Door closer

An automatic door closer comprising a fluid-containing housing including an end wall;

• a damper piston mounted in said housing for movement in a first direction during closing of the door and in a second direction during opening of the door;
• first energy storing means for urging said piston in said first direction with a first force;
• second energy storing means for permanently urging said piston in said first direction with a second force which is weaker than said first force, said first and second energy storing means being installed in said housing at one side of said piston and each thereof comprising a compression spring, the compression spring of said first energy storing means surrounding the compression spring of said second energy storing means and the compression spring of said first energy storing means reacting against said end wall;
• stressing means operable to prevent said first energy storing means from urging said piston in said first direction so that the piston is then movable in said second direction against the oppostion of said second energy storing means but the piston need not overcome the resistance of said first energy storing means;
• and motor means actuatable to operate said stressing means, said stressing means comprising a sleeve-like member which surrounds the compression spring of said second energy storing means and has an abutment against which the compression spring of said first energy storing means bears to urge said sleeve-like member toward engagement with said piston.

An automatic door closer comprising a fluid-containing housing;

• a damper piston mounted in said housing for movement in a first direction during closing of the door and in a senond direction during opening of the door;
• first energy storing means for urging said piston in said first direction with a first force;
• second energy storing means for permanently urging said piston in said first direction with a second force which is weaker than said first force, said first energy storing means comprising a first spring and said second energy storing means comprising a second spring which acts directly upon said piston and is disposed between said piston and said first spring;
• a hollow extension for said first spring;
• stressing means operable to prevent said first energy storing means from urging said piston in said first direction so that the piston is then movable in said second direction against the opposition of said second energy storing means but the piston need not overcome the resistance of said first energy storing means;
• and motor means for operating said stressing means, said stressing means comprising a second piston which is reciprocable in said extension in said first and second directions to stress said first spring in response to movement in said second direction.