Patent Application
20190377302
The present invention relates to timepieces comprising a timepiece movement fitted with a tourbillon bearing in a carriage a mechanical resonator, formed of a balance and a balance-spring, and an escapement device. The term tourbillon is also sometimes referred to by those skilled in the art as a karussel. Furthermore, such a timepiece movement comprises a barrel arranged to accumulate mechanical energy and a geartrain kinematically linking the tourbillon carriage to the barrel.
Timepiece movements fitted with a tourbillon have been known for a long time. The term ‘tourbillon’ is generally used to refer to such a timepiece movement and even a watch fitted with such a timepiece movement.
In a conventional tourbillon, the carriage functions as a second wheel set. It comprises a second pinion and it is actuated via this second pinion by a medium wheel. The carriage bears a conventional escapement formed of an escape wheel set and a pallet fork, in particular a Swiss lever escapement. The force is transmitted to the escape wheel set via the pinion thereof which meshes, in the manner of a planetary wheel, with a fixed second wheel secured to the plate.
The operation of a conventional Swiss lever escapement is well known to those skilled in the art. The escape wheel has a plurality of teeth which engage with two pallets borne by the pallet fork. Each pallet has at the free end thereof an inclined plane. To generate a sprung balance maintenance impulse, one of the teeth of the escape wheel presses tangentially against the inclined plane of one of the two pallets, so as to exert a force torque on the pallet fork which is thus rotated by the escape wheel, the latter being rotated by the rotation of the carriage via the fixed second wheel. The maintenance impulse ends when the impulse beak, included in each tooth of the escape wheel, is situated at the bottom of the inclined plane. Thus, to generate a maintenance impulse, the escape wheel must be capable of being rotated over an angular distance corresponding to the angular distance, relative to the axis of rotation of the escape wheel set, from the inclined plane of the pallet with which it interacts. However, as stated, the rotation of the escape wheel is intimately linked with that of the tourbillon carriage, a kinematic linkage being provided between the escape wheel and the tourbillon carriage. Consequently, to rotate that escape wheel, it is necessary to set in rotation the tourbillon which has a relatively high inertia. The maintenance impulse transmitted to the balance is therefore limited in intensity by the inertia of the tourbillon and also of the geartrain kinematically linking the tourbillon carriage to the barrel. The inertia of the tourbillon carriage is added to the escape wheel, which increases the inertia thereof.
The tourbillon mechanism is known to average the vertical positions and therefore enhance the working of a timepiece movement in a wristwatch when worn. However, in a conventional movement, the tourbillon increases the inertia of the escapement device as the tourbillon carriage rotates integrally with the escape wheel. This limits the acceleration that may be sustained by the escape wheel. The impulse transmitted to the balance being dependent on the rotation of the escape wheel, it is not possible to increase the frequency above 5 Hz reliably in chronometric terms. As a result, the possible oscillation frequency for the sprung balance of such a tourbillon mechanism is limited. Thus, the oscillation frequency of a conventional sprung balance in a tourbillon is generally less than five Hertz (5 Hz) and may in some specific cases attain 5 Hz. It is usually equal to three Hertz, for example. It is understood that this limits the working accuracy that can be obtained with a timepiece movement fitted with a conventional tourbillon.
Thus, the remarkable advantage of the tourbillon for the working accuracy on wearing a watch incorporating same is impaired, due to conventional escapement operation, by the high inertia generally exhibited by the carriage thereof.
The aim of the present invention is that of a providing a solution to the problem of the conventional tourbillon mentioned above, so as to help increase the chronometric benefit of a tourbillon, in particular increasing the working accuracy of the timepiece movement fitted with a tourbillon according to the invention by the arrangement of a mechanical resonator in the tourbillon carriage, having an oscillation frequency Fo greater than conventional frequencies, preferably greater than five Hertz (Fo>5 Hz).
The invention therefore concerns a timepiece comprising a timepiece movement fitted with a tourbillon, that comprises a carriage arranged rotating about a main axis, a barrel, arranged to accumulate mechanical energy, and a geartrain kinematically linking the tourbillon carriage to the barrel. The tourbillon bears a mechanical resonator, formed of a balance and a balance-spring, and an escapement device. According to the invention, the escapement device is a magnetic escapement that comprises an escape wheel set formed of an escape pinion and a magnetic structure or magnetic structures having a general annular shape centred on an axis of rotation of the escape wheel set. The magnetic escapement further comprising a magnetic element that, or a plurality of magnetic elements each whereof is arranged so as to have an oscillating movement that is synchronous with the oscillation of the mechanical resonator and that has a radial component different to zero relative to said axis of rotation. The magnetic element or each of the magnetic elements of the plurality of magnetic elements is coupled, at least momentarily periodically, with the magnetic structure or the magnetic structures such that the escape wheel set rotates by a predetermined angular period at each oscillation period of the balance. Then, according to the invention, the magnetic escapement has, in normal timepiece movement operation, alternately energy accumulation phases, from a conversion of mechanical energy supplied by the barrel into magnetic potential energy in the magnetic escapement, and transfer phases of energy accumulated in the magnetic escapement to the magnetic resonator.
Finally, the magnetic escapement is arranged such that:
Owing to the features of the timepiece according to the invention, in particular to the type of magnetic escapement selected to equip the tourbillon, the energy impulses transmitted to the mechanical resonator to maintain same are not limited in intensity by the inertia of the tourbillon carriage. In fact, even the inertia of the geartrain no longer influences the generation of these energy impulses. Indeed, only the inertia of the pallet fork (in the event of a stopper being envisaged) influences the dynamics of the maintenance impulses supplied by the magnetic escapement to the mechanical resonator. It shall be noted that the pallet fork forms herein a magneto-magnetic converter. Thus, these maintenance impulses may be briefer, i.e. occur in very limited time intervals which are no longer dependent on the inertia of the tourbillon. These remarkable features help enhance the working accuracy of the timepiece movement and in particular enhance the isochronism of the mechanical resonators formed by a sprung balance. Furthermore, they make it possible to arrange in the tourbillon mechanical resonators having a high quality factor, in particular a sprung balance having a much higher natural oscillation frequency than that of a usual sprung balance for a conventional tourbillon, in particular a natural frequency greater than 5 Hz.
The magnetic escapement according to the present invention therefore makes it possible to temporally dissociate the periodic transmission of a certain quantity of energy from the barrel to the magnetic escapement, which is arranged to accumulate same momentarily, and the transmission of this accumulated energy from the magnetic escapement to the mechanical resonator.
Thus, owing to the magnetic escapement as selected within the scope of the invention to equip a tourbillon, the maintenance impulses supplied by the magnetic escapement to the mechanical resonator may be generated essentially without rotation of the escape wheel and substantially independently of such a rotation. Thus, the inertia of the geartrain and the inertia of the tourbillon carriage no longer impede the generation of the maintenance impulses. What is important is the radial nature of the force arising essentially to generate each maintenance impulse after a magnetic potential energy accumulation phase in the magnetic escapement, such that the fact that the carriage rotates or not or merely by a small angle has substantially no impact on the generation of the maintenance impulses. For this reason, the tourbillon mechanism fitted with a magnetic escapement according to the invention can deliver maintenance impulses of short duration and of relatively high intensity.
In one advantageous embodiment, the mechanical resonator comprises a balance which is pivoted magnetically in the tourbillon carriage, which comprises for this purpose two magnetic bearings. This particular variant makes it possible, in addition to the various advantages provided by the magnetic escapement selected, to significantly limit differences in working of the mechanical resonator between the horizontal positions and the vertical positions (the latter being averaged by means of the tourbillon). It is therefore understood that it thus becomes possible to obtain a tourbillon watch having a very high working accuracy.
The invention will be described in more detail below with reference to the annexed drawings, given by way of non-limiting examples, and in which:
With reference to
The timepiece comprises a timepiece movement 2 fitted with a tourbillon 4 comprising a carriage 6 arranged rotating about a main axis 8, a barrel 10 arranged to accumulate mechanical energy and a geartrain 11 kinematically linking the tourbillon carriage to the barrel. The tourbillon bears a mechanical resonator 14, formed of a balance 16 and a balance-spring 15, and an escapement device 18. The tourbillon is pivoted between a bottom plate 3 and a bridge 9. The escapement device consists of a magnetic escapement that comprises an escape wheel set 20 formed of an escape pinion 24 and a first escape wheel 22, the latter comprising a first magnetic structure 26 having a general annular shape and centred on an axis of rotation 28 of the escape wheel set.
The magnetic escapement comprises a stopper 30 coupling momentarily, in each oscillation alternation of mechanical resonator 14, this mechanical resonator with escape wheel set 20. This stopper and the escape wheel set are pivoted between a portion of carriage 6 and an escape bridge 19 borne by this carriage. The stopper is subjected, when the mechanical resonator oscillates, to a to-and-fro movement interspersed with rest phases wherein the stopper is alternately stopped in two rest positions where it respectively abuts against two pins 36 and 37.
In the variant shown, the stopper is formed by a pallet fork bearing two magnetic elements 32 and 33 each arranged so as to have an oscillating movement that is synchronous with the oscillation of the mechanical resonator and that is oriented essentially along a radial direction relative to axis of rotation 28 of the pallet fork. The two magnetic elements are similar and situated on the same side of escape wheel 22. They are both coupled simultaneously in a similar manner to the first magnetic structure, which is arranged such that these two magnetic elements are coupled therewith continuously (or quasi-continuously) and such that the respective magnetic couplings thereof are added together. The operation of this magnetic escapement will be described in more detail hereinafter.
In the variant shown, escape wheel set 20 comprises a second wheel 38 comprising a second magnetic structure 40 that has a planar symmetry with the first magnetic structure 26 and that is situated at a distance therefrom so as to enable the two magnetic elements 32 and 33 to be situated, when they oscillate, at least momentarily between the first and second magnetic structures. The two magnetic elements 32 and 33 interact, similarly, simultaneously with the first and second magnetic structures, such that the effects are added together. The two magnetic elements are coupled with the first and second magnetic structures such that the escape wheel set rotates by a predetermined angular period at each oscillation period of the balance 16. The first and second magnetic structures and are formed respectively of a first permanent magnet and a second permanent magnet that each have an axial magnetisation and the same polarity. The two magnetic elements of the pallet fork are each formed of a permanent magnet having an axial magnetisation and an inverted polarity relative to the first and second magnets, so as to be subject to a magnetic repulsion force with each of the two magnetic structures.
Preferably, first and second wheels 22 and 38 bear respectively a first ferromagnetic structure 44 and a second ferromagnetic structure 46 covering respectively the first and second magnetic structures on both external sides of the set consisting of these first and second magnetic structures, so as to form in association with some fastening pins (see
As a general rule, the magnetic escapement is arranged so as to have, in normal timepiece movement operation, alternately energy accumulation phases, from a conversion of mechanical energy supplied by the barrel into magnetic potential energy in the magnetic escapement, and transfer phases of energy accumulated in the magnetic escapement to the magnetic resonator. Each energy accumulation phase and subsequent energy transfer phase occur during a time interval equal to half an oscillation period of the mechanical resonator.
Within the scope of the first embodiment, the arrangement of the magnetic escapement mentioned in the preceding paragraph and the operation of this magnetic escapement will be described hereinafter with reference to
Firstly, the two magnetic structures 26 and 40 define together, in each of the two rest positions of pallet fork 30, increasing magnetic potential energy portions PC1, respectively PC2 for magnetic elements 32 and 33 of pallet fork 30 that are both coupled, herein continuously, with the two magnetic structures. In the variant described, these increasing portions are defined substantially by a magnetic track 58 comprised in each of the two magnetic structures 26 and 40, this magnetic track having a particular outline, alternately re-entering and exiting relative to a median geometric circle. During normal timepiece movement operation, this particular outline is suitable for magnetic potential energy accumulation on a rotation of the escape wheel set over a certain magnetic distance, while the pallet fork is alternately in both rest positions thereof. Each magnetic track 58 is formed by the permanent magnet constituting the corresponding magnetic structure, this permanent magnet being arranged in magnetic repulsion with the permanent magnets constituting both magnetic elements 32 and 33, as previously described.
Increasing portions PC1 and PC2 thus define magnetic potential energy accumulation gradients in the magnetic escapement. During each energy accumulation phase, the two magnetic structures 26, 40 and therefore the escape wheel set are subjected to a magnetic force torque (represented schematically in
During each energy accumulation phase, it can be said that the two magnetic elements 32 and 33 of the pallet fork, that are coupled with both magnetic structures 26 and 40, climb together one of the angular magnetic potential energy accumulation gradients PC1 respectively PC2, by a certain rotation of the escape wheel set, while pallet fork 30 is in a rest phase. However, it will be noted that this consists of magnetic interaction energy such that it is the assembly of ‘magnetic structures and magnetic elements’ that climbs the angular magnetic potential energy gradients. In the case of a coordinate reference associated with the timepiece movement, it is in fact rather the escape wheel set that climbs increasing portions PC1 and PC2 of potential energy curves 66 and 68, since it rotates while the magnetic elements are immobile. Nevertheless, if a coordinate reference associated with the escape wheel set and fixed in relation thereto is considered, then it is these two magnetic elements that climb the increasing portions. It is understood therefore that this is equivalent.
In
More specifically, in the variant described, two successive magnetic barriers BM1 or BM2 are offset angularly by an angular period P. Both magnetic elements of the pallet fork are offset angularly, relative to axis of rotation 28, substantially by an angle equal to 3P/2 (generally an odd number of half-periods P/2). In each of the two rest positions of the pallet fork, when one of the two magnetic elements is coupled with an exiting part of track 58, the other is coupled with a re-entering part of this track. Then, when the first magnetic element is presented in front of an outer magnetised area 60, the second is presented in front of an inner magnetised area 62, and conversely.
During normal timepiece movement operation, the magnetic barriers are arranged so as to generate, on the two magnetic elements having climbed a preceding angular gradient, a relatively high magnetic force torque opposing the drive torque applied by the barrel to the escape wheel set, to be able to thus stop the angular progress of the escape wheel set. For a given mechanical force torque, the escape wheel set finally stops at a substantially determined angular position (status corresponding to
Then, during each energy transfer phase, both magnetic elements 32 and 33 are each subjected to a radial magnetic force FR1 and FR2 (status corresponding to
As in a conventional Swiss lever escapement, each alternation of the pallet fork 30 starts with an initial driving of this pallet fork by the balance via an impulse pin 50 (pin having a truncated disk profile) which is placed between the two horns of fork 52 of the pallet fork. This initial phase enables magnetic elements 32 and 33 to each be subjected to an initial radial movement before they are subjected, in a subsequent phase of the alternation in question of the oscillating movement thereof, to a drop in magnetic potential energy such that the magnetic escapement is subjected overall to a decrease in magnetic potential energy, referenced D1 and D2 in
The arrangement of the magnetic escapement described above, from which results the profile of each of the two curves 66 and 68, therefore enables this magnetic escapement to convert into mechanical energy magnetic potential energy accumulated in the preceding energy accumulation phase so supply same to the pallet fork in the form of a force torque working while the pallet fork rotates. Thus, the pallet fork becomes driving and supplies an energy impulse to the balance via fork 50 thereof, as in a conventional mechanical escapement, to maintain the oscillation of the sprung balance. The magnetic escapement selected within the scope of the invention is remarkable in that the energy transfer can occur without any rotation of the escape wheel set, as shown in
It will be noted that the magnetic escapement selected within the scope of the first embodiment is substantially at constant force; i.e. the decreases in magnetic potential energy in the energy transmission phases to the balance remain substantially constant in the useful operating range of the timepiece. This is a property of the magnetic system of the magnetic escapement selected (see
As a general rule, within the scope of the first embodiment, the selected magnetic escapement comprises stopper coupling momentarily, in each oscillation alternation of the mechanical resonator, this mechanical resonator with the escape wheel set, the stopper bearing a magnetic element or a plurality of magnetic elements and being subjected when the mechanical resonator oscillates, to a to-and-fro movement interspersed with rest phases wherein the stopper is alternately stopped in two rest positions. A magnetic structure or plurality of magnetic structures define in the two rest positions of the stopper respectively a first magnetic potential energy curve and a second magnetic potential energy curve, both as a function of the angle of the escape wheel set and each having:
Then, the increasing portions of the first magnetic potential energy curve are respectively offset angularly relative to the increasing portions of the second magnetic potential energy curve, each magnetic barrier of one of the first and second magnetic potential energy curves being situated angularly between two successive magnetic barriers of the other of these first and second magnetic potential energy curves.
Furthermore, the magnetic escapement is arranged such that:
Finally, the magnetic escapement is further arranged such that:
The variant of the first embodiment represented comprises six outer magnetised areas 60 forming as many magnetic stops to momentarily stop the escape wheel and also six inner magnetised areas 62 also forming as many magnetic stops. It will be noted that the number of outer/inner magnetised areas may be different and preferably greater. Thus, in a further variant, the number of outer/inner magnetised areas is equal to ten or twelve. It will further be noted that, in another variant, it is envisaged to have only inner magnetised areas or, preferably, only outer magnetised areas.
In an advantageous variant, represented in
As the invention makes it possible to increase the oscillation frequency of the sprung balance, even considerably, it is envisaged for this purpose, particularly to maintain the angular speed of the tourbillon carriage at one revolution per minute, that the tourbillon bears an intermediate wheel set 74 of which intermediate wheel 76 meshes with escape pinion 24 and intermediate pinion 78 meshes with fixed second wheel 80 comprised by the timepiece movement. The intermediate wheel set is a reducer wheel set of the rotational frequency of the escape wheel set and is herein arranged such that the tourbillon carriage performs one revolution on itself per minute. In an advantageous variant, the oscillation frequency Fo of the mechanical resonator is greater than five Hertz (Fo>5 Hz). In a preferred variant, this frequency is substantially equal to or greater than 6 Hz (Fo>=6 Hz) and, in a specific variant, the oscillation frequency of the mechanical resonator has a value situated between, inclusive, eight Hertz and twelve Hertz (8 Hz=<Fo=<12 Hz). It will be noted that an intermediate wheel set is already useful for lower sprung balance oscillation frequencies, for example for three Hertz (Fo=3 Hz), as the escape wheel set performs in the example shown one revolution per six sprung balance oscillation periods, which corresponds to a rotational frequency much greater than that of a conventional toothed escape wheel.
Rotational frequency FRot of the escape wheel is determined by the frequency of mechanical resonator Fo and by the number of outer magnetised areas 60, respectively the number of inner magnetised areas 62. In a general variant, rotational frequency FRot (number of revolutions per second) of the escape wheel set is between, inclusive, one quarter and one sixteenth of oscillation frequency Fo of the mechanical resonator (Fo/16=<FRot=<Fo/4). This means that the number NPA of outer 60 or inner 62 magnetised areas/magnetic stops is between four and sixteen (4<=NPA<=16), since FRot=FO/NPA. In a first example with a mechanical resonator oscillating at three Hertz (Fo=3 Hz) and the toothing of fixed wheel (80) comprising 108 teeth, the intermediate pinion comprises 70 teeth, while escape pinion (24) comprises 18 teeth. In a second example with a mechanical resonator oscillating at six Hertz (Fo=6 Hz) and the toothing of the fixed wheel comprising 120 teeth, the intermediate pinion comprises 12 teeth and the intermediate wheel comprises 72 teeth, while the escape pinion comprises 12 teeth.
Two variants of the first and second embodiments will be described hereinafter. The first variant is represented in
The variant in
With reference to
Magnetic structure 126 is annular and formed alternately of annular sectors 128, wherein are arranged magnets in magnetic repulsion with magnets 102 and 103 when they are presented alternately facing these annular sectors, and of annular sectors 130 formed of a non-magnetic material, such as brass or aluminium. Each pair of adjacent annular sectors defines an angular period of the magnetic structure. Preferably, the magnets of magnetic structure 126 have angularly an increasing thickness in the opposite direction of the direction of rotation envisaged for the escape wheel set, so as to have an air gap that decreases between each and magnet 102, 103 passing above (when the escape wheel set rotates) and also a magnetic flux that intensifies. For such an advantageous variant,
When the mechanical resonator is in the neutral position thereof (minimum mechanical energy position represented in
It is observed in
The magnetic escapement also defines descending radial magnetic potential energy gradients 138 descended alternately by the two magnets 102 and 103 after having climbed respectively the rising angular gradients 136. As the magnetic force exerted on each magnet 102, 103, descending a descending radial gradient, is oriented perpendicularly to level lines 134, it is then subjected, during energy transfer phases, essentially a radial magnetic force, relative to axis of rotation 28, during each alternation of the oscillation movement of the mechanical resonator and in the direction of this oscillation movement during this alternation, such that the magnetic escapement then converts into mechanical energy magnetic potential energy accumulated in the preceding energy accumulation phase to be able to maintain the oscillation of the mechanical resonator. The decrease in magnetic potential energy in the magnetic escapement therefore results essentially from work of the radial magnetic force applied alternately on each of the two magnetic elements, this work of the radial magnetic force being transmitted directly to the mechanical resonator, such that this mechanical resonator receives a mechanical energy impulse in each alternation of the oscillation movement thereof.
The descending radial gradients 138 extend over a certain angular distance such that the continuous movement of the escape wheel has no repercussions in respect of the particular features sought within the scope of the present invention. Indeed, what is important is that the main radial force exerted alternately on each of the two magnets fastened to the balance is practically not dependent on any rotation of the escape wheel set. Indeed, it is observed in
Finally, it will be noted that a fusee (similar to fusee 12 represented within the scope of the first embodiment) incorporated in the timepiece movement makes it possible to equalise the force torque supplied by the barrel to the tourbillon carriage, such that the escape wheel set is subjected to a constant torque during normal timepiece movement operation. Within the scope of the third embodiment, such a fusee makes it possible to obtain a stationary operating phase throughout the useful operating range of the timepiece movement, with the oscillation amplitude of the balance remaining constant and maintenance impulses supplying to the balance the same quantity of mechanical energy. All the benefit provided by a fusee for equalising the force torque in a conventional mechanical timepiece movement is provided to the timepiece according to this third embodiment.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18176488.7 | Jun 2018 | EP | regional |
