How Does a Torque Converter Work?

In this video I cover the purpose and operation of the turbine, stator, impeller, and torque converter clutch. I hope the explanation and practical give you some insight into how these parts work to not only transfer power from the engine to the transmission, but also how it drives the transmission pump and doubles the torque output of the engine when you take off from a dead stop. I've wanted to make this video for some time. In fact I've had the fans sitting in the back of the shop for almost a year. Now that I have the Automatic Transmission Dissection video under my belt I thought I would add a torque converter dissection into the mix. I hope you enjoy this video and that it gets you a better understanding of torque converter operation. Especially since I killed my air compressor cutting this one in half.

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ETCG

Due to factors beyond the control of EricTheCarGuy, it cannot guarantee against unauthorized modifications of this information, or improper use of this information.  EricTheCarGuy assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. EricTheCarGuy recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video.  Due to factors beyond the control of EricTheCarGuy, no information contained in this video shall create any express or implied warranty or guarantee of any particular result.  Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not EricTheCarGuy.

[briengardner]

I watched a few other videos on TC and was generally confused, but this tied it all together for me. You're a true teacher because you put thought into choosing words, examples and demonstrations that are practical and appropriate for the audience. Well done, you should consider a career in teaching.

[Sagaris]

This is 9 years old and is better quality than some modern videos I watch. Well done.

[dandoran]

I'm 60 years old and I finally understand how a torque converter works.
THANK YOU

[hravuri]

You are so knowledgeable. You are a gifted teacher. As an engineer myself, I find your videos super informative. Keep up the great work.

[benjmiester]

That fan demo was genius!  Very good job explaining this!

[dannyhampton]

I have been a diy person all my life and worked on my own cars, I fully understood all about the engine function and how it all worked together but until now have never known how a torque converter worked and why it was needed, just took it for granted and never tried to understand it because i couldn't see inside the sealed unit and now it is exposed and the knoledge you have shared is priceless for people like myself. well done!!

[DaveSomething]

I've taken a college course on auto trans... this was much more informative in 20 mins than the 3 months it took my teacher to do nearly the same.

[dennislovin]

And I'm 75 years old, and think this is one of the best mechanical and physics presentations I've ever seen. Thank you!

[vatorres]

This is by far the best instructional video of a torque converter I have ever seen. I am not a mechanic by any means, but his visual aids really lets you see how everything works. If Eric is an instructor in school, he must be putting out some "REALLY" good mechanics.

[adjest]

"i hope this video can help you in some small ways"

dude. BIG. IT HELPED ME BIG. I NEVER understand how TC works but the fan demo you showed was really genius and that contributes to 100% of my understanding. Thank you ! you're the best !

[jackt]

That was well done. I started out in automotive engineering. When starting out, there is a big difference in the rpm between the impeller and turbine. The impeller is then acting like a centrifugal pump accelerating the fluid to the outside and at an angle against an opposing angle on the turbine blades which are not spinning, making them a bit like a bucket on water wheel to extract some of the kinetic energy after which it is routed to the stopped or lower velocity inner diameter of the turbine, and back toward the inner diameter of the impeller where it will be sucked in and accelerated again. However, with the large difference in velocity and the opposite angle, the remaining kinetic energy opposes the impeller so there can be no torque gain unless you redirect and reuse that energy with a stator to assist the impeller. The stator attempts to rotate backwards and it cannot because the sprag/roller/one-way clutch doesn't allow it to, and it redirects the fast-moving fluid into the direction of the impeller at to further accelerate the fluid, which is where you get torque multiplication, ~2:1. However, as the turbine rpm gains equilibrium with the impeller, the turbine now produces its own back pressure from centrifugal force, thereby mostly balancing this out. However, with the angle of the inner turbine blades plus the rotation of the turbine being almost as fast as the impeller, the stator will now rotate with the impeller and turbine to give the best flow. This point is called couple or lockup, although it is not really coupled or locked up, but it will be less than 10%, slower depending on the converter, and torque multiplication will be 1:1. Thus, max torque multiplication occurs when the impeller is turning and the turbine is stopped. If something is wrong with the stator and it rotates in both direction, acceleration will be poor. If it won't move in either direction, it will add a load on the engine during coupling and cause heat buildup. Then came lockup torque converters where they actually do lock the impeller and turbine together physically, so they tend to refer to the former as couple rather lockup. The difference between a torque converter and a fluid coupling is the stator, which enables the multiplication of torque. So are fluid couplings obsolete? No. They are used in a lot of applications to isolate vibration between driving and driven members, and even gentle startups when an engine is running at a fixed RPM like electric engines and fluid is slowly added such as to start a conveyor belt with tons of product on it.

The stall speed is the maximum rpm that the engine can turn when using all of its power against a stopped turbine. Logically, that depends on how much torque the engine has. While true, with something relatively heavy such as transmission fluid, small changes in RPM make big changes in torque to make a small rpm change, so it won't vary by as much as you think, which is why they can categorize them by stall speed. You can also see that the smaller the diameter, the faster you will have to spin it to equal the same outside velocity to achieve the same centrifugal force and pumping action on the fluid plus they have less area on the blades so a 1" difference in diameter can make a substantial difference in stall rpm. The stall rpm will vary more with torque variations as well, but still not by a lot. Of course the First Law of Thermodynamics states that neither matter nor energy can be created or destroyed. When the engine creates all of that high velocity fluid against a stationary turbine, the energy has to be dissipated somewhere, and it is. The engine horsepower is converted to heat, which is why the transmission cooler in the radiator, unless you have a wimpy engine in which fins on the outside of the converter and air holes in the bellhousing can do the job. Larger diameter converters are more efficient even during coupling. However, when overdrive transmissions and higher gear ratios became more and more popular, engine rpm dropped near or below where coupling would occur even at speed, so there were efficiency losses with more power going up in heat in the converter. This made the move to lockup converters compelling.

From automotive engineering to aviation mechanic to military pilot, the engines made perfect sense to me right away because they use a stator to similar effect as torque converter except jet engines don't allow the stators rotate with the rotors because it is always pumping, unlike a torque converter, thus unnecessary. Another difference is the stators are where the compression is occurring when it converts the kinetic energy into static pressure, and redirects the flow direction into the rotor blades of the next stage. Torque converters don't compress the fluid but rather add to the kinetic energy to be expended against the turbine by feeding accelerated fluid back into the impeller to be further accelerated.

[Rolly]

I'm a 50 year transmission master rebuilder, well done, I know how it works but I enjoyed watching you video, I give you a 100%.

[gary]

I'm a geezer and throughout my entire life (thus far) I've never had a clue how torque converters work. Outstanding video, I loved the two fans demo, excellent. Thanks a ton, now I can pass my thanks through a torque converter and virtually double my thanks.. so thanks two tonnes.

[RazgrizNinjaEX]

Your practical gave me the "AHA!".
10/10.

[brendonkrahn]

Almost 8 years later this is still the best video on how these Donuts work. Thanks!

[JasonLuther]

I've watched you for almost 10 years and this is one of my favorite videos I have ever seen, in forms of technical knowledge and visual aid. I understood how TC's worked but could never explain it to another person myself. Always saw it as a compontent that just needed replaced as a whole and never got into the guts of it. Eric you're a legend

[JohnnyG]

This is amazing, your attention to detail and terminology, the clear and thorough explanations, that practical demonstration. You're an amazing educator!

[johnscott]

Eric, this is a very lucid explanation of an automatic transmission. And showing all of the major parts makes for a great explanation. Thank you very much.

[williambush]

Best explanation I've seen so far of how a torque converter works. Really appreciate how you took a complicated subject and broke it down so that a layman could understand it. Your a good teacher.

[Bill-ndqd]

My 1993 Oldsmobile started stalling at stoplights all of sudden. Thought I had a big problem. Finally got the car home after pissing off a whole lot of drivers behind me. Turned out to be the converter lockout solenoid. Part was $20, solenoid was under the transmission cover on the driver's side. Was a fairly simple repair and car was back to normal. A very small part that caused a big headache on the road. Excellent video by the way.