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Unformatted text preview: Chapter 10 GEARS: KINEMATIC ANALYSIS AND SELF'CTION 8 in. dia. Figure 10.22 Gear train with an idler gear' Therefore, the train value is only dependent on the size of the first and last gears' The diameter, or the number of teeth, of the center gear does not influence the train value. The center gear is termed anidler gear. lts function is to alter the direction of the output motioi, yer nor affect the magnitude of that motion. To illustrate this function, consider an arrangement where gear 2 mates directly with geat 4- The re- sulting train value would be rv : (-vR ,-r : -* Thus, the idler gear serves to reverse the direction of the output' As mentioned, the size of the idlei gear does not influence the kinematics of the train. In practice, this idler gear can be sized to conveniently locate the centers of the input and output g.urr. Ofiourse, because all three gears mesh, they must have identical diametral pitches and Pressure angles. 10.15 PLANETARY GEAR TRAINS The gear trains presented in preceding sections all had gear centers. attached to fixed bodies. With planetary gear trains, this restriction is removed. In these trains, a link that holds the center oflhe geart is allowed to move. A planetary gear train' which is also called an epicyclic train' is shown in Fig' 1'0'23' Planetary trains can be used to achieve large speed reductions in a more compact space than a conventional gear train. However, a greater benefit is the ability to readily alter the train value. Because all links are capable of moving,,one can alter the train value by holding different gears or carriers. In practice, switching the fixed link is accomplished with brake or clutch mechanisms, thus releasing one link and fixing anoth.i. Fo. this fixing anoth....
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This note was uploaded on 08/08/2011 for the course MAE 162A taught by Professor Glenn during the Spring '08 term at UCLA.
- Spring '08