(57) An automatic door closer comprises a casting 10, a sliding assembly 20, a drive assembly
30, a tube shaped piston 41 and a first resilient member 51. The casting 10 has a
front chamber 111, a rear chamber 113, a middle chamber 112 in communication with
the front chamber 111 and the rear chamber 113, a shaft hole 12 penetrating the middle
chamber 112 and a first oil passage 13. The first oil passage 13 has an oil inlet
13a in communication with the front chamber 111 and an oil outlet 13b in communication
with the rear chamber 113. The sliding assembly 20 disposed within the middle chamber
112 of the casting 10 comprises a slider 21 disposed between the oil inlet 13a and
the oil outlet 13b, a first roller 22 and a second roller 23, wherein the first and
second rollers 22, 23 arc disposed within the slider 21 respectively. The drive assembly
30 comprises a shaft 31 and an eccentric cam 32 coupled to the shaft 31, the shaft
31 is pivotally disposed within the shaft hole 12 of the casting 10, the eccentric
cam 32 is located within the slider 21 and contacts against the first and second rollers
22, 23 of the sliding assembly 20. The tube shaped piston 41 disposed within the rear
chamber 113 of the casting 10 has a first end portion 411 and a second end portion
412 opposite to the first end portion 411, the first end portion 411 is connected
with the first roller 22. The first resilient member 51 is disposed within the front
chamber 111 of the casting 10 serving for pushing the slider 21 of the sliding assembly
20 to move.
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