CH714013A2 - Skeleton watch comprising a movement independent of the middle part. - Google Patents

Abstract

The invention relates to a skeleton watch (1) comprising: - a case on which an ice and a base are fixed; - a movement (12) comprising: - a frame (13); Time display means (27); - A gear mechanism (55) in gear engagement with the time display means (27); A motor (56) comprising: an electromagnet (57); • a stator (58); A rotor (59) carrying a gear (60) in gear engagement with the gear mechanism (55); An electronic circuit (61) comprising: a quartz (62) piezoelectric; • a calculator (63) connected to the quartz (62) and the stator (58) by means of electrical conductors (64); - An auxiliary board (65) which carries the electronic circuit (61), this auxiliary board (65) being distinct from the bottom and fixed on the frame (13).

Description

Description

Technical Field [0001] The invention relates to the field of watchmaking. More specifically, it relates to a quartz skeleton watch, that is to say a watch with analog display (with needles) and electric motor, which lets its internal organs appear, at least in part.

Technological background [0002] A European skeleton watch is known from European patent EP 3 60 140 which comprises a middle part carrying an upper crystal and a back, as well as a frame carrying the watch hands and placed in a space circumscribed by the middle between the upper glass and the back.

This watch is powered by an electric quartz circuit. This circuit includes areas and conductors directly formed on the bottom.

This watch is satisfactory but remains perfectible.

First, interventions requiring depositing the bottom are likely to damage the beaches and the conductors, especially when the watchmaker introduces screwdriver blades to separate the case back (which can scratch the beaches or the conductors ), or when it leverages the bottom for the same purpose (which flexes the bottom and can crack the pads or the conductors).

Second, the fact that the conductors and the pads are directly formed on the bottom (intended to be in direct contact with the skin) subjects them to thermal cycles (depending on whether the watch is worn or not) also liable to to damage.

Third, the removal of the bottom, which may prove necessary to identify a fault found for example in the mechanism, cuts the electrical circuit, and thereby blocks the mechanism, to the detriment of the identification of the fault.

Claims (10)

Summary of the invention [0008] The invention aims to propose a skeleton watch which fulfills at least one of the following objectives: - protect the electronic circuit from shocks and stresses during any interventions on the watch requiring access to the movement; - thermally insulate, as much as possible, the electronic circuit from the bottom; - allow the watch to run even when the case is removed during an intervention. To this end, a skeleton watch is proposed comprising: - a middle part which defines an interior space; - a mirror and a back fixed to the middle on either side of it to close the interior space; - a movement which includes: - an openwork frame having a front face and a rear face; - time display means mounted, on the side of the front face of the frame, on a central spindle integral with the latter, these time display means notably comprising a minute hand and a hand hours; - a reduction mechanism in gear engagement with the time display means; - an engine comprising: • an electromagnet; • a stator; • a rotor carrying a pinion in gear engagement with the reduction mechanism; - an electronic circuit comprising: • a piezoelectric quartz; • a computer connected to the quartz and the stator by means of electrical conductors; CH 714 013 A2 - an auxiliary plate which carries the electronic circuit, this auxiliary plate being distinct from the bottom and fixed to the frame on the side of its rear face. In this way, the movement is independent in particular of the bottom, and the electronic circuit is protected from shocks and stresses during interventions requiring the removal of the bottom. According to a particular embodiment, the movement comprises a plate on which the electronic circuit is integrated, this plate being mounted on the auxiliary plate by being interposed between the latter and the frame. The movement may also include a wedge interposed between the plate and the auxiliary plate. The reduction mechanism is preferably mounted between the frame and the auxiliary plate. The reduction mechanism typically comprises an intermediate wheel, in gear engagement with the rotor pinion, and a medium wheel, in gear engagement with the intermediate wheel and the minute wheel. The watch may further include a battery case provided with a barrel housed in an aperture formed in the frame, and lugs which project radially from the barrel and are interposed between the frame and the auxiliary plate. In this case, the watch can also include a pair of contactors partially housed in the battery case, each contactor having an external tab applied against a range of current collection from the electrical circuit. As for the time display means, they include for example: - a minute wheel, integral with the minute hand; - a sun wheel, integral with the spindle; - an hour wheel, integral with the hour hand. An epicyclic train mounted in rotation on the minute hand, and which comprises a lower planetary wheel in gear engagement with the sun wheel, and an upper planetary wheel, integral with the lower planetary wheel and in gear with the hour wheel. The stator is for example in the form of an insert inserted between the frame and the auxiliary plate. According to a particular embodiment, the electromagnet comprises a coil wound on a bar interposed between the frame and the auxiliary plate, in contact with the stator. Brief Description of the Figures [0021] Other objects and advantages of the invention will appear in the light of the description of an embodiment, given below with reference to the appended drawings in which: fig. 1 is a perspective view showing an assembled skeleton watch; fig. 2 is an exploded perspective view showing the skeleton watch of FIG. 1; fig. 3 is an exploded perspective view illustrating the mounting of the time display means and the reduction mechanism; fig. 4 is an exploded view from above illustrating the assembly of the movement; fig. 5 is an exploded view from below illustrating the assembly of the movement; fig. 6 and an exploded view illustrating the assembly of the auxiliary plate and the electronic circuit; fig. 7 is a perspective view, in partial section (along the plane VII-VII of FIG. 4), showing the assembled movement. Detailed description of the invention [0022] In FIG. 1 and in fig. 2 shows a watch 1 skeleton, so called because part of its internal organs are visible. This watch 1 has a middle part 2, which can in particular be made of metal (for example steel), or in a synthetic material (for example in a composite material comprising a polymer matrix loaded with fibers, typically carbon). Watch 1 also includes, for wearing on the wrist, a bracelet 3 which is fixed on the middle part 2 between horns 4 formed projecting therefrom. In the example illustrated, the middle part 2 has a rectangular outline, but this shape is not limiting. In particular, this outline could be rounded (for example circular or oval). CH 714 013 A2 The middle part 2 has an opposite front face 5 and rear posterior face 6, and defines, between them, an interior space 7. Watch 1 also includes a lens 8 and a bottom 9, fixed to the middle part 2 on either side thereof (the lens 8 on the side of the front face 5; the bottom 9 on the side of the rear face 6) to close the interior space 7. The ice 8 can be made of mineral or synthetic glass (for example in ruby); the bottom 9 is advantageously metallic. As illustrated in fig. 2, the base 9 can be fixed to the rear face 6 of the middle part 2 by means of screws 10. As seen in Figs. 1 and fig. 2, the watch 1 further comprises a bezel 11, affixed to the front face 5 to ensure the fixing of the crystal 8 to the middle part 2, while ensuring a finish pleasing to the eye. Watch 1 finally includes a watch movement 12, hereinafter simply referred to as "movement". As we will explain, this movement 12, when assembled, forms a unitary component independent of the middle part 2 and the back 9. This movement 12 comprises, firstly, an openwork frame 13 whose function is to support certain movable members, as we will see below. This frame 13 is advantageously made of a material which does not conduct electricity, in particular in a synthetic material (for example made of polymer, or in a composite material comprising a polymer matrix loaded with fibers, typically carbon). If the frame 13 is made of polymer (for example polyoxymethylene, POM, or polytetrafluoroethylene, PTFE), or a short fiber composite, it can be manufactured by plastic injection. The frame 13 has a front face 14 and a rear face 15 opposite. The external contour of the frame 13 corresponds substantially to the internal contour of the middle part 2, in which it is intended to be fitted. Thus, according to an embodiment illustrated in the drawings, and in particular in FIGS. 2 to fig. 5, the frame 13 has a rectangular outline, but this shape is not limiting, and the outline could be rounded (for example circular or oval depending on the outline of the middle part 2). As illustrated in FIGS. 3 and fig. 4, the frame 13 includes: - Two lateral uprights 16 which extend parallel to each other and each have an upper end 17 and a lower end 18; - A high cross 19 which connects the uprights 16 between their upper ends 17; - a central island 20, which connects to the lateral uprights 16, at their upper ends 17 (that is to say at their junction with the top cross member 19), by a pair of upper branches 21 diagonally; - A lower platform 22, which is connected to the central island 20 by a bridge 23, and at the lower ends 18 of the lateral uprights 16 by a pair of lower branches 24 diagonally. The upper cross member 19, the upper branches 21 and the central island 20 define between them a large upper opening 25. The lateral uprights 16, the central island 20, the bridge 23, the lower platform 22 and the lower branches 24 define between them large lateral openings 26. Together, the upper branches 21, the central island 20, the bridge 23, the platform 22 and the lower branches 24 thus form a cross-supporting structure which, with the openings 25.26, gives the watch 1 sound skeletal appearance. The movement 12 comprises, secondly, time display means 27 mounted on the frame 13 and whose function is to indicate the hour and the minutes. More specifically, these time display means 27 are mounted, on the side of the front face 14 of the frame 13, on a central pin 28 integral with the latter. According to an embodiment illustrated in particular in FIG. 3, the pin 28 is force fitted into a bore 29 made in the central island 20, substantially at the geometric center of the frame 13. As seen in FIG. 3, the pin 28 is stepped; it extends projecting from the front face 14 of the frame 13 and comprises a first stage 30; a second stage 31, of diameter less than the first stage 30, a third stage 32, of diameter less than the second stage 31, and ends, at a front end, by a threaded stud 33. The time display means 27 include a minute hand 34 and a hour hand 35, driven by respective synchronous rotational movements in a reduction ratio of 1 / 12th, that is to say that the hour hand 35 completes a twelfth of a revolution when the minute hand 34 completes one complete revolution. As illustrated in FIG. 3, the time display means 27 includes a minute wheel 36, integral with the minute hand 34. This minute wheel 36 is of large diameter; it includes for example 120 teeth. The attachment of the minute wheel 36 to the minute hand 34 is for example achieved by means of a rivet 37, force-fitted into bores 38, 39 formed respectively in the minute hand 34 and the 36 minute wheel, as illustrated by the exploded view on the right in fig. 3. The minute hand 34 includes an indexing arrow 40, intended to indicate the number of minutes elapsed in an hour, and a plate 41 which extends diametrically opposite the arrow 40 of indexing. CH 714 013 A2 The sub-assembly comprising the minute hand 34, the minute wheel 36 and the rivet 37, is mounted in free rotation on the first stage 30 of the spindle 28. The time display means 27 also include a sun wheel 42 secured to the spindle 28. This sun wheel 42 is mounted over the minute hand 34 by being fixed by hunting on the second stage 31 of the pin 28 so as to be in recessed connection with the frame 13. The time display means 27 also includes a hour wheel 43, secured to the hour hand 35. The mutual fixing of the hour wheel 43 and the hour hand 35 is advantageously carried out by driving. More precisely, this fixing can be carried out by oriented hunting, the hour wheel 43 carrying a sleeve 44 force fitted into a bore 45 formed in the hour hand. The sub-assembly comprising the hour hand 35 and the hour wheel 43 is mounted in free rotation on the third stage 32 of the spindle 28, above the sun wheel 42. To limit friction, a curved washer 46 is preferably interposed between the hour wheel 43 and the sun wheel 42. To maintain this sub-assembly on the spindle 28, a nut 47 is fixed to the stud 33 over the hour hand 35. The time display means 27 include, finally, a planetary gear 48 rotatably mounted on the plate 41 of the minute hand 34. This epicyclic train 48 comprises a lower planetary wheel 49, in gear engagement with the sun wheel 42, and an upper planetary wheel 50, integral with the lower planetary wheel 49 and in gear with the hour wheel 43. According to an embodiment illustrated in the exploded view at the top right of FIG. 3, the fixing of the upper planetary wheel 50 to the lower planetary wheel 49 can be carried out by riveting. More specifically, the upper planetary wheel 50 is fitted onto a rivet 51 integral with the lower planetary wheel 49, after which a crown of this rivet 51 is deformed to ensure the fixing of the upper planetary wheel 50 on the lower planetary wheel 49. As illustrated in the center of FIG. 3, the planetary gear 48 is fixed in free rotation on the plate 41 of the minute hand 34, by means of a pin 52 which, passing with play through a bore 53 formed in the rivet 51, comes s fit without play in a hole 54 made in the plate 41. The movement 12 comprises, thirdly, a reduction mechanism 55 in gear engagement with the time display means 27. This reduction mechanism 55 will be detailed below. In Watch 1, the energy source which rotates the needles 34, 35 is electric. To ensure the transformation of electrical energy into mechanical energy, and the transmission of mechanical energy to the time display means 27, the movement 12 comprises: - fourthly, a stepping motor 56 comprising: - an electromagnet 57; - a stator 58 in electrical contact with the electromagnet 57; - A rotor 59 carrying a pinion 60 in gear engagement with the reduction mechanism 55; - fifthly, an electronic circuit 61 comprising: a piezoelectric quartz 62; - a computer 63 connected to the quartz 62 and the electromagnet 57 by means of electrical conductors 64. Unlike most quartz watches, which include an electronic circuit wholly or partly formed on the bottom, the electronic circuit 61 is here dissociated from the bottom 9. To this end, the movement 12 includes an auxiliary plate 65 which carries the electronic circuit 61. This auxiliary plate 65 is distinct from the bottom 9; it is fixed to the frame 13 on the side of its rear face 15, as illustrated in particular in FIG. 5. As seen in Figs. 4 and fig. 5, the auxiliary plate 65 has a shape similar to that of the frame 13. However, the plate 65 has a thickness less than that of the frame 13. Thus, like the frame 13, the auxiliary plate 65 comprises: - two lateral uprights 66; - A high cross 67 which connects the side uprights 66; - a central island 68, which is connected to the lateral uprights 66 by a pair of upper branches 69 diagonally; - a lower platform 70, which is connected to the central island 68 by a bridge 71 and to the lateral uprights 66 by a pair of lower branches 72 diagonally. CH 714 013 A2 [0058] In this way, when the auxiliary plate 65 and the frame 13 are superimposed (fig. 2, fig. 7), they extend in continuity with one another. The auxiliary plate 65 can be made of a metallic material (for example steel). In this case, it can be produced by cutting (typically with a laser or a water jet) a thin sheet metal element. The advantage of a metallic material is the structural rigidity which it gives to movement 12, for the benefit of the precision of the operation of the time display means 27. According to a particular embodiment illustrated in the drawings, and in particular in FIG. 6, the electronic circuit 61 is not directly formed on the auxiliary plate 65: the movement 12 includes for this purpose a plate 73 on which the electronic circuit 61 is integrated. The plate 73 is advantageously made of an insulating material, for example in a polymer or in a composite material comprising a polymer matrix loaded with fibers (typically carbon). As seen in FIG. 6, the plate 73 has a substantially complementary contour of a central part of the frame 13 and the auxiliary plate 65. More specifically, in the example illustrated, the contour of the plate 73 is complementary to the islands 20, 68, the bridges 23, 71, the lower platforms 22, 70 and the lower branches 24, 72. The electronic circuit 61 includes various components integrated on the plate 73, including quartz 62 (including the invisible oscillating element, is housed in a housing) and the computer 63. Electrical conductors 64, directly metallized on the plate 73, connect the various components to ensure the transmission of energy or information. Areas 74, 75 are also directly metallized on the plate 73, namely, in particular: a pair of pads 74 for capturing the electric current, disposed on ears 76 projecting from the plate 73, and - A pair of ranges 75 for transmitting an electrical signal (from the computer 63) to the electromagnet. The plate 73 is mounted on the auxiliary plate 65 by being interposed between the latter and the frame 13. To allow the mounting of the plate 73 (with the electrical circuit 61) without forming any additional thickness on the frame 13, the latter is thinned at the level of the central island 20, of the bridge 23, of the platform 22 and lower branches 24 (cf. fig. 5). To ensure precise positioning of the plate 73 relative to the frame 13, the plate 73 is provided with holes 77 which are threaded on pins 78 formed projecting from the ends of the lower branches 24 of the frame 13. According to a particular embodiment, the movement 12 comprises a wedge 79 interposed between the plate 73 and the auxiliary plate 65. This wedge 79, which has a contour similar to that of the plate 73, is made of an electrically insulating material; its function is to electrically isolate the plate 73 from the auxiliary plate 65, to avoid any short circuit in the electronic circuit 61. The positioning of the wedge 79 relative to the frame 13 is also carried out using holes 80 formed in the plate 73, which are threaded on the pins 78. The computer 63 receives quartz 62 pulses at a predetermined fixed frequency, which clock an alternating electrical signal sent to the electromagnet 57. According to an embodiment illustrated in particular in FIG. 4, the electromagnet 57 comprises a coil 81 wound on a metal bar 82 interposed between the frame 13 and the auxiliary plate 65, in (electrical) contact with the stator 58. As can also be seen in FIG. 4, the bar 82 is pierced with positioning holes 83 which are threaded onto the pins 78. The electromagnet 57 gives the stator 58 a magnetization, the polarity of which reverses over a period defined by the alternating electrical signal from the computer 63 and passing through the coil 81. In the example illustrated, the stator 58 is in the form of an insert, interposed between the frame 13 and the auxiliary plate 65, and more precisely between the frame 13 and the bar 82 of the electromagnet 57. The stator 58 comprises two arms 84 in V which are connected at a top 85. At their ends opposite the top 85, the arms 84 are provided with positioning holes 86 which are threaded on the pins 78. The stator 58 is provided, at its top 85, with a central bore 87 in which the rotor 59 is housed. The rotor 59 is provided with a magnetized counterweight 88 which, driven by the polarity changes of the stator 58, drives the rotor 59 with sequential rotational movements at a predetermined angle. The rotor 59 is provided with an axis 89; it is mounted in free rotation between the frame 13 and the auxiliary plate 65 - and more precisely between the frame 13 and the plate 73, which comprise respective coaxial holes 90, 91 for guiding this axis 89. According to an embodiment illustrated in particular in FIGS. 4 and fig. 5, the reduction mechanism 55 is also mounted between the frame 13 and the auxiliary plate 65. CH 714 013 A2 As seen in FIG. 3, the reducing mechanism 55 comprises an intermediate wheel 92, in gear engagement with the pinion 60 of the rotor, and a medium wheel 93, in gear engagement with the intermediate wheel 92 and with the minute wheel 36. The intermediate wheel 92 and the middle wheel 93 each comprise a respective axis 94, 95 guided by holes 96, 97 made in the frame and by corresponding holes 98, 99 made in the plate 73. Watch 1 comprises, in sixth place, a battery case 100 provided with a barrel 101 housed in the upper opening 25 of the frame 13, and legs 102 which project radially from the barrel 101 and are interposed between the frame 13 and the auxiliary plate 65. More specifically, the legs 102 are provided with bores 103 which come to fit on pins 104 protruding from the frame 13, on the side of its rear face 15. In the example illustrated in fig. 5, where the legs 103 (like the pins 104) are four in number, two pins 104 are located substantially in the middle of the upper branches 21; a third counter 104 is located on the central island 20; a fourth pin 104 is located in the middle of the top rail 19. At least some of the pins 104 (in this case the pins 104 formed on the upper arms 21 and the pin 104 formed on the top cross member 19) are advantageously formed in notches 105 made in the rear face of the frame 13, substantially complementary to the legs 103 and in which they come to fit. The housing 100 is configured to accommodate a button-type battery 106, typically a lithium battery, which comprises an anode 107 (positive pole) forming the periphery of the battery 106, and a cathode 108 (negative pole) forming a face of it. To capture the current from the battery 106 and electrically supply the electronic circuit 61, the watch 1 comprises a pair of contactors partially housed in the housing 100, namely: - An anode contactor 109, comprising a blade 110 which comes laterally into contact with the anode 107 and an external tab 111 pierced with a hole 112 and applied against a range 74 of capture of electronic circuit 61; - A cathode contactor 113, which comprises a disc 114 in contact with the cathode 108, and an external tab 115 pierced with a hole 116 and applied against the other range 74 of capture of the electrical circuit 61. According to an embodiment illustrated in particular in FIG. 4, the housing is provided with a cutout 117 which gives a glimpse of the disc 114 of the cathode contactor 113. In this way, it is possible to engrave it to write therein indications relating, for example, to the brand under which watch 1 is marketed. To assemble watch 1, the procedure is as follows. We start by assembling and mounting on the frame 13 the time display means 27, as illustrated in FIG. 3. To this end, the spindle 28 is mounted on the frame 13, by forcing it into its central bore 29, on the side of its rear face 15. The sub-assembly comprising the minute hand 34 and the minute wheel 36 is formed, which is fixed together by means of the rivet 37 and which is mounted in free rotation on the first stage 30 of the pin 28. Then, by driving, the sun wheel 42 is mounted on the second stage 31 of the spindle 28. The epicyclic train 48 is formed, by riveting the upper planetary wheel 50 on the lower planetary wheel 49. Then the planetary gear 48 is mounted on the minute hand 34 by means of the pin 52 which comes to be fitted (in free rotation) in the bore 53 of the rivet 51 and (in force) in the hole 54 made in the plate 41, making sure to mesh the lower planetary wheel 49 with the sun wheel 42. Then forming the sub-assembly comprising the hour wheel 43 and the hour hand 35, by oriented hunting thereof on the sleeve 44. Then we mount this sub-assembly in free rotation on the third stage 32 of spindle 28, by interposing the washer 49 curved between the hour wheel 43 and the sun wheel 42. Then the nut 47 is screwed onto the stud 33 to hold the sub-assembly comprising the hour wheel 43 and the hour hand 35 on the sleeve 44. The time display means 27 are thus secured to frame 13. It is then necessary to return the frame 13 to orient the rear face 15 upwards in anticipation of mounting the battery housing 100, the motor 56, the reduction mechanism 55 and the electronic circuit 61. The stator 58 is first mounted, by affixing it to the lower platform 22 by threading the positioning holes 86 on the pins 78. Then the rotor 59 is mounted, by threading its axis 89 in the hole 90, the counterweight 88 being housed in the bore 87 of the stator 58. The wheel 93 is then mounted by inserting its axis 95 in the hole 97, then the intermediate wheel 92 by threading its axle 94 in the hole 96. The electromagnet 57 is mounted by threading the holes 83 for positioning the bar 82 on the pins 78. It is then necessary to mount the battery housing 100 on the frame 13. To this end, the legs 102 are fitted into the notches 105; the bores 103 are threaded onto the pins 104. The cathode contactor 113 is then reported in CH 714 013 A2 placing the disc 114 at the bottom of the battery case 100, and threading the hole 116 on a pin 104 of one of the upper branches 21. Then the anode contactor 109 is brought in by introducing the blade 110 into the battery case 100 and threading the hole 112 on a pin 104 of the other upper branch 21. The battery 106 can then be introduced into the housing 100, and the latter can be closed by means of a cover (not shown). As a variant, the battery 106 is intended to be held in the housing 100 by the bottom 9. The plate 73 carrying the electronic circuit 61, the shim 79 and the auxiliary plate 65 are then attached and mounted (in this order) on the frame 13. In doing so: - The holes 77 in the plate 73 are threaded on the pins 78 of the frame 13; - The holes 80 in the wedge 79 are also threaded on the pins 78 of the frame 13; - the axis 89 of the rotor is threaded into the hole 91 of the plate 73; - the axle 94 of the intermediate wheel 92 is threaded into the hole 98 of the plate 73; - the axle 95 of the medium wheel 93 is threaded into the hole 99 of the plate 73. The auxiliary plate 65 is then added to be fixed to the frame 13 by covering the plate 73 and the wedge 79. The plate 65 is fixed directly to the frame 13, by means of screws 118 which, passing through holes 119 formed in the plate 65, are caught in bores 120 formed in the pins 78, 104. The assembly of the movement 12 is thus completed, as illustrated (in partial section) in FIG. 7, and in fig. 2. The movement 12 is functional (assuming that the electronic circuit 61 is powered by a battery 106). We see that, both structurally and functionally, the movement 12 is independent of the middle part 2 and the back 9 (we do not take into account, here, a possible time-setting mechanism). The movement 12 can then be mounted in the middle part 2. To this end, the movement 12 is fitted into the interior space 7. To ensure proper positioning of the movement 12, the middle part 2 is advantageously provided, on its inner periphery, with a flange 121 on which the movement 12 is applied (and more specifically the auxiliary plate 65). The movement 12 is fixed to the middle part 2 by means of screws 122 which, through bores 123 formed in bulges 124 protruding from the flange 121, become caught in the auxiliary plate 64, or directly in frame 13. The bottom 9 is fixed to the rear face 6 by means of the screws 10; the glass 8 is attached to the front face 5 and subjected thereto by means of the bezel 11, which is fixed to the middle part 2 by force fitting or by means of screws (not shown). As already mentioned, in operation, the computer 63 generates, on pulses received from the piezoelectric quartz 62, an alternating electrical signal sent to the electromagnet 57, whose stator 58 drives the rotor 59 with sequential rotational movements. The rotation of the rotor 59 is transmitted with reduction, via the pinion 60, the intermediate wheel 92 and the average wheel 93, to the minute wheel 36. The computer 63 is programmed, and the pinion 60 and the wheels 36, 92, 93 dimensioned, so that the minute wheel 36 (and the minute hand 34 with) performs one complete rotation in one hour. The sun wheel 42, the planetary gear 48 and the hour wheel 43 are dimensioned so that the reduction ratio, noted r, between the sun wheel 42 and the hour wheel 43 is 1 / 12th. By noting: N1 the number of teeth of the sun wheel 42, N2 the number of teeth of the lower planetary wheel 49, N3 the number of teeth of the upper planetary wheel 50, N4 the number of teeth on the hour wheel 43, the reduction ratio r is written: NI N3 N2N4 To obtain a reduction ratio r of 1 / 12th, we can thus choose as below the numbers N1, N2, N3 and N4: CH 714 013 A2 / VI = 33 N2 = 36 N3 = 46 ZV4 = 46 [0108] The structure of the movement 12, and in particular its subdivision into a frame 13 (carrying the time display means 27) and an auxiliary plate 65 (carrying the electronic circuit 61) fixed to the frame 13 , allows the movement 12 to be separated from the middle part 2, which has the following advantages: - during any interventions on watch 1, requiring access to movement 12, the electronic circuit 61, sandwiched between the frame 13 and the auxiliary plate 65, is well protected from shocks and constraints; - The electronic circuit 61 is well thermally isolated from the bottom 9, and therefore protected from the stresses and thermal cycles to which it is subjected; - the removal of the back 9, during an intervention on watch 1, does not affect the running of the movement 12, since the electronic circuit 61, the motor 56 and the time display means remain integral. claims 1. Skeleton watch comprising: a middle part (2) which defines an interior space (7); a crystal (8) and a bottom (9) fixed on the middle part (2) on either side of the latter to close the interior space (7); - a movement (12) which comprises: an openwork frame (13) having a front face (14) and a rear face (15); - time display means (27) mounted, on the side of the front face (14) of the frame (13), on a central spindle (28) integral with the latter, these display means of the hour (27) comprising in particular a minute hand (34) and an hour hand (35); - a reduction mechanism (55) in gear engagement with the time display means (27); - an engine (56) comprising: • an electromagnet (57); • a stator (58); • a rotor (59) carrying a pinion (60) in gear engagement with the reduction mechanism (55); - an electronic circuit (61) comprising: • a piezoelectric quartz (62); • a computer (63) connected to the quartz (62) and the stator (58) by means of electrical conductors (64); characterized in that the movement (12) comprises an auxiliary plate (65) which carries the electronic circuit (61), this auxiliary plate (65) being distinct from the bottom (9) and fixed to the frame (13) on the side of its rear face (15). 2. Watch (1) according to claim 1, characterized in that the movement (12) comprises a plate (73) on which the electronic circuit (61) is integrated, this plate (73) being mounted on the plate (65) auxiliary by being interposed between it and the frame (13). 3. Watch (1) according to claim 2, characterized in that the movement (12) comprises a shim (79) interposed between the plate (73) and the plate (65) auxiliary. 4. Watch (1) according to one of the preceding claims, characterized in that the reduction mechanism (55) is mounted between the frame (13) and the auxiliary plate (65). CH 714 013 A2 5. Watch (1) according to claim 4, characterized in that the reduction mechanism (55) comprises a wheel (92) intermediate, in gear engagement with the pinion (60) of the rotor (59), and a wheel ( 93) medium, in gear engagement with the intermediate wheel (92) and the minute wheel (36). 6. Watch (1) according to one of the preceding claims, characterized in that it comprises a battery case (100) provided with a barrel (101) housed in an aperture (25) formed in the frame (13) , and legs (102) which project radially from the barrel (101) and are interposed between the frame (13) and the auxiliary plate (65). 7. Watch (1) according to claim claim 6, characterized in that it comprises a pair of contactors (109, 113) partially housed in the battery case (100), each contactor (109, 113) having a tab (111, 115) applied externally against a range (74) for capturing the current of the electrical circuit (61). 8. Watch (1) according to one of the preceding claims, characterized in that the time display means (27) comprise: - a minute wheel (36), integral with the minute hand (34); a sun wheel (41) secured to the spindle (28); an hour wheel (43), integral with the hour hand (35); - a planetary gear train (48) rotatably mounted on the minute hand (34), and which comprises a lower planetary wheel (49) in gear engagement with the sun wheel (41), and a planetary wheel (50) upper, integral with the lower planetary wheel (49) and in gear engagement with the hour wheel (43). 9. Watch (1) according to one of the preceding claims, characterized in that the stator (58) is in the form of an insert inserted between the frame (13) and the auxiliary plate (65). 10. Watch (1) according to claim 9, characterized in that the electromagnet (57) comprises a coil (81) wound on a bar (82) interposed between the frame (13) and the plate (65) auxiliary , in contact with the stator (58). 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