Apparatus for providing constant torque output from a door closer or operator

A door closer or operator includes a pivoting pinion on the door closer housing for transmitting door motion, and a cam connected thereto. A connecting member extends along a spring and engages the peripheral edge of the cam. Rotation of the cam causes a change in length of the portion of the connecting member between the position tangent to the cam peripheral edge and the spring second end to expand or compress the spring, resulting in a force transmitted along a longitudinal axis of the connecting member as a result of spring deflection. The cam peripheral edge has a profile with a varying radial distance between the cam axis and the connecting member at the position tangent to the cam peripheral edge such that the radial distance is changed as the spring expands or compresses to maintain a desired constant torque about the axis of the cam and pinion.