New Unipiston clutch piston technology in series production; enables better fuel economy

6 November 2014

Federal-Mogul Powertrain’s new high-modulus injection-molded Unipiston clutch pistons are now in series production at the company’s facility in Chivasso, Italy. The technology was a 2013 Automotive News PACE Award Winner in the process category.

Unipiston is a one-piece, rubber-to-metal bonded piston that hydraulically engages clutches to activate the gearshift. The compact one-piece design reduces the number of leak paths while improving reliability and simplifying assembly, and allows transmission designers more flexibility, including increased clutch apply pressures, higher rotational clutch speeds, and larger diameter clutches. This flexibility enables transmissions with additional clutches to be packaged in a smaller space, while providing improved fuel economy, reduced emissions and enhanced vehicle performance.

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The PACE Award citation noted that increasing hydraulic pressures and reduced packaging space in new generation dual clutch and automatic transmissions have triggered the need for higher tensile strength and higher modulus (stiffer) elastomer lips on bonded pistons to resist deflection and wear. However, the higher viscosity of materials satisfying these requirements inhibits flow in the injection molding process.

To produce a high-modulus bonded piston using environmentally-friendly materials, Federal-Mogul Powertrain developed a new elastomer material, tooling and manufacturing processes. Higher productivity, lower scrap rates, and an industry-leading doubling of modulus was the result.

Federal-Mogul Powertrain now has the unique ability to manufacture bonded clutch pistons using a high-modulus, environmentally-safe material. The breakthrough allows us to offer bonded clutch pistons designed with an elastomeric material possessing a modulus approximately twice as high as production bonded pistons on the market today, resulting in at least twice the life in high-pressure cyclic bench testing than current production products.

Conventional bonded piston seal materials manufactured using traditional injection molding are limited in their modulus to around 10 megapascals (MPa) because elastomer viscosity increases with modulus, resulting in challenges when filling the mold cavity. Federal-Mogul Powertrain’s combined development of the new elastomer material and manufacturing process results in a Unipiston with a modulus of more than 20 MPa, which cannot be attained using traditional injection molding processes.

The introduction of the original bonded clutch pistons by Federal-Mogul almost 30 years ago helped make clutch pistons more compact and easier to assemble. High-modulus bonded pistons mark a similar breakthrough and usher in a new era of more efficient, more compact transmissions.