(BQ) Part 2 book "Mechanical engineer's pocket book" has contents: Power transmission, power transmission - belt drives, tapers, fluid power transmission systems, mechanical properties, ferrous metals and alloys, linear tolerancing, standard systems of limits and fits,. and other contents. | 5 Power Transmission Power transmission: gear drives Some typical gear drives Straight tooth spur gears Rack and pinion: converts rotary to linear motion Pinion Rack 352 Mechanical Engineer’s Pocket Book Single-helical tooth spur gears Double-helical tooth spur gears Power Transmission Straight tooth bevel gears Worm and worm wheel 353 354 Mechanical Engineer’s Pocket Book Simple spur gear trains Driver Driver Driven Idler Driven Simple train (a) Driver and driven gears rotate in opposite directions. (b) The relative speed of the gears is calculated by the expression: rev/min driver number of teeth on driven ϭ rev/min driven number of teeth on driver Example Calculate the speed of the driven gear if the driving gear is rotating at 120 rev/min. The driven gear has 150 teeth and the driving gear has 50 teeth: 120 150 ϭ rev/min driven 50 rev/min driven ϭ 120 ϫ 50 ϭ 40 rev /min 150 Power Transmission 355 Simple train with idler gear (a) Driver and driven gears rotate in the same direction if there is an odd number of idler gears, and in the opposite direction if there is an even number of idler gears. (b) Idler gears are used to change the direction of rotation and/or to increase the centre distance between the driver and driven gears. (c) The number of idler gears and the number of teeth on the idler gears do not affect the overall relative speed. (d) The overall relative speed is again calculated using the expression: rev/min driver number of teeth on driven ϭ rev/min driven number of teeth on driver Compound spur gear train Driven gear Intermediate gear I1 Intermediate gear I2 Driver gear (a) Unlike the idler gear of a simple train, the intermediate gears of a compound train do influence the overall relative speeds of the driver and driven gears. (b) Both intermediate gears (I1 and I2) are keyed to the same shaft and rotate at the .
