Why Automatic Transmission is USELESS without Torque Converter

Introduction to Torque Converter

From previous post, we know that engine needs connect to transmission in order to turn the wheels. Now, since you are much knowledgeable, for me to state that might even sound ridiculous.

Anyways, we need a connector between the two parts. Why do we need a connector? Why don't we just glue the crank shaft from engine to input shaft that connects to transmission?

This post will cover

• What is torque converter and what does it do?
• The components and structure
• How it works

Let's get on to it.

Going back to the question thrown in the introduction, when your engine is running but when you want to halt, meaning wheels need to cease at a point, what would happen if the shafts from engine and transmission are just glued together? Either your wheels never stop or things are going to break apart. That's why we need torque converter for automatic transmission.

Torque converter is what connects engine and transmission. Energy from engine needs to be transferred to transmission so that in the end wheel rotates, hence movement of vehicle. (I know, I said it 10X already! It's THAT important!!) For manual transmission, there is clutch that plays the same role of connecting engine and transmission.

Again, in other words, your wheels won't rotate without torque converter.

Torque converter consists of impeller, turbine, stator, and housing that covers up the components. Impeller and turbine faces each other and moves in the same direction when vehicle is in motion.

Impeller - As engine runs, crank shaft rotates, and impeller receives the rotational energy from the crank shaft, thus rotates as well.

Turbine - Turbine connects to input shaft which exerts torque on transmission gears.

Stator - This is the key part as it acts to multiply torque to impeller by directing fluid in a certain way, exerting more torque on the impeller.

Housing - The housing that covers the components is also filled with fluid. This fluid is the medium that rotates turbine. It travels back and forth between the impeller and the turbine.

How a torque converter works is very easy.

As engine rotates, your impeller rotates emitting fluid towards turbine. Then the fluid enters and exerts force on turbine, as effect, turbine rotates. Eventually, the fluid once got into the turbine exits and flow towards impeller.

However, the direction of fluid without any interference just impede the rotating direction of impeller. It needs a device that changes the direction and in the end add more torque on the impeller. That way, impeller can in return send more volume of fluid to turbine, hence, faster rotation on input shaft connected to transmission.

Now, let's take a look how torque converter operates with respect to a vehicle's motion

Static - Phase when a driver's transmission is in gear but the brake is applied. The impeller is running as engine is likewise, the speed gap between impeller and turbine is very large, resulting in maximum torque multiplication.

• If you have hard time understanding, think of it this way. We know that impeller and turbine eventually rotates in the same direction but never in opposite. For instance, if you are throwing a ball towards a car in front of you moving in the same direction and expect the ball to bounce back the hardest, when would you throw? You throw it when the car in front of you is barely moving, that is, when the speed gap is the largest between your vehicle and the other.

Acceleration - A vehicle is accelerating but there's still fair amount of rotational speed gap between the impeller and the turbine. As mentioned , the torque multiplication depends on the speed difference between the two.

Coupling - The turbine has reached 90% of the speed of the impeller. Less mass of fluid is being sent back to the impeller from the former. Torque multiplication is almost at a stop.

Today we've covered how torque converter works and as I stressed out, it's vital if you want to have your car moving. Now, some of you with ceaseless curiosity are heavily interested in finding out how clutch for manual operates and how it is different from torque converter. So then, we'll cover this in the next post.

One Line Summary

Torque converter is a connector between engine and transmission and operates through rotation of impeller and turbine that send back and forth fluid towards each other.

On to the next one.