GB904502A - Control for controllable pitch propeller or fan - Google Patents

Abstract

904,502. Fluid-pressure servomotor-control systems. HARTZELL INDUSTRIES Inc. Oct. 3, 1960 [April 27, 1960], No. 33897/60. Class 135. [Also in Groups XXVI and XXXIII] A controllable pitch propeller, as shown a propeller fan driven through a gear-box 54 by a motor 20 and having blades 16 which propel cooling air through a heat exchanger and are adjusted to maintain a constant temperature of cooled fluid leaving the heat exchanger, comprises a piston 82 or diaphragm for adjusing the pitch through a plate 74 and rods 72 engaging eccentric blocks 68 attached to the blade roots, a controller 50 for the piston 82 mounted on the cylinder 80 which rotates with the fan, a negative feedback connection comprising a spring 92 between the piston and the controller, and a rotary union 44 by which a pneumatic control pressure is transmitted from a conduit 34 to a conduit 48 leading to a chamber 142 in the controller, and a pneumatic or hydraulic actuating fluid is conveyed from a conduit 46 to conduits 52, 108. The control pressure, which is varied by a recording instrument (not shown) in accordance with variations of the temperature of the cooled fluid leaving the heat exchanger, acts on a differential diaphragm assembly 100, 102 to move an element 124 which has a passage 122 leading to exhaust 128. Downward movement of the element 124 away from the end of a valve stem 116 thus connects a chamber 114, which communicates with the upper end of the cylinder 80 through a passage 130, with exhaust to cause upward movement of the piston 82 until the spring 92 causes the passage 122 to be closed by the stem 116. Upward movement of the element 124 causes a ball element 118 on the stem 116 to connect the chamber 114 with the actuating fluid conduit 108 and thereby to cause downward movement of the piston. A loading spring 132 adjustable by a screw 138 acts on the element 124. The piston 82 or diaphragm may be loaded by a fluid cushion instead of the spring 86. Alternatively, it may be double-acting in which case it is controlled by a pair of valve assemblies mounted on opposite sides of a hinged arm which controls the valve assemblies by coating with nozzles and is actuated by a bellows subject to the control pressure. Over-riding manual or automatic controls may be provided for reversing the pitch of the propeller.