US2971324A

US2971324A - Lever escapement for timepieces

Info

Publication number: US2971324A
Application number: US711749A
Authority: US
Inventors: Beyner Andre
Original assignee: Ebauches SA
Current assignee: Ebauches SA
Priority date: 1957-03-16
Filing date: 1958-01-28
Publication date: 1961-02-14
Anticipated expiration: 1978-02-14

Description

Feb. 14, E NE 2,971,324-

LEVER ESCAPEMENT FOR TIMEPIECES Filed Jan. 28, 1958 IN VEN TOR.

Hndre' Begner BY United States Patent LEVERESCAPEMENTFORTIMEPIECFS Andre Beyner, Neu c'hatel, Switzerland, as'signor to Ebauches S.A., Neuchatel, Switzerland Filed Jan. 28, 1953, SenNo. 711,749 Claims priority, appllcation switzerland Mar. 16,1957

7 Claims. .(Cl.-:58-'-28) The present invention relates "toa lever escapement for timepieces, and more particularly"to a magnetic device for holding the lever in its end positions. The-said device is particularly intended for electric timepieces having a driving bala'nce in which transforma'tion of the reciprocating motion of the balance into a unidirectional motion is effected by means of an escape mechanism including a roller keyed on'thebalance staff, a lever, and an :escape "wheel. The mechanism' being such thatthe escape wheel is controlled by the lever and is rotated always in the same direction.

Since the escape wheel is driven by the lever, there is no draft effect of the wheel on the lever in order to hold the latter against the banking pins. The lever, therefore, is free, thus causing a frequent interaction of the guard pin and of the small roller, which serve for locking the lever. This interaction impairs the quality of the timing adjustment of the timepiece.

A number of devices have already been proposed for holding the lever against the banking pins. Most of these devices are mechanical and include springs, jumpers, etc. by means of which the lever can be retained in each of its end positions. These devices are generally difiicult to construct and must be adjusted by the worker who assembles the timepiece and require frequent lubrication.

Another device has been proposed for holding the lever against the banking pins, chiefly in mechanical watches. In this known device, the arrangement of the escapement is modified so as to do away with the draft effect of the escape wheel on the lever, and the lever is held against the banking pins by magnetic means, e.g. by magnetic banking pins. The device forming the subjectmatter of the present invention is based on this principle but presents many improvements and advantages over the known construction.

In a timepiece with a driving balance, the motor of which is not polarized, it is essential that the moving armatures rigidly fixed to the balance and the stationary armatures or pole shoes of the stator not become permanently magnetized as the magnetism would cause a lack of isochronism. The above-mentioned prior magnetic device leads, owing to its design, to the magnetization of the armatures of the motor through magnetic leakage.

The device according to the invention aims at avoiding any magnetic leakage. It is broadly characterized by a permanent magnet secured to the pillar plate of the movement of the timepiece, two magnetic banking pins bearing against the ends of the said magnet and defining the geometrical path of the lever and cooperating for this purpose with a member made from a magnetizable material, said member being keyed on the pallet arbor and having two holes in each of which is engaged one of said banking pins, the said member permitting closing practically completely the magnetic circuit of the permanent magnet and providing the attracting effect required for the lever.

The accompanying-drawing sh'ows,=byway of example, one embodiment-of the invention.

Fig. 1 is a plan view of this embodiment.

Fig. -2 is a cross se'ction'al view taken along the line II-II in Fig. l. v

Fig. 3 is a fragmentary view of a modification of the invention.

The device illustrated in the drawing comprises a permanent magnet 1 consisting of a bar relatively long with respect to its section. The magnet 1 is made from an'alloy' having'a great remanence and a great coercive force, suchas 'the products Ticonal or Alnico (registered trade names). 'The magnet 1 is magnetized in its longitudinal direction, 'so-that, for instance, the south pole is situated 'le'ft-and-thenorth pole right in Figs. 1 and 2. 'Tliepermanent'magnet 1 is secured in a manner not illustrated to the pillar plate 2, in a recess 3 provided in the'bottom face'ofthe pillar plate 2. Two cylindrical pins 4 and-'5, made from an alloy having a very high magnetic permeability,'-a're" driven into the pillar plate 2 'and' be'ar ag'ain'st the endsof the'magnet 1. The pins 4 and' S extend at right'a'n'glesto'themagnet 1. The magnet 1, therefore, forms a bridge over the pins 4 and-5.

In order to close as completely as possible the magnetic field of the magnet 1 and of the

pins

4 and 5, a magnetic shunt, consisting of a metal sheet 6 cut out from a material having a very high magnetic permeability and a low remanence, is keyed on the pallet arbor 7. The section of the shunt 6 is determined in such a manner that it should by no means be saturated by the flux of the permanent magnet 1. In the plate 6 are provided two

round holes

8 and 9.

The lever 10, pivoted between the pillar plate 2 and the pallet bridge 11, is of the type in which the fork lies by the side of the pallets, but it is to be understood that it might as well be of the type in which the fork would lie approximately on the imaginary straight line conmeeting the axis of the escape wheel to the axis of the lever.

The plate 6 is keyed on the pallet arbor 7 and the

pins

4 and 5 are arranged in the pillar plate 2 in such a manner that the movement of the lever 10, defined by its lift angle, is limited by the fact that the walls of the

holes

8 and 9 of the plate 6 come into contact with the

banking pins

4 and 5. Thus, in each of both end positions of the lever 10, the magnetic circuit is closed practically without any gap. Its reluctance is therefore extremely low with respect to the leakage reluctance of the magnet 1 towards the armatures of the motor, which represents a great advantage with respect to the known above-mentioned device including merely magnetic banking pins.

On the other hand, the described device has the following advantage: Upon the movement of the lever 10 relatively to the

banking pins

4 and 5, these pins permanently remain within the

round holes

8 and 9 of the magnetic shunt 6, so that the device, during the whole movement of the lever 10, works with very low rcluctances of the magnetic circuit. Since the attraction of the shunt 6 by the

pins

4 and 5 might be relatively strong as the shunt 6 sticks to the

banking pins

4 and 5, a thin sleeve 12 made from a non-magnetic material may be secured to the pins, at the height of the shunt 6, so as to provide a small gap preventing the shunt 6 from sticking to the

pins

4 and 5. The sleeve 12 may eonof the permanent magnet 1, whatever the position of the lever 10 may be.

Although the described device is more particularly intended for use in electric timepieces with a driving balance, it is to be understood that it can also be used in mechanical timepieces. v

While I have described and'illustratedone embodiment of my invention, I do not wish to unnecessarily limit the scope thereQf, but reserve the'right to make such modifications and rearrangements of the several parts as may come within the purview of the accompanying claims.

What I claim is: g

1. In a timepiece movement, a pillar plate, a spindle, a swingable escapement lever keyed on said spindle, a permanent magnet secured to the pillar plate, two magnetic banking pins bearing against the ends of said magnet, a member made of a magnetizable material, said member being keyed on the spindle of said lever and having two holes in each of which is engaged with play, one of said banking pins, so as to draw the'lever into its end positions and to hold it in these positions, said banking pins thus limiting the oscillatory movement of said lever, said member being so'shaped as to practically completely close the magnetic circuit of the permanent magnet.

2. In a timepiece movement according to claim 1, said permanent magnet consisting of a bar relatively long with respect to its section and being magnetized in its longitudinal direction.

3. In a timepiece movement according to claim 1, a recess provided in the bottom face of the pillar plate, said permanent magnet being accommodated in said recess.

4. ha timepiece movement according to claim 1, said banking pins extending at right angles to said permanent magnet. V

5. In a timepiece movement according to claim 1, said holes in said member being round.

6. In a timepiece movement according to claim 1, said holes in said member having an elongated shape.

7. In a timepiece movement according to claim 1, a thin sleeve made of a non-magnetizable material, said sleeve being secured to said banking pins, at the level of said member, so as to form a small gap preventing said member from sticking to said banking pins.

References Cited in the "file of this patent UNITED STATES PATENTS 2,669,089 Straumann Feb. 16, 1954 FOREIGN PATENTS 141,629 Australia June 18, 1951