Sunshade device with a buffer to smoothen retraction of a screen

Abstract

In a sunshade device, a roller is journalled in an elongated housing and has a screen wound therearound. The roller is biased to rotate in a screen-winding direction for winding the screen thereon. A drive gear is fixed to the roller. A threaded rod parallel to the roller is fixed in the housing, and has a follower gear sleeved threadedly thereon. The follower gear is formed with grooves arranged around the rod axis and meshing with the drive gear. Each groove has a groove bottom, and first and second groove ends formed respectively at first and second end portions of the follower gear. The groove bottom at the first groove end is displaced from the rod axis by a distance smaller than that of the groove bottom at the second groove end.

I claim:  
     
         1 . A sunshade device comprising: 
 an elongated housing formed with a slit;    a roller mounted rotatably in said housing and having a roller axis;    a screen wound around said roller and having a connecting end secured to said roller, and a distal end opposite to said connecting end and extending out of said housing via said slit;    a biasing unit for biasing said roller to rotate in a screen-winding direction for winding said screen thereon so as to move said screen to a retracted position, in which said distal end of said screen is disposed adjacent to said housing, said roller being further rotatable in a screen-unwinding direction opposite to the screen-winding direction against biasing action of said biasing unit for unwinding said screen therefrom so as to permit movement of said screen to a stretched position, in which said distal end of said screen is moved away from said housing;    a drive gear fixed to said roller, said drive gear having an outer surface formed with a plurality of drive teeth which are arranged around said roller axis;    a threaded rod mounted fixedly in said housing, disposed parallel to said roller, and having a rod axis; and    a follower gear sleeved threadedly on said threaded rod, said follower gear having first and second end portions opposite to each other along said rod axis, said follower gear further having an outer surface formed with a series of meshing grooves that are arranged around said rod axis and that mesh with said drive teeth on said drive gear, each of said meshing grooves extending from said first end portion to said second end portion of said follower gear, and having a groove bottom extending along length of a respective one of said meshing grooves, a first groove end formed at said first end portion of said follower gear, and a second groove end opposite to said first groove end and formed at said second end portion of said follower gear, said groove bottom at said first groove end of each of said meshing grooves being displaced from said rod axis by a first distance, said groove bottom at said second groove end of each of said meshing grooves being displaced from said rod axis by a second distance, said first distance being smaller than said second distance,    rotation of said roller in the screen-winding direction resulting in corresponding rotation of said follower gear to cause linear movement of said follower gear along said threaded rod in a first direction for moving said second end portion of said follower gear toward said drive gear, rotation of said roller in the screen-unwinding direction resulting in corresponding rotation of said follower gear to cause linear movement of said follower gear along said threaded rod in a second direction opposite to the first direction for moving said second end portion of said follower gear away from said drive gear, said drive teeth on said drive gear being in frictional contact with said groove bottoms of said meshing grooves at said second groove ends when said second end portion of said follower gear is moved to be disposed proximate to said drive gear, thereby generating a resistance force to retard rotation of said drive gear and said roller in the screen-winding direction.    
     
     
         2 . The sunshade device as claimed in  claim 1 , wherein said follower gear has a truncated-cone shape and has cross-sections which gradually diverge from said first end portion to said second end portion of said follower gear.  
     
     
         3 . The sunshade device as claimed in  claim 1 , further comprising a mounting axle extending co-axially into said roller and having one end extending out of said roller and fixed to said housing, said biasing unit including a coiled torsion spring received in said roller and sleeved on said mounting axle, said biasing unit having a first end engaging said mounting axle, and a second end opposite to said first end and connected to said roller so as to provide a biasing force for biasing said roller to rotate in the screen-winding direction.  
     
     
         4 . The sunshade device as claimed in  claim 1 , further comprising a hook member for engaging said distal end of said screen so as to retain said screen at the stretched position.