April 12, 2007

Development of the world's highest speed thrust needle roller bearing

[ World's highest thrust needle roller bearing rotational speed realized by optimized cage and roller design of cage ]

NTN corporation(hereafter NTN) has developed a high-speed thrust needle roller bearing to enable 1.5 million dmn value to meet the high speed requirements of high powered electric motor units for hybrid cars and the multiple gear range of automatic transmissions.

In recent years, high-speed needle roller bearings have become required for high powered electric motor units for hybrid cars and the multiple gear range of automatic transmissions in the pursuit of more fuel efficiency vehicles.

NTN's design features the following:

- Improved surface finish of the cage pocket contact with the roller end, while maintaining the conventional cage configuration which has a good oil flow.

- Special contact configuration of roller end and cage pocket which does not affect roller movement.

- Point contact of the roller end and cage pocket at the center point of the roller end with low circumferential velocity is made possible by the configuration of roller end curvature.

These features enable to curb the wear and seizure of the cage, and improve the permissible rotational speed from the conventional 900,000 dmn to the world's highest 1.5 million dmn. In addition, the temperature rise at high-speed operation is reduced by 35% in comparison with conventional bearings while the lubrication reliability is improved.

[ Features ]

(1)	World's highest rotational speed :
	1.5 million dmn value ( improved by 67% in comparison with NTN's conventional bearing ) [ Rotational speed 21,000 min^-1, with bearing pitch dia. 71.5 mm ]
(2)	Improvement of lubrication reliability with low temperature increase:
	Reduction of temperature rise by 35% ( in comparison with conventional products when operated in 900,000 dmn range under oil temp of 80°C )

[ Application ]

Electric motor units for hybrid cars, Automatic transmissions and CVT. In addition, NTN is pursuing general industrial machine applications.

[ Reference ]

*	dmn = dm ( Bearing pitch dia. mm ) × n ( Rotational speed, min^-1 Ex. : When bearing of 100 mm dm is operated at n = 20,000 min^-1, dmn value is 100 × 20,000 = 2 million

[ Product photo ]

High speed thrust needle roller bearing [ I.D. 62.8 × O.D. 80 × Width 2.5 mm ]

[ Structure ]

Cross-section drawing of high speed thrust needle roller bearing

[ Sales points ]

[ Technical approach ]

Apply new process to cage pocket outer side to improve surface finish and enlarge area at contact point
- ⇒Decrease cage wear(Improvement of anti-drilling property)
Optimize configuration of roller end and rolling surface
- ⇒Decrease cage wear (Improvement of anti-drilling property), Decrease temperature rise
Optimize internal design
- ⇒Decrease cage wear (Improvement of anti-drilling property), Restrain temperature rise

[ Performance ]

Permissible rotational speed of new product:
- dmn value is more than 1.5 million which is more than 1.6 times com to conventional products
Decrease temperature rise [ as compared with conventional products ]
- ·Temperature increase with bearaing operating at approx. 900,000 dmn (oil temp. 80°C):35% less than conventional product