Torque responsive disconnect for a V-belt driven element

In the variable speed V-belt drive of a combine harvester threshing cylinder, the driven sheave is torque-responsive, responding automatically to adjust drive belt tension according to the torque being transmitted. A linear hydraulic actuator, integral with the drive sheave, is used to adjust an axially movable sheave half with respect to a fixed sheave half so as to vary sheave effective diameter and hence driven speed. At any given speed setting, oil is trapped in the hydraulic actuator and oil pressure varies according to separating force between the halves of the drive sheave which in turn depends upon belt tension. A pressure switch, connected so as to sense the oil pressure, has a set point such that at a predetermined maximum (overload) belt tension, the switch is actuated so as to declutch or disconnect the drive sheave from its power source, thus protecting the threshing cylinder and drive components from damage. The signal from the pressure switch may be used also, or alternatively to actuate an operator warning signal.