In most automatic transmissions, the type of gear set used is the planetary (epicyclic) gearset.
Understanding the Planetary Gearset in Automatic Transmissions
The core mechanism responsible for changing gear ratios in the most common types of automatic transmissions is the planetary gearset. Unlike the manual transmission's arrangement of gears on parallel shafts, the planetary gearset uses a more compact and versatile design.
How it Works
A basic planetary gearset consists of three main components:
- Sun Gear: Located at the center.
- Planet Gears: Several gears that orbit the sun gear, typically mounted on a carrier.
- Ring Gear: An outer gear with internal teeth that meshes with the planet gears.
By holding one component stationary and driving another, the third component provides an output, resulting in different gear ratios (forward, reverse, or neutral). This configuration allows for multiple gear ratios within a single compact unit.
Why Planetary Gearsets Are Preferred
Planetary gearsets offer several advantages that make them ideal for automatic transmissions:
- Compactness: They are highly efficient in space utilization.
- Multiple Ratios: A single set can provide various gear ratios.
- Smooth Shifting: Transitions between gears can be managed smoothly, especially with hydraulic control.
- Torque Multiplication: They effectively multiply torque.
According to the provided reference: "The most common type of automatic transmission is the hydraulic automatic, which uses a planetary (epicyclic) gearset, hydraulic controls, and a torque converter." This highlights the fundamental role of the planetary gearset in these prevalent transmission types.
Common Automatic Transmission Types Using Planetary Gears
The primary type is the traditional hydraulic automatic transmission, which relies on a complex system involving:
- Planetary Gearsets: Providing the different gear ratios.
- Hydraulic Controls: Using fluid pressure to engage and disengage components (via clutches and bands) to select gear ratios.
- Torque Converter: A fluid coupling that transmits engine power to the transmission and allows the engine to idle while the vehicle is stopped in gear.
While other automatic transmission technologies exist (like continuously variable transmissions - CVTs or dual-clutch transmissions - DCTs), the hydraulic automatic with its planetary gearsets remains widespread.
