4. (12 points) A compound reverted spur gear train is to be designed to reduce the speed of a 180HP engine's rotating shaft from 3500rpm to 100rpm exactly. (a) (5 points) Specify appropriate numbers of teeth (N2, N3, N4 and N5) to minimize the gearbox size. A pressure angle of 20° is used for all the gears. Interference of gears is not acceptable. (b) (5 points) If all the gears are cut with 20° full-depth system. Assume a diametral pitch of 6 teeth/in, and allowable stress of 60kpsi. Find a suitable face width for gear 5 (see the following figure). (C) (2 points) Provide at least two (2) solutions (by modifying some parameters above, while keeping the same gear train value) to further reduce the size of the gear box. 2. 2 3