Patent Application
20080193067
This invention relates to a tapered roller bearing for rotatably supporting one of a plurality of planetary rotary members that rotate about a common axis and also about their own axes.
Many of tapered roller bearings, in which a plurality of tapered rollers are arranged circumferentially between raceways of inner and outer rings, include a conical retainer comprising small- and large-diameter annular portions facing the small- and large-diameter end surfaces of the tapered rollers, respectively, and a plurality of bridges that connect the small- and large-diameter annular portions together, and defining pockets between the adjacent bridges in which the respective tapered rollers are received. Another type of known tapered roller bearings include a comb-shaped retainer having no small-diameter annular portion and having its bridges connected together by the large-diameter annular portion only like comb teeth.
Such retainers are formed by pressing a metal plate such as a steel plate, or by machining a metal material such as steel or brass. Many of such retainers have their bridges, which define the roller pockets, guided by the tapered rollers. Another type of retainers include bent protrusions extending from the small-diameter annular portion and supported by the raceway of the inner ring, the outer periphery of the small-diameter flange of the inner ring, or the raceway of the outer ring (as disclosed e.g. in JP patent publication 2004-293730A).
On the other hand, planetary speed reducers are known which can achieve a large speed reduction ratio. Typical such planetary speed reducers are planetary gear speed reducers. Planetary gear speed reducers comprise a sun gear mounted on an input shaft, an internal gear fixed e.g. to a housing, a carrier having pins each rotatably supporting one of a plurality of planetary gears disposed between the sun gear and the internal gear. When the planetary gears are rotated about the axis of the sun gear and their own axes, their rotation about the axis of the sun gear is transmitted to an output shaft (as disclosed in JP patent publication 07-103320A). Planetary roller speed reducers are also known in which the sun gear, internal gear and planetary gears of the above planetary gear speed reducers are all replaced by rollers (as disclosed in JP patent publication 08-130853A).
In many of small-sized such planetary speed reducers, their planetary gears or rollers are supported by needle bearings, whereas in many of medium- to large-sized such planetary speed reducers, their planetary gears or rollers are supported by tapered roller bearings, self-aligning roller bearings or cylindrical roller bearings.
To the retainer of a tapered roller bearing supporting each of the planetary rotary members (planetary gears or rollers) of a planetary speed reducer, which rotate about their common axis as well as about their own axes, in addition to the centrifugal force due to rotation of the planetary rotary member about its own axis, the centrifugal force due to rotation of the planetary rotary member about the common axis is also applied. The centrifugal force due to rotation of the planetary rotary member about the common axis tends to move the retainer so as to be offset from the center of the bearing. Thus, as the centrifugal force due to rotation about the common axis increases with an increase in the rotational speed about the common axis, if the retainer is of the type in which its bridges are guided by the tapered rollers, because the retainer is offset from the bearing center, some bridges are pressed hard against the tapered rollers, so that these bridges may be abraded severely, or may be destroyed due to concentration of bending moment on their portions connected to the annular portions.
With the type in which the retainer is guided by a bearing ring as disclosed in JP patent publication 2004-293730, while the bridges are not abraded or destroyed, because the bent protrusions extending from the small-diameter annular portion have guided surfaces at their free ends which are guided by the raceway of the inner ring, the outer periphery of the small-diameter flange of the inner ring, or the raceway of the outer ring, the contact area between the guided surfaces and the guiding surface on one of the bearing rings is small, so that the contact surface pressure is high. This increases the possibility of wear and seizure at the guiding and guided surfaces. One way to prevent such wear and seizure at the guiding and guided surfaces would be to improve the material or the properties of guiding surface on one of the bearing rings so as to reduce the frictional resistance between the guiding and guided surfaces. But because the material of the bearing rings, i.e. inner and outer rings has to be selected taking preferentially and primarily into consideration their rolling fatigue life, it is difficult to improve the material or the properties of the guiding surface so as to improve the frictional resistance between the guiding and guided surfaces.
Also, if the raceway of the inner or outer ring is used as the guiding surface, because the protrusions have to be inserted between the tapered rollers, the guided surfaces of the protrusions are present only at portions of the entire circumference, so that the contact area of the guided surfaces tends to be relatively small. Also, because the raceways of the inner and outer rings are axially inclined, axial component forces act on the guided surfaces of the retainer, so that the inner end surface of one of the annular portions defining the roller pockets tends to be pressed against the end surfaces of the tapered rollers. If the inner end surface of one of the annular portions is pressed against the end surfaces of the tapered rollers, torque loss of the bearing increases.
An object of the present invention is to provide a tapered roller bearing for supporting one of planetary rotary members that rotate about a common axis and their own axes in which it is possible to prevent wear and seizure between a guided surface of the retainer and the guiding surface.
In order to achieve this object, the present invention provides a tapered roller bearing for rotatably supporting a planetary rotary member having a central axis and rotatable about the central axis and about an axis other than the central axis, the tapered roller bearing comprising an inner ring having a first raceway, an outer ring having a second raceway, a plurality of tapered rollers disposed between the first and second raceways, a retainer retaining the tapered rollers in position, and one of an inner ring spacer keeping the inner ring in position and an outer ring spacer keeping the outer ring in position, the retainer having a guided portion having a guided surface extending the entire circumference thereof and guided by the one of the inner ring spacer and the outer ring spacer.
With this arrangement, it is possible to ensure a sufficiently large contact area between the guided surface on the retainer and the guiding surface on the inner ring spacer or the outer ring spacer, thereby reducing the contact surface pressure therebetween. Because the guiding surface is formed on the spacer, for which it is not necessary to ensure a rolling fatigue life as with the bearing rings, it is possible to readily improve the material and properties of the guiding surface so as to reduce e.g. the frictional resistance between the guiding and guided surfaces. This in turn makes it possible to prevent wear and seizure between the guided surface of the retainer and the guiding surface. Further, since the guiding surface formed on the inner or outer ring spacer is not axially inclined, no axial component forces act on the guided surface of the retainer, so that the inner end surfaces of the annular portions defining the roller pockets would not be pressed against the end surfaces of the tapered rollers.
By forming a hardened surface layer on the guiding surface of the inner or outer ring spacer that guides the guided surface of the retainer, the wear resistance of the guiding surface improves. The hardened surface layer may be formed by carbonitriding.
By forming a lubricating film on the guiding surface of the inner or outer ring spacer that guides the guided surface of the retainer, the frictional resistance of the guiding surface decreases. The lubricating film may be formed by phosphate film treatment.
By annularly shaping the guided portion of the retainer, it is possible to further increase the contact area between the guided surface and the guiding surface.
By forming the retainer from steel and forming a hardened surface layer on the guided surface of the guided portion, the wear resistance of the guided surface improves. The hardened surface layer may be formed by Tufftride treatment or by partial hardening.
By forming the retainer from a resin, the frictional resistance decreases. Such resins include polyamide resins such as nylon, fluororesins such as polytetrafluoroethylene, polyetherketone resins such as polyetheretherketone, polyamideimide resins, polyimide resins, polyphenylene sulfide resins, and a mixture thereof. If necessary, to the resin may be added fibrous reinforcing materials such as carbon fiber and glass fiber, flaky reinforcing materials such as mica and talc, microfiber reinforcing materials such as potassium titanate whiskers, solid lubricants such as polytetrafluoroethylene, graphite and molybdenum disulfide, and sliding reinforcing materials such as calcium phosphate and calcium sulfate.
By forming the retainer from high-strength brass too, it is possible to reduce the frictional resistance of the guided surface.
The present invention also provided an assembly for rotatably supporting a planetary rotary member having a central axis and rotatable about the central axis and about an axis other than the central axis, the assembly comprising a pair of tapered roller bearings combined in a back-to-back arrangement, and each comprising an inner ring having a first raceway, an outer ring having a second raceway, a plurality of tapered rollers disposed between the first and second raceways, and a retainer retaining the tapered rollers in position, and an outer ring spacer disposed between the outer rings of the pair of tapered roller bearings, the retainer of each of the tapered roller bearings having a guided portion having a guided surface extending the entire circumference thereof and guided by the outer ring spacer.
The tapered roller bearing according to the invention can be most advantageously used to support a planetary rotary member in the form of a planetary gear or a planetary roller in a planetary speed reducer.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which:
Now referring to the drawings, the embodiments of the present invention are described.
The conical retainer 5 is formed by pressing a steel plate, and includes a disk portion 5d extending radially inwardly from the outer end of the small-diameter annular portion 5a, and an annular portion 5e axially outwardly extending from the radially inner end of the disk portion 5d so as to form a right angle with the disk portion 5d. The annular portion 5e is guided by the radially outer surface of the inner ring spacer 6a. Specifically, the annular portion 5e has a radially inner guided surface 7 which is guided by the radially outer surface of the inner ring spacer 6a, which serves as a guiding surface. On this radially outer guiding surface of the inner ring spacer 6a, a hardened surface layer is formed by carbonitriding, and further a lubricating film is formed by phosphate film forming treatment. On the guided surface 7, a hardened surface layer is formed by Tufftride treatment.
The comb-shaped retainer 8 is formed by machining high-strength brass, and includes an annular rib 8c extending radially outwardly from the annular portion 8a and having a radially outer guided surface 7 guided by the radially inner surface of the outer ring spacer 6b. On the radially inner (guiding) surface of the outer ring spacer 6b, as in the first embodiment, a hardened surface layer is formed by carbonitriding, and further a lubricating film is formed by phosphate film forming treatment.
In the embodiment of
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-32087 | Feb 2007 | JP | national |
