Spur Gears School of Engineering（直齿圆柱齿轮工程学院）.pptVIP

Gear Nomenclature Example 8-1) Gear has 44 teeth, ?=20°, full depth involute form diametral pitch Pd = 12 Pitch Diameter Circular Pitch Pd NG 3.667 inch = = DG 12 t/in 44 teeth = (p) NG DG .2617 in/t = = Pc p 44 t 3.667in = Gear Nomenclature Example Addendum Dedendum Pd 1 .0833 in = = a 12 t/in 1 = Pd 1.25 .1042 in = = b 12 t/in 1.25 = Gear Nomenclature Example Clearance Whole Depth ht = a+b = .1875 in Working Depth hk = 2*a = .16667 in Pd .25 .0208 in = = c 12 t/in .25 = Gear Nomenclature Example Tooth Thickness Outside Diameter 2 PC .1309 in = = t 2 .2617in = Pd N+2 2.833 in = = O.D. DO = Gear Nomenclature Notes Clearance maybe a problem for small pinions driving large gears, therefore they won’t mesh and will lock up (See Table 8-6) As NP decreases so does max NG If design necessatates small pinion, maybe able to increase clearance by undercutting gear tooth (See Figure 8-14) Summary of Gear Nomenclature: DP = Pitch diameter of pinion DG = Pitch diameter of gear NP = No. teeth (t) for pinion NG = No. teeth (t) or gear Pd = diametral pitch = N/D = constant for meshing gears p = circular pitch = pD/N = constant for meshing gears nP = speed of pinion (rpm) nG = speed of gear (rpm) VR = velocity ratio = nP/nG = NG/NP Power = constant across mating gears or series system: Pin = Pout Power in branched system is conserved: Pin = PA + PB + ….. Torque will change!! Conclusion: Total speed reduction = 1750/68 = 25.7 Torque increase = 25.7 Power = constant!! Gear Trains Train Value = TV = Product of the values for each gear pair in the train nin nout = = TV (VR1)(VR2). . . . Gear Train Alternate Solution = TV (VR1)(VR2)(VR3) 30 22 = TV 8.4 = * 68 30 * 68 25 ni nout = TV = ni nout = TV 208 rpm ccw = 1750 rpm 8.4 Tout = 8.4 Tin !! Lots of Torque YouTube Gear Animations: Speed Reducers: /watch?v=7LReoWPg_pMfeature=related ? /watch?v=1_jbZVBXjWcfeature=related ? Automotive Differential: /watch?v=iBLE0_Sjqw4feature=related Manual Transmissi