OK, what transmission is in the current Volt?

"Full of the sound of the Gran Fury, signifying nothing." (granfury) 09/04/2018 at 00:48 • Filed to: None

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One site says one speed automatic, which really wouldn’t be an automatic since it isn’t changing gears. Another site says CVT.

So, when you’re putting it into reverse, is it changing to a reverse gear in a gearbox or is it just reversing polarity on the motor?

Being a manual transmission die-hard I feel uncomfortable driving automatics because the car moves without me doing anything, something that is counterintuitive in my little world. I want to switch to neutral when at lights or in stop-and-go traffic, but I know that this is bad for a conventional automatic transmission and should be avoided. But what about the Volt? Is there really a transmission, and if not, is it OK to flip to neutral in those situations  when I don’t want the car to move?

wafflesnfalafel > Full of the sound of the Gran Fury, signifying nothing. 09/04/2018 at 01:14

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I really like those Volt wheels.... (is that odd?)

Full of the sound of the Gran Fury, signifying nothing. > wafflesnfalafel 09/04/2018 at 01:26

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No, not odd -  those are quite nice.

smobgirl > Full of the sound of the Gran Fury, signifying nothing. 09/04/2018 at 01:39

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This is not something I thought I cared about but now I really want to know. I hope someone clarifies before I wake up.

(I’m also reminded of desperately  needing to look up transmission info when Formula E was announced, but that’s useless for you too)

Spanfeller is a twat > Full of the sound of the Gran Fury, signifying nothing. 09/04/2018 at 02:24

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I seriously doubt it’s a CVT, an electric motor does not require conventional transmissions under most circumstances. If anything I’d understand some sort of gear step, but a CVT would drain too much energy and end up making the car less efficient

Unlike automatic cars with ICE motors, a vehicle with an electric motor doesn’t have a “stall” speed, so the car doesn’t move slowly “creep” unless you configure it to simulate creep (as tesla does) 

Nibbles > Full of the sound of the Gran Fury, signifying nothing. 09/04/2018 at 03:03

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So under battery power the motors drive the wheels entirely. If battery power is too low, the ICE takes over. It has a planetary set (from what I can find, two speeds) that bypasses the electric motor

Cé hé sin > Full of the sound of the Gran Fury, signifying nothing. 09/04/2018 at 05:01

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Electric drive, like a diesel/electric locomotive. When the engin e takes over from the battery it runs the motor via an alternator. At higher speed though the engine is clutched directly to the motor and drives the car mechanically with one fixed gear. So to answer your question, when being powered by the engine there’s effectively a CVT for much of the time as engine speed and road speed aren’t directly related. Once the engine drives the car mechanically it’s as if you were in top gear all the time.

bhtooefr > Full of the sound of the Gran Fury, signifying nothing. 09/04/2018 at 05:28

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In the current Volt, it’s using a 2-mode power split transmission.

I’m actually not sure what it does in neutral, TBH - an input split power split transmission (like what Toyota, Ford, Mazda, and some Nissan hybrids use ) just cuts power to the motors - no power to or from MG1 (in Toyota parlance) or MGA (in GM parlance) , the engine can spin, but no torque makes it to the wheels. I’d guess that the 2-mode transmission works the same way, but I’m not sure.

In any case, a 2-mode power split transmission adds some clutches and a layer of complexity to add a compound split mode - same idea as input split, but the gearsets are reconfigured (and there’s two) such that MGA slows down with vehicle speed, instead of speeding up with vehicle speed (and the torque path is more convoluted, IIRC). There’s also an intermediate mode that’s passed through while shifting from input split to compound split, that’s a fixed gear ratio between the engine and the wheels - in limited conditions, it’ll actually use this if it’s more efficient.

Reverse is actually difficult for a power split if the engine’s running, but it can still do it, just with speed limitations. But, it does just spin MGB (in GM parlance), the main traction motor, backwards. (This isn’t, AFAIK, done by reversing polarity, but rather by reversing the phases, as it’s a 3-phase motor.)

This is probably worth a read: https://gm-volt.com/2015/02/20/gen-2-volt-transmission-operating-modes-explained/

Now, as far as actually flipping to neutral... in a conventional automatic, I’m actually not sure why it would be bad, it’d unload a lot of components, but the fluid pump would still be spinning AFAIK.

In a power split transmission... there are two situations where neutral should be avoided. In motion if significant speeds can be attained is the big one (as the transmission can’t control its internal speed and MGA could overspeed). The other one is at a low state of charge, as neutral prevents the engine from being started if it’s not already running, and it prevents charging even if it is already running. Basically, if you’re going through a carwash at a low state of charge and have to go to neutral , cut large draws like AC.

BrianGriffin thinks “reliable” is just a state of mind > Full of the sound of the Gran Fury, signifying nothing. 09/04/2018 at 05:52

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https://gm-volt.com/2015/02/20/gen-2-volt-transmission-operating-modes-explained/

Uh...neither. But closer to a regular trans than a CVT. FWIW, putting an auto car into neutral isn’t bad for the car, it’s just bad for you in case you need to make any quick moves while the car is in neutral.

Also as someone who primarily drives autos, losing that “transmission creep” in a manual is really weird to me and takes getting used to, too. 

Full of the sound of the Gran Fury, signifying nothing. > Spanfeller is a twat 09/04/2018 at 06:11

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The Volt definitely simulates auto trans creep, even though it’s technically not necessary, and is something I wish could be disabled. It’s probably just there to make those  used to the behavior of conventional automatic transmissions happy, and probably can't easily be changed. 

StndIbnz, Drives a MSRT8 > Full of the sound of the Gran Fury, signifying nothing. 09/04/2018 at 08:29

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Seems like the Volt question has been answered, so I’ll go a little further into the Neutral in an auto question.

It’s no big deal. Done.

In the ZF 8-speeds, 3 clutches are on to transmit power. In N, 1 of the clutches turns off and sometimes another 1 will drop down to “holding/ready” pressure. Fluid pump is still spinning, as thats driven by the engine. When you go back into D (or R), the clutches that are off are reapplied and off you go. Now, if you tip in with the pedal while doing this, the clutches will apply faster so you can get going. Still not an issue though.

Hell, you can even put the trans in N while you’re coasting down.  The trans will still be applying 1 clutch so it’s prepared to go into the correct gear as soon as you put it back into D.

I like cars: Jim Spanfeller is one ugly motherfucker > Full of the sound of the Gran Fury, signifying nothing. 09/04/2018 at 09:28

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My understanding is that it's a 1 speed auto, same as the Prius. 

facw > Full of the sound of the Gran Fury, signifying nothing. 09/04/2018 at 09:49

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I want to switch to neutral when at lights or in stop-and-go traffic, but I know that this is bad for a conventional automatic transmission and should be avoided 

I’ve definitely read something recommending doing this for long lights in one of my older cars.

I think it’s pretty much irrelevant today though, as my understanding is that a modern automatic transmission will automatically go into neutral when the car is stopped and the brake pedal is depressed.

Going into neutral while the car is in motion is supposed to be bad because the transmission may overheat.

deekster_caddy > Full of the sound of the Gran Fury, signifying nothing. 09/04/2018 at 12:35

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There are no gears in the “transmission”. It’s two electric motors with a planetary driving the main ring gear, and that’s it. The center electric motor can be driven by the gas engine. Both motors can spin in either direction.

So, picture this. Engine running at 1,000 RPM, spins main motor forward at 1,000 RPM and secondary motor backward at 1,000 RPM. Car not moving. Driver presses throttle, secondary motor slows down, main motor (and gas engine) continues at 1,000 RPM, car starts moving forward. Now car is at 15 MPH, main motor at 1,000 RPM, secondary motor at -500RPM. Make sense? (I’m totally guessing on the output drive ratio, but the point is the same)

This system doesn’t need the gas motor running at all, it’s just part of my example.

I recently read a post from someone who wanted to see what happened, was going 60 MPH forward, shifted to reverse and floored the throttle. He got full regen, and when the car eventually slowed to 0 it started moving backwards. I’m not trying that with mine, but the principle holds - there are no shifting gears inside the ‘transmission’.

Editing for a couple things - I didn’t expand the comments and see that this was well explained already. Also, you can shift to Neutral anytime you want. The engine CAN run in neutral, there is no physical change except that the motors aren’t pushing anymore.

BaconSandwich is tasty. > bhtooefr 09/04/2018 at 14:01

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That was an awesome explanation!

gmporschenut also a fan of hondas > Full of the sound of the Gran Fury, signifying nothing. 09/06/2018 at 20:30

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