How does torque converter function in an automatic transmission?

The function of a torque converter in an automatic transmission is to facilitate smooth gear shifting by allowing the engine to remain engaged with the transmission while providing the ability to change gears without the need for a manual clutch. This component operates using hydraulic fluid and enables the automatic transmission to smoothly transition between different gear ratios as the vehicle accelerates or decelerates. The torque converter also allows for a degree of slip between the engine and transmission, which contributes to fluid coupling and helps in enhancing drivability.

While other options mention important functionalities regarding vehicle operation, they do not capture the primary role of engaging and disengaging the engine with the transmission for automatic gear shifting. This characteristic is essential for the convenience and efficiency of operating an automatic vehicle, avoiding the complexities of manual clutch operation.