Free Tips on Torque Converter Operation

The torque converter is one of the least understood components in an automatic transmission equipped vehicle. I will attempt to explain what it does and how it does it.
The torque converter has a few different functions.
We first need to understand that there is no direct link between the crankshaft and the transmission input shaft (except in the case of a lock up style converter, but we'll talk about that later). This means that the first function of the converter is to connect the crankshaft and the input shaft so the engine can move the vehicle; this is accomplished through the utilization of a fluidic coupling effect.
The torque converter also replaces the clutch that is required in a manual transmission; this is how an automatic transmission vehicle can come to a stop while still being in gear without stalling the engine.

The torque converter also acts as a torque multiplier, or extra gear ratio, to help the car get moving from a stop. In modern day converters this theoretical ratio is anywhere between 2:1 and 3:1.
Torque converters consist of 4 major components that we need to concern ourselves with for the purpose of explanation.
The first component, which is the driving member, is called the impeller or "pump". It is connected directly to the inside of the converter housing and because the converter is bolted to the flexplate, it is turning anytime that the engine rotates.
The next component, which is the output or driven member, is called the turbine. The transmission's input shaft is splined to it. The turbine is not physically connected to the to the converter housing and can rotate completely independently of it.
The third component is the stator assembly; its function is to redirect the flow of fluid between the impeller and the turbine, which gives the torque multiplication effect from a standstill.
The final component is the lock up clutch. At highway speeds this clutch can be applied and will provide a direct mechanical link between the crankshaft and input shaft, which will result in 100% efficiency between the engine and transmission. The application of this clutch is usually controlled by the vehicle's computer activating a solenoid in the transmission.
Here's how it all works. For the sake of simplicity, I will use the common analogy of two fans which represent the impeller and the turbine. Let's say that we have two fans facing each other and we turn only one of them on- the other fan will soon begin to move.