Polyamide (PA) is playing a key role in enhancing fuel economy through its usage as cage material for tandem pinion ball bearings in passenger car axles including the one in the 2013 Ford C520 Escape. The 30% glass fiber-reinforced grade Stanyl TW200F6 PA46 from DSM Engineering Plastics (Birmingham, MI) contributes to a 1.5% saving in fuel consumption compared with an all-steel tapered roller bearings.
Polyamide cages facilitate design of energy-efficient auto bearings
In total, four Ford vehicles, two Chrysler vehicles and GM's Cadillac ATS utilize the injection-molded bearings, with GM also planning to use them on truck axles and differentials starting in the spring of 2013. The tandem ball bearings are manufactured by Schaeffler Technologies (Herzogenaurach, Germany).
In automotive differential, axle and power take-off (PTO) applications, steel cages are traditionally used in taper roller bearings. "Metal is used in the cages of these all steel solutions due to strength and chemical resistance to hypoid gear oil," says Bill Burnham, Business Development Manager, Powertrains, at DSM Engineering Plastics. "This type of oil is typically quite aggressive upon most plastic materials."
For the more energy-efficient tandem ball bearings, however, the cost position at which they must compete precluded the use of a steel cage. Tandem ball bearings are more efficient on account of the lower rolling resistance of ball bearings (less contact area) versus roller bearings.
"Stanyl TW200F6, [however], demonstrated acceptable resistance to Hypoid Gear oil up to 150°C, as well as an appropriate balance of stiffness and flexibility necessary to insert the ball bearings into the cage and retain them," says Burnham. Dimensional stability was also a factor in material selection.
Currently 12 different cages have been developed for use in these tandem bearings with sizes ranges from 30 to 70 mm in diameter. The mass of each cage ranges from 5 to 9 grams. This new bearing work as drop-in replacements for all tapered roller bearings.
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