When an automatic transmission enters lockup, a solenoid-operated clutch mechanism engages, physically connecting the turbine and impeller of the torque converter. This locks the two components together, eliminating the relative motion and fluid circulation within the converter. By eliminating the slipping action, lockup reduces fluid heating and improves transmission efficiency, resulting in better fuel economy and reduced wear on transmission components.
Engine lockup typically occurs at higher vehicle speeds, usually above 40-50 mph (64-80 km/h), when the engine has sufficient torque to propel the vehicle without relying on the torque multiplication effect of the torque converter. However, the specific lockup speed may vary depending on factors such as engine power, vehicle weight, transmission design, and throttle position.
Lockup also plays a role in preventing overheating of the automatic transmission. Under heavy load conditions or while climbing steep grades, the torque converter can generate excessive heat due to the increased fluid circulation and slipping. By engaging lockup, the mechanical connection between the engine and transmission reduces heat buildup, preventing potential transmission damage.
However, engine lockup is not always engaged. Under some circumstances, such as during acceleration, downshifting, or when the vehicle speed drops below a certain threshold, the transmission may disengage lockup for optimal performance and driver comfort.
