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Discussion Starter #1
We have recently bought a 2014 Volt. I have an engineering background and I am very impressed with the technology. I am still trying to figure out what the Brain is doing when the ICE is on; I watch the energy screen and it seems to switch between engine, battery, and engine and battery with a logic that I can't figure out. I am willing to assume that the car is smarter than I am, but is there a logic block diagram anywhere that shows what the brain is thinking when ICE is on, and the relationship to the electric motors?

I have also always wondered why Chevy didn't include the ability to charge the battery completely with the ICE genset - that seems to me to be a reasonable thing to have, and although not as efficient as wall charging, it might come in handy in certain circumstances, as when you are out in the woods somewhere off the grid.

Best Regards,

e.
 

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The ECU flops back and forth during warmup

In effect
1. Warmup = 0kw
2. After warm engine revs harder to catch up and fill buffer
3. Motor rpms stabilize as the buffer fills
4. Kws flop as the car locks in RPMs of the ice so it can lock the engine to the wheels
5. At lower speeds the motor fills the buffer slowly then shuts on/off as the buffer is filled / depleted.
 

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Think of it this way. When the battery is drained or you are running in hold mode, that is the battery level that the car is trying to maintain. The volt is trying to minimize ICE startups and shutdowns, so if you punch it, there's a delayed reaction before the ICE kicks in and tries to slowly replenish the used electricity. Similarly, if you have been running hard and hit a stop light, the ICE will keep running for awhile, and sometimes suddenly stop because it is about to exceed it's target.

I too wish there were a hold+ mode where it maintains a charge, but also recaptures regen to slowly creep up on long trips. But pretty much everything is in the name of efficiency, not necessarily convenience for the driver trying to game the system. The volt really does have a mind of its own, and eventually you'll get used to it and ignore all the telemetry that the car displays. That happened to me exactly at 2 years of ownership. I stopped trying to hypermile and just drive it hard like a jackrabbit, taking on any and all pony cars and ricer boys at stop lights. The car is much more enjoyable that way.
 

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There is no ability to fully recharge the battery with the ICE because there is no advantage to doing so. The car functions as an electric car even though the battery has been depleted to the point where the ICE must turn the generator to produce more electricity. As you pointed out, it is not as cost effective to run the ICE to turn the generator to produce electricity as it is to use grid power to charge the battery to get the electricity to run the car (which holds true as long as gasoline costs more that grid electricity).

Here are a few youtube videos that explain the workings of the Gen1 that should appeal to your engineering bent:

https://www.youtube.com/watch?v=AX5ZwzNwTc4

https://www.youtube.com/watch?v=an-VyIau-FM

https://www.youtube.com/watch?v=343-NQKOvLg
 

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When watching the power flow meters, consider that the Volt is an EV first and an ICE/Hybrid second. This means the car will always switch to EV if there's sufficient power in the batteries. What it's not doing, however, is turning off the ICE engine completely - it's still letting the car's momentum turn the ICE engine to manage the ICE's fluid pumps and oil pressure.

As for not charging the batteries completely from the ICE, there is a political reason in addition to the technical reasons posted earlier. If the Volt could fully charge the high voltage batteries from ICE it would fall out of the political definition of a EV and lose many of the tax credits currently available.
 

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When watching the power flow meters, consider that the Volt is an EV first and an ICE/Hybrid second. This means the car will always switch to EV if there's sufficient power in the batteries. What it's not doing, however, is turning off the ICE engine completely - it's still letting the car's momentum turn the ICE engine to manage the ICE's fluid pumps and oil pressure..
I do not think this is true. Gen 1 have no low-speed mechanical connection between wheels and ICE at all. And the ICE certainly stops shortly after the car does at lights and stop signs.
 

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The ECU flops back and forth during warmup

In effect
1. Warmup = 0kw
2. After warm engine revs harder to catch up and fill buffer
3. Motor rpms stabilize as the buffer fills
4. Kws flop as the car locks in RPMs of the ice so it can lock the engine to the wheels
5. At lower speeds the motor fills the buffer slowly then shuts on/off as the buffer is filled / depleted.
Correct, with minor revision. 1 - warmup is 6kW for 50s (will skip if the engine is warm from being used recently and go straight to later modes)

I do not think this is true. Gen 1 have no low-speed mechanical connection between wheels and ICE at all. And the ICE certainly stops shortly after the car does at lights and stop signs.
Correct, off is off. RPM is zero. Volt never spins the engine without fuel while driving, only during engine maintenance mode (EMM).
 

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Discussion Starter #10
Thanks everyone for the helpful replies. I think I understand how the drive system works, it is an impressive piece of technology. I assume the ICE starts and stops so frequently under certain conditions (city driving) because that is the most efficient way of proving needed power to the motors.

Best Regards,

e
 

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Thanks everyone for the helpful replies. I think I understand how the drive system works, it is an impressive piece of technology. I assume the ICE starts and stops so frequently under certain conditions (city driving) because that is the most efficient way of proving needed power to the motors.

Best Regards,

e
There is a minimum threshold which prevents the ICe from starting and stopping too much when going through stop and go traffic. So sometimes the ICE will charge the battery a little bit even when you are stopped. Then sometimes it will dip into the battery a little bit even when you are moving. It does what it does, I've stopped worrying about it or even trying to game the system to eek out more range.
 

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Discussion Starter #12
My first long trip with the Volt (250 miles) I spent a long time staring at the energy screen and I think I have it figured out. The ICE bounces between the discharge/charge limits set for the battery. The electric motor(s) come on sometimes in combination with the ICE when warranted. At the end of the trip, and very low speeds around town, the car was in electric-only mode, probably because the ICE had charged the battery somewhat. Very cool.

Best Regards,

e
 

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I do not think this is true. Gen 1 have no low-speed mechanical connection between wheels and ICE at all. And the ICE certainly stops shortly after the car does at lights and stop signs.
I can guarantee the Volt, regardless of generation, is not letting the ICE shutdown completely when running with no usable battery charge. It simply takes too long to restart the ICE when needed (up to a minute at high speed/high load). Instead, the car is putting the ICE into Deceleration Fuel Cut-Off (DFCO). In DFCO mode the fuel injectors are turned off and the engine is being turned by the transmission. DFCO can be entered and exited about twice a second so this is a very quick and nearly seamless transition. The EcoTec 1.4 engine in the gen 1 can run in DFCO as low as 1250 RPM. At speeds lower than this the car will need to use the fuel injectors to idle the engine between 700 and 900 RPM.

Also, I remember reading somewhere that the gen 1 Volt's ICE engine is capable of providing mechanical propulsion, despite GM's initial advertising that the ICE was only used for electric power generation. It may not be a direct connection as in a traditional gas transmission, but the linkage is there.

As for allowing the ICE to turn off when stopped, by all means do this whenever possible. You're getting 0 MPG when stopped and running the engine. GM ensured enough battery reserve to start moving the car and restart the ICE in this situation.
 

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According to a survey I took, a future CT6 PHEV will have a 'charge battery' mode in addition to hold.

I can see this being helpful if it is chauffeur-driven. The car can be charged from gas anywhere so that the passengers always get the library-quiet EV experience.
 

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Yes, it does. As all cars with the start-stop technology do.
Start/stop technology only turns off ICE when the vehicle is stopped. While moving in any charge sustaining mode the Volt doesn't let the ICE shut down. Instead it turns off the fuel injectors whenever possible to propel the car on battery alone. It simply takes too long to start a completely turned off ICE engine. I drove nearly a minute (slightly over a mile at 80 MPH) on I-76 going up the slight hill eastbound out of Hudson, CO between the time my 2017 "depleted" the battery, starting the switch over to ICE and the time ICE took completely over. There are a lot of mechanical components to start before brining the ICE up to speed to take over and those components take time. By turning off only the fuel injectors and letting the drive wheels keep the ICE turning at speed you can reduce the restart time from close to a minute down to a fraction of a second - the support systems never get turned off in this operating mode.

When stopped, there is no reason not to turn the ICE completely off and use battery to get going again.
 

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Start/stop technology only turns off ICE when the vehicle is stopped. While moving in any charge sustaining mode the Volt doesn't let the ICE shut down. Instead it turns off the fuel injectors whenever possible to propel the car on battery alone. It simply takes too long to start a completely turned off ICE engine. I drove nearly a minute (slightly over a mile at 80 MPH) on I-76 going up the slight hill eastbound out of Hudson, CO between the time my 2017 "depleted" the battery, starting the switch over to ICE and the time ICE took completely over. There are a lot of mechanical components to start before brining the ICE up to speed to take over and those components take time. By turning off only the fuel injectors and letting the drive wheels keep the ICE turning at speed you can reduce the restart time from close to a minute down to a fraction of a second - the support systems never get turned off in this operating mode.

When stopped, there is no reason not to turn the ICE completely off and use battery to get going again.
Volt does turn the engine completely off, to zero RPM. I can show you 300000 lines of logs from August to prove it.
The time it takes to start back up is maybe 1-2 seconds.
MGA is a 55kW motor that gets the engine spinning to 1400RPM within a second and then the fuel injectors start up and the engine continues under its own power.
The engine is never spinning while driving without fuel except for perhaps a handful of seconds before it is shut off entirely (even that was rare in my data collection).
That's a waste of energy that could otherwise be more efficiently captured and used via the electric motors doing regen braking.
Even when the battery is completely full, the engine is not spun without fuel to brake the car. The two motors oppose each other to slow the vehicle via regeneration losses.

What you describe is the initial cold start up routine of about a minute. That's a one shot deal and does not happen when the engine is warm. Instant on.
 

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Drive mine all the time in hybrid mode with battery depleted. The engine constantly shuts off. Zero RPM.


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