Patent Publication Number: US-2021173342-A1

Title: Free direct escapement mechanism for a timepiece

Description:
TECHNICAL FIELD 
     The present invention relates to the field of watchmaking. It concerns, more specifically, a free direct escapement mechanism. 
     The invention also relates to a timepiece incorporating such an escapement mechanism. 
     STATE OF THE ART 
     Anchor escapements are certainly the most common type of escapement in mechanical watch mechanisms, at least in the so-called free escapement class. Associated with a regulating organ, typically of the pendulum or sprung balance assembly type, an anchor escapement makes it possible to maintain the oscillations of said regulating organ by transmitting to it by regular impulses, at a determined frequency, a fraction of the mechanical energy of the mechanical energy source of a said watch mechanism, usually comprising at least one barrel spring. At the same time, the escapement also allows the oscillations of the regulating organ to be counted and thus the time to be counted. 
     Numerous variants of anchor escapements have been proposed in the state of the art and are well known to the man of the art in the field of watchmaking. Their limitations, which are equally well known, are mainly a propensity to disturb the isochronism of the oscillations of the regulating organ due to the successive shocks and friction between the anchor and the regulating organ on the one hand and the anchor and the escapement wheel on the other, as well as a low mechanical efficiency, mainly for the same reasons. Indeed, it is usually considered that an anchor-type escapement only transmits a limited amount, of the order of only 30%, of the driving force it receives from the driving source to the regulating organ. 
     Anchor escapements, on the other hand, are praised for their reliable operation and are also self-starting. 
     Robin-type anchor mechanisms have the advantage of better performance than Swiss anchor escapement mechanisms. The Robin escapement is an escapement that combines the advantages of the detent escapement (high efficiency and direct transmission of energy between the escapement wheel and the balance) with those of the anchor escapement (better operating safety). It is a direct impulse free escapement from the escapement wheel to the balance, the anchor of the escapement mechanism essentially constituting a lever equipped with two locking pallets and which tilts between two extreme locking positions of the escapement wheel outside the impulse phases. Their efficiency is highly praised because they allow a substantial gain in energy transmission to the regulating organ compared to a Swiss anchor escapement, the energy transmitted being around 50%. 
     However, the angle of lift of the Robin anchor is very small (about 5°) compared to the classical Swiss anchors (about 15°), which makes it difficult to apply the usual solution of securing the latter by guard pin and plate. For this purpose, alternative solutions were proposed in documents EP 1 122 617 B1 and EP 2 444 860 A1 or EP 2 407 830 B1. However, these Robin escapement mechanisms and associated safety devices are delicate to implement, so much so that they have never experienced massive commercial and industrial development, which their intrinsic technical performance could justify. 
     The purpose of the present invention is also to provide a direct and free watch escapement mechanism which is as simple and reliable to operate as a Swiss lever escapement but which benefits from singularly improved chronometric performances, at least similar to those of direct impulse escapements without however presenting their difficulties of operation. 
     Finally, the invention has the purpose of offering a timepiece comprising such an escapement mechanism. 
     DISCLOSURE OF THE INVENTION 
     For this purpose, the present invention provides an anchor escapement mechanism according to claim  1 , as well as a timepiece provided with such an escapement and defined in claim  20 . 
     The invention thus proposes, according to a first object, a direct impulse free escapement mechanism for a timepiece, comprising: 
     an escapement wheel, extending in a plane P 1  and rotatable about a first axis of rotation perpendicular to this plane and provided with a series of peripheral teeth, said teeth defining by their ends during rotation of the escapement wheel a circular trajectory C, 
     a locking device comprising at least one locking pallet arranged to cooperate in abutment with a tooth of the escapement wheel in at least one locking position of said locking device, 
     at least one control pallet capable of being attached to a regulating organ pivoting about an axis of rotation in order to cooperate with at least one complementary unlocking organ of the locking device in order to unlock the locking device from the escapement wheel in a unlocking position at each alternation of said regulating organ, 
     impulse pallets capable of being attached to said regulating organ to cooperate each on an impulse plane with a tooth of the escapement wheel to transmit a direct impulse to said regulating organ. 
     In accordance with the invention, the escapement mechanism is characterised in that the locking device is arranged to undergo a draw by the escapement wheel in each locking position and that the teeth of the escapement wheel and the impulse pallets are configured and arranged such that the impulses occur outside the plane P 1  of the escapement wheel. 
     The mechanism of the invention thus proposes in an inventive manner to move the impulse place of the escapement wheel on the impulse pallets attached to the regulating organ out of the plane P 1  in which the escapement wheel extends and rotates. It is thus possible to reduce the dimensions of the portion of the teeth of the escapement wheel which is active to provide an effective impulse on the impulse plane of the impulse pallets, while allowing out of impulse, thanks to the associated draw, a free path of the regulating organ in rotation on its axis during which the impulse pallets describe a trace between the teeth of the escapement wheel parallel to the plane P 1  of the latter. It is thus possible, by playing on the orientation of the plane of impulse of the impulse pallets, to obtain an angle of lift of the regulating organ which is very small in comparison with known escapements, with a maximum rotational amplitude of up to 300°, thus providing a very good quality factor for the mechanism of the invention, which is moreover self-starting. 
     According to an embodiment, at least part of the teeth of the escapement wheel form a projection perpendicular to the plane P 1  of said escapement wheel. Such a protrusion makes it easy to shift the impulse place of the escapement wheel to the impulse pallets attached to the regulating organ out of the plane P 1  of the escapement wheel. 
     In contrast to the impulse pallets, the at least one locking pallet is preferably arranged on the locking device to cooperate with the teeth of the escapement wheel at least partially in the plane P 1  of said escapement wheel. In particular, this ensures good stability and a good draw of the escapement wheel on the locking device during the locking phases without disturbing the regulating organ which then freely alternates in rotation between the teeth of the escapement wheel. 
     According to an embodiment of the mechanism of the invention, the impulse pallets are arranged so as to be integral in rotation with the regulating organ that their impulse plane describes a trace whose width, measured in a trace of the escapement mechanism, is at most equal to half the pitch separating two teeth of the escapement wheel. This ensures that the regulating organ can move freely between the teeth of the escapement wheel, especially between the projecting parts of the teeth, without risk of shocks between the impulse pallets and the teeth of the escapement wheel. 
     According to a preferred embodiment, the impulse pallets are arranged in a rotationally fixed manner on the regulating organ in such a way that the angle of lift at the regulating organ is between 10° and 35°, preferably between 15° and 30°. 
     In an embodiment, the locking device comprises a locking anchor provided with a first and a second locking pallet and integral with a return lever rotatably mounted about an axis between two locking positions passing through the unlocking position, said locking and unlocking positions being determined by at least two retaining stops on either side of a first end of the return lever and a complementary unlocking organ arranged at a second end of said return lever. This embodiment has the advantage of being very easy to adjust, using an anchor locking device which can be controlled in a more conventional way by the return lever interacting directly with limiting pins or stops on the one hand and the unlocking pallet of the regulating organ on the other hand by means of a fork or similar as described below. 
     Thus, in this embodiment the complementary unlocking organ can be advantageously formed of an almond-shaped ring in which the axis of the regulating organ extends such that the control pallet moves without contact along the inner walls of said ring during normal operation of the escapement mechanism, said ring defining a control cam, a notch for unlocking the control pallet being formed in the inner wall of said ring in a position of alignment with a longitudinal axis of the return lever. The almond-shaped ring thus forms a functional security for the escapement. 
     Alternatively, the complementary unlocking organ may be formed by a fork comprising two horns separated by a notch and devoid of a guard pin or the like, said horns being symmetrical with respect to a longitudinal axis of the return lever passing through the axis of rotation and the centre of the notch and extending from said notch along an arc of a circle. 
     Preferably, said impulse pallets are fixed on an impulse plate integral with the regulating organ and extending in a plane P 2  parallel to the plane P 1  of the escapement wheel. 
     The teeth of the escapement wheel then comprise an impulse finger projecting from the plane P 1  to engage the impulse plane of the impulse pallets out of said plane P 1 , the radial ends of said impulse and locking teeth describing the circular trajectory C. 
     Advantageously in this embodiment, the control pallet is a pin attached to the impulse plate. 
     In another embodiment of the escapement mechanism of the invention, the locking device comprises a return lever carrying at a first end said locking pallet and being rotatably mounted about an axis between the locking position and the unlocking position, determined by at least one retaining stop and at least one control cam arranged so as to be rotationally rigid with said regulating organ. This embodiment has the advantage of requiring only one locking pallet, and provides a simple and compact escapement structure. 
     In this embodiment, the complementary unlocking organ comprises a unlocking arm integral with the return lever and provided at a free end with a unlocking tooth arranged to cooperate with said control pallet in said unlocking position. 
     In addition, the control cam comprises a cam surface and a cam notch formed in said cam surface for cooperation with a cam follower formed at a second end of the return lever opposite to said locking pallet, said control cam and said return lever being respectively arranged such that said cam follower falls into said cam notch in said unlocking position and is pushed out of the notch to pivot the return lever and bring the locking pallet into the path of the escapement wheel in the locking position. 
     In this particular embodiment, the control pallet may be a pallet fixed on a plate which is rotationally fixed to the regulating organ and movable in a plane P 3  parallel to and distinct from the plane P 1  of the escapement wheel. 
     Alternatively, the control cam may comprise a ring and a notch formed on an inner rim of said ring, a cam follower pin at the free end of the unlocking lever extending into said ring, so that said cam follower falls into said cam notch under the action of the unlocking pallet in said unlocking position and is pushed out of said notch to pivot the return lever and bring the locking pallet into the path of the escapement wheel in the locking position. 
     In this alternative, the ring may be formed by a peripheral groove on the cam and the control pallet may be a pin fixed on the control cam in a position radially aligned with said cam notch with respect to the axis of rotation of the regulating organ. 
     In this embodiment, the impulse pallets are each fixed on an impulse plate integral with the regulating organ and extending respectively in a first plane P 2 ′ and a second plane P 2 ″, the planes P 2 ′, P 2 ″ being symmetrical with respect to the plane P 1  of the escapement wheel. 
     In order to cooperate with said impulse pallets and the locking pallet of the locking device, the escapement wheel then comprises a regular alternation of teeth comprising an impulse bar projecting symmetrically with respect to the plane P 1  of said escapement wheel to engage the impulse pallets out of said plane P 1  and teeth devoid of projections with respect to the plane P 1 , the radial ends of said teeth describing the circular trajectory C. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other details of the invention will become clearer on reading the following description, with reference to the attached drawings in which: 
         FIG. 1  shows in perspective an escapement mechanism according to the invention in a first embodiment and an associated regulating organ such as a balance represented schematically; 
         FIG. 2  shows the escapement mechanism of  FIG. 1  in top view, at the dead centre of the escapement; 
         FIG. 3  shows a front view of the escapement mechanism from  FIG. 1  at the escapement dead centre; 
         FIG. 4  shows the escapement mechanism of  FIG. 1  in top view, at the end of an impulse phase; 
         FIG. 5  represents a front view of the escapement mechanism of the invention at the end of an impulse phase as shown in  FIG. 4 ; 
         FIG. 6  shows the escapement mechanism of  FIG. 1  in top view, in the locking position during the free alternation of the regulating organ; 
         FIG. 7  is an enlargement of  FIG. 6  showing a play between the back of an impulse pallet and an impulse plane of a tooth of the escapement wheel of the mechanism; 
         FIG. 8  shows in perspective an escapement mechanism according to the invention in a second embodiment, comprising a locking device with a single locking pallet and an unlocking arm; 
         FIG. 9  is a top view of the escapement mechanism of  FIG. 8 ; 
         FIG. 10  is a top view of the escapement mechanism of  FIG. 9 . 
         FIGS. 11 to 13  show a variant of the escapement mechanism of  FIGS. 8 to 10  in which the locking device has an annular control cam and a cam follower attached to a unlocking arm. 
     
    
    
     MODES OF CARRYING OUT THE INVENTION 
     The present invention proposes a free escapement mechanism  1  of a new kind, designed and arranged to exploit and combine, in a free escapement with direct impulses, the advantages of reliability, simplicity of adjustment and self-starting of a Swiss anchor escapement well known to watchmakers for decades by singularly improving its performance by significantly reducing the angle of lift at the regulating organ while allowing a large amplitude in rotation of the latter, thus offering a quality factor far superior to known escapements. In addition, direct pulse operation promotes high energy efficiency. 
     It advantageously presents a very simple and compact structure, compatible with the use of regulating organs of the sprung balance type classically used in pocket watches or wristwatches, offering the unprecedented possibility of working at the level of the regulating organ with low amplitudes and high frequencies or conversely with large amplitudes of oscillations and lower frequencies, in all cases with increased performance, whether in terms of isochronism or chronometry, compared to the majority of existing anchor mechanisms. 
     These combined advantages are obtained according to the invention and as shown in  FIGS. 1 to 13  by a direct impulse free escapement mechanism  1 , comprising an escapement wheel  2  having a series of peripheral teeth  3 , a locking device  4  arranged to cooperate in abutment with a tooth  3  of the escapement wheel  2  in a locking position and in this position to undergo a draw, and impulse members  9  capable of being attached to a regulating organ  5  such as a sprung balance so that the latter periodically receives an impulse from a tooth  3  of the escapement wheel  2  in order to maintain its oscillations, said teeth  3  and the impulse members  9  being configured and arranged so that the impulses occur outside the plane P 1  of the escapement wheel  2 . 
     This is made possible according to the invention by an original conformation of the teeth  3  of the escapement wheel  2 , of which at least a part forms a projection perpendicular to the plane P 1  of said escapement wheel, as well as an adjusted configuration and orientation of the impulse organs  9 , in such a way that the respective pulse planes of said teeth  3  and of said impulse members  9  interact directly outside the plane P 1  of said escapement wheel  2  at each alternation of the regulating organ closest to the dead centre of the mechanism, therefore with a low angle of lift and a minimum of disturbance of the regulating organ at the impulse. The locking draw ensures free movement of the regulating organ during the locking phases over its entire amplitude of movement between the projecting parts of the teeth of the escapement wheel  2 . 
     In practice, the teeth  3  of the escapement wheel form at their free end a protrusion, which has a length measured perpendicular to the plane P 1  of the escapement wheel  2 , greater than the thickness of the felloe  22  of the escapement wheel  2 . This protrusion defines a substantially triangular shape which is represented schematically in the figures by a shoulder line at the end of each tooth  3 . In addition, the impulse members  9 , for example consisting of ruby pallets, of the escapement mechanism  1  of the invention are advantageously arranged integral in rotation with the regulating organ  5  such that their impulse plane describes a trace whose width, measured in a path of the escapement mechanism, is at most equal to half the pitch separating two teeth  3  of the escapement wheel  2 . This allows escapement  1  to be configured such that the angle of lift at the regulating organ  5  is between 10° and 35°, preferably between 15° and 30°, in other words lower than any other escapement mechanism known to date. 
     The locking device  4  is configured to disturb as little as possible the operation of the regulating organ  5  and thus to cooperate with the teeth  3  of the escapement wheel at least partially, and preferably completely, in the plane P 1  of said escapement wheel  2 . Combined with the particular configuration of the projections of the teeth  3 , this gives the escapement wheel  2  the ability to cooperate alternately with the locking device  4  and the impulse members  9  in superimposed and secant parallel planes of said teeth  31 . The impulse and locking phases of the escapement mechanism of the invention thus intervene not only separately from one another but in different planes, or levels, of the mechanism, which allows a very compact construction and a minimum of disturbances, while offering a wide choice of frequency and amplitude of operation of the regulating organ due to the possible entanglement of the circumcircles of the escapement wheel  2  and its teeth  3  and of the impulse organs  9 . 
     The escapement mechanism  1  of the invention is presented more particularly in the figures under two particular embodiments, shown respectively in  FIGS. 1 to 7  and  FIGS. 8 to 13 . 
     With reference first of all to the first embodiment, concerning the escapement mechanism  1  of the invention. It comprises an escapement wheel  2  extending in a plane P 1  and provided with peripheral teeth  3  and rotatably mounted about an axis of rotation X 1  perpendicular to this plane P 1 . Said teeth  3  define by their free ends a circular trajectory C during the rotation of the escapement wheel  2 . In a conventional way, this escapement wheel  2  is associated with an escapement pinion  21  driven on a pivot of axis X 1  common to the escapement wheel  2  and by which the latter can be coupled in use to the finishing gear train and the driving source of a watch movement in which the escapement mechanism  1  is integrated to maintain the oscillations of a regulating organ  5  of the movement, rotatably mounted around an axis of rotation X 2 . 
     In accordance with the invention, the teeth  3  of the escapement wheel  2  each have a protruding portion on the surface of the escapement wheel  2  to allow transmission of impulses to the regulating organ  5  out of the plane P 1  of the escapement wheel  2 . These projections are formed in this embodiment by an impulse finger  31  projecting with respect to the plane P 1  in order to engage, at each step of rotation of the escapement wheel  2 , the impulse plane  9   p  of a first or second impulse pallet  9  fixed to an impulse plate  91  integral with the regulating organ  5  and extending in a plane P 2  parallel to the plane P 1  of the escapement wheel  2 . Advantageously, said impulse pallets  9  are fixed to the plate  91  by any suitable means and they also extend, as can be seen from  FIGS. 1, 3 and 5  in particular, projecting perpendicularly to the plane P 2  of the plate  91  in the direction of the escapement wheel  2 . The impulse fingers  31  of the teeth  3  of the escapement wheel  2  and impulse pallets  9  integral with the regulating organ  5  are thus arranged “head to tail” to ensure their interaction outside said plane P 1 , and more particularly here between the planes P 1  and P 2  of the escapement wheel and impulse plate  91 , respectively. 
     As shown, the impulse surfaces  9   p  of the impulse pallets  9 , on which the fingers  31  of the teeth  3  of the escapement wheel  2  slide and act, have a flat surface. They can also advantageously have a curved, concave or convex shape, in order to provide a progressive acceleration of the impulse or to symmetrize the impulse on each of the impulse pallets  9  with respect to the X 2  axis of the regulating organ  5 . Thus, one can play directly on the path of the escapement, by acting on the movements of the impulse pallets  9  in relation to the escapement wheel  2 , at the level of their angular values, their speeds and the transmitted torques. 
     Escapement mechanism  1  also has a locking device  4 , which is itself rotatable about an axis of rotation X 3 . The axes of rotation X 1 , X 2 , X 3  of the escapement wheel  2 , the regulating organ  5  and the locking device  4  are preferably parallel to each other. The regulating organ  5 , which is not part of the escapement mechanism  1  as such, may consist of a sprung balance well known to the watchmaker or any other oscillating regulating organ, such as for example a knife resonator as proposed by the applicant in patent application WO 2016/012281 A1. 
     The locking device  4  comprises a bar-shaped return lever  42  which is rotatably mounted on a pivot about the axis X 3  and to which an anchor  43 , which is made of the same material as the return lever  42  and is riveted or driven onto the pivot of rotation of the latter, is attached, at the ends of the arms of which are arranged two locking pallets  41  each having a locking plane  41 r for alternately forming an abutting locking surface for the teeth  3  of the escapement wheel  2  in two extreme positions of rotation of the return lever  42  about its axis X 3 , called locking positions, one position of which is shown in  FIGS. 5 and 6 . 
     The pivoting of the return lever  42  in rotation about the axis X 3  to move the locking anchor  43  between the two locking positions is controlled as in a conventional anchor escapement by the regulating organ  5  acting on one end of the return lever  42 . This interaction takes place on each alternation in a so-called unlocking position by means of a unlocking pallet  6 , for example formed by a pin  61 , fixed to the impulse plate  91  on a complementary unlocking organ  44  formed at said first end  42  of the return lever  42 . This interaction induces the pivoting of the return lever  42  around the axis X 3  and thus the unlocking of the locking anchor  43 , more precisely of one of the locking pallets  41 , of one tooth  3  of the escapement wheel  2  prior to an impulse given by another tooth  3  of the escapement wheel on one of the impulse elements  9  of the regulating organ  5 . In addition, the angular travel of the return lever  42  is also limited by limiting stops  7 , e.g. formed by pins, arranged on both sides of the second end of the return lever  42 . These stops  7  determine the locking positions of the locking anchor  43  such that each locking pallet  41  is located in the trajectory C defined by the teeth  3  of the escapement wheel when the return lever  42  comes into contact with one of the stops  7 . The return lever  42  and the locking anchor  43  are then held in place during the free course of the regulating organ  5  after impulse by the draw effect of the escapement wheel  2  on the locking anchor  43  and the return lever  42 . 
     As can be seen from  FIGS. 2 and 3 , the return lever  42  and the locking anchor  43  are arranged in relation to the regulating organ  5  and the escapement wheel  2  in such a way that, in the dead centre of the escapement shown in  FIG. 1 , the locking pallets  41  are located at a distance from the axis of rotation X 1  of the escapement wheel  2  greater than the radius of the circumcircle C of the teeth  3  of the escapement wheel  2 , when at the same time the ends of the impulse pallets  9  intersect said circumcircle C, and are thus located at a distance from the axis of rotation of the escapement wheel  2  smaller than the radius R. 
     By this configuration, at the dead centre of the escapement  1 , the pulse planes  9   p  of the impulse pallets  9  are located in the path of the fingers  31  of the teeth  3  of the escapement wheel, while the locking pallets  41  are located outside this path. Also, the rotation of the escapement wheel  2  necessarily involves the engagement by a finger  31  of an impulse plane  9   p  of an impulse pallet  9  and the driving of the regulating organ  5  in rotation around its axis. This ensures a self-starting character to the escapement mechanism  1  of the invention. 
     Another advantageous feature is that the impulse fingers  31  and impulse pallets  9  are also shaped so that in each locking position the impulse pallets  9  can fully circulate between the fingers  31  of the teeth  3  of the escapement wheel  2 , thus ensuring a maximum amplitude of angular deflection at the regulating organ  5 , which in this case can be up to 300°. For this purpose, as shown in particular in  FIGS. 6 and 7 , the rear flank of the fingers  31  is chamfered, thus giving a triangular shape to the fingers  31 , so as to free a play J at the rear end of each impulse pallet  9  when the regulating organ  5  passes freely in the locking position of the escapement wheel  2 . 
     In the example shown in  FIGS. 1 to 7 , the complementary unlocking organ  44  is advantageously formed by an almond-shaped ring  443  in which the axis X 2  of regulating organ  5  extends. This ring  443  is configured so that during normal operation of the escapement mechanism  1  the control pallet  6  integral with the regulating organ  5  circulates without contact along the internal walls  444  of said ring, which thus define a control cam  8  for the unlocking of the return lever  42 . A unlocking notch  45  is formed in the inner wall of said ring  443  in a position of alignment with a longitudinal axis of the return lever passing through the axis of rotation X 3  thereof. This unlocking notch allows, in a conventional manner, the control pin  61  to fall at each alternation of the regulating organ so as to cause the return lever  42  to pivot and the locking anchor to be unlocked. Such a ring  443  has the advantage by a very simple configuration to provide not only the unlocking but also the safety of the escapement, the internal walls of the ring preventing in case of impact any untimely unlocking out of impulse. 
     However, the complementary unlocking organ  44  could be in a different form than that shown in  FIGS. 1 to 7 . It may in particular be formed by a fork comprising two horns separated by a notch and devoid of a guard pin or the like, said horns being symmetrical with respect to the longitudinal axis of the return lever  42  passing through the axis of rotation X 3  and the centre of the notch and extending from said notch along an arc of a circle. 
       FIGS. 8 to 13  show a second embodiment of the escapement mechanism according to the invention. This embodiment differs from the previous one in that it simplifies the locking device  4 , which has only one locking pallet  4  whose movement is controlled by a trigger-type unlocking device. In addition, only one out of two teeth  3  of the escapement wheel  2  actually participates in the impulses by acting alternately on two parallel levels of impulses on either side of the plane P 1  of the escapement wheel  2 , as described below. 
     With reference to  FIGS. 8 and 10  in particular, the escapement mechanism  1  of this second embodiment comprises an escapement wheel  2  extending in a plane P 1  rotatably mounted about an axis of rotation X 1  perpendicular to this plane P 1 . The escapement wheel  2  is provided with peripheral teeth  3  defining by their free ends a circular path C during the rotation of the escapement wheel  2 . The number of teeth  3  of the escapement wheel  2  in this second embodiment is equal to twice that of the escapement wheel of the escapement mechanism according to the first embodiment, in order to compensate in particular for the removal of the second locking pallet  41  at the locking device  4 , as will be described below. In a conventional way, the escapement wheel  2  is associated with an escapement pinion  21  driven on a pivot of axis X 1  common to the escapement wheel  2  and by which the latter can be coupled in use to the finishing gear train and the driving source of a watch movement in which the escapement mechanism  1  is integrated to maintain the oscillations of a regulating organ  5  of the movement, rotatably mounted around an axis of rotation X 2 . 
     In an original way, the teeth  3  of the escapement wheel  2  comprise a regular alternation of teeth  3  comprising an impulse bar  32 , forming two symmetrical projections on either side of the plane P 1  of the escapement wheel  2 , and teeth  3  without projections and contained substantially in the plane P 1 , as in an ordinary escapement wheel  2 . The impulse bars  32 , shaped in practice like two fingers  31  of the first embodiment symmetrical with respect to the plane P 1 , are arranged to engage an impulse plane  9   p  of a first and a second impulse pallet  9  fixed respectively to an upper impulse plate  91  and a lower impulse plate  92  integral with the regulating organ  5  and extending respectively in two planes P 2 ′, P 2 ″ parallel and symmetrical with respect to the plane P 1  of the escapement wheel  2 . 
     The impulse pallets  9  also extend, as can be seen in  FIGS. 8, 10 and 12  in particular, projecting perpendicular to the P 2 ′, P 2 ″ planes of plates  91 ,  92  in the direction of the escapement wheel  2 . Each impulse pallet  9  is thus arranged “head to tail” with one of the projecting portions of the impulse bars  32  formed one tooth in  2  of the escapement wheel so as to provide impulses alternately between plane P 1  and plane P 2 ′ on the one hand and between plane P 1  and plane P 2 ″ on the other hand on each alternation of the regulating organ  5 . 
     As shown, the impulse surfaces  9   p  of the impulse pallets  9 , on which the fingers  32  of the teeth  3  of the escapement wheel  2  slide and act, have a flat surface. They can also advantageously have a curved, concave or convex shape, in order to provide a progressive acceleration of the impulse or to symmetrize the impulse on each of the impulse pallets  9  with respect to the X 2  axis of the regulating organ  5 . Thus, one can play directly on the path of the escapement, by acting on the movements of the impulse pallets  9  in relation to the escapement wheel  2 , at the level of their angular values, their speeds and the transmitted torques. 
     The escapement mechanism  1  also has a locking device  4 , rotatably mounted about an axis of rotation X 3 . This locking device  4  is, as previously presented, extremely simplified and comprises only a single locking pallet  41  arranged at one end of an arcuate return lever  42  rotatable about a pivot of axis X 3  between a locking position, shown in  FIGS. 8, 9 and 11  and an unlocking position, shown in  FIG. 13 . These two positions are determined by a retaining stop  7 , formed by a single pin, and a control cam  8  arranged as an integral part of the rotation of said regulating organ  5 . 
     The pivoting of the return lever  42  in rotation about the axis X 3  between the locking position and the unlocking position is controlled by the regulating organ  5  via an unlocking pallet  6  acting on a complementary unlocking organ  44  integral with the lever  42  on the one hand and the control cam  8  acting directly on the return lever  42  on the other hand. 
     In the embodiment shown in  FIGS. 8 to 10 , the control pallet  6  is a pallet  61  attached to a plate  62  which is fixed to the regulating organ  5  and arranged on the upper impulse plate  91 . The unlocking pallet  61  and its plate  62  are thus mobile in a plane P 3  parallel and distinct from the plane P 1  of the escapement wheel  2  and the planes P 2 ′, P 2 ″ of the impulse plates  91 ,  92 . The control pallet  6  is arranged to trigger the unlocking of the locking device  4  from its locking position, i.e. more specifically to release the locking pallet  41  from its engagement against a tooth  3  of the escapement wheel in order to allow the transmission by the latter of an impulse on one of the impulse pallets  9  at each alternation of the regulating organ  5 . For this purpose, the unlocking pallet  6  cooperates with a complementary unlocking organ  44  which is formed by a unlocking arm  441  which is integral in rotation with the return lever  42  and which in this example is driven on the pivot point of the return lever  42 . The unlocking arm  441  has a unlocking tooth  442  at one free end, on the sides of which the unlocking pallet  61  is supported in the unlocking position prior to the impulse and pushes the unlocking arm  441  to swivel the return lever  42  about its release axis X 3  counter-clockwise (according to the convention of the figures). 
     This rotation of lever  42  to unlock the locking pallet  41  from the escapement wheel is, however, secured by control cam  8  which controls the rotation of the return lever  42  at a free end  421  of the latter opposite the locking pallet  41  and forming a cam follower. For this purpose, the control cam  8  is formed by a shaft of axis X 2  integral with and/or forming part of the axis or pivot of the regulating organ  5 , said shaft being embedded between the upper  91  and lower  92  impulse plates. The cylindrical peripheral surface  81  of this shaft forms a cam surface in which a unlocking notch  82  is formed. The return lever  42  is so arranged in relation to the escapement wheel  2  and the regulating organ  5  that, in the locking position, it rests against the stop  7  and its end  421  is positioned opposite, but not touching, the cam surface  8 , the locking pallet  41  resting on its locking plane  41 r against a tooth  3  of the escapement wheel. Thus, in the event of impacts, said end  421  comes into contact with said cam surface  81 , preventing rotation of the return lever  42  and thus any unlocking of the locking pallet  41 . Such an unlocking is only permitted in the unlocking position, in which the cam follower  421  falls into the cam groove  82  simultaneously with the pushing of the unlocking pallet  61  onto tooth  442  of the unlocking arm  441 . This drop of the cam follower  421  into the notch releases the rotating lever  42  which rotates under the thrust undergone by the arm  441 , releasing the locking pallet  4 . The escapement wheel  2  rotates and gives an impulse to the regulating organ  5  via an impulse strip  32  on an impulse pallet  9 . During the rotation of the regulating organ  5  under the impulse of the escapement wheel  2  the cam follower  421  is pushed back by the cam surface  81  while the regulating organ begins its free alternation, which causes the return lever  42  to rotate clockwise, bringing the locking pallet  41  back into the path C of the escapement wheel, thus providing the stop necessary for the locking phase, and under the effect of the draw force forcing the return lever  42  against the retaining stop  7 . 
     The unlocking and locking phases are thus easily controlled and secured by the control cam  8 , without any risk of unintentional release in the event of shocks and out of pulses, even at high oscillation frequencies of the regulating organ  5 . 
       FIGS. 11 to 13  show escapement mechanism  1  in its second embodiment with an alternative unlocking and safety mechanism. In this embodiment, the control cam  8  is formed by a ring with a circular inner wall or rim forming a cam surface  81  in which a cam notch  82  is recessed. In the example shown, the ring  8  can be formed from a circle concentric to the axis X 2  and attached to the regulating organ  5  by gluing or other means of attachment to the upper impulse plate  91 . The ring  8  can also be made of material in one piece with the impulse plate  91 . The unlocking pallet  6  is then formed by a finger or feeler  61  which is fixed to the regulating organ  5  and whose free end is aligned and partially penetrates into notch  82  of the ring. 
     The cam follower  421  consists of a pin or the like driven into the free end of the unlocking lever  441  and extending into said ring  8 . 
     Thus, as shown in  FIG. 13  and in accordance with the operating principles previously defined with reference to  FIGS. 8 to 10 , the cam follower  421  falls into said cam notch  82  under the action of the unlocking pallet  61  in said unlocking position and is pushed out of the notch  82  opposite the inner cam surface  81  of the ring in the locking position. 
     In another embodiment not shown, the cam ring  8  could also be formed by a circular groove on the upper impulse plate  91  in which the cam follower pin  421  would be housed, said groove having a said cam notch and the unlocking pallet  6  then being formed by a pin radially aligned with the cam notch with respect to the axis of rotation X 2  of the regulating organ  5 . 
     Finally, as in the embodiment of  FIGS. 1 to 7 , the escapement mechanism  1  in the second embodiment of  FIGS. 8 to 13  is also self-starting. As can be seen from  FIG. 13  in particular, the return lever  42  is arranged in relation to the regulating organ  5  and the escapement wheel  2  in such a way that, in the unlocking position, therefore just before the dead centre of the escapement, the locking pallet  41  goes away from the circumcircle C of the teeth  3  of the escapement wheel  2 , when at the same time the ends of the impulse pallets  9  intersect said circumcircle C, and are thus located at a distance from the axis of rotation of the escapement wheel  2  smaller than the radius R. 
     By this configuration, at the dead centre of the escapement  1 , the impulse planes  9   p  of the impulse pallets  9  are located in the path C of the teeth  3  of the escapement wheel, while the locking pallet  41  is located outside of this path. Also, the rotation of the escapement wheel  2  necessarily involves the engagement by a bar  32  of an impulse plane  9   p  of an impulse pallet  9  and the driving of the regulating organ  5  in rotation around its axis and the driving of the escapement mechanism  1  according to the invention.