Patent Grant
10222746
This application claims priority from European Patent Application No 15202458.4 of Dec. 23, 2015, the entire disclosure of which is hereby incorporated herein by reference.
The present invention concerns a mechanical timepiece movement comprising a balance and an escapement with a pallet-lever associated with the balance. In particular, the invention concerns a Swiss lever escapement.
Mechanical timepiece movements equipped with a sprung balance and a Swiss lever escapement have been known for a long time. This escapement comprises a pallet-lever provided with a fork and a guard pin, an impulse pin integral with the balance and cooperating with the fork to provide the balance with impulses for maintaining its oscillation. Next, the timepiece movement further comprises two banking pins or solid bankings for limiting the rotation of the pallet-lever in both directions. These pins define two locking positions for the pallet-lever between which it oscillates.
During each vibration of its oscillation, the pallet-lever passes through various phases: A locking phase, an unlocking phase, an impulse phase and a safety phase. During the locking phase or period, the pallet-lever rests against a banking pin, the escape wheel is immobile and the impulse pin describes an ascending and then descending supplementary arc. The unlocking phase concerns the unlocking of an escape wheel tooth resting on a locking-face of a first pallet-stone of the pallet-lever during each locking phase. This phase is generated by the impulse pin of the balance which rests on a first horn of the fork, with the balance then moving the pallet-lever through an unlocking-angle. During the impulse phase, the second horn of the fork rests against the impulse pin and exerts a force on the latter as a result of the torque provided by the escape wheel, whose aforementioned tooth applies a force on an impulse-face of the first pallet-stone. During this impulse phase, the balance receives an impulse for maintaining its oscillations and the pallet-lever continues its rotational movement through an impulse-angle. Finally, during the safety phase, the impulse pin is released from the fork and describes another ascending and then descending supplementary arc. The pallet-lever then effects the end phase of its rotation through a safety-angle, called the “run to the banking”, which ensures that the impulse pin is released from the fork and an escape wheel tooth is correctly positioned on the locking-face of the second pallet-stone.
During the locking phase, the guard pin of the pallet-lever ensures that the pallet-lever remains substantially in its locking-angle position. In a main embodiment, there is provided a safety roller integral with the balance staff and having a slot to allow the pallet-lever to rotate during the coupling between the impulse pin and the fork. The end of the guard pin is located at a short distance from the lateral surface of the safety roller when the pallet-lever is in one of its two locking positions resting on a banking pin. In particular, during the locking phases, when an undesired force acts on the pallet-lever, the pallet-lever may leave its locking position on the pin concerned and the guard pin then comes into contact with the lateral surface of the safety roller, which will result in a disruption to the oscillating motion of the balance. This causes a problem for the proper operation of the regulator. In any event, it is desirable for such an event to be as brief as possible. In a mechanical movement where the source provides mechanical energy to the escape wheel to maintain oscillating motion, as is the case with the Swiss lever escapement described above, draw is caused in the locking phases or periods by the escape wheel cooperating with the pallet stone on which it rests. This mechanical draw defines a return force for the pallet-lever which alternately presses it against the banking pins and returns it to said banking pins after the timepiece movement is subjected to shocks or sharp accelerations which momentarily drive the pallet-lever in rotation.
There are also known timepiece movements wherein energy is provided directly to the balance by a drive source, the balance is then a mechanical drive element which, on the one hand, transmits energy to drive a gear train and on the other hand, is used for regulating the rate of the movement by means for counting its oscillations. In this regard, CH Patent 573136 discloses an electrically maintained balance and a system for counting its oscillations formed by an inverted lever escapement. Electromechanical movements of this type are arranged and operate very differently from timepiece movements equipped with a Swiss lever escapement. In particular, given that the escape wheel is not subjected to an energy source other than that provided by the balance, this escape wheel does not exert any draw as in the case of a mechanical movement in which the drive energy is provided by a barrel, which drives, in particular the escape wheel. Since there is no mechanical draw, this document indicates that draw can be obtained by a magnet mounted on the pallet-lever and two positioning pins a priori made of a ferromagnetic material. These pins continuously attract the pallet-lever, the overall force of attraction being directed towards the pin closest to the magnet, which enables the pallet-lever to be held in its locking positions in which it rests alternately on the pins.
The Swiss lever escapement has proved capable of good regulation of a mechanical timepiece movement. However, this type of escapement remains a complex mechanism and it is sensitive to shocks and to sharp accelerations as explained above. In particular, it is difficult to simultaneously optimise two important parameters which are the efficiency of such an escapement and safety in the event of shocks, since the pallet-lever is the first element affected by these two technical features. It is known that even a small vibration or any rebounding of the pallet-lever during the locking periods results in disruption to the balance (via the guard pin which comes into contact with the safety roller and rubs against the latter), which impairs efficiency and chronometry. In known embodiments, the draw of the pallet-lever and therefore the holding thereof against a banking pin limiting its rotation, are ensured only by a certain torque applied to the pallet-lever by the escape wheel. It is noted that this torque may be too low, or completely lacking during part of the supplementary arc of the pin/balance, particularly in optimised escapements with a substantially constant torque because the escape wheel in such mechanisms advances slowly.
It is an object of the invention to overcome the aforementioned drawbacks of a conventional lever escapement and in particular to increase the force returning the pallet-lever to the banking pins during the locking periods, while minimising the consequences for chronometry and the efficiency of the escapement, or without impairing the latter and even allowing for some improvement in the dynamic operation of the escapement.
To this end, the invention concerns a mechanical timepiece movement wherein the escapement lever carries at least a first permanent magnet which has an axis of magnetisation oriented substantially tangentially to its circular axis of displacement when the pallet-lever is subjected to movements of rotation, this timepiece movement comprising a first element and a second element of high magnetic permeability respectively arranged on either side of at least a first permanent magnet so as to be substantially aligned on its circular axis of displacement. Next, the timepiece movement is characterized in that it further includes a second permanent magnet and a third permanent magnet respectively integral with the first and second elements of high magnetic permeability and each arranged on an opposite side to said at least a first magnet relative to said two elements of high magnetic permeability, and in that said at least a first magnet and a first assembly formed of the second magnet and the first element of high magnetic permeability, respectively a second assembly formed of the third magnet and the second element of high magnetic permeability, are arranged to generate, between the at least a first magnet and the first assembly, respectively the second assembly, a force of magnetic attraction on a first section of the aforementioned angular distance and a force of magnetic repulsion on a second section of said angular distance, and such that the second section corresponds to distances of separation between them which are greater than the distances of separation corresponding to the first section.
In a preferred embodiment, the first and second elements of high magnetic permeability have respective central axes that are substantially coincident with the respective axes of magnetisation of the second and third magnets, these respective central axes being substantially tangent to the circular axis of displacement of the first magnet.
As a result of the features of the invention, as will be explained in detail hereafter, there is obtained a particular magnetic draw which has the advantage of being exerted over only a relatively short angular distance from the locking position of the pallet-lever abutting on a banking element limiting its rotation. This short angular distance is followed by an angular range in which the pallet-lever is magnetically pushed back from the aforementioned banking element. Thus, in a Swiss lever escapement, in addition to increasing draw and consequently limiting the risk of disrupting the oscillating motion of the balance, the magnetic system of the invention, positively contributes to the transmission, by the pallet-lever, of a maintaining impulse to the balance, up to a central angular position of the pallet-lever. Other features of the invention will also appear from the detailed description of the invention.
Embodiments of the invention will be described below with reference to the annexed drawings, given by way of non-limiting example, and in which:
With reference to
Pallet-lever 4 carries two permanent magnets 20 and 22, which each have an axis of magnetisation oriented substantially tangentially to its circular axis of displacement 30 when the pallet-lever is subjected to rotational motions during its oscillation. The circular axes of displacement of the two magnets are coincident. Next, the timepiece movement comprises two elements of high magnetic permeability 26 and 27, which are respectively arranged on either side of the assembly formed of the two magnets 20 and 22, so as to be substantially aligned on circular axis 30. In the variant represented in
The timepiece movement further comprises two other permanent magnets 28 and 29, which are respectively integral with the two elements of high magnetic permeability. Magnet 28, respectively magnet 29 is arranged on the opposite side to magnet 20, respectively magnet 22 carried by the pallet-lever with respect to element 26, respectively element 27. Next, in projection along the circular axis of displacement 30, magnet 20 is of opposite polarity to the polarity of magnet 28, and magnet 22 is of opposite polarity to the polarity of magnet 29. The two elements 26 and 27 have respective central axes which are substantially coincident with the respective axes of magnetisation of magnets 28 and 29, these respective central axes being substantially tangent to the circular axis of displacement of magnets 20 and 22. The magnetic system formed of the various aforementioned magnetic elements thus comprises two identical magnetic devices arranged in an inverted manner on either side of a vertical plane of symmetry of the fixed magnetic elements. To explain the operation of each of these two magnetic devices incorporated in the escapement of the invention, there is represented, in
Device 32 comprises, on the one hand, a fixed assembly comprising a first magnet 28, respectively 29, and an element of high magnetic permeability 26, respectively 27, and on the other hand, a second magnet 20, respectively 22, which is arranged to move with respect to the fixed assembly. It will be noted that the following explanation is also valid for the other embodiments of the invention. The element of high magnetic permeability is arranged between the first magnet and the second magnet. This intermediate element is arranged to be in contact with or close to the first magnet. It consists, for example, of a carbon steel, tungsten carbide, nickel, FeSi or FeNi, or other alloys with cobalt such as Vacozet® (CoFeNi) or Vacoflux® (CoFe). The element of high magnetic permeability is characterized by a saturation field BS and a permeability μ. The first and second magnets are, for example, made of ferrite, FeCo or PtCo, rare earths such as NdFeB or SmCo. These magnets are characterized by their remanent field.
The element of high magnetic permeability 26, 27 has a central axis 34 which substantially coincides with the axis of magnetisation of the first magnet and also with the axis of magnetisation of the second magnet. The respective directions of magnetisation of the magnets are opposite; i.e. these magnets have reverse polarities along central axis 34. This central axis corresponds to the axis of displacement of the second moving magnet.
As a result of the arrangement of the element of high magnetic permeability between the two magnets wherein this element is situated and held close to the first magnet or against the latter, moving magnet 20, 22 is subjected to an overall force of magnetic repulsion which tends to move it away from element 26, 27 when the distance between the moving magnet and the element is greater than a distance Dinv; whereas the moving magnet is subjected to an overall force of magnetic attraction which tends to move it closer to element 26, 27 and, if there is no resistance, to hold it against the element when the distance between the moving magnet and the element is less than distance Dinv. The overall force of magnetic attraction thus defines a return force or a draw force of the moving magnet towards the element of high magnetic permeability, despite the fact that the two magnets are arranged with reverse polarities. Preferably, the distance between the first fixed magnet and the element of high magnetic permeability is smaller than or substantially equal to one tenth of the length of the first magnet along its axis of magnetisation.
Curve 36 of
In magnetic device 32, the axes of the magnets and the central axis of the element of high magnetic permeability are coincident and are collinear with the axis of displacement of the moving magnet. However, it will be noted that this magnetic device can remain functional without these conditions, since the direction of relative motion may, in particular, form a certain angle relative to central axis 34. The axis of displacement of the moving magnet may be a circular axis when the magnet is subjected to a rotational movement, as is the case in the escapement according to the invention. In such case, it will be noted that it is preferable that the axes of magnetisation of the two magnets tend to be aligned when the distance between them decreases, in particular in first section 38 of relative distance D.
The remarkable operation of magnetic device 32 is advantageously employed in the escapement of the timepiece movement according to the invention which combines two such identical magnetic devices to generate antisymmetric magnetic behaviour on the angular travel of the pallet-lever between its two locking positions and to define a bistable magnetic system for the pallet-lever in the presence of a mechanical force that is exerted thereon during pulses provided to the balance in both of its directions of oscillation More particularly, first magnet 20 and a first assembly consisting of magnet 28 and the first element of high magnetic permeability 26, respectively second magnet 22 and a second assembly, consisting of magnet 29 and the second element of high magnetic permeability 27, are arranged to generate between the first magnet and the first assembly, respectively the second magnet and the second assembly, a force of magnetic attraction on a first section of an angular distance between them and a force of magnetic repulsion on a second section of said angular distance, and such that the second section corresponds to distances of separation between them which are greater than the distances of separation corresponding to the first section.
In the
Curve 42 is substantially antisymmetric, with the overall magnetic force cancelled out at central point 44. It is understood that the behaviour of the magnetic system is symmetric, starting from this central point, both in the direction of first banking element 24, and in the direction of second banking element 25 or, in other words, the behaviour of the magnetic system is identical whether the pallet-lever moves from a first banking element towards the second banking element or vice versa. Thus, the magnetic forces are identical in both directions of rotation of the pallet-lever and thus in each of its vibrations. The aforementioned first and second assemblies and the respective moving magnets carried by the pallet-lever are arranged such that an overall magnetic force exerted by the first and second assemblies on the two moving magnets, and thus on the pallet-lever, is substantially cancelled out when the geometric centre of the two magnets is located substantially in the plane of symmetry of the first and second assemblies (at central point 44). Next, starting from this plane of symmetry along the circular axis of displacement of the moving magnets towards the first assembly, respectively the second assembly, the overall magnetic force defines, in a first angular range (section 48A, respectively 48B), a force of magnetic repulsion and then, in a second angular range (section 46A, respectively 46B) approaching the first assembly, respectively the second assembly, a force of magnetic attraction relative to the first or second assembly. The magnetic system according to the invention thus generates, in a first part of a first half vibration of any vibration of the pallet-lever, an overall force of magnetic attraction, defining a magnetic draw additional to the mechanical draw generated by the escape wheel, and, in a second part of this first half vibration, an overall force of magnetic repulsion.
There will be described below, with reference to
Escapement 52 is further distinguished by its two elements of high magnetic permeability 26A and 27A which are of cylindrical shape. Next, it differs in the positioning of moving magnet 54 on lever 10 of the pallet-lever, as the first and second fixed magnetic assemblies are arranged on either side of this moving magnet along its axis of displacement 30. Finally, in escapement 52, the elements of high magnetic permeability 26A, 27A also form the banking elements limiting the oscillating motion of the pallet-lever, with magnet 54 held in abutment with these elements in the locking periods of the pallet-lever. Thus, the two elements of high magnetic permeability are respectively coincident with the two banking elements. To protect the moving magnet in the event of shocks occurring at the end of the vibrations of the pallet-lever, a protective layer 56 is provided on the two lateral surfaces of this oscillating magnet which respectively move into abutment with the magnetic elements 26A and 27A.
Pallet-lever 4A is provided with a guard pin 12 cooperating with a lateral surface of the pivot shaft or of a roller 58 mounted around the latter, the guard pin being used to prevent the pallet-lever drawing away further than a safety-angle when the pallet-lever is in either of its two locking positions during its locking periods. The balance is represented in cross-section above safety roller 58. This balance comprises an impulse pin 60 integral with its pivot arbor and which cooperates with fork 8A to allow the latter to provide the balance with pulses for maintaining its oscillation by means of a drive force applied to an escape wheel (not represented) which is coupled to the pallet-lever. It will be noted that fork 8A extends lever 10, and guard pin 12 is arranged below the general plane of the pallet-lever.
In a preferred variant, the magnetic system of the invention is arranged such that, in the locking periods or phases, the clearance angular distance of guard pin 12 is less than or substantially equal to the magnetic draw angular distance corresponding to section 46A, respectively 46B on the graph of
The escapement of the second embodiment is represented in
After the actual unlocking, the pallet-lever moves forward under the impulse from the escape wheel until the second horn of the fork collides with the impulse pin (in this description, this catch up period of the balance occurs in the unlocking phase, but it may also be considered as a distinct phase). Initially, the force of magnetic attraction opposes the movement of the pallet-lever but this force rapidly diminishes with the angular distance. The unlocking phase may occur over an angle corresponding to 10%-20% of the total travel of the pallet-lever between the two banking elements preventing its rotation. It will be noted that during the catch up period, the magnetic force is very small and negligible in the example corresponding to curve 42.
Next, substantially as far as angular position 42C, is the impulse phase wherein the pallet-lever provides energy to the balance (maintenance). The corresponding impulse angular distance is represented in
It will be noted that there is slight magnetic braking at end of the impulse phase (in magnetic repulsion range 48B, which for the vibration concerned here, defines a magnetic braking range for the pallet-lever in rotation). This final magnetic braking dissipates very little energy during the impulse phase. It will be noted that it then continues during the safety phase; which is an advantage for limiting the impact against the second banking element. During the safety phase, after receiving a maintaining impulse, the pallet-lever travels through a safety angular distance before reaching abutment with the second banking element. Preferably, the magnetic system of the invention is arranged such that the safety angular distance is mostly situated within an angular range of magnetic braking of the rotating pallet-lever and thus of magnetic repulsion relative to the second banking element which moving magnet 54 is moving towards. Finally, in the final part of the safety phase, the pallet-lever is accelerated under the effect of an overall force of magnetic attraction towards the second banking element, which again constitutes a mechanical draw force for the next locking period of the pallet-lever.
It will be noted that the spherical shape is advantageous for the elements of high magnetic permeability because it is possible to make ferromagnetic microballs with a very high precision and a very good surface state, without affecting the magnetic properties of these elements. Further, for tribology and in the event of shocks with oscillating magnet 54, it is preferable to rest the pallet-lever against a ball rather than against a flat surface which may be irregular and not perfectly parallel to the hard layer 56 deposited on the lateral surfaces of the magnet.
| Number | Date | Country | Kind |
|---|---|---|---|
| 15202458 | Dec 2015 | EP | regional |
| Number | Name | Date | Kind |
|---|---|---|---|
| 2669089 | Straumann | Feb 1954 | A |
| 2964901 | Beyner | Dec 1960 | A |
| 2971324 | Beyner | Feb 1961 | A |
| 3183426 | Haydon | May 1965 | A |
| 3292438 | Korr | Dec 1966 | A |
| 3446007 | Cohen | May 1969 | A |
| 3611707 | Scholz | Oct 1971 | A |
| 3630018 | Nicholas | Dec 1971 | A |
| 3956941 | Faivre | May 1976 | A |
| 20070201317 | Houlon | Aug 2007 | A1 |
| 20150220061 | Stranczl | Aug 2015 | A1 |
| 20160357149 | Stranczl | Dec 2016 | A1 |
| Number | Date | Country |
|---|---|---|
| 286913 | Nov 1952 | CH |
| 573 136 | Feb 1976 | CH |
| 667885 | Mar 1952 | GB |
| WO 2006045824 | May 2006 | WO |
| Entry |
|---|
| European Search Report dated May 3, 2016 in European Application 15202458.4, filed Dec. 23, 2015 (with English Translation of Categories of cited documents & Written Opinion). |
| Number | Date | Country | |
|---|---|---|---|
| 20170185041 A1 | Jun 2017 | US |
