Automatic Transmission Torque Converters
Transmissions have always been complex systems, and they get more sophisticated every year. With the introduction of new technologies, such as CVT’s, dual-clutch, and semi-automatic – and transmissions with up to 10 gears – modern cars overall become more complicated. One thing that remains consistent is the torque converter. Its purpose is straightforward – transfer power, or torque, from the engine to the transmission.
Cars with automatic transmissions don’t have clutches, so they need a way to let the engine keep turning while the wheels and gears in the transmission come to a stop. Manual transmission cars use a clutch that disconnects the engine from the transmission. Automatic transmissions use a torque converter. A torque converter is a coupling that relies on a fluid hydrodynamic to allow the engine to spin independently of the transmission. When the engine is idling, such as at a stop light, the amount of torque going through the torque converter is small, but still enough to require some pressure on the brake pedal to stop the car from creeping. When you release the brake and step on the gas, the engine speeds up and pumps more fluid into the torque converter, causing more power (torque) to be transmitted to the wheels.
Getting the Power from Engine to Transmission
Inside the torque converter are three main parts. The first part of the assembly is called the impeller, also known as the pump. It is filled with fluid and it spins with the engine crankshaft. The faster it spins, the more force is created as the fluid flows through it faster and harder.
The impeller forces the fluid into another assembly of blades called the turbine. The turbine sits opposite the impeller and rotates as the fluid from the impeller hits its blades. As the fluid flows through the turbine, it is repeatedly transferred from the outer part to the inner part of the turbine, and returned to the impeller. This constant circulation of fluid flow from impeller into turbine, then back to impeller, creates a fluid coupling.
As the transmission fluid returns to the impeller to keep the cycle going is where the torque is created. At this point the fluid is flowing in a different direction than it was originally as it came out of the impeller. It has to be reversed, which slows the fluid and magnifies torque. This is where the stator comes in. The stator is another series of fins located between the two turbines on the transmission shaft. Its blades are angled so that when the transmission fluid flows into them, it reverses direction and gets channeled back to the impeller. When the vehicle stops, the stator’s one-way “clutch” causes it to stop spinning, which breaks the hydrodynamic circuit.
3 Phases of Operation
The engine provides power to the impeller, but the impeller doesn’t rotate because the driver keeps pressure on the brake, such as when at a stop light. The vehicle does not move, but it does not stall.
Acceleration occurs when the driver releases the brake and steps on the gas pedal. The impeller rotates faster, and there is a large difference between the impeller and turbine speed. The converter produces torque multiplication, which is necessary for acceleration.
As the vehicle approaches cruising speed, the turbine rotates at nearly the same rate as the impeller, and torque multiplication ceases. At this stage, the torque converter is a simple fluid coupling. The automatic transmission uses a lockup clutch to lock the turbine to the impeller. This eliminates power loss and keeps the car moving steadily. Because the impeller is mounted to the torque converter housing, and the converter is connected to the engine, the impeller gets its power from the engine. The turbine is connected to the output shaft, which sends power to the transmission.
Is the Problem the Torque Converter or Transmission?
Torque converter problems can be misinterpreted as symptoms of a failing transmission. Unfortunately, this might lead people to think they need expensive repairs, or even a full transmission replacement. Replacing the torque converter is cheaper. Diagnosing the cause of a transmission issue isn’t easy, but AAMCO Minnesota’s local technicians can help. It might just be a fluid leak, or something else altogether – our transmission inspection and diagnostics help us find the problems and recommend the right services.
Shaking and Shuddering
If your car shakes and shudders, it could mean the lockup clutch is malfunctioning. This might occur at speeds around 35-45 miles per hour. It’s a very noticeable problem and feels like you’re driving on a rough road with a lot of small bumps. A worn out lockup clutch can make the transition from acceleration to direct drive difficult, and it’s a sign that you need to have your transmission checked.
I your car overheats, it could be a sign that the transmission fluid pressure is low, and there could be a problem with the torque converter. If the converter is overheating, it won’t be able to transfer power from the engine to the transmission. This results in poor acceleration and excessive wear and tear on the transmission.
A damaged fin or bearing in the torque converter can cause hesitation in the transmission shifting, or the transmission to slip out of gear entirely. This is because the engine torque is not being efficiently converted into the hydraulic pressure needed to shift gears within the transmission. Slipping might also be caused by insufficient or too much fluid in the transmission.
You need an experienced transmission specialist who can honestly tell you what needs to be done.
If you have questions about your car’s transmission, engine, repair or maintenance needs, AAMCO Minnesota can help. Stop by or call a local AAMCO Minnesota repair shop for a Multi Point Vehicle Courtesy Check for your transmission and related systems. We’ll winterize your car and get you ready for the cold, snowy winter driving months ahead. We can handle all your scheduled car maintenance and repairs, from brakes to factory recommended maintenance.
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