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Discussion Starter #1
The gas engine starts when the battery is at 20% charge, how long does it run while I am driving? Does it recharge the battery and then shuts off? Thank you. Hugh
 

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The following applies to the Gen1. The engine will cycle on and off depending on the level of charge in the traction battery. The goal is to keep the level around 20% while you are driving. The demand for energy will fluctuate due to road conditions and your requirements. If you don't have a heavy foot on the accelerator pedal, you will find that you can travel a good distance with the engine off before it again comes on to turn the generator to replace used energy. If you are traveling at highway speeds, you may find that the engine is on most of the time to keep the level of charge in the 20% range. It is not desirable, nor will it occur, that the engine completely recharge the traction battery. Gasoline costs more than electricity.


Under some load conditions the engine torque will be split between turning the generator and turning the wheels in order to gain even more efficiency.
 

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The engine will not run enough to fully charge the battery. The engine will run just enough to power your driving and maintain the existing low level of battery charge. If you want a full charge on the battery, plug it in.
 

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Mountain Mode charges the battery up to 2 bars and then keeps it there so at two bars it becomes like Hold, i.e. the engine is providing all of the power unless you are in a high demand situation, climbing a mountain (that's why they call it Mountain Mode) or hard acceleration. In Normal mode the engine doesn't run until the battery is empty, then all of the power comes from the engine, the Volt is just a hybrid under those circumstances.
 

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If you select Mountain Mode after the Volt's battery is fully depleted the gas engine will engage motor generator A to charge the Volt's battery while you drive, building up approx. 2 bars (20% SOC) on the Volt's battery meter. The Volt Owner's Manual suggests that you engage MM at least 20 minutes before beginning to drive up a steep grade so that there is sufficient time to build up the battery reserve. The gas engine will continue to run in MM even after the battery SOC has reached 20%. The Volt will use the battery charge to assist the gas engine as required, for example when passing another vehicle while driving on the ascent. On the descent the gas engine may shut off if the amount of energy recovered using regen is sufficient to power the Volt's wheels. This would also happen if you were driving in Hold Mode whether or not the battery had any charge as you start the descent. On a long descent you may end up with 2 or 3 bars of battery SOC from the recaptured energy.

In a different scenario where you are not ascending a steep grade, if you engage MM with a battery SOC greater than ~20% the Volt will run on battery until the battery SOC reaches ~20%, then start the gas engine to build up a small buffer at the 20% SOC point. If the power demand is low enough the Volt will turn off the gas engine, coast for a short distance, then use the small battery buffer but not go below 20% SOC. If possible the Volt will recover some energy via regen if on a slight downgrade, then turn on the gas engine as needed to maintain the 20% SOC. This is the same as when operating in Hold Mode except you chose to set the SOC threshold to be MM's 20% instead of whatever battery SOC remained when you engage Hold Mode.
 

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The gas engine starts when the battery is at 20% charge, how long does it run while I am driving? Does it recharge the battery and then shuts off? Thank you. Hugh
My understanding is that when running in Extended Range Mode (fully depleted battery, or Hold Mode), the generator powers the motor. In effect, switching from Electric to Extended Range Mode "unplugs" the motor from the battery output and "plugs" it into the generator output. Keeping the battery charged at the "switch to gas" or Hold state of charge is a separate generator function.

As described in illustrations explaining the Gen 2 Low Extended Range Mode, "MGA’s electric output is sent down to MGB to power the wheels" (Wikipedia has similar language regarding the Gen 1 Volt).

Fueling the motor with generator output is far more efficient than keeping the motor running off the battery power while continually recharging the battery via the generator.
 

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Discussion Starter #7
Thank you everyone for the answers. Does that mean that the gas engine is connected to the wheels?
 

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Thank you everyone for the answers. Does that mean that the gas engine is connected to the wheels?
Yes. In the Gen 2 Volt, most of the time, when the gas engine is running and powering motor generator A (MGA) the gas engine is also coupled to the drive wheels. Most of the power generated by MGA (up to 48kW) is used to power MGB. MGB is also coupled to the drive wheels. Any unused power is sent to the high voltage battery.
 

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Yes. In the Gen 2 Volt, most of the time, when the gas engine is running and powering motor generator A (MGA) the gas engine is also coupled to the drive wheels. Most of the power generated by MGA (up to 48kW) is used to power MGB. MGB is also coupled to the drive wheels. Any unused power is sent to the high voltage battery.
I know at highway speeds the gen2 Volt engine is directly coupled to the wheels. I thought at lower speeds it was coupled to the wheels through an eCVT electronic continuously variable transmission, in addition to using the car's momentum to charge the battery through MGA, with MGB assisting in moving the car forward.

But maybe jcanoe has it correct, and that it is a series connection at low speeds, generating electricity through MGA to drive MGB. Anybody know which is correct? Does the gen2 Volt have a continuously variable transmission for use at low speeds that is also driving the wheels?
 

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I always end up referring back to this article on the differences between the Gen 1, Gen 2 drive trains: https://gm-volt.com/2015/02/20/gen-2-volt-transmission-operating-modes-explained/

The article describes the 5 drive modes of the Gen 2 Volt. These are grouped under charge depleting (CD1, CD2) and charge sustaining (CS1, CS2, CS3).

CD1 and CD2 are easy to understand as these modes respectively employ one (MGB) or both (MGA, MGB) of the Volt's electric motor generators.

CS1 is also known as Split Input mode. The output of the ICE is split between powering the wheels and powering MGA (here MGA functions as a generator) to send power to MGB (here MGB functions as a motor and powers the wheels). When the Volt is stopped or coasting the ICE shuts down and the Volt temporarily reverts to CD1 mode. When resuming driving (as from a traffic signal) the Volt switches from CD1 to CD2 and MGA is used in place of having a separate starter motor to spin up the ICE.

CS2 also known as Fixed Ratio, the full power of the ICE is sent to the wheels, ICE RPM is tied to the speed of the Volt (fixed ratio.) As the Volt transitions between CS1 and CS2, MGA spins down and is locked out by a clutch. MGB provides regenerative braking. Under low torque conditions MGB can direct some power to the battery. (CS2 is considered the most efficient CS mode as it minimizes most of the electric conversion losses.)

CS3, Compound Split mode: The power from the ICE is split between the wheels and the ring gear of Planetary Gear Set 2 (PG2), this effectively gives a higher gear ratio. By controlling the RPM of MGA and by turning MGB slowly or even backwards the ICE RPM and torque can be controlled. During regenerative braking power from MGB can be sent to MGA or back to the battery. (I always lose my way trying to understand CS3.)
 

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I always end up referring back to this article on the differences between the Gen 1, Gen 2 drive trains: https://gm-volt.com/2015/02/20/gen-2-volt-transmission-operating-modes-explained/

The article describes the 5 drive modes of the Gen 2 Volt. These are grouped under charge depleting (CD1, CD2) and charge sustaining (CS1, CS2, CS3).

CD1 and CD2 are easy to understand as these modes respectively employ one (MGB) or both (MGA, MGB) of the Volt's electric motor generators.

CS1 is also known as Split Input mode. The output of the ICE is split between powering the wheels and powering MGA (here MGA functions as a generator) to send power to MGB (here MGB functions as a motor and powers the wheels). When the Volt is stopped or coasting the ICE shuts down and the Volt temporarily reverts to CD1 mode. When resuming driving (as from a traffic signal) the Volt switches from CD1 to CD2 and MGA is used in place of having a separate starter motor to spin up the ICE.
...
I found this Prius gen2 http://eahart.com/prius/psd/ era link that shows how the "Power Split Device" somehow emulates a variable speed tranmision in the Prius. I think the gen2 Volt in CS1 is similar and provides a CVT at low speeds, but honestly, I still don't quite get it. CS3 is the same as CS1 but for highway speeds when the power demand is too high so the engine needs to REV at higher RPMs than the CS2 direct single speed engine to wheels gearing would allow to get sufficient horsepower. The Java simulation at the bottom of the Prius page I linked too is really cool.

So I think there is no CVT, at least in the sense of https://en.wikipedia.org/wiki/Continuously_variable_transmission. An eCVT, yes, but I still don't understand how that magically works, and how much energy is going in and out of the MGA/MGB in CS1 mode. Are there two planetary gears in the Volt?
 

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Yes, The Gen 2 Volt transmission has 2 planetary gear sets and 2 clutches. The article notes that the power output of MGA is 48kW.
 

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The gas engine starts when the battery is at 20% charge, how long does it run while I am driving? Does it recharge the battery and then shuts off? Thank you. Hugh
Yes. Up to about 23% charge. There's a little window between the two, small enough to keep the engine hot, but large enough that it doesn't start up just because of a momentary guest of wind or something. You can get a mile or two out of that window if you're travelling easy enough and already at speed, or you can go through it in 50 yards going from a dead stop to city-thoroughfare speeds. (It says a LOT about how little energy it takes to just KEEP going instead of START going, doesn't it?)
 

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Discussion Starter #14
With a Volt on a 100 mile run the first 50 miles is on battery power, the last 50 miles the gas engine runs the whole time. You have to plug in to charge the battery. How does the Malibu hybrid system work?
 

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With a Volt on a 100 mile run the first 50 miles is on battery power, the last 50 miles the gas engine runs the whole time. You have to plug in to charge the battery. How does the Malibu hybrid system work?
The Malibu Hybrid operates much like the Gen 2 Volt when running in Normal Mode (Charge Depletion followed by Charge Sustainment.) The Malibu Hybrid can travel at up to 55 MPH on the battery (but only for short distances.) The Malibu Hybrid has a much smaller battery than the Volt ~1.5kWh and does not plug in to recharge. The Malibu has a slightly larger, more powerful gas 1.8L 4-cylinder gas engine than the Gen 2 Volt's 1.5L engine. <https://media.chevrolet.com/media/us/en/chevrolet/vehicles/malibu-hybrid/2019.html
 

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The Malibu Hybrid operates much like the Gen 2 Volt when running in Normal Mode (Charge Depletion followed by Charge Sustainment.) The Malibu Hybrid can travel at up to 55 MPH on the battery (but only for short distances.) The Malibu Hybrid has a much smaller battery than the Volt ~1.5kWh and does not plug in to recharge.
It seems to use a fair chunk of it, though. One reviewer I saw driving around though semi-rural suburbs got like 3.5 miles out of a period of no-ICE driving, and it wasn't noticeably downhill either. That's more buffer than the Volt seems to allow in its normal CS low- and high-water SOC.
 

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It seems to use a fair chunk of it, though. One reviewer I saw driving around though semi-rural suburbs got like 3.5 miles out of a period of no-ICE driving, and it wasn't noticeably downhill either. That's more buffer than the Volt seems to allow in its normal CS low- and high-water SOC.
No doubt you could travel 3 or more miles using the 1.5kWh battery. The only issue is there is no way to proactively charge the battery unless you live at the top or bottom of a long hill. The battery is only charged during regen. There is no plug or Mountain mode in the Malibu Hybrid.
 
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