Belt tensioner combination and a method of installing a tensioner on a belt

A combination comprising:

• a belt trained about a plurality of pulleys in a belt drive system;
• and
• a tensioner assembly including a rotary member that is rotationally engaged by one side of said belt when said tensioner assembly is positioned in an operative position, said rotary member being rotationally mounted on an arm that pivots about a fixed pivot axis and said rotary member having a rotational axis that is parallel with said fixed pivot axis;
• wherein the geometric configuration of the combination permits over-center positioning and self-locking of the tensioner assembly in the operative position such that when the tensioner assembly is positioned in the operative position, the vector sum of force applied by the belt to the periphery of said rotary member extends at at least a small angle relative to a line passing through said rotational and pivot axes, with the vector sum of force applied by the belt to the periphery of said rotary member acting in a direction to bias said arm toward and hold said arm in said operative position;
• and
• wherein the geometric configuration of the combination is such that as said rotary member is being moved into said operative position by pivoting said arm about said fixed pivot axis from an initial, belt installation position toward said operative position, the vector sum of force applied by the belt to the periphery of said rotary member initially acts in a direction to oppose pivoting movement of said arm toward said operative position but changes direction relative to said line passing through said rotational and pivot axes as said arm passes through a central or neutral position so as to bias said tensioner assembly toward and ultimately hold said tensioner assembly in said operative position, said central or neutral position being a pivotal position at which the vector sum of force applied by the belt to the periphery of said rotary member extends directly along the line passing through said rotational and pivot axes.