Viton® fluoroelastomer has helped Toyota meet tough US PZEV (Partial Zero-Emissions Vehicle) Phase III evaporative emissions standards for the Camry Hybrid car. The automaker was able to reduce fuel evaporation from a vital fuel pump sender seal to below the required 54mg/day by replacing the HNBR material with Viton®.
The Toyota Camry Hybrid is powered by a 2.4 liter 4-cylinder hybrid DOHC 16-valve VVT-i engine (generating 147 hp at 6000 rpm, and 138 lb.-ft. at 4400 rpm), coupled with a permanent magnet AC synchronous motor (output 199 lb.-ft at 0-1500 rpm, and 105 kW at 4500 rpm) supplying additional power and torque in assist mode. Estimated fuel economy is impressive, with up to 35 mpg (6.72 liters/100 km) claimed for highway motoring.
Near Zero Permeation with DuPont™ Viton® Fluoroelastomer
When the California Air Resources Board (CARB) changed its PZEV test requirements to Phase III fuel (Fuel C + Ethanol), permeation through existing HNBR fuel pump sender seals increased dramatically from the prescribed level of 54mg/day to 140mg/day, using the SHED test method.
The DuPont team in Japan worked closely with Toyota Motors Technical Group and Toyoda Gosei to develop the new fuel pump sender seal to overcome the permeation problem. Following DPP tests, the decision was taken to replace the HNBR rubber sealing material with Viton® GLT fluoroelastomer.
As a result, the permeation volume of Phase III fuel through the seal wall of Viton® has dropped to less than 1/20th of the previous level, from 1908 gms-mm/m2/day to less than 96 gms-mm/m2/day, easily meeting the tough PZEV requirement (see Figure 1). And oil resistance also improved.
In addition, since Viton® is stiffer and has better compression set-ability than HNBR at low temperature, a greater compression force could be used with Toyota’s metal fuel tank locknut than before, yielding a tighter seal with less permeation.
Viton® as Standard Equipment
The switch to Viton® has helped Toyota meet to the PZEV-Phase III fuel evaporation limit of less than 54mg/day. As a result, the new fuel pump sender seal of Viton® is now standard equipment on the next generation Toyota Camry Hybrid car, and also future Toyota hybrids.
About DuPont™ Viton® Fluoroelastomers
Viton® fluoroelastomers help automotive manufacturers meet today’s and tomorrow's tough LEV II (Low Emission Vehicle), PZEV and Euro 5 and 6 automotive evaporative emissions control legislation by providing fuel system sealing capability for the lifetime of the vehicle (15 years/150,000 miles) at operating temperatures well above 150°C (with peak temperatures at 225°C) or as low as -40°C. Viton® also resists permeation and attack from new flex fuel/alcohol/ether blends, biofuels and engine oils.