Abstract:
A cylindrical roller bearing having preloading capability is disclosed. A preloading mechanism having an annular groove having a deformable raceway and which is configured to accept a segmented support ring is incorporated into either the outer race of the inner race. A plurality of fasteners are installed in holes in the flanges of the annular groove and into the segmented support ring. By tightening the fasteners, the flanges of the annular groove are tightened against the segmented support ring, thereby deforming the deformable raceway from an arcuate shape to a flat or slightly crowned shape, placing a preload on the rollers of the bearing. The amount of preload is determined by the angular and dimensional interface between the segmented support ring and the annular groove.

Description:
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&#39;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. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of the cylindrical roller bearing of the present invention. 
     FIG. 2 is a front view of the support ring. 
     FIG. 3 is a sectional view of the support ring. 
     FIG. 4 is a sectional view of the outer ring. 
     FIG. 5 is a sectional view of the cylindrical roller bearing outer ring subassembly. 
     FIG. 6 is a sectional view of an second embodiment of the present invention. 
    
    
     Please note that the angles and radii shown in FIG. 1, FIG. 3, FIG. 4, FIG.  5  and FIG. 6 are not to scale and have been greatly exaggerated to better show the geometric relationship between the components of the cylindrical roller bearing of the present invention. The actual dimensions and dimensional relationships between the bearing components are as described elsewhere herein. 
     Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention discloses a cylindrical roller bearing having a preload mechanism for preloading the internal components of the bearing. While either the inner race or the outer race may be configured to incorporate the preloading mechanism of the present invention, the first embodiment described herein incorporates the preloading mechanism into the outer race of the bearing. 
     Referring now to the drawings, FIG. 1 depicts a first embodiment of preloadable cylindrical roller bearing A. The cylindrical roller bearing A is configured to fit between two machine components, such as a shaft and a housing, to enable one of the components to rotate relative to the other with minimal friction. The cylindrical bearing A includes an inner race  1  in the form of an annular channel and having an axis X, an outer race  2  also in the form of an annular channel which shares the axis X with the inner race  1  and which surrounds the inner race  1 , and rollers  3  in the form of cylindrical rollers located between the inner race  1  and the outer race  2  to enable the inner race  1  to rotate relative to the outer race  2 , or vice versa, with little torque. In addition, the bearing A may have a cage  4  which is likewise located between the inner race  1  and the outer race  2 . The cage  4  maintains the proper spacing between the rollers  3 . 
     The inner race  1 , which is configured to fit around a shaft or similar machine component, has an inner raceway  5  that is cylindrical and is presented outwardly away from the axis X, and two ribs  6 . The inner race  1  also has two end faces  7  located at the ends of the inner raceway  5  and which are squared off with respect to the axis X. Each of the two ribs  6  have a rib face  8  and a rib diameter  9 . The inner raceway  5  is located between the two ribs  6  and is generally perpendicular to the two rib faces  8 . Two undercuts  9  are positioned at the intersection of the two rib faces  8  and the ends of the inner raceway  5 . Typically, one end face  7  will abut a shoulder on a shaft or similar component and the other end face  7  will abut a clamping device, such as a nut, so as to position the inner race  1  firmly onto the machine component. 
     The rollers  3  are arranged in one or more rows around the inner race  1  and on the inner raceway  5 , there being essentially line contact between the side faces of the rollers  3  and the inner raceway. The two ribs  6  act to contain the rollers  3  within the inner race  1 . The rollers  3  are generally cylindrical and are sized to allow the rollers to operate smoothly while traveling on the inner raceway between the two ribs  6 . The cage  4  acts to maintain the proper spacing between the rollers  3 . The rollers  3  fit between the inner race  1  and the outer race  2  and roll along the inner raceway  5  and an outer raceway  10  of the outer race  2  when relative rotation occurs between the race  1  and  2 . 
     In this embodiment, the preload mechanism is incorporated into the design of the outer race. The preload mechanism includes an annular groove  13 , a ring segment  12 , and a deformable raceway. The deformable raceway in the present embodiment is the outer raceway  10 . It will be appreciated that the deformable raceway may be either the outer raceway or the inner raceway and still remain within the scope of the present invention as long as the elements of the preload mechanism are present. 
     In FIG. 1, the outer race  2  has a raceway  10  that is presented inwardly toward the axis X and toward the inner raceway  5  of the inner race  1 . The outer race  2  has two end faces  11  at each end of the outer raceway  10 . A two-piece support ring  12  is positioned within an annular groove  13  of the outer race  2 . A plurality of fasteners  14  retain the support ring  12  within the annular groove  13  of the outer race  2 . 
     FIG. 2 shows that the support ring  12  is actually constructed of two support ring segments  15 . Each segment  15  is substantially a semicircle having a series of holes  16 . The sectional view of FIG. 3 shows the configuration of the cross section of each of the two segments  15 . The thickness of the support ring segment  15  is indicated by the dimension H Support  and the width of the support ring is indicated by the dimension L Support . Each of the support ring segments  15  has a front face  17 , a rear face  18 , an outside face  19 , and an inside face  20 . The front face  17  is not perpendicular to the outside face  19 , but is instead offset in relation to the inside face  20  by an angle designated as α Support . In like manner, the back face  18  is also offset in relation to the inside diameter by the same angle α Support . The inside face  20  of the support ring segment is arcuate having a radius with the dimension of R support . The cross sectional design of the support ring segments  15  is designed to fit into the annular groove  13  of the outer race  2 , and to cooperate with the annular groove to effect a preload of the internal components of the cylindrical roller bearing A. 
     The value of the angle α Support  varies directly with the amount of desired operating preload which is desired within the cylindrical roller bearing A. For example, if more preload is required, the value of the angle α Support  is increased. If less preload is required, the value of the angle α Support  is decreased. 
     As shown in FIG. 3, the series of holes  16  in the described embodiment of the present invention are through holes passing through the entire thickness of the support segment  15 . 
     FIG. 4 shows the annular groove  13  in the outer race  2 . The annular groove  13  is in the outside diameter of the outer race  2 , and has two flanges  22 , two inside faces  23 , and an inside diameter  24 . The two inside faces  23  of the flanges  22  are slightly angled toward the two end faces  11  at an angle of α Ring . The value of the angle α Ring  is coordinated with the angle α Support  of the support ring segment  15  and is calculated based upon the amount of desired operating preload which is required within the cylindrical roller bearing A. The inside diameter  24  is initially cylindrical and coincides with the axis X of the cylindrical roller bearing A. A series of bolt holes  16 A are machined and countersunk in the end faces  11  of the flanges  22 . The series of bolt holes  16 A are sized and located to match the series of holes  16  in the two support ring segments  15 . The annular groove  13  is centered on the vertical axis Y of the outer race  2  and has a depth of H Ring  from the outside diameter of the flanges  22  to the annular groove inside diameter  24 . The outer raceway  10  is also centered on the Y axis of the outer race  2  and is arcuate, having a radius of R Ring i . The radial section height H Support  of the two support segments  15  is equal to or slightly greater than the radial height H Ring  of the annular groove  13  of the outer race  2 . This allows the flanges  22  of the outer race  2  to have movement even after mounting of the outer race  2  and support segments  15  as a subassembly in the application, while the support segments  15  are firmly contacting the two inside surfaces  23  of the annular groove  13  to support the outer race  2 . 
     In assembly of the cylindrical roller bearing A, the two support ring segments  15  are placed within the annular groove  13  of the outer race  2 . It will be appreciated that the angle α Support  of the tw o support ring segments  15  and the angle α Ring  of the outer race  2  leave two gaps  25  between th e support ring segments and the outer raceway as shown in FIG. 5 When the plurality of fasteners  14  are installed through the holes  16  of the support ring segments  15  and through the holes  16 A of the outer race  2 , the tightening of the fasteners  14  draws the flanges  22  of the outer raceway toward the front face  17  and the rear face  18  of the two support ring segments  15 . Addditionally, as the fasteners  14  are tightened, the outer raceway  10  of the outer race  2  deforms. Thus, the outer raceway  10  of the outer race  2  i s manufactured with a designed axial profile of R Ring i  such that when the outer race  2  is deformed due to the tightening of the plurality of fasteners  14 , the outer raceway  10  is changed from the arcuate shape into a cylindrical or slightly crowned shape, thus resulting in a preload on the internal components of the cylindrical roller bearing A. In a similar manner, the value of radius R Support  is such that the inside face  20  of the two support ring segments  15  will match the annular groove inside diameter  24  as it will exist after the plurality of fasteners  14  have been fully tightened. This allows full support of the load bearing portion of the outer race  2  during operation of the cylindrical roller bearing A under heavy loads. 
     It will be appreciated, however, that other embodiments of the present invention may utilize holes in the support ring  12  which are not through holes and still remain within the scope of the dimension. In such an embodiment, the holes may be tapped blind holes to allow the use of threaded fasteners to attach the support ring  12  to the outer race  2 . In other embodiments, other types of fasteners may also be used. In yet other embodiments, the outer race  2  may simply be clamped in such a manner as to compress the flanges  22  as needed to deform the outer raceway  10  from its initial arcuate shape to the final generally cylindrical shape. In fact, any type of mechanism may be used as long as the support ring  12  is secured to the outer race  2  and allows for the uniform deformation of the outer race  2  as described herein to effect a preload on the internal components of the cylindrical roller bearing A. 
     One possible way to assemble this particular embodiment of the cylindrical roller bearing A is to position the two support segments  15  within the annular groove  13  of the outer race  2 , and loosely install the plurality of fasteners  14  into the holes  16 A of the outer race  2  and holes  16  of the support segments  15 . The inner race  1 , including the rollers  3 , is then: installed on the shaft of the machine component and then this shaft assembly is inserted into the outer race  2 . After the rollers  3  have been properly positioned on the outer raceway  10  of the outer race  2 , the internal components of the cylindrical roller bearing A can then be preloaded by tightening the fasteners  14  until the inside faces  23  of the outer race  2  contacts the front face  17  and the rear face  18  of the two support segments  15 . 
     FIG. 6 shows roller bearing B which is a second embodiment of the present invention wherein the preloading mechanism is incorporated into the inner race instead of the outer race. Thus, the annular groove  25  of the preloading mechanism is in the inner race  26 . Except for this difference, the components of the second embodiment, as well as the dimensional relationships between the components of the second embodiment, are identical to the first embodiment described in detail above. 
     While the above description describes various embodiments of the present invention, it will be clear that the present invention may be otherwise easily adapted to fit any configuration where a bearing having preloaded may be utilized. 
     In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.