Principles Of Function, Planetary Gear
X = locked
| 1. Rear planetary train (Ravigneaux) | 6. Input shaft |
| 2. Front planetary train | 7. Driven gear |
| 3. Planetary gear | 8. Oil pump |
| 4. Sun gear | 9. Differential |
| 5. Ring gear | 10. Driven counter rotating gear |
The TG-81SC gearbox has two planetary gear sets, of which the front is a Lepelletier planetary train and the rear is a Ravigneaux planetary train. This results in a compact gearbox with relatively small external dimensions.
A Lepelletier planetary train is characterized by two sets of planet gears. A Ravigneaux planetary train is characterized by means of it having two sun gears and two sets of planet gears.
The gear ratios of the planetary gears are controlled by four clutches (C1, C2, C3, C4) and two brakes (B1, B2).
The number of planetary gears depends on the engine's cylinder displacement and can therefore differ from what is shown here.
Clutches, brakes and freewheel
| Component | Function |
| Clutch C1 | Connects the front planetary gear carrier with the rear planetary train's small sun gear. |
| Clutch C2 | Connects the input shaft with the rear planetary gear carrier. |
| Clutch C3 | Connects the front planetary gear carrier with the rear planetary train's large sun gear. |
| Clutch C4 | Locks the front planetary gear carrier with the rear planetary gear's large sun gear |
| Brake B1 | Locks the rear planetary train's large sun gear. |
| Brake B2 | Locks the rear planetary train's planetary gear carrier. |
| Freewheel F1 | Locks the rear planetary gear carrier so that it does not go counter-clockwise. |
Planetary train, Ravigneaux
| 1. Large sun gear | 4. Inner planetary gear |
| 2. Small sun gear | 5. Ring gear |
| 3. Outer planetary gear | 6. Planetary wheel carrier |
The characteristic of a Ravigneaux planetary train is that several gears can be used in comparison to a conventional planetary train. It is compact (takes up little room) in relation to the number of possible ratios. The Ravigneaux planetary train has two sun gears of different diameters and two sets of planetary gears, an inner and outer set. The inner planetary gears are in constant mesh with the outer planetary gears and the small sun gear. The outer planetary gears are in constant mesh with the ring gear and large sun gear.
The planetary train has a common planetary gear carrier for both sets of planetary gears.
| 1. Small sun gear | 4. Outer planetary gear |
| 2. Large sun gear | 5. Ring gear |
| 3. Inner planetary gear | 6. Planetary wheel carrier |
The ratios are obtained through different combinations of locked and/or connected components. The table displays the principle for how the ratios are obtained from large ratio, 1, to small ratio, 8, and counter rotation (i.e. reverse with large ratio).
| Combination | Power in | Locked | Power out |
| 1 | Small sun gear, Inner planetary gear, Outer planetary gear | Planetary gear carrier | Ring gear |
| 2 | Small sun gear, Inner planetary gear, Outer planetary gear, Planetary gear carrier | Large sun gear | Ring gear |
| 3 | Small sun gear and large sun gear, Ring gear, Planetary gear carrier | Inner planetary gear, Outer planetary gear | Ring gear |
| 4 | Small sun gear, Large sun gear, Inner planetary gear, Outer planetary gear, Planetary gear carrier | No component | Ring gear |
| 5 | The small sun gear, Inner planetary gear, Outer planetary gear, The planetary gear carrier | No component | Ring gear |
| 6 | Large sun gear, Outer planetary gear, The planetary gear carrier | Large sun gear | Ring gear |
| 7 | Large sun gear, Outer planetary gear, Planetary gear carrier | No component | Ring gear |
| 8 | Outer planetary gear, Planetary gear carrier | Large sun gear | Ring gear |
| Reverse | Large sun gear, Outer planetary gear | Planetary gear carrier | Ring gear |