Window Shade Having a Resistance Balancing Mechanism

Abstract

A window shade comprises first and second rails, and a shading structure and a suspension cord connected between the first and second rails. The second rail includes a resistance balancing unit and a cord winding unit to which the suspension cord respectively connects. The resistance balancing unit comprises a housing having an abuttal surface, a pulley pivotally connected with the housing, and a torsion spring. The pulley has a winding portion around which the suspension cord is wrapped, and a shaft portion extending coaxial to the winding portion from a side thereof. The torsion spring is tightly mounted around the shaft portion and has at least one end. The pulley when rotating in one direction drives the end of the torsion spring to push against the abuttal surface of the housing, whereby the torsion spring loosens to allow rotation of the pulley relative to the torsion spring.

1 . A resistance balancing unit suitable for use with a window shade, comprising:
 a housing having an abuttal surface;   a pulley pivotally assembled with the housing, the pulley having a winding portion around which a suspension cord is wrapped, and a shaft portion extending coaxial from a side of the winding portion; and   a torsion spring tightly mounted around the shaft portion and having at least one end, wherein the pulley when rotating in one direction drives the end of the torsion spring to push against the abuttal surface of the housing, whereby the torsion spring loosens to allow the pulley to rotate relative to the torsion spring.   
     
     
         2 . The resistance balancing unit according to  claim 1 , wherein the housing has a first face and a second face, the suspension cord entering the housing from the first face, wrapping around the winding portion, and extending outside the housing from the second face. 
     
     
         3 . The resistance balancing unit according to  claim 2 , wherein the first face and the second face are substantially perpendicular to each other. 
     
     
         4 . The resistance balancing unit according to  claim 2 , wherein the first face and the second face are substantially parallel to each other. 
     
     
         5 . The resistance balancing unit according to  claim 2 , wherein the housing includes a blade assembled at the second face, the blade and an edge of the housing defining a slit for passage of the suspension cord. 
     
     
         6 . The resistance balancing unit according to  claim 5 , wherein the blade is movably assembled with the housing, and is operable to press against the suspension cord. 
     
     
         7 . The resistance balancing unit according to  claim 1 , wherein the suspension cord wraps around the pulley about one or more turn. 
     
     
         8 . A window shade comprising:
 a first rail;   a second rail;   a shading structure disposed between the first rail and the second rail; and   at least a suspension cord connected between the first and second rails;   wherein the second rail includes a resistance balancing unit and a cord winding unit, the suspension cord respectively connecting with the resistance balancing unit and the cord winding unit, the resistance balancing unit comprising:
 a housing having an abuttal surface; 
 a pulley pivotally connected with the housing, the pulley having a winding portion around which a suspension cord is wrapped, and a shaft portion extending coaxial from a side of the winding portion; and 
 a torsion spring tightly mounted around the shaft portion and having at least one end, wherein the pulley when rotating in one direction drives the end of the torsion spring to push against the abuttal surface of the housing, whereby the torsion spring loosens to allow the pulley to rotate relative to the torsion spring. 
   
     
     
         9 . The window shade according to  claim 8 , wherein the housing has a first face and a second face, the suspension cord enters the housing from the first face, wraps around the winding portion, and extends outside the housing via the second face. 
     
     
         10 . The window shade according to  claim 9 , wherein the first face and the second face are substantially perpendicular to each other. 
     
     
         11 . The window shade according to  claim 9 , wherein the first face and the second face are substantially parallel to each other. 
     
     
         12 . The window shade according to  claim 9 , wherein the housing includes a blade assembled at the second face, the blade and an edge of the housing defining a slit for passage of the suspension cord. 
     
     
         13 . The window shade according to  claim 12 , wherein the blade is movably assembled with the housing, and is operable to press against the suspension cord. 
     
     
         14 . The window shade according to  claim 8 , wherein the suspension cord wraps around the pulley about one or more turn. 
     
     
         15 . The window shade according to  claim 8 , wherein an adjustment that increases a distance between the first and second rails causes the suspension cord to unwind from the cord winding unit and drives the pulley in rotation, which results in the end of the torsion spring to push against the abuttal surface, whereby the torsion spring is loosened and the pulley is allowed to rotate relative to the torsion spring. 
     
     
         16 . The window shade according to  claim 8 , wherein an adjustment that reduces a distance between the first and second rails causes the suspension cord between the first and second rails to become loose, which results in the cord winding unit to wind the suspension cord under a spring force. 
     
     
         17 . The window shade according to  claim 8 , wherein the torsion spring recovers a tightened state on the pulley to stop the pulley when the first and second rails are stationary. 
     
     
         18 . The window shade according to  claim 8 , wherein the resistance balancing unit is spaced apart from the cord winding unit. 
     
     
         19 . The window shade according to  claim 8 , wherein the cord winding unit includes a casing, a winding drum, a coiled spring connected with the winding drum, and a guide roller movable along a shaft portion, the guide roller sliding along the shaft portion to facilitate uniform winding of the suspension cord on the winding drum during an adjustment that reduces a distance between the first and second rails.