Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2002-05-09
2004-01-27
Footland, Lenard A (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
Reexamination Certificate
active
06682226
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to a cylindrical roller bearing and, more particularly, to a cylindrical roller bearing having preloading capability.
2. Description of Related Art
Cylindrical roller bearings typically have radial clearance within the bearings themselves. The radial clearance allows for the bearing components to be easily assembled without interference. There are a few cylindrical roller bearing configurations, however, that operate with zero or negative clearance, that is, in a preloaded condition. This is typically achieved by driving the inner race onto a tapered shaft, or using specially designed bearings which are intentionally out-of-round, otherwise known as 2 or 3 point lobing. An example of such out of round bearings are those used generally in aerospace applications such as jet engines.
Bearings having positive clearance can have degraded performance under some operating conditions. The clearance allows a roller to move independently of the bearing races and other rollers. When the roller is outside the loaded zone of the bearing, this movement can lead to skidding and scuffing damage on the contact surfaces of the raceways and roller, as well as damage or breakage of a roller cage. Also, bearings having positive clearance cannot be optimized for roller load sharing and fatigue life because the optimal fatigue performance is obtained when the bearing is mounted with zero or negative clearance, that is, in a preload condition.
Bearings which have been driven onto a tapered shaft can also have other problems. Tensile hoop stresses are developed by driving the bearing onto the tapered seat, which can degrade the fatigue performance of the bearing. Also, the bearing bore diameter is usually sized and matched to the shaft to ensure the correct drive-up results can be obtained. This is costly and time consuming for the bearing manufacturer and the end user. These types of bearings are normally used in printing presses and in steel rolling mills.
The intentionally out-of-round condition that is used to preload a cylindrical roller bearing is also difficult to manufacture precisely. The stack up of the bearing outside diameter, outer raceway, rollers, inner raceway, bore and seat(s) must all be considered when designing this type of bearing system. The lobes are designed to eliminate the clearance needed at assembly when the bearing is pressed into position. After such installation, the bearing is preloaded at two or three azimuth locations, and this is used to prevent the roller elements from sliding. In addition to the tight tolerances required to manufacture such out-of-round bearings, the loads placed on the bearings must be small to ensure that the overall bearing radial deflection is smaller than the preload created by the lobes, or else the positive effects of preloading are lost. Finally, this method of obtaining a preload does not optimize the bearing fatigue performance because the load sharing is not uniform in this condition. Instead, two or three points carry higher loads than the rest of the raceway-roller contacts, which are not operating in a preload condition, but are operating in a clearance condition.
The present invention overcomes these and other problems by providing a cylindrical roller bearing which is capable of preloading the internal components of the bearing without the detrimental side effects of accelerated wear and fatigue found in other types of more costly preloaded cylindrical bearings.
SUMMARY OF THE INVENTION
The present invention resides in a cylindrical roller bearing having the ability to preload the bearing's internal components through the use of a preloading mechanism. The preloading mechanism includes an annular groove configured within either the inner or outer race, and into which a two piece support ring is installed. The flanges of the annular groove are bolted together with fasteners which go through the flanges and the support ring, resulting in the preloading of the raceway radially to preload the internal components of the bearing.
By applying a preload between the bearing raceways and the roller s, the rollers will be continuously loaded, thereby eliminating the possibility of gross sliding of the rollers, and reducing the skidding and scuffing problems that can cause premature damage of the rollers or bearing raceways. Such preloaded cylindrical roller bearings are useful in applications such as printing presses, rolling mills, and aerospace jet engines, or wherever a preloaded cylindrical bearing would be beneficial. Additionally, the present cylindrical roller bearing system can also be used in high speed, lightly loaded applications to reduce the risk of the previously mentioned skidding and scuffing damage. The present cylindrical roller bearing system can also be used, with minimal risk of cage damage, where large accelerations and/or decelerations of the bearing roller complement are expected.
In a bearing which has positive clearance, and is thus not preloaded, large accelerations can cause the rollers to exert impact forces on the pin or bridge of the rollers cage, possibly leading to cage damage and other bearing component damage. In contrast, the preloaded bearing in the present invention reduces the possibility of roller sliding, thus reducing the impact loads and the resulting cage damage. Additionally, the present invention does not introduce tensile hoop stresses to the bearing inner race, and delivers a uniform radial raceway deformation to induce preloading.
Finally the proposed method of preloading the cylindrical roller bearing allows for application and assembly specific angles and profiles to be ground on the faces and seats of the support ring. This angle defines the amount of bowing the raceway has, which directly correlates to the amount of preload.
Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter.
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Knudsen Roger D.
Kotzalas Michael N.
Footland Lenard A
Polster Lieder Woodruff & Lucchesi L.C.
The Timken Company
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