One of the planetary gearsets from our transmission has a ring gear with 72 teeth and a sun gear with 30 teeth. We can get lots of different gear ratios out of this gearset.
|
Input |
Output |
Stationary |
Calculation |
Gear Ratio |
| A |
Sun (S) |
Planet Carrier (C) |
Ring (R) |
1 + R/S |
3.4:1 |
| B |
Planet Carrier (C) |
Ring (R) |
Sun (S) |
1 / (1 + S/R) |
0.71:1 |
| C |
Sun (S) |
Ring (R) |
Planet Carrier (C) |
-R/S |
-2.4:1 |
Also, locking any two of the three components together will lock up the whole device at a 1:1 gear reduction. Notice that the first gear ratio listed above is a reduction — the output speed is slower than the input speed. The second is an overdrive — the output speed is faster than the input speed. The last is a reduction again, but the output direction is reversed. There are several other ratios that can be gotten out of this planetary gear set, but these are the ones that are relevant to our automatic transmission.
