Electromechanical clock movement comprising a mobile bearing a display member and provided with a braking device

Abstract

The electromechanical timepiece movement (2) comprising an electromechanical motor (54), a display wheel (30) arranged so as to be able to be rotated by the electromechanical motor and comprising a shaft (36) intended to carry a display hand (48), and a braking device associated with the display wheel and comprising a braking spring (10) and a washer (8) arranged between the braking spring and the shaft of the display wheel, the braking spring being arranged so as to be able to generate on the display wheel, as soon as this display wheel is subjected to a rotational driving torque, a braking torque via the washer against which this braking spring presses. The washer and the braking spring are arranged so that the washer remains stationary and without rotation during normal operation.The braking spring generally exerts a pressure force towards said shaft to generate, between a lateral surface of the washer and a surface of revolution of the shaft, a friction force which generates the braking torque.

Description

Technical field of the invention

[0001] The present invention relates to an electromechanical watch movement comprising a mobile bearing a display member, in particular a hand, and provided with an anti-shake device, also called an anti-float device, formed by a braking device acting on the mobile to prevent shaking of the rotating display member and also floating of this member in the time intervals and periods when the display member is stationary. Technological background

[0002] Document CH 580301 discloses an anti-shake device for a timepiece mobile, in particular a chronograph mobile hereinafter also called a 'chrono mobile', comprising a shaft provided with a pinion, which meshes with a clutch wheel, herein called a drive wheel, forming a clutch device for a chronograph mechanism. It should be noted that a shaft provided with pivots to guide its rotation is also called an 'axis' in watchmaking.The anti-shake device of the second hand of the chronograph function is formed by a friction device comprising a wire spring bearing obliquely against said shaft which has for this purpose a truncated conical shoulder, the wire spring having a bearing point in the angle formed by this shoulder and a circular cylindrical portion, which has a diameter corresponding to the minimum diameter of the shoulder, and exerting at this location an oblique force on said shaft, so that the teeth of the pinion press against the drive wheel and a lower annular surface of the shaft, opposite said shoulder and orthogonal to the axis defined by the shaft, presses axially against a bearing in which the chronograph wheel pivots. The spring is designed to be rectilinear in the absence of stress.This spring is fixed to the movement frame on the side of a first end while a part of the side of the second end is under tension and presses against the shaft, as explained above.

[0003] For several reasons, this anti-shake device presents a problem in controlling the frictional moment of force applied to the chronograph wheel. In addition, there is nothing to adjust this frictional moment of force. Then, when the chronograph hand is withdrawn, the spring is subjected to an axial force which can damage this spring.

[0004] Document DE 6800934 U describes a solution for improving the control of the frictional force moment applied to a seconds wheel. According to the teaching of this document, the wire spring or leaf spring is fixed, at its first end part, by a riveting technique to a plate which is held in suspension by a rivet having a head, with a slot in the manner of a screw, arranged on one side of a bridge which is opposite the side where the plate is located. The rivet has an intermediate cylindrical part which is introduced into a hole in the bridge with a greasy friction allowing to subject, using a tool, a certain rotation to the rivet and thus to the plate and therefore to the first end part of the spring.The second end part of the friction spring is free and radially supported against a plastic washer force-fitted / press-fitted onto the shaft of the second wheel set, this washer having a lateral groove in which the second end part of the spring is placed. The planned system is very difficult to mount in the watch movement. First, the friction spring must be fixed to the plate, by inserting its first end part into a slot and then pushing material on the two edges of this slot to perform a first riveting. Then, the plate with the friction spring must be brought to one inner side of the bridge after having inserted the rivet into the hole in the bridge from the other side. Then, the end of the rivet must be crushed and a second riveting must be performed to fix the plate to the rivet.It is noted that at each stage of the assembly of the friction spring to the plate and then to the bridge, via two successive riveting operations, there is a high risk of damaging the friction spring. Finally, the bridge, plate and friction spring assembly is mounted in the watch movement, a priori simultaneously with the introduction of a pivot of the arbor of the second wheel set, carrying the grooved washer, in a bearing arranged in the bridge concerned. Such an assembly requires that the spring is not superimposed on the grooved washer because the spring is integral with the bridge and the grooved washer, intended to receive the free end of the spring under tension, is integral with the arbor. Thus, a first assembly / disassembly position is provided for the spring and a second working position in which the free end of the spring is brought into the groove of the washer and the spring is tensioned.To move from one position to the other, the watchmaker must act on the head of the rivet with a tool, which causes the spring to lose its set tension when disassembled for maintenance. Thus, each time the seconds wheel is assembled, the braking force moment must be adjusted again. The assembly method provided here is difficult to implement and requires a lot of time.

[0005] Furthermore, this anti-shake device imperfectly solves the problem of adjusting the moment of force applied to the second wheel set to prevent it from shaking, because the friction force is defined in particular by the profile of the lateral groove of the plastic washer and the shape of the end of the spring which is inserted into this groove and presses radially on the washer. Such a friction force is difficult to control and reproduce, because it depends strongly on the dimensions of the spring and the groove, their respective configurations and their respective surface conditions. Another problem comes from the fact that the assembly of an intermediate part on the shaft of the second wheel set will generate an increase in the radial beat of the wheel set, therefore a greater variation than in the absence of such an intermediate part, in particular if the spring pressed directly on a conventional shaft whose radial beat is less.Furthermore, in the event of vibrations or shocks to the watch, the second free end of the spring could detach from the grooved washer, and would no longer guarantee a constant braking torque. Worse, in the event of a violent shock, the spring fixing plate, held only by friction, could move angularly and modify the brake adjustment. Summary of the invention

[0006] The present invention aims to solve the problems of the prior art mentioned above in the case of an electromechanical movement of which at least one display wheel set, intended to carry a display member, also presents a problem of shaking / floating due to the fact that this display wheel set is not subjected to a torque of force for holding it in place outside the time intervals of rotational drive by a watch motor. In particular, the invention proposes an anti-shaking / anti-floating device for a display wheel set, rotated by an electromechanical motor, which is easy to mount and which can, in a preferred variant, be mounted in a step preliminary to the mounting of the display wheel set in question.

[0007] To this end, the present invention relates to an electromechanical timepiece movement comprising an electromechanical motor, a display wheel set arranged so as to be able to be rotated by the electromechanical motor and comprising a shaft intended to carry a display member, and a braking device associated with the display wheel set and comprising a braking spring and an intermediate piece arranged between the braking spring and the shaft of the display wheel set. The braking spring is arranged so as to be able to generate on the display wheel set, as soon as this display wheel set is subjected to a rotational drive torque, a braking torque via the intermediate piece against which this braking spring presses.The intermediate part and the braking spring are arranged in such a way that the intermediate part remains stationary and without rotation in normal operation, this intermediate part having a lateral surface, pressing against a surface of revolution of said shaft, and a support surface against which the braking spring generally exerts a pressure force in the direction of the shaft to generate, between the lateral surface and the surface of revolution, a friction force which generates said braking torque.

[0008] In a preferred general variant, the intermediate piece exerts exclusively radial pressure on the shaft of the display mobile.

[0009] In a main embodiment, the braking spring is a wire spring or a leaf spring whose longitudinal axis is located in a geometric plane parallel to a general plane of movement.

[0010] In a main embodiment, the movement comprises an eccentric whose axis of rotation is perpendicular to said geometric plane and which is arranged so as to press radially against the braking spring in order to be able to vary, by rotation around its axis of rotation, said generally radial pressure force exerted by the braking spring on the intermediate part. Brief description of the figures

[0011] The invention will be described below in more detail with the aid of the appended drawings, given as non-limiting examples, in which: there Figure 1 is a bottom view of a main embodiment of an electromechanical watch movement according to the invention, certain parts of this movement being omitted to better show a braking device according to the invention; the Figure 2 is an enlarged partial view of the electromechanical clock movement of the Figure 1, showing the braking device provided according to the invention; the Figure 3 is a perspective view of the braking device of the main embodiment of the Figures 1 And 2 ; there Figure 4 is a horizontal sectional view of the electromechanical clock movement through the braking device of the Figures 2 and 3 , which is here in a pre-assembled state occurring following a preliminary step of mounting the braking device which precedes the mounting of the display wheel in the movement; Figure 5 is a partial sectional view, along section line VV of the Figure 4 , of the partially assembled watch movement following said preliminary step, this sectional view passing through the central axis of a tube intended to receive part of the shaft of the display wheel; Figure 6 is a sectional view, along section line VI-VI of the Figure 2 , of the electromechanical clock movement of the Figure 1, this view passing through the axis of rotation of the shaft of the display wheel and showing the braking device once the display wheel is mounted in the movement; the Figure 7 schematically and partially represents a particular variant of the main embodiment; the Figures 8A and 8B schematically and partially represent two advantageous variants of the main embodiment; the Figure 9 schematically and partially represents another particular variant of the main embodiment; and the Figure 10 schematically and partially represents a second embodiment of the invention. Detailed description of the invention

[0012] In reference to the Figures 1 to 6 , a main embodiment of an electromechanical clock movement 2 according to the invention will be described below.

[0013] The electromechanical watch movement 2 includes: an electromechanical motor 54, in particular of the stepping type, which comprises a rotor 56 provided with a pinion 58, a first wheel set 30, forming a display wheel set, intended to carry a display member 48, in particular a second hand, and driven in rotation by a second wheel set 52, which is driven in rotation by the rotor 56, via its pinion 58, when the electromechanical motor 54 is activated, a braking spring 10 arranged so as to be able to generate on the first wheel set 30, as soon as this first wheel set is subjected to a rotational driving torque, a braking torque intended to prevent a trembling of the display member 48 and also a permanent radial force which keeps the display member in a stable position when the latter is stationary, also between driving pulses, and thus prevents a floating of this display member.

[0014] According to the invention, the electromechanical timepiece movement 2 comprises a braking device 6 acting on the display wheel set 30 and comprising the braking spring 10 and an intermediate piece 8 arranged between the braking spring and a shaft 36 of the first wheel set 30. The braking spring is arranged so as to be able to generate on the display wheel set, as soon as this display wheel set is subjected to a rotational drive torque, a braking torque via the intermediate piece against which this braking spring presses. For this purpose, the intermediate piece has a lateral surface 9, pressing against a surface of revolution 35 of the shaft, and a bearing surface 25 against which the braking spring generally exerts a pressure force in the direction of the shaft to generate a friction force between the lateral surface 9 and the surface of revolution 35, this friction force generating the braking torque.Thus, the braking torque is exerted on the first mobile / display mobile by the braking spring via the intermediate piece against which the braking spring presses. The intermediate piece 8 and the braking spring 10 are arranged in such a way that the intermediate piece remains stationary and without rotation during normal operation. The shaft 36 of the first mobile 30 and the intermediate piece are configured in such a way that the surface of revolution 35 of the shaft can slide on the lateral surface 9 under dynamic friction force which generates the braking torque. Before the surface of revolution slides on the lateral surface, a static friction force generates the braking torque and thus keeps the shaft stationary.

[0015] Preferably, the intermediate part 8 exerts an exclusively radial pressure on the shaft 36 of the first mobile 30. According to an advantageous characteristic, the braking spring 10 exerts an exclusively radial overall pressure force on the intermediate part. The bearing surface 25 is opposite the lateral surface 9, that is to say that the bearing surface is located on one side of the intermediate part 8 which is opposite another side of this intermediate part defining the lateral surface 9. This variant is advantageous because the braking device bears on a turned part whose radial runout varies little and thus gives a constant braking torque for a given friction force between the surface of revolution 35 and the lateral surface 9.In an advantageous variant shown in the figures, the surface of revolution 35 of the shaft 36 is cylindrical and axial and the lateral surface 9 of the intermediate part is axial, that is to say that the cylindrical surface of revolution 35 and the lateral surface 9 are oriented along the axis of rotation 42 of the first wheel set 30 which coincides with the central axis of the shaft 36, the lateral surface 9 and the cylindrical surface of revolution 35 therefore being parallel to this axis of rotation 42. In a preferred variant, the intermediate part 8 and the braking spring 10 are configured so that said pressure force remains constant once the display wheel set is mounted in the movement and the braking device is fully mounted and adjusted.

[0016] According to a main variant, the braking spring 10 is a wire spring or a leaf spring whose longitudinal axis is located in a geometric plane parallel to a general plane 50 of the electromechanical watch movement 2.

[0017] According to the variant shown, the intermediate part 8 is a washer having a central cylindrical opening in which, without the interaction of the braking spring 10, the shaft 36 of the first mobile 30 would slide and rotate freely, said lateral surface 9 of this washer 8 being defined by the cylindrical surface, preferably circular (i.e. of revolution), of its central cylindrical opening.

[0018] According to a particular variant, the washer 8 has on its periphery a circular groove 24 defining the bearing surface 25 and into which is introduced at least partially a part of the braking spring 10 which exerts the radial pressure force. In particular, the groove 24 has a generally "V" shaped cross section and the braking spring 10 is a wire spring of circular section, as shown in Figures 5 And 6 This arrangement allows the brake spring to be positioned axially in its middle part in contact with the washer. The spring is therefore not free to move axially.

[0019] As non-limiting examples, in a first variant, at least the portion of the washer 8 defining its central cylindrical opening is made of a Copper Beryllium (CuBe) alloy when at least the portion of the shaft defining the surface of revolution 35 is made of steel, or vice versa. This first variant makes it possible to obtain good tribological results. In a second variant where said portion of the shaft is made of steel or CuBe, at least the portion of the washer defining its central cylindrical opening is made of polymers. Preferably, the entire washer is made of polymers. This second variant makes it possible to have, in particular, advantageous self-lubrication.In other variants in which the shaft is made of steel or a copper alloy (for example CuBe or brass), at least the part of the washer defining its central cylindrical opening is made of bronze, nickel or gold, in particular in the form of a thin layer deposited on a base of another material in the case of nickel or gold, or more generally of a metal alloy containing gold or nickel. In other variants, at least the part of the washer defining its central cylindrical opening is made of ceramic, in particular ruby ​​or zirconia.

[0020] It will be noted that the material of the brake spring can be selected so as to optimize the elastic characteristic of this spring and also its manufacture, without having to worry about problems of friction and wear, given that the washer and more generally the intermediate part is intended to be static, that is to say stationary and without rotation, in normal operation of the electromechanical watch movement. In the case of the washer, to prevent its rotation, one can either act on the shape of the intermediate part and / or on the shape of the brake spring as this will be explained in more detail later, or act, in particular in the case of a washer, on the materials forming the spring and at least the external part of the intermediate part in contact with the spring and / or on a surface treatment of these parts allowing to have a high friction force between the brake spring and the intermediate part.

[0021] According to another preferred variant, the braking spring 10 is arranged in the electromechanical watch movement 2 in such a way that a middle part between its two end parts presses radially against the bearing surface 25 of the intermediate part / washer 8. More precisely, the braking spring 10 is arranged in such a way that a middle part of this braking spring exerts said pressure force on the bearing surface 25 of the intermediate part / washer 8. For this purpose, the two end parts of the braking spring, located respectively on both sides of said middle part, are constrained by two distant parts 16 and 20 of the watch movement in such a way that this middle part exerts the pressure force on the bearing surface of the intermediate part / washer.This configuration of the braking device is advantageous because it allows constant pressure of the braking spring on the bearing surface of the intermediate piece / washer. In addition, this configuration is less sensitive to vibrations and shocks than if the braking spring had an anchor point at one of its ends and a contact point at its other end.

[0022] In a particular variant, the brake spring 10 is curved in its middle part and the bearing surface 25 of the intermediate part / washer 8 has in said geometric plane a convex curvature, relative to the shaft 36 of the first mobile 30, and in particular a circular curvature in the case of the washer, which in a first variant the middle part of the brake spring follows along the bearing surface. In a second variant, the radius of curvature of the middle part is provided smaller than the average radius of curvature of the bearing surface, so that the brake spring presses at "two points" of the bearing surface, that is to say at two distinct locations, on the intermediate part / washer. It will be noted that, with a substantially "V" groove, a spring with a circular section presses locally at a pair of axially aligned points.Thus, in such a configuration of the groove and the braking spring, this spring presses at two pairs of angularly spaced points with each pair of points aligned in an axial direction, thus at "two points" in projection in the general plane of the spring, which is parallel to the general plane 50 of the movement. Finally, these variants do not exclude other advantageous variants in which the average radius of curvature of the middle part is provided larger than the radius of curvature of the bearing surface, which has the consequence that the radial pressure is then exerted at "one point" (i.e. at a pair of points aligned in an axial direction, but at a single point in projection in the general plane of the spring / general plane 50 of the movement).

[0023] According to an advantageous variant, as shown in Figures 2 to 4, the braking spring 10 is not fixed to the movement by a specific part, but it is kept under tension by two parts 16 and 20 of this movement against which two end portions of the braking spring located respectively on both sides of a middle portion of this braking spring pressing radially against the intermediate part, which is in particular the washer 8. The direction of the force applied by the two parts 16 and 20 on the spring is reversed with respect to the direction of the reaction force of the intermediate part / washer 8 on the middle part of the spring. These forces, which are exerted on the braking spring in the geometric plane (horizontal plane orthogonal to the axis of rotation 42 of the shaft 36 merged with its central axis) in which its longitudinal axis is located, generate a stress which holds the braking spring in place.Then, to prevent the spring from moving axially / vertically, and in particular from its middle part coming out of the groove 24, there are provided on each of the two said sides respectively two parts of a plate 4 which define lower axial stops for the braking spring. On a first side there is provided an upper groove 14 (on the analog display side) in the plate 4, which is arranged so that its bottom, forming a thin horizontal wall, limits below a possible movement of the part of the spring located on this side. On the second side, the braking spring is partially located above a small projecting part 18. The plate 4 is located below an intermediate plate 60 of the watch movement 2, which defines the general plane 50 of the movement and fixedly supports the base of a tube 44 in which the shaft 36 of the display wheel set 30 passes, the central axis of this tube defining the axis of rotation 42.The intermediate plate 60 defines an upper axial stop for the spring 10. The base of the tube 44 can support the washer 8, in particular when mounting the washer before installing the spring, and therefore forms a support for the washer. It will be noted that in another variant, the element 44 constitutes a barrel which is movable in rotation.

[0024] Various other advantageous variants are shown schematically in Figures 7, 8A and 8B . The variant of the Figure 7 is characterized by a braking spring 10A with a middle part having two bends 71 ​​and 72 which are separated by a straight section 70 (without stress), which is supported, substantially in its middle, against the circular washer 8. This ensures at all times a "one-point" support of the braking spring 10A on the washer 8. The variants of the Figures 8A to 8Bare characterized by an intermediate piece 68 which is not circular, but which is formed by a truncated washer having a straight zone 80. In the variant of the Figure 8A , the braking spring 10 has, in its middle part, an elbow 74 which is located opposite the right zone 80 of the truncated washer 68. In the variant of the Figure 8B , the spring 11 is straight / rectilinear without constraint and, when it is put under tension to press against the intermediate piece, it bends a little (concave curvature seen from the intermediate piece) so that it presses at both ends of the straight zone 80 of this intermediate piece. Thus, in the variants of the Figures 8A and 8B, the braking spring 10, respectively 11 exerts two forces F1 and F2 respectively at the two ends of the straight zone 80. The two forces F1 and F2 are globally radial, that is to say that their sum at a midpoint is radial. However, each of the two forces exerts a moment of force on the intermediate part 68, so that, if the spring moves longitudinally and one of the two forces F1 and F2 decreases relative to the other, the intermediate part 68 then automatically undergoes a small rotation so as to reestablish a balance of the two opposing moments of force which are exerted on it. The variant of the Figure 8B is preferable because the risk of rotation of the truncated washer is lower. In addition, this variant allows the desired braking torque to be maintained even if the braking spring undergoes, during an impact or sudden acceleration, a certain longitudinal displacement. However, the variant of the Figure 8A, with a bent spring, is less likely to undergo longitudinal displacement in the event of an impact. The variant with a truncated washer is advantageous in preventing the intermediate piece from rotating during normal operation, which is important for ensuring a constant braking torque as set. The variants of the Figures 8A and 8B ensure at all times a "two-point" support in projection in the geometric plane of the spring.

[0025] A particular variant is shown schematically in Figure 9 . This variant, like that of the Figure 7, is designed to ensure at all times a pressure of the braking spring 10B at "one point" on the intermediate part 78 which has a generally square shape with rounded corners. The braking spring 10B has a bend 76 such that the two straight parts of this spring on both sides of the bend have between them an angle greater than 90° but relatively close to this value, for example an angle equal to 110°. One of the rounded corners of the intermediate part is positioned in the bend 76 of the spring which exerts, when this spring and the intermediate part 78 are stationary, a substantially radial force F on the intermediate part. If, in particular under the action of an impact, the spring 10B moves, the direction of the force varies so that the intermediate part then undergoes a moment of force which drives it into rotation.This ensures that the same angle of the square intermediate piece remains at all times in the bend 76 of the brake spring and a pressure at "one point". In addition, in normal operation (brake spring stationary), this variant allows the intermediate piece to be kept stationary (without rotation), thus ensuring a constant and well-defined braking torque on the shaft of the mobile.

[0026] According to a preferred variant of the invention, the braking device 6 comprises an eccentric 20 whose axis of rotation is perpendicular to the general plane 50, and therefore parallel to the central axis / axis of rotation 42 of the mobile 30, and which is arranged so as to press radially against the braking spring in order to be able to vary, by a rotation around its axis of rotation, said radial pressure force exerted by the braking spring on the intermediate part / washer. In the advantageous variant explained in Figures 1 And 2, the eccentric 20 constitutes one of the two parts which keep the braking spring under tension. Thus, by rotating the eccentric 20, the stress on this spring is varied, which makes it possible to adjust a braking torque applied to the first mobile 30 (chronograph mobile) when it is subjected to a rotational drive torque. This configuration is advantageous because it is not sensitive to vibrations and shocks. In another variant, another device for adjusting the radial force is provided, in particular a device provided with a pressure member capable of being moved linearly.

[0027] There Figure 10shows another embodiment of the invention in which the braking spring 11 is straight / rectilinear (without constraint). This spring is rigidly fixed at one of its two ends in a fixed part 82 and whose angular positioning in the geometric plane is not modifiable, thus avoiding any involuntary displacement or due to an impact. The groove of the part 82 in which the end of the spring 11 is inserted is oriented so that a median zone of the spring exerts a radial pressure force F on the washer 8, this spring then having between the fixing part 82 and the point of support of the spring on the washer a first convex curvature (seen from the washer).Preferably, at the other end of the spring, to adjust the radial force F, an eccentric is provided which, in this embodiment, is located on the same side of the braking spring as the washer 8 which forms the intermediate part between the braking spring and the shaft of the mobile concerned. Thus, the braking spring 11 also has a second convex curvature between said support point and the eccentric 20, this second curvature being weaker than the first curvature because the radial force F is not zero. It will be noted that the variant shown in . Figure 10defines a construction of the single-point support type, i.e. with the brake spring resting at "one point" on the washer, according to the definition given above. In another variant of the "two-point" type, a star-shaped intermediate piece is provided, for example with four to six points, each with a small rounding. The slightly convex brake spring presses at all times on two points of the star-shaped intermediate piece, thus exerting two forces forming, at their central point, an overall pressure force which is radial. In other words, the two forces generate two moments of force on the intermediate piece which are of the same intensity and opposite. It should also be noted that in the event of an impact, the braking device cannot be deregulated.

[0028] THE Figures 4 and 5show the electromechanical watch movement 2 with the braking device 6 pre-mounted in a preliminary step occurring before the assembly of the first wheel set 30. This preliminary assembly of the braking device 6 is advantageous. It is made possible in particular by the fact that the force exerted by the braking spring is radial and by the fact that the washer 8 is provided above a pinion and a wheel 32 forming the first wheel set. Thus, the shaft 36 of the first wheel set can be mounted from below the watch movement and through the central opening of the washer 8. Figures 1 to 3 And 6 show the electromechanical clock movement 2 after the first mobile 30 has been fitted into this movement and the braking device in a functional state.

[0029] To allow preliminary assembly of the braking device 6, the washer 8 is arranged on a support (base of the tube 44) at the plate 4 which has at the periphery of the washer a stop surface 26 located horizontally opposite the washer and diametrically opposite said bearing surface 25, so that the washer 8 and the braking spring 10 can be mounted beforehand in the electromechanical watch movement 2, before assembly of the first wheel set 30, with the washer bearing against the stop surface 26, as shown in FIG. Figures 4 and 5 .

[0030] In a preferred variant, the stop surface 26 is arranged in such a way that, following the prior assembly of the washer 8 and the braking spring 10, the central cylindrical opening of the washer has at least one overlapping zone with the central circular opening of a barrel or tube 44, into which a part of the shaft 36 of the first wheel set 30 is then introduced, so that the shaft can, when the first wheel set is assembled in the electromechanical watch movement 2, penetrate into the two central openings without having to initially exert a radial force on the washer. As this can be seen in Figure 5, in the variant shown, the central cylindrical opening of the washer 8 is not entirely superimposed on the central circular opening of the tube 44. Preferably, at least the major part of the opening of the washer is superimposed on the central opening of the tube. It will be noted that, in the example given, the shaft 36 of the first wheel set 30 is introduced into a tube 44 which is fixed. The upper end of the shaft, intended to receive a second hand, has a smaller diameter, which makes it easier to introduce this shaft into the two central openings, when mounting the display wheel set 30, when the initial superposition of the two central openings, in the pre-mounted state of the braking device, is only partial.

[0031] Once the first mobile 30 is mounted in the watch movement, the washer 8 no longer bears against the side wall 26 of the plate 4, but bears by its central cylindrical opening against the shaft 36 of the first mobile, more precisely against a surface of revolution 35, advantageously cylindrical and axial, of this shaft. This first mobile can then be driven in rotation at times, on command, by the electromechanical motor 54 via the second mobile 52.

[0032] The present invention has been described in detail for a 30 second wheel set, but the braking device of the invention can be provided for other wheels of an electromechanical watch movement, in particular for a minute wheel set or a chronograph wheel set.

[0033] The invention has several advantages, some of which have already been explained previously. The braking device 6 comprises an eccentric 20 which makes it possible to easily adjust the radial pressure force exerted by the braking spring on the intermediate part / washer 8 and via the latter the radial force applied to the shaft 36 of the first mobile 30, and to adjust the frictional force moment applied to this first mobile. The eccentric 20 allows adjustment of the braking torque once the braking device is fully mounted in the electromechanical watch movement and without having to remove the braking spring in order to slightly modify its initial shape.Given the presence of the washer 8 between the braking spring 10 and the shaft 36, and in addition to the fact that the forces present are intended to be radial, the installation of the second hand 48 on the first wheel set 30 and especially its removal, for example when changing this hand or for cleaning the electromechanical watch movement, cannot damage the braking spring which is the delicate element in the braking device 6, the washer 8 being much more robust and able to withstand a certain axial pressure against its support.

[0034] The braking device 6 is such that it is protected against stresses which could damage it during the assembly of other parts of the electromechanical watch movement, in particular during the assembly of the display wheel set 30. During disassembly of the watch movement 2, and in particular of the display wheel set, the braking device 6 can remain in place without its adjustment being modified.

[0035] The braking device according to the invention makes it possible to define the friction moment of force relatively precisely in advance, given that the lateral surface 9 of the intermediate part, in particular of the washer 8, has a height which is generally much greater than that of the braking spring, that the material of the intermediate part / washer 8 can be selected and that the diameter of the surface of revolution, defining a cylindrical and axial surface, of the shaft 36 against which the intermediate part / washer 8 bears is precisely determined.

Claims

1. Electromechanical timepiece movement (2) comprising an electromechanical motor (54), a display wheel (30) arranged so as to be able to be driven in rotation by the electromechanical motor and comprising a shaft (36) intended to carry a display member (48), and a braking device (6) associated with the display wheel and comprising a braking spring (10, 10A, 10B, 11) and an intermediate piece (8, 68, 78) arranged between the braking spring and the shaft of the display wheel, the braking spring being arranged so as to be able to generate on the display wheel, as soon as this display wheel is subjected to a rotational driving torque, a braking torque via the intermediate piece against which this braking spring presses, the intermediate piece and the braking spring being arranged so that the intermediate piece remains stationary and without rotation in normal operation, the intermediate piece having a lateral surface (9),pressing against a surface of revolution (35) of said shaft, and a bearing surface (25) against which the braking spring generally exerts a pressure force in the direction of said shaft to generate, between the lateral surface and the surface of revolution, a friction force which generates said braking torque., 2. Watch movement according to claim 1, characterized in that the intermediate part (8, 68, 78) exerts exclusively radial pressure on the shaft (36) of the display mobile (30).

3. A clockwork movement according to claim 1 or 2, wherein the shaft defines a central axis (42), characterized in that said surface of revolution (35) is cylindrical and axial and said lateral surface (9) is axial.

4. Watch movement according to any one of the preceding claims, characterized in thatthe braking spring (10, 10A, 10B, 11) is a wire spring or a leaf spring whose longitudinal axis is located in a geometric plane parallel to a general plane (50) of the movement.

5. Watch movement according to claim 4, characterized in that the brake spring (10, 10A, 10B, 11) is arranged in such a way that a middle part of this brake spring exerts said pressure force on said bearing surface of the intermediate part (8, 68, 78); and in that two end parts of the braking spring, located respectively on both sides of said middle part, are constrained by two distant parts (16, 20) of the watch movement so that this middle part exerts the pressure force on said bearing surface.

6. Watch movement according to claim 5, characterized in thatthe braking spring (10, 10A, 10B) is not fixed to the watch movement but is kept under tension by said distant parts (16, 20) of this watch movement against which said two end parts of the braking spring press in two respective directions in said geometric plane.

7. Watch movement according to claim 5 or 6, characterized in that this movement comprises an eccentric (20) whose axis of rotation is perpendicular to said geometric plane and which is arranged so as to press against the braking spring (10, 10A, 10B, 11) in order to be able to vary, by rotation around its axis of rotation, said pressure force exerted by the braking spring on the intermediate part (8, 68, 78).

8. Watch movement according to any one of the preceding claims, characterized in thatthe intermediate part is a washer (8) having a central opening through which the shaft (36) of the display wheel passes, said lateral surface (9) of this washer being defined by a cylindrical surface of its central opening.

9. Watch movement according to claim 8, characterized in that the washer (8) has on its periphery a groove (24) defining said bearing surface (25) and into which is introduced at least partially a part of the braking spring (10) exerting said pressure force in the direction of said shaft.

10. Watch movement according to any one of the preceding claims, characterized in thatthe intermediate piece (8) is arranged opposite a stop surface (26) which is diametrically opposite said bearing surface (25), so that the intermediate piece and the braking spring can be mounted beforehand in the electromechanical watch movement, before mounting the display wheel (30), with the intermediate piece bearing against the stop surface.

11. Watch movement according to claim 10, characterized in thatthe stop surface (26) is arranged in such a way that, following the prior assembly of the intermediate piece (8) and the braking spring (10), the central cylindrical opening of the intermediate piece has at least one overlapping zone with the central cylindrical opening of a barrel or tube (44), rotatably movable or fixed, into which a part of the shaft (36) of the display wheel (30) is introduced, so that the shaft can, when the display wheel is assembled in the electromechanical watch movement, penetrate into the two central circular openings without having to initially exert a radial force on the intermediate piece.

12. Watch movement according to any one of the preceding claims, characterized in thatat least a portion of the shaft (36) defining said surface of revolution (35) is made of steel or a copper alloy and at least a portion of the intermediate piece (8) defining said lateral surface (9) is made respectively of a copper alloy or steel.

13. Watch movement according to any one of claims 1 to 11, characterized in that at least a portion of the shaft (36) defining said surface of revolution (35) is made of steel or a copper alloy and at least a portion of the intermediate piece (8) defining said lateral surface (9) is made of polymers.

14. Watch movement according to any one of claims 1 to 11, characterized in thatat least a portion of the shaft (36) defining said surface of revolution (35) is made of steel or a copper alloy and at least a portion of the intermediate piece (8) defining said lateral surface (9) is made of a ceramic, in particular ruby ​​or zirconia, or a material containing gold or nickel and forming an outer layer at least partially covering the intermediate piece.

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