How does the Torque Converter AT gearbox work?

9216 · 19th June 2022, 17:59

Hello all,
I would like to have some clarity on the working principle of Torque Converter transmissions. I have read many articles and seen many videos on the subject, but still am not clear how speed ratios change. Most sources give an almost stereotyped explanation of an impeller and a turbine, with a stator in between. This makes me view the TC like a CVT, with no fixed gear ratios. Yet TCs are qualified as 6-speed, 7-speed etc. If a set of normal gear system follows the TC, it is not seen explained anywhere. If that is the case, a TC is acting more like a clutch than a transmission.

Welcoming any clarity on the subject.

Thanks.

Turbohead · 19th June 2022, 18:14

The Torque Converter is the equivalent of a clutch in a manual transmission. It sits between the engine and the gearbox.

How the automatic gearbox works is written in detail in this link:
https://auto.howstuffworks.com/autom...ansmission.htm

clevermax · 19th June 2022, 19:57

TC, by itself, will not be able to change speed ratios. Typically TC is mated to an auto gearbox, which changes the speed ratios. Hope this helps.

As you said, it's very hard to get this insight from the internet where everybody goes on to explain the impeller, turbine, and all that arrangement only.

Another point which we might fail to notice is that, modern TCs aren't always running in fluid coupling mode. They have lockup clutch and when the vehicle is going smoothly, TC is fully locked up and there's no loss due to the fluid coupling. Some people think that TCs are always working in the fluid coupling mode.

ajayc123 · 19th June 2022, 20:26

This video gave me some idea. Towards the end it calls out how the gearbox is linked to tq.

https://youtu.be/u_y1S8C0Hmc

mvadg · 19th June 2022, 21:30

Quote:

Originally Posted by ajayc123

This video gave me some idea...
https://Youtu.be/u_y1S8C0Hmc

Yes, this video explains it with animation.

Quote:

Originally Posted by clevermax

TC, by itself, will not be able to change speed ratios. Typically TC is mated to an auto gearbox, which changes the speed ratios...

There's quite a bit of torque multiplication in the TC itself. This is managed by the stator that sits in between, inside the TC. Video above explains.

Dr.AD · 19th June 2022, 21:40

Quote:

Originally Posted by 9216

Welcoming any clarity on the subject.

This topic is already discussed at length here: https://www.team-bhp.com/forum/techn...c-gearbox.html (Understanding what is inside your Torque-Converter automatic gearbox)

As explained in that thread, there are planetary gears in torque convertor-based automatics which do the job of changing gear ratios (and thus making it a multi-speed unit, such as the modern 8-speed TC). The TC by itself merely acts as a clutch, and the job of changing the speed ratios is done by the planetary gears.

ajayc123 · 19th June 2022, 21:55

Just one quick question. What triggers the change in the gear ratio in the planetary gear system? Does the signal come from ecu or does the tq (rpm) trigger the gear change? Or is it something else?

ph03n!x · 19th June 2022, 21:58

Quote:

Originally Posted by ajayc123

Just one quick question. What triggers the change in the gear ratio in the planetary gear system? Does the signal come from ecu or does the tq (rpm) trigger the gear change? Or is it something else?

From the TCU - the transmission control unit. Yes, based on RPM/ Load among other factors as pre-programmed.

mvadg · 19th June 2022, 22:14

Quote:

Originally Posted by 9216

Hello all,
I would like to have some clarity on the working principle of Torque Converter transmissions...

Thanks.

https://youtu.be/inJYu8me4eQ

This is a Fuji Rabbit Superflow. It just has a torque converter, no gearbox. Ratios are changed in the TC using the stator.
But for efficiency, the modern AT has a TC which acts as a clutch AND a torque multiplier, and in addition, has a planetary gear box, with 3, 4,6,... gears as explained here:

https://youtu.be/ARd-Om2VyiE

clevermax · 19th June 2022, 23:19

Quote:

Originally Posted by mvadg

There's quite a bit of torque multiplication in the TC itself. This is managed by the stator that sits in between, inside the TC. Video above explains.

Yes, I'm well aware of this, and I'm experiencing this first hand. My engine develops quite a decent amount of torque for a 1 ton family car (~320Nm as per Wolf) and with the TC in the equation, the overall torque feel is immense, especially when I accelerate hard in second & third gears.

The reason why I did not mention about this in the previous post is because the OP was confused about where the gear ratio change happens in the TC setup. Didn't want to add to the confusion.

The Regera is a good case study, just the seventh gear and a TC, as Christian explained it.

19th June 2022, 17:59	#1
9216 BHPian Join Date: Mar 2009 Location: Palakkad Posts: 61 Thanked: 170 Times	How does the Torque Converter AT gearbox work? Hello all, I would like to have some clarity on the working principle of Torque Converter transmissions. I have read many articles and seen many videos on the subject, but still am not clear how speed ratios change. Most sources give an almost stereotyped explanation of an impeller and a turbine, with a stator in between. This makes me view the TC like a CVT, with no fixed gear ratios. Yet TCs are qualified as 6-speed, 7-speed etc. If a set of normal gear system follows the TC, it is not seen explained anywhere. If that is the case, a TC is acting more like a clutch than a transmission. Welcoming any clarity on the subject. Thanks.
	(3) Thanks

19th June 2022, 18:14	#2
Turbohead Senior - BHPian Join Date: Jul 2015 Location: Chennai Posts: 1,363 Thanked: 5,738 Times	re: How does the Torque Converter AT gearbox work? The Torque Converter is the equivalent of a clutch in a manual transmission. It sits between the engine and the gearbox. How the automatic gearbox works is written in detail in this link: https://auto.howstuffworks.com/autom...ansmission.htm
	(3) Thanks

19th June 2022, 19:57	#3
clevermax Senior - BHPian Join Date: Jun 2006 Location: Tvm/Amsterdam Posts: 2,086 Thanked: 2,640 Times View My Garage	re: How does the Torque Converter AT gearbox work? TC, by itself, will not be able to change speed ratios. Typically TC is mated to an auto gearbox, which changes the speed ratios. Hope this helps. As you said, it's very hard to get this insight from the internet where everybody goes on to explain the impeller, turbine, and all that arrangement only. Another point which we might fail to notice is that, modern TCs aren't always running in fluid coupling mode. They have lockup clutch and when the vehicle is going smoothly, TC is fully locked up and there's no loss due to the fluid coupling. Some people think that TCs are always working in the fluid coupling mode. Last edited by clevermax : 19th June 2022 at 20:06.
	(2) Thanks

19th June 2022, 21:55	#7
ajayc123 BHPian Join Date: Apr 2012 Location: Delhi Posts: 917 Thanked: 2,364 Times	re: How does the Torque Converter AT gearbox work? Just one quick question. What triggers the change in the gear ratio in the planetary gear system? Does the signal come from ecu or does the tq (rpm) trigger the gear change? Or is it something else?
	() Thanks