AU639479B2 - Ceramic bearing - Google Patents

Description

639479 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 Form COMPLETE SPECIFICATION FOR OFFICE USE Short Title: Int. Cl: Application N~umber: Lodged: Complete Specif ication- Lodged: Accepted: Lapsed: Published: Priority: Related Art: TO BE COMPLETED BY APPLICANT Name of Applicant: WING HICHCERA CO,, LTD.

Address of Applicant: 1-56, lMiyamae-cho, Rizunarni-shi, Gifu-Ken, JAPAN Actual Inventor: Terunobu Momo~e and Tetsuo Shibata Address for Service: GRIFFITH HACK CO 71 YORK~ STREET SYDNEY NSW 2000 Complete Specification for the invention entitled-, CERAI4IC BEARING The following statement: is a full description of this invention, including the best method of performing it 'known to us: 21149-C:COS;RK 5188A.,rk 2 FIELD OF THE INVENTION The present invention relates to a ceramic bearing which is able to support a shaft to which thrust load and a radial load are applied simultaneously or separately.

DESCRIPTION OF THE PRIOR ART It is known to use a sliding bearing or a rolling bearing to support a rotary shaft in a machine frame, for example.

There are different types of rolling bearings, such as ball bearings, roller bearings and needle bearings which are provided with a rolling member such as balls, rollers and needles, respectively, between an inner ring and an outer ring. As well, other kinds of radial bearing and thrust bearing exist which may be used to support a load applied to a shaft which is engaged with the inner ring. Deep-groove type bearings, angular ball type bearings, and tapered-roller type bearings are known and may be used to support a shift to which a radial load and a thrust load are applied simultaneously. These rolling bearings are standardised and are selected by choosing the most appropriate one at the time when a machine is designed.

Some sliding bearings are constructed with a metal support made of steel, cast iron, copper or the like. A white metal layer is laminated thereon, or an oil impregnated alloy is laminated upon or embedded in the support. Other sliding bearings are constructed from gun metal, synthetic resin or the like which is formed to a 30 sleeve shape. Generally, in conventional sliding bearings, bearings which support the radial load and bearings which support the thrust load are separately standardised.

The above rolling bearing and sliding bearings have 35 distinct characteristics. Accordingly, when deciding on a suitable bearing these characteristics must be 5 considered.

149-C/27,01.93 3 However, the rolling bearings and sliding bearings may still prove troublesome. For example, in rolling bearings the phenomenon of rolling fatigue limits their service life. The rolling bearings have low resistance to heat stres3. Further, rolling bearings have a relatively large number of components which makes them costly.

In sliding bearings, friction losses are high due to the sliding contact between the outer periphery of the shaft with the inner periphery of the bearing. This problem necessitates applying forced lubrication or self lubrication to the contact surfaces of the shaft and the bearing. In addition, when a shaft supports a radial load and a thrust load simultaneously, a commercially available radial bearing and a market thrust bearing must be used in combination, or a new bearing must be designed.

Recently, ceramics having high compression strength and friction resistance and small friction coefficients have been developed. The present applicant has developed several kinds of ceramic bearings. (See Japanese patent application No. 63-325933) rr Furthermore, US 4,634,300 discloses a rolling bearing constructed with a ceramic roller as a rolling 25 body. The bearing has resistance to temperature and corrosion, but still has a large number of components.

SU YARY OF THE INVENTION In one aspect of the present invention there is S° provided a ceramic bearing comprising: a ceramic bearing comprising: a ceramic inner ring including a first axial hole rhaving a first axis for fixedly receiving a shaft therein, the inner ring further having an outer periphery with a first cylindrical surface which is coaxial with the first axis and a first sliding surface which has a ,tapering profile and which extends at an angle with respect to the first cylindrical surface; and 39 9 4a ceramic outer ring having an inner periphery with a second cylindrical surface, which is coaxial with the first axis and which slidably contacts the first cylindrical surface, and a second sliding surface which slidably contacts the first sliding surface.

It is an advantage that an embodiment of the present invention provides a ceramic sliding bearing which is able to support a shaft to which a radial load and a thrust load are applied simultaneously or separately.

It is a further advantage that an embodiment of the present invention provides a ceramic bearing having a small number of parts.

An embodiment of the present invention provides a ceramic bearing having a ceramic inner ring and a ceramic outer ring wherein the ceramics inner ring (hereinafter referred to as "inner ring") defines an axial hole for receiving a shaft. A related embodiment has an inner ring having an outer periphery which defines a cylindrical surface having an axis which is coaxial with an axis of the axial hole, and a plane surface which is perpendicular to the axial hole. The ceramic outer ring (hereinafter referred to as "outer ring") defining a cylindrical surface which slidably contacts the cylindrical surface defined by the outer periphery of the 25 inner ring, and a plane surface which slidably contacts the end portion of the inner ring. When a shaft is fixedly received in the axial hole and a radial load and a thrust load are applied to the shaft, the radial load is supported by the cylindrical surfaces defined by the 30 inner ring and the outer ring, while the thrust load is also supported by the plane surfaces of the inner ring and the outer ring.

In an embodiment of the present invention the outer periphery of the inner ring defines a cylindrical surface 35 having an axis which is coaxial with an axi of an axial hole provided in the inner ring for fixedly receiving a shaft therdlin, and a tapered surface. The inner periphery of the outer ring defines a cylindrical surface .0 a a 0 4,

S

a a *so.

0

S

SOS

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@000 00

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a 0S 0 and a sliding surface. When a shaft is fixedly received in the axial hole, a radial load applied to the shaft is supported by the cylindrical surfaces defined by the inner and outer rings, and a thrust load applied to the shaft is supported by contact of the sliding surface of the outer ring with the tapered surface of the inner ring.

Since the bearings embodied by the present invention comprise fewer parts compared with conventional rolling bearings, the cost of the bearing is thereby lowered.

Furthermore, since the shaft is fixedly received in the axial hole defined by the inner ring, sliding does not happen between the shaft and the inner ring.

Accordingly, abrasion does not occur to the shaft even after long periods of use.

Since the inner and outer rings are constructed of ceramic material, sliding friction is low thereby decreasing heat generated due to friction. Further, expansion due to the heat is low thereby reducing the generation of stresses between a machine frame and shaft.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an exploded view of a related embodiment of a ceramic bearing; f Figure 2 is a cross-sectional view of the related 25 embodiment of figure 1; Figure 3 is a partial cross-sectional view of the OSO" inner ring of the related embodiment shown in figure 1; 0 Figure 4 is a cross-sectional view of an embodiment :.0o of the present invention; Figure 5 is a partial cross-sectional view of the inner ring of the embodiment shown in figure 4; Figure 6 is a partial cross-sectional view of S*0" another embodiment of an inner ring for use with the embodiment shown in figure 4; 35 Figure 7 is a cross-sectional view of a por'.ion of 0!0 the outer ring of the embodiment shown in figure 4; and Figure 8 is a cross-sectional view of another embodiment of the present invention.

0 0 21149-/18.063 6 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In figures 1 and 2, a related embodiment of a ceramic bearing, bearing A, is shown which comprises an inner ring 1 and an outer ring 2.

The inner ring 1 is formed from an oxide ceramics material such as PSZ (partially stabilised zirconia) or alumina by filling a mould, press forming and sintering the pressed product at 1500 0 C to 1600 0

C.

At the centre of the inner ring 1, an axial hole 4 for fixedly receiving a shaft 3 is defined. The axial hole 4 is dimensioned so as to be slightly smaller than the diameter of the shaft 3 in order to receive shaft 3 in a press fit.

Numeral 5 is the axis of axial hole 4. Axis corresponds to the axial centre of bearing A.

An outer periphery of the inner ring 1 defines cylindrical surface la. Cylindrical surface la slidably contacts a cylindrical surface 2a defined by an inner periphery of the outer ring 2. Cylindrical surfaces ia and 2a have axis which are coaxial with axis 5. A radial load applied to the shaft 3 is transmitted to the outer ring 2 through the cylindrical surfaces la, 2a. The diameter of the cylindrical surface la is dimensioned to provide sufficient strength for supporting the radial load on the bearing, and a radial length of the inner ring 1 is dimensioned to provide sufficient strength for supporting a thrust load on the bearing.

The outer periphery of the inner ring includes an end surface of a front side (left side of figure 2) of the inner ring which defines a plane surface Ib substantially perpendicular to the axis 5. The plane surface lb slidably contacts a plane surface 2b defined by the outer ring 2 to transmit a thrust load applied to the shaft 3 to the outer ring 2. An end surface of a rear side (right side of figure 2) of the inner ring 1 defines a plane surface Ic which is substantially perpendicular to the axis 5 and against which abuts a J 7 step portion 3b of a journal portion 3a defined by the shaft 3.

The outer ring 2 is formed, by filling a mould with an oxide ceramics material such as PSZ or alumina press forming and sintering the formed product at 1500 0 C to 1600 0

C.

An inner periphery of the outer ring 2, defines a cylindrical surface 2a having a clearance relative to the cylindrical surface la defined by the outer periphery of the inner ring 1. The cylindrical surface 2a slidably contacts the cylindrical surface la of the inner ring 1 and the radial load applied to the shaft 3 is transmitted through the inner ring 1 to the cylindrical surface 2a.

For this purpose, the cylindrical surface 2a has an axis which is coaxial with the axis The inner periphery of the outer ring 2 further defines a plane surface 2b which is substantially perpendicular to the cylindrical surface 2a connecting therewith, and at a right angle to axis 5. The plane surface 2b slidably contacts the plane surface Ib defined by the inner ring 1, and a thrust load applied to the shaft 3 is transmitted through the inner ring 1 to the plane surface 2b.

A hole 2c is defined at the centre of the outer 25 ring 2. The hole 2c extends from plane surface 2b to plane surface 2e. The hole 2c has a diameter dimensioned for loosely receiving shaft 3 which is fixedly received in the axial hole 4 of the inner ring 1.

An outer periphery 2d of the outer ring 2 defines a 30 cylindrical surface having an axis which is coaxial with the axis 5. The plane surface 2e of the outer ring 2 is substantially perpendicular to the axis 5. Outer periphery 2d and plane surface 2e are fixedly received in a machine frame or casing-6.

35 The axial hole 4, the cylindrical surface la, and the plane surface Ib of the inner ring 1, the cylindrical surface 2a, the plane surface 2b, the hole 2c, the outer periphery 2d and the plane surface 2e of the outer ring 2 8 are formed simultaneously when the inner and outer rings are press-formed.

In the above forming process, the dimension accuracy for the inner ring 1 and the outer ring 2 on the order of a design dimension 0.005mm can be obtained for each part. Further, average surface roughness on the order of about 0.8 micron can be obtained.

In order to construct a bearing having the inner ring 1 and the outer ring 2, the cylindrical surface la and the plane surface Ib of the inner riag are inserted within a hollow portion of the outer ring 2 comprising the plane surface 2b connecting with cylindrical surface 2a. By slidably contacting the cylindrical surfaces la, 2a and the plane surfaces Ib, 2b respectively, the shaft 3 fixedly received in the inner ring 1 can be supported.

It may be necessary to perform a grinding operation on the cylindrical surface la, the cylindrical surface 2a and the surface of the outer periphery 2d, in order to achieve a desired accuracy for bearing A.

It may be necessary to lap each contact surface including cylindrical Furfaces 2a, la and plane surfaces 2b, Ib after engaging the inner ring 1 with outer ring 2.

The lapping can be performed by providing a grinding S. agent such as diamond powders, etc. to each contact surface and performing a relative rotation between inner ring 1 and outer ring 2.

The bearing A can be made to operate more smoothly by grinding or lapping the inner ring 1 and outer ring 2 respectively.

30 A case where the shaft 3 is supported by the bearing A constructed as above will be described with reference to figure 2.

In figure 2, the outer ring 2 which comprises the bearing A is fixedly attached to the machine frame 6. At 35 the axial hole 4 of the inner ring 1, a journal portion 3a of the shaft 3 is engaged thereto and the step portion 3b of the shaft 3 is abutted against abutting surface ic of the inner ring 1.

49.C/27,01.93 9 If a radial load having a direction shown by arrow and a thrust load having a direction shown by arrow are applied to the shaft 3 simultaneously, the radial load is transmitted to the inner ring 1 from the journal portion 3a and transmitted to the outer ring 2 by way of the cylindrical surfaces la and 2a. Further, it is transmitted to the machine frame 6 where it is supported.

The thrust load is transmitted from the step portion 3b of the shaft 3 to the abutting surface Ic of the inner ring and is transmitted to the outer ring 2 through the plane surfaces Ib and 2b. Subsequently, it is transmitted to the machine frame 6 from the plane surface 2b, thereby being supported by frame 6.

Thus, with bearing A it is possible to support the shaft 3 to which the radial load and the thrust load are applied simultaneously or separately by forming the cylindrical surfaces la, 2a having axis which are coaxial with the axis 5, and forming the plane surfaces Ib, 2b formed substantially perpendicular to the axis 5 so that they may slidably contact each other.

In bearing A, it is necessary to choose a dimension for the diameter of the cylindrical surface la and for the radial length of the plane surface Ib according to S, the radial load and the thrust load to be applied to the shaft 3. Accordingly, when the radial load applied to the shaft 3 is large, the strength of the inner ring can be increased by enlarging the diameter of the cylindrical surface la. However, when the diameter of the cylindrical surface la is enlarged, the contact area between the plane surfaces Ib and 2b becomes larger.

Relative sliding velocity between the contact surfaces becomes larger in proportion to a radial dimension along the surfaces. Thus, friction loss increases. In order to decrease the friction loss, it is desirable to form a S 35 bevelled or radius portion Id, as shown in figure 3, having a comparatively large dimension which connects the cylindrical surface la and the plane surface lb of the inner ring 1.

211.'49-CI27,o1.93 10 By providing the bevelling portion id on inner ring 1, it is possible to reduce the contact area of the cylindrical surfaces la, 2a with the plane surfaces Ib, 2b without reducing the strength of the inner ring 1. In other words, it is possible to reduce the friction loss at the plane surfaces Ib and 2b by decreasing the area where the radial load and thrust load are applied.

Although surface loads on the contact surfaces become high due to reducing the contact area of the cylindrical surfaces la and 2a and the plane surfaces Ib, 2b, the contact surfaces are sufficiently pressure resistant because the inner ring 1 and the outer ring 2 are made of ceramic material.

It is also possible to mate the inner ring 1 smoothly to a concave surface connecting the cylindrical surface 2a and the plane surface 2b of the outer ring 2 by providing bevelled portion Id on the inner ring 1.

The end surface of the rear side of the inner ring 1 may have a small step which defines an abutting surface le as shown in figure 3. The abutting surface le can be made perpendicular to the axis 5 with a high degree of accuracy. Further, by forming the inner ring 1 with the abutting portion le, even when the journal portion 3a of the shaft 3 is engaged with the axial hole 4 of the inner 25 ring 1 and the step portion 3b is abutted against the abutting surface le, there is no chance of contact l 'between the step portion 3b and the outer ring 2.

An embodiment of the present invention, bearing B, 30, is shown in figure 4. Bearing B comprises an inner ring 30 l and an outer ring 2. In figure 4, elements having features like those of the related embodiment, bearing A, have the same numbers, and a detailed explanation thereof is omitted.

As shown in figure 5 and figure 6, cylindrical 35 surface la having an axis coaxial with the axio 5 is S provided at the front side on the outer periphery of the inner ring 1. At the rear side of the cylindrical b '149.C/18.Q 3 lCJ^ 11 surface la, a taper surface If is defined which extends from the cylindrical surface la with an enlarging diameter.

The taper surface If slidably contacts a sliding surface 2f defined by the inner periphery of the outer ring 2, thereby transmitting the thrust load from the shaft 3 to the outer ring 2.

A cylindrical surface Ig ha7ving an axis coaxial with the shaft 5 extends from the taper surface if. The cylindrical surface Ig is not essential for operation of the bearing B and does not contact outer ring 2.

In this embodiment, the sliding surface 2f of the outer ring 2 is defined at a rear end of the cylindrical surface 2a. A base portion lh of the taper surface If slidably contacts the sliding surface 2f. Since it is difficult to form the base portion lh as a sharp corner during formation of the inner ring 1, it is desirable to form a ring shape groove ii around the periphery of the inner ring 1 at a position corresponding to the base portion Ih.

The ring-shaped groove li ensures complete contact of the base portion Ih with the sliding surface 2f around the entire periphery of the inner ring 1.

Further, the taper surface if defined by the inner ring 1 has a length which is larger than a length of the sliding surface 2f. In order to accomplish this, it is desirable that the taper surface if extends from the cylindrical surface la to the cylindrical surface Ig as shown in figure 5. Further, as shown in figure 6, 30 bearing B may be constructed with the length of the taper surface If being larger than the length of the sliding surface 2f, and a plane surface Ij substantially perpendicular to the axis 5 extending from the taper surface if to the cylindrical surface Ig.

35 The inner periphery of the outer ring 2, defines a cylindrical surface 2a having a fixed clearance with respect to the cylindrical surface la defined by the inner ring 1 and having a length approximately equal to a F49-C/27.01.93 12 length of the cyindrical surface la. At the rear end of the cylindrical surface 2a, the sliding surface 2f slidably contacts the taper surface if defined by the inner ring 1 as shown in figure 4. Figure 7 shows a detailed configuration of the sliding surface 2f. The sliding surface 2f slidably contacts base portion Ih which is a part of the taper surface If defined by the inner ring 1 and receives the thrus't load applied to the shaft 3 transmi t ted through the inner ring 1.

The plane surface 2b substantially perpendicular to the axis 5, extends from the rear side of the cylindrical surface 2a. The intersection of the cylindrical surface 2a and the plane surface 2b defines the sliding surface 2f which is preferably tapered at an angle equivalent to an angle of the taper surface if. The sliding surface 2f need not have a taper shape but instead may have a curved shape.

For the sliding surface 2f having a taper shape, contact of the sliding surface 2f wr h the taper surface if is a planar contact, while for the sliding surface 2f having a curved shap<e, contact of the sliding surface 2f with the taper surface if is a linear contact.

A cylindrical surface 2g extends from the plane surface 2b. A diameter of the surface 2g is larger than a diameter of the cylindrical surface Ig defined by the inner ring 1. Accordingly, the surface 2g does not c* aontact the inner ring 1.

In the bearing B having the inner ring 1 and the outer ring 2 described above, the cylindrical surface la S 30 And the taper surface If of the inner ring 1 are in contact with the cylindrical surface 2a and the sliding surface 2f of the Oute rina 4, chereby supporting shaft 3 fixedly received in inner ring 1.

.9 A radial load applied to ta shaft is transmitted to 35 the inner ring from the journal portion 3a, and is transmitted to the outer ring 2 through the cylindrical surfaces la, 2a and is further transmitted to the machine frame from the outer ring 2 where it is supported the 13 same as in the above mentioned first embodiment. A thrust load applied tc the shaft is transmitted to the inner ring 1 through the abutting surface le from the step portion 3b of the shaft and is transmitted to the outer ring 2 through the sliding surface 2f, and is further transmitted to the machine frame from the outer ring 2 where it is supported in like manner to the first embodiment.

Another embodiment o2 the present invention, bearing C, is shown in figure 8. Bearing C is constructed comprising the inner ring 1 and the outer ring 2.

The outer periphery of the inner ring defines the cylindrical surface la at the rear side of the inner ring 1 and further defines the taper surface if which decreases in diameter as it extends towards a front side of the inner ring 1. The inner periphery of the outer ring 2 defines the cylindrical surface 2a, The plane surface 2b is perpendicular to the axis 5 and extends radially inwardly from the cylindrical surface 2a, The O cylindrical surface 2g has an axis which is coaxial with the axis 5 and exnends from the plane surface 2b. The f: sliding surface 2f is defined by the intersection of the plane surface 2b and the cylindrical surface 2g the same as in the second embodiment described above. The diameter of the plane surface 2b is larger than that of the axial hole 4 of the inner ring 1 and smaller than that of the cylindrical surface la.

The bearing C supports a radial load applied to the shaft which is fixedly reeived in the axial hole 4 by contact of the taper surface if and the sliding surface 2f, "By using appropriate calculations a diameter of the cylindrical surface 2g can be selected which maintains pressure on the contact surfaces within acceptable 3 5 limits.

In the above bearings A, B and C, since the inner ring 1 and the outer ring 2 are made of ceramics

I

S- 14 material, friction coefficient thereof is small and friction loss in the bearing is also small. By using ceramic material to support the shaft, there is no need for lubrication between the cylindrical surfaces la and 2a, the taper surface If and the sliding surface 2f.

Even when heat is generated due to friction since a coefficient of thermal expansion for ceramics is about 8 to 11 x 10- 6 o C, excessive thermal stress due to thermal expansion will not be produced. Further, as ceramics have an upper temperature operating limit between 600 0

C

to 1000 0 C, there is little likelihood of deterioration of the inner ring 1 and the outer ring 2 due to excessive heat generation.

o S S

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Claims (9)

1. A ceramic bearing comprising: a ceramic inner ring including a first axial hole having a first axis for fixedly receiving a shaft therein, the inner ring further having an outer periphery with a first cylindrical surface which is coaxial with the first axis and a first sliding surface which has a tapering profile and which extends at an angle with respect to the first cylindrical surface; and a ceramic outer ring having an inner periphery with a second cylindrical surface, which is coaxial with the first axis and which slidably contacts the first cylindrical surface, and a second sliding surface which slidably contacts the first sliding surface. 15

2, A ceramic bearing according to claim 1, wherein the second sliding surface is a tapered surface which lies flush against the first sliding surface and wherein the second sliding surface extends at an angle with respect to the second cylindrical surface. 0

3, A ceramic bearing according to claim 1, wherein the second sliding surface is a curved surface. 0 S

4, A ceramic bearing according to claim 2 or 3, wherein the second sliding surface is separated from the second s "cylindrical surface by a first plane surface.

5. A ceramic bearing according to any one of claims 1 to 3, wherein the inner ring has a groove extending around the outer periphery between the first cylindrical o" surface and the first sliding surface.

6, A ceramic bearing according to claim 5, wherein the inner ring has a third cylindrical surface which extends at an angle with respect to the first s.ii4ing surface and which is coaxial with the first axis; and 49CI/1 8.05.93 I I I -16 the outer ring further comprises a first plane surface extending at an angle with respect to the first axis and a fourth cylindrical surface which is coaxial with the first axis and which extends from the first plane surface; and wherein the distance from the first axis to the fourth cylindrical surface is greater than the distance from the first axis to the third cylindrical surface.

7. A ceramic bearing according to any one of the preceeding claims wherein the outer ring has a second axial hole dimensioned to loosely receive the shaft, and wherein the second axial hole has a second axis which is coaxial with the first axis.

8. A ceramic bearing according to any one of the 15 preceding claims wherein the outer periphery of the inntr ring has an outwardly extending step and defines a first abutment surface between the step and the first axial hole, and wherein the first abutment surface is substantially perpendicular to the first axis and is S0 20 provided for abutment with a second abutment surface defined on the shaft. o 9. A ceramic bearing substantially as herein described with reference to any one of figures 4 to 8 of the accompanying drawings.

•9 DATED this 18th day of May 1993 WING HIGHCERA CO, LTD se**: By their Patent Attorney GRIFFITH HACK CO

1149-C/18,05.93