Structure For adjusting inside Circumference of Helmet

Abstract

A structure for adjusting inside circumference of a helmet is implemented as a strap assembly coupled to a rear side of a safety helmet or bicycle helmet and includes a casing and a cover fitted therein. The cover is sequentially connected with a transmission gear, a resilient element, a positioning gear and a knob. By pressing the knob, the positioning gear is disengaged from toothed portions on an inner periphery of the cover, thereby allowing the knob to rotate an end of the transmission gear. Consequently, a first driving portion of the transmission gear drives two straps inserted in the casing to move toward or away from each other. The knob is released after a relative position of the straps is adjusted. The resilient element returns the positioning gear into engagement with the toothed portions on the inner periphery of the cover.

1 . A structure for adjusting an inside circumference of a helmet, implemented as a strap assembly coupled to a rear side of a safety helmet or a bicycle helmet and comprising a casing bilaterally provided with apertures which can be passed through by two straps, respectively, and be fitted in by two ends of a cover centrally formed with a hole, so that driving components and a knob for adjusting a relative position of the two straps can be assembled with the casing and the cover, the structure being characterized in:
 the cover fitted in the casing being centrally formed with a protruding section having the hole and an inner periphery bilaterally provided with toothed portions, so that a first driving portion formed on an inner side of a transmission gear can penetrate the hole of the cover while a tubular section centrally and protrudingly formed on the casing can penetrate a hole centrally formed on the transmission gear;   the transmission gear further having an outer side formed with a second driving portion which can be inserted into a resilient element and engaged with a positioning gear centrally formed with inner teeth, wherein the positioning gear has an outer periphery formed with teeth which can mesh with the toothed portions on the inner periphery of the protruding section of the cover; and   the knob having an inner side formed with inner teeth and being penetrable by a threaded fastener, wherein the knob is disposed adjacent to a side of the positioning gear, so that the threaded fastener passing through the knob can be securely connected with the tubular section of the casing that passes through the transmission gear;   wherein the knob can be pressed to drive the positioning gear out of engagement with the toothed portions on the inner periphery of the protruding section of the cover, allowing an end of the transmission gear to be rotated by the knob, so that the first driving portion formed on the inner side of the transmission gear drives the two straps inserted in the casing to move toward or away from each other in a predetermined manner, and wherein the knob can be released after the relative position of the two straps is adjusted, allowing the resilient element to push the positioning gear outward to its original position, in which the positioning gear once again meshes with and is retained by the toothed portions on the inner periphery of the protruding section of the cover.   
   
   
       2 . The structure for adjusting the inside circumference of the helmet as claimed in  claim 1 , wherein the toothed portions on the inner periphery of the protruding section of the cover have chamfered inner edges, which are facing inward of the strap assembly, while the teeth on the outer periphery of the positioning gear that mesh with the toothed portions on the inner periphery of the protruding section of the cover have chamfered outer edges, which are facing outward of the strap assembly, thereby allowing the positioning gear to be smoothly disengaged  15  from and reengaged with the toothed portions on the inner periphery of the protruding section of the cover. 
   
   
       3 . The structure for adjusting the inside circumference of the helmet as claimed in  claim 1 , wherein the second driving portion on the outer side of the transmission gear has an unchamfered outer edge, which is facing outward of the strap assembly, while the inner teeth on the inner side of the knob have unchamfered inner edges, which are facing inward of the strap assembly, so that the second driving portion of the transmission gear cannot easily enter in between the inner teeth of the knob, thereby securing a relative position of the transmission gear and the two straps.