Page 194 - Mechatronics with Experiments

180 MECHATRONICS

4 4
Ring gear Ring gear
3 N 4 3 N 4
Planetary gear Planetary gear
1 1
Sun gear Sun gear
N 3
2 2 N 3
N 1 N 1
Carrier Carrier

(a) (b)

4 4
Ring gear Ring gear
3 N 4 3 N 4
Planetary gear Planetary gear
1 1
Sun gear Sun gear
2 N 3 2 N 3
N 1 N 1
Carrier Carrier

(c) (d)
FIGURE 3.26: Four common configurations of planetary gears: (a) sun gear is fixed: directions
of rotation of planetary gear and carrier are same, (b) ring gear is fixed: directions of rotation of
planetary gear and carrier are opposite, (c) planetary carrier is fixed, non-planetary operation
(idler). (d) planetary gear is fixed to the carrier (cannot rotate about the carrier axis). Locked
condition. All components rotate as one unit, gear ratio is 1:1.

2. Ring gear is fixed (w = 0.0): sun gear and planetary carrier rotate in the same
4
directions, planetary gear rotates about its own shaft in the opposite direction (Figure
3.26b). This is also called the walking planetary gear condition.
3. Planetary carrier is fixed (w = 0.0): functions as a non-planetary gear. The planetary
2
gear acts as an idler gear. This is called the idling planetary gear condition (Figure
3.26c).
4. The planetary gear is fixed, while the sun, ring, and carrier are allowed to move
(Figure 3.26d). In this condition, all components move as one unit, as if they are
connected to each other with a one-to-one (1 : 1) gear ratio.
5. None of the planetary gear components are fixed (Figure 3.25), two of the components
are used as the input shaft and one of the component outputs is used as the output.
This results in a continuously variable transmission (CVT or also sometimes called
“split torque transmission” (STT), because the torque delivered to the output shaft is
“split” between two input shaft sources).