HK1252772B - Timepiece movement comprising a device for equalising a motor torque - Google Patents

Description

Watch movement including a device for equalizing dynamic torque

Technical Field

The present invention relates to a timepiece movement comprising a mechanism and a barrel configured to drive the mechanism via a kinematic connection, the kinematic connection being configured to apply a driving torque to the mechanism, the barrel comprising a barrel wheel and a power spring arranged in the barrel wheel so as to apply a motor torque to the mechanism, the motor torque varying with the degree of winding of the power spring. The timepiece movement also comprises an equalisation device kinematically connected to the barrel so as to be drivable by the barrel and capable of applying an auxiliary torque that adds to the power torque to form the driving torque. The auxiliary torque is configured to vary according to the degree of winding of the power spring so as to offset variations in the motor torque, thereby substantially equalising the driving torque.

Background Art

Watch movements that include balancing devices corresponding to the above definition are known. Devices with a main shaft for compensating for variations in the torque provided by the barrel are also known. Particularly known is the "stackfreed," a balancing device used in Germany in the 16th and 17th centuries to compensate for variations in the winding of a watch movement's mainspring. In practice, this involves a braking device consisting of a leaf spring carrying a roller at its end. The roller presses against the edge of a helicoidal cam, also known as a spiral, which is movably connected to the barrel. When the mainspring is fully wound, the leaf spring presses the roller firmly against the most protruding part of the spiral, while when it is less wound, the leaf spring presses the roller less firmly against the least protruding part. Because friction is roughly proportional to the applied pressure, its variations offset variations in the power torque. By appropriately adjusting the cam profile, the power can, in principle, be made nearly constant. A significant disadvantage of the "stackfreed" is that the resulting high friction absorbs a significant portion of the power. Another disadvantage is that, like most other known restoring devices, the leaf spring ages and gradually loses its elasticity. Furthermore, the intense friction causes accelerated wear of the components. Finally, as is well known, timepiece components are often of very small dimensions. Under these conditions, the fact that the mainspring is often quite sensitive to tolerances presents another problem.

Summary of the Invention

An object of the present invention is to overcome the above-mentioned drawbacks of the prior art. The invention achieves this object by providing a timepiece movement according to the appended claim 1 .

Within the useful range of the mainspring's winding degree, the formula according to which the change in the auxiliary torque offsets the change in the power torque is equivalent to stating that the derivative of the auxiliary torque with respect to the winding degree has an opposite sign to the derivative of the power torque with respect to the winding degree. Furthermore, it has been found that the derivative of the auxiliary torque with respect to time has an opposite sign to the derivative of the power torque with respect to time.

The balancing device according to the present invention comprises a first magnetic element and a second magnetic element, each arranged to exert a magnetic force on the other that varies depending on their relative position or the degree of winding of the mainspring. The auxiliary torque generated by the balancing device is caused by this variable magnetic force. In a main embodiment, at least one of the first and second magnetic elements comprises a permanent magnet. In an advantageous variant, the two magnetic elements are formed, respectively, by a bipolar permanent magnet and a cam made of a high-permeability magnetic material. Generally, a "magnetic cam" should be understood as a magnetic element having at least one physical parameter (radial/lateral or axial, as the case may be) that plays a role in the magnetic interaction considered between the cam and another magnetic element associated with the cam, and that varies depending on the direction of relative displacement between the cam and the other magnetic element so as to generate a magnetic force between them, together with the other magnetic element, the strength of which varies depending on the relative displacement. It should be noted that the physical parameter in question can be a parameter inherent to the cam, such as the magnetic flux intensity provided by the magnetized material forming the cam, or a parameter related to the other magnetic element, in particular the distance between them.

The balancing device according to the present invention offers several advantages. In particular, it forms a contactless system, allowing the generation of the variable assisting torque it provides to be frictionless. Furthermore, it is known that the magnetic force induced by a permanent magnet is a conservative force derived from magnetic potential energy. Therefore, the assisting torque provided by the balancing device also originates from magnetic potential energy, making the energy dissipated by the balancing device of the present invention during the entire winding/relaxing cycle of the mainspring theoretically zero. The advantages conferred by this balancing device are therefore readily understood if one understands that, in particular with a "force-balancing wheel"-type device, the energy used for the assisting torque is dissipated entirely.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will emerge on reading the following description, given purely by way of non-limiting example and with reference to the accompanying drawings, in which:

- Figures 1A and 1B are two basic views respectively showing two alternative configurations of the same magnetic cam that can be used in the balancing device of a timepiece movement according to the invention;

FIG2 is a partial plan view of a timepiece movement according to a first specific embodiment of the invention; this partial view shows the barrel and the balancing device;

FIG3 is a partial perspective view from the side of a timepiece movement according to a second specific embodiment of the invention; this partial view shows a portion of the barrel and the balancing device;

FIG4 is a partial perspective view of the watch movement of FIG3 , seen from below; this partial view shows a part of the barrel and the balancing device;

FIG. 5 is a partial perspective view from below of the barrel and balance device of FIGS. 3 and 4 ; some parts have been omitted to allow the magnetic cam and the magnet to be shown.

DETAILED DESCRIPTION

1A and 1B show two alternative arrangements of a magnetic system formed by a first magnetic element and a second magnetic element, respectively, for an balancing device according to the invention. In both arrangements shown, the first magnetic element and the second magnetic element are a magnetic cam and a dipole magnet, respectively. The cam is planar and made of a magnetic material (e.g., NdFeB, SmCo, or PtCo) to form a second permanent magnet, or of a ferromagnetic material. The cams 3A, 3B are each arranged to rotate about an axis 5 perpendicular to the general plane of the cams. The dipole magnet is mounted here so as to be fixed relative to the cam, with its north-south axis oriented substantially in the direction of the axis of rotation 5.

In the examples of Figures 1A and 1B, the bipolar magnet 7 is arranged in the same plane as the cams 3A and 3B, respectively. A radial magnetic system for the cam-magnet assembly is the subject of this disclosure. In these examples, the cams are either formed from a magnet with a substantially radial magnetization, where the magnetization is in the same direction as the magnetization of the bipolar magnet, so that the magnetic interaction is attractive, or from a magnetic material with high magnetic permeability, which also interacts with the bipolar magnet in an attractive manner. In the illustrated variant, the cams 3A, 3B are in the form of a spiral, and the profile of the cam opposite the bipolar fixed magnet (hereinafter also referred to as the "edge") is helical (i.e., a rotation forming a geometric spiral shape), so that the distance between the fixed magnet and the cam changes as the cam rotates about axis 5. Due to this helical shape, the edge of the cam is not completely perpendicular to its radius. As a result, the magnetic attraction force exerted by the magnet on the cam (indicated by the arrow labeled Fm) is not purely radially oriented, so this force Fm has a tangential component (indicated by the arrow labeled Ft).

The two configurations schematically illustrated in Figures 1A and 1B differ in the direction of the cam's edge's inclination, or in other words, the direction of the spiral defined by that edge. In fact, it can be seen that in Figure 1A , the distance between the edge of cam 3A and magnet 7 gradually increases during the cam's counterclockwise rotation, while in Figure 1B , conversely, the distance between the edge of cam 3B and magnet 7 gradually decreases during the cam's similarly counterclockwise rotation. Consequently, the strength of the magnetic attraction varies. Referring first to Figure 1A , it can be seen that the distance between the cam's edge and magnet gradually increases during the aforementioned rotation. This increase in distance brings with it a concomitant decrease in the strength of the tangential magnetic force exerted by magnet 7 on cam 3A. It should be noted that in variations where the cam is formed from a magnetized material, in addition to the variation in magnetic force strength caused by the varying distance between the cam and the fixed magnet, the angular variation in the magnetic flux intensity generated by the cam can result in a complementary variation in strength. This increases the tangential and angular magnetic forces, which contributes to the assistive torque of the balancing device. Referring now to FIG. 1B , in contrast to FIG. 1A , a reduction in the distance between the magnet and the cam results in a concomitant increase in the strength of the magnetic force. FIG. 1A also illustrates that the tangential component Ft of the magnetic force is opposite to the direction of rotation of cam 3A. In contrast, in FIG. 1B , the orientation of the tangential component is aligned with the direction of rotation of cam 3B. In summary, the configuration of FIG. 1A generates a force that opposes the rotation of the cam, with the strength of this force decreasing with rotation, while the configuration of FIG. 1B generates a force with the same mathematical sign as the direction of rotation of the cam, with the strength of this force increasing with rotation. In other words, the configuration of FIG. 1A generates a torque in the opposite direction of the cam's rotation, while the configuration of FIG. 1B generates a torque in the same direction as the cam's rotation.

The arrangement of the magnetic equalizing device does not necessarily comprise a radial magnetic system as shown in Figures 1A and 1B. In fact, as will be seen in more detail in the second embodiment further described with reference to Figures 3 to 5, the arrangement of the cam-magnet assembly can form an axial magnetic system. In this case, the second magnetic element (a bipolar magnet) is not arranged in the same plane as the cam, but above or below the cam, so that the magnetic interaction between the magnet and the cam generates a force whose resultant has a main component parallel to the axis of rotation of the cam. It should be noted that a radial or axial arrangement is not always accompanied by a radial or axial magnetization of the elements of the magnetic assembly. In fact, especially in radial magnetic systems, when the cam is formed by a magnet, the magnetization axis of the cam can be axial. The same applies to the magnet associated with the cam.

FIG2 is a partial plan view of a timepiece movement according to a first specific embodiment of the present invention. This partial view shows only the movement components that are indispensable for understanding the present invention. The other components, in particular the going train and the winding mechanism, may be conventional and are not shown.

The movement shown in Figure 2 includes a barrel 11, which includes a pinion 13 mounted on its shaft. When the barrel's mainspring (not shown) unwinds while driving at least one of the movement's mechanisms, pinion 13 rotates clockwise. As shown in this figure, pinion 13 drives an auxiliary reduction gearing system, which first includes a first movement formed by a wheel 15 and a pinion 17. Wheel 15 is arranged to mesh with barrel pinion 13, while pinion 17 is arranged to mesh with wheel 19. Gear 19 carries a radially oriented bipolar magnet 107, mounted eccentrically on its plate. A magnetic spiral cam 103 is fixed opposite and concentric with wheel 19. Furthermore, two radial limit stops 21 and 23 are provided, integral with magnetic cam 103. The limit stops 21 and 23 are preferably made of a non-magnetic material and are arranged on either side of the discontinuity 22 of the edge of the cam so that the magnet 107 can never move relative to this discontinuity.

The transmission ratio of the reduction gearing, to be described, varies with the number of rotations the barrel makes between its fully wound and fully unwound states. In fact, this ratio must be greater than the number of rotations of the barrel, so that the pivot angle of magnet 107, integral with wheel 19, is always less than 360°. In other words, the arrangement is such that, for each rotation of the barrel between its fully wound and fully unwound states, wheel 19, carrying either the first or second magnetic element, makes at least one rotation. In the illustrated example, the barrel's shaft makes seven rotations to move the barrel's spring from fully wound to fully unwound, or vice versa. On the other hand, the transmission ratio of the reduction gearing is 8.4. Under these conditions, during operation of the watch, wheel 19 rotates slightly less than 5/6 of a turn clockwise. Two limit stops 21 and 23 define the two extreme angular positions of wheel 19 by stopping magnet 107 at one or the other end of its travel.

In the auxiliary reduction gearing just described, wheel 19 rotates in the same direction as the pinion of barrel 13. Under these conditions, when the barrel's mainspring (not shown) relaxes during movement operation, wheel 19 and magnet 107 rotate clockwise. Because the variable radius of cam 103 increases in the counterclockwise direction, the tangential component Ft of the magnetic attraction between magnet 107 and cam 103 acts on movable magnet 107 in the counterclockwise direction. Therefore, when the barrel's mainspring relaxes and wheel 19 rotates clockwise, the magnetic force opposes this rotation. Furthermore, the strength of the magnetic force decreases as the mainspring relaxes. It will be appreciated that the balancing device just described provides an auxiliary magnetic torque that counteracts the dynamic torque, and that the magnitude of this auxiliary magnetic torque decreases in proportion to the magnitude of the dynamic torque as the barrel's mainspring relaxes. From what has been explained with respect to Figures 1A and 1B, it will be further understood that, according to an alternative variation of the first embodiment, the balancing device can also easily provide an auxiliary magnetic torque that enhances the dynamic torque, and when the mainspring of the barrel relaxes, the magnitude of the auxiliary magnetic torque increases as the dynamic torque decreases.

According to the invention, the barrel of a watch movement is configured to drive the clockwork via a kinematic connection that provides the power torque to the clockwork. In the case of a watch movement, the kinematic connection configured to drive the clockwork typically comprises a speed-increasing gearing (for example, the clockwork driven is an escapement with a Swiss pallet fork, and the speed-increasing gearing forms the going train of the watch movement). According to a first variant, the going train (not shown) is driven directly by pinion 13 of the barrel. In this case, it will be noted that the going train is arranged parallel to the equalizing device (as with a standard "equalizing wheel"). In another variant, the mechanism is driven by the barrel via the equalizing device. In this case, at least a portion of the auxiliary gearing of the equalizing device forms the kinematic connection between the barrel and the mechanism.

Referring again to FIG. 2 , it can be seen that the barrel wheel of barrel 13 does not include any external toothing. This is a so-called smooth barrel. In fact, similar to what is known regarding spindle-moving devices, the present invention requires that the balancing device be fixed to the barrel at a certain angle. In other words, the two limit angles for the angular travel of wheel 19, defined by limit stops 21 and 23, must correspond to the "fully wound" and "fully relaxed" states of the barrel's spring, respectively. To meet this constraint, in a variant in which the bipolar magnet is fixed relative to the barrel's support (the plate), both winding and relaxing of the barrel's spring are arranged to act on the same movable part of the barrel. Thus, according to the example of FIG. 2 , both the drive of the mechanism and the winding of the barrel are exerted by pinion 13 of the barrel, which is also connected to the balancing device. Winding can be achieved, in a manner known per se, via the winding crown and/or via an oscillating mass. Furthermore, the winding mechanism may mesh directly with barrel pinion 13, or with another gearing element downstream of the barrel pinion. However, it should be noted that, in another variant in which the bipolar magnet rotates integrally with the barrel shaft, the barrel may be wound and unwound via the barrel shaft and the barrel wheel, respectively, or vice versa.

It should be noted that the equalizing device just described can also be used in conjunction with a power reserve indicator. To this end, in a first variant, a pointer is mounted on the axis of wheel 19. In a second variant, to reduce the angular travel of the power reserve indicator or, in particular, to provide an indicator with linear motion, a rod is connected to cam 103. This rod defines a cam follower and is arranged to abut against the side surface of cam 103. The power reserve indicator can be integral with the rod or formed by a separate element actuated by the rod.

The detailed views of Figures 3 to 5 illustrate a second embodiment of the present invention, corresponding to a minute repeater watch movement. The minute repeater mechanism is a ringing mechanism driven by a dedicated barrel. The ringing mechanism operates via hammers that, when actuated, repeatedly strike a ringing spring. A particular feature of this mechanism is that the speed at which the ringing occurs depends on the magnitude of the driving torque received by the barrel.

Referring first to Figures 3 and 4 , the barrel (generally designated 111 ) can be seen. The barrel shown is formed by a barrel wheel of barrel 131 housing a mainspring 133, a barrel cover 135 (shown in Figure 5 ) that closes the housing formed by the barrel wheel, and a barrel arbor 137 that passes through the barrel and pivots, via its ends, between the plate and a bridge (not shown). As can be seen again in Figure 4 , barrel arbor 137 is integral with a toothed movable element comprising pinion 113 and wheel 139.

Figures 3 and 4 again illustrate the winding rack 141 and the one-way wheel assembly 143. One-way wheel assemblies are known per se. In this example, wheel assembly 143 comprises an input wheel 145 meshing with the winding rack 141 and an output wheel 147 (visible in Figure 3) meshing with the barrel pinion 113. The toothed wheels 145 and 147 are coaxial and pivotable relative to each other. One of these wheels carries a coaxial ratchet (not shown) sandwiched between the input and output wheels. A pawl (not shown) pivots on the plate of the wheel opposite the ratchet. This pawl is locked against the periphery of the ratchet by a spring (not shown). The pawl is configured to engage the teeth of the ratchet when the input wheel rotates counterclockwise and to slide against the ratchet when the input wheel rotates clockwise.

Barrel 111 is designed to drive a ringing wheel mechanism (not shown) via the teeth of wheel 139. As already mentioned, wheel 139 is integral with barrel shaft 137. It will be appreciated that as the barrel's spring gradually unwinds, the barrel shaft transmits a power torque to wheel 139, driving it counterclockwise. This power torque varies with the barrel's degree of winding. Furthermore, because the torque driving the ringing mechanism varies with the barrel's degree of winding, the speed at which the ringing is performed also depends on the barrel's degree of winding. It should be noted that wheel 139 rotates less than one full revolution between its fully wound and fully unwound states. Magnet 207 is positioned on wheel 139 so that it does not pass over the discontinuity of the cam's edge when the barrel is unwound between these two extreme states.

The barrel is wound using rack 141. The watch wearer can manually activate the rack using a button (not shown) or a slider (not shown) located on the watch case. When the watch wearer activates the rack, it pivots, simultaneously driving the input wheel 145 of the one-way wheel assembly 143 in the counterclockwise direction. The output wheel of the one-way wheel assembly is driven by the input wheel, which in turn drives the barrel's pinion 113, which rotates slightly less than one revolution clockwise, thereby winding the barrel 113. When the watch wearer then releases the slider or button, a spring (not shown) locks the rack in the direction opposite to the arrow in Figure 4. The rack's reset stroke has the effect of driving the input wheel 145 of the one-way wheel assembly in the clockwise direction. Because the one-way wheel assembly does not transmit rotation in the clockwise direction, the barrel's shaft is not driven in the reverse direction.

FIG5 is a partial perspective view from below of a second embodiment, also the subject of FIG3 and FIG4 . In FIG5 , certain components, including the rack and wheel 139, have been omitted to allow for visibility of the two magnetic elements of the balancing mechanism according to the present invention. In the example shown, these two magnetic elements are a magnetic cam 203 and a cylindrical bipolar magnet 207. As can be seen, the cam shown is very similar to the magnetic cams 3 and 103 described above. Cam 203 is concentrically mounted on the barrel shaft and fixed to its cover 135. Bipolar magnet 207 itself is mounted on the plate of wheel 139 at a distance from the axis of rotation, thereby aligning with the cam. Thus, unlike in the first embodiment, the bipolar magnet is not arranged in the same plane as the cam, but rather in a plane above and parallel to the cam's plane. In this case, the magnet preferably has an axial magnetization direction (parallel to the barrel's axis of rotation). It will be appreciated that under these conditions, the magnetic interaction between the magnet and cam has a different, substantially axial, primary direction. It will therefore be mentioned that the arrangement of the equalizing device is here of the axial type, which has the advantage of being generally more compact than devices of the radial type.

In the ringing mechanism just described, magnet 207, integral with wheel 139, rotates in the same direction as barrel shaft 137. Under these conditions, as the mainspring of barrel 133 relaxes while driving the ringing mechanism, magnet 207 rotates counterclockwise relative to the cam. As shown in Figure 5, the radial width of cam 203 increases during the counterclockwise rotation. Under these conditions, the strength of the magnetic interaction between the magnet and cam increases as the mainspring of the barrel relaxes. The resulting magnetic potential energy creates a tangential force on the magnet. Thus, the balancing device just described provides an auxiliary torque applied to the mainspring shaft that is in the same direction as the dynamic torque and increases as the dynamic torque decreases.

Furthermore, it is understood that various modifications and/or improvements obvious to a person skilled in the art may be applied to the embodiments of the subject matter of the invention without departing from the scope of the invention as defined by the accompanying claims.

Claims (13)

1. A watch movement comprising a mechanism and a mainspring barrel (11; 111), the mainspring barrel (11; 111) being configured to drive the mechanism via a motion connector, the motion connector being configured to apply a driving torque to the mechanism, the mainspring barrel including a power mainspring (133) configured to allow the mainspring barrel to apply a driving torque, the watch movement characterized in that it further includes an equalizing device (3, 7; 103, 107; 203, 207) movably connected to the mainspring barrel so as to be driven by the mainspring barrel and to apply an auxiliary torque, the auxiliary torque being added to the driving torque to form a combined torque. The driving torque is generated by the auxiliary torque, which varies with the winding degree of the power spring to counteract the variation in power torque caused by the power spring, thereby substantially balancing the driving torque within the useful range of the winding degree; and the balancing device includes a magnetic system formed by a first magnetic element (3; 103; 203) and a second magnetic element (7; 107; 207), the first magnetic element and the second magnetic element being arranged such that when the balancing device is driven by the spring barrel, they move relative to each other by applying a magnetic force to each other, the magnetic force varying with the relative position occupied by the first magnetic element and the second magnetic element and generating the auxiliary torque. 2. The watch movement according to claim 1, characterized in that the auxiliary torque applied by the balancing device (103, 107) counteracts the power torque. 3. The watch movement according to claim 1, characterized in that the power torque and the auxiliary torque applied by the equalizing device (203, 207) have the same direction. 4. The watch movement according to claim 1, wherein the first magnetic element (3; 103; 203) is a magnetic cam. 5. The watch movement according to claim 4, wherein the magnetic cam has a helical shape. 6. The watch movement according to claim 4 or 5, wherein the magnetic cam is formed of a ferromagnetic material. 7. The watch movement according to claim 4 or 5, characterized in that the magnetic cam (3; 103) and the second magnetic element form a radial magnetic system. 8. The watch movement according to claim 4 or 5, characterized in that the magnetic cam (203) and the second magnetic element form an axial magnetic system. 9. The watch movement according to any one of claims 1 to 5, characterized in that the second magnetic element (7; 107; 207) is a bipolar permanent magnet. 10. The watch movement according to any one of claims 1 to 5, characterized in that the mechanism driven by the mainspring barrel (11) includes an escapement for the spiral balance wheel. 11. The watch movement according to any one of claims 1 to 5, characterized in that the mechanism driven by the mainspring barrel (111) is a ringing mechanism. 12. The watch movement according to any one of claims 1 to 5, characterized in that the equalizing device includes an auxiliary reduction gear device kinetically connected to the mainspring barrel, one wheel (19) of the auxiliary reduction gear device carrying the first magnetic element or the second magnetic element, and arranged to rotate less than one revolution when the mainspring barrel rotates multiple revolutions between a fully wound state and a fully relaxed state. 13. The watch movement according to claim 12, wherein the equalizing device further comprises at least partially a device for indicating power reserve.