US3465515A - High-frequency watch movement - Google Patents

Description

Se t. 9, 1969 F. JAQUET 3,465,515

HIGH-FREQUENCY WATCH MOVEMENT Filed Oct. 31, 1966 United States Patent 3,465,515 HIGH-FREQUENCY WATCH MOVEMENT Francis Jaquet, Le Locle, Neuchatel, Switzerland, as-

signor to Girard-Perregaux et Cie. S.A., Neuchatel, Switzerland, a Swiss company limited by shares Filed Oct. 31, 1966, Ser. No. 590,768 Claims priority, application Switzerland, Nov. 3, 1965, 15,170/ 65 Int. Cl. G04b 17/06 US. Cl. 58-107 8 Claims ABSTRACT OF THE DISCLOSURE A Watch movement having a balance assembly which oscillates in the range of 31,000 to 60,000 oscillations per hour and which has a moment of inertia of less than 9 mg. cm

The present invention is directed to a watch movement having a high frequency of oscillation in the balance wheel.

It is customary, in commonly known watch movements, for the balance wheel to oscillate 18,000 times per hour whereby the escape wheel is freed and advances one-half its tooth pitch, five times per second. In order to realize this, the characteristics of the hairspring are determined as a function of the moment of inertia of the balance wheel so that the natural frequency of the assembly will result in the desired number of oscillations.

Optimum operating precision is obtained through reduction of friction between moving parts of the movement, this necessitating exceedingly high precision i the manufacture of said parts. Additionally, operating precision is sought through improved structural arrangements in the movement.

The operating precision of a movement is expressed in terms of quality factor and it depends particularly upon the moment of inertia of the balance assembly. Given certain values of amplitude and frequency of oscillation in the isochronous assembly, the quality factor value will be directly proportional to the closeness with which the moment of inertia of the balance assembly approaches a particular defined value.

In certain measuring instruments such as meters or chronometers for sports events, the oscillating assembly is constructed so as to oscillate at a very high frequency so that the second hand marks the tenth, fiftieth or onehundredth of a second. In this instance, the amplitude of the oscillations is small while the balance has a relatively high moment of inertia. The structural arrangements which are therefore necessitated are cumbersome, costly and delicate. Such instruments are not portable watches, and when they are driven by a drive spring, their reserve power does not exceed about ten hours.

The energy which the escape wheel must impart to the balance-hairspring assembly per unit of time in order to sustain its movement depends on various factors of which the frequency of oscillation of the assembly is an important one. The friction in the bearings, between the lever fork and the rollers as well as the friction and impact between the pallet stones and the escape wheel increase with the frequency. The same is true of the losses in the hairspring itself.

Now the total energy consumed in the oscillating assembly and in the escapement constitutes the greatest portion of the total energy consumed by the watch. It determines the dimensions to be given the mainspring and the barrel so that the watch can operate for a sufficiently long time Without it being necessary to rewind it. The operating life of a mechanical watch, namely its reserve power, must be a minimum of 35 hours. The higher the frequency of the oscillations of the balance,

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the more energy the watch consumes and, therefore, the larger its barrel must be.

For a long time it has been considered basic that in ordinary watches a frequency of 18,000 oscillations per hour represented an optimum compromise. This value made it possible to produce an isochronous assembly having good dynamic stability while avoiding excessive losses so that it was possible easily to store in a barrel of acceptable dimensions the energy necessary to assure an operating power of 35 to 38 hours.

However, it has been noted for some time that if an oscillating assembly is driven at a frequency of more than 18,000 oscillations per hour, the disrupting effect of external blows and changes in position decreases progressively as the frequency increases.

Thus, Wristwatches of customary dimensions have already been produced which have a power reserve of more than 35 hours and the balance-hairspring assembly of which oscillates at a frequency of 21,600 oscillations per hour. In these watches the moment of inertia of the balance has a normal value of, for instance, between 12 and 20 mg. cm. however, it has not been possible up to now to produce mechanical watches of high precision and acceptable dimensions which contain an oscillating assembly adjusted to a frequency of more than 21,600 oscillations per hour since no means were known which would make it possible to give such watches a sufiicient power reserve.

It is an object of this invention, therefore, to provide a Watch movement having a balance assembly which oscillates at higher than 21,600 oscillations per hour while simultaneously having a drive spring capable of providing a relatively high reserve power, said movement requiring relatively small overall dimensions.

Specifically, it is an object of this invention to provide a watch movement whose balance assembly oscillates between 31,000 and 60,000 oscillations per hour while the drive spring provides a reserve power of at least 35 hours.

It is further an object of this invention to provide a watch movement wherein the balance assembly oscillates Within the aforementioned range and has a moment of inertia of less than 9 mg. cm.

All other objects are intended which are inherent in the invention as disclosed and claimed herein with reference to a preferred embodiment which is described with reference to the drawing, wherein:

FIGURE 1 is a plan view of the mainspring barrel of one embodiment;

FIGURE 2 is a perspective view of the end of the mainspring housed in the barrel of FIGURE 1; and

FIGURE 3 is a plan view of a conventional balance assembly of the type to which the present invention is applicable.

In the disclosed embodiment, the watch comprises an oscillating assembly of conventional type such as is shown in FIGURE 3 consisting of a balance 8 and a hairspring 9 mounted between a pillar plate and a cock. According to a preferred embodiment, the moment of inertia of the balance is 7.1 mg. cm. Its diameter is 8.5 mm. and the height of the rim 10 is 0.46 mm. As a variant, it will be possible in certain cases to impart a slightly higher value to the moment of inertia of the balance. The hairspring has its inner end connected to the staff 14 of the balance 8 and its outer end connected to a fixed part of the movement and is thereby arranged so as to oscillate the balance 8 at a natural frequency of 36,000 oscillations per hour, the amplitude of the oscillations being about 320. The characteristic of the hairspring is 2.00 dynes-cmfi-radians. At least one arm 15 connects the staff 14 to the rim .10, the staff and rim being (as is well known) integrally rotatable with each other. The staff of the balance bears a large plate and a small plate constituting a transmission means which cooperates with the escapement lever 11 the pallets 13 of which engage alternately in the toothing of an escape wheel 12 in order to sustain the isochronous movements of the oscillating balance assembly so as to regulate the speed of the movement gear train. The escape wheel is of metal and, in the given example, has twenty-one teeth. It is treated with molybdenum bisulfide which avoids the necessity of lubricating the pallets. It is rigidly connected with a pinion having seven leaves, the modulus of whichis 0.07016; this pinion is in engagement with the toothing of a seconds wheel which has 100 teeth. The gear train of the movement comprises, furthermore, a third wheel and a center wheel, the latter carrying at the end of .its staff a cannon pinion on which there pivots an hour cannon wheel. These last two parts pass through the central opening of the dial and carry a minute hand and an hour hand respectively. The center pinion is in engagement with the peripheral toothing on the mainspring barrel which pivots between the plate and one of the bridges of the movement and which contains a mainspring which is hooked on the one hand to the core of the staff of the barrel and on the other hand by a flange to the wall of the drum.

The barrel is shown in FIGURE 1. The inner face of its side wall 1 has a hook 2 against which there abuts the end of a flexible band 3. The latter extends against the wall 1 along an arc of about 90. Its rear end is welded at 6 to the drive or mainspring 4 whose end 5 itself extends beyond the rear end of the flange 3 and rests against the wall 1. By this arrangement, the spring 4 remains concentric to the barrel whatever is the extent to which it is wound. Thus, FIGURE 1 shows in dotdash lines the positions of the band 3 and of the end of the spring 4 when the latter is wound to the maximum. The forces exerted on the drive spring are thus equalized insofar as possible so that it is possible to impart to the spring 4 a characteristic which assures a power reserve of 38 hours while developing in completely wound state a torque of 1400 g. mm.

The dimensions of the spring 4 are as follows: its length is 287 mm., its width 1.2 mm. and its thickness 0.136 mm. As can be noted from FIGURE 2, the flange 3 is slightly narrower than the spring 4. Furthermore, the thickness of the spring 4 is relatively large. The ratio between the diameter of the core 7 and the thickness of the drive spring is 22. The drive spring is made of a bimetallic alloy.

The drive spring described may be housed without difficulty in the barrel 1 of ordinary construction, the total height of which is 1.7 mm. and the inside diameter 10.3 mm., the core diameter being 3 mm. The toothing of this barrel which engages with the center pinion comprises a number of teeth which is in the ratio of 7 to 1 with that of the center pinion so that five cocking turns correspond to a power reserve of 35 hours. The spring 4 assures a power reserve of up to 37.6 hours, corresponding to 5% cocking turns.

The movement is housed in a wristwatch case of customary construction comprising a case band bezel provided with horns, a bottom plate fastened to the bezel case band and a glass covering the dial. As a variant, the movement could also be housed in a pocketwatch case.

In one embodiment comprising an oscillating assembly having a natural frequency of 31,000 oscillations per hour, one could also use a 15 tooth escape wheel whose pinion would be in engagement with the toothing of the seconds wheel.

Such an escape wheel could also be used in a movement whose oscillating assembly oscillated at a frequency of more than 31,000 oscillations per hour. The wheel train would then comprise an additional runner between the seconds wheel and the escape pinion.

The presence of an additional runner between the seconds wheel and the escape wheel would make it possible, by using a 21 tooth escape wheel, to increase the frequency of the oscillating assembly to about 60,000 oscillations per hour.

The movements described above could comprise on their side opposite the plate an oscillating mass having the shape of a circular sector pivoting at the center of the movement and extending to its periphery, and a transmission device assuring the rewinding of the drive spring. Such an embodiment Will, of course, be intended more particularly for a wristwatch.

The frequency of the oscillating assembly being of a value far higher than the values customary in pocketwatches or Wristwatches which have a power reserve of 35 to 38 hours, the ratio between the power consumed in the oscillating assembly and that which is consumed by the gear train in the form of friction is increased. The increase in this ratio and the improvement in the stability of the oscillating assembly relative to impacts or changes in position, result in a considerable improvement in the precision of the watch.

It has been found, furthermore, that the variations in amplitude between the different operating positions were very slight. One can, therefore, adjust the characteristics of the oscillating assembly in such a manner that the average amplitude of the oscillations is less than 320 under normal conditions. Thus, this average amplitude may be reduced to about 270, measured in horizontal positions.

The use of a balance having a moment of inertia of 7.1 mg. cm. thus makes it possible to construct a watch movement whose oscillating assembly oscillates at a frequency of between 31,000 and 60,000 oscillations per hour and whose drive spring has a power reserve of more than 35 hours and can be housed in a case of customary dimensions and shape. The watch has a precision of operation far greater than that of other known watches.

This result could also be obtained by usinga balance whose moment of inertia has a different value from that of the disclosed embodiment. Thus, the moment of inertia of the balance could be less than the value indicated, but no elss than 6.3 mg. cm. if the frequency of the oscillating assembly is about 36,000 oscillations per hour. The moment of inertia of the balance could also be increased beyond 7.1 mg. cm. but must remain less than 9 mg. cm.

In order to benefit from the great advantages afforded by the watches described above, their precision being far greater than that of the customary watches whose balance oscillates at 18,000 or 21,600 oscillations per second, it is of course necessary to equip the movement with a regulator which permits a very precise adjustment of the frequency. For this purpose, there is advantageously used a regulating system in which the regulator itself has a toothed sector in engagement with a worm mounted horizontally on the cock.

What is claimed is:

1. A watch movement comprising a balance assembly which includes an oscillatable balance wheel conventionally associated with a hairspring, an escapement means, and the movement gear train, said wheel having a moment of inertia of less than 9 mg. cm. and the assembly including a hairspring which provides a natural frequency to the balance wheel in the range of 31,000 to 60,000 oscillations per hour.

2. The movement of claim 1, said moment of inertia being at least equal to 6.3 mg. cm and said balance wheel oscillating at least 36,000 oscillations per hour.

3. The movement of claim 2, including a mainspring which in fully wound condition provides a torque substantially equal to 1400 g. mm.

4. The movement of claim 3, said balance wheel having an amplitude substantially equal to 270 degrees.

5. The movement of claim 2, including a mainspring which provides a reserved riving force suflicient to drive said movement for at least 35 hours.

6. The watch movement of claim 1, comprising a barrel and a mainspring wound in the form of a plurality of helical turns housed therein, said barrel having an outer peripheral wall and a central staff, said spring being wound about said staff with the inner end of said spring being attached to said staff, a flexible band extending between said spring and said wall and attached at one point to said wall and at another point to said spring, said band being flexibly bendable relative to the point at which it is attached to said wall pursuant to winding and unwinding of said spring.

7. The movement of claim 6, said band extending along substantially 90 degrees of the extent of said wall and being attached to said spring at a point displaced from the outer end of said spring.

8. The movement of claim 7, said band being attached to said spring at a point whereby said band maintains the outer turn of said spring concentric with said staff regardless of the extent to which said spring is wound.

References Cited UNITED STATES PATENTS RICHARD B. WILKINSON, Primary Examiner GEORGE H. MILLER, JR., Assistant Examiner US. Cl. X.R. 58l 14

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