Patent GB-1199175-A (GB)
Title: Engine Drive System
IPC: F16F15/12
Filed: 1967-07-26
Abstract: 1,199,175. Shaft couplings. CONTINENTAL MOTORS CORP. 26 July, 1967 [1 Aug., 1966], No. 34283/67. Headings F2U and F2S. In a resonant frequency control for selectively altering the natural vibration frequency of a drive system, e.g. connecting the crank-shaft of an engine with the propeller shaft of an aircraft, to eliminate build-up of harmonic vibrations at certain engine speeds, drive from the crankshaft (10), Fig. 1 (not shown), to a shaft (14) connected through gearing (16), (18) to the propeller shaft (20), is effected through a coupling 12 having two modes of operation; (a) a first mode in which it rigidly connects the shafts (10), (14) so that the natural frequency of the system is high; and (b) a second mode in which it resiliently connects the shafts so that the natural frequency of the system is low, the coupling operating in its first mode at low speeds and, prior to it reaching a speed corresponding to the high natural frequency, it is centrifugally changed to its second mode so that the shafts are never rotating at the same speed as their effective natural frequency. As shown, the coupling comprises two pairs of interengaging axially extending arms 22, 30 connected to the shafts (10), (14), each arm 30 carrying two pistons 44 spring biased into engagement with the arms 22. The pistons are carried in cylinders 32 supplied with oil through one-way valves 52, from inlets 50, e.g. from the engine oil system, and connected by a passage 34 which, at low speeds, is blocked by a spring- loaded centrifugal mass 36 to provide hydraulic lock-up of the pistons and hence rigid engagement of the arms 22, 30. With increasing speed, the mass 36 moves and the passage 34 is opened to connect the cylinders 32 and hence release hydraulic pressure, the pistons 44 being urged by springs 48 only into engagement with arms 22 providing a resilient connection between the arms 22 and 30. The stiffness of springs 48 may be selected to provide any desired difference between the two natural frequencies. Again, Figs. 3, 4 (not shown), a drive shaft (100) is provided with a single arm (108) carrying two pistons and cylinders, as described, abutting the ends of an arm (132) on the driven shaft (102), the arm (132) being also provided with three spaced rectangular apertures, each carrying a coil spring (142) which engage in corresponding apertures in a radial arm (146) and a retainer plate (152) carried by the drive shaft (100). Again, Fig. 5 (not shown), the mass (116) in the channel connecting the cylinders in the arm (108) may be replaced by a valve, the opening of which is controlled by fluid pressure, the fluid pressure source being responsive to the speed of shaft 100. Again, Figs. 6, 7 (not shown), for those cases where only a small difference between the natural frequencies is required, or where even the relatively low natural frequency is of a high order, the stiff springs 48 of the embodiment shown are replaced by weak springs (236), the resilient connection between the driving and driven shaft, being effected by a torsion grill shaft (224). The passages 34 may provide a restricted orifice between the cylinders, or the masses 36 may have a restricted bore therein to connect the cylinders even when in their closed position, to provide damping throughout the whole speed range.