US Patent 7353928 Torque coupling assembly with venting passage

A torque-coupling assembly comprises a hydraulic fluid reservoir provided for storing a supply of a hydraulic fluid, a hollow coupling casing rotatable by an outside drive torque, a hydraulic pump located within the coupling casing to generate a hydraulic pressure, a supply passage fluidly connecting the hydraulic fluid reservoir to a suction passage of said hydraulic pump and a venting passage. The venting passage is provided for operatively fluidly connecting the supply passage to an ambient atmosphere for selectively enabling or disabling the hydraulic pump.