Patent GB-712154-A (GB)
Title: Improvements in or relating to mechanism for preloading gearing
IPC: F16H57/12
Filed: 1952-07-31
Abstract: 712,154. Toothed gearing. UNITED AIRCRAFT CORPORATION. July 31. 1952 [Jan. 8. 1952], No. 19384/52. Class 80 (1) [Also in Group XXXIII] Backlash in a gear train interconnecting the pitch-changing mechanisms of two propeller hubs 24, 26 driven by contra-rotating shafts 50. 52 is eliminated by preloading the train by imposing a constant torque between the outer hub 26 and a gear 328, Fig. 2, which normally rotates therewith but which undergoes a temporary relative rotation at any change of pitch, said backlash-eliminating torque being provided by the centrifugal force on two eccentrically weighted gears 320 which are rotatably carried on studs on the hub 26 and mesh with the gear 328, said gears being normally stationary on their own axes so that the centrifugal force on the weighted portions constantly urges the gear 328 in a clockwise direction relative to the hub 26. The gears 320 may be so proportioned that their angular movement does not exceed 45 degrees, or may be proportioned so as to be ineffective ,for valve positions in which backlash is unimportant. The outer hub 26 contains a valve 60 controlling hydraulic motors (not shown) which effect pitch-changing of the outer Nades 30. This valve ds operated by a pivoted cam follower engaging a cam track on a sleeve carrying the gear 328 and a ;gear 82, said gear 82 being normally rotated in the same direction and at the. same speed as the hub 26, so that there is no movement of the cam follower, by reversing gears 292,.driven by a gear 80 on a sleeve geared (70, 68) to the blade synchronizing gear 56 of the inner hub. The reversing gears are carried by a housing 44 which is free to rotate but which is normally held stationary by a gear train connecting the inner hub 24 with the blade synchronizing gear 110 of the outer hub. This train comprises a gear 140 on a sleeve attached to the hub 24, reversing gears 300 carried by the housing 44 and connecting the gear 140 with a gear 138, a gear 134 mounted on the sleeve carrying the gear 138, an idler gear and gears 118, 116, 114. Since the blades 30 are normally locked by their hydraulic motors, gear 134, and therefore also gear 138, rotate with the hub 26. Since hubs 26, 24 are rotated at the same speed and in opposite directions by the shafts 52, 50 it follows that so long as there is no change of pitch gears 138 and 140 are rotated in opposite directions and the reversing gears 300 hold the housing 44 stationary. When the pitch of the blades 28 is changed (by hydraulic means not shown), gear 80 is rotated relatively to the 'hub 24 and consequently gear 82 and its cam track are rotated relatively to the hub 26, thereby moving valve 60 to change the pitch of the blades 30. This change effects a follow-up rotation of gear 134 relatively to the hub 26, thereby varying the relationship between the oppositely-rotating gears 138, 140. This variation effects a movement of the housing 44 and a consequent variation in the relationship between the gears 80, 82 such that the cam track is moved relatively to the hub 26 to return the valve to its original position. It is stated that if the propellers are driven in opposite directions at unequal speeds it is preferable to change the ratios of the gears associated with the housing 44 so as to maintain the housing stationary.. Specification 688,170, [Group XXXIII], is referred to.