January 31, 2008
Development of “Planetary Gear Assembly” for Automobile Transmissions
Realizing the need for high speed and downsizing, along with the use of long life technology and strength analysis technology
NTN Corporation (hereafter NTN) has developed a “Planetary Gear Assembly” for automobile transmissions, which handles high speed and is compact.
Currently, with regard to automobile transmissions, a planetary gear mechanism is used, not only in the mainstream automatic transmission (AT), but also in the CVT and hybrid systems that are increasingly being used. Especially in the AT, due to the trend of more shifts - from the conventional 4 to 5 shifts to shifts of 6 to 8, the planetary gear portion rotates at a higher speed and the bearings used must respond to higher rotational speeds.
This increased shifting and higher rotational speeds cause the Cage and Needle rollers used in the planetary gear unit to run under a condition like the planetary motion that they revolve, along with their own rotation. This causes a centrifugal force to be applied, causing higher stress on the cage than with fewer shifts. This results in a need for an increase in the strength of the cage. In addition, in order to respond to the demand for downsizing and weight reduction of the transmission, the strength of the gear tooth flank and the dedendum should be increased. Also, the bearing life must be improved because the durability of the entire planetary gear unit must be improved.
The “Planetary Gear Assembly” developed by NTN for automobile transmissions, is a unit product composed of a carrier, gear, bearing and washer, with the bearing designed for a maximum planetary gear rotational speed of 25,000 RPM. This was done by utilizing a highly technological analysis to optimize the shape of the cage (conventional specification requires a maximum planetary gear rotational speed of 17,000 RPM), as well as using a special surface treatment applied to the gear. Also, a special heat treatment is performed on the bearing so that when compacted 20%(in width direction), the bearing will have the same life.
NTN will be ready for the mass production, and begin receiving orders from automobile and transmission manufactures, targeting a launch into the market in 2010.
[ Features ]
| (1) | Response to high speed rotation : | 25,000 rpm(conventional specification requires 17,000 rpm) |
| (2) | Pitting life of gear : | 4 times longer(compared to conventional gear) |
| (3) | Gear width of 20% reduction (for the same life) | |
[ Application ]
Automobile transmissions(AT, CVT, hybrid system)
[ Product Photo ]
 Appearance of planetary gear ASSY |
 Planetary gear + Bearing + Washer + Shaft |
 Needle roller with cage + Shaft |
[ Location used ]
