Detent escapement for a timepiece

The blocking member (6) or detent member of the escapement carries a follower (20) which ends in a beak (21) which cooperates with a small roller (23) comprising a notch (22). When the locking pallet-stone (7) of the blocking member releases itself from the teeth of escapement wheel (2), the beak (21) penetrates in the notch (22). The return of the pallet-stone (7) in the locking position is caused by a rising flank (25) of said notch, said rising flank being inclined such that the beak (21) is forced to follow and climb over said flank when the small roller (23) rotates. The arrangement allows the escapement to resist to shocks and consequently to omit the return spring acting on the blocking member.

This application claims priority from European Patent Application 03027929.3 filed Dec. 4, 2003, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a detent escapement for a timepiece including an escapement wheel, a balance on the pin of which are fixed a large roller fitted with an impulse pallet-stone and a first actuating finger, a blocking member in the form of a lever hinged on a pin, said blocking member carrying a locking pallet stone, a second actuating finger and a follower which ends in a beak, said escapement further including an elastic member acting on one of the actuating finger to drive the other finger and actuate the blocking member when the roller rotates in a first direction and to move around said other finger without driving the roller when said roller rotates in a second direction opposite to the first, the pin of the balance further carrying a small roller in the circular periphery of which a notch is made and in which the beak of the follower penetrates when the locking pallet-stone releases itself from the escapement wheel.

BACKGROUND OF THE INVENTION

A detent escapement answering the above description has already been proposed and disclosed in the old Swiss Patent No. CH-3299 in the name of Emile James.FIG. 1of the present description shows a detent-lever pivoted at one of its ends in accordance with a conventional design of this type of escapement.

The balance pin40carries a large roller41, a first small roller42having a notch43and a second roller44carrying an actuating finger45. The detent-lever46is pivoted on a pin47. It carries a locking pallet-stone48a pin49, a beak50and a strip spring51. The detent-lever46is returned to the rest position by a spiral return spring53.

At the moment when the actuating finger45raises the detent-lever46with the assistance of the strip spring51, the beak50penetrates the notch43at the same time that the escapement wheel52moves forward one step. During the additional arc, the beak50is released from the notch and is in proximity to the circular periphery54of the first small roller42in the position shown in the Figure.

This arrangement has the advantage of preventing a tooth of the wheel52from leaving the locking pallet stone48when the timepiece receives a shock. Indeed, at that moment, the beak50abuts for a brief moment against the circular periphery54of the first small roller42, which stops the detent-lever46which is immediately returned to the rest position by the spiral return spring53.

The foregoing identifies a weakness affecting the detent escapement, namely that it is very sensitive to shocks, thus this escapement is reserved especially for chronometers of large dimensions or marine chronometers that are not mechanically stressed, said escapement having the reputation of not being suited to wristwatches. In order to prevent the locking pallet-stone to release itself from the escapement wheel inadvertently, it has already been proposed, in addition to the above-mentioned solution, to fit the blocking member with an additional finger arranged to prevent the rotation of the escapement wheel in the case where such an inadvertent release occurs (see for example the work by Huguenin, Guye and Gauchat, Neuchâtel 1975, FIG. 17-5) entitled “Echappements et Moteurs pas à pas”.

Referring again to the afore-cited Swiss Patent, one note however that removal of the beak50from the notch43is only possible owing to the spiral spring53, which exerts a return force on the detent-lever46. Indeed, the notch43carries almost radial sheer flanks preventing any removal of the beak which might be caused simply by rotation of the roller itself.

One could thus omit the return spring if one would shape the notch and the beak which penetrates therein in such a way that the return effect of the detent is caused by the rotation itself of the roller. This is one object the present invention.

SUMMARY OF THE INVENTION

For this purpose, the detent escapement according to the invention, in addition to answering the definition of the first paragraph of this description, is characterised in that the return of the pallet-stone in the locking position is caused by a rising flank of said notch, said rising flank being arranged such that the beak climbs over said flank when the small roller rotates in said first direction.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 2,3and4illustrate the detent escapement that forms the subject of the present invention. The escapement includes an escapement wheel2fitted with teeth3. Although not shown in the drawings, the escapement wheel is driven by the gear train of the timepiece, which receives its driving force from a barrel. The Figures show a large roller4mounted on the pin or arbour16of the balance (not shown). The large roller4is fitted with a first actuating finger14and an impulse pallet stone5receiving pulses from teeth3of wheel2. The system also shows a blocking member in the form of a lever6hinged on a pin8. The blocking member6carries a locking pallet-stone7, a second actuating finger11and a follower20terminated by beak21. The locking pallet-stone cooperates with teeth3of wheel2. The escapement further includes an elastic member acting on one of the actuating fingers—in the case ofFIGS. 2 to 4on finger14—to drive the other finger—finger11in this case—and actuate blocking member6when roller4rotates in a first direction a and to move around the other finger—finger11here—without driving it when the roller rotates in a second direction b opposite to the first.

Herein lies the principle of all detent escapements in which the impulse is only given to the balance once per oscillation during which the escapement wheel rotates through one angular step, whereas, in the lever escapement, said wheel moves forward one half-step at each alternation. This is one of the advantages provided by the detent escapement since the energy wasted because of the inertia of the escapement wheel only occurs once per oscillation instead of once per alternation.

FIGS. 2 to 4further show that the balance arbour or pin16carries a small roller23in the circular periphery24of which there is made a notch22. As will be shown hereinafter, beak21of the follower20penetrates notch22when locking pallet-stone7is released from teeth3of escapement wheel2.

More specifically,FIGS. 2 to 4show that blocking member6includes a first arm9which carries locking pallet-stone7and a second arm10which carries the second actuating finger and follower20which ends in beak21. More specifically also, these same Figures suggest that elastic member12acts on first actuating finger14. The construction illustrated inFIGS. 2 to 4differs in this from that illustrated inFIG. 1showing the prior art.

As was stated hereinbefore, the prior art also provides a small roller cooperating with a follower to make the escapement resistant to shocks exerted on the timepiece, but does not omit a spiral spring returning the lever to the rest position. It is an object of the present invention to propose a construction which omits any return spring, taking advantage of the rotation of the roller in order to accomplish such return. In this perspective, the escapement of the present invention is characterised in that the return of locking pallet-stone7to the rest position is caused by a rising flank25of notch22made in the periphery24of small plate23, this flank being slanted such that beak21in which follower20ends, climbs over said flank25when the small roller is rotating in the first direction a.

The embodiment described shows an elastic member12located between large and small rollers4and23. This member will not be described in detail here since it can take various forms, its essential role being to act on first finger14to drive second finger11in one rotational direction a of the rollers and to climb over or move around said finger11in the opposite rotational direction b. It will be observed here that the elastic member could be arranged on blocking member6and act on finger11of said blocking member. In that case, finger14would be a finger fixedly implanted on roller4.

Finally the invention could be applied to the escapement described hereinbefore in the prior art, provided that the first small roller42carries a notch43with a properly slanted flank, which would enable spiral return spring53to be omitted (seeFIG. 1).

The operation of the detent escapement will now be described in detail with reference toFIGS. 5 to 11, which illustrate different phases of operation.

InFIG. 5, roller4is rotating in the direction arrow a. Second finger14onto which elastic member12acts, enters into contact with first finger11of blocking member6. Locking pallet-stone7of blocking member6is completely engaged in tooth60of escapement wheel2, which is locked. Beak21of follower20presents itself at the entry of notch22

InFIG. 6, roller4continues its travel in the direction of arrow a. Second finger14drives first finger11of blocking member6and swing it in the direction of arrow c bringing pallet-stone7at the very beginning of its release from tooth60. Beak21penetrates into notch22.

InFIG. 7, escapement wheel2is free and rotates in the direction of arrow c. Tooth61of wheel2enters into contact with impulse pallet-stone5of large roller4, causing a new pulse to be given to said roller which rotates together with the balance fixed thereto, in the direction of arrow e. Second finger14is about to be released from first finger11.

InFIG. 8, the impulse given by tooth61to pallet-stone5is in progress; second finger14has unhooked from first finger11driving beak21of the follower at the start of flank25of notch22made in small roller23.

The end of the impulse is shown inFIG. 9. Tooth61is about to leave pallet-stone5. Small roller23has been driven by tooth61in the direction of arrow a, which has forced beak21to climb over flank25and forced locking pallet-stone7to insert itself in the space separating teeth60and62, blocking member6then rotating in the direction of arrow f.

InFIG. 10, tooth62has just come into contact with locking pallet-stone7. The kinetic energy of wheel2is then exerted on pallet-stone7by tooth62, which forces pallet-stone7to stop at the bottom of tooth62and blocking member6to abut against a stop pin63as shown inFIG. 11. From this moment onward, blocking member6—more specifically its arm10—is held against limit stop63with a certain force. This is a security device for holding the blocking member while the balance exerts its additional arc of oscillation, a so-called drawing device which opposes resistance to the release of pallet-stone7when shocks are applied to the timepiece. The drawing is generally defined by an angle α formed by the locking plane70of pallet-stone7and a perpendicular line71raised on a radius72of the blocking member, at the point of contact73of tooth60and of pallet-stone7(seeFIG. 2).

FIG. 11also shows that beak21of follower20has come out of notch22. It can be seen that in this situation, beak21which is at the end of follower20, is arranged to be immobile in proximity to the circular periphery24of small roller23but without touching the latter. Rollers4and23are then totally free to travel thought their additional oscillation, either one alternation in the direction of arrow a then one alternation in the opposite direction, after which a cycle starts again with the situation shown inFIG. 5.

It will be noted finally that notch22has a V-shaped aperture. The entry or trailing flank80will have to be shaped so as not to disturb the introduction of beak21when locking pallet-stone7is released from escapement wheel2.

Likewise, the exit or rising flank25will have to be shaped so as to ensure that at the end of the impulse function, locking pallet-stone7is on the trajectory of a tooth of the escapement wheel in order to intercept and then stop it.