For several years the only way to meet Partial Zero Emission Standards (PZEV) was with a steel gas tank having few holes to be sealed. But plastic tanks are about 30% lighter, on average, and present less difficulty forming odd shapes to take advantage of space available around components underneath a car. PZEV requirements decreased the allowable emissions from fuel tanks from 2 grams per 24 hours to 15 milligrams per 24 hours. Plastic composites were too permeable to volatiles to meet this standard. In addition, sealing the holes in a tank created more possibilities for leakage. It appeared that the only way to meet the standard was with a steel tank with a minimum number of holes to seal.
TI Automotive solved this problem with two developments: forming the tank from a layered tubular extrusion that includes emission-resistant poly-amide, developed in collaboration with Elf Atochem (PERMBLOK®) and Ship-in-a-Bottle construction. TI inserts the fuel pump and fuel gauge assembly into an extruded tube of PERMBLOK and molds the tank around it without any joining seams to seal. Sealing is necessary only for the fill pipe and gas line. Coaxial extrusion of PERMBLOK directly to the Ship-in-a-Bottle molding operation is a significant technical achievement.
The resulting tank emits less than 10 mg of volatiles in 24 hours from large tanks having complex shapes. The tank is 30 percent lighter, corrosion-resistant, and less costly than steel formed into similar complex shapes, needed for design flexibility on today's vehicles. In addition, TI Automotive found that the new process permits developing a new tank design faster, and with less tooling expense. Assembling the pump and gauge unit without a tank around it reduced scrap. This innovation renewed the competitive position of plastic gas tanks in the industry. The first tank of its kind went on a production vehicle in 2004, was designed for the BMW 3-series in 2006, and has been field monitored for continuing lifetime performance since. It easily meets California PZEV standards.