GB169429A - Improvements in or relating to revolution counters and revolution direction indicators particularly adapted for ships' propeller shafts - Google Patents

Abstract

169,429. McNab, A. Sept. 20, 1920, [Convention date]. Revolution-direction indicators; differential speed indicators. - An instrument for registering the revolutions per minute and the total revolutions irrespective of direction of each propeller shaft of a twinscrew vessel, and also for indicating the direction of revolution of each shaft, comprises a casing 3 with a dial 6 graduated in revolutions, total-revolution counters 25, 25', pointers 28, 28<1> movable over the dial to indicate tens of revolutions and also the directions, and hundreds-of-revolutions wheels 74, 74<1> driven from the pointer spindles. The mechanisms for the two propeller shafts are substantially identical. A shaft 7 driven from the starboard shaft drives a secondary shaft 12, Fig. 3, through a clutch 9, and the total counter 25 is driven from this shaft 12 through bevel gearing 15, 16, a crank 19 and connecting-rod 20, and an arcuate pawl 23 and ratchet 24. The other total counter 25<1> is similarly driven but the pawl shaft 26 is extended to the opposite end of the counter. The shaft 29 of one pointer 28 carries a loose worm wheel 34 driven by a worm 73 on a shaft 68 driven through wheels 68 from a wheel 48 loose on the shaft 12. This wheel 48 is connected to the shaft 12 when desired by a friction clutch 55 operated from a push-rod 60 extending through the casing and fitted with a knob 5. The inner end of the pushrod is provided with a double-bevelled head 61 engaged by a knife-edged spring detent 62. The worm-wheel' 34 drives the pointer shaft 29 through a friction clutch member 36, which is provided with a cam portion 87, Fig. 2, adapted to rock an arm 84 once in each revolution of the pointer and thereby oscillate an arcuate pawl 79 to advance the hundreds wheel 74. A similar arm 84<1> for the other hundreds wheel 74<1> is held by a weight 89 against a cam on a clutch member 47, Fig. 3, on the hollow shaft 31 of the second pointer 28<1>. The boss of the pointer 28 may be turned by means of an external knob 42, or may be moved along its shaft to bring a pin 44 on the pointer into engagement with a hole in the other pointer 28<1>, whereby both pointers may be reset to zero when the secondary clutches 55, 55<1> are opened. The hundreds wheels are zeroized manually through shafts 75, 75<1> extending through the casing. For measuring the revolutions per minute the secondary clutches are closed for a determined interval and the readings are taken from the hundreds wheels and pointers. The dial is suitably marked to indicate the direction of revolution, and the pointers are distinguished by colour or otherwise.