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Torque Converter, How does it work ?

Most of us enjoy the smooth and effortless feeling of driving in an automatic transmission car

The driving is effortless because you don't need to worry about gear changing, and you don't have a clutch pedal to operate in

An automatic transmission car the work of the clutch pedal is automatically done by a hidden component

Which is truly an engineering marvel the torque converter.

The torque converter can even multiply the torque. Let's see how this purely mechanical device performs its tasks

Assume you are driving along smoothly, and you have to apply the brakes

When you press the brake pedal the vehicles drive wheels stop turning

This means that the drive shaft and the Associated transmission should also stop spinning

But here comes the issue by applying the brakes you are not stopping the engine

So at the time of braking if the engine and transmission are mechanically connected

This would lead to a serious mechanical failure or the engine will stall

You need a motion isolator for this purpose. this motion isolator is the torque converter?

The torque converter is able to efficiently isolate the engine rotation from the transmission at the time of braking

In normal driving conditions it transfers the engine rotation and power to the transmission

Let's see how it works

This is a really simplified torque converter. It is basically a pump and a turbine immersed in transmission liquid

The pump is directly connected to the engine so it always turns at the engine speed

The liquid surrounding the pump will be pushed outwards due to the centrifugal force and it's pressure increases

The rotation of the pump adds a swirl to the liquid leaving the pump

The turbine sits near to the pump and the high energy fluid coming out of the pump turns the turbine

The turbine is connected to the transmission

This way the engine power is transferred to the transmission via the transmission fluid?

More specifically this configuration is known as a fluid flywheel

When we introduce a component called a reactor between the turbine and pump it becomes a torque converter

One of the main duties of the reactor is to send the fluid from the turbine back to the pump efficiently

We will discuss more functions of the reactor later

With this configuration even if the transmission comes to a sudden halt it will not affect the engine rotation

Slippage between the pump and turbine is allowed here since they are connected by the fluid

During normal operation the pump will be able to transfer motion and power to the turbine

It should be noted that the turbine turns at slightly lower rpm than the pump due to energy loss in the fluid

This is a simplified torque converter

But you will never find this kind of configuration in any actual torque converter

The pump and turbine of an actual torque converter is shown here

In an actual torque converter the pump sits near to the transmission

And the turbine sits near to the engine

Let's give proper colors to the components for better understanding

Rotation from the engine is transmitted to the pump with the help of a cover

The turbine output Rotation is transmitted to the transmission using a central shaft

However, why is this arrangement made more complex than the previous case

the answer for this comes from mechanical rather than fluid mechanics

For the efficient operation of a torque converter the pump and turbine should both rotate in line with the crankshaft centerline

The pump is directly connected to the engine crankshaft, so that will always be centered

However, the turbine is independent of this unit

this means that a bearing has to be used between the turbine and the crankshaft

as Illustrated

in order to make sure the turbine is also centered to the crankshaft

In the current configuration one can achieve this quite easily however in the previous configuration

This is very difficult since the turbine is far away from the crankshaft

Now you might be wondering why this device which isolates motion is named as a torque converter

This is because one of the most important functions of this device is to multiply the torque as the vehicle starts to move

Let's see how the torque converter does this

The reactor is connected to a stationary shaft via a one-way clutch this means the reactor will be able to turn in one direction

But not In the opposite

For ease of understanding let's increase the spacing between the components

Now consider the situation as the vehicle starts here the pump is spinning at the engine speed

But the turbine speed is lower and is slowly increasing

This means that the fluid which leaves the turbine travels almost axially as shown

This fluid when it hits the reactor blades will try to spin the reactor as shown

But the one-way clutch in the reactor prevents this motion

So what happens is that the fluid will be diverted in the same direction as the pumps rotation due to the stationary reactor as shown?

In short the pump which adds swirl to the flow receives an already swirled fluid

This makes the work of the pump easier and a greater pressure addition happens across the pump

this highly pressurized fluid generates an amplified torque at the turbine and thus the

transmission and the vehicle receives a greater level of torque as the vehicle starts to move

However as the turbine speed increases

The fluid leaving the turbine becomes more inclined as shown

and at one point of time

the inclined flow hits the other side of the reactor blades

The reactor is free to spin in this direction

so the reactor spins in the same direction as the pump and the turbine

You can see that the swirl generation of the pump Inlet is lesser than the previous case

And the torque multiplication ceases

Here the turbine will be rotating at almost 90 percent of the pump speed

This is a brilliant design

As the vehicle starts to move when the driver needs maximum torque

The Torque converter Multiplies the torque

when the turbine attains a threshold speed

the torque multiplication automatically ceases

Thus the reactor plays a crucial role at the vehicle start?

But without the reactor the torque converter will not perform well even in normal operation

Let's see why

You might have noticed that the blades of the turbine are curved

They are curved almost 90 degrees to absorb maximum energy from the fluid

This means the turbine blades will always force the fluid to leave in a direction opposite to the rotation of pump and turbine

due to this even at hide turbine speed the fluid swirl at the turbine outlet will be minimum

If we do not use a reactor this very low swirl will affect the performance of the pump and the whole torque converter very badly

With the introduction of reactor the flow gets diverted again, and the pump receives the fluid with improved swirl

Even in normal operation you will find that the turbine turns slower than the pump in a torque converter

This is due to energy loss within the coupling fluid

To eliminate such energy losses modern torque converters use a lock-up clutch

By activating this clutch during the normal operation

The turbine will be mechanically locked with the pump unit and they will turn at the same speed

This eliminates energy loss due to the fluid friction

Before winding up the video, let's summarize the uses of this brilliant mechanical device

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