How Does an Automatic Transmission Work?

An automatic transmission can seem like magic. Also known as auto or self-shifting, the automatic transmission doesn’t require you to shift gears manually in order for them to change. It happens as you drive. The automatic transmission uses a combination of fluid, mechanical, and electrical engineering. Here is an overview of how an automatic transmission works.

What is a transmission?

A transmission is what allows a car move into different gears. Without a transmission, your car would be stuck in one gear regardless of the speed and power required to move your vehicle. If you’re driving up a steep hill, your car’s needs are different from if you’re in rush-hour traffic in the city. Basically the automatic transmission helps your engine spin at an optimal rate for the driving conditions and all you have to do is press the brake or gas pedal.

Parts of the Automatic Transmission

Parts of the automatic transmission include: a torque converter, oil pump, band breaks, planetary gear set, clutch packs, valve body, output shaft, and hydraulic system.

The torque converter is what stops your car from moving when you turn on the engine. It connects and disconnects power from the engine and is found between the engine and the transmission. Once you put the transmission into drive and your car is moving, the rest is automatic.

The planetary gear set is the heart of the automatic transmission. It’s what allows you to reverse and achieve five levels of forward drive. This one set of gears produces all the gear ratios. The planetary gear set is made up of three components: the sun gear, the planet gear, and the ring gear.

The band breaks are responsible for gears in the planetary gear set to be tight or loose allowing them to spin at different speeds.

The valve body can be considered the brain of the automatic transmission. The different valve passages direct different pressures of transmission fluid to different areas. Depending on how much pressure you put on the gas pedal will determine where the transmission fluid goes in the valve body. The clutch pack is then activated and will smoothly shift the transmission into a different gear.

Transmission (or hydraulic) fluid acts as a coolant and lubricant within the transmission system and helps to prevent corrosion. It transmits power from the engine to the transmission. Its role is important in the automatic transmission.

How an Automatic Transmission Works

When you turn on your car, the engine is on, but the car doesn’t move. When you step on the gas, the torque converter pump spins faster, sending transmission fluid toward the turbine. This fluid force is what turns the wheels. The operation of automatic transmission is all about transmitting different rotation speeds into the ring and sun gears. By holding the planet carrier, sun, or ring steady, a different gear ratio is achieved.

As you can see, the automatic transmission involves a lot of parts and movements to work. As complicated as it all seems, it’s hard to deny that it’s an impressive system!