thepolymer to provide excellent resistance to moisture," says Padden. Aheat-treated Stanyl polyamide 46 used in an intermediate gear achieves 30percent weight reduction while retaining an aged endurance performance thatmatches carbon fiber, according to Padden.

The Stanyl 46 compound is 50 percent filled with glass fiberbut has the same filling efficiency as a 30 percent glass compound because of ahigh-flow additive and use of a fluroropolymer as an additive. A ribbed webimproves fiber orientation in a flange that goes as thin as 1.3 mm.

The post mold heat-treating process was also used to improvethe heat deflection temperature of polyamide 6 by 36 percent, to better than 260Cfor an electric motor brush card. The improved heat resistance allowed designof an all-plastic part.

"The motor power level would typically dictate metal brushboxes mounted to plastic cards due to high temperature exposure," says Padden.

For another part in the assembly - a secondary access cover - DSMcreated a proprietary dye that allows for very high speed laser welding with noblistering or vaporization.

In an interview at K 2010 in Düsseldorf, Germany, BertHavenith, global automotive technical manager, says DSM plans to use thematerials' technology in electronic throttle control actuators used by Europeanand Asian car manufacturers as well as the U.S OEMs.

Four processors contributed significantly to the technologydevelopment: gear specialist ABA-PGT ofManchester, CT; Dynaplas,Toronto; GRWTechnologies, Grand Rapids, MI; and Insertech, Cary, IL.

Other innovations in the ETC actuator include a new class ofDC brush motor, tri-blend ball bearing grease, and 0.2 degree digital position sensing.