JP7495816B2 - Tapered roller bearings - Google Patents

Description

This invention relates to tapered roller bearings used in the reducers of robots and construction machinery, and in particular to tapered roller bearings of the outer ring flange type, in which a flange protruding radially inward is formed on the large diameter end of the outer ring raceway surface of the outer ring, out of the four ends: the small diameter end and large diameter end of the outer ring raceway surface of the outer ring, and the small diameter end and large diameter end of the inner ring raceway surface of the inner ring.

An outer ring rib type tapered roller bearing in which a rib is not formed on the large diameter end of the inner ring raceway of the inner ring, and a rib protruding radially inward is formed only on the large diameter end of the outer ring raceway of the outer ring is disclosed in Patent Document 1 and Patent Document 2, but there are hardly any products in practical use.

Japanese Utility Model Application Publication No. 1-85521 JP 2016-196944 A

The primary reason for this is that, compared to an inner ring rib type tapered roller bearing in which a rib is formed on the large diameter end of the inner ring raceway surface of the inner ring, an outer ring rib type tapered roller bearing in which a rib is formed on the large diameter end of the outer ring raceway surface of the outer ring has an extremely reduced load capacity for pure axial loads.
Generally, in order to improve the moment rigidity and bearing life of a tapered roller bearing, it is effective to increase the roller size (roller diameter).

However, in the case of tapered roller bearings with outer ring ribs, if the bearing cross-sectional height and bearing PCD are kept the same and the roller size is increased, the thickness of the outer ring rib becomes thinner, which raises concerns about a decrease in the strength of the outer ring rib, making it difficult to put into practical use.

The objective of this invention is to find design criteria for a practical outer ring rib type tapered roller bearing that has sufficient moment load and bearing life without drastically reducing the load capacity of pure axial load compared to an inner ring rib type tapered roller bearing, and that does not involve concerns about reduced strength of the outer ring rib.

In order to solve the above problems, this invention focuses on the relationship between the roller diameter and the thickness of the outer ring rib, and has discovered that by setting the relationship between the roller diameter and the thickness of the outer ring rib within a specified numerical range, it is possible to obtain a practical outer ring rib type tapered roller bearing that has a load capacity for pure axial loads that is not extremely low compared to inner ring rib type tapered roller bearings, has sufficient moment loads and bearing life, and is free of concerns about a decrease in the strength of the outer ring rib.

That is, this invention relates to a tapered roller bearing comprising an outer ring having an outer ring raceway surface on its inner peripheral surface, an inner ring having an inner ring raceway surface on its outer peripheral surface, a number of tapered rollers arranged to roll freely between the outer ring raceway surface and the inner ring raceway surface, and a cage having a number of pockets that house and hold the tapered rollers at predetermined intervals, and in which a rib protruding radially inward is formed at the large diameter end of the outer ring raceway surface of the outer ring out of four ends: the small diameter end and large diameter end of the outer ring raceway surface of the outer ring, and the small diameter end and large diameter end of the inner ring raceway surface of the inner ring, the contact angle is 40° to 50°, and the relationship between the thickness E of the outer ring rib and the roller large diameter side diameter Dw satisfies 0.19 < E/Dw < 0.44.

In this invention, the contact angle is the angle between the bearing center axis and the outer ring raceway surface, the thickness E of the outer ring rib is the distance from the contact point between the outer ring raceway surface and the outer ring rib surface to the outer diameter surface of the bearing, and the large diameter side diameter Dw of the roller is the diameter of the large diameter side end face of the tapered roller.

If the radial size of a tapered roller bearing is constant, that is, if the bearing cross-sectional height H and bearing outer diameter D are constant, and the roller size (roller diameter) is increased, the load capacity Cr increases, and the bearing life and moment rigidity can be increased. However, by increasing the roller size, the thickness E of the outer ring rib becomes thinner, reducing the strength of the rib and raising the concern that the rib may crack due to excessive load. However, by designing an outer ring rib type tapered roller bearing to satisfy the numerical specifications stipulated in this invention, that is, by setting the contact angle to 40° to 50° and satisfying the relationship between the outer ring rib thickness E and the roller large diameter side diameter Dw of 0.19 < E/Dw < 0.44, a tapered roller bearing with an outer ring rib that has a pure axial load capacity that is not extremely low compared to an inner ring rib type tapered roller bearing, has sufficient moment load and bearing life, and is free of concerns about reduced strength of the outer ring rib.

FIG. 1 is an explanatory diagram showing a schematic representation of the component forces of the outer ring side rolling element load, the inner ring side rolling element load, and the rib side rolling element load when a pure axial load is applied to an outer ring rib type tapered roller bearing in which a rib portion is formed on the large diameter end of the outer ring raceway surface of the outer ring. FIG. 1 is an explanatory diagram showing a schematic representation of the component forces of the outer ring side rolling element load, the inner ring side rolling element load, and the rib side rolling element load when a pure axial load is applied to an inner ring rib type tapered roller bearing in which a rib portion is formed at the large diameter end of the inner ring raceway surface of the inner ring. 1 is an enlarged partial cross-sectional view of an outer ring flange type tapered roller bearing according to an embodiment of the present invention, taken along a pillar portion of a cage. FIG. 2 is a side view of a tapered roller used in an outer ring flange type tapered roller bearing according to an embodiment of the present invention. FIG. 4 is an enlarged partial cross-sectional view showing the outer ring flange type tapered roller bearing of FIG. 3 mounted in a housing. FIG. 4 is a schematic diagram conceptually showing the contact area between a large rib portion on the outer ring side and a tapered roller of the outer ring rib type tapered roller bearing of FIG. 3 . 4 is an enlarged view showing a state in which tapered rollers are pressed against a roller guide surface of a cage in the outer ring flange type tapered roller bearing of FIG. 3 . FIG. 4 is an enlarged view showing a state in which tapered rollers are pressed against the claws of the cage in the outer ring flange type tapered roller bearing of FIG. 3 . FIG. 5(a), (b), and (c) are enlarged partial cross-sectional views showing a procedure for inserting the roller-retainer assembly into the outer ring. 13 is a graph showing moment stiffness ratios for examples in which the contact angle is changed in various ways. 1 is a graph showing life ratios for examples in which the contact angle is changed in various ways. FIG. 2 is an enlarged cross-sectional view of an inner ring flange type tapered roller bearing taken along a pillar portion of a cage. 13 is an enlarged partial cross-sectional view showing the state in which the inner ring flange type tapered roller bearing of FIG. 12 is assembled into a housing. FIG. FIG. 13 is a schematic diagram conceptually showing the contact area between a large rib portion on the inner ring side and a tapered roller of the inner ring rib type tapered roller bearing of FIG. 12 .

The following describes an embodiment of the present invention with reference to the attached drawings.

As shown in FIG. 3, the tapered roller bearing 11 according to the embodiment of the present invention comprises an outer ring 12 having an outer ring raceway surface 12a on its inner peripheral surface, an inner ring 13 having an inner ring raceway surface 13a on its outer peripheral surface, a number of tapered rollers 14 arranged to roll freely between the outer ring raceway surface 12a and the inner ring raceway surface 13a, and a cage 15 having a number of pockets that accommodate and hold the tapered rollers 14 at a predetermined interval. Of the four ends, namely the small diameter end and large diameter end of the outer ring raceway surface 12a of the outer ring 12, and the small diameter end and large diameter end of the inner ring raceway surface 13a of the inner ring 13, a flange portion 12b that protrudes radially inward is formed on the large diameter end of the outer ring raceway surface 12a of the outer ring 12, and is of an outer ring flange type.

The tapered roller bearing 11 of this invention eliminates the small flange at the small diameter end of the inner ring 13 and increases the roller length by the length of the small flange to achieve a high load capacity, while forming a flange 12b that protrudes radially inward at the large diameter end of the outer ring raceway surface 12a of the outer ring 12, eliminating the flange at the large diameter end of the inner ring raceway surface 13a of the inner ring 13.

The tapered roller bearing 11 of this invention has a contact angle α set at a steep gradient of 40° to 50° to achieve high moment rigidity, and the tapered roller bearing 11 of the embodiment shown in Figure 3 has a contact angle α set at 45°.

In a tapered roller bearing 11 with a steep contact angle of 40° to 50°, a large space is created in the axial direction between the large-diameter end of the outer ring raceway surface 12a of the outer ring 12 and the large-diameter end face of the inner ring 13, and this space is utilized to form a flange portion 12b that protrudes radially inward in this invention.

By forming a flange 12b that protrudes radially inward at the large-diameter end of the outer ring raceway surface 12a of the outer ring 12 and eliminating the flange at the large-diameter end of the inner ring raceway surface 13a of the inner ring 13, it is possible to achieve a more compact axial size.

In other words, as shown by the two-dot chain line in Figure 3, if the axial width when a flange 12b is formed on the large diameter end of the inner ring raceway surface 13a of the inner ring 13 is T', the axial width of the inner ring 13 can be made thinner by eliminating the flange on the large diameter end of the inner ring raceway surface 13a of the inner ring 13, and since the axial width when a flange 12b that protrudes radially inward is formed on the large diameter end of the outer ring raceway surface 12a of the outer ring 12 is T, the axial width can be made more compact by the amount of T'-T.

As in this invention, by forming a flange 12b that protrudes radially inward on the large-diameter end of the outer ring raceway 12a of the outer ring 12, the flange can be made more rigid than in the tapered roller bearing 1 with an inner ring flange as shown in FIG. 11, in which the flange is formed on the large-diameter end of the inner ring raceway 13a of the inner ring 13.

In other words, when comparing the case where a flange 12b protruding radially inward is formed on the large-diameter end of the outer ring raceway 12a of the outer ring 12 as shown in FIG. 3 with the case where a flange 3b is formed on the large-diameter end of the inner ring raceway 3a of the inner ring 3 as shown in FIG. 12, even if the height C of the flange (the radial distance between the intersection of the raceway surface and the flange surface and the flange apex) is the same, the contact area between the roller end face and the outer ring flange surface shown in FIG. 6 is approximately 7% larger than the contact area between the roller end face and the inner ring flange surface in the inner ring flange type tapered roller bearing shown in FIG. 14, and the area receiving the induced thrust force generated in the roller is larger in the outer ring flange type, so the stress in the contact area is lower and the contact strain between the roller end face and the flange surface is smaller.

In addition, as in the inner ring flange type tapered roller bearing shown in FIG. 12, when a flange portion 3b is provided at the large diameter end of the inner ring 3, the induced thrust force generated in the tapered roller 4 is received by the flange portion 3b as shown by the white arrow in FIG. 13, and the bending stress applied to the flange portion 3b may cause distortion in the flange portion 3b. However, in the outer ring flange type tapered roller bearing, as shown by the white arrow in FIG. 5, the induced thrust force generated in the tapered roller 14 is received by the housing 6 as the bending stress applied to the flange portion 12b of the outer ring 12, so the rigidity of the flange portion 12b is increased. In the inner ring flange type tapered roller bearing in FIG. 12, the symbol 2 indicates the outer ring, 2a indicates the outer ring raceway surface, and 5 indicates the cage.

This invention achieves an outer ring rib type tapered roller bearing that has a contact angle of 40° to 50° and a relationship between the outer ring rib thickness E and the roller large diameter Dw that satisfies 0.19 < E/Dw < 0.44, thereby providing sufficient moment load and bearing life without drastically reducing the load capacity of pure axial load compared to a bearing with a rib formed on the large diameter end of the inner ring raceway surface of the inner ring, and without the risk of a decrease in the strength of the outer ring rib.

The relationship between the roller diameter (large-diameter roller diameter Dw) and the thickness E of the outer ring rib is expressed as E/Dw, and the larger this value is, the thicker the thickness E of the outer ring rib is and the smaller the large-diameter roller diameter Dw is.

Tapered roller bearing 11 of this invention has a contact angle of 40° to 50°, and when the external load is kept constant, and the PCD and roller size and number of the bearing are constant, and only the contact angle is changed, the moment stiffness is as shown in the graph in Figure 10, and the life ratio is as shown in the graph in Figure 11. When a comprehensive evaluation of each contact angle is made from the graphs in Figures 10 and 11, the results are as shown in Table 1, and it was confirmed that by setting the contact angle to 40° to 50°, it is possible to achieve both moment stiffness and life of the bearing.

In this invention, the numerical specification that the relationship between the outer ring flange thickness E and the roller large diameter Dw is 0.19 < E/Dw < 0.44 was obtained from the results in Tables 2 to 4, in which the radial size of the bearing was kept constant, i.e., the bearing cross-sectional height H and the bearing outer diameter D were kept constant, and the contact angle α was changed to compare the moment load, bearing life, and flange strength.

In Tables 2 to 4, ◯ for life and moment stiffness indicates a practical range (long life, high moment stiffness), while × indicates a range where the bearing function is less reliable (shorter life, low moment stiffness) compared to ◯.
In addition, in terms of flange strength, ◯ indicates a safety factor of 1.2 or more, which means high reliability, while × indicates a safety factor of less than 1.2, which means a region of low reliability.

The safety factor of the flange strength is defined as follows:
Safety factor of flange strength = Maximum stress generated in the flange when the bearing is loaded with a static rated radial load C0r / Allowable fatigue stress for general bearing steel.
This safety factor of 1.2 standard, as stated in the "Japan Society of Mechanical Engineers - Fatigue Strength Design Materials," is a general-purpose safety factor standard for fatigue strength that is used in a wide range of fields, including railway vehicles and automobiles.

In Tables 2 to 4, the ranges of E/Dw where the bearing life, moment rigidity and flange strength are ◯ are surrounded by double lines and are 0.19 to 0.46 at a contact angle of 40°, 0.19 to 0.45 at a contact angle of 45°, and 0.18 to 0.44 at a contact angle of 50°.
The range enclosed by the double line in Tables 2 to 4, that is, the range of 0.19<E/Dw<0.44 for a contact angle of 40 to 50°, is the region in which the life and moment rigidity performance are high, and the flange strength and safety factor are high.

In the case of tapered roller bearings, when the roller size, number of rollers, contact angle, roller angle, and angle x between the contact point of the roller with the rib and the rib side raceway surface are the same, a comparison is made between a bearing as shown in Figure 2 in which a rib is formed on the large diameter end of the inner ring raceway surface of the inner ring (hereafter referred to as an "inner ring rib bearing") and a bearing as shown in Figure 1 in which a rib is formed on the large diameter end of the outer ring raceway surface of the outer ring (hereafter referred to as an "outer ring rib bearing"), and the results show that under pure axial (Fa) load, the outer ring rib bearing is stronger than the inner ring rib bearing. The rolling element load (outer ring side rolling element load Fo, inner ring side rolling element load Fi) and the contact surface pressure between the rolling element and the raceway increase, but if the contact angle is set to 40°-50° and the roller angle is set to 3.5° or less, as in this invention, the increase in the rolling element load (outer ring side rolling element load Fo, inner ring side rolling element load Fi) and the contact surface pressure with the raceway during a pure axial (Fa) load can be suppressed, and the rolling element load and the contact surface pressure with the raceway during a pure radial (Fr) load can also be suppressed.

The formula for calculating the rolling element load when a pure axial load is applied to the outer ring flange bearing shown in FIG. 1 and the inner ring flange bearing shown in FIG. 2 is as follows:
Fio: Rolling element load on the outer ring side (inner ring flange bearing)
Foo: Rolling element load on the outer ring side (outer ring flange bearing)
Fii: Rolling element load on the inner ring side (inner ring flange bearing)
Foi: Rolling element load on the inner ring side (outer ring flange bearing)
Fir: Rolling element load on flange side (inner ring flange bearing)
For: Rolling element load on flange side (outer ring flange bearing)
α: Angle between the bearing center axis and the outer ring raceway surface θ: Angle between the bearing center axis and the inner ring raceway surface β: Roller angle x: Angle between the contact point of the roller with the rib and the rib side raceway surface
Y: Contact angle between the roller large end face and the inner ring rib (θ + x)
δ: Contact angle between roller large end face and outer ring rib (α-x)
In this case, the result is as follows:
Fio = Fa / sin α
Foo = Foi (sinθ sinδ + cosθ cosδ) / (cosα cosδ + sinα sinδ)
Fii = Fio (sinα sinY + cosα cosY) / (cosθ cosY + sinθ sinY)
Foi = Fa / sin θ
Fir = (Ficosθ - Ficosα) / sinY
For = (Focosθ - Focosα) / sinδ

Using the above formula, the maximum rolling element load and maximum contact surface pressure are calculated for each example where a pure axial load Fa is applied, the contact angle is between 40° and 50°, and the roller angle is 3.5° or less, and for each example where the contact angle is 40° or less and the roller angle is 3.5° or more, and the results are shown in Tables 5 to 11.

From the results of Tables 5 to 11, it was confirmed that when comparing outer ring rib bearings and inner ring rib bearings with the same bearing dimensions, with the maximum rolling element load and maximum contact surface pressure of the inner ring rib bearing set at 100%, the outer ring rib bearings specified in this invention can suppress the increase rate of both the maximum rolling element load and the maximum contact surface pressure to within 10% of the inner ring rib bearing, whereas the outer ring rib bearings not specified in this invention have an increase rate of more than 10% in at least one of the maximum rolling element load and maximum contact surface pressure compared to the inner ring rib bearing.

In this invention, the retainer 15 can be made of resin.

As shown in Figures 7 and 8, the retainer 15 has a large diameter ring portion 15a on the large diameter side and a small diameter ring portion 15b on the small diameter side, a roller guide surface 15c that guides the tapered rollers 14 on the outer diameter portion, and claws 15d that hold the tapered rollers 14 on the inner diameter surface. The roller guide surface 15c that guides the tapered rollers 14 and the claws 15d that hold the tapered rollers 14 may be reversed. In addition, a notch 15e is provided on the outer peripheral surface of the large diameter ring portion 15a of the retainer 15 to avoid interference with the flange portion 12b of the outer ring 12.

As shown in Figure 7, if the roller circumscribing circle diameter when the tapered roller 14 is pressed against roller guide surface 15c on the outer diameter side of the cage 15 is P, and the roller circumscribing circle diameter when the tapered roller 14 is pressed against claw 15d on the inner diameter side of the cage 15 is P' as shown in Figure 7, when the roller-retainer assembly is inserted into the outer ring 12 in the procedure shown in Figures 9(a), (b), and (c), the rib height C of rib portion 12b is the same, but the contact angle α, rib outer diameter angle γ, and |P-P'| are variously changed, and the ease of insertion of the roller-retainer assembly into the outer ring 12 is evaluated. These results are shown in Tables 13 to 17.
From the results in Tables 12 to 16, it was confirmed that when the contact angle is 40 to 50°, |P-P'|≧C, and the flange outer diameter angle γ is 35° to 50°, the roller-retainer assembly has good insertability into the outer ring 12.

This invention is not limited to the above-described embodiment, and can of course be embodied in various other forms without departing from the spirit of the invention. The scope of the invention is indicated by the claims, and further includes the equivalent meanings set forth in the claims, and all modifications within the scope of the claims.

11: Bearing 12: Outer ring 12a: Outer ring raceway surface 12b: Flange portion 13: Inner ring 13a: Inner ring raceway surface 15: Cage 15a: Large diameter ring portion 15b: Small diameter ring portion 15c: Guide surface 15d: Claw 15e: Notch portion

Claims (1)

A tapered roller bearing comprising an outer ring having an outer ring raceway surface on its inner peripheral surface, an inner ring having an inner ring raceway surface on its outer peripheral surface, a plurality of tapered rollers arranged to roll freely between the outer ring raceway surface and the inner ring raceway surface, and a cage having a plurality of pockets which house and hold the plurality of tapered rollers at specified intervals, wherein a rib portion is formed on the large diameter end of the outer ring raceway surface of the outer ring out of four ends, namely, the small diameter end and the large diameter end of the outer ring raceway surface of the outer ring, and the small diameter end and the large diameter end of the inner ring raceway surface of the inner ring, wherein the contact angle is 40° to 50°, and the relationship between the thickness E of the outer ring rib and the large diameter side diameter DW of the rollers is 0.19<E a notch is formed in the outer peripheral surface of a large diameter ring portion of the retainer so that the thickness of the ring portion is thinner than the thickness of a column portion having the retainer guide surface, and a roller circumscribing circle diameter P when the rollers abut against the guide surface of the retainer and a roller circumscribing circle diameter P' when the rollers abut against the claws of the retainer satisfy the relationship |P-P'|≧C with respect to the outer ring rib height C from the raceway surface, and a rib outer diameter angle γ is 35° to 50°.

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