GB874108A - Variable pitch impellors - Google Patents

Abstract

874,108. Axial-flow fans. TOTHILL, G. R. Feb. 12, 1958 [Feb. 13, 1957], No. 4544/58. Class 110 (1). A variable-pitch impeller comprises a hub connected to the drive shaft by resilient means which oppose rotation of the shaft relative to the hub from an equilibrium position, impeller blades pivotally mounted on the hub by radial shafts, a pair of pins carried on the inner end of each blade shaft and spaced apart so as to be located on opposite sides of the drive shaft, a nut restrained from rotational movement and engaging a screw-threaded portion of the drive shaft, a flange extending radially from the nut and interposed between each pair of pins, and means which bias at least one pin of each pair against the flange. In the fan shown, each impeller blade 14, Figs. 1 and 2, is carried by a radial shaft 18, Figs. 1, 6 and 8, pivotally mounted on a hub 11 and in an outer ring 84. A flange 37 on the inner end of each shaft 18 carries pins 41, 42 which straddle a flange 62 on a nut 53 and are urged against the flange by spring-pressed discs 61, 611. The nut 53 engages a screw-threaded portion 56 of the drive shaft 13 and is prevented from rotating relatively to the hub 11 by engagement with guides 51 or, alternatively, splines. The drive shaft 13 is connected to the hub 11 by clock springs 63, 64 which are coiled in opposite directions. When the fan is stationary, the blades 14 overlap one another as shown in Fig. 1 and close the opening in the mounting frame 95, the inner and outer peripheries of the blades abutting against sealing flanges on the hub 11 and ring 84. The blades and sealing flanges may be coated with soft rubber or plastics. Stationary flanges 96, 97 form a labyrinth seal around the ring 84. The ring 84 may be journalled on the flange 97, either directly or through a ball-bearing, and flange 96 may be eliminated if the ball-bearing carries its own seal. The fan can be driven in either direction, according to the direction of air flow required, by a reversible motor 93. On starting, the inertia of the fan prevents it from attaining the same speed as the motor, and shaft 13 consequently rotates relatively to the hub 11, winding up one or other of the springs 63 and 64, depending on the direction of rotation, and unwinding the other. The relative rotation causes axial displacement of the nut 53 in one direction or the other, causing the flange 62 to push one or other of the pins 41 and 42 to pivot each blade 14 into an operative position. Eventually, the fan attains the same speed as the motor 93, and the blades 14 assume an equilibrium position depending on the aerodynamic forces and the spring forces. The flange 61<SP>1</SP> and its associated spring may be omitted.