Manual Transmission
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| Illustration 1 | g01085657 |
In a manual transmission, power is transferred through the gears on the shafts by sliding the gears so the gears mesh. Power is transferred by using a collar to hold the driven gears to the shafts. Combinations of levers, shafts, and/or cables control the shifting forks that physically move the gears or the collars. In most cases, a flywheel clutch is used to interrupt the flow of power during the shift.
The power shift transmission is a train of gears that can be shifted without interrupting the flow of power. Instead of physically sliding a gear or a collar, hydraulically activated clutches control the flow of power. In a power shift transmission, the gears are constantly in mesh.
The major advantage of a power shift transmission is quicker response when the operator shifts from one gear to another. This allows a quick change of speeds. Power shift transmissions may be shifted under loads with no loss of productivity.
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| Illustration 2 | g01085658 |
A hydraulic clutch consists of a clutch pack (discs and plates) and a clutch piston. The clutch is engaged when pressurized oil pushes the clutch piston against the discs and plates. When the discs and plates are pushed together, friction allows power to flow through them. Discs are connected to one component. Plates are connected to another component. Power is transmitted from one of the components through the clutch pack to the other component.
The power shift transmission uses internal oil pressure to engage hydraulic clutches. When the operator selects a gear position, hydraulic oil engages the clutches that route power to the selected gears. Each combination of clutches results in a different gear ratio and a different speed.
When a clutch is no longer needed, oil flow stops and the clutch is released. Spring force moves the clutch piston away from the discs and the plates, this allows the held component to spin freely. Power flow through that clutch stops.
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| Illustration 3 | g01085661 |
The gear train transfers the power from the engine through a train of gears to the drive wheels. The most common types of power shift transmission gear trains are the countershaft transmission (Illustration 3, right diagram) and the planetary transmission (left diagram).