机械零件设计英文PPT教案_精品.pptVIP

10.7 Summary of Gear Design 1) Suggested design procedure Based on functional specifications and contemplated system configuration, generate a first conceptual sketch of the gear train, including required reduction ratio, proposed number of teeth for each gear, gear shaft centerlines and bearing locations, and any other geometrical constraints. Identify potential failure modes, and select tentative gear materials. Select tentative manufacturing and finishing methods appropriate to the application. Tentatively select a tooth system, then, using specified power and speed requirements, perform a complete force analysis to determine torques, speeds, and transmitted loads at each mesh in the gear train. * Calculate a tentative diametral pitch (or module), based on calculations for surface endurance (or bending calculations), which indicates that there is a balance between failure by tooth bending fatigue and surface fatigue durability. Calculate the centerline distance. For each gear, calculate or estimate the other geometrical dimensions as well as the pitchline velocities. If necessary, repeat the design process. The design procedure for helical gears follows the same pattern as for spur gears except for the complications introduced by the inclined teeth. * The harder and smoother the working surfaces of the teeth are, the greater the load they can take without suffering from pitting. So the resistance of the tooth surfaces to pitting can be improved by increasing their strength, surface finish and employing correct lubricants. In open-type gears where there is little or no oil, pitting is an extremely rare phenomenon since the initial cracks developed in surface layer are usually worn off before the progressive pitting sets in. * Under the action of excessive loads the surface of steel teeth at HB 350 may suffer plastic deformations, while at HB 350 the surfaces of cast-iron teeth may be subjected to brittle failure. Because of the relative motion between t