Patent Publication Number: US-7712953-B2

Title: Vertical clutch device for timepiece

Description:
The present invention relates to a clutch device for a timepiece and more particularly for a chronograph. 
   In a chronograph, the chronograph wheel that holds the chronograph hand is linked with the seconds wheel via a clutch. The clutch can take up a coupled position corresponding to the chronograph&#39;s working position where the chronograph wheel is driven by the seconds wheel, and an uncoupled position corresponding to the chronograph&#39;s stopping position where the chronograph wheel is not driven by the seconds wheel and is immobilised by a brake. 
   The present invention relates to a type of clutch that is particularly appreciated, that is, the vertical clutches. Contrary to the horizontal clutches, the vertical clutches do not cause any jumping of the chronograph hand when the chronograph is set to work. 
   A vertical clutch generally comprises on one and the same arbor a first mobile part comprising a toothed wheel, and a second mobile part comprising another toothed wheel and a coupling cone. The toothed wheel of the first mobile part is engaged with the seconds wheel. The toothed wheel of the second mobile part is engaged with the chronograph wheel. The coupling cone cooperates with a clamp which in its opening and closing is controlled by a column wheel. Closing of the clamp moves the mobile parts apart against the action of a spring, whereas an opening of the clamp brings the mobile parts into mutual contact under the action of the spring. With the clamp open (coupled position), the mobile parts are kept in mutual contact by the spring, and the first mobile part drives the second mobile part by friction. With the clamp closed (uncoupled position), the second mobile part is not in contact with the first mobile part, and thus is not driven. 
   For sufficient friction between the mobile parts in the coupled position, the spring that keeps them in contact must have a large force. Moreover, grease usually is used to produce adhesion in the metal—metal contact of the mobile parts. This grease is degraded rather rapidly with time, and thus must be regularly replaced. In addition, this grease does not remain in place, and by moving within the chronograph mechanism may damage it or at least disturb its operation. 
   The present invention aims at providing a vertical clutch device that permits using a spring of smaller force and does not require use of the grease just cited. 
   To this end a clutch device for timepiece and notably for chronograph is provided that comprises first and second coaxial, rotary mobile parts that can assume a relative axial coupled position in which a rotation of the first mobile part causes a rotation of the second mobile part, and a relative axial uncoupled position in which a rotation of the first mobile part does not cause a rotation of the second mobile part, characterised in that it further comprises a friction element of a viscoelastic material intercalated between the mobile parts so as to transmit the rotation of the first mobile part to the second mobile part in the coupled position. 
   Particular embodiments of the invention are defined in the appended dependent claims  2  to  7 . 
   The present invention also provides a chronograph mechanism such as defined in the appended claim  8 . 

   
     Further characteristics and advantages of the present invention will become apparent when reading the following detailed description of a preferential embodiment that is given while referring to the appended drawings in which: 
       FIG. 1  is a view in axial section of a clutch according to the invention, in a coupled condition; 
       FIG. 2  is a view in axial section of the clutch according to the invention, in an uncoupled condition; 
       FIG. 3  is a plan view from above, of the clutch according to the invention in the coupled condition; 
       FIG. 4  is a plan view from above, of the clutch according to the invention in the uncoupled condition. 
   

   Referring to  FIGS. 1 to 4 , a vertical clutch device for chronograph according to the invention comprises a lower rotary mobile part  1  and an upper rotary mobile part  2 , both mounted on a coupling axis  3  pivoted in two bearings  4 ,  5 . The lower mobile part  1  consists of a toothed wheel mobile in rotation around the axis  3  and resting on a collar  6  of axis  3 . This lower mobile part  1  is permanently engaged with the seconds wheel  7  of the movement that makes one revolution per minute. The upper mobile part  2  is movably mounted about axis  3 , or more precisely about a pipe  8  driven onto axis  3 . The upper mobile part  2  consists of several coaxial elements rigidly assembled, viz., a toothed wheel called upper coupling wheel  9 , a coupling cone  10 , and a coupling pipe  11 . The coupling pipe  11  surrounds pipe  8 , so as to be mobile in rotation and in translation, and at its periphery has bearing surfaces  12 ,  13  onto which are driven the upper coupling wheel  9  and the coupling cone  10 . Coupling cone  10  is located between the upper coupling wheel  9  and the lower mobile part  1 , and by its annular upper flat surface is in contact with the annular lower flat surface of the upper coupling wheel  9 . The upper coupling wheel  9  is permanently engaged with the chronograph wheel  14  the arbor of which holds the chronograph hand, that is, the hand of the seconds counter. 
   A washer  15  movably mounted in rotation around pipe  8  above the upper mobile part  2  is separated from the upper coupling wheel  9  by a spring  16 . Spring  16  has an annular central segment  17  that surrounds pipe  8 , and a certain number of blades  18 , for example six, extending from the central segment  17 , one out of any two resting on the upper coupling wheel  9  and the others resting on washer  15 . In  FIGS. 1 and 2 , two blades  18  only can be seen. Spring  16  keeps washer  15  axially abutting an annular shoulder  19  of pipe  8 , and tends to move the upper mobile part  2  away from washer  15 , so as to bring the upper mobile pad  2  closer to the lower mobile part  1 . 
   The upper mobile part  2  can move in axial translation on pipe  8  between a coupled position represented in  FIG. 1  where the upper mobile part  2  is pressed against the lower mobile part  1 , and an uncoupled position represented in  FIG. 2  where the mobile parts  1 ,  2  have been moved apart. In the coupled position, the lower mobile part  1  drives the upper mobile part  2  by friction, so that the movement of the seconds wheel  7  is transmitted to the chronograph wheel  14 . The frictions between pipe  8 , upper mobile part  2 , spring  16  and washer  15  have the effect that elements  1 ,  2 ,  3 ,  8 ,  15 , and  16  in the coupled position rotate jointly. In the uncoupled position, the lower mobile part  1  rotates without driving the upper mobile part  2 , and hence does not transmit the movement from the seconds wheel  7  to the chronograph wheel  14 . 
   The axial displacement of the upper mobile part  2  is controlled by a clamp  20  that can be closed so as to come into contact with the coupling cone  10  and raise it against the action of spring  16  ( FIGS. 2 and 4 ), or opened so as to allow spring  16  to push the upper mobile part  2  against the lower mobile part  1  ( FIGS. 1 and 3 ). As is apparent from  FIGS. 3 and 4 , one  21  of the two arms  21 ,  22  of clamp  20  controls the other arm  22 , and cooperates with a column wheel  23  through a beak  24 . In the classical way, column wheel  23  is controlled by a start-stop push button (not represented) of the chronograph. Every time the push button is pressed, the column wheel  23  will turn by one step, which closes or opens clamp  20  depending on the position of beak  24  relative to the columns. In every other angular position of the column wheel  23  ( FIG. 4 ), beak  24  rests against a column  25  of wheel  23  against the action of a return spring  26  of clamp  20 , which keeps clamp  20  in its closed position. In the remaining angular positions of column wheel  23  ( FIG. 3 ), beak  24  is between two columns  25 , and clamp  20  is kept in its open position by the action of return spring  26 . 
   During the change from the coupled to the uncoupled position, clamp  20  pushes the upper mobile part  2  against washer  15  while spring  16  remains between them, which causes the entire set of 1, 2, 3, 8, 15, and 16 to rise up to the point where a shoulder  27  of axis  3  rests against the upper bearing  4 . In the uncoupled position, the frictions between axis  3  and bearing  4 , between pipe  8 , upper mobile part  2 , washer  15 , and spring  16 , and between clamp  20  and coupling cone  10  have the effect that the set of 2, 3, 8, 15, and 16 stops turning, which stops the chronograph wheel  14 . No specific brake is needed, therefore, to stop the chronograph wheel  14 . The lower mobile part  1  turns around axis  3  in this uncoupled position. 
   During zero resetting of the chronograph after its stopping, a hammer (not represented) strikes a heart-shaped cam, which causes the chronograph wheel  14  to rotate to the zero position of the chronograph hand. This rotation of chronograph wheel  14  gives rise to a rotation of the upper mobile part  2 . Washer  15  and spring  16  are driven in this rotation by friction with the upper mobile part  2 , the set of 2, 15, 16 thus turning around axis  3  and pipe  8 . 
   The chronograph may include a function known as “flyback” that allows a resetting of the chronograph to zero while it is working. In this case clamp  20  is closed by a lever (not represented) under the action of a zero-resetting push button so as to stop the chronograph, and the zero-resetting hammer is then actuated. 
   According to the invention, mobile parts  1 ,  2  in the coupled position of the clutch are not pushed against one another directly but, rather, via a gasket  30  made of a viscoelastic material. This gasket  30  has an annular, typically toric, shape coaxial with axis  3  and is housed in an annular recess  31  that is defined by the coupling pipe  11  and the coupling cone  10  and is open downward, that is, toward the lower mobile part  1 . Part of gasket  30  projects beyond recess  31 , so that in the coupled position of the clutch gasket  30  is squeezed between the bottom of recess  31  and the lower mobile part  1  by the action of spring  16  while the lower and upper mobile parts  1 ,  2  are not touching. In this coupled position, the friction developing on the one hand between gasket  30  and the lower mobile part  1  and on the other hand between gasket  30  and the upper mobile part  2  prevents any slipping of the upper mobile part  2  relative to the lower mobile part  1 , and thus makes these two mobile parts  1 ,  2  solid in rotation. In the uncoupled position of the clutch, gasket  30  does not touch the lower mobile part  1  any more, so that the upper mobile part  2  is disconnected from the lower mobile part  1 . 
   In practice, gasket  30  has an inner diameter that is smaller than the smallest inner diameter of recess  31 , so that gasket  30  is introduced and held in recess  31  by being radially stretched there. The elements of the upper mobile part  2  are assembled by first placing gasket  30  around the coupling pipe  11 , then driving the coupling cone  10  around coupling pipe  11  and gasket  30 . 
   Thanks to gasket  30 , strong friction is obtained between the lower and upper mobile parts  1 ,  2  in the coupled position, so that spring  16  need not be strong, that is, need not be strongly tensioned. The risk of permanent deformation or rupture of spring  16  thus is limited. Moreover, using friction grease is no longer necessary. 
   The viscoelastic material forming gasket  30  is, for example, natural rubber or synthetic rubber such as neoprene, polybutadiene, polyurethane, silicone, etc. The lower and upper mobile parts  1 ,  2  may be made of any appropriate material, typically a metallic material. 
   In a variant realization, gasket  30  could be housed in the lower mobile part  1  rather than in the upper mobile part  2 .