EP2466397B1 - Rotating clock component with peripheral guide - Google Patents

Description

Field of the invention

The invention relates to a watch mobile, chosen from an oscillator mechanism, or an escape mechanism, or a display mechanism, or a time-setting train, or a striking mechanism, or a mechanism for calendar, or a chronograph mechanism, or a counter mechanism, or a split-second mechanism, said mobile having a first guide surface arranged to cooperate in a complementary manner, directly or indirectly, with a second guide surface associated with a bridge, for pivotally mounting said mobile relative to said bridge about a pivot axis.

The invention also relates to a watch movement comprising at least one bridge and at least one such mobile

The invention also relates to a timepiece comprising at least one such watch movement, and / or at least one bridge and at least one such mobile.

The invention relates to the field of watch mechanisms, and in particular the field of mechanical watches.

Background of the invention

Very often, the performance of watch movements, or the possibility of housing complications or particular functionalities, are limited by the need to guide the pivoting mobiles by pivots fixed on plates or bridges. These guides are generally made, at least for mobile high angular speed, by the cooperation, each side of the mobile, between an axis that includes this mobile, and a stone that includes the plate or bridge.

Cantilever mountings, which would clear the space at least one side of the mobile, to accommodate other components of the movement, are rare, because of the care required to manufacture them, and high cost associated with their manufacture. An example is provided by the patent CH 682 871 in the name of FREDERIC PIGUET, for the manufacture of an ultra-thin movement, in which all the mobiles are mounted cantilever on a single plate, each using a ball bearing mounted, a part on the plate, and on the other hand on an axis that includes the mobile. In this same patent, a ratchet is drum-shaped surrounding the barrel, and is rotated on its periphery by three rollers each rotated on a ball bearing, and the barrel is pivoted in the ratchet by means of a ball bearing. Such an arrangement greatly improves accessibility within the movement compared to conventional movements, but the mobiles remain equipped with small diameter axes, and their adjustment in the bearings requires a high precision, and it is necessary to provide axial holding means. This axial retention can be done by shrinking the axis in the inner race of the bearing, which spreads its application to mobiles made of fragile materials such as silicon or the like.

It is also known, for large mobiles, and slow angular velocity, such as vortices, carousels, or barrels, a maintenance on a relatively large diameter range and with a ball bearing thick, as in the patent CH 687 795 in the name of OMEGA, which describes a cantilevered vortex supported on its base only by such a bearing. A flying carousel like that of the patent application EP 1 995 650 on behalf of BLANCPAIN has a cage carried by a mobile large diameter, carried by a ball bearing attached to a bridge.

However, these applications only relate to high-inertia mobiles, and there is no known alternative to conventional guidance axis and pivot for mobile lower inertia, and / or higher angular velocity.

The document is still known FR 2 886 995 A1 in the name of SEIKO INSTR INC, which describes a self-winding watch with oscillating weight with external ball bearing.

The document CH 700 673 A2 in the name of GESCHWIND PETER still describes a movement where the barrel, the gear train and the exhaust are not carried by bridges, but only by a central ball bearing.

Moreover, it is generally necessary to equip the pivots of the most sensitive organs, such as those of the regulating mechanism, by shock absorbers, which represent a significant cost and bulk.

For these same regulating mechanisms, it is still necessary to limit the influence of the play compensations of the pivots according to the position in the space of the timepiece, which generally lead to different operating parameters according to this position, and, in particular, to variations in the amplitude of the oscillation of the rockers.

Summary of the invention

The invention proposes to overcome the drawbacks of the prior art by proposing a guidance of mobiles, in particular watch mobiles of lower inertia, or / and of greater angular velocity, which guarantees a perfect and identical guidance in all cases. positions, a very low sensitivity to shocks, and which releases, in a complicated timepiece, space to accommodate complications without the hindrance of trees making it difficult to insert these mechanisms of complication.

When, in a preferred but nonlimiting application, the invention relates to the guidance of rockers, it ensures the regularity of the amplitude of oscillation regardless of the position of the balance in space. For this purpose, the invention relates to a watchmaker according to independent claim 1.

According to another characteristic of the invention, said first guide surface constitutes an inner race of ball rolling.

According to another feature of the invention, said mobile constitutes, with said bridge on the one hand, and a plurality of balls on the other hand, a ball bearing of which said first guide surface constitutes an internal raceway of said balls. , and an outer bearing race of said balls is constituted by said second guide surface that includes said bridge or which is attached to said bridge.

According to another characteristic of the invention, said mobile is made of silicon or a material derived from MEMS or "LIGA" technologies.

According to another characteristic of the invention, said mobile comprises a plurality of balls and constitutes a ball bearing of which said first guide surface constitutes an internal raceway of said balls, and said mobile has an outer cage comprising said second guide surface. which constitutes an outer race of rolling said balls, said outer cage being arranged to be mounted on said bridge.

The invention also relates to a watch movement comprising at least one bridge and at least one such mobile, characterized in that said at least one bridge comprises at least one surface which either constitutes said second guide surface and is then of revolution about said pivot axis D, or is arranged to receive an outer cage comprising said second guide surface oriented about said pivot axis D, said second guide surface being arranged to cooperate coaxially with said first guide surface that includes said mobile, either directly or through balls.

According to a characteristic of the invention, said bridge comprising said second guide surface, and said mobile having said first guide surface, constitute, with a plurality of balls inserted and held between said second guide surface and said first guide surface, a ball bearing.

The invention also relates to a timepiece comprising at least one such watch movement, and / or at least one bridge and at least one such mobile, characterized in that said at least one bridge comprises at least one surface which, or constitutes said second guide surface and is then of revolution about said pivot axis, or is arranged to receive an external cage comprising said second guide surface centered around said pivot axis, said second guide surface being arranged to cooperate coaxially with said first guide surface that includes said at least one mobile, either directly or by means of balls.

When, in a preferred but nonlimiting application, the invention relates to the guidance of rockers, it ensures the regularity of the amplitude of oscillation regardless of the position of the balance in space.

Brief description of the drawings

• la figure 1 représente, de façon schématisée et en vue de dessous, un mobile, en l'occurrence un balancier-spiral d'horlogerie, dont la serge du balancier constitue une surface de guidage intérieure d'un roulement à billes, dont la cage extérieure est chassée dans un pont, ce balancier-spiral étant monté caréné dans ce pont;
• la figure 2 représente, de façon schématisée et en vue de dessus, le mobile de la figure 1 ;
• la figure 3 représente, de façon schématisée et en élévation, le mobile de la figure 1 ;
• la figure 4 représente, de façon schématisée et en coupe par son axe de pivotement, le mobile des figures 1 à 3, en position de montage avec la cage extérieure du roulement chassée dans le pont ;
• la figure 5 représente, de façon schématisée et en perspective en vue de dessus, le mobile de la figure 1 ;
• la figure 6 représente, de façon schématisée et en perspective en vue de dessous, le mobile de la figure 1,
• la figure 7 représente, de façon schématisée et en coupe par un plan passant par son axe de pivotement, un détail de la périphérie d'un mobile selon une variante de l'invention ;
• la figure 8 représente, de façon analogue à la figure 7, un détail d'une autre variante de l'invention,
• la figure 9 représente, de façon schématisée et en vue de dessous, un mobile, en l'occurrence un balancier-spiral d'horlogerie, dont une douille

Other features and advantages of the invention will appear on reading the detailed description which follows, with reference to the appended drawings, in which:

• the figure 1 represents, schematically and in a view from below, a mobile, in this case a clockwork balance-spring, whose balance lever constitutes an inner guide surface of a ball bearing, whose outer cage is driven away in a bridge, this spiral-balance being mounted careened in this bridge;
• the figure 2 represents, schematically and in a top view, the mobile of the figure 1 ;
• the figure 3 represents, schematically and in elevation, the motive of the figure 1 ;
• the figure 4 represents, schematically and in section through its pivot axis, the mobile of Figures 1 to 3 , in mounting position with the outer race of the bearing driven into the deck;
• the figure 5 represents, schematically and in perspective in a view from above, the mobile of the figure 1 ;
• the figure 6 represents, schematically and in perspective in view from below, the mobile of the figure 1 ,
• the figure 7 represents, schematically and in section through a plane passing through its pivot axis, a detail of the periphery of a mobile according to a variant of the invention;
• the figure 8 represents, in a similar way to figure 7 , a detail of another variant of the invention,
• the figure 9 represents, schematically and in a view from below, a mobile, in this case a balance-spiral clock, including a socket

• la figure 10 représente, de façon schématisée et en vue de dessus, le mobile de la figure 9 ;
• la figure 11 représente, de façon schématisée et en coupe selon le tracé AA de la figure 10, le mobile de la figure 9, en position de montage avec la cage extérieure du roulement chassée dans le pont ;
• la figure 12 représente, de façon schématisée et en coupe selon le tracé BB de la figure 10, le mobile de la figure 9 ;
• la figure 13 représente, de façon schématisée et en perspective en vue de dessus, le mobile de la figure 9 ;
• la figure 14 représente, de façon schématisée et en perspective en vue de dessous, le mobile de la figure 9.

fixed on the rocker is an inner guide surface of a ball bearing, the outer cage is driven in a bridge, the sprung balance being mounted flying in this bridge;

• the figure 10 represents, schematically and in a top view, the mobile of the figure 9 ;
• the figure 11 represents, schematically and in section along the line AA of the figure 10 , the mobile of the figure 9 , in mounting position with the outer race of the bearing driven into the deck;
• the figure 12 represents, schematically and in section along the line BB of the figure 10 , the mobile of the figure 9 ;
• the figure 13 represents, schematically and in perspective in a view from above, the mobile of the figure 9 ;
• the figure 14 represents, schematically and in perspective in view from below, the mobile of the figure 9 .

Detailed Description of the Preferred Embodiments

The invention relates to the field of watch mechanisms, and in particular the field of mechanical watches.

The invention relates, as visible in the figures, a mobile 1 clock. This mobile 1 is of the type of lower inertia, and / or of greater angular velocity, and is chosen from an oscillator mechanism, or an escape mechanism, or a display mechanism, or a setting wheel. time, or a striking mechanism, or a calendar mechanism, or a chronograph mechanism, or a counter mechanism, or a split-second mechanism. This list is by no means exhaustive of the possibilities of the invention, but includes the preferred applications. This mobile 1 is arranged to pivot about a pivot axis D.

According to the invention, the mobile 1 comprises a first guide surface 2, which is arranged to cooperate in a complementary manner, directly or indirectly, with a second guide surface 3 associated with a bridge 50, for the pivotal mounting of the mobile 1 relative to the bridge 50 about a pivot axis D.

According to the invention, the first guide surface 2 is of revolution about the pivot axis D and is located in the vicinity of a median plane P that comprises the mobile 1 and which is substantially orthogonal to said pivot axis D, of way to maintain this mobile 1 recessed or cantilever relative to the bridge 50.

Advantageously, the mobile 1 is free of guide shaft in the direction of the pivot axis D on either side of the guide surface 2, which allows its use in ultra-thin movements, and which makes it possible to use for other applications the outer space on either side of the mobile 1.

Preferably, the first guide surface 2 is on the largest possible diameter of the mobile 1, and preferably at its periphery, that is to say in the region radially furthest from the pivot axis D.

In a preferred application, the mobile 1 comprises, on either side of this median plane P, first application means 4 of a first pair with respect to the pivot axis D and second means of application of a second pair with respect to the pivot axis D, so as to distribute the stresses exerted on the moving part 1 at these first application means 4 and these second application means 5 on the part of and other than the first guide surface 2.

As visible on the Figures 5 and 6 preferably, the first guiding surface 2 is constituted by at least one peripheral guiding surface 6 that the mobile 1 comprises, or / and by at least one runway surface 7 that comprises at least one lane 8 attached to the mobile 1. Preferably, as visible on the figure 7 , a peripheral surface 6 is integrated in the mobile 1, and a removable track 8 is reported on the latter, which allows the insertion of intermediate components, such as beads 11 in this case. The first guide surface 2 may also be constituted by two tracks 8 attached to the mobile 1, as visible on the figure 8

Naturally, a number of tracks 8 greater than 2 is possible, but in practice it is preferably limited to two essentially for reasons of size and cost of production.

In a preferred manner, according to the invention, the first guiding surface 2 constitutes an internal race 9 of ball bearing 11.

In a manner peculiar to the invention, the watchmob 1 constitutes, alone or with the bridge 50, a ball bearing 10.

In a first version, the mobile 1 constitutes, with said bridge 50 on the one hand, and a plurality of balls 11, on the other hand, a ball bearing 10 whose first guide surface 2 constitutes an internal race track 9. these balls 11, and an outer race of rolling balls 11 is constituted by the second guide surface 3 that includes the bridge 50, or which is reported on the bridge 50, for example at a ring or the like. In an advantageous variant of this first version, the mobile 1 is monobloc. Preferably, it is made of silicon or a material from MEMS or "LIGA" technologies, which allows it to accumulate complex geometry, very precise tolerances, and elasticity of certain zones that it comprises. These materials are of particular interest for the manufacture, in particular, low inertia mobiles and high angular speed, such as rockers and the like. The invention provides an even greater flexibility of use of such mobiles, by freeing their design from the presence of guide pins at the pivot axis. The combination of the type of ducted or flying assembly proposed by the invention, and such materials, is therefore particularly advantageous.

In a second version, preferred because more versatile, the mobile 1 comprises a plurality of balls 11 and is a ball bearing 10 whose first guide surface 2 constitutes an inner race 9 rolling balls 11. The mobile 1 then comprises a external cage 12, which comprises the second guide surface 3, which constitutes an outer race of rolling balls 11, this outer cage 12 being arranged to be mounted on the bridge 50. The mobile 1 can thus be a subset ready to to be mounted on a bridge 50. Advantageously, the outer cage 12 is then made of a non-brittle material, especially a metal alloy, allowing its insertion by driving into a housing or a bore of the bridge 50. Preferably, in this second version , the mobile 1 consists of this outer cage 12, the plurality of balls 11, and a one-piece body which is made, as above, in silicon or in a mat riau from the MEMS or "LIGA".

A mixed embodiment is also possible with a one-piece mobile body of silicon or the like, and the variant with one or more tracks 8 attached to the periphery 2 of the mobile 1 is advantageous when using a mobile body 1 of fragile material or sensitive to shocks.

In a particularly advantageous application of the invention, the mobile 1 is a balance spring 13 or a rocker 14 having a serge 15, and the first guide surface 2 is on the periphery of this serge 15, and preferably on the largest diameter of said serge 15 relative to the pivot axis D. The first torque application means 4 are constituted by a pin 16 of plate 17 that includes the spring balance 13 or rocker 14 of a first side of the serge 15, and the second torque application means 5 are constituted by a pin 18 when the mobile 1 is a balance-spiral 13, or a spiral 19 when the mobile 1 is a rocker 14. Preferably, the first surface of 2 is directed radially towards the opposite side to the pivot axis D.

The figures illustrate a mobile 1 constituted by a sprung balance 13 comprising a rocker 14 provided with a plate 17 and a pin 16 so as to cooperate with an exhaust mechanism, and a spiral 19 conventionally attached to a point d attaches to the balance 14 on the one hand, and a pin 18 fixed to a plate or a bridge 50, which is hereinafter referred to as "bridge", on the other hand.

The invention also relates to a watch movement 100, comprising at least one bridge 50 and at least one such mobile 1. According to the invention, this bridge 50 comprises at least one surface which either constitutes the second guide surface 3 and is then of revolution about the pivot axis D, or is arranged to receive an outer cage 12 comprising the second guide surface 3 centered around the pivot axis D, this second guide surface 3 being arranged to coaxially cooperate with the first guide surface 2 that this mobile 1 comprises, either directly or by means of balls 11.

In a preferred manner and as visible in the figures, in this movement 100, the bridge 50 comprising the second guide surface 3, and the mobile 1 having the first guide surface 2, constitute, with a plurality of balls 11 inserted and maintained. between the second guide surface 3 and the first guide surface 2, a ball bearing 10.

Preferably, the balls 11 are kept at a distance from one another by spacing means 20, such as a basket or a plurality of housings, that includes the bridge 50, and / or the mobile 1, or / and the movement 100.

In a preferred application shown in the figures, the movement 100 comprises a balance-spring or a balance, and the bridge 50 comprises a housing 21 of a peg 18 for hooking a hairspring and fixing means or / and position adjustment 22 of such a stud 18, or comprises means for fixing a secondary bridge comprising such a housing 21 of a pin 18 and such fixing means and / or position adjustment 22. These can be made in the form of a screw bearing on one or more surfaces of the peak to adjust its position, for example pivoting in the case of a peg, or height, or other.

In the application shown in Figures 1 to 6 , the movement 100 comprises a mobile 1 which is a spiral balance 13 streamlined in a bridge 50 and comprises a spiral 19 fixed to a pin 18 itself attached to the bridge 50 or a secondary bridge fixed on the bridge 50. L The invention thus makes it possible to produce a completed and pre-set subassembly comprising a bridge, a bolt, a sprung balance, means for pivoting the sprung balance, which is ready to be mounted on another bridge or on another plate, thus rationalizing the assembly and the adjustments, and simplifying the final assembly. The invention also makes the after-sales service easier since it may be sufficient to exchange a simple block consisting of such a subset.

In the application shown in Figures 9 to 14 , the movement 100 comprises a mobile 1 which is a flying balance, which is not fully ducted, but guided on an intermediate diameter, at a bushing 23 that includes the balance 14 or which is fixed thereto, this sleeve 23 then carries the first guide surface 2. This arrangement allows easy reutilization existing balances, which can be modified by removing their guide pins and by laying by driving, gluing, or the like, such a bushing 23 .

The invention also relates to a timepiece 1000 comprising at least one watch movement 100, or / and at least one bridge 50 and at least one such mobile 1.

In this timepiece, such as a watch, at least one bridge 50 has at least one surface which either constitutes the second guide surface 3 and is then of revolution about the axis of pivoting D, or is arranged to receive an outer cage 12 comprising this second guide surface 3 centered around the pivot axis D, the second guide surface 3 being arranged to cooperate coaxially with the first guide surface 2 that comprises this mobile 1, either directly or via balls 11.

In another embodiment, the support between the first guide surface 2 and the second guide surface 3 can be made directly at the level of antagonistic surfaces, but it is difficult to ensure a sufficiently low level of friction losses. while being compatible with the great longevity required by a timepiece.

In short, by this innovative design, the invention makes it possible to ensure, for mobiles such as balances, perfect and identical guidance in all positions, a very low shock sensitivity.

The streamlined or flying arrangement of the mobile makes it possible to dispense with the guiding axes, the corresponding pivots, and releases, in a complicated timepiece, space for accommodating complications without the hindrance of shafts making difficult to insert these mechanisms of complication. In addition, lubrication problems are reduced thanks to the choice of guides made in the form of ball bearings.

The combination with mobiles made of silicon or with MEMS or "LIGA" technologies makes it possible, again, to reduce the number of components, to reduce their inertia, to increase their sizing accuracy, and thus to make their adjustments easier.

The invention further allows the production of oscillator subassemblies ready to be mounted, pre-adjusted and ready for use.

Claims (18)

1. Timepiece wheel set (1), being a member part of an oscillator mechanism or of an escapement mechanism, wherein said wheel set (1) comprises a first guide surface (2) arranged to cooperate in a complementary manner, directly or indirectly with a second guide surface (3) associated with a bridge (50), for pivotably mounting said wheel set (1) relative to said bridge (50) about a pivot axis (D), said first guide surface (2) is generated by revolution about said pivot axis (D), is located on a median plane (P) of said wheel set (1) said median plane (P) which is substantially orthogonal to said pivot axis (D), so as to keep said wheel set (1) careened or in a cantilever arrangement relative to said bridge (50), and wherein said wheel set (1) is guided at a distance from said pivot axis (D), characterized in that said wheel set (1) includes, on both sides of said median plane (P), a first means (4, 16) of applying torque relative to said pivot axis (D) and a second means (5, 18, 19) of applying torque relative to said pivot axis (D), so as to distribute the stresses exerted on said wheel set (1) at said first torque applying means (4, 16) and said second torque applying means (5, 18, 19) on both sides of said first guide surface (2).
2. Timepiece wheel set (1) according to claim 1, characterized in that said first guide surface (2) is formed by at least one peripheral guide surface (6) comprised in said wheel set (1), and/or by at least one raceway surface (7) comprised in at least one raceway (8) added to said wheel set (1).
3. Timepiece wheel set (1) according to claim 2, characterized in that said peripheral guide surface (6) is integrated in said wheel set (1) and in that it includes a said raceway (8) added to said wheel set (1), said raceway (8) being removable to allow the insertion of balls (11).
4. Timepiece wheel set (1) according to claim 1, characterized in that said first guide surface (2) is formed by the combination of two raceways (8) added to said wheel set (1).
5. Timepiece wheel set (1) according to one of the preceding claims, characterized in that it forms, with said bridge (50) on the one hand, and a plurality of balls (11) on the other hand, a ball bearing (10) wherein said first guide surface (2) forms an internal raceway (9) for said balls (11) and wherein an external raceway for said balls is formed by said second guide surface (3) comprised in said bridge (50) or which is added to said bridge (50).
6. Timepiece wheel set (1) according to the preceding claim, characterized in that it is single-piece and made of silicon or in a material derived from MEMS or "LIGA" technologies.
7. Timepiece wheel set (1) according to claim 5 or 6, characterized in that it includes a plurality of balls (11) and forms a ball bearing (10) wherein said first guide surface (2) forms an internal raceway (9) for said balls (11) and in that said wheel set (1) comprises an external ball race (12) including said second guide surface (3) which forms an external raceway for said balls (11), said external ball race (12) being arranged to be mounted on said bridge (50).
8. Timepiece wheel set (1) according to one of the preceding claims, characterized in that said first continuous guide surface (2) is over the largest possible diameter of revolution about said pivot axis (D) of said wheel set (1) at the periphery thereof.
9. Timepiece wheel set (1) according to one of the claims 1 to 7, characterized in that it is a sprung balance (13) or a balance (14) comprising a rim (15), and in that said first guide surface (2) is at the periphery of said rim (15).
10. Timepiece wheel set (1) according to claim 9, characterized in that said first means (4) of applying torque is formed by an impulse pin (16) of a roller (17) comprised in said sprung balance (13) or balance (14) on a first side of said rim (15), and in that said second means (5) of applying torque is formed by a balance spring stud (18) when said wheel set (1) is a sprung balance (13) or by a balance spring (19) when said wheel set (1) is a balance (14).
11. Timepiece wheel set (1) according to claim 9 or 10, characterized in that said first guide surface (2) is located on the largest diameter of said rim (12) relative to said pivot axis (D).
12. Timepiece wheel set (1) according to claim 9 or 10, characterized in that said timepiece wheel set (1) is a flying balance, and in that said first continuous guide surface (2) is carried by a sleeve (23) comprised in said balance (14) or a balance (14) comprised in said sprung balance (13), or which is fixed to said balance (14), on an intermediate diameter which is smaller than the largest diameter of said rim (15) relative to said pivot axis (D).
13. Timepiece movement (100) including at least one bridge (50) and at least one wheel set (1) according to one of the preceding claims, characterized in that said at least one bridge (50) comprises at least one surface which, either forms said second guide surface (3) and is then generated by revolution about said pivot axis (D), or is arranged to receive an external ball race (12) comprising said second guide surface (3) centred on said pivot axis (D), said second guide surface (3) being arranged to cooperate coaxially with said first guide surface (2) comprised in said at least one wheel set (1), either directly or via balls (11).
14. Movement (100) according to the preceding claim, characterized in that said bridge (50) comprising said second guide surface (3) and said wheel set (1) comprising said first guide surface (2) form a ball bearing (10) with a plurality of balls (11) inserted and held between said second guide surface (3) and said first guide surface (2).
15. Movement (100) according to the preceding claim, characterized in that said balls (11) are held at a distance from each other by a spacer means (20) comprised in said bridge (50) and/or said wheel set (1) and/or said movement (100).
16. Movement (100) according to one of claims 13 to 15, characterized in that said at least one bridge (50) includes a housing (21) for a balance spring stud (18) for attaching a balance spring and a means of securing and/or adjusting the position (22) of said stud (18), or comprises a means of securing a secondary bridge comprising a housing (21) for a stud (18) and a securing and/or position adjusting means (22).
17. Movement (100) according to one of claims 13 to 16, characterized in that said wheel set (1) is a sprung balance (13) careened in said bridge (50) and includes a balance spring (19) fixed to a balance spring stud (18) which is in turn secured to said bridge (50) or to a secondary bridge secured to said bridge (50).
18. Timepiece (1000) including at least one timepiece movement (100) according to one of claims 13 to 17 and/or at least one bridge (50) and at least one wheel set (1) according to one of claims 1 to 12, characterized in that said at least one bridge (50) includes at least one surface which either forms said second guide surface (3) and is then generated by revolution about said pivot axis (D), or is arranged to receive an external ball race(12) comprising said second guide surface (3) centred on said pivot axis (D), said second guide surface (3) being arranged to cooperate coaxially with said first guide surface (2) comprised in said at least one wheel set (1) either directly or via balls (11).

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