[Indian2003]

Many of you know you have a torque converter in your automatic transmissions but few know what is inside. The torque converter is a piece of complex engineering. The guy who invented the autobox must have loved working with liquids.

I went over to the trade school I worked at in 2009. A model had been made of the torque converter from my car. This so the students can see inside and learn how things work.
The first year students made it themselvs with some guidance.

These kids are tired of school and instead of dumping them and giving up, they are given a new chance to pursue their hobby which are automobiles. They have 4 hours of theory and 4 hours of practical work every day. At the end of the year they have to pass an exam and then go on a 2 year apprenticeship at a workshop. Another exam later they become qualified master mechanics and different companies wait in line to snap them up.

All but 1 passed in my group in 2009 and today have well paid jobs, some of them running the workshops of different car and truck dealers. Most of them continued to work at same workshop where they were once an apprentice.

The torque converter from the outside.


The insides







Te lock-up gear that is a direct connection between the motor and drive axles.

[padmrajravi]

Thank you for this. You seem to be the right person to ask a question that has been troubling me for some time. How do the n-speed torque converter gearboxes work? As far as I know the coupling is liquid in case of torque converter. So in that case, for a 6 speed torque convertor, wont they need an actual clutch other than the lockup clutch ? But I haven't see any reference to an actual clutch when talking about a torque converter. Is there some other magic, I am not aware of ?

[Indian2003]

Originally Posted by padmrajravi

So in that case, for a 6 speed torque convertor, wont they need an actual clutch other than the lockup clutch ? But I haven't see any reference to an actual clutch when talking about a torque converter. Is there some other magic, I am not aware of ?

Torque converters have some sort of friction plates. In mine there was a friction disc. All automatic boxes have friction plates in a housing as in motorcycles. The lock-up disc has no friction materials and locked mechanically by the disc.

The AT is not a fit and forget unit. I have heard car salesmen recomend automatic transmissions as maintanence and clutch free but that is a lie or dont have a clue as to what they say.

I was at the Suzuki dealer a few months ago to look at the Ignis for a member of thisa forum. I asked about the size of the engine, does it have side airbags, how many airbags does the car have, and is the 4X4 system traditional a mechanical system or is it a Haldex system.

The guy did not have a clue, he thought the Ignis had a 3 cylinder engine with enough power. He was sure there were 2 and his partner said there must be side airbags because the A pillar was very big. All he could say about the 4X4 system was that it was very good.

[Guna]

Automatics based on TC also have planetary gears. Torque converter is just the part which is playing the role of the clutch.

[Madrasin_selvan]

The Torque Converter in an AT is used to maintain the Fluid Coupling between the Engine and Transmission. This Fluid Coupling helps in transfer of power from one shaft to the transmission shaft.

The Transmission Shaft leads into the Automatic Transmission where the Planetary Gear Sets are placed. For a 6 Speed Transmission there are two planetary gear sets working in combination, while for a 8 speed you need one more gear set and so on. The Clutch Discs help in moving the Gear Sets, while the Transmission Control Module sends signal according to the Throttle Input and Drive Conditions. The movement of the Clutch Discs are operated through the Valve Body (the black color part) or Sump placed at the Bottom/side of the AT.

The Torque Converter Automatic Gearbox is one big of Engineering. The Tolerances involved in the AT are so miniscule that even a 0.1mm change can lead to oil leakage and performance loss.

In short --> Throttle Input -> Transmission Control Module -> Sends signal through Actuators to Valve Body -> Releases Fluid to engage or disengage the Clutch -> Planetary Gear Set moves to increase or decrease the Speed.

[zeng]

Originally Posted by padmrajravi

Thank you for this. You seem to be the right person to ask a question that has been troubling me for some time. How do the n-speed torque converter gearboxes work? As far as I know the coupling is liquid in case of torque converter. So in that case, for a 6 speed torque convertor, wont they need an actual clutch other than the lockup clutch ? But I haven't see any reference to an actual clutch when talking about a torque converter. Is there some other magic, I am not aware of ?

A typical complete Automatic Transmission consists of various individual sub-assemblies like :
a )Standalone Torque Converter aka fluid coupling which receives mechanical power from engine crankshaft/engine flywheel via external ring gear being part of Torque Converter assembly (as pictures above);
b )It is a fluid coupling in itself with or without lockup clutch component transferring power from engine flywheel to input shaft of epicyclic gear set(s) adjacent and outside of Torque Converter assembly; and
c )Torque Converter output shaft would receive mechanical power from fluid coupling (with no lockup clutch in operaton) or from lockup clutch set (as and when lockup clutch is put into operation), hence splined to and transfer mechanical power to input shaft of epicyclic gear set(s).

The above 3 sub-sets of components (a, b, and c) is housed internally in one complete housing/assembly as pictured.

d )Epicyclic gear set(s) whose input shaft receives power from Torque Converter Output shaft from (c) above;

e )This incoming power is controlled and directed by sub-assemblies within Automatic Transmission Housing like:
e1)Clutch/piston set assemblies for varying speeds of 1,2, R, N etc ;
e2)control valve and its actuator system;

Sub-sets (d) and (e) are housed internally within the Transmission Housing proper adjacent and bolted to Torque Converter Housing/assembly.

f )In varying transmission speeds of 1,2 , R, N etc , the output shaft of Epicyclic gear set delivers mechanical power to Propeller shaft(s) in the case of a RWD or to Front axle half-shafts in the case of FWD.

Just my 2 cents.

[KSingh]

One of the simple and best explanation of torque converter I came across is given here:
https://www.claytex.com/tech-blog/to...transmissions/

The coupling between drive and driven shaft is done through turbine and impeller (fluid coupling). The torque converter consists of a turbine, a pump/impeller, a stator and a lock-up clutch.

In simple words fluid coupling can be imagined as two table fans kept facing each other and when one fan is operated (by electric motor) other will start rotating without any power input.

OPERATION

Stall: The impeller or pump receives the mechanical energy produced by the engine, but the turbine does not rotate because the brakes are still applied.

Acceleration: The brakes are no longer applied and the acceleration pedal is pressed, as a result, the impeller rotates faster and produces torque multiplication working in conjunction with the turbine.

Coupling: At this stage, the vehicle speed has increased, hence, the turbine reaches approximately 90% of the speed of the impeller and the torque multiplication ceases. Modern torque converters use a lock-up clutch to reduce the energy losses within the coupling fluid by mechanically locking the turbine to the impeller.

[chethan.ram]

Thank you so much for sharing this. Mine is a torque converter gear box and it is good to know what is inside. I was actually thinking today about the same and I would have done some research to understand the different types of AT gear boxes. Your post came at the right time.

[Indian2003]

Originally Posted by zeng

A typical Standalone Torque Converter aka fluid coupling which receives mechanical power from engine crankshaft/engine flywheel via external ring gear being part of Torque Converter assembly (as pictures above);

Just my 2 cents.

I have to disagree. In the picture above, the ring gear is welded to the torque converter. The ring gear is only for the starter motor to crank the engine. The mechanical power to the torque converter is via a flex plate that connects the crankshaft to the torque converter. Without a flex plate there is no connection.

Some models have the starter gear welded to the flex plate itself but it does not transmit power to the torque converter. The flex plate takes care of that.

The flex plate is of very thin metal and cracks easily if the engine block and gearbox is not perfectly alligned with guide solid or hollow dowels.


Attachment 2225568


One with the ring gear.

[SS-Traveller]

Originally Posted by Indian2003

Many of you know you have a torque converter in your automatic transmissions but few know what is inside.

Thanks for bringing this topic up. Too often, we find people referring to automatic transmissions as torque converter automatic (TC) vs. CVT vs. DSG vs. AMT (e.g., look at this article).

Originally Posted by padmrajravi

How do the n-speed torque converter gearboxes work?
...for a 6 speed torque convertor, wont they need an actual clutch other than the lockup clutch ?

As explained above, the torque converter is nothing but the clutch, without requiring a C-pedal to operate it. Now, what is commonly referred to as a TC or torque converter automatic (e.g. the Ciaz / XL6 4-speeder), is an automatic gearbox running a set of planetary gears (which is a whole different topic to explain), connected to the engine through the torque converter.

Just to clarify, the Baleno / Glanza has a CVT (constantly variable transmission) gearbox, BUT it is connected to the engine through a torque converter as well! So technically speaking, both the XL6 and the Baleno automatics are TC automatics - except that the gearbox is planetary in the former, and CVT in the latter.

Our auto journalists need to wake up and learn their automotive ABC's before writing misleading articles like this.

Originally Posted by Indian2003

I have to disagree. In the picture above, the ring gear is welded to the torque converter.

Ring gears are never welded, if I may be allowed to point out a specific technicality again - they are press-fitted after heating to a certain temperature. Once it cools and shrinks, it grips the flywheel firmly. Broken ring gear teeth will necessitate replacing the outer toothed ring only, not the entire unit.

[Leoshashi]

Originally Posted by SS-Traveller

Just to clarify, the Baleno / Glanza has a CVT (constantly variable transmission) gearbox, BUT it is connected to the engine through a torque converter as well! So technically speaking, both the XL6 and the Baleno automatics are TC automatics - except that the gearbox is planetary in the former, and CVT in the latter.

+1. Sharing pics of Torque converter units of Baleno CVT and XL6 AT:

Baleno CVT, part number 2:



XL6 AT, part number 6:

[Indian2003]

Originally Posted by SS-Traveller

Ring gears are never welded, if I may be allowed to point out a specific technicality again - they are press-fitted after heating to a certain temperature. Once it cools and shrinks, it grips the flywheel firmly. Broken ring gear teeth will necessitate replacing the outer toothed ring only, not the entire unit.

This is true on flywheels where they are pressed on after being heated. The picture above clearly shows the welds. Both ring gears on the torque converter and the flex plate are welded.

[Sid_pk]

This is my first post in TeamBHP. I have been following this site from ages and always wanted to contribute. This post on Torque converter is possibly the best place to start from.
Writing this post based on my experience in selecting torque converter and designing of automatic and powershift transmissions for Off-highway vehicles.
To explain the principle: Imagine two fans facing each other, rotating one of the them will make the other one rotate but with a much slower speed. Now imagine the two fans inside a closed chamber, this would make the second fan (or driven fan) go turn a little faster. Now replace air in the chamber with oil and you have much better speed transfer from the driver fan to the driven fan, but with lot of loss in efficiency. The driver fan in the fluid coupling is called the pump and the driven fan is the turbine. Obviously, the pump and turbine are designed to have a good efficiency. This is the principle of fluid coupling and this sort of fluid coupling is used in small and low-cost forklifts.
Taking this fluid coupling further, there is a stator added between the pump and turbine. The pump draws the fluid from the center and throws it on the turbine near the circumference. The turbine reacts to this fluid at the circumference and allows the fluid to drain close to the center. The stator picks up this fluid from the turbine and redirects it towards the pump and increases the volume of fluid in the pump. As the volume increase, the force applied on the turbine increases hence you get the torque increase. Thus, the name "Torque converter". The increase in torque is highest at lower speed. This is the reason for the good pickup from the torque converter transmissions. As the speed of the turbine increases the torque multiplication reduces (as the turbulent flow in the coupling changes to laminar flow). These sort of torque converters are used in vehicles which do not travel in single direction for a longer duration and have frequent start and stops. For example: Backhoe Loaders, Wheel loaders.
With Torque converter couplings, you will not be able to achieve 100% efficiencies. And hence lower fuel efficiency. Taking this further, a lockup clutch is introduced into the system. This clutch mechanically locks the pump and turbine when the torque multiplication becomes closer to 1. With the lockup clutch, one can achieve ~100% efficiency. These torque converters with lockup are used in cars, trucks, and busses where customers are more concerned about the fuel efficiency.
I have worked on transmission where the torque multiplication is as high as 7 (thanks to the twin turbine design in torque converter). And, as low as 1.3 on city buses where the pickup is not so important.
Efficiently, the torque at the wheel (at startup) is the function of gear ratio and the torque multiplication from the converter.

[josephilip]

I am a noob when it comes to TC transmissions. Could someone explain in detail how the locking mechanism works. That is, how the engine and gearbox connects mechanically when the rpm kind of matches without any fluid coupling. And also if it happens with all TC transmissions.

[clevermax]

Since the thread title says "Understanding what's inside your Torque-Converter automatic gearbox" - I just wanted to put this info for the sake of clarity.

There is Torque Converter and then there is the Automatic Gearbox. Both are different, and a combination of both makes the transmission system in a TC-equipped AT vehicle.

The first post may make some people think that the torque converter itself is the automatic transmission in its entirety, which is wrong. Torque converter alone isn't a gearbox.

The entire transmission system would look like this:


(Image Courtesy: hodgedodge.com)

What you see on the left is the torque converter, and what is to its right is the auto gearbox.

Originally Posted by josephilip

And also if it happens with all TC transmissions.

Yes, the lockup happens with almost all modern TC-equipped AT vehicles. Running always on fluid coupling mode is grossly inefficient.

One more picture of the entire AT gearbox - the TC is on the right side in this picture - easy to spot it by its shape.


(Image Courtesy: Autocar UK)