Belt tensioner

Abstract

A belt tensioner employing helical compression springs in series arrangement in a housing located on a support structure to rotate another structure pivotally mounted on the support structure. An idler pulley is located on the rotatable structure and bears against a belt to both tension it and dampen vibrations. The helical compression springs operate on a plate rigidly attached to a movable shaft, which shaft bears directly or preferably indirectly through a thrust linkage on a shoulder of the rotatable structure. The springs, a thrust assembly and shaft are all mounted in a housing which is substantially filled with liquid which dampens the movement of the rotatable structure by the liquid being forced to flow through a restriction in the thrust assembly as it passes from one chamber to another inside the housing. The constant diameter shaft passes through the housing and its end cap, it being sealed hydraulically at each end. This permits shaft movement to occur without any volume change inside the housing. The rotatable structure is pivotally mounted to the support structure with its rotational axis being displaced and perpendicular to the spring thrust axis. The pressure of the liquid within the tensioner housing due to the thermal expansion of the liquid can be reduced by employing a closed cell elastomeric foam insert in one of the liquid filled chambers of the housing.