Ii 3 n3 t2 the speed ratio of the gear train as shown

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Unformatted text preview: e gear train as shown in Fig. 13.1 (b) is obtained by multiplying the equations (i) and (ii). ∴ T N1 N T × 2= 2× 3 N2 N3 T1 T2 or T N1 =3 N3 T1 i.e. Speed ratio = Speed of driver No. of teeth on driven = Speed of driven No. of teeth on driver and Train value = Speed of driven No. of teeth on driver = Speed of driver No. of teeth on driven Similarly, it can be proved that the above equation holds good even if there are any number of intermediate gears. From above, we see that the speed ratio and the train value, in a simple train of gears, is independent of the size and number of intermediate gears. These intermediate gears are called idle gears, as they do not effect the speed ratio or train value of the system. The idle gears are used for the following two purposes : 1. To connect gears where a large centre distance is required, and 2. To obtain the desired direction of motion of the driven gear (i.e. clockwise or anticlockwise). 13.4. Compound Gear Train Gear trains inside a mechanical watch When there are more than one gear on a shaft, as shown in Fig. 13.2, it is called a compound train of gear. We have seen in Art. 13.3 that the idle gears, in a simple train of gears do not effect the speed ratio of the system. But these gears are useful in bridging over the space between the driver and the driven. Chapter 13 : Gear Trains l 431 But whenever the distance between the driver and the driven or follower has to be bridged over by intermediate gears and at the same time a great ( or much less ) speed ratio is required, then the advantage of intermediate gears is intensified by providing compound gears on intermediate shafts. In this case, each intermediate shaft has two gears rigidly fixed to it so that they may have the same speed. One of these two gears meshes with the driver and the other with the driven or follower attached to the next shaft as shown in Fig.13.2. Fig. 13.2. Compound gear train. In a compound train of gears, as shown in Fig. 13.2, the gear 1 is the driving gear mounted on...
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