General Motors is globally adopting a newly designed
electronic throttle control (ETC) actuator that reduces weight compared to
previous designs by 15 percent and improves performance.
"The new design also supports up to 5 mm lower hood line over prior designs with associated fuel savings," says Jack Stockbridge, an electrical technical specialist with GM Powertrain.
The improved aerodynamics and weight savings are achieved in part through materials' innovations in seven components, including a new concept in post-mold heat treating that improves moisture resistance.
GM has been a leader in applying electronic throttle control, which removes the mechanical link between the accelerator pedal and the throttle body. A sensor located at the gas pedal measures pedal angle and transmits a signal to the engine control module (ECM), which directs an electric motor to open the throttle at the appropriate rate and angle. Other sensors also provide data.
ETC is said to offer outstanding throttle response and greater reliability than a mechanical connection, which typically uses a cable that requires adjustment. The throttle can be moved irrespective of the position of the driver's accelerator pedal and facilitates cruise, traction, and stability control.
The new electronic throttle control actuator was developed as a USCAR project, and none of the technology is patented. Details of the new component were unveiled at the judging of the Society of Plastics Engineers Automotive Division Innovation Awards. The actuator was a finalist in the competition. Winners were announced Nov. 9 (see sidebar below).
"This single actuator provides an optimal interface for the global range of engines with throttle bores spanning 40 mm to 85 mm," says Stockbridge. It combines the combined "worst case" limit specifications of GM Ford, and Chrysler. USCAR, founded in 1992, is an umbrella organization for collaborative research among the three largest US.-based car makers.
Some automotive engineers in Detroit are somewhat cynical about meaningful innovation coming from USCAR, but the electronic throttle control actuator appears to have real substance.
The three primary technology developers on the project are GM, Continental Automotive Systems, and DSM, a Dutch producer of engineering plastics that has U.S. headquarters in Evansville, IN.
Interestingly, one of the key materials technologies in the project 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 cited by Toyota in gas pedal failures.
DSM application development engineers, led by Tony Padden, developed a new post-mold heat treatment process that improves moisture resistance of engineering plastics and also improves wear properties.
"The heat treatment reduces the lattice structure of the polymer to provide excellent resistance to moisture," says Padden. A heat-treated Stanyl polyamide 46 used in an intermediate gear achieves 30 percent weight reduction while retaining an aged endurance performance that matches carbon fiber, according to Padden.
The Stanyl 46 compound is 50 percent filled with glass fiber but has the same filling efficiency as a 30 percent glass compound because of a high-flow additive and use of a fluroropolymer as an additive. A ribbed web improves fiber orientation in a flange that goes as thin as 1.3 mm.
The post mold heat-treating process was also used to improve the heat deflection temperature of polyamide 6 by 36 percent, to better than 260C for an electric motor brush card. The improved heat resistance allowed design of an all-plastic part.
"The motor power level would typically dictate metal brush boxes mounted to plastic cards due to high temperature exposure," says Padden.
For another part in the assembly - a secondary access cover - DSM created a proprietary dye that allows for very high speed laser welding with no blistering or vaporization.
In an interview at K 2010 in Düsseldorf, Germany, Bert Havenith, global automotive technical manager, says DSM plans to use the materials' technology in electronic throttle control actuators used by European and Asian car manufacturers as well as the U.S OEMs.
Four processors contributed significantly to the technology development: gear specialist ABA-PGT of Manchester, CT; Dynaplas, Toronto; GRW Technologies, Grand Rapids, MI; and Insertech, Cary, IL.
Other innovations in the ETC actuator include a new class of DC brush motor, tri-blend ball bearing grease, and 0.2 degree digital position sensing.