Abstract:
Escapement device of a timepiece movement includes an escapement wheel, a first mobile having means of locking with the escapement wheel and of mechanical transmission with the escapement wheel, a second mobile and the balance roller. The second mobile has means of locking with the escapement wheel and means of mechanical transmission with the escapement wheel and the first mobile. The mobiles are driven by the escapement wheel tangentially.

Description:
This application claims priority to International Application No. PCT/EP2012/060825 filed Jun. 7, 2012; the entire content is incorporated herein by reference. 
     BACKGROUND 
     The present invention relates to an escapement device for clockwork, particularly for a wristwatch of the spiral balance type. 
     SUMMARY 
     The escapement device in a mechanical watch is the master part designed, on the one hand, to deliver the necessary energy for maintaining the oscillatory motion of the mechanical oscillator, and on the other hand to transmit the frequency of oscillation to the gear train driving the time display. 
     The most widely used escapement device is currently the Swiss lever escapement. This type of escapement has been the subject of numerous studies and publications. The manual entitled “Théorie d&#39;horlogerie” [Clockwork Theory], published by the Federation of Swiss Technical Schools, as well as the manual “Echappement et moteurs pas à pas” [Escapements and Stepping Motors] from the same publisher, describe in detail the operation of this type of escapement. The major drawbacks of this type of escapement are: 
     low efficiency: best efficiency is on the order of 30% to 40%; 
     manufacturing difficulties: to obtain the aforementioned efficiencies, the Swiss lever requires several highly precise final fine-tuning steps; 
     limited operating frequency: driving of the lever by the escape wheel is not tangential; during the mechanical impulse, the tooth of the escape wheel slides along the lever pallet, which leads to a wear problem for high operating frequencies. 
     To resolve the wear problem, patent EP 0 018796 A2 proposes a tangential drive type of escapement. The disadvantage of this type of escapement is the necessity of using two stacked wheels, which increases the inertia of the escapement and consequently reduces efficiency; moreover, the number of highly precise final fine-tuning steps is as great as that of a Swiss lever escapement. 
     Another type of tangential drive escapement well known in the literature is the detent escapement. This type of escapement has one active alternation, that is the escape wheel advances and delivers the mechanical impulse once per period of oscillation of the spiral balance wheel. 
     The aim of the present invention is to correct the flaws of the known escapements mentioned above by proposing a tangential drive escapement device with two active alternations per period of oscillation, with a single escape wheel and which nevertheless consumes less energy in its operation than the Swiss lever escapement. 
     To this end, the escapement as defined in Claim  1  has only one escape wheel and, thanks to the outside angles of each mobile which run from the locking face toward the driving face and which have the same direction as the principal direction of rotation of the escape wheel (during the impulse phase), the operation requires less energy because friction is reduced between the escape wheel and each mobile. In other words, the locking and driving faces of each mobile are arranged such that, during the driving or impulse phase, the escape wheel and the mobile then in contact with the escape wheel have opposite directions of rotation; the drive during the impulse phase is tangential. The escapement according to the present invention is therefore simple because it only has one escape wheel, but increases the operating reserve and can be used at high oscillation frequencies. It can also be noted that, according to this arrangement, transmission of energy from the escape wheel to the balance is effective. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a general plan view of an embodiment of the escapement device according to the invention; 
         FIG. 2  shows the first rest position of the escapement of  FIG. 1 ; 
         FIG. 3  shows the position of the escapement of  FIG. 1  just after disengaging from the first rest position; 
         FIG. 4  shows the phase of energy transmission from the escape wheel to the balance when the latter rotates in the counter-clockwise direction; 
         FIG. 5  shows mobiles  2  and  3  and the escape wheel  1  in the first rest position; 
         FIG. 6  shows the outside angle αe between the surface normals n 61  and  62  of the input pallet as well as the outside angle αs between the surface normals n 63  and  64  of the output pallet of a Swiss lever escapement; 
         FIG. 7  shows the end of the phase of energy transmission from the escape wheel to the balance when the latter is turning in the counter-clockwise direction; 
         FIG. 8  shows the second rest position of the escapement of  FIG. 1 ; 
         FIG. 9  shows the position of the escapement of  FIG. 1  just after disengaging from the second rest position; 
         FIG. 10  shows the phase of energy transmission from the escape wheel to the balance when the latter is turning clockwise; 
         FIG. 11  shows the end of the phase of energy transmission from the escape wheel to the balance when the latter is turning clockwise; 
         FIG. 12  shows the mobile  2  of the escapement device of  FIG. 1 ; 
         FIG. 13  shows a variant embodiment of the locking face  23  of the mobile  2 ; 
         FIG. 14  shows a variant embodiment of the locking face  33  of the mobile  3 ; 
         FIG. 15  shows the case where the pitch diameters of each mobile  2  and  3  are equal; 
         FIG. 16  shows a variant of the locking face of the second mobile; 
         FIG. 17  shows a variant of the locking face of the first mobile; 
         FIG. 18  shows a variant of the locking face of the second mobile. 
     
    
    
     DETAILED DESCRIPTION 
     In the present application, reference will be made to outside angles which are measured in the same direction as that traveled by the point of contact between the escape wheel and the mobile body considered. In the present application, this comes down to saying that the direction in which this angle is measured is opposite to the direction of rotation considered when releasing the escape wheel. 
     One embodiment of the escapement device according to the invention is shown in  FIG. 1 , in plan and in elevation in 3 section planes shown in broken lines. The escapement device according to  FIG. 1  includes: 
     an escape wheel  1  driven by the barrel through the transmission wheels; this escape wheel rotates about the axis  11  in the counter-clockwise direction; 
     a mobile  2  pivoting about the axis  21 , comprising a first toothed structure with impulse faces  22  and locking faces  23  as well as a second toothed structure  24 ; 
     a mobile  3  pivoting about the axis  31 , comprising a first toothed structure with impulse faces  32  and locking faces  33 , a second toothed structure  34  and a third toothed structure  35 . 
     Though it is not directly a part of the escapement device,  FIG. 1  also shows the plate of the balance  4  pivoting about the axis  41  and comprising the toothed structure  42 . 
     The following figures describe the principal operating steps of the escapement device according to the invention. 
       FIG. 2  shows the first rest position of the escapement of  FIG. 1 . 
     In this figure, the balance is turning clockwise. The toothed structure  42  of the balance is moving away from the toothed structure  35  of the mobile  3 . The tooth of the escape wheel  1 , under the influence of the barrel torque, exerts a force F on the locking face  33  of the mobile  3 . This locking face  33  is arranged so that the direction of the force F passes substantially in proximity to the center of the mobile  3 . Under these conditions, the escape wheel is locked and consequently immobilizes the mobile  3  and the mobile  2  by way of the toothed structures  24  and  34 . 
       FIG. 3  shows the position of the escapement of  FIG. 6  just after leaving the first rest position. 
     In this figure, the balance is turning counter-clockwise. The toothed structure  42  of the balance comes into contact with the toothed structure  35  and causes the mobile  3  to turn clockwise. This action frees the tooth of the escape wheel from the locking face  33 . The necessary mechanical energy for disengaging is extremely small because it is used only to overcome the friction of the escape wheel on the locking face  33  and to displace the mobiles  2  and  3  a few degrees. In this application example, the angular displacement of the mobiles  2  and  3  during disengagement is about 4 degrees. 
       FIG. 4  shows the phase of energy transmission from the escape wheel to the balance when the latter is turning counter-clockwise. 
     In this figure, the tooth of the escape wheel  1  presses on the impulse face  32  and drives the mobile  3  in the clockwise direction. The mechanical energy of the escape wheel is transmitted to the balance thanks to the toothed structures  42  and  35 . The mobile  2  is also driven by the mobile  3  by the toothed structures  34  and  24 . It is noted that, unlike a Swiss lever escapement, the driving of the mobile  3  by the escape wheel is substantially tangential to the trajectory of the impulse face  32 . 
     The tangential driving of the mobile  3  by the escape wheel is obtained thanks to the particular arrangement of the faces  33  and  32  of the mobile  3 . 
       FIG. 5  shows the mobiles  2  and  3  as well as the escape wheel  1  in the first rest position. 
     The vector n 33  represents the surface normal (hereafter called “normal”) to the locking face  33  at the locking point of the tooth of the escape wheel, the vector n 32  represents the normal passing through the center of the impulse face  32  of the mobile  3  and α 3  represents the outside angle between n 33  and n 32 . 
     One of the particular characteristics of the escapement according to the invention is manifested by an outside angle α 3  having the same sign as that of the angle of rotation of the escape wheel. In this exemplary embodiment, the outside angle α 3  and the angle of rotation of the escape wheel are positive with respect to the trigonometric direction. 
     These characteristics are also found on the outside angle α 2  between the normal n 23  to the locking face  23  and the normal n 22  to the impulse face  22  of the mobile  2 . 
     By way of comparison,  FIG. 6  shows the outside angle αe between the normal n 61  to the locking face  61  and the normal n 62  to the impulse face  62  of the input pallet, as well as the outside angle αs between the normal n 63  to the locking face  63  and the normal n 64  to the impulse face  64  of the output pallet, of a Swiss lever escapement. 
     It is observed that the outside angles αe and αs are of opposite sign to that of the angle of rotation of the escape wheel. 
       FIG. 7  shows the end of the phase of energy transmission from the escape wheel to the balance when the latter is turning counter-clockwise. In this end of the energy transmission phase, the tooth of the escape wheel leaves the impulse face  32  of the mobile  3  and the locking face  23  of the mobile  2  is positioned facing the tooth of the escape wheel  1 . During this time, the balance follows its supplementary oscillation arc while moving its toothed structure  42  away from the toothed structure  35  of the mobile  3 . 
       FIG. 8  shows the second rest position of the escapement of  FIG. 1 . 
     In this figure, the balance is turning counter-clockwise. The toothed structure  42  of the balance is moving away from the toothed structure  35  of the mobile  3 . The tooth of the escape wheel  1 , under the influence of the barrel torque, exerts a force F on the locking face  23  of the mobile  2 . This locking face  23  is arranged so that the direction of the force F passes substantially in proximity to the center of the mobile  2 ; consequently, the escape wheel is locked and immobilizes the mobile  2  as well as the mobile  3  by way of the toothed structures  24  and  34 . 
     The phases of engagement, of energy transmission and the end of the energy transmission when the balance is turning clockwise are manifest in similar fashion to those already presented when the balance is turning counter-clockwise. 
     The following figures illustrate these different phases: 
       FIG. 9  shows the position of the escapement of  FIG. 1  just after disengaging from the second rest position; 
       FIG. 10  shows the phase of energy transmission from the escape wheel to the balance when the latter is turning clockwise; 
       FIG. 11  shows the end of the phase of energy transmission from the escape wheel to the balance when the latter is turning clockwise. 
     After this energy transmission phase in the clockwise direction, the escape wheel is again locked at the locking face  33  and the operating cycle begins again. 
     It is observed that the escapement device according to the invention has two active alternations per period of oscillation of the spiral balance and that the escape wheel advances at each alternation by an angle equal to 180°/N, N being the number of teeth of the escape wheel; moreover, the same tooth of the escape wheel is successively locked on the locking face  33  and  23 . It can be deduced that the angle between the locking points on the faces  33  and  23  with respect to the center of rotation of the escape wheel is also equal to 180°/N. 
       FIG. 12  shows, in plan and in perspective, the mobile  2  of the escapement of  FIG. 1 . 
     In this exemplary embodiment the locking face  23  consists of a plane the normal to which at the locking point passes substantially in proximity to the center of rotation of the mobile  2 . It is also possible to obtain the same effect by replacing this plane by a cylindrical surface the cylinder axis whereof passes through the center of rotation of the mobile  2 . However, if the abovementioned surfaces allow locking of the escape wheel, they do not make it possible to guarantee with precision the locking position, due to the rebound due to the impact between the tooth of the escape wheel and the locking face, at the end of the energy transmission phase and just before the rest phase. 
     To improve the precision of locking, a variant embodiment of the locking face  23 , shown in  FIG. 13 , consists of replacing this plane by a concave surface. 
       FIG. 15  shows the case where the pitch diameters (Dp) of the gears  24  and  34  are equal, so as to minimize the differences in inertia between the two mobiles  2  and  3 . 
       FIGS. 16 and 17  show a variant of the locking face, respectively of the first and of the second mobile, where these surfaces are concave and consist of two secant planes inclined at an angle v, so as to offer secure locking in the event of an impact or a rebound of the escape wheel  1  on one of the first or second mobiles  2  or  3 . With this implementation, the relative angular position of the escape wheel  1  relative to the first and second mobiles  2  and  3  is guaranteed and there is no possibility of undesired rotation. 
       FIG. 18  shows a variant of the locking face  33  of the second mobile. The plane n shows the plane normal to the vertical surface passing through the locking point between the second mobile  3  and the escape wheel  1  and the center of rotation of the second mobile  3 . The first plane of the locking face  33  forms an angle β relative to the plane n. A nonzero angle β offers better shock resistance of the escape wheel; on the other hand it causes recoil of the escape wheel during disengagement and consequently a loss of energy on disengagement. The second locking plane forms an angle γ relative to the plane n. A high value of γ makes it possible to improve the precision of locking; on the other hand, it causes considerable rebound of the escape wheel  1  prior to locking. Different trials have shown that the value of the angle v=180−((β+γ) comprised between 120° and 170° represents the best compromise between good locking security, minimal or zero rebound at the end of the impulse and minimum energy loss on disengagement. 
     It will be understood that various modifications and/or improvements obvious to the person skilled in the art can be applied to the different embodiments of the invention described in the present description without departing from the scope of the invention defined by the appended claims.