Patent ID: 8365802

Claim:
A drum driving device for a window shade comprising a housing fixed to a frame of the window shade, a cord pulley rotatably received in the housing and having a cord wound around the cord pulley, a drum rotatably mounted to a drum shaft received in the housing, and a single-direction clutch device mounted between the drum and the cord pulley, with the clutch device comprising: a chamber defined in the housing and coaxial to an axis of the housing; a driving shaft coaxially mounted to the cord pulley; a transmission shaft mounted in the chamber, with the transmission shaft having an outer diameter slightly smaller than an outer diameter of the driving shaft; and a driving spring mounted to an inner periphery of the chamber and around the driving shaft and the transmission shaft in the chamber, with the driving spring being in tight contact with the driving shaft and the inner periphery of the chamber, and with the transmission shaft extended out of the chamber and connected to the drum, with the cord pulley including a coaxial positioning axle to which the transmission shaft is mounted, with the positioning axle including a positioning ring on an end face of the positioning axle, with a spacing between the end face of the positioning axle and an end face of the driving shaft being slightly larger than a spacing between the end face of the driving shaft and an end face of an axial hole of the transmission shaft facing the end face of the driving shaft, with the transmission shaft including an inner transmission shaft rotatably mounted to the positioning axle, with the transmission shaft further including an outer transmission shaft coupled to the inner transmission shaft, with the inner transmission shaft including the axial hole and a transmission ring, with the transmission ring including an insert end, with the outer transmission shaft including a connecting head having a groove, with the insert end engaged in the groove, with the outer transmission shaft further including a rotary head extending out of the chamber, with the rotary head coupled to a drum driving shaft, with the driving shaft having a connecting block coupled to the drum.