Roller bearing

Abstract

The contact portion of the end face of a conical roller, which is a portion to be slidingly contacted with a collar portion, is ground such that the outer contour line of the section thereof has a continuously curved line which passes through at least not only the first point but also between the third position and fourth position.

Description

The present invention relates to a roller bearing such as FIG. 3 is a partial section view of a second embodiment of a roller bearing according to the present invention;This is illustrated by the fact that the reference line emanating from the outer contour line 13b refers to the entirety of the hatched area formed between the first point P_A and the third positon P_C and the fourth position P_D. Also, the present end face is ground so as to have a continuously curved shape which decreases in the radius of curvature as it goes outwardly in the radial direction thereof (for example, in case where the radii of the points P_A, P_D and P_B are expressed as R_A, R_D and R_E respectively, R_A>R_D>R_E). By the way, the end face 13a of the cylindrical roller 13 is ground on a horizontal or vertical duplex head grinder using an elastic grindstone having a Young's modulus set in the range of 10 MPa to 500 MPa.

Next, FIG. 3 shows a partial section view of a second embodiment of a roller bearing according to the present invention. As shown in FIG. 3, a roller bearing according to the present embodiment comprises an outer ring 11, an inner ring 12, a conical roller 16 and a retainer 14; and, in the right (in FIG. 3) end portion of the inner ring 12, there is formed a collar portion 15. The collar portion 15 is used to guide the cylindrical roller 13 in the circumferential direction of the outer ring 11 and inner ring 12. In case where the maximum diameter of the conical roller 16 is 2R, the height h from the raceway surface 12a of the inner ring 12 to the leading end of the collar portion 15 is set such that h=approx. 0.6R. Also, the collar portion 15 has a roller guide surface 15a extending almost at right angles to the raceway surface 12a of the inner ring 12. The conical roller 16 is structured such that, while its end face 16a is slidingly contacted with the roller guide surface 15a of the collar portion 15, it rolls on the raceway surface 12a of the inner ring 12.

Now, FIG. 4 shows the contact portion of the end face of the conical roller 16, which is a portion to be slidingly contacted with the collar portion 15. As shown in FIG. 4, the contact portion of the end face of the conical roller 16 to be slidingly contacted with the collar portion 15 is ground into a convexly spherical shape by an elastic grindstone (not shown). Also, in case where the diameter of the conical roller 16 is expressed as 2R, a position in which the end face 16a of the conical roller 16 intersects with the center axial line CL of the conical roller 16 is expressed as an original point P_o, a position distant from the original point P_o by 0.65R in the outside diameter direction of the conical roller 16 is expressed as a first point P_A, a position distant from the first point P_o by 0.85R in the outside diameter direction of the conical roller 16 is expressed as a second point P_B, a position distant from the second point P_B by 0.0065R in the axial direction of the conical roller 16 is expressed as a third position P_C, a position distant from the second point P_B by 0.01R in the axial direction of the conical roller 16 is expressed as a fourth position P_D, the contact portion of the end face of the conical roller 16 to be slidingly contacted with the collar portion 15 is ground by an elastic grindstone so as to have a continuously curved shape in which the outer contour line 16b of the section of the end face of the conical roller 16 passes through the first point P_A as well as passes between third position P_C and fourth position P_D. By the way, the end face 16a of the conical roller 16 is ground on a horizontal or vertical duplex head grinder using an elastic grindstone having a Young's modulus set in the range of 10 MPa to 500 MPa.

Rotation Evaluation Test 1

A rotation evaluation test was conducted on the cylindrical bearing (roller diameter: 19 mm, collar portion height h: 3.65 mm) shown in FIG. 1 under the following conditions, while the temperatures of the outer ring in the test were measured. FIG. 5 shows the results of the outer ring temperatures measured. Here, FIGS. 10(a) to 10(c)) respectively show the shapes of the end faces of rollers used in the present rotation evaluation test.

TEST CONDITIONS


Test bearing:                NJ218E
Maximum number of rotations: 4300 min−1
Axial load:                  5880N
Radial load:                 9800N
Oil bath lubrication:        VG68

In FIG. 5, solid lines a1 and a2 respectively show the outer ring temperatures of a cylindrical roller bearing (which is hereinafter referred to as a comparison example) in case where a drop quantity G (see FIG. 2) at a position distant by 0.85R from the point Po in the outside diameter direction of the bearing is set such that G=0.00011R (roller diameter: 19 mm, 9.5×0.00011=approx. 1 μm) which exists between the two points P_B and P_C in FIG. 2. Also, dotted lines b1 and b2 respectively show the outer ring temperatures of a cylindrical roller bearing (which is hereinafter referred to as an embodiment 1) in case where a drop quantity G at a position distant by 0.85R from the point P_o in the outside diameter direction of the bearing is set such that G=0.0005R (roller diameter: 19 mm, 9.5×0.0005=approx. 5 μm) which exists at the P_C in FIG. 2. Further, solid lines c1 and c2 respectively show the outer ring temperatures of a cylindrical roller bearing (which is hereinafter referred to as an embodiment 2) in case where a drop quantity G at a position P_D distant by 0.85R from the point P_o in the outside diameter direction of the bearing is set such that G=0.003R (roller diameter: 19 mm, 9.5×0.003=approx. 24 μm) which exists at the P_B in FIG. 2.

By the way, in grinding the roller end faces, similarly to the related art, there was used a horizontal duplex head grinder; and, in the embodiments 1 and 2, as a grindstone for grinding the end faces of the cylindrical rollers, there was used an elastic grindstone having a Young's modulus of 16 MPa (normally, a grindstone including a virtified bond has a Young's modulus of about 50000 to 100000 MPa, and a grindstone including a resinoid bond has a Young's modulus of about 5000-20000 MPa). Also, referring to the section shapes of the end faces of the rollers shown in FIG. 10, they may satisfy the condition that, for example, when they are drawn by a horizontal linear-type shaping machine with a vertical magnification of about 500 to 2000 (a horizontal magnification of about 5 to 20), the continuity and drop quantities thereof can be confirmed at the respective points.

As shown in FIG. 5, in the comparison example, in case where the rotation speed of the bearing reaches 1720 min⁻¹, the outer ring temperature exceeds 100° C. and, on the other hand, in the embodiments 1 and 2 of the present invention, even in case where the rotation speed of the bearing reaches 1720 min⁻¹, the outer ring temperature does not exceed 80° C. The reason for this is as follows: that is, in the comparison example, the surface pressure of the collar portion end face to be slidingly contacted with an intersecting point portion between the end face of the cylindrical roller and the chamfer portion of the cylindrical roller increases to a very great extent to thereby cause the outer ring temperature to rise (both of the solid lines a1 and a2 show that the outer ring temperature rises up to about 100° C. before the rotation speed reaches 1720 min⁻¹; and, on the other hand, in the embodiments 1 and 2, since there does exist such an edge portion as in the comparison example, the surface pressure does not rise so high when compared with the comparison example.

Also, when the embodiments 1 and 2 are compared with each other, the embodiment 2 is lower in an increase in the outer ring temperature than the embodiment 1. This may be because the quantity of lubricating oil to be introduced into between the end face of the cylindrical roller and collar portion varies according to the drop quantities.

By the way, although not shown, in the case of a roller bearing the drop quantity of which at a position distant by 0.85R from the point P_o is larger than the point P_D in FIG. 2 (about 40 to 50 μm), there were obtained test results which are almost similar to the embodiment 2. However, in this case, the grinding time using an elastic grindstone increases over the embodiment 2.

Rotation Evaluation Test 2

Another rotation evaluation test 2 was conducted on roller bearings each using a cylindrical roller having a diameter of 14 mm under the following conditions, and the outer ring temperatures were measured. FIG. 6 shows the results of the rotation evaluation test 2. Here, the shapes of the end faces of the rollers used in the test are as shown in FIGS. 11(a) and 11(b).

TEST CONDITIONS


Test bearing:         NJ308E (roller diameter: 14 mm, L = 15 mm,
                      collar portion height h = 2.80 mm)
Maximum number of     8000 min−1
rotations:
Axial load:           392N
Radial load:          9800N
Oil bath lubrication: VG68

In FIG. 6, solid lines a3 and a4 respectively show the outer ring temperatures of a cylindrical roller bearing (which is hereinafter referred to as a comparison example) in case where a drop quantity G (see FIG. 2) at a position distant by 0.85R from the point P_o in the outside diameter direction of the bearing is set such that G=0.00014R (roller diameter: 14 mm, 7×0.00014=approx. 1 μm) which exists between the two points P_B and P_C in FIG. 2. Also, dotted lines b3 and b4 respectively show the outer ring temperatures of a cylindrical roller bearing (which is hereinafter referred to as an embodiment 3) in case where a drop quantity G at a position distant by 0.85R from the point P_o in the outside diameter direction of the bearing is set such that G=0.0014R (roller diameter: 14 mm, 7×0.0014=approx. 10 μm) which exists between the P_C and P_D in FIG. 2.

As shown in FIG. 6, in the comparison example, in case where the number of rotations reaches 3000 min⁻¹, the outer ring temperature exceeds 70° and, in the embodiment 3, even in case where the number of rotations reaches 3000 min⁻, the outer ring temperature does not exceed 70°.

As can be seen clearly from the test results shown in FIGS. 5 and 6, since the contact portion of the end face of the cylindrical roller 13, which is a portion to be slidingly contacted with the collar portion 15, is ground such that the outer contour line of the section thereof has a continuously curved shape which passes through at least not only the first point P_A but also between the third position P_C and fourth position P_D, lubricating oil can be introduced easily into between the end face 13a of the cylindrical roller 13 and collar portion 15. Thanks to this, the frictional heat occurring between the cylindrical roller 13 and collar portion 15 can be reduced without enforcing special working on the end face 13a of the cylindrical roller 13 and the roller guide surface of the collar portion 15 or without changing the shape of the roller greatly.

Next, the inventors checked the relationship between the Young's modulus of a grindstone and the drop quantity of the 0.85R point of the roller end face with respect the 0.65R point of the roller end face. FIG. 7 shows the results of this check. And, the inventors also checked the relationship between the Young's modulus of a grindstone used to grind the end face of a roller and the friction quantity of the grindstone. FIG. 8 shows the results of this check.

As shown in FIG. 7, in the case of a grindstone having a Young's modulus of 5000 MPa or more, since the support rigidity of an abrasive grain is high, in case where interference between the roller end face and grindstone exceeds a certain value, removal due to grinding is allowed to start. Thanks to this, interference up to the chamfer portion of the roller is not obtained but there is formed a flat end face, so that there can be obtained the stable length of the roller.

On the other hand, in the case of a grindstone having a Young's modulus of 500 MPa or less, the roller end face can be gradually ground into a continuously curved shape and, as shown in FIG. 7, the drop quantity of the roller end face increases. Further, in case where a grindstone having a small Young's modulus is used, the drop quantity increases. However, in the case of a grindstone having a Young's modulus of 10 MPa or lower, contrary to a grindstone having a high Young's modulus, the length dimension of the roller becomes unstable and the grinding time also increases. As shown in FIG. 8, which shows the relationship between the grindstone wear (the wear quantity when grinding 1000 pcs. of rollers each having a diameter of 7.5 mm is considered as the average wear quantity) and Young' modulus, in case where the Young's modulus of the grindstone is small, the grindstone wear tends to increase and, especially, in the case of 15 MPa or less, the grindstone wear increases. With the above conditions taken into consideration, preferably, the Young's modulus may be set in the range of 150 MPa to 15 MPa.

Rotation Evaluation Test 3

The inventors conducted a third rotation evaluation test on the conical roller bearing under the following conditions, and checked the relationship between the drop quantity G of the conical roller end face and the time taken up to occurrence of seizure after stop of supply of lubricating oil. FIG. 9 shows the results of the check.

TEST CONDITIONS


Test bearing:                HR30306C
Maximum number of rotations: 6000 min−1
Axial load:                  4000N
Lubricating oil:             Gear oil
Quantity of Oil supplied:    480 cc/min.

In FIG. 9, Δ designates a conventional conical roller bearing and ◯ stands for a conical roller bearing according to the present invention.

As shown in FIG. 9, in case where a ratio G/R (which is hereinafter referred to as the roller end face drop quantity ratio) of the drop quantity G of the roller end face to the radius R of the conical roller 16 is 0.0065 (which exists between P_B and P_C in FIG. 4) or less, seizure occurs in a relatively early stage; but, in case where the roller end face drop quantity ratio G/R is equal to or larger than 0.0065 which is larger than P_C in FIG. 4, seizure becomes hard to occur. Also, even in case where the roller end face drop quantity ratio G/R exceeds 0.01 which is larger than P_D in FIG. 4, the effect thereof is not different so much from that of the roller end face drop quantity ratio G/R of 0.01, but only the grinding time increases. Therefore, preferably, the drop quantity ratio of the conical roller end face G/R may be set in the range of 0.0065 to 0.01.

As can be clearly understood from the test results shown in FIG. 9, since the contact portion of the end face of the conical roller 16, which is a portion to be slidingly contacted with the collar portion 15, is ground such that the outer contour line of the section thereof has a continuously curved line which passes through at least not only the first point P_A but also between the third position P_C and fourth position P_D, lubricating oil can be introduced easily into between the end face 16a of the conical roller 16 and collar portion 15. Thanks to this, the frictional heat occurring between the conical roller 16 and collar portion 15 can be reduced without enforcing special working on the end face of the conical roller 16 and the roller guide surface of the collar portion 15 or without changing the shape of the roller greatly.

As has been described heretofore, according to the present invention, there can be provided a roller bearing which can reduce the frictional heat generated between the roller and collar portion without enforcing special working on the end face of the roller and the roller guide surface of the collar portion or without changing the shape of the roller greatly.

Claims

1. A roller bearing including a collar portion formed in the end portion of a ring for guiding a plurality of cylindrical rollers in the circumferential direction of the ring, wherein a diameter of each of said cylindrical rollers is expressed as 2R,

a position in which an end face of said cylindrical roller intersects with a center axial line of said cylindrical roller is expressed as an original point,

a position distant from said original point by 0.65R in an outside diameter direction of said cylindrical roller is expressed as a first point,

a position distant from said first point by 0.20R in the outside diameter direction of said cylindrical roller is expressed as a second point,

a position distant from said second point by 0.0005R in the axial direction of said cylindrical roller is expressed as a third position,

a position distant from said second point by 0.003R in the axial direction of said cylindrical roller is expressed as a fourth position, and

the contact portion of the end face of said cylindrical roller to be slidingly contacted with said collar portion is ground so as to have a continuously curved shape in which the outer contour line of the section of said end face of said cylindrical roller passes through said first point and passes between any one point in a line extending from said third and position through said fourth positions position.

2. The roller bearing as set forth in claim 1, wherein the longitudinal elastic coefficient of an elastic grindstone for finishing the end face of said roller is set in the range of 10 MPa to 500 MPa.

3. A roller bearing including a collar portion formed in the end portion of a ring for guiding a plurality of conical rollers in the circumferential direction of the ring, wherein a diameter of each of said conical rollers is expressed as 2R,

a position in which an end face of said conical roller intersects with a center axial line of said conical roller is expressed as an original point,

a position distant from said original point by 0.65R in an outside diameter of said conical roller is expressed as a first point,

a position distant from said first point by 0.20R in the outside diameter direction of said conical roller is expressed as a second point,

a position distant from said second point by 0.0065R in the axial direction of said conical roller is expressed as a third position,

a position distant from said second point by 0.01R in the axial direction of said conical roller is expressed as a fourth position, and

the contact portion of the end face of said conical roller to be slidingly contacted with said collar portion is ground so as to have a continuously curved shape in which the outer contour line of the section of the end face of said conical roller passes through said first point passes between said third and fourth positions.

4. The roller bearing as set forth in claim 3, wherein the longitudinal elastic coefficient of an elastic grindstone for finishing the end face of said roller is set in the range of 10 MPa to 500 MPa.

5. A roller bearing including a collar portion formed in an end portion of a ring for guiding a plurality of cylindrical rollers in the circumferential direction of the ring, wherein a contact portion of an end face of each of said cylindrical rollers to be slidingly contacted with said collar portion is ground so as to have a continuously curved shape in which the radius of the outer contour line of said end face contact portion decreases as the outer contour line goes outwardly in the radial direction of the roller.