There have been a very great number of proposals for altering the effect of fans, propellers and other fluid-moving devices, hereinafter all referred to as fans, in response to various requirements, most commonly in response to the temperature of a motor cooling fluid. Sometimes the fluid mover is activated and de-activated when desired, as by a clutch or the like; more often the pitch of the blades of the fluid mover is changed in response to requirements. On aircraft it is usual to change propeller pitch to meet speed requirements; on earth and water vehicles it is usual to change the pitch of the blades of cooling fans to meet motor temperature requirements. For example, see U.S. Pat. Nos. 2,620,886, 3,265,886 and 3,406,898.
So far as known, the pitch-changing means is usually closely associated with and carried by the shaft which drives the fluid-moving device, hence the pitch changing means cannot easily be made as rugged and dependable as desired, especially for large power vehicles.
As to phase-changing devices in general, it has been proposed to shift the angular position of a driven shaft relative to that of a driving shaft, for example in one specific form, to shift the spans of a driving belt, as by controlled idlers. This, however, would have no point and give no advantage in connection with changing the pitch of fan blades.