CH716126B1 - Constant force mechanism for a timepiece. - Google Patents

Abstract

The invention relates to a constant force mechanism (1) for a timepiece comprising: a force input arranged to be driven via a mainspring; a force output (6c) arranged to drive a regulating system, said force output (6c) being coaxial with said force input; a constant force spring (5) having a first end arranged to be driven by said force input and a second end (5a) arranged to drive said force output (6c); an intermittent reloading system (6a, 2e) arranged to allow said force input to pivot in discrete steps depending on the rotation of said force output (6c); characterized in that one of said ends is integral in rotation with an adjusting wheel (2c), the latter being integral in rotation with a first of said force input and of said force output (6c) when the mechanism (1) is running, in that said adjusting wheel meshes with an adjusting pinion (2b) mounted on a movable frame (2a) which is also fixed in rotation to the same of said force input and said force output ( 6c) when the mechanism is running, and in that said pinion (2b) is arranged such that the angular ratio between said adjustment wheel (2c) and said frame (2a) is adjustable.

Description

Technical area

The present invention relates to the field of watchmaking. It relates, more particularly, to a constant-force mechanism arranged to ensure a substantially constant drive torque for the regulating system, which is independent of the winding state of the mainspring.

State of the art

[0002] In general, a constant-force mechanism comprises a constant-force spring arranged kinematically between a force input driven by a mainspring and a force output which drives a regulating system such as an escapement-balance-spring assembly, such that the constant force spring drives said output.

[0003] So that the constant-force spring does not discharge, an intermittent reloading system is provided. This system periodically locks and releases the inlet depending on the rotation of the outlet, which ensures that the winding state of said spring remains substantially unchanged. The driving torque of the regulating system consequently remains substantially unchanged provided that the torque provided by the mainspring is adequate to wind the constant-force spring.

[0004] Several variants of this type of mechanism have been developed.

[0005] The first, and perhaps the most successful, is revealed by the document CH296060. This constant force mechanism is arranged coaxially, and is therefore particularly compact.

[0006] The force input comprises an input mobile comprising a pinion integral in rotation with a plate to which is fixed a first end of the constant force spring. The other end of the latter is fixed to an output wheel set, which directly or indirectly drives an escape wheel set. A planet pinion is rotatably mounted on said plate so that it rolls on fixed internal teeth. This pinion is also integral in rotation with a star which is arranged to be blocked and released by a pin mounted on the output mobile, depending on the angular ratio between the input and output mobiles.

[0007] When the mechanism operates, the constant-force spring drives the output mobile, and the pin blocks the rotation of the star. The entry mobile is thus blocked and cannot pivot. Consequently, the output mobile is angularly offset relative to the input mobile. When the pin crosses the top of a tooth of the star, the latter is released, which allows the entry mobile to pivot to catch up with the exit. The planet pinion rolling on the fixed teeth, it pivots around its own axis of rotation until the next tooth of the star abuts against the pin, again blocking the entry mobile. Then, the cycle starts again, the torque to which the output mobile is subjected remaining between limits close to each other.

[0008] Since the constant-force spring is thus maintained in a relatively constant winding state, the driving torque of the escapement varies little, which keeps the amplitude of the oscillations of the balance wheel relatively constant. Excellent isochronism of the regulating organ is thus obtained.

Another example of such a system is revealed by the document EP1445669. This system applies a similar general principle, but uses an escapement-like system to trigger each rotational step of the force input. By modifying the angular position of the ferrule of the constant-force spring, the preload of the constant-force spring can be modified, which adjusts the drive torque of the regulating system and therefore the amplitude of its balance wheel.

[0010] However, this adjustment is difficult for the watchmaker, and is difficult, if not impossible, to adapt to the coaxial system mentioned above.

The object of the invention is therefore to provide a simple and precise adjustment of the preload of the constant force spring which can be applied to the same extent to at least each of the types of constant force mechanism mentioned above.

Disclosure of Invention

More specifically, the invention relates to a constant force mechanism as defined by claim 1. This mechanism comprises: a force input arranged to be driven directly or indirectly by a mainspring; a force output arranged to directly or indirectly drive a regulating system such as a balance-spring assembly associated with an escapement, said output being coaxial with said input; a constant force spring having a first end arranged to be driven by said input and a second end arranged to drive said output; an intermittent recharging system arranged to allow said inlet to pivot in discrete steps as a function of the rotation of said outlet, this intermittent recharging system being for example that of the coaxial type described in the document CH296060, of the exhaust type described in the document EP1445669 or any similar type.

According to the invention, one of said ends is fixed in rotation to an adjustment wheel which is in turn fixed in rotation either to said input or to said output at least when the mechanism is in operation and is in functioning. This adjustment wheel meshes directly or indirectly with an adjustment pinion mounted on a movable frame which is also integral in rotation with the same element chosen from among said input and said output mentioned in the preceding sentence, at least when the mechanism is in operation. Finally, said pinion is arranged such that the angular relationship between said adjustment wheel and said frame is adjustable. The gear between the adjustment pinion and the adjustment wheel thus renders the end in question integral in rotation with the movable frame when the mechanism is operating, while allowing this angular offset by the watchmaker.

[0014] In one embodiment based on the mechanism of document CH296060, the adjustment wheel may for example be integral in rotation with a shaft which carries an input pinion, the adjustment pinion being mounted on the mobile frame . In a variant based on the mechanism of document EP1445669, the adjustment wheel may for example be a ring gear on its outside which is carried by the movable frame and to which the outer end of said spring is fixed, said adjustment pinion being also carried by said chassis. In such a mechanism, it is immaterial whether the mobile frame is part of the entrance or the exit since the arrangement works equally well in each configuration.

[0015] Therefore, by rotating the pinion, the angular ratio between the gear wheel and the frame can be changed with great precision, which changes the spring preload with similar precision. The output torque of the mechanism can therefore easily be predetermined by the watchmaker in order to define the amplitude of oscillation of the regulating member, without requiring any dismantling or difficult handling of a ferrule.

[0016] Advantageously, said pinion is mounted with fatty friction on said movable frame, which is a particularly easy solution to implement.

[0017] Advantageously, said movable frame carries a satellite pinion integral in rotation with a stop wheel, said pinion meshing with fixed teeth (which may be internal or external teeth), the angular position of which relative to an element frame can be adjustable. For example, said fixed toothing can be carried by a ring comprising a radial slot in which takes place an eccentric element mounted with fatty friction in a hole provided in a frame element. Other alternatives are possible, as used in rackets (e.g. opposing screw arrangements, a clamping screw, friction mounting, ...) By these means, the angular position of the fixed teeth can be adjusted to compensate for backlashes in the mechanism.

[0018] Advantageously, said mechanism can be incorporated into a timepiece movement further comprising a chronograph mechanism driven by a power take-off which is kinematically upstream of said constant-force spring. Consequently, the flow of force driving the chronograph does not pass through the constant-force spring, and the maintenance torque of the regulating system is therefore not influenced by the state of the chronograph. The latter is thus driven by the force which is typically „lost“ in such a movement.

[0019] Advantageously, said power take-off is integral in rotation with said force input of said constant-force mechanism.

[0020] Advantageously, the movement further comprises a vertical clutch arranged between said power take-off and said chronograph mechanism.

Brief description of the drawings

Other details of the invention will appear more clearly on reading the following description, made with reference to the appended drawings in which: Fig. 1 is an isometric view of one embodiment of a constant force mechanism according to the invention; Fig. 2 is a plan view of the mechanism of FIG. 1; and Fig. 3 is a sectional view of the mechanism of Figure 1.

Embodiment of the invention

[0022] Figures 1 and 3 illustrate a non-limiting embodiment of a constant force mechanism 100 which is based on that described in the document CH296060. The principle of the invention can also be applied to a system of the type described in the document EP1445669, mutatis mutandis.

[0023] The mechanism 100 is driven from a barrel (not shown) via a going train, of which only the average mobile 1 has been shown. This mobile 1 meshes with a force input pinion 2h mounted integral in rotation with a shaft 2f that comprises a force input mobile 2. This mobile 2 is pivotally mounted in a "flying" manner by means of a ball bearing 7 whose outer part is fixed to a frame element (not shown).

[0024] The force entry mobile 2 also comprises a frame, which carries a 2d satellite pinion integral in rotation with a 2nd stop wheel with wolf teeth, the 2d satellite pinion meshing with a fixed internal toothing 8a carried by a ring 8 which is secured to a frame element (not shown). The input mobile 2 is arranged in the present case to perform one revolution per minute, but other speeds of rotation are of course possible.

The mechanism also comprises a force output wheel set 6, the output wheel 6c of which meshes with a pinion which comprises an escape wheel set 9, and a support 6b of which carries a pivoting beak 6a which cooperates with the wheel d 2nd stop in order to retain and release the latter according to the angular relationship between the input mobile 2 and the output mobile 6. This spout 6a is carried by a terminal element 5a of a constant-force spring 5 of the shape spiral, the terminal element 5a being pivotally mounted on the support 6b. The inner end 5b of the spring 5 is integral in rotation with the shaft 2f, the spring 5 therefore connecting the input wheel set 2 and the output wheel set 6.

[0026] When the mechanism 1 is in operation, the spout 6a retains the toothing of the second stop wheel, and consequently blocks the rotation of the input wheel set 2. Thus, the output wheel set 6 shifts angularly with respect to to the mobile input 2 until the spout 6a no longer retains the tooth of the 2nd stop wheel. Subsequently, the latter is released, which allows the input mobile 2 to pivot slightly, thus resetting the spring 5, the beak 2a blocking the next tooth of the stop wheel.

[0027] The gear ratios as well as the geometry of the 2nd stop wheel in the embodiment are arranged such that the latter is released once per balance wheel alternation (not shown), but other frequencies of release are within the reach of those skilled in the art. The drive torque available at the output wheel 6c therefore varies very little, which ensures a constant amplitude of the oscillations of the balance.

According to the invention, the pre-winding of the constant-force spring 5 is adjustable and, for this purpose, the input mobile 2 further comprises an adjustment wheel 2c integral in rotation with the shaft 2f. The adjustment wheel 2c meshes with an adjustment pinion 2b mounted with friction on the frame 2a so that the watchmaker can offset the frame 2a angularly with respect to the shaft 2f by acting on the pinion 2b via an ad hoc tool such as a screwdriver. Alternatively, the pinion 2b can be mounted free to rotate and fitted with a pawl or the like preventing untimely rotation. In the sense of the invention, the frame 2a is considered to be integral in rotation with the shaft 2f and therefore with the force input 2h during its normal operation, even if the angular relationship between these elements can be adjusted by the watchmaker. Indeed, the cooperation between the pinion 2b and the wheel 2c makes the shaft 2f integral in rotation with the frame 2a at all times except during an adjustment of the preload of the spring 5 by the watchmaker.

The inner end 5b of the spring 5 being integral in rotation with the shaft 2f, said angular offset is used to wind or unwind the spring 5, which adjusts its prewinding.

[0030] Consequently, the torque available at the output wheel 6c can be modified, which makes it possible to act indirectly on the amplitude of the balance wheel in order to optimize it.

The same principle for adjusting the preload of the spring 5 can also be applied to the escapement constant force mechanism of document EP1445669 or to any other similar mechanism. A person skilled in the art can therefore add on the one hand an adjustment wheel 2c, in particular in the form of a crown, which is integral in rotation with the outer end of the spring, on the other hand an adjustment pinion 2b mounted on the frame mobile. This modification is within the abilities of those skilled in the art and therefore does not require any more detailed explanation. By pivoting the pinion, the preload of the spring can thus be adjusted, the gear between the pinion and the adjustment wheel making the outer end of the spring integral in rotation with the frame when the mechanism is operating. It should also be noted that, in mechanisms of the type described by document EP1445669, it is irrelevant whether the shaft or the mobile frame is integral in rotation with the force input (the other being of course integral in rotation with the force output): indeed, the system works just as well if the central axis acts as input or output.

To return to the illustrated embodiment, the angular position of the fixed internal toothing 8a can also be adjusted by means of an eccentric adjustment 8c. The rod of this eccentric 8c is mounted by friction in a corresponding hole in a frame element, and its head takes place in a radial slot 8b which is made in the ring 8. By pivoting the eccentric 8c by means of a ad hoc tool such as a screwdriver, the watchmaker can modify the angular position of the toothing 8a in relation to the other elements and can thus adjust the penetration of the beak 6a into the toothing of the stop wheel 2e, in order to free from the indexing of different mobiles.

[0033] For completeness, we also note that the movement in which the constant force mechanism 1 according to the invention is integrated may also include a chronograph mechanism (partially shown in the figures), arranged kinematically independent of the spring. constant force 5 similar to the arrangement described in EP1445669. The power take-off of the chronograph mechanism is therefore located on a mobile which is kinematically upstream of the spring 5, the flow of force which drives said chronograph therefore passing neither through the spring 5 nor through the output mobile 6. Consequently starting the chronograph has no influence on the maintenance torque of the regulating system. This is because the chronograph is driven by the excess force that is normally 'lost' in a movement incorporating a constant force mechanism.

In the illustrated embodiment, a chronograph drive wheel 2g, which serves as a power take-off for the chronograph, is arranged integral in rotation with the shaft 2f such that it causes an input of a vertical clutch 3, which will not be described in detail. The release of this clutch drives a chronograph second hand 10. Since the release of the stop wheel takes place once per alternation of the balance wheel, the input wheel set also pivots once per alternation of the balance wheel, which allows the second hand a resolution of twice the oscillation frequency (i.e. one tenth of a second in the case where the balance wheel beats at a frequency of 5 Hz or one eighth of a second for a balance wheel at 4 Hz). The second hand 10 can be arranged to perform one revolution in a desired period, such as one revolution per second, per two seconds, per 30 seconds, per minute or any other desired speed of rotation. The other elements of the chronograph mechanism are well known to those skilled in the art and will therefore not be described further here.

Although the invention has been described above in connection with specific embodiments, additional variants are also possible without departing from the scope of the invention as defined by the claims.

Claims (10)

1. Constant force mechanism (1) comprising: - a force input (2h) arranged to be driven via a mainspring; - a force output (6c) arranged to drive a regulating system, said force output (6c) being coaxial with said force input (2h); - a constant force spring (5) having a first end (5b) arranged to be driven by said force input (2h) and a second end (5a) arranged to drive said force output (6c); - an intermittent reloading system (6a, 2d, 2e, 8a) arranged to allow said force input (2h) to pivot in discrete steps depending on the rotation of said force output (6c); characterized in that one of said ends (5b) is integral in rotation with an adjusting wheel (2c), the latter being integral in rotation with a first of said force input (2h) and of said force output (6c) when the mechanism (1) is running, in that said adjustment wheel meshes with an adjustment pinion (2b) mounted on a movable frame (2a) which is also integral in rotation with said first of said force input (2h) and said force output (6c) when the mechanism is in operation, and in that said pinion (2b) is arranged such that the angular ratio between said adjustment wheel (2c) and said frame (2a) is adjustable. 2. Constant force mechanism (1) according to claim 1, wherein said adjustment pinion (2b) is mounted with friction on said movable frame (2a). 3. Constant force mechanism (1) according to one of the preceding claims, wherein said movable frame (2a) carries a planet gear (2d) integral in rotation with a stop wheel (2e), said planet gear ( 2d) meshing with a fixed toothing (8a). 4. Constant force mechanism (1) according to the preceding claim, wherein the angular position of said fixed toothing (8a) relative to a frame element is adjustable. 5. Constant force mechanism (1) according to the preceding claim, wherein said fixed toothing (8a) is carried by a ring (8) comprising a radial slot (8b) in which takes place an eccentric element (8c) carried by a frame element. 6. Clock movement comprising a constant force mechanism (1) according to one of claims 1 to 5. 7. Clock movement according to the preceding claim, further comprising a chronograph mechanism driven by a power take-off (2g) which is kinematically upstream of said constant-force spring (5). 8. Clock movement according to the preceding claim, wherein said power take-off (2g) is integral in rotation with said power input (2h). 9. Clock movement according to one of claims 7 and 8, further comprising a vertical clutch (3) arranged between said power take-off (2g) and said chronograph mechanism. 10. Timepiece comprising a timepiece movement according to one of claims 6 to 9.