What is the primary function of the torque converter in an automatic transmission?

The primary function of the torque converter in an automatic transmission is to multiply engine torque. It serves as a crucial component that connects the engine to the transmission, allowing the vehicle to move more smoothly and efficiently. When the engine generates power, the torque converter amplifies the torque created by the engine before it is transmitted to the transmission. This is particularly beneficial during situations where more power is needed, such as when accelerating from a stop or climbing a hill.

The torque converter also employs a fluid coupling mechanism that helps to prevent stalling by allowing the engine to continue running while the vehicle is stationary. By multiplying the torque, it enables the vehicle to achieve better performance without needing to engage a manual clutch, making it a key element in the functionality of an automatic transmission.

The other options address important aspects of the automatic transmission but don’t define the primary role of the torque converter. While cooling the transmission is necessary for its longevity, and fluid pressure is vital for various transmission functions, these are secondary roles compared to the torque multiplication that directly impacts the vehicle's acceleration and performance. Changing gears automatically is also a function of the transmission as a whole rather than specifically of the torque converter.