Facts

• A torque converter resembles a big doughnut
  
  The torque converter is a fluid coupling that connects and disconnects the engine and the transmission. Seating inside the converter housing between the engine and the automatic transmission, it has the form of a big doughnut, about a foot and a half in diameter and six inches wide. Imagine two fans facing each other inside this doughnut: an impeller and a turbine. As the engine rotates the impeller at great speeds, it causes the oil inside to whirl at high speed, spinning the turbine in front at great speed as well. A stator, a smaller fan rotating along with the impeller, helps to improve oil circulation. And once the transmission connects to the turbine through a connecting shaft, power from the engine is transferred to the transmission.
  
  

Identification

• A converter impeller and stator
  
  A typical torque converter is made out of four parts: an impeller, a turbine, a stator (a smaller fan) and housing. All three components-impeller, turbine and stator-have curved fan blades. The housing, commonly made of two pieces of steel welded together, serves not only as a protective cover for the fans but also as a seal container for the transmission oil.
  
  

Function

• The torque converter has the same function as the clutch in a manual transmission, but uses fluid to transmit power instead of friction. When you start the engine and have the transmission in "Park" or "Neutral," the turbine inside the converter remains uncoupled to the transmission, but the impeller inside is rotating slowly. Once you shift the transmission to "Drive," "Reverse," "First" or "Second" gear, the torque converter couples to the engine through the transmission input shaft. And as the engine accelerates, the crankshaft inside the engine, the converter, impeller and oil begin to spin much faster. Now the oil has the force to rotate the turbine, transmitting this power to the transmission internal drive members and gear sets.
  
  

Features

• Filled with automatic transmission oil, a torque converter becomes very heavy. This weight allows it to function as a flywheel in a manual transmission. As a flywheel, the torque converter smooths out engine pulses as it rotates at high speeds. The inertia caused by the torque converter overcomes much of the vibration that otherwise might be transferred to the transmission and the drive-line connected to the wheel assemblies of the vehicle.
  
  

Types

• However, a torque converter is not perfect. That is why some converters come equipped with a pressure plate assembly, commonly called lockup torque converter. The pressure plate allows the impeller to lock on to the turbine during high-speed acceleration. This mechanism eliminates any amount of slippage between the impeller and turbine found in conventional converters when the transmission is in high gear. The result is an increase in fuel economy.