Spherical plain bearing with inner sleeve

A spherical plain bearing comprising an inner ring provided with a spherical outer surface and with lateral surfaces, an outer ring provided with a corresponding spherical inner surface mounted on the outer surface, and a sleeve mounted into a bore of the inner ring. The inner ring comprises at least three part rings which are mounted in contact in the circumferential direction one relative to another. At least one protrusion is provided on an outer surface of the sleeve and extends into a groove formed on the bore of the inner ring. The sleeve leaves the lateral surfaces free of the inner ring.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Non-Provisional Patent Application, filed under the Paris Convention, claiming the benefit of Europe Patent (EP) Application Number 14175241.0 filed on 1 Jul. 2014 (1 Jul. 2014), which is incorporated herein by reference in its entirety.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of spherical plain bearings, notably those used in the aeronautics industry.

BACKGROUND ART OF THE INVENTION

In the aeronautics industry, it is known to use a spherical plain bearing for preventing two members, such as a rod and a structural part, from moving axially relatively while allowing a relative rotational movement of the members.

Such bearing generally comprises an inner ring having a truncated spherical outer surface and an outer ring having a truncated spherical inner surface in contact with the outer surface. The inner and outer rings thus have three degrees of freedom in rotation, while being firmly fixed to each other in translation.

In order to obtain a light spherical plain bearing, it is known to form the inner ring from a metal or from a metal alloy having a low density, for example titanium, titanium alloys, aluminum and aluminum alloys. However, the frictional behavior of such metals and metal alloys is not compatible with the stresses applied in operation to the inner ring by the shaft onto which is mounted the bearing.

Accordingly, the spherical plain bearing may further comprise a sleeve mounted into the bore of the inner ring and made from a material having good friction properties as described for example in EP-B1-1 431 597. The disclosed sleeve comprises, at one end, a radial shoulder axially bearing against a frontal surface of the inner ring.

With such a sleeve, the angular slewing capacity of the spherical plain bearing is limited. Besides, it is necessary to foreseen additional axial retaining means to prevent relative axial movement between the sleeve and the inner ring.

BRIEF SUMMARY OF THE INVENTION

One aim of the present invention is to overcome these drawbacks.

In one embodiment, the spherical plain bearing comprises an inner ring provided with a spherical outer surface and with lateral surfaces, an outer ring provided with a corresponding spherical inner surface mounted on the outer surface, and a sleeve mounted into a bore of the inner ring. The inner ring comprises at least three part rings which are mounted in contact in the circumferential direction one relative to another. At least one protrusion is provided on an outer surface of the sleeve and extends into a groove formed on the bore of the inner ring. Alternatively or in combination, at least one protrusion is provided on the bore and extends into a groove formed on the outer surface. The sleeve leaves free the lateral surfaces of the inner ring.

With such design, the angular slewing capacity of the spherical plain bearing is increased since the sleeve does not cover the lateral surfaces of the inner ring. Besides, the protrusion provided on the sleeve, and/or on the inner ring, and the corresponding groove enable to achieve the axial retention of the sleeve relative to the inner ring without additional separate means.

Preferably, a radial gap is provided between the protrusion(s) and a bottom of the associated groove.

The protrusion(s) may extend radially. Preferably, the protrusion(s) comprise sloped frontal surfaces engaging with corresponding sloped sidewalls of the associated groove.

In one embodiment, only one protrusion is provided. The protrusion may be located in a radial plane passing through the centre of the sleeve and of the inner ring.

Preferably, at least one part ring of the inner ring comprises chamfers formed at least at one end of the bore of the part ring.

The part rings of the inner ring may be identical one to another. Alternatively, at least one of the part rings of the inner ring may have a reduced length in the circumferential direction with regard to the other part rings.

Advantageously, the inner ring is made from a material having a density smaller than the one of the material of the sleeve. The sleeve may be made from bronze and/or the inner ring may be made from titanium.

In one embodiment, at least one of the inner and outer surfaces of the rings is coated with an antifriction and/or wear resistance coating. In order to obtain both low friction and high wear resistance, the spherical inner surface of the outer ring may be coated with a physical vapor deposition coating such as a diamond like carbon (DLC) coating or a tungsten-DLC (WCC) coating. The thickness of the coating may be equal to 5 μm for example. The spherical outer surface of the inner ring may be coated with a thermal spray coating such as a copper-nickel-indium (CuNiJn) coating. The thickness of the coating may be equal to 150 μm for example.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

As illustrated onFIGS. 1, 3 and 4, a spherical plain bearing10, with an axis12, comprises an outer ring14, an inner ring16onto which is mounted the outer ring, and an inner sleeve18mounted into a cylindrical bore16aof the inner ring.

The outer ring14comprises an outer surface14a, an opposite inner surface14bhaving a spherical concave shape and opposite radial lateral (not referenced) which axially delimit the surfaces14a,14b. The inner ring16comprises the bore16aand an outer surface16bmounted in radial contact against the inner surface14bof the inner ring and having a spherical complementary convex shape. The inner ring16further comprises two opposite radial lateral surfaces16c,16dwhich axially delimit the bore16aand the outer surface16bof the ring.

The inner ring16is formed by the assembling of three segments or part rings20,22,24which are mounted bearing against one another in the circumferential direction. The inner ring16is subdivided in the circumferential direction by the three distinct parts20to24. Each part ring20,22,24bears circumferentially at each end with one of the other part. The outer surfaces of the part rings20to24form the spherical outer surface16bof the inner ring. The inner surfaces of the part rings20to24form the bore16a. Advantageously, the inner ring16is made from a material having a density smaller than the one of the material of the sleeve18. The inner ring16may be made for example from titanium.

The sleeve18, of tubular shape, is mounted in radial contact against the bore16aof the inner ring. The sleeve18comprises a cylindrical bore18a, an outer cylindrical surface18band two opposite radial lateral surfaces18c,18dwhich axially delimit the bore and the outer surface. The lateral surfaces18c,18dare respectively coplanar with the lateral frontal surfaces16c,16dof the inner ring. The sleeve18leaves free the lateral surfaces16c,16dof the inner ring. The lateral surfaces16c,16dare not covered by the sleeve18. The sleeve18may be made from bronze.

The sleeve18further comprises an annular rib26extending radially from the outer surface18btowards the inner ring16. The rib26projects into a groove28provided on the bore16aof the inner ring. The groove28is directed radially outwards and is formed on the bore16a. Each part ring20,22,24comprises a segment of the groove28. In the illustrated example, the rib26is located in a radial plan passing through the centre of the inner ring16.

The outer diameter of the rib26is greater than the diameter of the bore16aof the inner ring so that a diametral interference exists between the sleeve18and the inner ring16. This surely prevents an axial displacement of the sleeve18relative to the inner ring16. The annular rib26forms an axial retaining means cooperating with a complementary retention means of the inner ring16. The sleeve18is locked in axial direction with regard to the inner ring16without additional means. The rib26engages into the groove28with frictional contact.

As shown more clearly onFIG. 2, the rib26of the sleeve comprises frontal sloped surfaces26a,26bengaging with corresponding sloped sidewalls28a,28bof the groove, and an outer surface26cextending axially between the surfaces26a,26b. The rib26interferes with the two opposed sidewalls28a,28bof the groove. A radial gap30exists between the outer surface26cof the rib and a bottom28cof the groove which is extended radially by the sidewalls28a,28b.

In the illustrated example, the rib26and the sleeve18are formed in one part. Alternatively, the rib26and the sleeve18may be two separate parts which are assembled together. Here, the rib26has an annular form. Alternatively, the sleeve may comprise a plurality of ribs spaced apart one to another in the circumferential direction.

In the illustrated example, the part rings20to24are identical one to another. In case of the mounting of the three part rings of the same size is not possible due to collision between the outer ring14and the last part ring to be mounted, the bearing may comprise a part ring having a reduced length in the circumferential direction with regard to the other part rings.

Alternatively or in combination, one of the part rings of the inner ring may comprise chamfers24aformed at least at one end of its inner surface as shown in the second example illustrated onFIG. 6, in which identical parts are given identical references. With such chamfers, the part ring24can be slightly inclined and pushed deeper when mounted inside the outer ring14.

Although the invention has been illustrated on the basis of a radial spherical plain bearing having an inner sleeve provided with a protrusion extending into a groove formed on the bore of the inner ring, it should be understood that the invention can be applied with an inverted arrangement, i.e. a protrusion provided on the bore of the inner ring and engaging into a groove formed on the outer surface of the sleeve. In another embodiment, it could also be possible to combine these two arrangements. In the disclosed embodiments, the inner ring comprises three part rings. Alternatively, it could be possible to foresee an inner having four part rings or more.