This application claims priority from European Patent Application No. 13199425.3 filed Dec. 23, 2013, the entire disclosure of which is hereby incorporated herein by reference.
The present invention concerns the technical field of magnetic devices for regulating the relative angular velocity of a wheel and at least one magnetic dipole integral with an oscillating element and, in particular, regulating devices of this type for use in the watch industry, especially in wristwatches.
The present invention also concerns a timepiece movement equipped with such a regulating device and a timepiece, especially, but not exclusively, a wristwatch provided with a timepiece movement of this type.
Numerous magnetic regulating devices of this type have been proposed in the prior art. U.S. Pat. No. 2,762,222, which discloses such a regulating device, may be cited by way of example.
To date, magnetic escapements of this type have not been integrated in wristwatches due their high shock sensitivity. Indeed, in the event of shocks, the oscillating structure or the oscillating magnet may move away from the ferromagnetic path and break the magnetic coupling between the oscillating structure and said path. In that case, the escape wheel is driven by the driving torque in an uncontrolled manner. Two situations may arise depending on the nature of the shock. Either, when there is a shock, the escape wheel jumps one or more step and then synchronises again with the oscillating structure, which leads to a loss of state impairing the chronometric performance of the watch. Or, the intensity and/or duration of the shock are such that the magnetic coupling between the wheel and the oscillating structure is permanently lost, this phenomenon is generally denoted by the term “uncoupling”. The oscillating structure then stops oscillating and the escape wheel is driven in rotation in an uncontrolled manner until the mainspring barrel is totally let down.
To overcome this problem, a first solution has been proposed consisting in strengthening the magnetic coupling between the escape wheel and the oscillating structure, for example, by reducing to a minimum the distance between the magnetic poles and the wheel. However, this solution is not entirely satisfactory in that it limits the possibilities of the wheel self-starting or presents problems of locking caused by the poles sticking on the escape wheel.
A second attempt to overcome this problem consisted in providing a plurality of mechanical stop members arranged on either side of the ferromagnetic path against which the oscillating magnet abuts as soon it moves away from its coupling path. Although this device can prevent the uncoupling of the escape wheel, it increases the size of the system and induces perturbations in the oscillating structure with every shock against the stop members, resulting in decreased chronometric performance in a similar manner to the problem of knocking in a conventional Swiss lever escapement.
It is therefore a main object of the invention to overcome the drawbacks of the aforecited prior art by providing a magnetic device for regulating the relative angular velocity of a wheel and of an oscillating structure of the type described above, including means intended to reduce or eliminate shock sensitivity (hereafter denoted as “anti-uncoupling means”).
It is also an object of the invention to supply a regulating device of this type wherein the anti-uncoupling means do not use energy derived from the barrel in normal operation.
It is also an object of the invention to provide a regulating device of this type wherein the anti-uncoupling means do not adversely affect the self-starting of the system.
It is also an object of the invention to provide a regulating device of this type wherein the anti-uncoupling means do not cause any friction and consequently any wear, dust or noise.
It is also an object of the invention to provide a regulating device of this type wherein the anti-uncoupling means do not increase the size of the device.
It is also an object of the invention to provide a regulating device of this type wherein the anti-uncoupling means are reliable, economical and easy to implement.
To this end, the invention concerns a magnetic device for regulating the relative angular velocity of a wheel and of at least one magnetic dipole integral with an oscillating device, said wheel or said dipole being driven by a motor torque, said wheel including a periodic, ferromagnetic pole path which alternates according to a central angle? and said at least one dipole being arranged to permit magnetic coupling with said ferromagnetic path and oscillation of said dipole at the natural frequency of the oscillating element during the relative motion of the wheel and of the magnetic dipole to regulate said relative angular velocity, said device being characterized in that said wheel further includes means for dissipating the kinetic energy of said at least one dipole when it moves away from said ferromagnetic path.
Thus, at the moment when the magnetic dipole tends to move away from the ferromagnetic path as a result of the acquisition of surplus kinetic energy, for example following a shock, the dissipation means of the present invention immediately dissipate said surplus energy and are intended to return the kinetic energy of the oscillating dipole to a level permitting the coupling thereof with said ferromagnetic path. This, on the one hand, limits the disruptive effects on chronometry resulting from uncoupling and, on the other hand, eliminates the risk of permanently losing the coupling between the oscillating dipole and the wheel after uncoupling.
It will also be specified that, within the scope of the invention, “magnetic dipole” refers to any means, of any form, producing a permanent magnetic field, that is to say the dipole could be formed by any type of permanent magnet or electromagnet.
Preferably, the kinetic energy dissipation means are arranged adjacent to said ferromagnetic path on at least one of the sides of said ferromagnetic path.
According to an advantageous embodiment of the invention, the kinetic energy dissipation means include non-ferromagnetic, electrical conductive sectors extending substantially in the plane of said ferromagnetic path and disposed on both sides of said ferromagnetic path. These sectors are preferably made of a material chosen from the group including gold, silver, copper, aluminium, platinum, palladium, titanium and nickel.
When the dipole leaves the ferromagnetic path subsequent to a shock, it is in motion facing non-ferromagnetic, electrically conductive sectors generating eddy currents in the sectors “overflown” by the dipole and which immediately oppose the movement of the dipole and tend to bring the oscillating dipole back to the ferromagnetic path and to re-establish magnetic coupling therewith.
Preferably, the non-ferromagnetic, electrically conductive sectors are electrically insulated from said ferromagnetic path, typically by an air gap or any other means of galvanic insulation.
This galvanic insulation makes it possible to reduce or remove any undesirable stray eddy currents which would appear in normal operation, especially when the dipole moves close to the edge of the ferromagnetic path.
Advantageously, the ferromagnetic path includes through slots extending substantially perpendicularly to the plane of the ferromagnetic path and/or the ferromagnetic path is formed by a concentric lamination of ferromagnetic material.
As a result of these characteristics, any undesirable stray eddy induction currents which would appear in normal operation in the ferromagnetic path are prevented, reduced or eliminated.
It is therefore understood that the eddy currents appearing in the non-ferromagnetic, electrically conductive sectors extending substantially in the plane of said ferromagnetic path and arranged on both sides of said ferromagnetic path, are desired eddy currents which contribute to the dissipation of kinetic energy in the dipole when the latter oscillates with an amplitude moving it away from the ferromagnetic path, whereas any eddy currents induced in the ferromagnetic path are undesirable stray eddy currents that it is desired to remove or at least reduce to a minimum.
According to an embodiment of the invention, the wheel includes an insulating substrate on at least one face of which are arranged the ferromagnetic path and the non-ferromagnetic, electrically conductive sectors.
According to a preferred configuration of the magnetic regulating device according to the invention, the magnetic dipole is a permanent magnet whose direction of magnetisation is perpendicular to the plane of the ferromagnetic path. The permanent magnet is comprised in an open structure defining a closed magnetic circuit and an air gap in which the wheel can move perpendicularly to the direction of magnetic flux generated by the magnet, the free ends of said structure extending substantially facing said ferromagnetic path when said oscillating element is at rest, the wheel being driven by the driving torque and the oscillating element is integral with a fixed frame.
The invention will be better understood upon reading the following description of a particular embodiment, provided by way of non-limiting illustration, and illustrated by means of the annexed drawings, in which:
a is a schematic cross-section of a first configuration of a magnetic regulating device according to the invention illustrating the means for dissipating the kinetic energy of the oscillating dipole and wherein the magnetic dipole is arranged on only one side of the ferromagnetic path.
b and 3c respectively show perspective and top views of an example embodiment of the magnetic regulating device shown in
a-5c and 5d-5f show graphs showing, as a function time, dynamic simulation of the effect of an abrupt increase in driving torque on the rotational speed of the rotor and on the resulting amplitude of the oscillating magnetic dipole, respectively for a prior art magnetic regulating device and a magnetic regulating device according to the invention.
a are partial top views of two variant embodiments of a ferromagnetic path including means of reducing eddy currents therein associated with kinetic energy dissipation means able to be fitted to a regulating device according to the invention.
b is a cross-section along the line VI-VI of
a is a schematic cross-section of a second configuration of a magnetic regulating device according to the invention, wherein a permanent magnet is arranged in a closed magnetic circuit and wherein the oscillating magnetic dipole is connected to a fixed frame and the magnetic path is integral with a rotor.
b is a variant of the configuration shown in
c shows a perspective view of a schematic example embodiment of the magnetic regulating device illustrated in
Referring to
Device 20 makes it possible to regulate the relative angular velocity of a wheel 22 and of a magnetic dipole, formed in this example by a permanent magnet 24, typically made of a neodymium, iron, and boron alloy. Magnet 24 is integral with an oscillating element 26, which is integral in turn with a rotor 28 rotating about an axis 28a and driven by a driving torque derived from a barrel (not shown) via a conventional going train with a predefined gear reduction ratio and of which only one wheel set 30 is shown in
In the illustrated example, rotor 28 is in the shape of an “S”, one end 28b of which carries oscillating element 26 and the other end 28c of which carries a counterweight 34 taking the form of a plate of suitable dimensions. Oscillating element 26 takes the general form of a frame including two opposite rigid posts 26a, 26b and two flexible posts 26c, 26d (symbolised by a spring in
Wheel 22 includes a periodic, ferromagnetic pole path 36 which alternates according to a center angle aligned on axis 28a (
The shape of ferromagnetic path 36 is devised to maintain a trajectory 38 of magnet 24 having a substantially sinusoidal shape closed on itself within the fixed reference of the frame. In this example, magnet 24 is arranged on only one side of the ferromagnetic path 36 comprised in wheel 22. Magnet 24 has a direction of magnetisation perpendicular to the plane of ferromagnetic path 36 as is particularly well illustrated in
Ferromagnetic path 36 is typically made of a material chosen from the group including soft iron, mu-metal or Supermalloy including nickel (75%), iron (20%), and molybdenum (5%). Ferromagnetic path 36 is typically cut into a plate made of one of these materials to define a ring including inner crenellations 36a and outer crenellations 36b each forming teeth of trapezoidal shape.
Regulating device 20 further includes means 40 for dissipating the kinetic energy of oscillating magnet 24 arranged adjacent to ferromagnetic path 36 on both sides thereof and in substantially the same plane, i.e. in the plane of ring 36 forming ferromagnetic path 36.
In the illustrated example, the kinetic energy dissipation means 40 include non-ferromagnetic, electrically conductive sectors typically made in the form of two rings 40a and 40b respectively interleaved inside and outside the ring forming ferromagnetic path 36. These sectors 40 are typically cut into a plate made of a material chosen from the group including gold, silver, copper, aluminium, platinum, palladium, titanium or nickel.
These non-ferromagnetic, electrically conductive sectors 40 are electrically insulated from ferromagnetic path 36 by means of an air gap or galvanic means 42 (
a to 5c and 5d to 5f are graphs showing, as a function of time, dynamic simulation of the effect of an abrupt increase in the driving torque (curves Cm1 and Cm2) on the rotational velocity of the rotor (curves Cv1 and Cv2) and on the amplitude of oscillation of the resulting oscillating magnetic dipole (curves Ca1 and Ca2), respectively for a prior art magnetic regulating device (without means for dissipating the kinetic energy of the magnet when it moves away from the ferromagnetic path) and for a magnetic regulating device 20 according to the invention.
The two curves Cm1 and Cm2 illustrated in
Two identical initial behaviours are noted in
Finally, it is also noted from curve Ca1 of
a and 7b respectively show a partial top view and cross-section of a second variant embodiment of a ferromagnetic path 36 able to be fitted to a magnetic regulating device 20 according to the invention. In this variant, ferromagnetic path 36 is made in the form of a laminated ring formed of a plurality of layers of ferromagnetic material insulated from each other and extending concentrically about a geometric axis A (
According to yet another variant that is not shown, magnetic path 36 may be made in the form of a laminated ring of the type described with reference to
According to one embodiment, ferromagnetic path 36 may be made in one-piece with wheel 22, for example as is shown in
According to a variant which is not shown, it is possible to arrange a ferromagnetic path 36 and inner 40a and outer 40b non-ferromagnetic, electrically conductive sectors on both surfaces of substrate 54, these elements being arranged in correspondence with each other. In such case, a permanent oscillating magnet 24 will be coupled to each of the ferromagnetic paths.
a shows a second configuration of a magnetic regulating device 20 according to the invention wherein the permanent magnet 24, oscillating in the direction symbolised by arrow D, is arranged in a magnetic circuit formed by a conductive frame 56, for example made of soft iron, and having a “C” shape, along which the magnet is integrated. In this configuration, oscillating magnet 24 is connected to a fixed frame 58 via return means MR and magnetic path 36 is integral with a rotor 60 driven in rotation by a motor torque C derived from a barrel via a conventional going train (not shown). Rotor 60 has an identical structure to wheel 22 described with reference to the preceding Figures. Wheel 22 moves inside air gap E delimited by the free ends of the branches of the “C”. Ferromagnetic path 36 carried by wheel 60 extends perpendicularly to the direction of magnetic flux generated by magnet 24. The free ends 56a, 56b of frame 56 are arranged substantially facing ferromagnetic path 36 when oscillating magnet 24 is at rest. The field lines Lc are thus guided inside the frame to above magnetic path 36 and are closed in passing therethrough so that the magnetic coupling of oscillating magnet 24 is improved.
b is a variant of the configuration shown in
c shows a perspective view of an example embodiment of the magnetic regulating device shown in
Finally, it will be noted that the regulating device according to the present invention can easily be integrated without adaptation in a timepiece movement in place of the conventional resonator formed by the balance spring and the escapement.
Number | Date | Country | Kind |
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13199425.3 | Dec 2013 | EP | regional |