US Patent 7421761 Door closer

A door closer comprises a spindle journaled in a housing and connected to turn with a door. Upon rotation of the spindle, a cam carried by the spindle effects linear movement of a slide assembly relative to the housing. A piston is connected with the slide assembly. Passages are provided in the housing to permit flow of fluid in the housing in response to movement of the piston. A spring assembly disposed outside of the housing is connected to the piston. Rotation of the spindle and cam during door opening moves the slide assembly, thereby compressing the spring assembly for storing energy for urging the piston and the slide assembly in the opposite door closing direction.