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# Or td 4 tb we know that t d dd m 224 4 56 ans t

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Unformatted text preview: s. Note : This picture is given as additional information and is not a direct example of the current chapter. or TD = 4 TB We know that T D = dD / m = 224 / 4 = 56 Ans. ∴ T B = T D / 4 = 56 / 4 = 14 Ans. ...(i) ...[From equation (i)] Let dB, dC and dD be the pitch circle diameters of sun wheel B , planet wheels C and internally toothed ring D respectively. Assuming the pitch of all the gears to be same, therefore from the geometry of Fig. 13.13, dB + 2 dC = dD Since the number of teeth are proportional to their pitch circle diameters, therefore TB + 2 TC = TD ∴ or 14 + 2 T C = 56 T C = 21 Ans. Example 13.10. Two shafts A and B are co-axial. A gear C (50 teeth) is rigidly mounted on shaft A. A compound gear D-E gears with C and an internal gear G. D has 20 teeth and gears with C and E has 35 teeth and gears with an internal gear G. The gear G is fixed and is concentric with the shaft axis. The compound gear D-E is mounted on a pin which projects from an arm keyed to the shaft B. Sketch the arrangement and find the number of teeth on internal gear G assuming that all gears have the same module. If the shaft A rotates at 110 r.p.m., find the speed of shaft B. Solution. Given : T C = 50 ; T D = 20 ; T E = 35 ; N A = 110 r.p.m. The arrangement is shown in Fig. 13.14. Number of teeth on internal gear G Let dC , dD , dE and dG be the pitch circle diameters of gears C, D, E and G respectively. From the geometry of the figure, dG d d d = C+ D+ E 2 2 2 2 or dG = dC + dD + dE l Chapter 13 : Gear Trains 449 Let T C , T D , T E and T G be the number of teeth on gears C, D, E and G respectively. Since all the gears have the same module, therefore number of teeth are proportional to their pitch circle diameters. ∴ T G = T C + T D + T E = 50 + 20 + 35 = 105 Ans. Fig. 13.14 Speed of shaft B The table of motions is given below : Table 13.9. Table of motions. Revolutions of elements Step No. Conditions of motion Arm Gear C (or shaft A) Compound gear D-E TC TD 1. Arm fixed - gear C rotates through + 1 r...
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