Improved articulated component, and mechanical system comprising such a component

Abstract

An articulated component (1) with one degree of freedom, comprising only two concentric metal rings (3, 4) which are rotatable relative to one another about a central axis (X1) and define a friction interface (5) therebetween, the component (1) comprising sealing means comprising: - a flange (7) and a first washer (8) disposed between the inner ring (4) and the flange (7); and - a first shoulder (9) projecting into the outer ring (3) and a second washer (10) disposed between the inner ring (4) and the first shoulder (9); the first washer (8) and the second washer (10) being made of a self-lubricating material, and being received in the inner diameter of the outer ring (3); the flange (7) being made of steel and fixed in a second shoulder (11) hollowed into the edge of the outer ring (3).

Description

Description Title of the invention: Improved articulated component, and mechanical system comprising such a component technical field

[0001] The present invention relates to an articulated component comprising only two concentric rings movable relative to each other and defining a friction interface between them. The invention also relates to a mechanical system comprising such a component.

[0002] The field of the invention is that of guiding elements ensuring a guiding function in translation or rotation, in continuous or alternating motion. Previous art

[0003] Typically, such a guide element consists of a ring, designed for mounting with articulation and / or sliding capacity of an element such as an axle or shaft.

[0004] In practice, such mechanical systems are subjected to significant stresses during operation: high pressure, corrosion, abrasion, and shocks. To improve their lifespan, lubrication is provided between the bushing and the shaft.

[0005] The ring may be fitted with arrangements acting as a grease reservoir, as described for example in documents EP0987456, WO2014091123 and WO201 4091124 on behalf of the Applicant.

[0006] When the mechanical system is in operation, grease gradually flows from the fittings to lubricate the friction interface between the ring and the shaft. Thus, the fittings allow for lubrication only during assembly, or with very long intervals between lubrications.

[0007] The Applicant has extensive expertise in the field of guidance systems, and continually seeks to improve existing systems.

[0008] She has already perfected the earlier art mentioned above with the teaching of document W02020 / 012092, and hereby aims to further perfect the teaching of said document W02020 / 012092. Description of the invention

[0009] One of the aims of the present invention is therefore to further improve the teaching of document W02020 / 012092 by proposing an improved articulated component, exhibiting in particular excellent resistance to wear and seizing, and an improved service life.

[0010] The Applicant carried out internal tests on a test bench which simulates rotation / oscillation cycles, of which 50,000 cycles on the bench correspond to approximately 500 hours of operation on the machine.

[0011] These tests have highlighted: - that a single internal ring free to rotate allows the friction surfaces to be renewed; - that the first and second washers made of a self-lubricating material prevents steel / steel contact while providing good tribological behavior, and limiting crushing.

[0012] Thus, an articulated component of this type, with arrangements capable of acting as a lubricant reservoir on the internal cylindrical friction surface of the outer ring, and on the internal cylindrical friction surface of the inner ring, allows for a number of cycles 4 times greater at projected pressures of 50 MPa.

[0013] It is for this reason that the Applicant selected features from the various possible embodiments described in document W02020 / 012092 to develop a single-degree-of-freedom articulated component comprising only two concentric metallic rings, rotating relative to each other around a central axis, defining a friction interface between them, and including: - an outer ring having a cylindrical internal friction surface, and - an inner ring having an external cylindrical friction surface and a cylindrical internal friction surface intended to receive a moving element guided by the component in rotation, oscillation and / or translation.

[0014] In which: - the friction interface is defined directly between the internal cylindrical friction surface of the outer ring and the external cylindrical friction surface of the inner ring, said friction interface receives a lubricant; - the cylindrical internal friction surface of the outer ring and the cylindrical internal friction surface of the inner ring have arrangements suitable for acting as a lubricant reservoir.

[0015] The component also includes sealing means designed to prevent lubricant leakage from the friction interface and to limit the axial play of the inner ring relative to the outer ring; said sealing means include: - a flange and a first washer on one side of the interface, the first washer being interposed between the inner ring and the flange and; - a first protruding shoulder inside the outer ring and a second washer on a second side of the friction interface, the second washer being interposed between the inner ring and the first shoulder.

[0016] The first washer and the second washer are made of a self-lubricating material.

[0017] In parallel, the Applicant identified that the freedom of movement of the inner ring generates axial forces during operation which can lead to premature wear of the washers as well as a separation of the stop flange in translation.

[0018] Thus, to remedy these problems, the flange is made of steel, preferably stainless steel, and fixed in a second shoulder cut into the edge of the outer ring, and is preferably welded to said outer ring with a continuous weld bead, such as with a continuous laser weld bead, instead of being a shrink-fit assembly, which structurally remains easily identifiable by a person skilled in the art.

[0019] Pull-out force tests were carried out by the Applicant, who found that a force of more than 24,000 N was required to pull off a flange welded by a continuous laser weld bead, versus about 9000 N for a flange welded with a discontinuous laser weld bead, and about 2000 N for a flange assembled by shrink fitting.

[0020] Furthermore, in order to reduce the axial forces experienced by the friction washers and the flange, the washers are received in the internal diameter of the outer ring, that is to say against the internal cylindrical friction surface of the outer ring, unlike the prior art in which the washers are received in a groove cut into the internal cylindrical friction surface of the outer ring.

[0021] In this way, it is possible to increase the bearing surfaces of the inner ring, which is free to rotate, and to reduce the stresses on the washers as well as on the flange.

[0022] Stress determination tests were carried out by the Applicant with an applied radial load of 380 kN, a radial clearance between the outer ring and the inner ring of 0.3 mm and an axial clearance of 0.3 mm in total between the inner ring and the first and second washers.

[0023] The results of these tests show a stress of 400MPa experienced with the previous design, i.e. with the self-lubricating material washers received in a groove cut into the internal cylindrical friction surface of the outer ring, which led to the breakage of one of the washers because the stress experienced was greater than the breaking limit of 370MPa of the washer.

[0024] Whereas with the design according to the invention, i.e. with the washers in contact with the internal cylindrical friction surface of the outer ring, the stress experienced was 300MPa, which did not cause the washer to break.

[0025] Furthermore, the Applicant identified that the different clearances also affected the performance of the friction washers.

[0026] Thus, advantageously, the component according to the invention comprises a radial clearance between the outer ring and the inner ring of between 0.05 mm and 0.3 mm, and / or a total axial clearance between the inner ring and the first and second washers of between 0.1 mm and 0.3 mm.

[0027] In particular, stress determination tests were carried out by the Applicant with a radial load of 380 kN applied in the inner ring, with the aforementioned design, i.e. with the friction washers in contact with the internal cylindrical friction surface of the outer ring, which show that with a radial clearance of 0.05 mm and an axial clearance of 0.1 mm, the value of the stress experienced by the washer is reduced to approximately 280 MPa.

[0028] Advantageously, the first and second washers are made of composite material to offer better resistance to the stresses suffered, and preferably they have a fibrous reinforcement such as a woven structure which has in particular excellent friction and wear resistance properties without lubrication even under heavy load.

[0029] These washers, for example, are made from a homogeneous polymer woven throughout their entire thickness. Such a washer has mechanical properties similar to those of brass and does not require lubrication.

[0030] To further improve wear resistance, the internal cylindrical friction surface of the outer ring and the internal cylindrical friction surface of the inner ring have preferably undergone a hardening surface treatment such as a nitrocarburizing treatment, and are for example varnished, and the second shoulder cut into the edge of the outer ring is devoid of surface treatment and any varnish so as not to weaken the laser weld of the flange.

[0031] In order to reduce wear on the friction interface between the inner and outer rings, the external cylindrical friction surface of the inner ring has an arithmetic mean roughness Ra of less than 0.8.

[0032] Preferably, arrangements suitable for use as a lubricant reservoir are in the form of cavities with a circular cross-section, regularly distributed around the central axis.

[0033] Finally, the invention also relates to a mechanical system, comprising a component articulated according to at least one of the aforementioned characteristics, and a movable element guided by the component in rotation, oscillation and / or translation. Brief description of the drawings

[0034] [Fig.1] is a perspective view of the articulated component of the invention.

[0035] [Fig. 2] is a longitudinal cross-sectional view of the component in Figure 1.

[0036] [Fig. 3] is a plan view of a mechanical system comprising the articulated component of Figure 1, and a movable element guided by the component.

[0037] [Fig. 4] is a cross-sectional view of a mechanical system in the form of a ball joint and comprising the component according to the invention. Detailed description of the invention

[0038] With reference to figures 1 to 4, the invention relates to an improved articulated component (1), and a mechanical system (S) comprising such a component and a movable element (2), such as an axis, guided by the component (1) in rotation (pivoting in a single direction, generally over several turns), oscillation (pivoting in two alternating directions, generally over a portion of a turn) and / or translation (displacement along the axial direction).

[0039] The articulated component (1) comprises only two concentric steel rings (3, 4) that are movable relative to each other in rotation around a central axis (X1). The two rings (3, 4) define a friction interface (5) between them which receives a lubricant, preferably grease.

[0040] The two rings (3, 4) include an outer ring (3) and an inner ring (4).

[0041] The outer ring (3) has a cylindrical internal friction surface and an external bearing surface, preferably cylindrical. The inner ring (4) has a cylindrical external friction surface and a cylindrical internal friction surface.

[0042] The internal cylindrical friction surface of the outer ring and the internal cylindrical friction surface of the inner ring have arrangements (6) suitable for serving as a lubricant reservoir, preferably in the form of cavities of circular cross-section, regularly distributed around the central axis (X1), and have undergone, for example, a nitrocarburizing surface treatment and are varnished to improve wear resistance.

[0043] To perform nitrocarburizing, the part is immersed in a bath containing molten salts or exposed to a nitrocarburizing gas at high temperatures (generally between 500°C and 630°C). The surface of the part reacts with nitrogen and carbon to form a compound layer (often composed of iron nitrides and carbon nitrides). This compound layer is typically between 5 µm and 30 µm thick. Beneath the compound layer, a diffusion zone forms, where the added elements diffuse into the base metal, creating a hardness gradient and improving mechanical strength. The thickness of this zone is typically between 100 µm and 500 µm.

[0044] The cylindrical internal friction surface of the outer ring (3) and the cylindrical external friction surface of the inner ring (4) define the friction interface (5) between them, radially to the central axis (X1). The cylindrical external friction surface of the inner ring (4) is hardened and has an arithmetic mean roughness of less than 0.8, for example obtained by grinding, and preferably it is polished to have an arithmetic mean roughness of less than 0.4.

[0045] The outer surface of the outer ring is designed for mounting the outer ring (3) in a bore. The internal cylindrical friction surface of the inner ring (4) is designed to receive the moving element (2), more precisely the cylindrical outer surface of said moving element (2). Thus, the moving element (2) is guided by the component (1) in rotation, oscillation, and / or translation.

[0046] The component (1) includes sealing means designed to prevent lubricant leakage from the friction interface (5). The component (1) thus forms a lubricated, sealed structure. Relative rotation between the rings (3, 4) is therefore greatly facilitated, and the risk of seizing is reduced.

[0047] The sealing means (60) include lateral elements (62, 64, 66 and 68) limiting the axial movement of the inner ring (4) relative to the outer ring (3). More specifically, the sealing means include a flange (7) and a first washer (8) on a first side of the interface (5), with the first washer (8) interposed between the inner ring (4) and the flange (7).

[0048] The sealing means also include a first shoulder (9) and a second washer (10) on a second side of the friction interface (5), The second washer (10) is interposed between the inner ring (4) and the first shoulder (9). The elements (7, 8, 9, 10) are annular and centered on the axis (X1). The first shoulder (9) belongs to the ring (10) and forms a projecting stop inside the outer ring (3). The elements (7, 8, 10) are separate from the rings (3, 4).

[0049] The flange (7) is made of steel, preferably stainless steel for corrosion resistance, and is fixed in a second shoulder (11) machined into the edge of the outer ring (3). The flange (7) is preferably welded to said outer ring (3) with a continuous laser weld bead (12), opposite the first shoulder (9). To receive the flange (7), a hard turning operation is performed on the second shoulder (11), which serves to position and center the flange (7), to remove the surface treatment and any varnish that weakens the weld.

[0050] The washers (8, 10) are made of a self-lubricating material, for example PTFE, to improve friction between the inner ring (4) and the outer ring (3), while limiting crushing. Since the washers (8, 10) prevent steel-on-steel contact while providing good tribological behavior, they have a thickness of approximately 2 mm.

[0051] Preferably, and to improve the strength of the washers (8, 10), they are made of composite material and have fibrous reinforcement, for example, a thin woven structure, on the order of 0.1 mm, which has excellent friction and wear resistance properties without lubrication, even under heavy loads. For example, the washers (8, 10) are made from a homogeneous polymer woven throughout their entire thickness.

[0052] The washers (8, 10) are preferably received within the internal diameter of the outer ring (3), that is, against the internal cylindrical friction surface of the outer ring (3), to increase the bearing surfaces of the inner ring (4), which is free to rotate, and to reduce axial stresses on the washers (8, 10) as well as on the flange (7). The second shoulder (11) on the edge of the outer ring (3) receives only the flange (7).

[0053] To further reduce stress on the washers (8, 10) and the flange (7), component (1) includes a radial clearance between the outer ring (3) and the inner ring (4) of between 0.05 mm and 0.3 mm, and a total axial clearance between the inner ring (4) and the first and second washers (8, 10) between 0.1 mm and 0.3 mm.

[0054] The component (1) is non-spherical, meaning it does not form a ball joint. The assembled component (1) has a single degree of freedom, namely the pivot joint between the rings (3, 4) around the central axis (X1). The rings (3, 4) are freely movable in rotation relative to each other around the axis (X1), but are not freely movable in the other degrees of freedom, in translation and rotation.

[0055] In practice, it is observed that the friction interface (5) between the two rings (3, 4) is subjected to priority stress. When this interface (5) seizes, the internal friction surface of the inner ring (4) in contact with the surface of the moving element (2) takes over as the wear surface.

[0056] Thus, the invention makes it possible to propose a resistant, compact and easy-to-implement articulated component (1), in which the axial stresses on the washers (8, 10) and the flange (7) are reduced to increase the service life.

[0057] Without departing from the scope of the invention, and with reference to Figure 4, the mechanical system according to the invention can be a ball joint. To this end, the component (1) is integrated into a ball joint housing (13), and the outer ring (3) of the component (1) comprises a domed outer surface. The outer surface of the outer ring (3) then becomes a friction surface.

Claims

Demands 1. Hinged component (1) with one degree of freedom, comprising only two concentric metallic rings (3, 4), movable in rotation relative to each other around a central axis (X1), defining a friction interface (5) between them, and including: - an outer ring (3) having a cylindrical internal friction surface; - an inner ring (4) having a cylindrical external friction surface and a cylindrical internal friction surface designed to receive a movable element (2) guided by the component (1) in rotation, oscillation and / or translation; wherein: - the friction interface (5) is defined directly between the internal cylindrical friction surface of the outer ring (3) and the external cylindrical friction surface of the inner ring (4), said friction interface (5) receives a lubricant; - the cylindrical internal friction surface of the outer ring (3) and the cylindrical internal friction surface of the inner ring (4) have arrangements (6) suitable for acting as a lubricant reservoir; - the component (1) comprises sealing means designed to prevent lubricant leakage from the friction interface (5) and to limit the axial movement of the inner ring (4) relative to the outer ring (3); and wherein said sealing means comprise: - a flange (7) and a first washer (8) on a first side of the friction interface (5), the first washer (8) being interposed between the inner ring (4) and the flange (7) and; - a first shoulder (9) projecting inside the outer ring (3) and a second washer (10) on a second side of the friction interface (5), the second washer (10) being interposed between the inner ring (4) and the first shoulder (9); and in which - the first washer (8) and the second washer (10) are made of a self-lubricating material, and are received in the internal diameter of the outer ring (3), i.e. against the internal cylindrical friction surface of the outer ring; - the flange (7) is made of steel and fixed in a second shoulder (11) cut into the edge of the outer ring (3).

2. Articulated component (1) according to claim 1, characterized in that it comprises a radial clearance between the outer ring (3) and the inner ring (4) of between 0.05 mm and 0.3 mm, and / or a total axial clearance between the inner ring (4) and the first and second washers (8, 10) of between 0.1 mm and 0.3 mm.

3. Articulated component (1) according to any one of the preceding claims, characterized in that the first washer (8) and the second washer (10) are made of composite material.

4. Articulated component (1) according to claim 3, characterized in that the first washer (8) and the second washer (10) have a fibrous reinforcement.

5. Articulated component (1) according to any one of the preceding claims, characterized in that the internal cylindrical friction surface of the outer ring (3), and the internal cylindrical friction surface of the inner ring (4), have undergone a hardening surface treatment and are optionally varnished, and the second shoulder (11) cut into the edge of the outer ring (3) is devoid of surface treatment and of the optional varnish.

6. Articulated component (1) according to claim 5, characterized in that the surface treatment is a nitrocarburizing.

7. Articulated component (1) according to any one of the preceding claims, characterized in that the external cylindrical friction surface of the inner ring (4) has an arithmetic mean roughness of less than 0.

8.

8. Articulated component (1) according to any one of the preceding claims, characterized in that the arrangements (6) are in the form of cavities of circular section, regularly distributed around the central axis (X1).

9. Articulated component (1) according to any one of the preceding claims, characterized in that the flange (7) is welded to the outer ring (3) with a continuous weld bead.

10. Mechanical system, comprising an articulated component (1) according to any one of claims 1 to 9, and a movable element (2) guided by the component (1) in rotation, oscillation and / or translation 11. Mechanical system according to claim 10, characterized in that the component (1) is integrated into a ball joint housing (13), and the outer ring (3) of the component (1) comprises a domed external surface.

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