Automatic opening and closing hinge assembly for portable electronic devices

1. 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.

2. The hinge assembly as claimed in claim 1 , wherein two projections extend from another end of the barrel opposite to the at least one latching post, and said another end of the barrel defines a limitative hole between the projections.

3. The hinge assembly as claimed in claim 2 , wherein one end portion of the torsion spring is received in the limitative hole of the barrel.

4. The hinge assembly as claimed in claim 3 , further comprising a compression spring, wherein the barrel defines a stepped hole, and the compression spring is received in the stepped hole of the barrel and the axis hole of the cam.

5. The hinge assembly as claimed in claim 4 , wherein one end of the end shaft defines a receiving hole, the end shaft defines at least one latching recess and at least one latching projection at said one end thereof, and the projection of the barrel is engaged with each latching projection or in each latching recess.

6. The hinge assembly as claimed in claim 5 , further comprising a central spring, wherein the central spring is received in the receiving hole of the end shaft and the stepped hole of the barrel.

7. The hinge assembly as claimed in claim 6 , wherein another end of the end shaft comprises a fixing portion, for engagement of the end shaft with the foldable electronic device.

8. The hinge assembly as claimed in claim 7 , wherein two fixing rings are provided on an outside wall of the end shaft, and at least one of the fixing rings defines a locking groove.

9. The hinge assembly as claimed in claim 8 , wherein one end portion of the torsion spring is received in the locking groove of the end shaft.

10. The hinge assembly as claimed in claim 9 , wherein the locking element comprises a plurality of restraining blocks axially extending from one end thereof, and the driving spring is located around the restraining blocks.

11. The hinge assembly as claimed in claim 10 , frther comprising a sleeve, the sleeve being located around the driving spring.

12. The hinge assembly as claimed in claim 11 , wherein the polygonal hole comprises a central through hole and at least one groove in communication with the through hole.