Statement (I): In an epicyclic gear train, the size of the gearbox is smaller than that of the spur gearbox for the same horsepower and the same velocity ratio. Statement (II): In an epicyclic gearbox, more than one pair of gear pinion contacts always exist, whereas it is not so in spur gearbox.
Statement (I): In an epicyclic gear train, the size of the gearbox is smaller than that of the spur gearbox for the same horsepower and the same velocity ratio. Statement (II): In an epicyclic gearbox, more than one pair of gear pinion contacts always exist, whereas it is not so in spur gearbox. Correct Answer Both Statement I) and Statement II) are individually true and Statement II) is the correct explanation of Statement I)
A epicyclic (planetary) gearbox gives high torque transmission with good stiffness and low noise, in a more compact footprint than other gearbox types.
Since planetary gears mesh with the sun gear and ring gear at several locations, more teeth are engaged to drive the load, compared to a conventional gear and- pinion mesh. Therefore, for the same load, planetary gearing requires smaller gears although in greater number than a standard pinion-to-gear reduction.
More than one pair of contact between pinion and gear results in less load per tooth of gear while in case of spur gearbox, the gears are having single contact and hence for epicyclic gears, the gearbox size is small for the same horsepower.
Therefore, statement II) gives exact explanation for statement I).