It may seem a long way in engineering and NVH terms from premium European cars such as Audi’s A5 and A7 to light duty trucks, but GKN Automotive has bridged that gap with its latest lightweight all-wheel drive (AWD) modular propshaft. Many pickups suffer a significant amount of unwanted NVH emanating from the front propshaft, with its two universal or CV joints and an interconnecting shaft positioned below and close to the passenger cabin. But now GKN Automotive has “re-characterized” its premium car driveline system to an entirely different vehicle category.
“With a traditional truck front propshaft, the level of noise entering the cabin is perceived as a drone,” explained Michael Miller, GKN’s propshaft product technology manager. “We’ve worked on applications of our new technology where the cabin NVH levels have been dramatically reduced. Positive results stem from the combination of joints used in our lightweight modular front propshaft.”
Opposed track design
The GKN propshaft forgoes the traditional Rzeppa type layout where all joints face open in the same direction. Instead it uses an opposed track designed to better balance the joint’s internal forces. Its flat, radial-offset construction allows weight reduction and increases articulation angles “The counter-track principle allows the tracks to steer the balls,” Miller said, “allowing the elimination of heat generating sphere surfaces of the cage to outer race, therefore allowing high speed CVJs to run more efficiently under higher angles typical of front propshafts.”
The new propshaft also incorporates what Miller describes as advanced sealing methods developed to protect components in extreme conditions and “vastly extend” lifecycles. “This has been achieved using over-molded technology, which chemically bonds rubber to a steel substrate,” Miller explained, “thus avoiding any additional sealing media or mechanically crimping of rubber to steel components.” The sealing system uses a base polymer Hydrogenated Nitrile Butadiene Rubber (HSB5 HNBR) developed in collaboration with Zeon Chemicals.
Miller said the big development program challenge for GKN was significant performance improvement with reduced weight. “The aim was to apply relatively sophisticated technologies seen in other segments but never applied to the full-size truck and SUV segment, where high load and robustness are imperative,” he said. “We had to ensure the CVJs remain lubricated throughout their lifespan despite the extreme uses of the vehicles. Both CVJs on the one-piece front propshaft utilize over molded boot designs which eliminate traditional sealing media components such as O-rings and gaskets by an integrated seal design in conjunction with the boot.”
The difference between the truck and car applications? It comes down to required running angles. The Audi applications are “low” (< 3°) articulation angle applications. The PX1-41 countertrack geometry used for an FCA application required a higher (~12°) continuous joint running angle. The new countertrack is an optimization of interface, sealing system and component complexity reduction for these new application requirements. Several models that now incorporate the scalable system are based on GM’s 2019 T1XX platform and include Silverado, Sierra, Suburban, Yukon and Escalade. It is also used on FCA’s DT platform for the RAM 1500.Continue reading »