Door closer

A door closer comprising:

• a closer casing having first and second end portions opposite to each other in a longitudinal direction;
• a pivot unit including
• a pivot axle having a drive end portion that extends into and that is retained rotatably in said first end portion of said closer casing, and a coupling end portion that extends out of said closer casing,
• a cam member mounted co-rotatably on said drive end portion of said pivot axle, and a cam follower member disposed in said closer casing and acted upon by said cam member for moving along the longitudinal direction between open and closing positions upon rotation of said pivot axle;
• a length-variable damping cylinder disposed in said closer casing and having one end coupled to said cam follower member and an opposite end anchored to said second end portion of said closer casing, said damping cylinder accumulating a restoring force upon movement of said cam follower member from the closing position to the open position, and releasing the restoring force to assist movement of said cam follower member from the open position back to the closing position;
• wherein said damping cylinder includes:
• an outer tube confining a tube space and having a closed first end, and a second end opposite to said closed first end and having a closure member mounted therein;
• a first piston disposed in said outer tube and partitioning said tube space into a pneumatic chamber filled with air and a hydraulic chamber filled with hydraulic fluid, said pneumatic chamber being confined by said closed first end and said first piston, said hydraulic chamber being confined by said first piston and said closure member;
• a second piston disposed in said outer tube and partitioning said hydraulic chamber into a first sub-chamber and a second sub-chamber, said second piston having a first face confronting said first piston and a second face confronting said closure member, said first sub-chamber being confined by said first piston and said first face of said second piston, said second sub-chamber being confined by said second face of said second piston and said closure member, said second piston further having a plurality of first fluid passages formed through said first and second faces for establishing fluid communication between said first and second sub-chambers;
• and a piston rod unit having a first end portion connected to said second piston, and an opposite second end portion extending through said closure member and disposed outwardly of said outer tube.