Published On: Wed, Mar 27th, 2013

✔ How semiautomatic transmission vehicles uses torque converter to replace a clutch.

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As you all know there are various types of transmissions. Basically we can classify the automobile transmissions as:

  1. Manual transmission.
  2. Automatic transmission.
  3. Semi-automatic transmission.

In this topic we will be getting into the details of those semi-automatic transmission vehicles which employ the torque converter. As you are aware, in manual transmission vehicles we use a clutch instead of torque converter.

What is the purpose of a torque converter and clutch?

The purpose of the torque converter and clutch are the same, both are used as a medium to transmit the power from the engine to the transmission. To be more precise, they are used to engage and disengage the engine from the transmission or gear box. Torque converts are used in automatic and semi automatic vehicles where as clutch is used in manual transmission vehicles.

How does a torque converter works?

Above explains the working of a torque converter.

Torque converter explained.

Torque converter explained.

Here we are explaining the working of torque converter in simple language with videos for easy understanding. So as we have mentioned above semiautomatic transmission vehicle employs torque converters. Torque converters are basically fluid couplings. They transmit the power from the engine to the transmission through a hydraulic linkage.

This is the most critical part in a torque converter, how this hydraulic linkage happens?

Stripping a torque converter and explaining its working with video.

Before getting into to that you should know, where is a torque converter is located?

See the figure below, the torque converter is located between the engine and the gear box. It is mounted to the flywheel of the engine.

What are the basic components of a torque converter?

  1. impeller.
  2. Turbine.
  3. Stator.
Turbine and Impellor

Turbine and impeller

impeller: as shown in the figures, the impeller is a part of the casing itself.

Turbine: it’s floating inside the torque converter and is linked to the input shaft of the transmission. This is the power take off unit; the power of the engine is absorbed by the turbine and supplied to the gear box/transmission.

Stator: it’s a one way clutch; its purpose is to reroute, the flow from the impeller to the turbine.

How does a torque converter works?

Torque converter is like a closed unit, as shown in the video; the impeller is a part of the casing in the torque converter. This impeller comes in the opposite side of the engine inside the torque converter. So when the torque converter rotates, the impeller works like a centrifugal pump. Due to the centrifugal force of rotation, the impeller channels the flow to the opposite side towards the turbine. As shown on the video and figures, the turbine is located opposite to the impeller. The flow hits the turbine result it to rotate.

The turbine is connected to the input shaft of the gear box, which is intern connected to the shuttle reverser. Thus the drive from the engine reached the gear box.

Stator, impellor and turbine

Stator, impeller and turbine

The line of power transmission using torque converter:

Engine – Flywheel – impeller of torque converter – turbine of torque converter – input shaft of gear box – shuttle reverser – propeller shaft – differential – axle shaft – rear wheels.

Now the question arises, why do we use the stator?

As shown in the figure and video, the stator is located at the centre portion of both the impeller and turbine. Its function is to redirect the flow coming from the turbine back to the impeller.

What happens if we don’t have

Turbine and stator

Turbine and stator

a stator?

Normal fluid coupling will not have a stator, but torque converters will. Its function is to properly redirect the flow from the turbine to the impeller. If we don’t have a stator, the flow coming from the turbine will hit the impeller in a negative angle there by slo

wing down the impeller and the engine (as impeller is a part of the torque converter casing itself).

So the stator reversed the flow coming from the turbine and allows it to hit the impeller in a positive direction with our slowing down the impeller.

Stator is also called as a one way clutch because it can rotate only on one direction.

What is torque multiplication in a torque converter?

Torque multiplication explained with video

It happens when the torque converted is stalled. That means when the engine is working and the turbine is locked or turbine starting to slow down compared to impeller, torque multiplication happens. When we apply brake while engine is working the turbine is stopped as the shaft connected from the turbine to the shuttle reverser of the gear box is locked. This make the fluid coming from the impeller hits the turbine and again gets redirected by stator to the impeller, which results in the addition of velocity of the fluid flowing. In different cycles this velocity adds up resulting in the accumulation of torque on the turbine this results in torque multiplication (as the same with, when the speed of the turbine is reduced compared to the speed of the impeller the flow will get redirected through the stator to the impeller and again to the turbine this also result in torque multiplication due to velocity addition) So when the brake is released the accumulated torque is carried away by the shaft of the turbine to the transmission. This helps the vehicle to attain a higher speed when it moves from a stop or brake.

What is called stalling of torque converter?

While driving the vehicle and if we apply the brake with the vehicle in gear, the stall happens. Because when we apply brake, the wheels stop, it stops the gear box to rotate and the turbine also stops, buy still the engine and torque converter will rotate. This will result in high heat generation inside the torque converter due to the slippage of fluid through the turbine (as it is stopped) and torque gets store on the turbine, this process is called stall.

Torque converter failures, which can occur:

  • If torque converter is stalled from a larger time the one way clutch of the stator may fail, due to excess heat generation.
  • Leak of torque converter.

turbine stator and impellor of a torque converter is shown torque converter opened

Advantages of using torque converter:

  1. Accidents that can occur due to clutch failures can be avoided.
  2. The discomfort of using clutch pedals can be avoided while driving.
  3. We can apply brake without putting the gears to neutral.
  4. Tortional vibration on engine can be reduced.
  5. Mechanical bonding of engine and transmission is avoided, reducing direct load to engine.

Disadvantages’ of torque converter?

  1. Reduces fuel economy.
  2. Costlier.

Failures that can happen to a torque converter explained with video.

If you have any doubts please feel free to ask through comments.

Comments

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Displaying 5 Comments
Have Your Say
  1. dhinesh says:

    can we increase or decrease the speed using torque convertor??

    • admin says:

      Dear Dhinesh,
      First we would like to thank you for the comment, this is the first comment for the new version of Techtrixinfo.com.

      Your Ans:
      AS the term itself implies,torque converter is used to increase torque (the rotational power)see this video to learn about torque (http://www.youtube.com/watch?v=HVACqGOfyGs)
      we cannot increase the speed using torque converter, the speed of the vehicle depends on the gear ratio selected in the transmission.
      I believe you are clear, if not please fell free to ask a new question we are ready to help you out.

  2. jebin says:

    Thank u..really useful stuff.gud work.

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