Light hollowed spherical plain bearing

A spherical plain bearing comprising an inner ring having an outer spherical contact surface and an outer ring having an inner spherical contact surface. The outer spherical contact surface of the inner ring cooperates with the inner spherical contact surface of the outer ring. At least one of the inner ring and the outer ring comprises at least one internal cavity running on at least a portion of the circumference of said ring.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Non-Provisional Patent Application, filed under the Paris Convention, claims the benefit of Europe Patent (EP) Application No. 14305746.1 filed on 20 May 2014, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The invention relates to a spherical plain bearing, to a bearing assembly comprising such a bearing and to a method for manufacturing such a spherical plain bearing.

BACKGROUND ART

Aircrafts are often equipped with spherical plain bearings. As aircrafts are getting lighter in order to reduce fuel consumption and improve maneuverability, bearings used in aircrafts must also be as light as possible.

It is known to use spherical plain bearings made of light materials, such as titanium, but such materials are costly. It is also known to increase the acceptable loads for the envelope of bearings manufactured with light but less resistant materials by adding a coating which locally improves the mechanical characteristics of the material. Such techniques do not prove satisfactory.

The aim of the invention is to provide a new spherical plain bearing, whose structure permits to obtain a bearing which is lighter than the bearings of the prior art, without deteriorating the mechanical properties of the bearing.

To this end, the invention concerns a spherical plain bearing comprising an inner ring and an outer ring, the inner ring comprising an outer spherical contact surface which cooperates with an inner spherical contact surface of the outer ring. This spherical plain bearing is characterized in that the inner ring and/or the outer ring comprises at least one internal cavity running on at least a portion of the circumference of said ring.

Thanks to the invention, the cavities make the rings of the spherical plain bearing lighter without substantially reducing their mechanical characteristics.

BRIEF SUMMARY OF THE INVENTION

According to further aspects of the invention which are advantageous but not compulsory, such a spherical plain bearing may incorporate one or several of the following features:On at least one of the rings, the or each cavity comprises ducts extending towards the spherical contact surface of the ring.A lubricant is inserted in the or each cavity.The or each ring comprises grooves provided on the spherical contact surface of said ring, and the ducts open into the grooves.At least one of the inner and outer rings comprises several cavities parallel to each other and extending around a central axis of the ring.The outer ring comprises two cavities extending around a central axis of the outer ring, the cavities being respectively located in the vicinity of a first axial end and a second axial end of the outer ring.The internal cavities are annular and extend on the whole circumference of the ring in which they are provided.

The invention also concerns a bearing assembly comprising a spherical plain bearing as mentioned here-above and a lubricant distribution device. Such a bearing assembly is characterized in that the lubricant distribution device is adapted to inject new lubricant in one of the cavities of one ring and to extract used lubricant from another cavity of the same ring.

The invention also concerns a method for manufacturing a spherical plain bearing as mentioned here-above, characterized in that the rings are manufactured by additive manufacturing.

The invention also concerns a method for manufacturing a spherical plain bearing as mentioned here-above, characterized in that the rings are manufactured by casting with cores.

The invention also concerns a method for manufacturing a spherical plain bearing as mentioned here-above, characterized in that the rings are manufactured as divided parts which are then assembled together.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a spherical plain bearing2. Spherical plain bearing2comprises an inner ring20, which is represented only onFIG. 1, and an outer ring22. Inner ring20comprises an outer spherical contact surface20A, and outer ring22comprises an inner spherical contact surface22A, which cooperates with outer spherical surface20A.

According to the invention, inner ring20and/or outer ring22comprise at least one internal cavity running on at least a portion of the circumference of inner ring20or outer ring22. As shown onFIG. 1, inner ring20comprises several internal cavities200extending around a central axis X20of inner ring20. Internal cavities200are annular and extend on the whole circumference of inner ring20. Cavities200form toroid volumes centered on axis X20. Cavities200are parallel to each other. In other words, the walls of cavities200which are perpendicular to axis X20are each parallel to each other.

Inner ring20extends between a first axial end202and a second axial end204. Inner ring20comprises five cavities200regularly distributed along central axis X20between axial end202and204. The radial length of cavities200decreases towards ends202and204.

Outer ring22comprises two internal cavities220aand220bwhich are annular and extend on the whole circumference of outer ring22. Cavities220aand220bof outer ring22extend around central axis X22of outer ring22and are respectively located in the vicinity of a first axial end222and a second axial end224of outer ring22along axis X22.

Internal cavities220a,220band200are provided in areas of inner and outer rings20and22in which the mechanical stresses are the lowest, depending on the operating conditions of spherical plain bearing2, so that the mechanical properties of bearing2are not substantially deteriorated by these cavities. Internal cavities200,220aand220bpermit to make lighter spherical plain bearings suitable for use in aircrafts.

Cavities220aand220beach comprises at least one duct226extending towards inner spherical contact surface22A. Ducts226are radial cylindrical holes which form a fluid link between cavities220aand220band inner contact surface22A.

Thanks to ducts226, cavities220aand220bcan form lubricant tanks. Before mounting in, for example, an aircraft, lubricant is inserted in cavities220aand220b. Ducts226permit to bring lubricant towards spherical contact surfaces20A and22A during the lifetime of bearing2. In order to improve lubricant circulation on the entire circumference of the spherical contact between inner ring20and outer ring22, at least one of outer and inner rings20and22comprises two circumferential grooves228aand228b. In the example of the figures, and as shown onFIG. 2, grooves228aand228bare provided on inner surface22A and can extend on the whole circumference of outer ring22. Advantageously, grooves228aand228bwhich are respectively aligned with cavities220aand220bso that ducts226open into grooves228aand228b.

An advantage of this feature is the reduction of maintenance when spherical plain bearing2is mounted in an aircraft. The presence of lubricant tanks in the bearing allows designing the bearings for the entire service life of an aircraft, so that the spherical plain bearings do not need to be dismounted or changed to bring a new quantity of lubricant or replace worn off parts.

As an optional feature, outer ring22includes grooves230provided on contact surface22A, which link grooves228aand228bto each other, so that lubricant contained in cavity220acan reach groove228band lubricant contained in cavity220bcan reach groove228a. This improves the circulation of lubricant.

Alternatively, grooves228a,228band230may be differently arranged on inner contact surface22A, and inner contact surface22A may comprise more than two circumferential grooves.

Inner ring20and outer ring22may be manufactured by casting with cores. The cores permit to obtain the internal cavities200,220aand220b.

Alternatively, inner ring20and outer ring22may be manufactured as divided parts, which are then assembled together. The shapes of cavities200,220aand220bare defined on complementary parts. Such a process avoids the use of complex casting systems.

Alternatively, inner ring20and outer ring22may be manufactured by additive manufacturing or 3D printing, which consists of creating a superposition of thin material layers by, for example, progressively laying down and melting a powder using a laser. The final shape of each ring including the cavities is directly obtained.

Spherical plain bearing2may be comprised into a bearing assembly which includes a non-shown lubricant distribution device adapted to inject new lubricant in one of the cavities of outer ring22and to extract used lubricant from the other cavity of outer ring22. For example the lubricant distribution device may inject new lubricant in cavity220aand extract used lubricant from cavity220b, via ducts226and grooves228a,228band230. Such a lubricant distribution device and the structure of plain bearing2permit to more easily extract used lubricant, which may contain metal particles likely to damage the spherical contact surfaces20A and22A, from bearing2.

According to a non-shown embodiment of the invention, inner ring20may also comprise ducts which extend between cavities200and spherical contact surface20A so that lubricant can be inserted in cavities200. A lubricant distribution device may also be adapted to run a lubricant circulation in inner ring20similar to outer ring22.

According to a non-shown embodiment of the invention, cavities200may be used to host electronic components or devices such as RFID tags or sensors.

According to another non-shown embodiment, the internal cavities200of inner ring20and/or the internal cavities220of outer ring22may extend only on a limited portion of the circumference of inner and outer rings20and22.

The features of the above-mentioned embodiments and variants can be combined to form new embodiments of the invention.