Patent GB-868121-A (GB)
Title: Improvements in or relating to speed governors
Inventor: CHILMAN JOHN ALFRED
IPC: G05D13/00
Filed: 1957-10-29
Abstract: 868,121. Centrifugal governors. ROTOL Ltd. Dec. 13, 1957 [Jan. 10, 1957], No. 1043/57. Class 57. In a centrifugal governor, particularly for an hydraulically-operated constant - speed variable-pitch propeller, comprising flyweights 12 loaded by a speeder spring 31 and controlling the displacement of a control member such as a spool valve 16, speed creep due to temperature variation is minimized by temperature responsive means which is located between an abutment and one end of the speeder spring, has a stop for limiting the extent by which it may contract, and acts to vary the load on the speeder spring to thereby compensate at least in part for changes in the speeder spring load due to change in temperature of the spring. The flyweights 12 are pivotally mounted at 13 on a rotatable sleeve 14 having ports 20 registering with an hydraulic fluid supply channel 19 and ports 22 and 23 registering with channels 24 and 25 respectively leading to the coarse and fine pitch sides of the variablepitch propeller motor. Ports 20 lead to a space 21 between lands 17 and 18 on the valve controlling ports 22 and 23. An internal passage 16a in the valve connects the chamber 26 above the land 17 with chamber 27 below the land 18 communicating with the suction side of the governor pump. The speeder spring 31 is compressed between a flange 29 on an extension of the spool valve and a fluid-filled bellows device 33 comprising a bellows 33a sealed between members 32 and 34 and slidably housed in a bush 35 mounted in a rack member 36 having a rack 36 engaged by a pinion 37 movable by a lever 38. A sleeve 39 is located between the member 34 and an inturned flange 36b of the member 36. The member 32 has a skirt 32a which by engaging the member 34 limits the contraction of the bellows device. A ball-bearing 30 is disposed between the flange 29 and the inner ends of the weights 12. The extension of the spool valve is connected at its extremity to a rod 40 having a lost-motion connection with a rod 41 loaded by a spring 43 and operated in emergency to move the valve 16. The load on the speeder spring and thus the datum setting of the governor may be varied by rotation of the pinion 37 by lever 38. In operation, the governor maintains the propeller at constant speed by controlling its pitch hydraulically by means of the valve 16. If the temperature of the hydraulic fluid increases during operation, the increase in effective length of the spring due to heating by the fluid and the resultant tendency to increase the datum setting of the governor is offset by the expansion of the bellows device 33 which increases the load on the spring. The bellows device is designed and has a coefficient of thermal expansion such that it compensates at least in part not only for changes in effective length of the speeder spring but also for the differential expansion between the governor casing and its components and for the effect of leakage variation in the system due to fluid viscosity changes. The bellows device may be replaced by a number of superposed bimetallic washers.