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Torque Converters Explained

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This topic contains 23 replies, has 12 voices, and was last updated by Avatar Alex 7 years, 2 months ago.

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  • #503095
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    EricTheCarGuy
    Keymaster

    I’ve wanted to make this video for some time. In fact I’ve had these fans sitting at the shop for almost a year waiting for this video to be made. I know that I screwed up some of the terminology but I’m hoping the concept of how a torque converter works is conveyed in this video. I look forward to your thoughts.

    http://www.youtube.com/watch?v=_U_d_tBn-HQ

Viewing 15 replies - 1 through 15 (of 23 total)
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  • #503119
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    spelunkerd
    Participant

    It was a great video for showing the details, and thank you for going through all that effort. It was interesting enough that I put some time in to read more about it.

    Unfortunately, according to several other sources, the impeller is directly connected to the motor, and the turbine is directly connected to the transmission. If you agree, it wouldn’t be too difficult to repost a second edition this video with corrected details. I think it could all be done electronically without refilming anything.

    Otherwise it will be a point of confusion for years to come….

    #503123
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    Justin B
    Participant

    Awesome Video!
    Question…. When I put my car in drive and have the foot on the brake is it solely hydraulic pressure that trys to make the car go forward or is the TC clutch slipping? is the clutch for the “lock up” aspect of the tranny?

    #503234
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    EricTheCarGuy
    Keymaster

    I’m aware that I got some of the terminology wrong. I also didn’t like the way some of the other information was presented. It’s for those reasons I’m going to make a new video to replace this one with. I’m going to pull this one when I get the new one finished.

    #503236
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    EricTheCarGuy
    Keymaster

    [quote=”jeb721″ post=51333]Awesome Video!
    Question…. When I put my car in drive and have the foot on the brake is it solely hydraulic pressure that trys to make the car go forward or is the TC clutch slipping? is the clutch for the “lock up” aspect of the tranny?[/quote]

    You don’t go into ‘lock up’ until you’re cursing down the highway. If the torque converter locks up at idle it will cause the engine to stall.

    #503252
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    Justin B
    Participant

    Right…. I noticed this in my Ridgeline at any cruising speed over 60 or 70? You can hit the gas and it feels like its a standard in the way that the revs wont move.

    Ok Lockup Torque converter… Got it. Better for gas mileage id take it.

    #503293
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    Pengy
    Participant

    You can easily see your torque converter lock up when it seems like there is an “extra” gear in your transmissions where your rpm drops a bit due to it locking up. The torque converter should also get out of lockup to raise RPMs and increase torque by using the torque multiplier when you give it enough gas though.

    I have also seen torque converters lockup in every gear (depending on what speed you are at and your current throttle positions) in newer vehicles. Which essentially makes the transmission an automated manual transmission in the engine->transmission connection, however the gears would still be clutch activated.

    #503366
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    Justin B
    Participant

    I have a 2008 Honda Ridgeline and I just read that the Lock up function is available in 2nd through 5th gear. I have been really paying attention to the tach and I have noticed the revs will go quite low, 1300RPM when cruising at 50-60. I can tell the converter is locked when I hit the gas a little, and the revs dont move at all. Love that lock up function. Ive had manuals most of my life.

    #503483
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    Mike
    Participant

    What happened to the video?

    #503799
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    slipknot1488
    Participant

    Only issue I had with the video, and everyone makes mistakes so please no one jump down my throat, was that I was always taught that the impeller was “driven” by the engine via the torque converter housing and power is transferred via transmission fluid to the turbine, which is splined to the input shaft of the tranny.

    #504387
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    LJ11194
    Participant

    Every automatic I’ve driven will roll forward on perfectly flat ground without any gas, if you do not use the brake. My truck will get almost up to 10 mph with no throttle (at idle speed, so it’s not a throttle problem) This almost makes it seem like the stator isn’t always necessary, except maybe on hills?

    #504414
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    spelunkerd
    Participant

    Eric’s video inspired me to read all about this topic last week. Although I didn’t find a great animation of how it works, the consensus explanation is that the stator is there to change the dynamics of how fluid returns to the impeller. Evidently if you don’t have a stator, fluid will return with the wrong angular momentum, effectively slowing the impeller down when hit with returning oil. That caused turbulence and wasted energy in the form of heat. So, the stator is a set of vanes that redirect oil return in the same angular direction that the impeller is turning, along the way giving the impeller a boost of incoming fluid that makes it easier to spin forward. That technology is surprisingly old and it seems to have been widely embraced by almost all of those who made automatic transmissions. I suspect a vehicle with no stator would have a slower jump off the line and less low end torque. The whole design is intriguing, especially the part about designing the stator to spin in one direction only.

    As far as forward movement in drive at a stop, I agree, and it’s annoying feature of the auto trans. I was actually surprised that the moving idle effect is so mild. The design of a torque converter is shaped like a round wheel, allowing fluid spinning off the axis to be flung outward, effectively putting rotational force at the end of a lever and so increasing torque dramatically when rpm’s increase. Oil flow takes on a corkscrew pattern and the challenge is to return fluid without wasting much of that energy as heat.

    I’m going to keep looking for a good animation, especially the details of what the stator pushes against and when it changes to freewheeling mode.

    #504417
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    LJ11194
    Participant

    It’s actually kind of nice not having to do anything buy remove pressure from the brake when inching forward in traffic and that situation is the main reason I don’t like driving a stick.

    Something I’ve always wondered is, does revving the engine in drive with your foot on the brake overheat or otherwise strain the torque converter?

    #504519
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    EricTheCarGuy
    Keymaster

    Here is the updated video along with an explanation of why I pulled the old one. BTW the old one will be available to Premium Members of this site after I’m able to post it.

    #504535
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    spelunkerd
    Participant

    It’s a great feeling to have it all come together conceptually, and the new video does just that. The one area I still had some problem with is the dynamics of how the stator works. I found an excellent pdf file written by Toyota, explaining it in much more detail. I’ll try to append it at the bottom of this note in case anybody else wants those details.

    The problem with using air fans as a conceptual tool is that the direction of flow across the stator doesn’t come from the impeller, it comes from retrograde return flow after it bounces off the turbine. Remember that the whole system is sealed, so total oil flow has to balance out.

    The second critical point is that the direction of oil flow across the vanes of the stator change, depending on relative impeller and turbine speed. When the speed of the impeller is much greater than the turbine, flow is largely a vortex, with oil coming off the turbine at such an angle that it hits the concave faces of the vanes of the stator, locking it up. Those locked vanes redirect oil flow to give the input of the impeller a torque boost.

    When the turbine speed rises, the dominant pattern of oil flow becomes more rotary, which changes the angle that the oil hits the stator. This time, the oil flow hits the convex back of the stator vanes, and return oil is already flowing in the right direction to optimize impeller input. If the stator were fixed in that setting, there would be a performance failure causing poor engine performance and overheating at highway speeds. So, the stator is designed to freewheel when pushed in that direction.

    For a longer and much better description of what I said above, read the following pdf file.

    Attachments:
    #504540
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    Roy French
    Participant

    Loved the part about stall speed and it’s relationship to the cam and engine torque. Although that’s not an easy thing to explain, you have done it. Has anyone else read about these new camless engines that are in development? They will have power all through the rpm range. Not sure if I’m ready for the challenge of repairing them.

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