Coupler of winding key with power spring
BACKGROUND OF THE INVENTION 
     A power spring is frequently used as a drive source for a musical box or toys. A winding key which is used to charge the power spring is generally connected, as by threadable engagement, with a winding shaft to which one end of the power spring is secured. This allows the key to be disengaged by turning it in the opposite direction. When such a winding mechanism is used in a toy used by an infant, a risk is possible that the infant may carry the key into his mouth as it is disengaged from the spring shaft. If the key is not put into the mouth, the key itself has a number of protuberances, which make it dangerous that the key be disengaged. To prevent this, the present applicant has previously proposed a winding key clamp which prevents the winding key from being disengaged once it is threadably engaged with a winding shaft (see Japanese Utility Model Publication No. 11,516/1976). 
     However, with the disclosed winding key clamp, when the winding key is turned in the direction opposite from the winding direction, a rotating drive is transmitted to a driven member contained within a toy through the winding shaft, thereby applying undue stresses upon the toy and to damage it. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a coupler of a winding key with power spring or the like in which a winding key which is threadably engaged with a winding shaft may be turned in a winding direction to to transmit the rotating drive to the shaft and may be turned in the opposite direction to cause an idle rotation thereof without the transmission of the rotating drive to the shaft and in which the disengagement of the winding key from the shaft is prevented to avoid risks of harm to infants and damage of the driven members. 
     In accordance with the invention, the coupler comprises a threaded member formed on one of a winding key and a winding shaft associated with a power spring and a bottomed aperture formed in the other in which a coiled spring is locked against withdrawal. The threaded member is threadeably engaged with the coiled spring to couple the key with the winding shaft. When the key is turned in a direction to spread the coiled spring, a rotating drive is transmitted to the shaft while the key rotates idly when it is turned in direction to tighten the coiled spring. 
     With the coupler of the invention, once coupled with the winding shaft, the winding key may be turned in the opposite direction from the winding shaft without transmitting a rotating drive to the winding shaft, thus preventing a damage which may be caused to driven members of a toy. Since the key, once coupled with the shaft, cannot be disengaged therefrom, no risk is caused to the infants. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal section of one embodiment of the invention. 
     FIG. 2 is a fragmentary cross section of the coupler shown in FIG. 1, illustrating its operation. 
     FIG. 3 is a longitudinal section of another embodiment of the invention. 
     FIG. 4 is a longitudinal section of a further embodiment of the invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is shown a coupler according to one embodiment of the invention. A hollow winding key 2 carries a knob 1 on one end, and has an interior bore or aperture 3 opening at its other opened end 8. The bore 3 is stepped, having an increased diameter portion 7 toward its open end 8 and having a reduced diameter portion 7a adjacent the bottom of the bore. A projection 4 is formed on the bottom or inner end of the bore 3, and a coiled spring 5 is received within the bore 3. The coiled spring 5 has an outer diameter which is greater than the diameter of the reduced diameter portion 6 and is less than that of the greater diameter portion 7 of the bore 3. In this manner, the spring 5 is a slight press fit in the portion 6, and is loosely fitted in the portion 7. The open end 8 of the winding key 2 is caulked or beveled inwardly, thus preventing a withdrawal of the spring 5 therefrom. 
     A driven member such as a frame of a toy is shown at 9, and a winding shaft 10 is rotatably supported therein. Inside the frame 9, a power spring 11 has its one end secured to the winding shaft 10. An end of the winding shaft 10 which projects externally of the frame 9 has a reduced diameter, and is formed with a male thread 12 having the same twist direction as the spring 5. The male thread 12 has a diameter which is chosen such that when it is engaged with the spring 5, it radially spreads the latter, but that when spreaded, the spreading alone cannot cause the spring 5 to bear against the greater diameter portion of the aperture 3. 
     In use, the winding key 2 containing the spring 5 is threadably engaged with the male thread 12 of the winding shaft 10. Since one end of the spring 5 bears against the projection 4, the rotation of the winding key 2 causes an integral rotation of the spring 5, which permits the male thread 12 to be forced inwardly into the spring 5 while spreading the latter until the position shown in FIG. 1 is reached where the key 2 is coupled with the winding shaft 10. Under this condition, the spring 5 located within the greater diameter portion 7 of the aperture 3 is received in a recess between adjacent threads of the male thread 12 as shown by the solid line in FIG. 2, thus leaving a small clearance with respect to the inner surface of the greater diameter portion 7 of the aperture 3. When the key 2 is turned further in the forward direction from the position shown in FIG. 1, a force is produced which spreads the spring 5 further radially outward, and hence the spring 5 will be displaced into abutment against the inner surface of the portion 7, as indicated by the phantom line in FIG. 2. Consequently, the rotating drive of the winding key 2 is positively transmitted to the winding shaft 10 through a portion of the spring 5 interposed between the portion 7 and the male thread member 12 and another portion of the spring 5 which bears against the reduced diameter portion 6 of the bore, thus enabling the winding of the power spring 11. 
     When the key 2 is turned in the opposite direction, the spring 5 returns into firm engagement with the threaded member 12, forming a clearance between the spring and the portion 7 of the aperture 3. The rotating drive of the key 2 functions to tighten the spring 5, so that there occurs a slip between the portion 6 of the wall of the bore 3 and the spring. Hence, the rotating drive of the key 2 is not transmitted to the winding shaft 10. In addition, the key cannot be disengaged from the shaft 10. Because the spring 5 is locked against withdrawal by the bevel of the open end 8 of the key 2, the key cannot be withdrawn from the winding shaft if it is axially pulled, thus achieving an assured prevention of withdrawal of the key. 
     FIG. 3 shows another embodiment of the invention in which the relative positioning of the aperture 3 and the male thread member 12 is reversed from that shown in FIG. 1. Specifically, in FIG. 3, one end of the key 2 is formed with a male thread member 22 and the free end of the winding shaft 10 is formed with a stepped and bottomed bore or aperture 23 therein which includes a reduced diameter portion 26 and a greater diameter portion 27. A coiled spring 25 of a diameter which is greater than the diameter of the portion 26 and which is less than the diameter of the portion 27 is received within the aperture 23, and is locked against withdrawal by an annular washer 24 which is fitted into the open end of the aperture 23. In this manner, the spring 25 is a slight press fit in the portion 26, and is loosely fitted inside the portion 27. It should be understood that the thread on the key 2 has the same twist direction as the spring 25. The diameter of the male thread portion 22 is chosen such that it radially spreads the spring 25 when it is engaged with the spring 25, but that there is left a small clearance between the spreaded spring 25 and the inner surface of the portion 27 of the aperture 23. 
     In use, the male thread member 22 of the key 2 is engaged with the spring 25 received within the shaft 10. As the key is turned, the male thread member 22 moves into the spring 25 as guided by the latter while spreading the latter until the key 2 is coupled with the winding shaft 10 as shown in FIG. 3. As the key 2 is further turned in this direction, a force is produced which further spreads the spring 25 to increase the diameter of the entire spring 25 until the latter bears against the inner surface of the portion 27 of the aperture 23. Thereupon, the rotating drive of the key 2 is positively transmitted to the winding shaft 10 through a portion of the spring 25 located between the portion 27 and the thread member 22 and another portion thereof abutting against the reduced diameter portion 26 of the aperture, thus transmitting the drive to a driven member, not shown. 
     When the key 2 is turned in the opposite direction, the spring 25 returns into engagement with the thread member 22, forming a clearance between the spring and the portion 27 of the aperture. The rotation of the key 2 acts to tighten the spring 25, whereby a slip occurs between the spring 25 and the portion 26 of the aperture wall, preventing the transmission of the drive from the key 2 to the winding shaft 10. The withdrawal of the key 2 as it is guided by the helical spring 25 is avoided. Because the spring 25 is locked against withdrawal by the washer 24, the key 2 cannot be withdrawn when it is axially pulled. It is preferred that the washer 24 be formed of a hard material so that an abrasion thereof is prevented when an end of the spring 25 rubs against the washer 24. 
     FIG. 4 shows a further embodiment of the invention which represents a modification of the embodiment shown in FIG. 3. Specifically, the winding shaft 10 is formed with an aperture 33 including a reduced diameter portion 36 in which a female thread area 38 of a short length is formed. A coiled spring 35 is received within the aperture 33 and has a close pitch. The length of the spring 35 is less than the overall length of the aperture 35. In other respects, the arrangement is similar to that shown in FIG. 3. 
     In use, a male thread member 32 which is formed on the winding key 2 is threadably engaged with the winding shaft 10. As the key is turned, the thread member 32 radially spreads the spring 35 while moving into the aperture 33 until the key 2 is coupled with the winding shaft 10 as shown in FIG. 4. However, because the spring 35 is wound in a close pitch, the frictional resistance acting between the thread member 32 and the spring 35 increases rapidly as the thread member 32 is increadingly engaged with the spring 35, and the integral rotation of the spring 35 with the key 2 may cause an end portion thereof to be threadably engaged with the female thread area 38. As the key 2 is turned further in the forward direction, the rotating drive from the key 2 acts to spread the spring 35 after its end has engaged a corresponding end portion of the female thread area 38, whereby the spring 35 bears against the greater diameter portion 37 of the aperture 33. Consequently, the rotating drive from the key 2 is positively transmitted to the winding shaft 10 through a portion of the spring 35 located between the portion 37 and the thread member 32 and another portion of the spring bearing against the female thread area 38, transmitting the drive to a driven member, not shown. 
     When the key 2 is turned in the opposite direction, the spring 35 rotates integrally with the key 2 since it is firmly engaged with the thread member 32 until the inner end of the spring 35 is disengaged from the female thread portion 38 whereupon a further rotation of the key 2 in the opposite direction causes an idle rotation of the key 2 relative to the winding shaft 10 without imparting any rotating drive thereto. Because the spring 35 is locked against withdrawal by the washer 34, the key 2 cannot be removed from the winding shaft 10. 
     It should be understood that in the embodiment shown in FIG. 1, the caulked portion 8 may be replaced by the use of a washer as illustrated in the embodiment shown in FIGS. 3 and 4. Similarly, in the embodiment shown in FIGS. 1 and 3, an annular spring washer having offset, opposite end faces which are staggered in the manner of a step may be disposed on the bottom of the aperture 3, 23. This provides a reinforcement of the projection 4, improving the abrasion resistance of the bottom of the aperture. When male thread members 12, 22, 32 of a reduced diameter is used, it is not always necessary to have a stepped form for the apertures 3, 23, 33.