Subtopic: Power transmission systems – gear trains, differential, final drives and power take-off
Question Statement:
A tractor epicyclic planetary final drive unit has a stationary ring gear (annulus) with $Z_{\text{ring}} = 64$ teeth, a rotating sun gear input with $Z_{\text{sun}} = 16$ teeth, and planet gears supported on a planet carrier output connected to the wheel axle shaft. The speed reduction ratio ($N_{\text{sun}}/N_{\text{carrier}}$) of this planetary unit is ________ (answer in integer).
Answer Key:
5
Step-by-Step Solution & Explanation
For an epicyclic planetary gear set with fixed ring gear, the velocity ratio is given by:
$\frac{N_{\text{sun}}}{N_{\text{carrier}}} = 1 + \frac{Z_{\text{ring}}}{Z_{\text{sun}}}$
Given $Z_{\text{ring}} = 64$ and $Z_{\text{sun}} = 16$:
$\frac{N_{\text{sun}}}{N_{\text{carrier}}} = 1 + \frac{64}{16} = 1 + 4 = 5$