GB2587430A

GB2587430A - Swivel joint

Info

Publication number: GB2587430A
Application number: GB1914099.5A
Authority: GB
Inventors: Sharpe Peter; Ramshaw Andrew
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2019-09-30
Filing date: 2019-09-30
Publication date: 2021-03-31
Also published as: GB201914099D0

Abstract

A swivel joint 100 for conveying hydraulic fluid in an aircraft from a first hydraulic fluid line connected to a spindle 101 of the swivel joint 100 to a second hydraulic fluid line connected to an outer cage 103 of the swivel joint 100. The swivel joint 100 comprises a first bearing 115 and a second bearing 117, each positioned on the spindle 101 to allow rotation of the spindle 101 and the first fluid line relative to the outer cage 103 and the second fluid line. Each of the bearings 115, 117 comprises a transfer port or conduit 122 providing fluid communication to the bearings 115, 117 and fluid conveyed by the swivel joint, in order to lubricate the bearings 115, 117 during use.

Description

SWIVEL JOINT

BACKGROUND OF THE INVENTION

100011 The present invention concerns a swivel joint for an aircraft. More particularly, but not exclusively, this invention concerns a swivel joint for carrying fluid, for example hydraulic fluid, and a method of manufacturing such a swivel joint. . [0002] Swivel joints are used in many fields of technology to provide fluid communication between two fluid lines whilst also permitting rotation of one of the fluid lines relative to the other. Swivel joints therefore find application in any situation in which a fluid line passes from a stationary part to a rotating part. It will be appreciated that the terms stationary and rotating are used in a relative sense and that therefore the stationary part need not actually be motionless.

[0003] A swivel joint of the prior art comprises a central spindle and an outer cage. The spindle comprises a first conduit running axially along the length of the spindle. The outer cage comprises a sleeve and a second conduit. The sleeve is of a suitable size and shape to receive the spindle and to allow it to rotate about its axis within the sleeve. The spindle is received in the sleeve such that the first conduit is positioned coaxially to the second conduit. Each of the first and second conduits are suitable for communicating fluid through the length of the conduit. One or both of the spindle and the sleeve also comprises a rotary seal between the spindle and the sleeve. The rotary seal prevents fluid leaking out of the interface between the spindle and the sleeve, whilst also permitting rotation of the spindle within the sleeve. Thus, the swivel joint provides fluid communication across the interface between the spindle and the sleeve, such that fluid is conveyed from the first conduit to the second. An outer end of each of the conduits is typically connected to a respective fluid line, such that the swivel joint provides fluid communication between the fluid lines. It will be appreciated that the described outer ends are the ends of the first and second conduits most distant from the interface between the spindle and the sleeve. The swivel joint further comprises a bearing comprising a greased set of ball bearings arranged in a raceway. The bearing is positioned between the -2 -spindle and the cage in order to provide location (to hold the spindle received in the sleeve) whilst also enabling low-friction rotation of the spindle within the sleeve. Thus, the swivel joint allows fluid communication between the first and second fluid lines whilst also allowing the first fluid line to rotate relative to the second.

[0004] Swivel joints are typically sealed to prevent contamination (for example by dust, or water) and may contain grease lubricated ball bearings to enable rotation whilst maintaining location. However, lubricants such as grease degrade over time leading to a loss of lubrication, which in turn leads to friction and abrasive wear of the ball bearings and the bearing race. This wear results in sub-optimal rotation and loss of location. Furthermore, the grease lubrication must be regularly replenished in order to maintain adequate levels of lubrication and protect the components of the bearing. Ultimately, the life of a ball-bearing hydraulic swivel will be limited by the life of the grease and wear on the ball bearings once lubrication is depleted [0005] Swivel joints exist in a number of configurations. The simplest configuration is that of a straight swivel joint (also known as a wrist swivel joint). In a straight swivel joint the two fluid lines meet the swivel joint in line and at the same angle, such that fluid is conveyed in substantially linear path through the swivel joint. The skilled person will appreciate that alternative configurations, such as elbow swivel joints and banjo swivel joints, can be provided by the use of combinations of right-angled fluid members and additional swivel joints. In all cases, the input and output fluid lines to a swivel joint rotate about a common axis, which can be said to be an axis of the swivel joint.

[0006] However, in use, swivel joints often experience side loads, typically caused by forces applied to one or both of the connected hoses. Side loads will be understood to comprise loads not in the direction of the axis of the swivel joint. Excessive side loads can result in increased wear on the bearing and on the rotary seal, causing a premature failure of the swivel joint. Furthermore, the bearing of a swivel joint requires regular maintenance in order to ensure sufficient lubrication of the bearing. Inadequate lubrication can result in wear on the balls of the bearing, changing their shape and so causing a loss of location. -3 -

[0007] There are various moving parts of an aircraft powered by, or otherwise associated with, hydraulic systems. Swivel joints are thus required for use in hydraulic lines that move relative to one another on an aircraft during operation. Failure of a single swivel joint in a fluid conveying system could potentially cause a failure of the entire system or sub-assembly with which it is associated. It is therefore very important when implementing a swivel joint on an aircraft, that the swivel joint is reliable and able to withstand the often harsh conditions aircraft equipment typically have to endure.

100081 The present invention seeks to mitigate one or more of the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved, for example more reliable, swivel joint for an aircraft.

SUMMARY OF THE INVENTION

[0009] The present invention provides, according to a first aspect, a swivel joint for an aircraft. The swivel joint comprises a spindle, the spindle comprising a first conduit; an outer cage, the outer cage comprising a second conduit expanding at one end into a sleeve; a first bearing; and a second bearing. The spindle is received in the sleeve such that the first and second conduits are coaxial and a seal is formed between the spindle and the outer cage. The first bearing and the second bearing are each located between the first conduit and the sleeve to facilitate rotation of the spindle within the outer cage. The second bearing is axially spaced apart from the first bearing. The first conduit is arranged to direct fluid flowing through the first conduit onto the first bearing and the second bearing to lubricate the bearings.

[0010] Having two bearings and spacing the second bearing apart from the first bearing in the axial direction improves the swivel joints ability to withstand side loads. Lubricating the first and second bearings using the fluid flowing through the joint enables the swivel joint to be self-lubricating, removing the need for periodic replenishment of special lubricant for the bearings (for example, grease). A swivel joint according to an embodiment of the invention may have a longer life, and be less prone to wear or fatigue, as a result of both the dynamic load bearing characteristics of the joint (e.g. less play with -4 -the use of two axially spaced apart bearings) and the continued lubrication of the joint with a source of fluid being cleaner and more uniform in characteristics that the grease of the bearings of the prior art, which deteriorates over time Less frequent servicing or inspection may be required.

[0011] The seal between the spindle and the outer cage may be provided at least in part by a first rotary sliding seal positioned around the spindle and between the spindle and the outer cage. The seal may be provided at least in part by a second rotary sliding seal, also positioned around the spindle and between the spindle and the outer cage, but axially spaced apart from the first rotary sliding seal. Use of one or more rotary seals allows the swivel joint to provide consistently convey fluid across the joint whilst also permitting rotation of the spindle within the outer cage. Use of multiple rotary seals can provide redundant sealing, and therefore increased reliability.

[0012] The first and second bearings may each comprise a set of rolling elements, for example bearing balls. The first and second bearings may each be held in position by and between the outer cage and the spindle. '[he outer sleeve may be coaxial to the second conduit. The first and second bearings may each comprise a cartridge bearing.

100131 The first bearing and the second bearing may be located axially in line. The first bearing and the second bearing may be located directly adjacent to each other. Locating the first bearing and second bearing axially in line can provide the swivel joint with improved resistance to side-loads.

[0014] The swivel joint may comprise a first hose. The first hose may be integral to the spindle. The spindle may comprise a thread on an external surface of the first conduit for connecting the first hose to the spindle.

[0015] The swivel joint may comprise a second hose. The second hose may be integral to the outer cage. The outer cage may comprise a thread on an external surface of the second conduit for connecting the second hose to the outer cage.

100161 The spindle may comprise a transfer port for each of the first and second bearings. The transfer ports may direct the fluid onto the bearings. -5 -

[0017] The swivel joint may comprise a spacer. The spacer may be located immediately adjacent to the first bearing and the second bearing. The spacer may be located between the first bearing and the second bearing.

[0018] The outer cage may be arranged to pre-tension the swivel joint. It may be that the pre-tensioning holds the spindle against the outer cage. Pre-tensioning the swivel joint can help to minimise relative axial movement of the parts of the swivel joint in the presence of axial forces on one or both of the attached fluid lines, and so reduce wear on the rotary seals.

[0019] The outer cage may be arranged to allow the spindle to move axially within the outer cage.

100201 As mentioned above, the bearings may comprise rolling elements (e.g. ball bearings). The swivel joint may comprise respective races in which the rolling elements of each of the first and second bearings ride. The races may each be shaped to conform to rolling elements of their respective bearing. Shaping the races of a bearing to conform to the rolling elements of the bearing increases the contact face of the rolling element, spreading the loads on and reducing wear of the rolling element. Providing an increased contacting surface area on the balls can provide improved location and reduce surface stresses. The races may have a coating of nitride or diamond material.

[0021] According to a second aspect of the invention there is also provided a swivel joint for conveying hydraulic fluid in an aircraft from a first hydraulic fluid line to a second hydraulic fluid line. The second hydraulic fluid line is connected to the first hydraulic fluid line by the swivel joint in a manner that allows relative movement between the first and second hydraulic fluid lines. The swivel joint comprises a first end for connecting to a first hydraulic fluid line, a second end for connecting to a second hydraulic fluid line, a straight section disposed between the first end and the second end, and first and second cartridge bearings. The straight section has a longitudinal axis and is configured to convey hydraulic fluid as it passes via the swivel joint. The first and second cartridge bearings each permit rotation about the longitudinal axis of the first end relative to the second end. Each cartridge bearing comprises inner and outer races, between which are held bearing balls arranged in a ring around the longitudinal axis. Each cartridge -6 -bearing and the swivel joint include at least one passageway which provides fluid communication between each ring of bearing balls and hydraulic fluid conveyed by the straight section. The cartridge bearing may comprise a metal raceway (for example a steel raceway) and may comprise rolling elements (for example ball-bearings) having a matched hardness to the raceway (e.g. the same hardness +/-20% , optionally the same hardness +/-10%). The rolling elements may be made of, or be coated with, ceramic material, such as silicon nitride. The rolling elements may be made of, or be coated with tungsten carbide. The ball-bearings may be made of or coated with diamond material. The swivel joint may comprise a central spindle on which the first and second cartridge bearings are mounted. The central spindle may comprise an integrated flange against which one or both of the first and second cartridge bearings abut. The swivel joint may comprise one or more outer cage parts, which hold in place one or both of the central spindle (if provided) and the cartridge bearings. There may be two outer cage parts that screw together, for example.

[0022] According to a third aspect of the invention, there is provided an aircraft comprising a swivel joint according to either of the first and second aspects. The swivel joint may comprise part of an actuation system for one of: a landing gear or a part thereof, a leading edge slat, a flap, or other controllable aerodynamic surface of the aircraft. The swivel joint may be arranged to direct hydraulic fluid to an actuator of the actuation system. The swivel joint may comprises a part of an aircraft landing gear. The swivel joint may be arranged to accommodate movement of the landing gear between a retracted position and an extended position. The swivel joint may be connected to a lock-stay hose of a landing gear.

[0023] According to a fourth aspect of the invention, there is provided a method of manufacturing a swivel joint for an aircraft. The swivel joint comprises a spindle with a first conduit, an outer cage with a second conduit expanding at one end into a sleeve, a first bearing, and a second bearing. The method comprises a first step of positioning a first bearing on an outer surface of the spindle such that a port in the spindle is aligned with the first bearing. The method comprises a second step of positioning a second bearing on the outer surface of the spindle such that a second port in the spindle is aligned with the second bearing and such that the second bearing is axially spaced apart from the first bearing. The method comprises a third step of placing the sleeve onto the first and second bearings such that the first and second conduits are coaxial and such that the bearings enable rotation of the spindle within the sleeve.

[0024] The method may comprise a step of setting the first and second bearings. Setting the first and second bearings comprises applying a predetermined axial tension between the spindle and one or both of the first and second bearings.

100251 The method may comprise a step of using an additive manufacturing process, for example 3D printing, to make one or more of the spindle, the first and second bearings, and the outer cage. One or more of the spindle, the first and second bearings, and the outer cage may be made by forging or machining.

100261 It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

DESCRIPTION OF THE DRAWINGS

100271 Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: 100281 Figure 1 shows a section view of a swivel joint according to a first embodiment of the invention; [0029] Figures 2a and 2b show an aircraft according to a second embodiment of the invention; and [0030] Figure 3 shows a flow diagram illustrating the steps of a method according to a third embodiment of the invention.

DETAILED DESCRIPTION

[0031] Figure I shows a section view of a swivel joint 100 according to a first embodiment of the invention. -8 -

[0032] The swivel joint 100 comprises a spindle 101 and an outer cage 103. The spindle 101 is substantially cylindrical and comprises a first conduit 105 running through the spindle 101 along its longitudinal axis. The outer cage 103 comprises a second conduit 107, which expands at one end into a sleeve 109. The spindle 101 is received in the sleeve 109. The spindle 101 and the internal volume of the sleeve 109 are both substantially cylindrical, so as to allow rotation of the spindle 101 within the sleeve 109. The second conduit 107 expands evenly into sleeve 109 such that the second conduit 107, the sleeve 109, and the spindle 101 when received in the sleeve 109, are all coaxial.

[0033] The first conduit 105 and the second conduit 107 are arranged such that, when the spindle 101 is received in the sleeve 109, the first conduit 105 and the second conduit 107 are coaxial. Each of the first conduit 105 and the second conduit 107 is arranged to provide fluid communication through the conduit. Thus, each of the first conduit 105 and the second conduit 107 serves to convey fluid from a first end of the conduit to a second end. It will be appreciated by a person skilled in the art that the conduits are not unidirectional, and that therefore fluid may be conveyed in either direction through the conduit.

100341 The swivel joint 100 further comprises a first rotary sliding seal 111. The first rotary seal 111 is positioned around the spindle 101 between the spindle 101 and the sleeve 109. Thus, when the spindle 101 is received in the sleeve 109 a seal is formed between the spindle 101 and the outer cage 103. The first rotary seal 111 therefore provides for fluid communication between the first conduit 105 and the second conduit 107. The swivel joint 100 can therefore be considered to comprise a first end, a second end, and a straight section disposed between the first end and the second end, the straight section being configured to convey fluid as it passes via the swivel joint 100. The first and second ends comprise the outer ends of the conduits of the swivel joint 100. It will be appreciated that the outer ends of the conduits refers to the ends of the first conduit 105 and the second conduit 107 which connect to other parts of a fluid conveying system.

[0035] In this example embodiment, the swivel joint 100 further comprises a second rotary sliding seal 113. The second rotary seal 113 is also positioned around the spindle 101 between the spindle and the sleeve 109 and is axially spaced apart from the first -9 -rotary seal 111. In this example embodiment, the second rotary seal 113 serves as a backup in case of failure of or leakage through the first rotary seal 111. Alternatively, the sealing between the spindle 101 and outer cage 103 may be provided in part by the first rotary seal 111 and in part by the second rotary seal 113. Thus, the first rotary seal 111 and the second rotary seal 113 can each be said to at least in part provide a seal between the spindle 101 and the outer cage 103. It will be appreciated that there is no requirement for the first rotary seal III and the second rotary seal 113 to be to the same design. In alternative embodiments, the first rotary sliding seal 111 may be of a different diameter, for example to accommodate an axial variation in the diameter of the spindle 101.

[0036] In this example, the first rotary seal III and the second rotary seal 113 are both secured to the spindle 101. However, it will be appreciated by a person skilled in the art that one or both of the first rotary seal 111 and the second rotary seal 113 may equally be secured to the outer cage 103.

[0037] The swivel joint 100 further comprises a first bearing 115 and a second bearing 117, each located on an outer surface of the spindle 101. 'Thus, the first bearing 115 and the second bearing 117 are each located between the spindle 101 and the sleeve 109. It will be appreciated by a person skilled in the art that each of the first bearing 115 and the second bearing 117 comprise a ring of rolling elements surrounding the spindle 101. Thus, each of the first bearing 115 and the second bearing 117 surrounds the spindle 101. The first bearing 115 is axially spaced apart from the second bearing 117. Spacing the first bearing 115 and the second bearing 117 axially gives the swivel joint 100 greater resistance to side-loads. The first bearing 115 and the second bearing 117 hold the spindle 101 in position within the sleeve 109, whilst also permitting rotation of the spindle 101 within the sleeve 109. It will be appreciated that the bearings permit rotation of the spindle 101 within the sleeve 109 by providing a low-friction coupling between the spindle 101 and the sleeve 109. It will also be appreciated that the low-friction coupling is provided in respect of rotation about the longitudinal axis of the spindle and bearings. Thus, the first bearing 115 and the second bearing 117 are each located between the first conduit 105 and the sleeve 109 to facilitate rotation of the spindle 101 within the outer cage 103.

-10 - [0038] Each of the first bearing 115 and the second bearing 117 comprises inner and outer races, within which ride the rolling elements of the bearing. In this example embodiment, the rolling elements comprise balls. In alternative embodiments, the rolling elements may comprise one or more of cylindrical, spherical, and tapered rollers. In embodiments, the races of each of the first bearing and/or the second bearing are shaped to conform to the rolling elements of the respective bearing. Thus, in the case of a ball bearing, the contact faces of the races may therefore comprise a curved surface having substantially the same radius as the respective bearing balls. Shaping the races to conform to the rolling elements riding within increases the contact face between each of the rolling elements and the races. The increased contact face spreads the loads applied to the rolling elements across a larger area of the rolling element and thereby reduces wear on the rolling element. Wear on rolling elements can result in the rolling elements becoming deformed such that the rolling elements are no longer the dimensions intended by design. This can allow the rolling elements to move axially within the bearing, which can further exacerbate wear of the bearing and result in a loss of location.

[0039] In this example embodiment, the first bearing 115 and the second bearing 117 each comprise a cartridge bearing. Thus, in this example, the swivel joint 100 can be said to comprise first and second cartridge bearings, each permitting rotation, about the longitudinal axis of the swivel joint 100, of a first end of the swivel joint 100 relative to a second end, wherein each cartridge bearing comprises inner and outer races between which are held bearing balls arranged in a ring around the longitudinal axis. It will however be appreciated by a person skilled in the art that other types of bearing are also equally useable. For example, the races of the first bearing 115 and second bearing 117 may be integrally formed on the spindle 101 and the outer cage 103. Similarly, in this example embodiment, the first bearing 115 and the second bearing 117 are substantially identical. However, it will be appreciated by a person skilled in the art that the first bearing 115 and the second bearing 117 need not be so, and may in fact be to different designs.

100401 Therefore, in combination with one or both of the first rotary seal 111 and the second rotary seal 113, the first bearing 115 and the second bearing 117 enable fluid communication through the swivel joint 100 whilst also permitting relative rotation of the spindle 101 and the outer cage 103.

[0041] In this example embodiment, the first bearing 115 and the second bearing 117 are located axially in line. To facilitate rotation of the spindle 101 within the outer cage 103, the first bearing 115 and the second bearing 117 must both enable a common axis of rotation. However, in alternative embodiments, the first bearing 115 may be of a different diameter to the second bearing 117, for example to fit a change in the outer diameter of the spindle 101.

[0042] Axial movement of the first bearing 115 and the second bearing 117 is prevented by a first circlip 119 located around the spindle 101 immediately adjacent to the first bearing 115 and a second circlip 121 located around the spindle 101 immediately adjacent to the second bearing 117. Movement in a first axial direction is inhibited by the first circlip 119, whilst movement in the opposite axial direction is inhibited by the second circlip 121.

[0043] In this example embodiment, the first bearing 115 and the second bearing 117 are separated by a spacer 123. Spacer 123 is located immediately adjacent to each of the first bearing 115 and the second bearing 117. Thus, the first bearing 115 abuts the spacer 123, which in turn abuts the second bearing 117. In alternative embodiments, the first bearing and the second bearing may be directly adjacent to one another, such that the first bearing 115 abuts the second bearing 117.

[0044] The purpose of the swivel joint 100 is to enable rotation within a fluid line. Thus, each end of the swivel joint 100 is connected to a fluid line. For example, an outer end of the first conduit 105 may be connected to a first fluid line and an outer end of the second conduit 107 may be connected to a second fluid line. Thus, the first embodiment of the invention provides a swivel joint for conveying fluid in an aircraft from a first fluid line to a second fluid line connected to the first fluid line by the swivel joint. The swivel joint operates to allow relative rotation between the first and second fluid lines.

[0045] Thus, in embodiments, the swivel joint 100 comprises a first hose. In this example embodiment, the spindle 101 comprises a thread on an external surface of the first conduit 105 corresponding to a thread on the first hose for connecting the first hose -12 -to the spindle 101. In alternative embodiments, the first hose is integral to the spindle 101. Similarly, in embodiments, the swivel joint 100 comprises a second hose. In this example embodiment, the outer cage 103 comprises a thread on an external surface of the second conduit 107 corresponding to a thread on the second hose for connecting the second hose to the outer cage 103. In alternative embodiments, the second hose is integral to the outer cage 103.

[0046] It will be appreciated by the skilled person that the fluid lines connected to each end of the swivel joint 100 may be provided by structures other than hoses, for example conduits, ducts, or pipes.

[0047] Preferably, the fluid conveyed by the swivel joint 100 is hydraulic fluid. However, the skilled person will appreciate that the swivel joint 100 is also suitable for conveying many other types of fluid, for example fuel.

[0048] In this example embodiment, the outer cage 103 is formed of a first part 125 and a second part 127. The first part 125 comprises a thread on an inner surface, and the second part 127 comprises a corresponding thread on its outer surface. thus, the first part 125 and the second part 127 can be screwed together to assemble the outer cage 103. Screwing and unscrewing the parts of the outer cage 103 in this manner enables the swivel joint 100 to be assembled as described below in relation to the fourth embodiment. [0049] It will however be appreciated by the skilled person that, in alternative embodiments, the outer cage 103 may comprise a single part. For example, the races of the first bearing 115 and the second bearing 117 may be integrally formed on the spindle 101 and the outer cage 103 and rolling elements may be fed into the bearings through respective ports in the sleeve 109. Thus, in embodiments of the invention, a single part sleeve serves to secure the connection of the spindle 101 to the outer cage 103.

100501 The spindle 101 further comprises a plurality of transfer ports 122. In this example embodiment, the spindle comprises two transfer ports 122 for each of the first bearing 115 and the second bearing 117. However, a person skilled in the art will appreciate that other numbers, shapes, and sizes of the transfer ports 122 are also equally usable. The transfer ports 122 are arranged to direct fluid flowing through the first conduit 105 onto the rolling elements of the bearings to provide lubrication. Thus, there is -13 -no need for a dedicated lubricant for the rolling elements of the bearings and the swivel joint 100 can therefore be said to be self-lubricating. The use of self-lubricating bearings can improve the lubrication of the rolling elements of the bearings by ensuring a continual supply of fresh lubricant, and so reduce wear on the rolling elements. The use of self-lubricating bearings also reduces the bearings' maintenance requirements, as there is no need to perform replacement and replenishment of dedicated bearing lubricants (e.g. grease).

100511 Thus, each of the first bearing 115, the second bearing 117, and the swivel joint 100 can be said to include at least one passageway which provides fluid communication between each ring of bearing balls and hydraulic fluid conveyed by the straight section of the swivel joint 100.

100521 In embodiments of the present invention, the outer cage 103 is arranged to pretension the swivel joint 100, such that the spindle 101 is held securely against the outer cage 103. Pre-tensioning the swivel joint 100 helps to ensure that the spindle 101 remains firmly received within the sleeve 109 in the presence of axial loads. In alternative embodiments, the outer cage 103 does not pre-tension the swivel joint 100. In other embodiments, the outer cage 103 is arranged to allow float within the swivel joint 100. [0053] In operation, fluid is conveyed from the first fluid line into and through the swivel joint 100, via the first conduit 105 and the second conduit 107, and into the second fluid line. As the fluid is conveyed through the first conduit 105, some of it passes into the transfer ports 122 and is directed onto the rolling elements of the first bearing 115 and/or the second bearing 117, providing lubrication of the rolling elements. Meanwhile, the first bearing 115 and the second bearing 117 allow the spindle 101 (and thereby also the first conduit 105 and first fluid line) to rotate relative to the outer cage 103 (and thereby also the second conduit 107 and the second fluid line). The first rotary seal III and the second rotary seal 113 ensure that reliable fluid communication is provided through the swivel joint 100 even as the spindle 101 rotates within the outer cage 103.

[0054] In alternative embodiments, the second conduit 107 of the swivel joint 100 comprises a 90° bend. Incorporating a 90° bend can, in certain applications, reduce the side-loads applied to the swivel joint 100. In alternative embodiments of the present -14 -invention, the first conduit 105 incorporates a 900 bend and the second conduit 107 is straight. It will be appreciated by a person skilled in the art that either one or both of first conduit 105 and second conduit 107 may incorporate one or more bends of any angle in order to meet the requirements of a given application.

[0055] Figures 2a and 2b show an aircraft 200 according to a second embodiment of the invention. The aircraft 200 comprises a swivel joint 100 according to the first embodiment of the invention. The swivel joint IOU comprises part of an actuation system, for example a hydraulic actuation system, for an aircraft subsystem. Thus, the swivel joint may be arranged to direct hydraulic fluid to an actuator of the actuation system. The aircraft subsystem may comprise any of a landing gear 201, a leading edge slat 203, and a flap 205. It will be appreciated by a person skilled in the art that the swivel joint of the present invention can also be applied to many other aircraft subsystems, for example to convey fuel in the aircraft fuel system. In embodiments of the invention, the aircraft comprises a plurality of swivel joints 100 to convey hydraulic fluid for use in one or more aircraft subsystems. In embodiments, the swivel joint 100 comprises a part of the aircraft landing gear 201, and is arranged to accommodate movement of the landing gear 201 between a retracted position and an extended position.

[0056] Figure 3 shows a flow diagram illustrating the steps of a method 300 of manufacturing a swivel joint for an aircraft according to a fourth embodiment of the invention.

[0057] An optional first step of the method 300, represented by element 301, comprises 3D printing a spindle, first and second bearings, and an outer cage. It will be appreciated that, in embodiments of the invention in which the sleeve comprises two parts (such as the first embodiment), this fourth step of the method 300 may comprise 3D printing a first part of the spindle and a second part of the spindle. In embodiments, the first step 301 may comprise forging or machining one of more of the spindle, the first and second bearings, and the outer cage.

[0058] A second step of the method 300, represented by element 303, comprises positioning the first bearing on an outer surface of the spindle such that a transfer port in the spindle is aligned with a corresponding port in the first bearing.

-15 - [0059] A third step of the method 300, represented by element 305, comprises positioning the second bearing on the outer surface of the spindle such that a second port in the spindle is aligned with a corresponding port in the second bearing and such that the second bearing is axially spaced apart from the first bearing.

[0060] A fourth step of the method 300, represented by element 307, comprises placing the sleeve onto the first and second bearings, such that the first and second conduits are coaxial and such that the bearings enable rotation of the spindle within the sleeve. It will be appreciated that, in embodiments of the invention in which the outer cage comprises two parts, this fourth step of the method 300 may comprise two sub-steps. A first of the sub-steps comprises placing the second part of the sleeve over the outer end of the spindle (and therefore also the accompanying bearings). A second of the sub-steps comprises inserting the inner end of the spindle (along with the second part of the sleeve) into the first part of the sleeve and screwing the second part into the first part. Thus, the outer cage is assembled around the spindle and bearings.

100611 An optional fifth step of the method 300, represented by element 309, comprises setting the first and second bearings by applying a predetermined axial tension between the spindle and one or both of the first and second bearings.

[0062] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0063] In the first, second, and fourth embodiments, the outer cage was comprised of two separate parts which were screwed together to assemble the outer cage. In alternative embodiments, the outer cage is a single part. In an example of such an embodiment, the races of the first bearing and the second bearing are integrally formed on the spindle and the sleeve and the swivel joint is assembled by feeding the rolling elements into the bearings through respective ports in the sleeve.

[0064] In the illustrated embodiments, the swivel joint comprises screw threads on the outer ends of the first and second conduits to facilitate the connection of first and second hoses. However, in alternative embodiments of the invention, the first hose is integral to -16 -the first conduit. Additionally or alternatively, the second hose may be integral to the second conduit.

[0065] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

[0066] The term 'or' shall be interpreted as 'and/or' unless the context requires otherwise.

Claims

-17 -CLAIMSI. A swivel joint for an aircraft, wherein the swivel joint comprises: a spindle, the spindle comprising a first conduit; an outer cage, the outer cage comprising a second conduit expanding at one end into a sleeve; a first bearing; and a second bearing; and wherein: the spindle is received in the sleeve such that the first and second conduits are coaxial and a seal is formed between the spindle and the outer cage; the first bearing and the second bearing are each located between the first conduit and the sleeve to facilitate rotation of the spindle within the outer cage; the second bearing is axially spaced apart from the first bearing; and the first conduit is arranged to direct fluid flowing through the first conduit onto the first bearing and the second bearing to lubricate the bearings.
2. A swivel joint according to claim I, wherein the seal between the spindle and the outer cage is provided at least in part by a first rotary sliding seal positioned around the spindle and between the spindle and the outer cage.
3. A swivel joint according to claim 2, wherein the seal between the spindle and the outer cage is provided at least in part by a second rotary sliding seal, also positioned around the spindle and between the spindle and the outer cage, but axially spaced apart from the first rotary sliding seal.
4. A swivel joint according to any preceding claim, wherein the first and second bearings are each held in position by and between the outer cage and the spindle.
-18 - 5. A swivel joint according to any preceding claim, wherein the outer sleeve is coaxial to the second conduit.
6. A swivel joint according to any preceding claim, wherein the first and second bearings each comprise a cartridge bearing.
7. A swivel joint according to any preceding claim, wherein the first bearing and the second bearing are located axially in line.
8. A swivel joint according to any preceding claim, wherein the first bearing and the second bearing are located directly adjacent to each other.
9. A swivel joint according to any preceding claim, further comprising a first hose, wherein the first hose is integral to the spindle.
10. A swivel joint according to any of claims 1 to 8, wherein the spindle comprises a thread on an external surface of the first conduit for connecting a first hose to the spindle.
11. A swivel joint according to any preceding claim, further comprising a second hose, wherein the second hose is integral to the outer cage.
12. A swivel joint according to any of claims I to 10, wherein the outer cage comprises a thread on an external surface of the second conduit for connecting a second hose to the outer cage.
13. A swivel joint according to any preceding claim, the spindle comprising a transfer port for each of the first and second bearings wherein the transfer ports direct the fluid onto the bearings.
-19 - 14. A swivel joint according to any preceding claim, further comprising a spacer located immediately adjacent to and between the first bearing and the second bearing.
15. A swivel joint according to any preceding claim, wherein the outer cage is arranged to pre-tension the swivel joint, such that the spindle is held against the outer cage.
16. A swivel joint according to any preceding claim, wherein the outer cage is arranged to allow the spindle to move axially within the outer cage.
17. A swivel joint according to any preceding claim, wherein the first bearing and the second bearing each comprise a set of bearing balls and the races of each of the first and second bearings are shaped to conform to balls of the respective bearing.
18. A swivel joint for conveying hydraulic fluid in an aircraft from a first hydraulic fluid line to a second hydraulic fluid line connected to the first hydraulic fluid line by the swivel joint in a manner that allows relative movement between the first and second hydraulic fluid lines, wherein the swivel joint comprises a first end for connecting to a first hydraulic fluid line, a second end for connecting to a second hydraulic fluid line, a straight section disposed between the first end and the second end, the straight section having a longitudinal axis and being configured to convey hydraulic fluid as it passes via the swivel joint, first and second cartridge bearings, each permitting rotation, about the longitudinal axis, of the first end relative to the second end, each cartridge bearing comprising inner and outer races between which are held rolling elements arranged in a ring around the longitudinal axis, each cartridge bearing and the swivel joint including at least one passageway which provides fluid communication between each ring of rolling elements and hydraulic fluid conveyed by the straight section.
-20 - 19. A swivel joint according to any preceding claim, wherein the swivel joint comprises part of an actuation system for one of: a landing gear, a leading edge slat, and a flap.
20. A swivel joint according to claim 19, wherein the swivel joint is arranged to direct hydraulic fluid to an actuator of the actuation system.
21. A swivel joint according to any preceding claim, wherein the swivel joint comprises a part of an aircraft landing gear, and is arranged to accommodate movement of the landing gear between a retracted position and an extended position.
22. An aircraft comprising a swivel joint according to any of claims 1 to 21.
23. A method of manufacturing a swivel joint for an aircraft, the swivel joint comprising a spindle with a first conduit, an outer cage with a second conduit expanding at one end into a sleeve, a first bearing, and a second bearing, the method comprising: positioning a first bearing on an outer surface of the spindle such that a port in the spindle is aligned with the first bearing; positioning a second bearing on the outer surface of the spindle such that a second port in the spindle is aligned with the second bearing and such that the second bearing is axially spaced apart from the first bearing; placing the sleeve onto the first and second bearings such that the first and second conduits are coaxial and such that the bearings enable rotation of the spindle within the sleeve.
24. A method according to claim 23, the method further comprising setting the first and second bearings by applying a predetermined axial tension between the spindle and one or both of the first and second bearings.-21 -
25. A method according to claim 23 or 24, the method thither comprising 3D printing the spindle, the first and second bearings, and the outer cage.