Torque converters are sealed units; their innards rarely see the light of day, and when they do, they’re still pretty hard to figure out!
Imagine you have two fans facing each other. Turn one fan on, and it will blow air over the blades of the second fan, causing it to spin. But if you hold the second fan still, the first fan will keep right on spinning.
That’s exactly how a torque converter works. One “fan,” called the impeller, is connected to the engine (together with the front cover, it forms the outer shell of the converter). The other fan, the turbine, is connected to the transmission input shaft. Unless the transmission is in neutral or park, any motion of the turbine will move the vehicle.
Instead of using air, the torque converter uses a liquid medium, which cannot be compressed – oil, otherwise known as transmission fluid. Automatic transmission cars use a torque converter. This article will discuss why automatic transmission cars need a torque converter and how a torque converter works.
The torque converter in an automatic transmission serves the same purpose as the clutch in a manual transmission.
The engine needs to be connected to the rear wheels so the vehicle will move, and disconnected so the engine can continue to run when the vehicle is stopped. One way to do this is to use a device that physically connects and disconnects the engine and the transmission – a clutch. Another method is to use some type of fluid coupling, such as a torque converter, which is located between the engine and the transmission.
There are three components inside the very strong housing of the torque converter which work together to transmit power to the transmission:
The pump inside a torque converter is a type of centrifugal pump. As it spins, fluid is flung to the outside, much as the spin cycle of a washing machine flings water and clothes to the outside of the wash tub. As fluid is flung to the outside, a vacuum is created that draws more fluid in at the center.
The fluid then enters the blades of the turbine, which is connected to the transmission (the spline in the middle is where it connects to the transmission.) The turbine causes the transmission to spin, which basically moves your car. The blades of the turbine are curved so that the fluid, which enters the turbine from the outside, has to change direction before it exits the center of the turbine. It is this directional change that causes the turbine to spin.
As the turbine causes the fluid to change direction, the fluid causes the turbine to spin.
The fluid exits the turbine at the center, moving in a different direction than when it entered. The fluid exits the turbine moving opposite the direction that the pump (and engine) are turning. If the fluid were allowed to hit the pump, it would slow the engine down, wasting power. This is why a torque converter has a stator.
The stator resides in the very center of the torque converter. Its job is to redirect the fluid returning from the turbine before it hits the pump again. This dramatically increases the efficiency of the torque converter.
In brief, the torque converter is a type of fluid coupling, which allows the engine to spin somewhat independently of the transmission. It is responsible for pressurizing automatic transmission fluid, a pressurization that supplies the force necessary to shift transmission gears.
A worn or dysfunctional torque converter can prevent transmission fluid from being properly pressurized, which in turn negatively impacts transmission gear function and operation. A systematic checkup by a professional is the best way to isolate the cause of the operating problems and recommend the most effective solution.
If properly tuned, this complex device can have a tremendous impact on your vehicle’s performance, economy and durability, and turn your automatic into a powerhouse!