Abstract:
A slip mechanism in the gear train of a clock comprises a gear wheel and an associated pinion coaxial with the gear. The gear wheel and pinion have interengaging surfaces for centering and rotatively guiding them relative to one another. A circle of resilient fingers on one of the gear wheel and pinions resiliently, frictionally and radially engage an annular friction surface of the other to provide a frictional coupling between them. Moreover hooks on the fingers retain the gear wheel and pinion in assembled relation to one another. In one embodiment the resilient fingers are integral with the pinion and are received in a concentric opening in the gear wheel of lesser diameter than a circle defined by the fingers in relaxed conditions. In another embodiment the resilient fingers are integral with the gear wheel and engage the outside of a concentric flange on the pinion of larger diameter than a circle defined by the fingers in relaxed condition. The pinion and gear can readily be formed of plastic material thus providing an inexpensive slip mechanism which can be easily assembled.

Description:
FIELD OF INVENTION 
     The present invention relates to a slip mechanism for a clock so as to provide a frictional coupling between two members of a gear train of the clock. 
     BACKGROUND OF THE INVENTION 
     In the prior art a slip mechanism gear is usual placed on a pinion and is coupled thereto by being urged strongly toward the pinion by a spring with a cork facing between the gear and the pinion so as to provide a frictional coupling between them. This method however has a disadvantage from the point of view of economy since it is necessary to provide a cork friction surface between the gear and the pinion. 
     As another prior art method it is known to form a metal gear and to integrate the metal gear with the pinion by molding with a plastic material. In this method however the slip torque is obtained by a holding force produced between the metal and plastic at the time of molding. Therefore the slip torque is subject to great variations with slight changes of the plastic. 
     In prior art slip mechanisms in which one or both of the pinion and gear are made of metal it has been necessary to resort to mechanical coupling means and also lubrication is required for the purpose of stabilizing the slip torque. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to eliminate the drawbacks and disadvantages of the prior art by providing a slip mechanism which is inexpensive and permits coupling with a simple operation. Moreover according to the invention both the pinion and the gear can readily be formed of plastic material thus providing an inexpensive slip mechanism which can be easily assembled and which eliminates the need of oiling by means of a combination of suitable plastic materials or by using a material containing a lubricant. 
     In accordance with the invention the slip mechanism of a clock comprises a gear and a pinion forming part of the gear train of the clock. The gear and pinion have interengaging circular guide portions for centering and rotatively guiding the gear and pinion relative to one another. One of the gear and pinion has an annular friction surface concentric thereto while the other of said gear and pinion has integral resilient fingers which resiliently, frictionally and radially engage the annular friction surface to provide a frictioning coupling between the gear and the pinion. Moreover hook portions on the resilient fingers retain the gear and pinion axially in assembled condition. 
     In one embodiment of the invention the resilient fingers are integral with the pinion and are received in a concentric opening in the gear of a lesser diameter than a circle defined by the resilient fingers in relaxed condition. In another embodiment the resilient fingers are integral with the gear and engage the outside of a concentric flange of the pinion having an outside diameter greater than the diameter of a circle defined by the fingers in relaxed condition. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The nature, objects and advantages of the invention will be more fully understood from the following description of preferred embodiments disclosed by way of example in the accompanying drawings in which: 
     FIG. 1 is a sectional view showing one embodiment of a slip mechanism in accordance with the invention; 
     FIG. 2 is a perspective view showing a part of the slip mechanism of FIG. 1, the same part also being in the embodiment of FIG. 5; 
     FIG. 3 is a sectional view of another part of the slip mechanism of FIG. 1, the same part being in the embodiment of FIG. 5; 
     FIG. 4 is a partial sectional view showing a second embodiment of the invention; 
     FIG. 5 being a sectional view of a third embodiment and 
     FIG. 6 being a partial sectional view of a fourth embodiment of the invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring first to the embodiment of the invention shown in FIGS. 1-3, an upper plate 1, an intermediate plate 2 and a lower plate 3 for rotatably supporting a gear train are secured to one another, for example by posts 4 and 5 and screws 6 and 7. A second hand shaft 8 is rotatably supported by the upper and intermediate plates 1 and 2 and a second hand wheel 9 and an integral first pinion 10 are secured to the second hand shaft 8. The second hand wheel 9 is driven by a pinion 9a of a motor M. A shaft 11 which is parallel to and spaced from the second hand shaft 8 is rotatably supported by the upper plate 1 and intermediate plate 2. The shaft 11 is provided at its lower end with an integral second pinion 11a in mesh with a minute hand gear wheel 15 as will be described below. The shaft 11 further rotatably and frictionally supports a first intermediate gear 12 in mesh with the pinion 10 of the second hand wheel 9. 
     The structure for frictionally coupling the first intermediate gear 12 with the pinion 11a to provide a slip mechanism for the gear train of the clock will now be described with reference to FIGS. 1, 2 and 3. Immediately above the second pinion 11a the shaft 11 is formed with a rotary bearing section 11b which is rotatably supported in a hole provided in the intermediate plate 2. A shoulder on the shaft 11 engages the upper side of the intermediate plate 2 to support the shaft in an axial direction. The upper tip of the shaft 11 is provided with a second rotary bearing section 11c which is rotatably supported in a hole provided in the upper plate 1. Adjacent the rotary bearing section 11c the shaft 11 is formed with a second shoulder engagable with the underside of the upper plate 1 so as to retain and position the shaft in an axial direction. 
     An intermediate portion of the shaft 11 is formed with a rotary guide flange 11d from the upper face of which three integral upright and flexible fingers 11f project. An outwardly projecting hook 11e is formed at the tip of each of the flexible fingers 11f. 
     With reference to FIG. 3the outer periphery of the intermediate gear 12 is provided with gear teeth 12a which mesh with the first pinion 10. A central portion of the intermediate gear 12 is formed with an annular flange providing a guide section 12b rotatably supported by engagement with the flange 11d of the shaft 11 so as to center and rotatively guide the first intermediate gear 12 with respect to the pinion 11a of the shaft 11. The intermediate gear 12 is further provided with an upwardly projecting collar portion which provides an annular frictional surface 12c adapted to be frictionally engaged by the integral resilient fingers 11f of the shaft 11. 
     By fitting the first intermediate gear 12 on the shaft 11 from the top thereof the first guide section 12b is engaged with and rotatably supported by the flange 11d of the shaft 11 so as to center the gear relative to the shaft and also to position it axially. Meanwhile the flexible fingers 11f are slightly flexed inwardly and are held in elastic contact with the frictional surface 12c by the resilience of the fingers. In other words, the inner diameter of the frictional surface 12c is made slightly smaller than the outer diameter of the circle defined by the integral flexible fingers 11f. At the same time the hooks 11e on the tips of the flexible fingers engage the end of the collar of the intermediate gear 12 providing the frictional surface 12c so that the gear can no longer be withdrawn from the shaft 11. Thus the hooks 11e together with the flange 11d of the shaft 11 position the first intermediate gear 12 in an axial direction relative to the shaft 11 and retain the gear 12 and the shaft 11 with its pinion 11a in assembled condition. 
     Continuing with a description of the gear train shown in FIG. 1, the minute hand gear wheel 15 is fixed on or integral with a hollow shaft 17 on the end of which there is fixed a minute hand 16. The minute hand gear wheel 15 has a pinion 14 which meshes with a second intermediate gear wheel 18 secured to a shaft 19 which is parallel to and spaced from the second hand shaft 8 and is rotatably supported by the intermediate plate 2 and lower plate 3. The second intermediate gear wheel 19 has a pinion 20 which meshes with an hour hand gear wheel 21 which is integral with or secured to an hour hand pipe 22 rotatably supported by the lower plate 3 and by the minute hand shaft 17. An hour hand 22a is provided on the lower end of the hour hand pipe 22 and a second hand 8a is fixed on the lower end of the second hand shaft 8. 
     A time correction gear wheel 23 in mesh with the second intermediate gear wheel 18 is fixed on a shaft 23a rotatably supported by the intermediate plate 2 and lower plate 3 and rotatable by a knob 23b provided at its upper end. 
     If the slip torque provided in the gear train by the frictional coupling between the pinion 11a and the first intermediate gear 12 is less than the static slip output of the motor M the first intermediate gear wheel 12 will slip with respect to the shaft 11 when a user rotates the time correction wheel 23 for correcting time so that only the pinion 11a, minute hand gear wheel 15 and subsequent gear wheels of the gear train are rotated in the setting operation. 
     A second embodiment shown in FIG. 4 will now be described. This embodiment is a modification of the slip mechanism of the embodiment shown in FIG. 1. The other parts of the gear train are similar to those of the first embodiment and hence will not be further described. 
     The slip mechanism of the embodiment illustrated in FIG. 4 comprises a shaft 111 which is formed at its lower end with an integral second pinion 111a. Immediately above the pinion shaft 111 is formed with a rotary bearing section 111b which is rotatably supported in a hole provided in the intermediate plate 2. The tip at the upper end of the shaft 111 is formed with a second rotary bearing section 111c which is rotatably supported by a hole provided in the upper plate 1. An intermediate portion of the shaft 111 is formed with a rotary guide section 111d and a downwardly extending cylindrical collar or flange 111e. 
     The slip mechanism further comprises a first intermediate gear wheel 112 provided at its periphery with gear teeth 112a in mesh with the second hand gear wheel pinion 10 (FIG. 1). At its center the first intermediate gear wheel 112 is formed with a guide hole 112b which is rotatably supported by the rotary guide section 111d of the shaft 111. At its intermediate portion the first intermediate gear wheel 112 is formed with a plurality of downwardly extending integral flexible fingers 112d which frictionally engage the flange 111e of the shaft 111. Moreover each of the fingers 112d is provided at its tip with an inwardly projecting hook 112c which engages the lower end of the flange 111e. 
     When the shaft 111 is inserted into the gear wheel 112 from below, the fingers 112d are flexed outwardly and embrace and frictionally engage the flange 111e of the shaft 111. Since the fingers 112 by their inherent resiliency are held in pressure contact with the outer surface of the flange 111e of the shaft 111 the gear 112 is frictionally coupled with the shaft 111 with a constant slip torque. The gear 112 is centered with respect to the shaft 111 by engagement of the central opening 112b of the gear with the rotary guide section 111d of the shaft 111. Moreover the gear 112 engages the upper face of the flange 111e while the hooks 112c on the fingers 112d hook over the lower end of the flange 111e so as to position the gear 112 and the shaft 111 axially with respect to one another and to hold them in assembled condition. 
     A third embodiment of the invention will now be described with reference to FIG. 5. This embodiment is a modification of the first embodiment with respect to the slip mechanism. The other parts of the gear train are similar to those of the first embodiment and will not be further described. 
     In the embodiment illustrated in FIG. 5, a leaf spring 224 is provided between the first intermediate gear 212 and a rotary guide flange 211d of the shaft 211. The spring 224 is an annular leaf spring having a doughnut-like plan view and a substantially U-shaped profile in section. 
     The annular spring 224 is first fitted over the three integral flexible fingers 211f and laid on the flange 221d of the shaft 211. Then the first intermediate gear wheel 212 is fitted on the shaft 211 from above whereby the flexible fingers 211f of the shaft 211 are flexed inwardly permitting the hole 212c of the intermediate gear wheel 212 to pass over the hooks 211e of the flexible fingers 211f and thereupon permitting the flexible fingers 211f to be restored by their resiliency toward their initial position, the hooks 211e snapping over the end of the flange providing the friction surface 211c. 
     A constant gap is formed between the top of the flange 211d of the shaft 211 and the lower surface of the gear 212 with the spring 224 clamped in this gap and exerting a force urging the gear 212 upwardly against the hooks 211e of the flexible fingers 211f. In this way the first intermediate gear 212 and shafts 211 are coupled by simple manual operation without any mechanical coupling operation and provide a constant slip torque between the gear 212 and the integral pinion 211a of the shaft 211. Moreover the gear 212 is centered with respect to the shaft 211 by a downwardly projecting flange 212b on the gear rotatively engaging the flange 211d of the shaft 211. 
     FIG. 6 shows a fourth embodiment of the invention in which the slip mechanism is similar to that shown in FIG. 4 except that an annular leaf spring 324 is provided between the pinion and the gear. The spring 324 has a doughnut-like shape in plan view and is substantially U-shaped in sectional profile. The spring is first laid on the flange 111e of the shaft 111 and the shaft 111 is inserted into the gear 112 from below whereby the integral flexible fingers 112d are flexed outwardly to embrace and frictionally engage the flange 111e of the shaft 111. In this way the gear 112 and the shaft 111 with its integral pinion 111a are frictionally coupled together. A constant gap is formed between the upper surface of the flange 111e of the shaft and the lower surface of the gear 112. The annular leaf spring 124 is received in this gap. Since the spring 124 is set to have a height slightly greater than that of the space when the spring is in relaxed condition, the spring 124 is flexed to a constant extent by its confinement in the space. Thus a constant pressure is provided between the gear 112 and the shaft 11 by the spring 124 thereby providing a constant slip torque between them. 
     While in the embodiments illustrated in the drawings and described, the slip mechanism is provided between the first intermediate gear and its associated pinion, similar effects can be obtained by providing the slip mechanism between other elements of the gear train, for example between the minute hand gear wheel and pinion. It will be recognized by those skilled in the art that other modifications may be made and that the invention is thus in no way limited to the embodiments shown by way of example in the drawings and herein described.