Associated assembly tooling and methods for a plain bearing unit

Abstract

Assembly ring 8 with flange 9 and assembly shaft 11 having frustoconical end 11a and sleeve insertion end 11b for inserting sleeve 2 and sleeve retention ring 6 to an inner bore 4b of swivel joint inn

Description

Title: Associated assembly tooling and methods for a plain bearing unit. Technical field of the invention The present invention concerns in general plain bearing units of the swivel joint type, which can be used inter alia in the aeronautics industry. More specifically, the invention relates to the assembly of a unit of this type. Prior art Typically, a plain bearing unit comprises an exterior ring provided with a spherical interior surface, and an interior ring provided with a spherical exterior surface. In the aeronautics industry, these units are often installed on joints of the swivel type, in order to adapt to the deformations of the structures, which can be caused by expansion. During maintenance operations, these joints need to be dismantled in order to release the unit. Thus, in order to facilitate the operations of assembly and dismantling, it is known for the interior ring to be able to take the form of a split ring, which is therefore produced in several parts. However, during the maintenance operations, the design in several parts of the interior ring can give rise to marks on the shaft of the joint at the slot(s) of the interior ring, thus making it necessary to have to carry out often costly replacement of the joints each time dismantling takes place. To eliminate this disadvantage, it is known to assemble an annular sleeve in the bore of the interior ring, in order to obtain a continuous cylindrical contact, without discontinuity with the shaft of the joint. In order to form a single unit which is easy to assemble and dismantle, the sleeve must be rendered integral with the interior ring. In the prior art, several methods for assembly of the sleeve on the interior ring are known, including a method consisting of equipping the sleeve with an annular support at one end, assembled supported axially against one of the frontal faces of the interior ring, and with a thread at the other end, on which there is screwed a nut which is supported against the other frontal face of the interior ring. However, these methods have certain disadvantages, in particular a lack of practicality, since the sleeve, which has to act as a wear part, needs to be easy to replace and assemble in the interior ring during maintenance operations. Hitherto, no specific tooling has made it possible to assemble a plain bearing unit of this type efficiently. Summary of the invention The objective of the invention is thus to eliminate this disadvantage by proposing a method for assembly of a plain bearing unit by means of assembly tooling. The plain bearing unit comprises a swivel joint which is provided with an interior ring comprising a spherical exterior surface, and with an exterior ring comprising a spherical interior surface which is assembled on the spherical exterior surface of the interior ring, a sleeve provided with an exterior surface assembled in the bore of the interior ring of the swivel joint, and a radially resilient retention ring, which extends in the interior of a groove provided in the bore of the interior ring of the swivel joint, and in the interior of a groove provided on the exterior surface of the sleeve. The assembly tooling comprises: a cylindrical assembly ring provided at an axial end with a flange; and an assembly shaft with a first part having a frustoconical form and a second assembly part of the sleeve, the assembly shaft being configured to be inserted into the bore of the interior ring of the swivel joint. In addition, the frustoconical form of the first part of the assembly shaft can correspond to a stepped frustoconical form comprising a plurality of successive bearings along the axis of the first part of the shaft. Each bearing can have a distinct diameter: - the first bearing having a first diameter corresponding to the interior diameter of the retention ring in the free state; - the second bearing having a second diameter larger than the first diameter, and corresponding to the exterior diameter of the retention ring in a configuration of resilient deformation, which is smaller than the inner diameter of the bore of the interior ring; - the third bearing having a third diameter larger than the first and second diameters, and smaller than the diameter of the bore of the sleeve. In addition, the third bearing of the part of the assembly shaft can have a length which is at least equal to half the length of the sleeve. Once the sleeve is inserted on the second part of the assembly shaft, the diameter of the exterior surface of the assembly part of the sleeve is smaller than, or the same as, the diameter of the bore of the interior ring of the swivel joint. The diameter of the exterior surface of the assembly ring is designed to be smaller than, or the same as, the diameter of the bore of the interior ring of the swivel joint. The invention also concerns a method for assembly of the plain bearing unit as previously defined, by means of assembly tooling. The method comprises the following steps: a step of positioning of the retention ring on the first part of the assembly shaft; a step of insertion of the sleeve on the second part of the assembly shaft; a step of assembly of the interior ring of the swivel joint in the bore of the exterior ring; a step of insertion of the assembly ring into the bore of the interior ring of the swivel joint, until the flange of the said ring abuts the interior ring; a step of insertion of the first part of the assembly shaft equipped with the retention ring into the interior of the bore of the interior ring axially on the side opposite the sleeve; a step of axial thrusting of the assembly shaft into the interior of the bore of the interior ring of the swivel joint, until the following is obtained: abutment of the retention ring against the assembly ring, and insertion of the retention ring into the interior of the groove of the interior ring by resilient deformation; then insertion of the said retention ring into the interior of the groove of the sleeve by resilient return, and rendering the sleeve and the interior ring of the swivel joint integral axially. Before the step of insertion of the first part of the shaft into the bore of the interior ring, a step is carried out of assembly of the interior ring in the exterior ring of the swivel joint. Next, during the step of axial thrusting of the assembly shaft, the abutment ring is maintained as far as the abutment of the retention ring against the assembly ring, thus giving rise to sliding of the retention ring along the first part of the assembly shaft, and insertion of the retention ring into the interior of the groove of the interior ring, by deformation. Thus, during the step of axial thrusting of the assembly shaft, and after the insertion of the retention ring into the groove of the interior ring, the assembly ring adheres to the first part of the said assembly shaft, and is released from the exterior ring. Subsequently, the method continues with a step of withdrawal of the assembly shaft from the bore of the interior ring, once the sleeve and the interior ring have been rendered integral axially. Thus, the sleeve and the swivel joint are rendered integral axially in a convenient manner by means of specific tooling. Brief description of the figures The present invention will be better understood by studying the detailed description of an embodiment, taken by way of example which is in no way limiting, and illustrated by the appended drawings, in which: [Fig.l] is a view in cross-section of a plain bearing unit according to an embodiment of the invention. [Fig.2] is a view in cross-section of the assembly tooling, more specifically of the assembly shaft on which there are inserted the sleeve and the retention ring in their successive positions. [Fig.3], [Fig.4], [Fig.6] are views in cross-section illustrating the assembly of the plain bearing unit by means of the assembly tooling. Detailed description of the invention [Fig.l] represents a smooth bearing unit 10 with an axis X-X', comprising a swivel joint 1 and a sleeve 2 mounted in the bore of the swivel joint. As will be described in greater detail hereinafter, the unit 10 also comprises a retention ring 6 interposed radially between the swivel joint 1 and the sleeve 2, in order to ensure that they are rendered integral axially. The swivel joint 1, with an axis X-X', comprises an interior ring 4 and an exterior ring 5 fitted on the interior ring. The interior 4 and exterior 5 rings are made of steel, titanium, nickel alloy, bronze, etc. The interior ring 4 is provided with a convex spherical exterior surface 4a, a cylindrical bore 4b radially opposite the exterior surface, and two opposite radial frontal faces (with no reference) delimiting axially the bore and the exterior surface. The interior ring 4 can be produced in several parts which are supported against one another. The interior ring 4 can be split along one or more planes passing via the axis X-X'. The interior ring 4 can also be in a single piece. The exterior ring 5 is provided with a concave spherical interior surface 5a, fitted on the spherical exterior surface 4a of the interior ring, with a cylindrical exterior surface 5b, radially opposite the interior surface 5a, and with two opposite radial frontal faces (with no reference) delimiting the interior and exterior surfaces axially. The interior surface 5a of the exterior ring and the exterior surface 4a of the interior ring, have a complimentary form. The exterior ring 5 can have a solid spherical form, or it can be produced in two parts, or it can also comprise notches on its exterior surface 5b. A groove 44 is formed in the bore 4b of the interior ring of the swivel joint. The groove 44 is oriented radially towards the interior, i.e. in the direction of the sleeve 2. The groove 44 is radially facing a groove 22 of the sleeve, which will be described in greater detail hereinafter in the description. The groove 44 is in this case annular. The groove 44 is delimited in the radial direction by two facing radial walls (with no reference) which are connected to one another by a base. The base of the groove 44 is offset radially towards the exterior in relation to the bore 4b of the interior ring. In the embodiment illustrated, the groove 44 has an axial width which is reduced in relation to that of the groove 22. Alternatively, the groove 44 can have an axial width which is larger than, or the same as, that of the groove 22. The sleeve 2 is mounted in the bore 4b of the interior ring which forms the bore of the swivel joint. The sleeve 2, with an axis X-X', has an annular form. The sleeve 2 is provided with a convex cylindrical exterior surface 2a mounted in the bore 4b of the interior ring of the swivel joint, with a cylindrical bore 2b radially opposite the exterior surface, and with two radially opposite frontal faces (with no reference) delimiting axially the bore and the exterior surface. The groove 22 is formed on the exterior surface 2a of the sleeve. The groove 22 is oriented radially towards the exterior, i.e. in the direction of the interior ring 18 of the swivel joint. The groove 22 is in this case annular. The groove 22 is delimited in the radial direction by two facing radial walls (with no reference) which are connected to one another by a base. The base of the groove 22 is offset radially towards the interior in relation to the exterior surface 2a of the sleeve. As previously indicated, the unit 10 also comprises the retention ring 6, in order to ensure that the swivel joint 1 and the sleeve 2 are rendered integral axially. The retention ring 6 is radially resilient. In other words, the retention ring 6 is resiliently deformable in the radial direction. The retention ring 6 extends in the interior of the grooves 22, 44 of the sleeve and the interior ring of the swivel joint. The axial thickness of the retention ring 6 is slightly smaller than the axial width of the groove 44 of the interior ring of the swivel joint, and than that of the groove 22 of the sleeve. The radial depth of the groove 44 is larger than the radial thickness of the retention ring 6. The retention ring 6 can be open at a point of its circumference. The retention ring 6 can be in the form of a circlip made of metal material. Alternatively, the retention ring 6 can be produced from synthetic material. In the free state, the retention ring 6 has an exterior diameter which is smaller than the diameter of the bore 4b of the interior ring of the swivel joint, and smaller than the diameter of the groove 44. The diameter of the groove 44 is taken at the level of its base. There is a radial gap between the retention ring 6 and the base of the groove 44. In the free state, the retention ring 6 has an interior diameter which is smaller than the diameter of the exterior surface 2a of the sleeve. In the embodiment illustrated, in the free state, the interior diameter of the retention ring 6 is smaller than, or the same as, the interior diameter of the groove 22. The interior diameter of the groove 22 is taken at the level of its base. The retention ring 6 is supported radially against the base of the groove 22. As a variant, in the free state, the interior diameter of the retention ring 6 could be larger than the diameter of the groove 22, while however remaining smaller than the diameter of the exterior surface 2a of the sleeve. In the embodiment illustrated, the retention ring 6 has a rectangular form in straight cross-section. Alternatively, the retention ring 6 can have other forms in straight cross-section, for example square or circular. [Fig.2] and [Fig.3] represent more clearly the assembly tooling used for the assembly of the unit 10 as previously described. The assembly shaft 11 is a component which is cylindrical of revolution and which, in the free state, is composed of two sections with different diameters delimiting two assembly parts 11a and lib, intended for the insertion respectively of the retention ring 6 and the sleeve 2. The first part 11a of the assembly shaft has a frustoconical form, which can advantageously be a stepped frustoconical form marked by distinct cylindrical bearings Pl, P2, P3 with diameters which increase along the axis of the part 11a of the assembly shaft 11. This configuration makes it possible in particular to control the adjustment of the retention ring to the different bearings, and to facilitate the progressive insertion of the retention ring into the groove 44 of the bore 4b of the interior ring 4, during the step of axial thrust of the assembly shaft 11. As shown in [Fig.2], each bearing Pl, P2, P3 of the first part 11a of the assembly shaft 11 thus has a distinct diameter corresponding to the positioning of the retention ring 6 during the steps of assembly of the plain bearing unit 1. On the first bearing Pl, the end of the assembly part 11a has a first diameter corresponding to the interior diameter of the retention ring 6 in the free state. This permits effortless positioning of the ring 6 on the assembly shaft 11. On the second bearing P2, the part 11a of the assembly shaft has a second diameter which is larger than the first diameter of the bearing Pl, corresponding to the exterior diameter of the ring 6 in a resilient deformation configuration. This diameter is smaller than the inner diameter of the bore 4b of the interior ring 4. By this means, it is possible for the ring 6, positioned on the part 1 la of the assembly shaft, to be inserted into the bore 4b of the interior ring 4. On the third bearing P3, the part 11a of the assembly shaft 11 has a third diameter which is larger than the first and second diameters of the bearings Pl and P2, and smaller than the diameter of the bore 2b of the sleeve 2. At this stage, the retention ring 6 is partly accommodated in the groove 44 of the interior ring 4. In addition, the third bearing 3 of the part 11a of the assembly shaft can have a length which is at least equal to half the length of the sleeve, such as to permit in the first stage the insertion of the retention ring 6 into the groove of the interior ring 4, then release of the assembly ring from the bore 5b of the exterior ring 5. The dimensioning of the bearing 3 of the first part 11a of the shaft 11 contributes towards maintaining the retention ring 6 in place, when the assembly shaft 11 is inserted into the bore 4b of the interior ring 4 during the assembly, and to progressive transition between the state of deformation of the ring 6 and its insertion into the groove 44 of the interior ring 4. Similarly, the length of the bearing 3 of the first part 11a of the shaft 11 also allows the assembly ring 8 to be released from the bore 4b of the interior ring 4 only after the insertion of the retention ring 6 into the groove 44 of the interior ring 4. If the length of the bearing 3 is too short, there can be both a risk of the assembly ring 8 being disengaged too early, i.e. before the ring 6 has been completely inserted into the groove 44 of the interior ring 4, and of the transition, by resilient return, between the deformed state of the ring on the part 11a of the assembly shaft 11, and its insertion into the groove 44, being sudden, with the risk of damaging the precision of the unit. Furthermore, the assembly shaft 11, and in particular the first part 11a of the assembly shaft, has dimensions such as to have a length sufficient to permit the insertion of the retention ring 6 before the disengagement of the assembly shaft 8 from the bore 5b of the exterior ring 5. As illustrated in [Fig.2], the retention ring 6 is designed to be positioned on the first part 11a of the shaft 11, and to slide radially by resilient deformation along the first part 11a of the assembly shaft, passing subsequently via the bearings Pl, P2, P3, thus permitting controlled and easy insertion of the ring 6 into the groove 44 of the interior ring 4. The second part lib of the assembly shaft 11 corresponds to an assembly part of the sleeve 2. The second part lib of the shaft is axially opposite the part 11a. The second part lib of the assembly shaft can be provided with a shoulder 14, permitting abutment of the sleeve 2 on the assembly shaft 11. The sleeve 2 is thus inserted into the second part lib of the assembly shaft 11, until it abuts the shoulder 14, thus assisting precise positioning and adjustment of the sleeve 2 on the assembly shaft 11. Inter alia, the shoulder 14 makes it possible to prevent the disengagement of the sleeve 2 from the assembly shaft 11, by limiting the axial movement of the sleeve 2 during assembly steps which will be described in greater detail hereinafter in the description. The diameter of the assembly part lib of the sleeve is smaller than, or the same as, the diameter of the bore 4b of the interior ring 4 of the swivel joint 1. The diameter of the assembly part lib of the sleeve is the same as the large diameter of the first part 11a of the shaft 11. [Fig.3] shows the assembly ring 8. The assembly ring 8 has a hollow cylindrical body provided at an axial end with a flange 9. The diameter of the exterior surface 8b of the assembly ring 8 is smaller than, or the same as, the diameter of the bore 4b of the interior ring of the swivel joint 1. Preferably, the exterior surface 8b of the assembly ring 8 is in contact with the bore 4b of the interior ring 4. This permits close adjustment of the assembly ring 8 when it is inserted into the bore 4b of the interior ring 4. Thus, the diameter of the interior surface 8a of the assembly ring 8 is smaller than the diameter of the bore 4b of the interior ring of the swivel joint 1. In addition, the assembly ring 8 has dimensions such as to leave the groove 44 of the interior ring 4 free, when the assembly ring 8 is inserted into the bore 4b of the interior ring 4, after the step of assembly of the interior ring 4 in the bore 5b of the exterior ring 5. The assembly ring 8 is thus flush with the radial wall of the groove 44 which is situated axially on the side of the flange 9. As a result of its configuration, the assembly ring 8 abuts the retention ring 6 during the insertion of the assembly shaft 11 into the bore 4b of the interior ring 4 of the swivel joint 1. The flange 9 of the assembly ring 8 forms a rim or a contact surface which extends from the exterior diameter of the assembly ring 8, thus making the flange 9 abut the interior ring 4 of the swivel joint 1, when the assembly ring 8 is inserted into the bore 4b of the interior ring 4 of the swivel joint 1, in a configuration as shown in figures [Fig.3], [Fig.4] and [Fig.5]. In order to proceed with the assembly of the unit 10 by means of the assembly tooling as previously described, the process is as follows. In a first stage, a step is carried out of preparation of the assembly tooling. During this step, the retention ring 6 is positioned on the first bearing Pl of the first part 11a of the assembly shaft 11, the sleeve 2 is inserted on the second part lib of the shaft 11, and the assembly ring 8 is inserted into the interior ring 4 of the swivel joint 1, until the flange 9 abuts the interior ring 4. Once the tooling has been arranged in an assembly configuration as shown in [Fig.3], and before the step of insertion of the assembly ring 8 into the bore 4b of the interior ring 4, a step is carried out of assembly of the interior ring 4 into the bore 5b of the exterior ring 5. Then, as illustrated in [Fig.4] and [Fig.5], the first part 11a of the assembly shaft, axially opposite the second part lib of the shaft 11 on which the sleeve 2 is positioned, is inserted into the bore 4b of the interior ring 4. During this axial thrusting step, the assembly ring 8 is retained in order for the retention ring 6 to abut the cylindrical body 8a of the assembly ring 8. By this means, during the axial thrust action, the retention ring 6 abutting the cylindrical body 8a of the assembly ring 8 will be driven in sliding by resilient deformation of the first part 11a of the assembly shaft, passing in succession via the bearings Pl, P2 and P3 as previously described. In fact, at each axial thrust of the assembly shaft 11, a force is applied in order to thrust the shaft 11 through the bore 4b of the interior ring. By maintaining the assembly ring 8 abutting the ring 6, this force of the assembly shaft 11 is transmitted to the abutment of the assembly ring 8, which will force the ring 6 to slide along the first part 11a of the shaft 11, adapting its diameter to the different bearings Pl to P3 by resilient deformation. The abutment of the assembly ring 8 also makes it possible to ensure that the ring 6 is retained along the part 11a of the assembly shaft, thus preventing premature disengagement until it is progressively inserted into the groove 44 of the interior ring. Thus, by means of the abutment of the retention ring 6 during the axial thrust of the assembly shaft 11, the assembly ring 8 drives the ring 6 in sliding along the first part 11a of the shaft, passing the bearings Pl to P3 in succession, until the ring 6 is inserted into the groove 44 of the interior ring. The step of axial thrusting of the shaft 11 is then continued, and at this stage, the retention ring 6, positioned at the third bearing P3 of the part 11a of the assembly shaft 11, is already partly accommodated in the groove 44, sufficiently to block axial movement of the interior ring 4. Finally, the step of axial thrusting of the assembly shaft 11 into the interior of the bore 4b of the interior ring 4 is continued, until the retention ring 6 is inserted into the interior of the groove 22 of the sleeve 2, by resilient return, when the grooves 22 and 44 are opposite one another, and the sleeve 2 and the interior ring 4 of the swivel joint 1 are rendered integral axially. In addition, once the assembly tooling has been removed, it can be envisaged to carry out a step of verification to ensure that the retention ring 6 is correctly positioned in the grooves 22 and 44 provided respectively on the exterior surface 2a of the sleeve 2, and in the bore 4b of the interior ring 4 of the swivel joint 1. In order to verify that the sleeve 2 and the interior ring 4 have been rendered integral axially, the sleeve is slid in both axial directions, so as to ensure that the unit cannot be dismantled. Optionally, an axial mechanical gap present can be tolerated during assembly of the sleeve 2 and 5 the interior ring 4 of the swivel joint 1. This mechanical gap corresponds to limited axial displacement of the sleeve 2 assembled in the bore 4b of the interior ring 4 of the swivel joint 1.

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