1.19 Knowing the parts of a vehicle: Automatic transmission system

The automatic transmission is a crucial component of a modern vehicle. It is responsible for transmitting engine power to the wheels, allowing the vehicle to move. In this chapter, we'll explore the major parts of an automatic transmission system and discuss their functions.

Automatic Transmission System Components

The automatic transmission system is made up of several major components, including the torque converter, oil pump, planetary gears, clutches and bands, valve body, and servo.

1. Torque Converter

The torque converter is the link between the engine and transmission. It uses a hydraulic fluid to transfer power from the engine to the transmission. The torque converter also allows the vehicle to stop in gear without shutting down the engine.

2. Oil Pump

The oil pump is responsible for pressurizing the transmission fluid. This fluid is used to lubricate the internals of the transmission, provide pressure to the clutches and bands, and help cool the transmission.

3. Planetary Gears

The planetary gears are the part of the transmission that actually changes gears. They are called "planetary" because they have a configuration similar to the solar system, with a central gear (the "sun") surrounded by several smaller gears (the "planets").

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4. Clutches and Bands

The clutches and bands in the transmission are used to control which planetary gears are active at any given time. When a clutch or band is engaged, it locks one of the planetary gears, changing the transmission ratio.

5. Valve Body

The valve body is the "brain" of the automatic transmission. It controls the flow of transmission fluid to the various clutches and bands, determining which gear the vehicle should be in. The valve body is controlled by a series of electrical solenoids which are activated by the vehicle's computer.

6. Servant

The servo is a hydraulic device that applies the necessary force to drive the bands in the transmission. There are usually several servos in an automatic transmission, each responsible for driving a specific band.

Operation of the Automatic Transmission System

The automatic transmission works in a rather complex way. When the vehicle is in gear, the torque converter transfers power from the engine to the transmission. The oil pump pressurizes transmission fluid, which is then routed through the valve body to engage the appropriate clutches and bands. This blocks the correct planetary gears, changing the gear ratio and therefore the vehicle's gear.

Knowing the parts of a vehicle and how they work is essential for proper maintenance. In the next chapter, we'll discuss how to maintain the automatic transmission system to ensure your vehicle continues to run smoothly.