US Patent 7621386 Viscous fan drive having modified land design and armature venting

A viscous fan drive in which the output drive to the fan is controlled by the movement of viscous fluid from a fluid reservoir and into the operating and working chamber of the coupling during normal operation. The input-coupling assembly and cover member are formed with a unique combination of continuous and non-continuous radially extending lands and grooves designed to distribute the viscous fluid in a continuous film throughout the shear zone so as to maximize output fan speed at a given input speed. An armature-venting feature is designed to simplify the opening and closing of the valve disk in an electronic version of the viscous fan drive depending upon the desired operating condition.