Self-starting profile for timepiece escapement

Abstract

One aspect of the invention relates to a watch escapement mechanism (100), comprising an anchor (10) and an escape wheel (20), said anchor (10) being arranged to cooperate with an inertial mass (40) of a mechanical oscillator (400), and, at the level of pallets (1) which carry or comprise said anchor (10), with teeth (2) of said escape wheel (20), wherein the contact between a pallet (1) and an escape tooth (2) (20) comprises at least three zones, a rest zone where the torque is in the negative direction, where the angle between the normal to the contact and the radial of the anchor is negative, a first zone corresponding to the first half-angle of lift where the torque is in the positive direction, where the angle ω1 is positive, and a second zone corresponding to the second half-angle of lift where the torque is in the positive direction, where the angle ω2 is positive.

Description

Technical field of the invention

[0001] The invention relates to a watch escapement mechanism, comprising at least one anchor and at least one escape wheel, said at least one anchor being arranged to cooperate, on the one hand, with an inertial mass of a mechanical oscillator, and subjected, directly or indirectly, to the action of elastic return means comprising said mechanical oscillator, and on the other hand, at the level of pallets which bears or comprises said anchor, with teeth which comprises said at least one escape wheel.

[0002] The invention relates to the field of watch escapement mechanisms. Technological background

[0003] One of the important properties of a watch escapement mechanism is self-starting. This is the escapement's ability to restart "on its own" after the balance wheel has stopped. There are two situations in which this property is important: At the end of the power reserve, the mainspring barrel is completely unwound, and the balance wheel stops. If, at this point, the mainspring barrel is wound using the stem, without moving the watch, the desired outcome is that the escapement restarts, meaning it sets the balance wheel oscillating again, without the watch needing to be moved. When the mainspring barrel is wound, a shock or sudden acceleration to the watch can momentarily stop the balance wheel, for example, in a position close to its resting position. The desired outcome is that, in the event of such a shock or sudden acceleration, the escapement restarts, meaning it sets the balance wheel oscillating again, without the watch needing to be moved again.

[0004] Most known exhaust systems can be roughly classified into two classes: potentially self-starting escapements, for example the Swiss anchor escapement and the coaxial escapement; intrinsically non-self-starting escapements, for example the detent escapement, widely used in marine chronometers, or the Robin escapement.

[0005] The criterion for distinguishing these two classes is whether, when the balance wheel is in its rest position (zero torque on the elastic return mechanisms: balance spring or flexible guide blades), the escape wheel can rest on a plane or not. If the escape wheel is resting on a plane when the balance wheel is in its rest position, then the escapement cannot start on its own.

[0006] Most escapements used in wristwatches are potentially self-starting, mainly because of the risk associated with acceleration: a shock or sudden acceleration must not stop the balance wheel, preventing it from starting to oscillate again.

[0007] Document CH 1 661 869 A4 shows an exhaust with an arrangement that facilitates self-starting. Summary of the invention

[0008] The invention described here relates to the optimization of the self-starting of an exhaust that is already potentially self-starting.

[0009] For a potentially self-starting escapement to begin, the mainspring torque must be sufficient to wind the balance spring, or more generally, to overcome the oscillator's restoring torque (e.g., the rigidity of the flexible guide). This means that when the mainspring barrel is almost fully unwound, a potentially self-starting escapement will not start on its own. When the mainspring barrel is fully wound, the situation depends on the caliber: some calibers start spontaneously, while others require a gentle nudge to begin.

[0010] The invention aims to improve the self-starting of calibers that are "potentially self-starting", but whose fully cocked barrel torque is not sufficient for the escapement to start on its own.

[0011] The invention consists of optimizing the shape of the pallet for the anchor and / or the tooth of the escape wheel to promote self-starting. This is achieved by creating a specific pallet and / or tooth geometry so that the restoring torque of the oscillator, transferred to the escape wheel, remains almost constant throughout the entire lifting angle.

[0012] For this purpose, the invention relates to a watch escapement mechanism according to claim 1.

[0013] The invention further includes a clockwork movement comprising such an escapement mechanism.

[0014] The invention further includes a timepiece, in particular a watch, comprising at least one such timekeeping movement. Brief description of the figures

[0015] The aims, advantages and features of the invention will become clearer upon reading the detailed description that follows, with reference to the attached drawings, where: there figure 1is a torque diagram, for the case of a standard Swiss lever escapement, the curve showing on the ordinate the restoring torque of the oscillator transferred to the escape wheel, as a function of the angle on the escape wheel on the abscissa; the figure 2 is a torque diagram that an escapement mechanism according to the invention aims to achieve; the figure 3 represents, schematically, partially and in plan view, on the left an anchor pallet, and on the right a tooth of the escape wheel bearing on this anchor pallet; the pallet has an evolving profile according to the invention, which is suitable for obtaining a torque diagram similar to that of the figure 2, and which comprises a succession of three zones: a resting plane, connected at the level of a first edge to a "leading balance" plane, connected at the level of a second edge to a curved "constant torque" surface; these specific designations are not exhaustive and concern the particular and non-exhaustive case of a balance-spring type oscillator; the figure 4 represents, in a similar way to the figure 3 , the case of a standard anchor pallet, and shows, on the left a standard anchor pallet, and on the right a tooth of the escape wheel resting on the edge of this standard pallet, which separates the initial rest plane and the impulse plane; the figure 5 shows the evolution of the torque, on the y-axis, as a function of the angle at the exhaust wheel on the x-axis, for the standard range of the figure 4This figure shows, on the one hand, an ideal case without friction represented by a dashed line, and on the other hand, a case with a coefficient of friction of 0.15 represented by a solid line; figure 6 represents, in a similar way to the figure 3 The case of an anchor pallet according to the invention, and shows, on the left, a pallet according to the invention, and on the right, a tooth of the escape wheel bearing on the second edge of this pallet, which separates two impulse zones: the "leading balance" plane where the elastic return means of the oscillator tend to drive the escape wheel, and the curved "constant torque" surface where these elastic return means tend to oppose the escape wheel. The profile of the standard pallet of the figure 4 is drawn in superposition, with a dashed line, along with its initial resting plane and its impulse surface. The resting plane of the pallet according to the invention is identical to that of the standard pallet of the figure 4 , whereas the single impulse plane of the standard pallet is replaced for the pallet according to the invention by two parts, the first part after the rest plane corresponds to the angular portion where the balance spring, or the flexible guide as the case may be, of the oscillator, assists the escape wheel in moving the pallet fork, and the following part corresponds to the angular portion where the balance spring, or the flexible guide, opposes the escape wheel in moving the pallet fork; the figure 7 , similar to the figure 5 shows the evolution of the torque, on the ordinate, as a function of the angle to the exhaust wheel on the abscissa, for the pallet according to the invention of the figure 6 This figure shows, on the one hand, an ideal case without friction represented by a dashed line, and on the other hand, a case with a coefficient of friction of 0.15 represented by a solid line; figure 8represents, schematically and in plan view, a detail of an anchor according to the invention; this figure includes, for certain surfaces of the pallet, the normal to this surface as a dashed line, and the radial line joining the pivot axis of the anchor to the middle of this surface as a solid line. It shows the direction and value of the various angles, the choice of which is important for achieving the objective of the invention; the figure 9 is a block diagram representing a timepiece, in particular a watch, containing a movement which includes means for storing and distributing energy and a gear train arranged to transmit energy to an escapement mechanism which includes an anchor and an escape wheel according to the invention, and a mechanical oscillator with an inertial mass returned by elastic return means, said inertial mass being arranged to cooperate with said anchor. Detailed description of the invention

[0016] The invention relates to a watch escapement mechanism 100, comprising at least one anchor 10 and at least one escape wheel 20. This at least one anchor 10 is arranged to cooperate, on the one hand, with an inertial mass 40 of a mechanical oscillator 400 and is subjected, directly or indirectly, to the action of elastic return means 50 comprising this mechanical oscillator 400. And this at least one anchor 10 is arranged to cooperate, on the other hand, at the level of pallets 1 which this anchor 10 carries or comprises, with teeth 2 comprising this at least one escape wheel 20.

[0017] According to the invention, at least one said pallet 1 and / or at least one said tooth 2 comprises an impulse zone having two zones, one for an angular portion where said elastic return means tend to drive said escape wheel 20, and the other for another angular portion where said elastic return means 50 tend to oppose said escape wheel 20, said two zones being arranged so as to minimize the maximum moment of the elastic return means seen by said escape wheel 20.

[0018] More particularly, each said pallet 1 and / or each said tooth 2 has an impulse zone comprising two zones, one for an angular portion where said elastic return means tend to drive said escape wheel 20, and the other for another angular portion where said elastic return means 50 tend to oppose said escape wheel 20, said two zones being arranged so as to minimize the maximum moment of the elastic return means seen by said escape wheel 20.

[0019] There figure 1shows the case of an earlier art escapement, for example a "standard" Swiss lever escapement, notably and not limited to that described by the Illustrated Professional Dictionary of Watchmaking, by M. GA Berner, ©< Swiss Watch Industry Federation FH, article 1660 F, where the curve showing on the ordinate the restoring torque CR of the oscillator transferred to the escape wheel, as a function of the angle on the escape wheel on the abscissa, has the form of a straight line between moment values ​​which are symmetrical: + Mmax, and - Mmax.

[0020] The angle range of the escape wheel corresponds to half the angle between two teeth θ= 360° / number of teeth / 2: this is the angle of advance of the wheel during one alternation of the oscillator, when the oscillator travels through the lift angle.

[0021] We see that in the left half of the angle range, the restoring torque of the oscillator (e.g., the balance spring torque) helps the anchor move (negative torque), so the balance wheel doesn't need any torque to move the anchor. Conversely, in the right half of the angle range, the restoring torque of the oscillator returns the anchor to its intermediate position, so the balance wheel must exert an increasingly greater torque to move the anchor (positive and increasing torque). The "intermediate position" here refers to the position of the anchor when the inertial mass of the oscillator is in its equilibrium position: in this position, elastic restoring mechanisms such as a balance spring or flexible guides exert no force or torque on the anchor.

[0022] The aim of the invention is to propose profiles of pallets and teeth such that the restoring torque CR of the oscillator transferred to the escape wheel is close to the shape visible on the figure 2 : a small angle range to the left, where the restoring torque of the oscillator transferred to the wheel is strongly negative; over this range, the elastic restoring means of the oscillator help the anchor to move forward, so the wheel has no torque to overcome; all the rest of the angle range where the torque is about constant, positive.

[0023] An energy-based approach demonstrates that by doing this, the torque required by the wheel to move the anchor will be up to four times lower than in the prior art. Indeed, when the friction coefficients are zero, mechanical energy is conserved. This means that the integral of the torque over the angle at the escape wheel must equal the elastic energy Eel in the oscillator's return spring when the oscillator moves out of the lift angle.

[0024] In the prior art, the integral of the torque over the angle of the escape wheel has a value of Mmax / 2 x θ / 2 (area of ​​each of the 2 left and right triangles of the figure 1 ), donc Mmax / 2 × θ / 2 = Eél , donc Mmax = 4 Eél / θ , And θ = 4 Eél / Mmax .

[0025] In the case of the invention, two cases are to be treated separately for the values ​​of the moments Mgauche (marked Mg on the figure 2 ) and Mdroite (marked Md on the figure 2 ) : In the left-hand range, the energy calculation gives: Mgauche × θ / 10 = − Eél , donc Mgauche = − 10 Eél / θ = − 2 , 5 Mmax and, in the right-hand range, Mdroite x θ x 9 / 10 = Eél, donc Mdroite = 10 / 9 × Eél / θ = env . 1 / 4 Mmax .

[0026] In the case where the friction coefficients are non-zero, these calculations are more complicated, but the rule "the torque required for self-starting becomes lower if we arrange for the restoring torque of the oscillator transferred to the wheel to be constant" generally remains valid.

[0027] The goal is therefore to define a suitable geometry for the paddles (or teeth) so that the restoring torque of the oscillator, transferred to the wheel, is approximately constant. figure 3 on the left side an anchor pallet 1, and on the right side a tooth 2 of the escape wheel 20 bearing on this anchor pallet 1, the pallet 1 has an evolving profile according to the invention, which is suitable for dealing with this problem, and which comprises a succession of three zones: A first zone Z1, including but not limited to a resting plane; a second zone Z2, where the elastic return means 50 of the oscillator 400 tend to drive the escape wheel; more particularly when the oscillator is a balance wheel and hairspring assembly, this second zone Z2 is a "leading balance wheel" surface, including but not limited to a "leading balance wheel" plane; a third zone Z3, where the elastic return means of the oscillator tend to oppose the escape wheel; more particularly when the oscillator is a balance wheel and hairspring assembly, this third zone Z3 is, including but not limited to, a "constant torque" surface. The tip of tooth 2 of the escape wheel 20 impels the anchor 10 across this entire third zone Z3. Once the tip of the tooth reaches the heel of pallet 1, the impulse on tooth 2 begins, where the "plane" of tooth 2 pushes on the heel of the pallet.

[0028] There figure 4shows, on the left a standard pallet of anchor 1, with a rest plane ZR and a pulse plane Z0, and on the right a tooth 2 of the escape wheel 20 resting on the edge of this standard pallet, which separates the rest plane ZR and the pulse plane Z0.

[0029] There figure 6 illustrates a palette 1 according to the invention.

[0030] The first zone Z1 according to the invention is the traditional resting plane ZR of a standard anchor pallet.

[0031] The second zone Z2 is connected to the first zone Z1 at the level of a first edge A. In a particular case, the second zone Z2 and the first zone Z1 are planar, and form a dihedral.

[0032] The third zone Z3 is connected to the second zone Z2 at a second edge B. In a particular case not shown, the second zone Z2 and the third zone Z3 are planar and form a dihedral angle. In another particular case not shown, the third zone Z3 is formed of two planar surfaces that form a dihedral angle.

[0033] Various simulations allow us to plot the curves of figures 5 and 7 , which show the evolution of the torque, on the ordinate, as a function of the angle at the exhaust wheel on the abscissa: the curve of the figure 5 for the standard pallet of the figure 4 ; the curve of the figure 7 for the palette according to the figure 3 specific to the invention.

[0034] THE figures 5 and 7 show, on the one hand, an ideal case without friction represented by a dashed line, and on the other hand, a case with a coefficient of friction of 0.15 represented by a solid line.

[0035] For the standard pallet of the figure 4 , there figure 5 The torque diagram from the simulation shows the "negative" torque of the spiral applied to the wheel, because the wheel tooth is not "glued" to the pallet. The maximum torque is approximately 0.59 without friction (0.85 with a friction coefficient of 0.15) (in arbitrary units).

[0036] There figure 6 The watch shows, on the left, a pallet according to the invention, and on the right, a tooth of the escape wheel bearing on the second edge B of this pallet, which separates the second zone Z2 from the third zone Z3. The profile of the standard pallet of the figure 4is drawn in superposition, with a dashed line, with its impulse surface Z0, its rest plane ZR being here constituted by the first zone Z1. It is clear that the anchor paddle according to the invention is, all other things being equal, elongated compared to the standard paddle, and that the impulse plane Z0 of the standard paddle is replaced by a composite surface resulting from the juxtaposition of the second zone Z2 and the third zone Z3. More particularly, the third zone Z3 comprises at least one flat surface, or, more particularly, is flat.

[0037] On the right side of the figure 7The torque diagram of the solution according to the invention is shown: optimized paddle (+ tooth): the maximum torque is approximately 0.29 without friction (0.45 with a friction coefficient of 0.15) (in arbitrary units for torque). The desired torque smoothing is indeed obtained, both in a theoretical variant without friction and in a variant close to real-world conditions with a friction coefficient of 0.15.

[0038] The relative gain in the return torque (CR) is close to a factor of 2, and less than the expected factor of 4. The reasons are: the actual impulse is not as symmetrical as in the diagrams; the "anchor - escape wheel" transmission ratio changes at the end of the impulse (when going from a "tooth tip - pallet plane" contact to a "tooth plane - pallet tip" contact), which already goes in the direction of optimization on a standard pallet.

[0039] There figure 8illustrates a geometric configuration suitable for this simulation. For each surface, the tangent to the curve is drawn at the midpoint of the relevant contact zone, and from this point, the following is drawn: a normal to the curve (and therefore perpendicular to this tangent) in dashed line, and a radial line joining the pivot axis of the anchor to this point, in solid line.

[0040] The angle from the normal to the radial does not always have the same direction. Here, an angle going in the trigonometric direction in the figure is called positive, and an angle going in the opposite direction is called negative.

[0041] More specifically: in a first zone Z1, in particular but not limited to a first plane, a first angle ω1, formed between on the one hand a first normal N1 to the first zone Z1 at a point P median of this first zone Z1 and on the other hand a first radial OP joining the pivot axis O of the anchor to this point P, is negative; the torque is in the negative direction; in a second zone Z2, in particular but not limited to a second plane, a second angle ω2, formed between a second normal N2 to the second zone Z2 at the point Q median of the second zone Z2 and a second radial OQ joining the pivot axis O of the anchor to this point Q, is positive; the torque is in the positive direction;in a third zone Z3, which is a curved surface in the variant illustrated by the figures, but which could also, but not limited to, include at least one third plane, a third angle ω3 formed between a third normal N3 to the third zone Z3 at the median point R of the third zone Z3 and a third radial OR joining the pivot axis O of the anchor to this point R is positive; the torque is in the positive direction.

[0042] More specifically, the second angle ω2 between the second normal N2 and the second radial OQ is less than atan(µ), where µ is the coefficient of friction between at least one pallet 1 and at least one tooth 2, the notation "atan" meaning the arctangent. The coefficient of friction µ is preferably between 0.10 and 0.30. More specifically, the coefficient of friction µ is between 0.12 and 0.24. Even more specifically, the coefficient of friction µ is equal to 0.2; the angle ω1 between the normal N1 and the radial OQ is then less than atan(0.2).

[0043] More specifically, the third angle ω3 between the third normal N3 and the third radial OR is greater than atan(µ). The friction coefficient µ is preferably between 0.10 and 0.30. More specifically, the friction coefficient µ is between 0.16 and 0.24. Even more specifically, the friction coefficient µ is equal to 0.2; the angle ω1 between the normal N1 and the radial OQ is then greater than atan(0.2).

[0044] It is understood that this geometry can be applied to both the pallets of the anchor and the teeth of the escape wheel.

[0045] The paddles can be fixed on the oscillator (friction rest).

[0046] The special profile described here can be on the tooth of the exhaust wheel.

[0047] More specifically, the contact between an anchor pallet 1 and a tooth 2 of the escape wheel 20 has at least three zones, a first zone, called the rest zone, where the torque is in the negative direction, where the angle between the normal to the contact and the radial of the anchor is negative, a second zone corresponding to the first half-angle of lift where the torque is in the positive direction, where the angle is positive and of a value less than a predefined value, and a third zone corresponding to the second half-angle of lift where the torque is in the positive direction, where the angle is positive and of a limited value greater than this predefined value.

[0048] More specifically, this predefined value is atan(0.2) in the case of a friction coefficient µ equal to 0.20; it would be atan(0.15) in the case of simulations of figures 5 and 7 with a coefficient of friction µ equal to 0.15.

[0049] The invention further comprises a watch movement 500, in particular and not limited to such as described in the Illustrated Professional Dictionary of Watchmaking, by M. GA Berner, ©< Swiss Watch Industry Federation FH, article 3091 A, comprising at least energy storage and distribution means 200 and a gear train 300 arranged to transmit energy to at least one such escapement mechanism 100, and at least one mechanical oscillator 400 with at least one inertial mass 40 returned by elastic return means 50, said inertial mass 40 being arranged to cooperate with said at least one anchor 10.

[0050] More specifically, the said mechanical oscillator 400 is a balance-spring oscillator.

[0051] Naturally, the invention applies to the case where the paddle 1 is made of a different material than the anchor 10 itself, which can allow for adjusting the optimal coefficient of friction µ. More particularly, at least one paddle 1 is attached to a body comprising the anchor 10, and is made of a different material than that of this anchor body.

[0052] More particularly, said mechanical oscillator 400 is a flexible-guided oscillator with at least one inertial mass 40 suspended by thin elastic blades constituting the elastic restoring means 50 of the oscillator 400.

[0053] The invention further includes a 1000 timepiece, in particular a watch, comprising at least one such 500 timepiece movement.

Claims

1. A timepiece escapement mechanism (100), including at least one lever (10) and at least one escapement wheel (20), said at least one lever (10) being arranged to cooperate, on the one hand, with an inertial mass (40) of a mechanical oscillator (400), and subjected, directly or indirectly, to the action of elastic return means (50) included in said mechanical oscillator (400) and, on the other hand, at pallets (1) carried by or included in said lever (10), with teeth (2) included in said at least one escapement wheel (20), at least one said pallet (1) and / or at least one said tooth (2) including an impulse zone including two zones, a second zone (Z2) for an angular portion where said elastic return means tend to drive said escapement wheel (20), and a third zone (Z3) for another angular portion where said elastic return means tend to oppose said escapement wheel (20), said two zones being arranged so as to minimise the maximum moment of said elastic return means seen by said escapement wheel (20) the contact between a said lever pallet (1) and one said tooth (2) of said escapement wheel (20) including at least three zones, a first zone (Z1) where the torque is of negative direction, where a first angle ω1 formed between a first normal to the contact (N1) and a first radial of the lever (OP) is negative, the second zone (Z2) corresponding to the first half angle of lift where the torque is of positive direction, where a second angle ω2 formed between a second normal to the contact (N2) and a second radial of the lever (OQ) is positive, and the third zone (Z3) corresponding to the second half angle of lift where the torque is of positive direction, where a third angle ω3 formed between a third normal to the contact (N3) and a third radial of the lever (OR) is positive.

2. The timepiece escapement mechanism (100) according to claim 1, characterised in that, in said second zone (Z2) corresponding to the first half angle of lift where the torque is of positive direction, said second angle ω2 between said second normal to the contact (N2) and said second radial of the lever (OQ) is positive and of a value which is less than a predefined value, and in said third zone (Z3) corresponding to the second half angle of lift where the torque is of positive direction, said third angle ω3 between said third normal to the contact (N3) and said third radial of the lever (OR) is positive and of limited value which is greater than said predefined value.

3. The timepiece escapement mechanism (100) according to claim 2, characterised in that said predefined value is atan (µ), where µ is the coefficient of friction between at least one said pallet (1) and at least one said tooth (2).

4. The timepiece escapement mechanism t (100) according to claim 3, characterised in that said coefficient of friction µ is comprised between 0.10 and 0.30.

5. The timepiece escapement mechanism (100) according to claim 4, characterised in that said coefficient of friction µ is equal to 0.2.

6. The timepiece escapement mechanism (100) according to one of claims 1 to 5, characterised in that at least one said pallet (1) is directly mounted on a body included in said lever (10), and is made of a material other than that of said body of said lever (10).

7. The timepiece escapement mechanism (100) according to one of claims 1 to 6, characterised in that said timepiece escapement mechanism (100) is of the potentially self-starting type.

8. The timepiece escapement mechanism (100) according to claim 7, characterised in that said timepiece escapement mechanism (100) is a Swiss lever escapement.

9. The timepiece escapement mechanism (100) according to claim 7, characterised in that said timepiece escapement mechanism (100) is a coaxial escapement.

10. A horological movement (500) including at least one escapement mechanism (100) according to one of claims 1 to 9, at least energy storage and distribution means (200) and a gear train (300) arranged to distribute energy to said escapement mechanism, and at least one mechanical oscillator (400) including at least one inertial mass (40) returned by elastic return means (50), said inertial mass (40) being arranged to cooperate with said at least one lever (10).

11. The horological movement (500) according to claim 10, characterised in that said mechanical oscillator (400) is a balance-spring oscillator.

12. The horological movement (500) according to claim 10, characterised in that said mechanical oscillator (400) is a flexibly guided oscillator with at least one said inertial mass (40) suspended by thin elastic blades constituting said elastic return means (50) of said mechanical oscillator (400).

13. A timepiece (1000) including at least one horological movement (500) according to one of claims 10 to 12.

14. The timepiece (1000) according to claim 13, characterised in that it is a watch.

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