Direct-impulse escapement, especially of detent type, for a horological movement

This escapement comprises a balance wheel (3), an escape wheel (1), a detent rocker (4) having an arresting element (4a) and an elastic clearance element (4c), means for inserting the arresting element into the path of the teeth of the escape wheel (1), and a clearance pin (7) rotating integrally with the balance wheel (3) in order to engage with the elastic clearance element (4c) of the rocker (4) once per period of oscillation of the balance wheel. The means for inserting the arresting element (4a) into the path of the teeth of the escape wheel (1) comprise a sliding surface (4b) integral with the detent rocker (4) and arranged so as to move into the path of the teeth of the escape wheel (1) when the arresting element (4a) leaves it, this sliding surface being shaped so as to return the arresting element (4a) to the locking position.

The present invention relates to a direct-impulse escapement, especially of detent type, for a horological movement, comprising a balance wheel attached to an impulse element, an escape wheel whose teeth intersect the path of the impulse element, a detent rocker having an arresting element and a clearance element, means for inserting the arresting element into the path of the teeth of the escape wheel, a clearance pin rotating integrally with the balance wheel, and means for engaging said clearance pin with the clearance element of the rocker once per period of oscillation of the rocker to clear the arresting element from the escape wheel tooth; in which said means for inserting the arresting element into the path of the teeth of the escape wheel comprise a sliding surface integral with the detent rocker and arranged so as to move into the path of the teeth of the escape wheel when the arresting element leaves it, this sliding surface being shaped so that the force applied to it by a tooth of the escape wheel causes the arresting element of the detent rocker to move back into the path of the teeth of the escape wheel.

One escapement that is particularly highly regarded for its general performance (efficiency and isochronism) is the so-called detent escapement which releases the gear train when the balance wheel rotates in one direction, while this same system allows the balance wheel to pass without any other action than the bending of the elastic clearance element during its return. This advantageous function can be obtained by using a flexible element (generally a strip) which is immobilized in one direction in order to allow the release of the escape wheel following the bending of a second flexible element. When the balance wheel is rotating in the reverse direction, the first strip is able to bend freely without releasing the escape wheel, thus avoiding a needless loss of energy.

The second flexible element is necessary to return the blocking lever to its initial position. However, at the moment of release of the escape wheel, the system has to overcome the draw of the escape wheel and the second flexible element, which results in a considerable loss of energy because the energy supplied to the second flexible element to deform it (some 50% of the total amount of energy that must be supplied to release the wheel) is lost.

The sizing of the detent (the flexible parts in particular) is clearly one of the critical points in developing the detent escapement. Sufficient stiffness is required to keep the escape wheel locked, but at the same time not too much energy must be required to release the escape wheel during the impulse that is supplied to the balance wheel, the risk being a not insignificant perturbation of the balance wheel/hairspring system and a large reduction in the associated efficiency. The unlocking torque required to release the escape wheel also represents a safeguard against knocks which defines a lower limit to the stiffness of the second flexible element.

A detent escapement of the type discussed above is described in U.S. Pat. No. 40,508.

This mechanism was much used in marine chronometry; it is expensive and sensitive, requires perfect execution, and is not easily converted to mass production. On the other hand, it is an excellent escapement, allowing very precise adjustment and consequently giving the best chronometric service.

However, in such an escapement, the draw of the escape wheel is the only safeguard. This is insufficient in the case of a wristwatch which is likely to suffer knocks which would seriously interfere with its correct running.

The object of the present invention is to at least partly solve the abovementioned disadvantages.

To this end, the present invention relates to a direct-impulse escapement, especially of detent type, for a horological movement according to Claim1.

The main advantage of such an escapement is that it increases the safety with respect to knocks. Moreover, the detent rocker with an arresting element and a sliding surface which move alternately into the path of the escape wheel teeth constitutes an additional safeguard.

The arresting element of the detent rocker comprises a safety surface situated outside of the path of the escape wheel teeth and adjacent to this path when the detent rocker is in the unlocking position. Advantageously, the length of this safety surface corresponds to the angle travelled by the escape wheel to communicate the movement impulse to the balance wheel, in order to prevent the premature return of the arresting element into the path of the teeth of the escape wheel. It is therefore a second safeguard.

The escapement illustrated inFIG. 1comprises an escape wheel1, the circular path of whose teeth intersect the path of an impulse pallet2integral with the balance wheel3connected to a hairspring (not shown).

A detent rocker4is able to move freely between two stops5,6. It comprises on the one hand an arresting element with a stop face4afor arresting a tooth of the escape wheel1, and on the other hand, a sliding surface4bto allow an escape wheel tooth to slide over this surface4band pivot the rocker in the anticlockwise direction so as to move the stop face back into the path of the teeth of the escape wheel1. This detent rocker4also has an elastic clearance element4cwhich is pressed against a stop4dand whose free end moves into the path of a clearance pin7integral with the balance wheel3.

The arresting element of the detent rocker4also has a safety surface4ewhich is located outside of the path of the teeth of the escape wheel1and adjacent to this path when the detent rocker4presses against the stop (FIGS. 3 to 6). This surface occupies an angle of the escape wheel1corresponding to the angle during which an escape wheel tooth communicates its impulse to the impulse pallet2of the balance wheel3.

A cycle of oscillation of the balance wheel/hairspring can be broken down into the different phases illustrated inFIGS. 1 to 11.

In the phase illustrated inFIG. 1, the balance wheel is turning anticlockwise. The stop face4aof the arresting element of the rocker4locks the escape wheel1, which in turn holds the rocker4against the stop6.

The phase illustrated inFIG. 2corresponds to the moment at which the clearance pin7integral with the balance wheel3meets the elastic clearance element4cpressed against the stop4d. Because of the stop4dand because of the anticlockwise rotation of the balance wheel3, the elastic clearance element4cbehaves like a rigid element.

The detent rocker4then moves, under the action of the clearance pin7, from pressing against the stop6to pressing against the stop5(FIG. 3), thus freeing the escape wheel1, one tooth of which had been arrested by the stop face4aof the arresting element of the detent rocker4.

Since the escape wheel1is subjected to the torque of the mainspring (not shown) transmitted by the going train (not shown), it is now driven clockwise. One of its teeth then meets the impulse pallet2of the balance wheel3(FIG. 4). This is the start of the impulse phase, in which the energy of the mainspring is transmitted to the balance wheel3in order to give it the energy necessary to keep it oscillating.

This impulse phase ends when the escape wheel tooth leaves the impulse pallet—that is, practically in the position illustrated inFIG. 5. As can be seen, throughout this impulse phase, the safety surface4eof the arresting element of the detent rocker4prevents the arresting element from moving into the path of the teeth of the escape wheel1as the result of a knock, for example.

After the impulse phase, the escape wheel1continues its rotation and one of its teeth meets the sliding surface4b(FIG. 6). As it slides against this surface4b, the escape wheel tooth turns the rocker4anticlockwise and moves it back against the stop6(FIG. 7). This pivoting movement also moves the arresting element of the rocker4back into the path of the teeth of the escape wheel1, so that one tooth of the escape wheel strikes the stop face4aof the arresting element and exerts on the rocker4a torque which holds it against the stop6(FIG. 8).

Meanwhile, the balance wheel3has continued turning in the anticlockwise direction until the hairspring brings it to a halt and makes it rotate in the clockwise direction.

When the clearance pin7meets the elastic clearance element4cof the detent rocker4(FIG. 9), it moves it off the stop4d(FIG. 10) without displacing the detent rocker4. The impulse pallet2of the balance wheel3passes between two adjacent teeth of the escape wheel1without touching them.

The balance wheel3goes on turning until it is brought to a halt by the hairspring and turned back anticlockwise (FIG. 11), thus commencing a new cycle of oscillation.

FIG. 12shows a variant of the impulse and clearance device connected to the balance wheel staff in place of the impulse pallet and in place of the clearance pin of the previous embodiment. This variant has a circular roller12provided with a tubular element12adesigned to be driven onto the balance wheel staff. This tubular element12ahas a partially circular outer section intersected by two parallel external flat faces12bon which is engaged an impulse ring13containing an opening13awhose cross section fits the external cross section of the tubular element12a. The impulse ring13is held axially between two driven retaining rings8a,8b. The impulse ring13has an impulse pin or face13bprojecting from the external lateral face of the impulse ring13. The pin of the impulse ring may be an attached component such as a pallet.

Two impulse pins9and10, of semicircular cross sections in this example, are driven into two diametrically opposite openings12c,12d, respectively, of corresponding cross sections formed in the roller12.

An inertial member11is provided with three openings11a,11b,11c, two11a,11bof which are eccentric and preferably symmetrical and diametrically opposed. One of these openings11bis semicircular and limited by two radii forming an angle of more than 180° to take a pivot impulse pin10of the inertial member11while allowing it room for angular movement. The other opening is elongate11ato accommodate the impulse pin9. The third opening is a central opening11cfor the loose passage of the tubular part12aof the roller12and can be used, in the absence of the opening11aand of the impulse pin9, to limit the angular movement of the inertial member11. A clearance pin11dprojects from the external lateral face of the inertial member11. This clearance pin11dis triangular in the example considered, with a driving face oriented radially with respect to the centre of the inertial member11and the other face sloping. The clearance pin11dcould also be formed by affixing a pallet such as a ruby pallet. The sloping face of the clearance pin11dserves to push the inertial element12back if a knock has moved it into a projecting position when it should be out of the way.

The inertial member11is located at the base of the tubular part12a. As seen inFIG. 12, the openings11a,11b,11care located, sized and shaped in such a way as to allow the inertial member11to perform a limited angular movement about the axis of the impulse pin10, which is parallel to the axis of the roller12driven onto the balance staff, and which forms the pivot member of the inertial member11. The elongate opening11alies symmetrically about a diameter of the inertial element11passing through the respective axes of the openings11b,11c, so that the two limit positions of the inertial member11are respectively situated symmetrically on either side of the balance staff.

In one angular position of the inertial member11, the clearance pin11dprojects from the outer edge of the circular roller12. As it turns clockwise, the radial face of the triangular pin meets the clearance element4c, which no longer needs to be elastic, so that the clearance pin11dlifts the detent rocker4.

The inertial member11has two stable positions, each depending on the direction of rotation of the balance wheel. Tests have shown that the inertial member11moves before the balance wheel has completed each of the two alternations making up its oscillation period, but its rotation about the impulse pin10starts in the vicinity of dead centre of the balance wheel (angle 0 of its position).

At dead centre, the balance wheel is moving at maximum speed and therefore changes from a positive acceleration to a negative acceleration (it begins to decelerate), and it is at this moment that the inertial effects begin to be felt.

When the inertial member11is moved clockwise about the axis of the impulse pin10, the clearance pin11dis retracted inside the outer edge of the circular roller12.

As a result, the clearance pin11ddoes not engage with the detent rocker4as it passes in front of the clearance element4c. Unlike all known escapements using direct impulse transmission, there is nothing for the clearance pin11dto overcome in order to pass the obstacle of the element4cof the clearance rocker4during the alternation of the balance wheel in which the latter receives no impulse tending to maintain its oscillating movement, because the pin is retracted within the circular edge of the roller12. There is therefore no loss of energy or perturbation of the oscillation period of the balance wheel.

When the balance wheel3arrives at the end of its anticlockwise rotation (FIG. 7), its deceleration once again moves the inertial member12, which returns to the position in which the clearance pin11dprojects out of the circular edge of the roller12.

The angular movement of the inertial member11between its two limit positions is only a few degrees, typically around 5° to 10°, these two limit positions being situated symmetrically on either side of the balance wheel staff. This inertial member11may be made of a low-density material because the inertial effect is always sufficient for it to function. The freedom of choice as to the external geometrical shape means that the inertial element can be made symmetrical, ensuring that the added unbalanced weight is low. Experimentation shows that with a low-density material such as silicon, the influence on the balance of the balance wheel is negligible.