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Torque Converter 101 - How a Torque Converter Works

Torque Converter

The torque converter is single-handedly responsible for making the modern automatic transmission an affordable reality for automobile buyers. Chances are, if you are driving a car whose transmission shifts for you, it's being done by a torque converter. Understanding how a torque converter works is critical to dealing with most of the issues that will face a mechanic looking at a faulty automatic transmission.

Three Major Parts

The torque converter itself is the doughnut-shaped "pod" that sits in front of the transmission in its bell housing. Inside, three major components are found: a turbine, a stator, and an impeller.

Looking at a torque converter that's been opened, we'll see the impeller at the engine side. That side of the converter is bolted to the flexplate so that the whole torque converter spins with the engine. As it spins, the impeller's blades act as a pump, pushing the fluid inside the torque converter towards the turbine at the far side. The turbine, which basically a reversed impeller, "catches" that fluid as its thrown towards it and spins, turning the transmission which in turn spins the driveshaft/axles and wheels to move the car.

In between the impeller and turbine is a stator. The stator is a smaller wheel and it controls the fluid flow between the impeller and turbine, creating a vortex which improves the efficiency of the fluid flow pattern. It turns in a direction opposite the impeller and turbine thanks to a one-way clutch on its bearing shaft. At idle, the stator is stationary on its shaft and throws fluid back towards the impeller. This means the impeller turns faster than the turbine.

As the vehicle speeds up, the stator begins to move as the turbine begins to match the impeller's speed. The fluid driving the impeller from the turbine begins to press from the reverse side, reflecting off the rounded housing and to the stator, which begins to spin. The spinning stator continues the fluid dynamics, eventually creating a speed match between the turbine and impeller.

During most of the torque converter's operation, the impeller and turbine spin at different speeds with the stator acting as the "break" between them to keep that dynamic. So long as the impeller spins at a rate faster than the turbine, torque is multiplied, reducing "gearing" between the engine and the wheels.

Common Torque Converter Problems

The most common problems in a torque converter are in the bearings which separate the components. Bearings between the turbine and stator, the stator and the impeller and the impeller and the outer housing.

Another common problem is the stator's clutch, which can bind or break. The former means the stator freezes in place and never spins, the latter means the stator spins all the time. With a frozen clutch, the transmission will likely overheat. With a free-spinning stator, the car will be sluggish and slow.