Volt's Trasmission Cooling
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Thread: Volt's Trasmission Cooling

  1. #1
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    Default Volt's Trasmission Cooling

    Hello everybody. I'm a prospective Volt owner and have found the resources on this website the most useful of all when trying to understand everything about the car. One of the hang-ups for me has been with the transmission, so I'm hoping someone can clear up this for me.

    I see that the Volt's transmission houses both MGA and MGB along with 3 clutches and a planetary gearset inside its own case, which apparently runs transmission fluid through a cooler. The question I have is what sort of fluid are we talking about here? I assume it has to be some sort of viscous oil-like fluid similar to what you would find in a regular automatic transmission, since there are gears. But is this same fluid running around the motors to cool them as well? The two motors are probably generating the majority of the heat in the transmission, and in the Nissan Leaf, its traction motor is water-cooled. How exactly is this fluid interacting with the motors? I mean is it on the outside of the motors, or all around the copper windings?

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    Supermachoman,

    The Volt uses regular GM "Dextron VI" transmission oil to pressurize the clutches and cool all three electric motors (Motor A, Motor B, and the auxiliary pump motor C). The oil is carried through dedicated passages at all times for a base level of circulation, but it can be increased in flow to Motor A or Motor B as needed if the temperatures begin to climb toward their material limits. The oil is sprayed on all parts of the windings and rotors and was enhanced through years of development. It is very rare that this active cooling is needed. If there's any issues with motors and temperatures, it is that the motors generally do not create enough heat compared to a traditional transmission. The Volt has a thermostat for the transmission oil cooler so that it will warm up more quickly for better efficiency.

    I hope this answers your question and helps in your purchase decision!
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  3. #3
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    Thank you very much for the quick reply. The presence of this fluid on the rotors must cause some friction that would reduce the overall efficiency of the motors. If so I assume the compromise is worth it in terms of durability and probably operating the motors in their peak efficiency temperature. Their durability in terms of being nearly no-friction electric motors seems unaffected to me.

    One of the reasons I want an electric car is because there is no internal friction going on within the apparatus doing work, meaning parts do not wear out as they do in a traditional ICE. People have put 200,000+ on RAV4 EVs and no problems. Replace the batteries and keep going just like when it was new (the interior/exterior are different matters of course, but they can be maintained at a low cost)

    Now of course I realize the perfect EV is not out there. Everywhere there are compromises. With a NEV, you compromise on top speed, range, and seating. With a Leaf, you compromise on range and price. With a Volt, you compromise on complexity. Still, I think the Volt can be pretty reliable in the long-term. In the case of the Volt, the ICE won't be running for very much of the time, and when it is, it is only going up to 4000rpm. So in 10 years I bet the ICE is still doing just fine with regular maintenance. It would be like a regular car that got driven around the neighborhood once a week for 10 years and has only about 40,000 miles on it.

    I am hoping to keep this car for a very long time. The battery is purportedly designed to last 10 years, so at that point I would like to hopefully replace the battery with a new and better one, and give it to my daughter to drive. The question is, even though the two motors may be fine, will the gears and clutches need to be replaced? In that case I'd be having to pay for a transmission rebuild, assuming there is somebody out there who can do it and I'm not forced to buy a new 4ET50. Toyota's power-split device is similar, and has had good longevity. I know nobody has a crystal ball. But what do people think? Is the transmission itself a compromise for the buyer in terms of long-term durability?

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  6. #4
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    Quote Originally Posted by supermachoman View Post
    Thank you very much for the quick reply. The presence of this fluid on the rotors must cause some friction that would reduce the overall efficiency of the motors. If so I assume the compromise is worth it in terms of durability and probably operating the motors in their peak efficiency temperature. Their durability in terms of being nearly no-friction electric motors seems unaffected to me.

    One of the reasons I want an electric car is because there is no internal friction going on within the apparatus doing work, meaning parts do not wear out as they do in a traditional ICE. People have put 200,000+ on RAV4 EVs and no problems. Replace the batteries and keep going just like when it was new (the interior/exterior are different matters of course, but they can be maintained at a low cost)

    Now of course I realize the perfect EV is not out there. Everywhere there are compromises. With a NEV, you compromise on top speed, range, and seating. With a Leaf, you compromise on range and price. With a Volt, you compromise on complexity. Still, I think the Volt can be pretty reliable in the long-term. In the case of the Volt, the ICE won't be running for very much of the time, and when it is, it is only going up to 4000rpm. So in 10 years I bet the ICE is still doing just fine with regular maintenance. It would be like a regular car that got driven around the neighborhood once a week for 10 years and has only about 40,000 miles on it.

    I am hoping to keep this car for a very long time. The battery is purportedly designed to last 10 years, so at that point I would like to hopefully replace the battery with a new and better one, and give it to my daughter to drive. The question is, even though the two motors may be fine, will the gears and clutches need to be replaced? In that case I'd be having to pay for a transmission rebuild, assuming there is somebody out there who can do it and I'm not forced to buy a new 4ET50. Toyota's power-split device is similar, and has had good longevity. I know nobody has a crystal ball. But what do people think? Is the transmission itself a compromise for the buyer in terms of long-term durability?
    As you say, no crystal balls. Having said that, I expect good reliability from the transmission and motors. There was a statement from GM a month ago mentioned here on the forums that the motor would last at least 600k:

    http://gm-volt.com/forum/showthread....motor-3-*-200K

    The transmission is about as simple as they get (the prius synergy drive and the LEAF direct gear being the only simpler ones.) There are clutches, but the car matches the speed on them before it engages them, so they never have to dissipate and significant amount of power on engagement.

    As you say, the ICE lives a much less strenuous life than most ICEs, and will see only about 30% (fleet average) of the miles the car sees. It also isn't state of the art. While I'm occasionally frustrated by the missed opportunities for ultimate efficiency, it also lacks the high pressure fuel pump that is breaking in so many cars right now, won't have turbo problems, and won't choke the intake manifold with soot deposits - it should be a very reliable little engine.

    The part the jury is out on is all the little things... I was interested and impressed that the transmission has a thermostat to bring it into the ideal range, but that's also something else to break (and if it can fail closed, could potentially lead to overheating.)

    The Volt is full of these little details to optimize efficiency, performance, or the experience, and most of them have moving parts to break. I'm not saying I expect them to fail often, but there are enough of them I'm not confident they won't eventually.
    Walter
    C4884 - White Diamond, purchased 10/15/11
    2016 Tesla X75D delivered 8/25/16

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    Don't forget the Volt has no conventional starter motor to wear out, (it uses the generator to start it) and, there is also no alternator to burn out.
    Jerry, Fresno, California
    2017 Bolt ordered, Orange Sunburst, w/all options,
    #536 2011 Crystal Red Volt,
    2012 Diamond White Volt, saved from the crusher, gift to my niece.
    1975 Cosworth Vega, stored
    1988 Formula Fiero, also saved from the crusher, in the midst of restoration.

  8. #6
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    The Volt has a direct drive transmission. Is this correct?

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    Quote Originally Posted by BlackVolt View Post
    The Volt has a direct drive transmission. Is this correct?
    Sometimes. At low speeds or under high loads, the ring gear of the planetary gear set is clutched to the transmission housing, which leaves the main motor (permenantly attached to the sun gear) connected to the wheels (always connected to the planet carrier through the differential) mechanically connected at a 7:1 ratio.

    However, to improve efficiency, at lower loads and speeds above ~45 mph, the ring gear is unlocked, and the second motor generator (and the engine when the engine is running in CS mode) are connected to the ring gear by another clutch (a third clutch allows the engine to be disconnected from the second motor.) This transforms the gearbox into a torque split system generally similar to the Toyota Hybrid Synergy Drive used in the Prius and other hybrids (the Prius actually puts one motor on the side with the wheels, the engine on one, and the other motor on the third, but the net effect is the basically the same.)

    This is still less complicated than the average automatic transmission, and the Volt has the advantage that it never operates the clutches under load or with big speed differences (which a normal automatic would have.)
    Walter
    C4884 - White Diamond, purchased 10/15/11
    2016 Tesla X75D delivered 8/25/16

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  10. #8
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    Quote Originally Posted by SharkVolt View Post
    Don't forget the Volt has no conventional starter motor to wear out, (it uses the generator to start it) and, there is also no alternator to burn out.
    The generator/motor actually brings the RPM up to normal idle before starting the ICE, one reason it is such a smooth transition from EV to CS mode.
    VIN#...B...01921 - Build completed 03/1/2011 - Picked up my new red Volt at Atlantic Chevrolet on Saturday March 26th, 2011 .Hidden Content

  11. #9
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    Quote Originally Posted by Chevrolet Customer Svc View Post
    Supermachoman,

    The Volt uses regular GM "Dextron VI" transmission oil to pressurize the clutches and cool all three electric motors (Motor A, Motor B, and the auxiliary pump motor C). The oil is carried through dedicated passages at all times for a base level of circulation, but it can be increased in flow to Motor A or Motor B as needed if the temperatures begin to climb toward their material limits. The oil is sprayed on all parts of the windings and rotors and was enhanced through years of development. It is very rare that this active cooling is needed. If there's any issues with motors and temperatures, it is that the motors generally do not create enough heat compared to a traditional transmission. The Volt has a thermostat for the transmission oil cooler so that it will warm up more quickly for better efficiency.

    I hope this answers your question and helps in your purchase decision!


    Thanks for a great answer Trevor. As an R&D guy I knew the answer but don't have the clearance to admit it <grin>.

    Pete Foss
    GM R&D

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  13. #10
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    Quote Originally Posted by saghost View Post
    As you say, no crystal balls. Having said that, I expect good reliability from the transmission and motors. There was a statement from GM a month ago mentioned here on the forums that the motor would last at least 600k:

    http://gm-volt.com/forum/showthread....motor-3-*-200K

    The transmission is about as simple as they get (the prius synergy drive and the LEAF direct gear being the only simpler ones.) There are clutches, but the car matches the speed on them before it engages them, so they never have to dissipate and significant amount of power on engagement.

    As you say, the ICE lives a much less strenuous life than most ICEs, and will see only about 30% (fleet average) of the miles the car sees. It also isn't state of the art. While I'm occasionally frustrated by the missed opportunities for ultimate efficiency, it also lacks the high pressure fuel pump that is breaking in so many cars right now, won't have turbo problems, and won't choke the intake manifold with soot deposits - it should be a very reliable little engine.

    The part the jury is out on is all the little things... I was interested and impressed that the transmission has a thermostat to bring it into the ideal range, but that's also something else to break (and if it can fail closed, could potentially lead to overheating.)

    The Volt is full of these little details to optimize efficiency, performance, or the experience, and most of them have moving parts to break. I'm not saying I expect them to fail often, but there are enough of them I'm not confident they won't eventually.
    Yeah, good info there. I think you are right. If something goes catastrophically wrong, it will be because some minor part failed leading to some snowballing like what you mentioned with the thermostat. The engineers had a specific goal and that was functionality/efficiency. Most people look for that, but I think I would have traded extra range etc for simplicity. Still not enough to keep me from buying one though. We shall see.

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