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The eBearing News
September 13, 2005
NTN Develops Thinnest Thrust Bearing
copyright © 2005 eBearing Inc.
NTN Corp. (Japan) said it has developed and scheduled production of what will be the
world's thinnest thrust bearings.
The company has developed two series of roller thrust bearings -- NW series for roller diameters
of 1.5mm to 2mm, and FW series with a section width allowing rollers only 1mm diameter.
At 1mm, the new FW thinnest-thrust-bearing overcomes manufacturability
and inherent strength limitations via a highly-engineered low-profile retainer.
NTN said it developed the new thrust bearings in response to demands by automakers to meet
ever-tightening drivetrain packaging constraints. In particular, automatic transmissions
are growing larger and getting heavier as they incorporate more ratios -- the 2-speed Torqueflite
of old has become the 6-speed Hydra-Matic 6T70, while Mercedes has the 7G-tronic 7-speed automatic,
and Lexus is said to be finalizing development of an 8-speed automatic transmission.
The demand for more ratios, to provide both better performance and fuel economy, also requires
more advanced electronic controls, more components, and stronger components to handle the power
output of the advanced engines often mated to these advanced transmissions.
All of this translates into an often counterproductive engineering focus on smaller, lighter, more
precise bearings that are also stronger, have longer service life, and improved manufacturability.
Adding complexity and rotating parts to a transmission
also results in more power lost to parasitic drag, throwing another spotlight on the bearings.
NTN's new thrust needle roller bearings follow traditional construction in that they are made up of
needle rollers, a cage -- usually two-piece, and races.
However, engineers found that traditionally designed retainers are the limiting factor in moving
smaller than 2mm section width. At less than 2mm, a traditionally designed two-piece retainer
of 0.4mm material is too thick in relative proportion to the rolling element. That extra material
operating under reduced clearance causes rolling element interference which does
not exist when the rollers are 2mm or larger.
NTN's solution was a redesigned cage, a "pocket pillar" design, incorporating high precision center
ribs, contacting the middle third of both the top and bottom of the rolling element.
This allowed the company to maintain the standard 0.4mm plate thickness for 1.5mm bearings, and
proved to be stronger than the standard retainer of a 2mm bearing.
For its even thinner FW series at 1mm section width, NTN moved to a more radically compressed
center-of-the-element pocket pillar design, and a more squared, low-profile section. The cage plate
thickness of the FW is actually thicker, at 0.7mm; as a result, the 1mm section width bearing's
retainer is three times stronger than the retainer of a standard 2mm bearing.
In addition to all of the performance breakthroughs and considerations,
NTN said the other positive development is that transmission and drivetrain engineers are now able to
put roller thrust bearings in applications
where higher-drag plain bearings and bushings had been the only potential solution.
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- by Bruce A. Carr
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tips and commercial sources.
Unauthorized reproduction is prohibited.
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Entire contents Copyright 1999-2008, eBearing Inc. All rights reserved.
eBearing.com and "... for everything that moves" are registered
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eBearing.com ... for everything that moves™
Entire contents Copyright © 1999-2008, eBearing Inc. All rights reserved.
eBearing.com and "... for everything that moves" are registered trademarks of eBearing Inc.
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