Patent ID: 7354363

Claim:
A tensioner for a power-transmitting belt comprising: a base; an arm pivotably attached to the base; a pulley rotatably attached to the arm for engaging a power-transmitting belt; a spring operatively connected to the arm and the base for urging the arm to pivot relative to the base such that the pulley on the arm engages the belt with a force to tension the belt; and a hydraulic strut pivotably attached at a first point to the base and pivotably attached at a second point to the arm such that pivotal movement of the arm on the base either extends or compresses the strut, the strut operable to restrict movement of the arm through asymmetric fluid damping, the strut comprising: a hydraulic cylinder; a piston rod axially mounted through the cylinder for relative reciprocal movement; a piston mounted on the piston rod for reciprocal movement therewith within the cylinder, the piston dividing the cylinder into a first fluid chamber and second fluid chamber; a fluid flow path between the first and second fluid chambers; a check valve within the hydraulic cylinder to provide greater restriction of fluid flow through the fluid flow path when the arm is lifted by the belt than when the arm moves toward the belt; and an electro-magnetic coil operable to generate a magnetic field across the fluid flow path when the electro-magnetic coil is energized; wherein the first and second fluid chambers within the strut contain magnetorheological fluid.