Composite driveshafts in production vehicles

The composite driveshaft appealed first to racing and supercar enthusiasts, to whom performance was paramount and cost was a secondary consideration. But the advantages of composites — reduced vehicle weight, greater corrosion resistance and others — overcame the disadvantage of higher up-front cost for a time, among some mainstream automakers as well. A few high-production vehicles well outside the supercar category were equipped by OEMs with composite driveshafts in the 1980s through the early 2000s, including the Nissan 350, Mazda RX8, Mitsubishi Montero, and Ford E100 Econoline vans.

During the same period, there also was a successful introduction of a hybrid driveshaft design that was notable in several respects. Between 1986 and 1996, Strongwell (Bristol, VA, US) manufactured the trademarked Spicer Graph Lite driveshaft for customer Dana Inc.’s (Maumee, OH, US) Spicer driveshaft division, starting with General Motors’ model year 1988 GMT-400 pickup trucks.

The opportunity arose, says Strongwell R&D manager Joe Spanovich, because the truck’s design allowed a maximum of 100 mm/4 inches within the chassis for the driveshaft. A full-length, one-piece aluminum shaft had insufficient stiffness, and Dana engineers did not want to install a two-piece steel shaft with a bearing, which would add assembly time, cost and complexity. Strongwell devised a method to pultrude axial carbon fiber tows over a hollow aluminum tube to create a hybrid metal/composite shaft, says Spanovich: “Many, many tests were done, severe tests, that took months to complete. But it was a lower-risk solution than an all-composite part.”

The aluminum shaft, which acted as a traveling mandrel, was first covered with a polyester surface veil/isolation barrier, to prevent galvanic corrosion. Unidirectional tows of carbon fiber from Hercules, which later became part of Hexcel (Stamford, CT, US), were pulled through a resin bath of DERAKANE epoxy vinyl ester (supplied by Dow Chemical Co., Midland, MI, US, and later acquired by Ashland Performance Materials, Columbus, OH, US) and laid lengthwise against the veil. The carbon-covered tube then exited through a precision bushing and a winder that wrapped the carbon tows with glass roving. Finally, another polyester veil was placed over the entire shaft, for added corrosion resistance.

The hybrid driveshaft was 60% lighter than the two-piece steel alternative, and saved 9.1 kg per vehicle. The longitudinal carbon fiber tows stiffened the aluminum shaft sufficiently that it could handle vehicle torque without resonant vibrations, says Spanovich, who adds that at peak production, the company made 50,000 parts per month. “At that time, we were the largest consumer of carbon fiber in the world,” he recalls.

Although early mass-production efforts were largely abandoned and OEMs did not fully embrace the technology, composite driveshafts are still produced by specialists for race cars, hot rods and other specialty applications. See, for example, CW’s recent Focus on Design feature story, titled, "Carbon composite driveshaft: Tailorable performance."