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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