Patent ID: 7117562

Claim:
An automatic opening and closing hinge assembly for joining a flip cover section to a body section of a foldable electronic device, comprising: a button having an open end; a locking element comprising at least one latching block at an outer wall thereof, and defining at least one polygonal hole therein; a main shaft including a shaft portion and a cylinder portion, the cylinder portion located at an intermediate portion of the shaft portion, the shaft portion comprising at least one latching protrusion at an end thereof, the cylinder portion comprising a cam surface distal from the latching protrusion, the cam surface comprising three peaks and three valleys at equal angular intervals, the latching protrusion engaging in the polygonal hole of the locking element and releasably locking the main shaft; a driving spring around the main shaft, one end of the driving spring resisting the locking element, another end of the driving spring resisting the cylinder portion; a cam, one end of the cam comprising a latching cam surface, another end of the cam defining at least one reverse rotating groove, the latching cam surface comprising three peaks and three valleys at equal angular intervals corresponding to the cam surface of the main shaft, the latching cam surface engaging with the cam surface of the main shaft, the cam further defining at least one positioning groove and a stepped axis hole, each positioning groove being adjacent to each of the at least one reverse rotating groove; a barrel, one end of the barrel comprising at least one latching post engaging in the at least one reverse rotating groove and rotating together with the cam, the barrel being configured for being fixed relative to one of the cover section and the body section; an end shaft being configured for being fixed relative to the other of the body section and the cover section; and a torsion spring comprising two end portions attached to the barrel and the end shaft respectively, the barrel rotating relative to the end shaft under urging by the torsion spring; wherein the button, the looking element and the driving spring are located around one end of the main shaft, and the cam and the barrel are located around another end of the main shaft.