TAPERED ROLLER BEARING

A tapered roller bearing includes an inner ring and an outer ring, and a plurality of rollers that are rollably disposed between raceway surfaces of the inner ring and the outer ring. A flange part is provided at one end portion or both end portions of the inner ring. Crownings are respectively formed on a rolling contact surface of each roller and the raceway surface of the inner ring. At least at one end portion of an effective contact length Le in a generatrix direction of the rolling contact surface of each roller and the raceway surface of the inner ring, a crowning drop amount in the raceway surface of the inner ring is smaller than a crowning drop amount in the rolling contact surface of each roller.

TECHNICAL FIELD

The present invention relates to a tapered roller bearing, and particularly relates to a tapered roller bearing used in a speed reducer, a construction machine, a steel industry, an automobile, and the like.

BACKGROUND ART

It is conventionally known that, in order to reduce an occurrence of an excessive contact surface pressure, i.e. a so-called edge load at both end portions in an axial direction of a contact portion in a roller bearing, a crowning is formed on a rolling contact surface of a roller or a raceway surface of a raceway ring (see, for example, Patent Document 1).

It is also known that a logarithmic crowning can make a bearing life longer, which does not cause the occurrence of the excessive contact surface pressure, i.e. so-called edge load from a central portion to both end portions in the axial direction of the contact portion with respect to an effective contact length Le in a generatrix direction.

In the meantime, as is apparent fromFIG. 10showing a logarithmic crowning together with a single circular arc crowning, in the logarithmic crowning, a drop amount increases gently from a center toward end portions and increases sharply when approaching the end portions. Therefore, it is difficult to form the logarithmic crowning on the roller or the raceway ring. For this reason, in Patent Document 1, a crowning of a circular arc combination is formed on the roller so as to provide a shape approximate to the logarithmic crowning.

Patent Document 1 also discloses that a sum σ of crowning drop amounts of a roller and an inner ring is designed to satisfy a range of an arbitrary crowning expression (an expression of a load range of 0.4×C to 0.6×C with respect to a dynamic load rating C) at two arbitrary points (two points of 0.425×Le and 0.5×Le with respect to an effective contact length Le), so as to approach the logarithmic crowning.

Further, in order to actually form crowning on the inner ring, a crowning shape is first processed by grinding, and then processed using a finishing grindstone to obtain a desired surface roughness (which affects a bearing life). Therefore, in finishing processing of the inner ring performed with the grindstone, an SF processing (finishing processing) is performed by moving the grindstone horizontally on the inner ring raceway surface while fitting the grindstone on the crowning, so as to obtain the desired surface roughness. A target shape may also be obtained in the SF processing.

However, in a tapered roller bearing or a cylindrical roller bearing, since a flange part is provided on an outer side in the axial direction of the raceway surface of the inner ring, when finishing processing is performed with the grindstone in order to form the logarithmic crowning on the raceway surface of the inner ring, it is difficult to obtain the desired surface roughness at the end portions of the raceway surface. In addition, in order to obtain the desired surface roughness, a longer time is required until the grindstone fits, so that a cycle time increases, the grindstone is in contact with the flange part, or it is necessary to additionally provide a complicated mechanism as described in Patent Document 2.

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF INVENTION

Technical Problem

The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a tapered roller bearing in which finishing processing can be easily performed on a rolling contact surface of a roller and a raceway surface of an inner ring while reducing an increase in cost due to an equipment modification or an increase in cycle time.

Solution to Problem

The above object of the present invention may be achieved by the following configuration.

(1) A tapered roller bearing includes:

an inner ring and an outer ring; and

a plurality of rollers that are rollably disposed between raceway surfaces of the inner ring and the outer ring,

wherein a flange part is provided at one end portion or both end portions of the inner ring,

wherein crownings are respectively formed on a rolling contact surface of each roller and the raceway surface of the inner ring, and

wherein at least at one end portion of an effective contact length Le in a generatrix direction of the rolling contact surface of each roller and the raceway surface of the inner ring, a crowning drop amount in the raceway surface of the inner ring is smaller than a crowning drop amount in the rolling contact surface of each roller.

(2) In the tapered roller bearing according to (1),

in a range of the effective contact length Le in the generatrix direction of the rolling contact surface of each roller and the raceway surface of the inner ring, a sum of the crowning of the rolling contact surface of each roller and the crowning of the raceway surface of the inner ring is set to be a logarithmic crowning of the following Equation (i) in at least two positions in the generatrix direction respectively,

where

δ is the sum of the crowning drop amounts in a generatrix direction position X of two contacting objects (roller and the raceway surface of the inner ring);

w is a contact load;

Le is the effective contact length in the generatrix direction;

E1, E2are Young's moduluses of the two contacting objects (roller and the raceways surface of the inner ring);ν1, ν2are Poisson's ratios of the two contacting objects (roller and the raceways surface of the inner ring); andb is ½ of a Hertz contact width.
(3) In the tapered roller bearing according to (1) or (2),

a central portion of the crowning of at least one of each roller, the inner ring, and the outer ring has a linear shape.

(4) In the tapered roller bearing according to any one of (1) to (3),

a crowning drop amount in a raceway surface of the outer ring is smaller than the crowning drop amount in the raceway surface of the inner ring.

Here, the “effective contact length Le” in the present invention is a length of a region where the rolling contact surface of each roller and the raceway surface of the inner ring actually contact with each other. A specific manner of defining the effective contact length Le will be described later in the description of embodiments.

Advantageous Effects of Invention

According to the tapered roller bearing of the present invention, the flange part is provided at one end portion or both end portions of the inner ring, the crownings are respectively formed on the rolling contact surface of each roller and the raceway surface of the inner ring, and at least at one end portion of the effective contact length Le in the generatrix direction, the crowning drop amount in the raceway surface of the inner ring is smaller than the crowning drop amount in the rolling contact surface of each roller. That is, by setting the crowning drop amount of the inner ring, whose end portion of the raceway surface cannot be approached by a grindstone due to the flange part, smaller than the crowning drop amount of the roller, it is possible to reduce an increase in cost due to an equipment modification and an increase in cycle time, and to easily perform finishing processing of the rolling contact surface of each roller and the raceway surface of the inner ring.

DESCRIPTION OF EMBODIMENTS

Hereinafter, tapered roller bearings according to several embodiments of the present invention will be described in detail with reference to the drawings.

First Embodiment

As shown inFIG. 1andFIG. 2, a tapered roller bearing10of the embodiment includes an inner ring11which has an inner ring raceway surface11aon an outer peripheral surface, an outer ring12which has an outer ring raceway surface12aon an inner peripheral surface, a plurality of tapered rollers13(hereinafter, simply referred to as “rollers13”.) which are rolling elements disposed between the inner ring raceway surface11aand the outer ring raceway surface12a, and a cage14which retains the plurality of rollers13at predetermined intervals in a circumferential direction.

The inner ring11includes a small diameter flange part11band a large diameter flange part11cat a small diameter side axial direction end portion and a large diameter side axial direction end portion of the inner ring raceway surface11a.

Further, in this embodiment, in order to reduce an occurrence of an edge load, crownings are respectively formed on a rolling contact surface13aof each roller13and the inner ring raceway surface11aof the inner ring11, and in the range of an effective contact length Le in a generatrix direction of the rolling contact surface13aof the tapered roller13and the raceway surface of the inner ring11, a sum of the crownings is set to a logarithmic crowning of the following Equation (i) in at least two positions in the generatrix direction.

Here, δ is the sum of the crowning drop amounts in a generatrix direction position X of two contacting objects (roller and the raceway surface of the inner ring);

w is a contact load;

Le is the effective contact length in the generatrix direction;

E1, E2are Young's moduluses of the two contacting objects (roller and the raceway surface of the inner ring);

ν1, ν2are Poisson's ratios of the two contacting objects (roller and the raceway surface of the inner ring); and

b is ½ of a Hertz contact width.

Here, the effective contact length Le is a length of a region where the rolling contact surface13aof the roller13and the raceway surface11aof the inner ring11can actually contact with each other. Specifically, there are several situations as schematically shown inFIG. 3AtoFIG. 3F, for example, depending on a difference in length between the rolling contact surface13aof the roller13and the raceway surface11aof the inner ring11and a difference in size between a chamfer13bof the roller13on both sides in the axial direction and a relief groove11dof the inner ring.

FIG. 3Ashows a case where the length of the rolling contact surface13aof the roller13and the length of the raceway surface11aof the inner ring11are the same. In this case, the effective contact length Le is the length of the rolling contact surface13aof the roller13or the raceway surface11aof the inner ring11.

FIG. 3Bshows a case where the length of the rolling contact surface13aof the roller13is longer than the length of the raceway surface11aof the inner ring11, and the raceway surface13aof the roller13extends on both sides in the axial direction outward from both end portions of the raceway surface11aof the inner ring11. In this case, the effective contact length Le is the rolling contact surface13aof the roller13.

FIG. 3Cshows a case where the length of the rolling contact surface13aof the roller13is longer than the length of the raceway surface11aof the inner ring11, the raceway surface11aof the inner ring11extends outward on one end side in the axial direction, and the raceway surface13aof the roller13extends outward on the other end side in the axial direction. In this case, the effective contact length Le is an overlapped portion in the axial direction of the length of the rolling contact surface13aof the roller13and the length of the raceway surface11aof the inner ring11.

FIG. 3Dshows a case where the rolling contact surface13aof the roller13is longer than the raceway surface11aof the inner ring11, and the raceway surface13aof the roller13extends outward on one end side in the axial direction, and the raceway surface11aof the inner ring11extends outward on the other end side in the axial direction. In this case, the effective contact length Le is an overlapped portion in the axial direction of the length of the rolling contact surface13aof the roller13and the length of the raceway surface11aof the inner ring11.

FIG. 3Eshows a case where the raceway surface11aof the inner ring11is longer than the rolling contact surface13aof the roller13, and the raceway surface11aof the inner ring11extends on both sides in the axial direction outward from both end portions of the raceway surface13aof the roller13. In this case, the effective contact length Le is the rolling contact surface13aof the roller13.

FIG. 3Fshows a case where the length of the raceway surface11aof the inner ring11is longer than the length of the rolling contact surface13aof the roller13, the raceway surface11aof the inner ring11extends outward on one end side in the axial direction, and the raceway surface13aof the roller13extends outward on the other end side in the axial direction. In this case, the effective contact length Le is an overlapped portion in the axial direction of the length of the rolling contact surface13aof the roller13and the length of the raceway surface11aof the inner ring11.

It is noted that crowning shapes of the rolling contact surface13aof the tapered roller13and the raceway surface11aof the inner ring11are not shown inFIG. 3AtoFIG. 3F.

A central position of the crowning shape on the rolling contact surface13aof the roller13coincides with a central position of the crowning shape on the raceway surface11aof the inner ring11. The central positions of the crowning shapes are set at arbitrary positions based on the rolling contact surface13aor the raceway surface11a. Therefore, the central position of the effective contact length Le and the central positions of the crowning shapes (positions of X=0 inFIG. 4) do not necessarily coincide with each other.

Further, in this embodiment, for the following reasons, the crowning drop amount in the raceway surface11aof the inner ring11is designed to be smaller than the crowning drop amount in the rolling contact surface13aof the roller13at end portions on both sides of the effective contact length Le in the generatrix direction.

Specifically, as shown inFIG. 4, the raceway surface11aof the inner ring11is a single circular arc crowning, and the rolling contact surface13aof the roller13is a crowning shape having a drop amount C obtained by subtracting a drop amount B of the single circular arc crowning from the sum δ of the logarithmic crowning given by Equation (i). That is, the arc shape of the crowning formed on the raceway surface11aof the inner ring11is designed such that the drop amount B at end portions on both sides of the effective contact length Le is smaller than the drop amount C of the raceway surface13aof the roller13when the drop amounts of both the raceway surfaces11aand13ain a middle portion in the axial direction of the effective contact length Le are zero.

Hereinafter, a difference in a fitting time of a grindstone100during finishing processing due to the difference in the drop amount at the end portions of the inner ring raceway surface11aor the rolling contact surface13awill be described below referring toFIGS. 5A to 5DandFIGS. 6A to 6D.

As shown inFIG. 5A, the finishing processing of the inner ring11is performed with the grindstone100by moving the grindstone100horizontally (along the generatrix direction) on the inner ring raceway surface11aso as to provide a desired surface roughness while fitting the grindstone100to the crowning shape.

At this time, in a case where the drop amount is large as shown inFIG. 5C, a distance L1between the end portion of the inner ring raceway surface11aand the grindstone100is farther than that in a case where the drop amount is small as shown inFIG. 5B, and therefore, the time (fitting time) until the grindstone100comes into contact with the end portion due to wearing of the grindstone100is required longer, so that a cycle time increases. In the drawing, a reference numeral11dschematically represents a relief groove between the inner ring raceway surface11aand the flange part11b.

In order to reduce the cycle time, the distance between the flange part11band the grindstone100is desired to be reduced as much as possible. However, as shown inFIG. 5D, when the grindstone100excessively approaches the flange part11b, the grindstone100comes into contact with the flange part11b. Therefore, management of the grindstone100is important in the finishing processing of the inner ring11, and the drop amount is better small when considering the processing cost.

In the meantime, as shown inFIG. 6A, the finishing processing of the roller13is also performed with the grindstone100by moving the grindstone100horizontally (along the generatrix direction) on the rolling contact surface13aso as to provide a desired surface roughness while fitting the grindstone100to the crowning.

In the case of finishing processing of the roller13, since no flange part is provided unlike the inner ring11, as shown inFIG. 6C, the grindstone100can approach the end portion of the roller13such that the distance L2between the end portion of the rolling contact surface13aand the grindstone100is shortened, and processing can be performed more easily as compared with a case where the drop amount of the inner ring11is large as shown inFIG. 5C.

However, when the grindstone100excessively approaches the end portion of the roller13as shown inFIG. 6D, the grindstone100cannot return from the rolling contact surface13aof the roller13, so that the grindstone breaks or the machine is damaged, and thus a sufficient margin is necessary to prevent the grindstone100from slipping off.

Considering the processing cost, since the management becomes complicated similarly to the inner ring11if the drop amount is large, the drop amount is better small. However, even if the drop amount is large, the roller13can be more easily processed than the inner ring11since the roller13can approach the end portions more easily as compared with the inner ring11.

Therefore, in this embodiment, instead of realizing the logarithmic crowning with either one of the roller13or the inner ring11of the tapered roller bearing10alone, as shown inFIG. 4, in consideration of cost and processability, the logarithmic crowning is obtained with the combination of the drop amounts of the roller crowning and the inner ring crowning, and the crowning drop amount in the inner ring raceway surface11ais set smaller than the crowning drop amount in the rolling contact surface13aof the roller13at the end portions on both sides of the effective contact length Le.

Further, in this embodiment, since the logarithmic crowning is realized by the sum δ of the drop amounts of the roller13and the inner ring11, the drop amount of the roller13is small, so that if crowning is not formed on the outer ring12as well, the drop amount of the outer ring12is insufficient. Therefore, it is expected that the outer ring12has a short life.

It is assumed a case where a logarithmic crowning is also formed with the roller13and the outer ring12similarly to the inner ring11. A contact state on the circumference as shown inFIG. 2, the inner ring11and the roller13have a convex-convex relationship, while the outer ring12and the roller13have a concave-convex relationship. Therefore, it is assumed that the outer ring12would have a lower surface pressure at the same crowning drop amounts.

As described above, since the processing of the crowning is easier when the drop amount is smaller, the processing cost can be reduced by omitting the crowning of the outer ring12, or forming a crowning having a smaller drop amount than the inner ring11, on the outer ring12(crowning drop amount: the inner ring>the outer ring).

The outer ring12may have a linear shape without forming a crowning.

In addition, the drop amounts in vicinity of the central portions of the crowning of the roller13, the inner ring11, and the outer ring12are small, and have little difference from a linear shape. Therefore, the central portion of the crowning of at least one of the roller13, the inner ring11, and the outer ring12may have a linear shape.

As described above, according to the tapered roller bearing10of the embodiment, the flange parts11band11care provided at both end portions of the inner ring11, crownings are respectively formed on the rolling contact surface13aof the roller13and the raceway surface11aof the inner ring11, and at end portions on both sides of the effective contact length Le in the generatrix direction, the crowning drop amount in the raceway surface11aof the inner ring11is set smaller than the crowning drop amount in the rolling contact surface13aof the roller13. Accordingly, by setting the crowning drop amount of the inner ring11, which cannot approach the end portion due to the flange parts11band11c, smaller than the crowning drop amount of the roller13, it is possible to reduce an increase in cost due an equipment modification and an increase in cycle time, and to easily perform finishing processing of the rolling contact surface13aof the roller13and the raceway surface11aof the inner ring11.

Further, in the embodiment, since the logarithmic crowning of the above Equation (i) is realized by the sum δ of the crowning drop amount of the rolling contact surface13aof the roller13and the crowning drop amount of the raceway surface11aof the inner ring11, it is possible to realize a long life of the bearing while keeping the processing cost low.

In the embodiment described above, in order to reduce the increase in cost as much as possible, the crowning drop amount in the raceway surface11aof the inner ring11is set smaller than the crowning drop amount in the rolling contact surface13aof the roller13at end portions on both sides of the effective contact length Le in the generatrix direction. However, from a viewpoint of reducing the increase in cost, the crowning drop amount of the raceway surface11aof the inner ring11may be set smaller than the crowning drop amount of the rolling contact surface13aof the roller13at least at one end portion of the effective contact length Le in the generatrix direction.

Second Embodiment

Next, a tapered roller bearing according to a second embodiment of the present invention will be described with reference toFIG. 7. In the embodiment, the crowning shapes of the raceway surface of the inner ring and the outer ring and the rolling contact surface of the roller are different from those of the first embodiment. Other configurations are similar to those of the first embodiment.

That is, in this embodiment, the raceway surface11aof the inner ring11is a logarithmic crowning having a small drop amount as shown inFIG. 7instead of the single circular arc crowning of the first embodiment. In addition, in this case, the rolling contact surface13aof the roller13has a crowning shape obtained by subtracting the drop amount of the logarithmic crowning of the inner ring raceway surface11afrom the sum δ of the logarithmic crowning given by the above Equation (i).

Further, in this case, the crowning drop amount of the inner ring crowning on the raceway surface11aof the inner ring11is smaller than the crowning drop amount of the rolling contact surface13aof the roller13over the entire effective contact length Le in the generatrix direction.

Similarly to the first embodiment, the raceway surface12aof the outer ring12also has a crowning shape or a linear shape.

Therefore, also in this embodiment, by making the drop amount of the inner ring11, which cannot approach the end portion of the raceway surface due to the flange part, smaller than the drop amount of the roller, it is possible to omit an equipment modification and reduce an increase in cycle time, and to easily perform finishing processing of the rolling contact surface13aof the roller13and the inner ring raceway surface11awithout increasing the cost.

Other configurations and operations are similar to those of the first embodiment.

The present invention is not limited to the above-described embodiments, and can be appropriately modified, improved, or the like.

For example, although the flange parts11band11cmay be provided at both end portions of the inner ring11in the above embodiment, the flange part may be provided only at one end portion. For example, the inner ring11may only have a large diameter flange part11cas in the tapered roller bearing10ashown inFIG. 8. In particular, in this case, the crowning drop amount of the raceway surface11aof the inner ring11is set smaller than the crowning drop amount of the rolling contact surface13aof the roller13at least at one end portion of the effective contact length Le, which is the side having the large diameter flange11c.

Further, although the tapered roller bearing has been described in the above embodiment, the present invention is also applicable to a cylindrical roller bearing in which the same problem exists. That is, for example, the cylindrical roller bearing10bshown inFIG. 9also includes an inner ring11, an outer ring12, a plurality of rollers13which are rollably disposed between the raceway surfaces11aand12aof the inner ring11and the outer ring12, and a cage14which retains the plurality of rollers13at predetermined intervals in the circumferential direction. InFIG. 9, the flange part11cis provided at one end portion of the inner ring11, however, the flange part may also be provided at both end portions of the inner ring11.

Also in such a cylindrical roller bearing, the crowning formed on any of the rolling contact surface13aof the roller13and the raceway surface11aof the inner ring11can be configured similarly to the tapered roller bearing described above, and the similar effect to that of the tapered roller bearing can be obtained.

That is, an embodiment of the present invention provides a cylindrical roller bearing including: an inner ring and an outer ring; and a plurality of rollers that are rollably disposed between raceway surfaces of the inner ring and the outer ring, wherein a flange part is provided at one end portion or both end portions of the inner ring, crownings are respectively formed on a rolling contact surface of each roller and the raceway surface of the inner ring, and at least at one end portion of an effective contact length Le in a generatrix direction of the rolling contact surface of each roller and the raceway surface of the inner ring, a crowning drop amount in the raceway surface of the inner ring is smaller than a crowning drop amount in the rolling contact surface of each roller.

In addition, in a range of the effective contact length Le in the generatrix direction of the rolling contact surface of each roller and the raceway surface of the inner ring, a sum of the crowning of the rolling contact surface of each roller and the crowning of the raceway surface of the inner ring is set to be a logarithmic crowning of the following Equation (i) in at least two positions in the generatrix direction respectively.

δ is the sum of the crowning drop amounts in a generatrix direction position X of two contacting objects (roller and the raceway surface of the inner ring);

w is a contact load;

Le is the effective contact length in the generatrix direction;

E1, E2are Young's moduluses of the two contacting objects (roller and the raceway surface of the inner ring);

ν1, ν2are Poisson's ratios of the two contacting objects (roller and the raceway surface of the inner ring); and

b is ½ of a Hertz contact width.

Accordingly, the logarithmic crowning is realized by the sum of the crowning drop amounts of crowning at the effective contact length Le in the generatrix line direction of the rolling contact surface of the roller and the raceway surface of the inner ring. Also, by setting crowning drop amount of the inner ring, which cannot approach the end portion of the raceway surface due to the flange part, smaller than the crowning drop amount of the roller, it is possible to reduce an increase in cost due to an equipment modification and an increase in cycle time, and to easily perform finishing processing of the rolling contact surface of the roller and the raceway surface of the inner ring.

In addition, in an embodiment of the cylindrical roller bearing of the present invention, similarly to the tapered roller bearing of the above embodiment, a central portion of the crowning of at least one of the roller, the inner ring, and the outer ring may have a linear shape.

Further, in an embodiment of the cylindrical roller bearing of the present invention, similarly to the tapered roller bearing of the first embodiment, the crowning drop amount in the raceway surface of the outer ring may be smaller than the crowning drop amount in the raceway surface of the inner ring.

In addition, in an embodiment of the cylindrical roller bearing of the present invention, the crowning shape of the raceway surface of the inner ring may be a single circular arc crowning or a logarithmic crowning, similarly to the tapered roller bearings of the first and the second embodiments.

The present application is based on Japanese patent application No. 2017-79212, filed on Apr. 12, 2017, and contents of which are incorporated herein by reference.

REFERENCE SIGNS LIST