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How Does a Torque Converter Works? Pros & Cons [PDF]

In this article, you learn what is torque converter and how it work? with its advantages and applications of Torque Converter.

Download the PDF file at the bottom of this article.

What is a Torque Converter?

A torque converter is a device that performs a function similar to that of a gearbox, that is, to increase the torque while reducing the speed. But whereas gearbox provides only a small number of fixed ratio, the torque converter provides a continuous variation of ratio from the lowest to the highest.

A torque converter is designed to obtain a mechanical advantage or gear ratio by hydraulic means in the same manner as gears do by mechanical means. It provides a maximum gear ratio starting from rest and gradually decreases that ratio as the vehicle gains speed.

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Construction of Torque Converter

The construction of torque converter is similar to that of fluid coupling, the only difference is that it has an additional stationary member called the reaction member. Thus, a torque converter consists of three principle member, instead of two, these are:

Construction of Torque Converter.
  1. Driving member or impeller or pump, which is connected to the engine.
  2. Driving member or rotor or turbine, which is connected to the propeller shaft.
  3. Stationary member or reaction member or stator, which is fixed to the frame. It is a member which makes it possible to obtain a change of torque between input and output shafts. The fluid coupling does not have this member and cannot produce any change of torque.
  4. The stator is mounted on a freewheeling one-way clutch so that it can turn in only one direction. A stationary shaft, called the reaction shaft, extends from the geared transmission in back of the converter through the pump to support the stator.

The driven member (turbine) faces the stator and is splined to the input shaft which rotates inside the reaction shaft and connects curve blades to project most of the oil into a hollow cylinder parallel to the axis of rotation.

The turbine is driven by the stream of oil sent to it the pump. The oil enters the blade section near the rim and passes through the blades. The entire assembly is contained and linked to the engine flywheel.

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Working of Torque Converter

When the engine is running idle, the pump produces a slow of oil, as the engine drives it. This slow circulation of oil is not sufficient to move the turbine.

When the throttle is opened wide, the engine speed increases and the pump moves faster projecting the oil toward the turbine. But the oil is still having less force which is insufficient to turn the turbine. Therefore the oil returns back to the pump. With almost no loss of velocity, except that due to friction.

Torque Converter Working Principle.

The net effect of the redirection of flow is to increase pump output. The pump output under these conditions is the output velocity that it is creating because of the engine torque, plus the velocity of the redirected oil.

A built-up output velocity of two to three times the output velocity due to the engine alone is achieved when the turbine to three stationary.

This makes the turning force of the turbine to three times that of the engine. The increased torque of the turbine enables it to rotate, and thus drives the input shaft, which in turn transmits the power to a geared section of the transmission.

Checkout video on how torque converter work?

Whereas the fluid coupling transmits the same torque as given to it by the engine, the torque converter increases the torque in the ratio of about 2:1 to 3:1. Thus, it serves the same purpose as that of a gearbox but in a better way.

In a gearbox, the torque variation is only in a finite number of steps, but in a torque converter, the torque variation is continuous. However, the efficiency of a torque converter is high only within narrow limits of speed.

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Torque Converter as a Fluid Coupling

The figure shows a simplified diagram of the single-stage three element torque converter. The three element – impeller, stator and turbine are clearly shown. Other designs have more element and additional stages to improve efficiency over a wide range.

A torque converter is a type of fluid coupling that uses a fluid to transmit torque from one shaft to another. The Converter has a stator, However, at higher speed, the torque converter works as a fluid coupling, giving the gear ratio 1:1.

Torque Converter as a Fluid Coupling

When the vehicle speed increases from slow to high, the need for mechanical advantages, decreases and the gear ratio of the torque converter gradually changes to that of a fluid coupling. It is so because the turbine speed gradually approaches the pump speed.

This reduces the vortex flow so that less oil is sent back to the pump by the turbine and stator. When the turbine speed reaches a point where the oil flow to the stator is no longer reflected, the stator starts to move with the rotating oil. This is the fluid coupling stage where the gear ratio becomes  1:1.

This action depends upon the throttle opening and vehicle load. At light throttle and steady load, the gear ratio may approach 1:1 at low speed. The torque converter automobile provides the effect of gear ratio as the need arises.

Such a condition as hill climbing or rapid acceleration produces the change. In descending steep grades, the torque converter is as effective as a fluid coupling in transmitting torque to produce engine braking.

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  1. It allows your vehicle to complete stop without stalling the engine.
  2. It makes driving easier.
  3. Torque converter gives more torque to your car when you accelerate out of the stop.
  4. Torque converter removes the clutch and produces the maximum torque compared to a vehicle equipped with a clutch.
  5. Modern torque converters increase the torque of the engine by two or three times.


  1. It has high efficiency within a narrow range of speeds.
  2. It also has high fuel consumption, which depends on the speed of engine rotation.
  3. These are quite expensive to maintain.
  4. They are likely to have a cavity, hence it is also a drawback.
  5. They require more fluid to be replaced from time to time.

Closing It Up

That’s it thanks for reading. So now, we hope that we have cleared all your doubts about Torque Converter. If you still have any doubts about the “Torque Converter Working” you can contact us or ask in the comments. If you like our article, then please share it with your friends.

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About Saif M

Saif M. is a Mechanical Engineer by profession. He completed his engineering studies in 2014 and is currently working in a large firm as Mechanical Engineer. He is also an author and editor at www.theengineerspost.com

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