Sealing device, rolling bearing, and rolling bearing for wheel

Prior to assembly of an elastic member (51) to a slinger (52), a radially inner surface (58) of a first portion (56) is formed in a concave shape, and a radially inner surface (59) of a second portion (57) is formed in a conical shape. The second axial lip (55) is adapted such that, after the elastic member (51) is assembled to the slinger (52) and when a second axial lip (55) is in a not-yet-worn state, the second axial lip (55) does not come into contact with a fixation section (65) of the slinger (52).

This application is the U.S. national phase of International Application No. PCT/JP2007/070615 filed 23 Oct. 2007, which designated the U.S. and claims priority to Japan Application No. 2006-287252 filed 23 Oct. 2006, the entire contents of each of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a sealing device and in particular to a sealing device preferably used for a rolling bearing in which a raceway member having a raceway surface consists of two or more cylindrical members only, a rolling bearing for a wheel, a water pump, or a motor using a roll bearing. Furthermore, the present invention relates to a rolling bearing and a rolling bearing for a wheel.

BACKGROUND ART

Conventional sealing devices include one described in JP 4-93571 U (Patent Document 1).

The sealing device is located between an inner race and an outer race of a rolling bearing for a wheel. The sealing device has a metal core, an elastic member fixed to the metal core, a slinger of L-shaped cross section, and a garter spring. The slinger consists of an axially-extending portion and a radially extending portion, and the elastic member has a radial lip which always slides on the axially-extending portion, a first axial lip which always slides on the radially extending portion, and a second axial lip which is positioned radially inside the first axial lip and slides on the radially extending portion. The second axial lip has an annular groove on a radially outer surface.

The garter spring has been inserted in the annular groove of the second axial lip. The garter spring urges or presses the second axial lip radially inward.

In the sealing device, the second axial lip is not in contact with the axially-extending portion while the second axial lip is in a non-worn state, and once the second axial lip becomes worn and the pressing force against the radially extending portion of the second axial lip becomes a predetermined force or less, part of a portion facing the axially-extending portion of the second axial lip comes into contact with the axially-extending portion and constitutes a radial seal.

The second axial lip in its non-worn state functions as an axial seal, while part of the portion facing the axially-extending portion of the second axial lip in its worn state functions as a radial seal. In this way, the sealing device is able to maintain a continuing stable seal function.

Against this background, there has been a demand for a significant reduction in the torque of a sealing device which seals rolling elements of a rolling bearing for a wheel from the outside. The conventional sealing device has a problem that the life of the second axial lip is short.

SUMMARY OF INVENTION

Technical Problem

It is therefore an object of the present invention to provide a sealing device, a rolling bearing, and a rolling bearing for a wheel, which are capable of significant reduction in torque and have a long life.

Solution to Problem

In order to solve the problem, sealing device according to an aspect of the present invention comprises:

a metal core which is fixed to and around a first bearing ring and has a radially extending portion extending in a radial direction of the first bearing ring;

a slinger having a cylindrical fixation section fixed to and around a second bearing ring and a flange section which extends in the radial direction from the fixation section and is positioned more outside in an axial direction of the second bearing ring than the radially extending portion of the metal core; and

an elastic member having a base fixed to the radially extending portion of the metal core and a lip section which is connected with the base and is slidable on the slinger,

wherein the lip section comprises a first axial lip which extends from the base toward the first bearing ring in the radial direction and outward in the axial direction and is slidable on the flange section, and a second axial lip which is positioned radially on the second bearing ring side of the first axial lip at a distance in the radial direction from the first axial lip and is slidable on the flange section;

wherein the second axial lip comprises a first portion which extends from the base toward the second bearing ring in the radial direction and outward in the axial direction, and a second portion which extends from an axially outer end of the first portion toward the first bearing ring in the radial direction and outward in the axial direction and is slidable on the flange section;

wherein in a state before the elastic member is assembled to the slinger, a surface that the first portion has on the second bearing ring side in the radial direction is a concave surface, while a surface that the second portion has on the second bearing ring side in the radial direction is a conical surface or a convex surface; and

wherein in a state after the elastic member has been assembled to the slinger, the second axial lip is positioned at a distance in the radial direction from the fixation section of the slinger while the second axial lip is in a non-worn state, and part of a portion facing the fixation section of the slinger of the second axial lip is slidable on the fixation section of the slinger while the second axial lip is in a worn state and in a state that pressing force against the flange section of the second axial lip has decreased by a predetermined amount or more due to wear of the second axial lip.

The term “radially extending” refers to extending in a direction with at least a radially extending component. For this reason, the term “radially extending” refers to not only extending in a direction with only a radial extending component but also extending in a combined direction with both of a radial extending component and an axial extending component.

Furthermore, in this specification, a “conical surface” is intended to be included in a concave surface, but not in a convex surface.

Regarding a so-called pack seal type sealing device having an elastic member and a slinger of L-shaped cross section, the sealing device having two radial lips and one axial lip, the inventors investigated the magnitude of torque caused by contact loads of the lips. As a result, the inventors discovered that the ratio of torque caused by the contact load of the two radial lips to the total torque reaches as much as the order of 80 percent and most of the torque is caused by the contact load of a radial seal.

Furthermore, it was found that, in the sealing device having the conventional configuration, the deformation of the portion on the metal core side of the radially inner axial lip is large when the assembly process is carried out, so that stress concentration occurs on that portion and the durability of that portion becomes small, resulting in a short life of the sealing device.

According to the present invention, the elastic member is in the state of being in noncontact with the fixation section of the slinger and having no radial lip until the pressing force against the flange section of the second axial lip decreases by a given magnitude or more, so that the torque can be significantly reduced until the pressing force against the flange section of the second axial lip decreases by the given magnitude or more. Thus, the fuel economy of an automobile or the like having this sealing device can be reduced.

Furthermore, according to the present invention, the surface on the second bearing ring side in the radial direction of the first portion assumes a concave shape before the elastic member is assembled to the slinger. Therefore, it is not necessary to deform a base side part of the first portion of the second axial lip intensively and excessively to bring the second axial lip into noncontact with the fixation section of the slinger in the assembly initial stage, in contrast to the case that the surface on the second bearing ring side in the radial direction of the first portion is a convex surface. Instead, the second axial lip can be brought into noncontact with the fixation section of the slinger by deforming the whole of the first portion almost evenly in its extending direction. In other words, locally excessive stress is not applied to part of the first portion, so that the durability of the second axial lip can be remarkably increased and the life of the sealing device can be thus increased.

Furthermore, according to the present invention, the surface on the second bearing ring side in the radial direction of the second portion is a conical surface or a convex surface before the elastic member is built in the slinger, so that the contact pressure between the second axial lip and the flange section of the slinger can be reduced and wear of the second axial lip can be thus restrained as compared with the case that the surface on the second bearing ring side in the radial direction of the second portion is a concave surface. Thus, a time until the second axial lip comes into contact with the fixation section of the slinger is prolonged, so that the state that the torque is remarkably small is sustained for a long term, as compared with the case that the surface on the second bearing ring side in the radial direction of the second portion is a concave surface

Furthermore, according to the present invention, part of the portion facing the fixation section of the slinger of the second axial lip comes into contact with the fixation section of the slinger and slides on the fixation section in the sate that the pressing force against the flange section of the second axial lip has decreased by predetermined force or more due to wear of the second portion of the second axial lip. Therefore, in a rolling bearing for a wheel, even if the wear of the second axial lip advances, foreign matter such as muddy water from the outside can be restrained from entering a compartment where rolling elements are located.

In one embodiment, a surface that the second portion has on the second bearing ring side in the radial direction is smoothly continuous.

The term “smoothly continuous” herein means that the surface on the second bearing ring side in the radial direction of the second portion is in the state of being able to be differentiated from one end to the other end in an axial section of the sealing device.

According to the embodiment, the surface on the second bearing ring side in the radial direction of the second portion is smoothly continuous, so that the stress caused by the deformation of the second axial lip at built-in time can be almost evenly distributed and exerted to the whole of the second portion. Furthermore, the second axial lip can be easily deformed radially outward in the assembly process, and a clearance can be created easily and accurately between the second axial lip and the fixation section of the slinger in the non-worn state of the first and second axial lips.

In one embodiment, in the state before the elastic member is assembled to the slinger, the surface that the first portion has on the second bearing ring side in the radial direction has, in a cross section of the elastic member taken in the axial direction, an increasing curvature as going outward in the axial direction.

The wording “increasing curvature as going outward in the axial direction” or similar wording is intended to cover such a case that the surface on the second bearing ring side in the radial direction of the first portion includes a portion the curvature of which is partially constant as going outward in the axial direction. For this reason, for example, the expression covers a case that the surface on the second bearing ring side in the radial direction of the first portion consists of a conical surface positioned on the base side and a concave surface which is smoothly continued from the conical surface and is defined by part of an ellipsoid of revolution.

According to this embodiment, in the axial section of the elastic member, the curvature of the surface radially on the second bearing ring side of the first portion increases as going outward in the axial direction before the elastic member is assembled to the slinger, so that the stress caused by the deformation of the second axial lip at the assembly time can be almost evenly distributed over and shared by the whole of the first portion, and the concentration of local stress is surely prevented from occurring in the first portion when the second axial lip is in noncontact with the fixation section.

In one embodiment, force to be received by the second axial lip is only force from the slinger.

According to this embodiment, there is no clamping member such as a garter spring pressing a portion facing the fixation section of the slinger of the second axial lip against the fixation section of the slinger, so that the portion facing the fixation section of the slinger of the second axial lip can be easily distanced from the fixation section in the assembly process when the second axial lip is pressed against the flange section of the slinger, as compared with the case that there is a clamping member such as a garter spring pressing the portion facing the fixation section of the slinger of the second axial lip.

A rolling bearing according to an aspect of the present invention comprises:

a sealing device according to the present invention;

an inner ring having at least one raceway surface;

an outer ring having at least one raceway surface; and

a plurality of rolling elements located between the raceway surface of the inner ring and the raceway surface of the outer ring,

wherein the sealing device is located so as to seal an opening on at least one side in the axial direction of a rolling elements compartment which is defined between an outer periphery of the inner ring and an inner periphery of the outer ring and which contains the rolling elements;

wherein the slinger of the sealing device is fixed to the inner ring; and

wherein a seal member including the elastic member and the metal core of the sealing device is fixed to the outer ring.

According to the present invention, because the roller bearing has a sealing device according to the present invention, the torque of the sealing device can be reduced at an operating time, and the fuel economy of a machine installed with the rolling bearing can be thus reduced.

A rolling bearing for a wheel according to another aspect of the present invention comprises:

a sealing device according to the present invention;

an inner shaft having a first raceway surface;

an inner ring fixed to the inner shaft and having a second raceway surface;

an outer ring having a third raceway surface and a fourth raceway surface;

a plurality of first rolling elements located between the first raceway surface and the third raceway surface; and

a plurality of second rolling elements located between the second raceway surface and the fourth raceway surface,

wherein the sealing device is located so as to seal an opening on at least one side in the axial direction of a rolling elements compartment which contains the rolling elements, the rolling elements compartment being defined by an inner periphery of the outer ring and portions facing the inner periphery of the outer ring in the radial direction of outer peripheries of each of the inner shaft and the inner ring;

wherein the slinger of the sealing device is fixed to the inner ring; and

wherein a seal member including the elastic member and the metal core of the sealing device is fixed to the outer ring.

According to the present invention, because the roller bearing for a wheel has a sealing device according to the present invention, the torque of the sealing device can be reduced at an operating time, and the fuel economy of a vehicle, such as an automobile, installed with the rolling bearing can be thus reduced.

Advantageous Effects of Invention

According to the present invention, a long life sealing device is provided, and the torque of the sealing device can be remarkably reduced, so that the fuel economy of an automobile or the like equipped with the sealing device can be reduced.

REFERENCE SIGNS LIST

DESCRIPTION OF EMBODIMENTS

The present invention will be described in detail below with reference to embodiments shown in the figures.

FIG. 1is an axial sectional view of a rolling bearing for a wheel having a sealing device according to an embodiment of the present invention.

The rolling bearing for a wheel has an inner shaft2, an outer ring3, an inner ring4, a plurality of first balls5, a plurality of second balls6, a first sealing device8according to an embodiment of the present invention, and a second sealing device9according to an embodiment of the present invention. The first balls5are first rolling elements, and the second balls6are second rolling elements.

The inner shaft2has, on one axial end of it, a radially-spreading brake disk mounting flange10shaped like a disk for mounting a brake disk11. A plurality of through holes for bolts are formed on a concentric circle whose center is substantially the center of the brake disk mounting flange10. The brake disk mounting flange10, the brake disk11, and a wheel member13are fixed together by a plurality of bolts15running therethrough, with the brake disk11in contact with the brake disk mounting flange10and with the wheel member13in contact with the brake disk11.

An inner ring4is fit around and fixed to the other axial end of the inner shaft2. An angular first raceway groove16providing a first raceway surface is formed on the inner shaft2between the inner ring4and the brake disk mounting flange10, while an angular second raceway groove17providing a second raceway surface is formed on the outer periphery of the inner ring4.

The outer ring3is located more on the other axial end side of the inner shaft2than the brake disk mounting flange10so as to radially face the inner shaft2. The outer ring3has, on the other axial end side, a radially-spreading flange14for mounting on a car body. A plurality of through holes for insertion of bolts for mounting the flange14on a car body (e.g. a knuckle) are formed in the flange14shaped like a disk. The outer ring3has an angular third raceway groove26providing a third raceway surface and an angular fourth raceway groove27providing a fourth raceway surface. Those grooves26and27are located on the inner periphery of the outer ring3with an axial distance in between. Also, the angular third raceway groove26is positioned more on the one axial end side than the angular fourth raceway groove27.

The first balls5are located at predetermined intervals in the circumferential direction while being kept by a cage18between the first raceway groove16of the inner shaft2and the third raceway groove26of the outer ring3. The second balls6are located at predetermined intervals in the circumferential direction while being kept by a cage19between the second raceway groove17of the inner ring4and the fourth raceway groove27of the outer ring3.

A first sealing device8is located near an opening on the one axial end side (brake disk mounting flange10side) between the inner shaft2and the outer ring3. The first sealing device8seals the opening on the one axial end side between the inner shaft2and the outer ring3. On the other hand, a second sealing device9is located near an opening on the other axial end side (opposite to the brake disk mounting flange10side) between the inner ring4and the outer ring3. The second sealing device9seals the opening on the other axial end side between the inner ring4and the outer ring3. The second sealing device9has the same structure as the first sealing device8.

FIGS. 2 and 3are sectional views illustrating the structure of the first sealing device8in detail. In particular,FIG. 2is an axial sectional view showing the positional relations between a metal core50, an elastic member51, and a slinger52in the assembly of the sealing device, wherein the elastic member51is shown in a position that the elastic member51would assume when the elastic member51does not receive any force from the slinger52, namely, when the slinger52is absent. On the other hand,FIG. 3is a sectional view showing the positions of the elastic member51and the slinger52in the state that the elastic member51has been built in the slinger52and that the elastic member51is not yet worn. The second sealing device9has the same structure as the first sealing device8. The second sealing device9is located near an opening on the other axial end side between the inner ring4and the outer ring3in the state of being axially reversed left to right inFIGS. 2 and 3. The description of the second sealing device9is omitted by applying the description of the first sealing device8.

As shown inFIG. 2, the first sealing device (simply referred to as the “sealing device” hereinafter)8has the metal core50, the elastic member51, and the slinger52. The metal core50and the elastic member51are fixed to each other and integrated. The metal core50and the elastic member51constitute a seal member48.

The metal core50is formed generally in the shape of a ring. The metal core50is shaped like a letter L in cross section. The metal core consists of a cylindrical axially-extending portion60and a radially extending portion61. The axially-extending portion60is fit in and fixed to the inner periphery of the outer ring3(shown inFIG. 1but not shown inFIG. 2) as a first bearing ring. The radially extending portion61extends radially inward from the other axial end side (left side inFIG. 2) of the inner periphery of the axially-extending portion60.

The slinger52is formed generally in the shape of a ring. The slinger52is shaped like a letter L in cross section. The slinger52has a cylindrical fixation section65and a flange section66connected with the fixation section65. The fixation section65is fit around and fixed to the outer periphery of the inner shaft2as a second bearing ring. It is needless to say that in the second sealing device9, the inner ring4is a part serving as the second bearing ring to which the slinger is fixed. The flange section66extends radially outward from the axial outer end (i.e., a right side end on the paper) of the outer periphery of the fixation section65. The flange section66is positioned axially outside of the radially extending portion61of the metal core50. Most of the flange section66except radially inner part of it axially faces the radially extending portion61through a gap.

The elastic member is formed in the shape of a ring. The elastic member51is fixed to the metal core50so as to cover the entire surface of the inner periphery of the axially-extending portion60and the entire surface of the axially outer end face of the radially extending portion61connected with the inner periphery of the axially-extending portion60. The elastic member has a base53, a first axial lip54, and a second axial lip55. The elastic member51is specifically made of rubber. As the rubber, for example, nitrile rubber, hydrogenated nitrile rubber, acrylic rubber, silicon rubber, and fluororubber can be preferably used.

The base53is located along the inner periphery of the axially-extending portion60and the axially outer end face of the radially extending portion61. The base53is fixed to the inner periphery of the axially-extending portion60and the outer end face of the radially extending portion61. The first axial lip54extends from the base53toward the outer ring3(seeFIG. 1) and axially outward (toward the flange section66).

The second axial lip55is positioned on the inner shaft2(seeFIG. 1) side in the radial direction (radially inside) of the first axial lip54at a radial distance from the first axial lip54. The second axial lip55has a first portion56and a second portion57. The first portion56extends from the base radially toward the inner shaft2and axially outward. The second portion57is connected with the axially outer end of the first portion56and extends radially toward the outer ring3and axially outward.

As shown inFIG. 2, the position that the elastic member51would take in the assembly when it is assumed that the elastic member51does not receive any force from the slinger52, overlaps the position of the slinger52. In particular, an axially outer end portion of the first axial lip54of the elastic member51and an axially outer end portion of the second axial lip55of the elastic member51overlap the flange section of the slinger52, and a bend portion at the junction between the first portion56and the second portion57of the second axial lip55(i.e., part of a portion radially facing the fixation section65of the second axial lip55) overlaps the fixation section65of the slinger52.

Furthermore, as shown inFIG. 2, before the elastic member51is combined with the slinger52, the radially inner surface58of the first portion56forms a concave surface, while the radially inner surface59of the second portion57forms a conical surface. In the axial section, the curvature of the radially inner surface58of the first portion56increases as going axially outward (i.e., toward the flange section66). Specifically, in the axial section of the elastic member, the radially inner surface58of the first portion56consists of a generally conical surface portion positioned on the base53side and a surface portion which is smoothly connected with the generally conical surface portion and is defined by part of an ellipsoid of revolution having an increasing curvature as going axially outward (i.e., toward the flange section66).

In the axial section, the radially inner surface59of the second portion57can be differentiated from one end to the other end and is smoothly continuous.

As shown inFIG. 3, the sealing device is assembled and mounted such that the first axial lip54and the second portion57of the second axial lip55slide on the flange section66of the slinger52by a relative revolution between the seal member48and the slinger52substantially around the axis of the rolling bearing for a wheel. Furthermore, as shown inFIG. 3, in a non-worn state after the sealing device is assembled and mounted in position, the second axial lip55is positioned at a radial distance from the fixation section65of the slinger52. In other words, as shown inFIGS. 2 and 3, when the sealing device is assembled, the metal core50and the slinger52are moved axially and relatively to each other so that the radially extending portion61of the metal core50and the flange section66of the slinger52approach each other, and thereby the first axial lip54and the second portion57of the second axial lip55move radially outward along the surface of the flange section66of the slinger52, so that the bend portion between the first portion56and the second portion57moves radially outward away from the outer periphery of the fixation section65. In this embodiment, there is no clamping member such as a garter spring pressing the bend portion radially inward, so that the bend portion can be easily and securely allowed to get away from the outer periphery of the fixation section65radially toward the outer ring3. If there is a clamping member such as a garter spring pressing the bend portion radially inward, the bend portion may not separate from the outer periphery of the fixation section radially toward the outer ring.

As described above, the position of the bend portion in the case that it is assumed that the elastic member51does not receive force from the slinger52is set such that the bend portion overlaps the fixation section65. When the pressing force against the flange section66of the second axial lip55has decreased by a predetermined magnitude or more due to wear of the second portion57of the second axial lip55, the bend portion comes into contact with the fixation section65of the slinger52and slides on the fixation section65by a relative revolution between the seal member48and the slinger52around the axis of the rolling bearing for a wheel. In other words, the bend portion acts as a radial lip while the sealing device is in the sate that the pressing force against the flange section66of the second axial lip55has decreased by the predetermined magnitude or more due to the wear of the second portion57of the second axial lip55.

A space surrounded by the first axial lip54, the second axial lip55, and the slinger52and a space surrounded by the second axial lip55and the slinger52are filled with a proper amount of grease as lubricant, or the grease is applied to the surfaces surrounding the spaces, and thereby the sliding face between the first axial lip54and the slinger52and the sliding face between the second axial lip55and the slinger52are lubricated. Furthermore, inFIG. 3, a rolling elements compartment positioned axially inside (i.e., a left side of the drawing sheet) of the first sealing device8communicates with a region surrounded by the second axial lip55and the slinger52and contains rolling elements (balls18and19in this embodiment). This rolling elements compartment is filled with lubricant (grease in this embodiment).

FIG. 4shows the ratio of a contact load of each lip to the total contact load in both a comparative sealing device and a sealing device according to the above embodiment which are in their non-worn state, as well as the ratio of the total contact load of the sealing device of the above embodiment to the total contact load of the comparative sealing device. The result shown inFIG. 4is a result in one experimental example

The comparative sealing device is a so-called pack seal type sealing device (generally indicated by reference numeral270inFIG. 7) composed of a metal core250, an elastic member251, and a slinger252of L-shaped cross section, the sealing device having two radial lips (an auxiliary lip273and a main lip272) and one axial lip271.

The position of the elastic member251shown inFIG. 7is a position that the elastic member251would take when the metal core250has a predetermined position relative to the slinger252in the assembly but when it is assumed that the elastic member251does not receive force from the slinger252.

As shown inFIG. 4, in the comparative sealing device270, the ratio of the contact load of the radial lips to the total contact load reaches as much as 80 percent, while the ratio of the contact load of the axial lip to the total contact load is the order of 20 percent. For this reason, if the contact load of the radial lips can be reduced, the torque can be significantly reduced.

The total contact load of the sealing device of the embodiment having two axial lips but no radial lip reaches only 40 percent of the total contact load of the comparative one, thus being reduced significantly.

FIG. 5shows the relation between the number of revolutions and the rotational torque in one experimental example for each of the comparative sealing device270and the sealing device of the embodiment.

The torque of the sealing device of the above embodiment is of the order of 50 percent of the torque of the comparative sealing device from a low number of revolutions to a high number of revolutions. In other words, the torque of the sealing device of the embodiment is significantly smaller than that of the comparative sealing device. This experiment was carried out without using lubricant for the sealing device of the embodiment as well as the comparative sealing device270.

According to the sealing device of the embodiment, the elastic member51is in the state of being in noncontact with the fixation section65of the slinger52and having no radial lip until the pressing force against the flange section66of the second axial lip55decreases by predetermined force or more, so that the torque can be significantly reduced by the order of 50 percent as compared with a sealing device having a radial lip until the pressing force against the flange section66of the second axial lip55decreases by predetermined force or more. Thus, the fuel economy of an automobile or the like having this sealing device can be reduced, the amount of CO2emissions of an automobile or the like having this sealing device can be reduced, and global warming can be restrained.

Furthermore, according to the sealing device of the above embodiment, the radially inner surface58of the first portion56is a concave surface before the elastic member51is assembled to the slinger52. Therefore, when assembling, it is not necessary to deform only part on the base53side of the first portion56of the second axial lip55intensively and excessively to bring the non-worn second axial lip55into noncontact state with the fixation section65of the slinger52, in contrast to the case that the first portion is convex. And, the second axial lip55can be brought into noncontact with the fixation section65of the slinger52by deforming the whole of the first portion56almost evenly in its extending direction. In other words, excessive stress is not applied locally to part of the first portion56, so that the durability of the second axial lip55can be remarkably increased and the life of the sealing device can be thus increased.

Furthermore, according to the sealing device of the above embodiment, the radially inner surface59of the second portion57is a conical surface before the elastic member51is assembled to the slinger52, so that the contact pressure between the second axial lip55and the flange section66of the slinger52can be reduced and wear of the second axial lip55can be thus restrained, as compared with the case that the radially inner surface of the second portion is a concave surface. Thus, a time until the bend portion of the second axial lip55comes into contact with the fixation section65of the slinger52can be increased, so that the state that the torque is remarkably small can be sustained for a long term, as compared with the case that the radially inner surface of the second portion is a concave surface.

Furthermore, according to the sealing device of the above embodiment, the radially inner surface59of the second portion57is smoothly continuous, so that the stress caused by the deformation of the second axial lip55during the assembly process can be almost evenly distributed to the whole of the second portion57and thus shared evenly by the whole of the second portion57. Furthermore, the second axial lip55can be easily deformed radially outward during the assembly process, and a predetermined clearance can be created easily and accurately between the non-worn second axial lip55and the fixation section65of the slinger52.

Furthermore, according to the sealing device of the above embodiment, prior to the assembly of the elastic member to the slinger, the curvature of the radially inner surface of the first portion56in its axial section increases as going axially outward. Therefore, the stress caused by the deformation of the second axial lip55during the assembly process can be almost evenly distributed to the whole of the first portion56and thus evenly shared by the whole of the second portion57, and the concentration of local stress can be surely prevented from occurring in the first portion56. Thus, the life of the sealing device can be further extended.

Furthermore, according to the sealing device of the embodiment, the bend portion comes into contact with the fixation section65of the slinger52and slides on the fixation section65after the pressing force against the flange section66of the second axial lip55has decreased by a predetermined magnitude or more due to the wear of the second portion57of the second axial lip55. Therefore, even if the wear of the second axial lip55advances, muddy water from the outside is restrained from entering the balls compartment containing the balls8and9of the rolling bearing for a wheel.

Furthermore, according to the sealing device of the above embodiment, force received by the second axial lip55is only force from the slinger52, and there is no clamping member such as a garter spring pressing a portion facing the fixation section65of the slinger52of the second axial lip55against the fixation section65of the slinger52. Thus, as compared with the case that there is a clamping member such as a garter spring pressing a portion of the second axial lip55against the fixation section65of the slinger52, the portion of the second axial lip55facing the fixation section65of the slinger52of the second axial lip55can be easily distanced from the fixation section65in the assembly process in which the second axial lip55is pressed against the flange section66of the slinger52.

Furthermore, since the rolling bearing for a wheel of the above embodiment has the sealing devices8and9according to the present invention, the torque of the sealing devices8and9can be reduced at an operating time, and the fuel economy of a vehicle such as an automobile having the rolling bearing for a wheel of the above embodiment can be thus reduced.

In the sealing device of the above embodiment, the radially inner surface59of the second portion57is a conical surface before the assembly process. However, in the present invention, the radially inner surface of the second portion may be a convex surface before the assembly process.

Furthermore, in the sealing device of the above embodiment, in the axial section of the elastic member, the radially inner concave surface58of the first portion56consists of a generally conical surface portion positioned on the base53side and a surface portion which is smoothly connected with the generally conical surface portion and is defined by part of an ellipsoid of revolution having an increasing curvature as going axially outward (i.e., toward the flange section66). However, in the present invention, the whole of the radially inner surface of the first portion56may be, in the axial section, a conical surface or a part of an ellipsoid of revolution having an increasing curvature as going axially outward (i.e., toward the flange section). In the present invention, the radially inner surface of the first portion may have any shape, in the axial section, provided that the curvature of it increases as going axially outward (toward the flange section).

Furthermore, in the rolling bearing for a wheel, the sealing devices8and9according to the above embodiment of the present invention are located near the openings on axial both sides of the rolling elements (balls) compartment (filled with lubricant). However, a sealing device according to the present invention may be located only near an opening on axial one side of the rolling elements (balls) compartment (filled with lubricant) of the rolling bearing for a wheel. The rolling elements may not be balls but rollers and may be both of balls and rollers. When the rolling elements are rollers, the rollers may include conical rollers and cylindrical rollers. But, the conical rollers are preferable. The second sealing device9of the above embodiment of the present invention is located near an opening on the other axial end side between the inner ring4and the outer ring3on which side the brake disk mounting flange10is not present. Therefore, the slinger50and the seal member48can be easily fitted around the inner ring4and the outer ring3, respectively.

FIG. 6is an enlarged cross-sectional view of the surroundings of a sealing device99, according to the present invention, included in a water pump.

The water pump has a pump shaft100, a mechanical seal101, a pump housing102, an outer ring105, and a sealing device99according to the present invention. The pump housing102has a drain hole107penetrating the pump housing102. Furthermore, the outer ring105is fit in and fixed to the inner periphery of the pump housing102.

The pump shaft100, the outer ring105, and the sealing device99make up part of a water pump bearing of the water pump. In other words, the inner periphery of the outer ring105is formed with a deep raceway groove and a cylindrical raceway surface, although not shown inFIG. 6, which are located with an axial distance in between on a side shown with an arrow “a” inFIG. 6of the sealing device and arranged in this order from the sealing device99. Also, the outer periphery of the pump shaft100is formed with a deep raceway groove and a cylindrical raceway surface, although not shown inFIG. 6, which are located with an axial distance in between on the side shown with the arrow “a” inFIG. 6of the sealing device and arranged in this order from the sealing device99.

A plurality of balls held by a cage are located at predetermined intervals in the circumferential direction between the raceway groove of the outer ring105and the raceway groove of the pump shaft100. Furthermore, a plurality of cylindrical rollers held by a cage are located at predetermined intervals in the circumferential direction between the cylindrical raceway surface of the outer ring105and the cylindrical raceway surface of the pump shaft100.

A metal core150of the sealing device99is fit in and fixed to the inner periphery of the outer ring105as the first bearing ring, while a slinger152of the sealing device99is fit on and fixed to the outer periphery of the pump shaft100as the second bearing ring. The sealing device99seals an opening between the outer ring105and the pump shaft100on the mechanical seal101side of the water pump bearing. In this way, cooling water in the pump chamber leaking through the mechanical seal101in the direction shown with an arrow “b” is prevented from entering the inside of the water pump bearing.

The cooling water leaking from the pump chamber is surely discharged to the outside in the direction shown with an arrow c through the drain hole107formed in the pump housing102. InFIG. 6, the reference numeral111denotes a rubber sleeve of the mechanical seal101, and the reference numeral110denotes a coil spring of the mechanical seal101.

When a sealing device according to the present invention is installed in a water pump as shown inFIG. 6, the torque of the water pump bearing in the water pump is reduced and the fuel economy of an automobile or the like having the water pump is thus reduced.

In the above embodiments, the sealing device according to the present invention is assembled to a rolling bearing for a wheel or in a water pump. However, a sealing device according to the present invention may be located so as to seal at least one opening between an outer ring and an inner ring in a rolling bearing in which an outer ring and an inner ring serve as raceway members having a raceway surface. Furthermore, a sealing device according to the present invention may be installed in a rolling bearing provided between a rotor member and a stator member of a motor. In this case, the operation cost of the motor can be reduced. A sealing device according to the present invention can be installed in any machine provided that the machine has a first member having an inner periphery and a second member having an outer periphery and the first member faces the second member in the radial direction of the inner periphery of the first member. And, the operation cost of such a machine provided with the sealing device according to the present invention can be reduced.