- In continuous use on GM vehicles for 30 years
- Cooperation between Nexteer Automotive, ABC Group & DuPont
- Hashtag: #SPEInnovationAwards
The first global implementation of a blow-moulded, thermoplastic elastomer (TPE) constant velocity joint (CVJ) half-shaft drive-axle boot seal used on 1984 model year Buick, Riviera, Cadillac Eldorado, and Oldsmobile Toronado sedans produced by then General Motors Corp. (GM) was selected as the 2014 Hall of Fame winner by the Automotive Division of the Society of Plastics Engineers for the group’s 44th-annual Automotive Innovation Awards Competition.
The 30 year history of the blow-moulded CVJ drive-axle boot seal
To be considered for a Hall of Fame award, an automotive plastic or composite component must have been in continuous service in some form for at least 15 years and preferably have been widely adopted within the automotive industry. This application meets the criteria: it has been in continuous use on GM cars and trucks for 30 years, and 85% of front-axle CVJ boot seals on light-duty vehicles worldwide now use TPE in this application to replace polychloroprene rubber.
This first TPE CVJ boot was the result of a cooperation between tier 1 Nexteer Automotive, formerly GM Saginaw Steering Gear Division (plastics, steering/driveline), tier 2 ABC Group (part manufacturer), and materials supplier E.I. DuPont de Nemours and Co. (Hytrel thermoplastic copolyester elastomer). The development started in 1977 and was led by Nexteer with boot design, testing, validation, and correlation to vehicle performance. The result was a successful introduction of a far more robust CVJ sealing that also was lighter, more durable, and less costly than the injection-moulded rubber boots it replaced.
Following successful launch of the rack & pinion boots in TPE, the three suppliers worked for several years to develop the CVJ boot application. Process innovations as well as specialized equipment were developed by ABC Group to blow mould what at the time was a new material. Challenges that had to be solved included parison control, material distribution to achieve thinner-walled parts and shot-to-shot consistency. Efforts paid off with DuPont developing a new grade of the TPE and ABC Group patenting process developments that permitted tighter tolerances on the sealing surface to prevent leaks, which had been a big issue with the era’s incumbent technology.
That first year, 250,000 of the parts were produced for the initial limited launch. The following year, in 1985, ABC Group produced 11-million of the TPE boots for GM cars and trucks. The application proved a resounding success. It offered initial tooling savings of $380,000 USD (versus the cost to injection mould either rubber or hard plastic). It was 65 grams / 2.3 ounces lighter than the rubber part it replaced (85 versus 150 grams / 3.0 versus 5.3 ounces). Technical developments in the application have continued, with current TPE CVJ boots weighing as little as
40 grams / 1.4 ounces.
The basic function of the part
The basic function of CVJ boots is twofold: first, it protects bearings in the constant-velocity joint by keeping out dirt, water, salt, ice, snow, mud, stones, and other road debris. Second, it keeps lubricating grease inside the CVJ as the drive axle rotates and propels the vehicle. At the time the application was developed, rubber boot failures accounted for the majority of drive-axle repairs. The team set out to develop a new boot that would solve performance problems inherent to the incumbent material.
Thermoplastic elastomer (TPE) constant velocity joint (CVJ) half-shaft drive-axle boot seal (source: ABC Group)
The challenges: from -40 degrees to chemical resistance
The part had to meet a challenging set of performance standards, including providing:
- Very good resistance to flexural fatigue to allow for high steering angles and dynamic suspension travel
- Broad temperature performance ranging from -40 to 121 degrees Celsius (-40 to 250 degrees Fahrenheit)
- Resistance to attack from chemicals (underhood fluids and greases) and ozone
- Resistance to punctures, impacts, and abrasion
- Dimensional stability at higher speeds
TPE boots are now considered “service for life” parts
The TPE boots extended product life and durability by 3-4 times and are now considered “service for life” parts, eliminating the need for replacement under normal conditions. The TPE material is also better for the environment, since the process does not generate scrap, the much longer service life means fewer parts are produced and replaced, and the parts are fully recyclable at the end of their use life. Now – 30 years after the first TPE CVJ boots hit the highway – the application still uses Hytrel resin, but weighs half (or less) what the original CVJ boots did, in part due to axle size reduction and the need for less grease.
On November 12 at SPE’s annual Automotive Innovation Awards Gala held at Burton Manor in Livonia, Mich., a representative from GM will accept the award on behalf of the original team that worked on the program. Members from ABC Group, Nexteer Automotive, and DuPont Automotive also will be recognized on stage.
