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Gen II Volts don't tell us much about what is happening in our 1.5L L3A engines when they start to produce KW to power the drive system. I was curious so I connected a monitor to the OBD port and generated a file that included the engine speed and the mass airflow over a period of about ten minutes. That data allowed me to generate the attached scatter chart which shows mass airflow (MAF), which is proportional to HP vs. RPM. In my case, my engine generated from 10HP to 50HP as it varied from 1000 RPM to 3500 RPM. Here is the scatter chart:
 

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Maybe somebody can help me with a theory or direct me to information on this site or elsewhere?
I have been trying to figure out the algorithm that the engineers used to control the engine. I know that they monitor the battery charge level and the drain from the drive motors to determine the amount of power to generate. However, my theory is that they set the engine throttle position at a level and primarily use generator load as the engine speed control mode.
For example, in our ICE cars, we control engine speed by modulating the accelerator pedal (i.e., the engine throttle). However, since ICE engines are far less efficient at low throttle settings, it makes sense that the Volt engineers would choose a greater throttle setting to minimize throttle losses in the engine. Then they would set the generator field speed (i.e., flux angle) to allow higher engine speed if more power is required.
I prepared the chart in my first note on this topic, above, which shows that mass airflow (MAF) is varying in a very linear fashion with RPM. This makes sense if the throttle is held at a fixed position, but the MAF would not be linear if the engine throttle position was varied significantly.
I did another test today which directly measured throttle position. This test showed that up to about 1,200 RPM, the throttle position was set at about 10%, probably just to keep the engine running. Once the engine went above that level, the throttle was increased to about 30% and it was modulated over the range from about 40% to 50% generally with few points nearing 60% at engine speeds up to about 3700 RPM.
It's no wonder the engine can seem a little bit intrusive when the car is running at low speeds and the engine is cranking out 50-60HP at 3,500 RPM to get the battery back to a nominal charge level.
Of course I can't do anything about controlling the engine, but the fun of the car to me is understanding some of the trade-offs the engineers made and what is happening under the hoodl
Again, if anybody has run across information around this topic, please advise. Thanks.
 

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Maybe somebody can help me with a theory or direct me to information on this site or elsewhere?
I have been trying to figure out the algorithm that the engineers used to control the engine. I know that they monitor the battery charge level and the drain from the drive motors to determine the amount of power to generate. However, my theory is that they set the engine throttle position at a level and primarily use generator load as the engine speed control mode.
This is exactly the case. Normal operation for the Volt is throttle wide open, generator draw manages RPM and the engine runs at a very constrained RPM. https://youtu.be/an-VyIau-FM?t=278 is where the Voltec Chief Engineer discussed this. (The whole series of Deep Dive videos is worth going through.)
 

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This is exactly the case. Normal operation for the Volt is throttle wide open, generator draw manages RPM and the engine runs at a very constrained RPM. https://youtu.be/an-VyIau-FM?t=278 is where the Voltec Chief Engineer discussed this. (The whole series of Deep Dive videos is worth going through.)
Both of those videos were made in 2010 and are discussions of the Gen1 Voltec drive, not the Gen2

Don
 

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Thanks hellsop! Exactly what I was hoping to find. I had seen the Weber State videos, but they were posted later. Will check out the series. Good stuff!
 

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Got any reason to think it's any different in Gen 2? If so, lay it out.
Seems to me the Gen 1 Volt could be described as an electric car that extends its range by generating more electricity as needed. The gas engine, whose primary function is to crank the smaller motor as a generator, can run full throttle, taking advantage of the benefits of premium gas to create the electricity that allows the car to continue operating as an electric car even when the battery is depleted.

The Gen 2 Volt, on the other hand, extends its range using a gas hybrid configuration to propel the car. Under moderate speeds and moderate torque demands (i.e., Fixed Ratio Extended Range Mode) the engine directly drives the wheels and the generator motor is off and locked.

Seems to me an engine operating as a generator and an engine operating as an automobile engine might have a different set of operating characteristics.
 

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Seems to me the Gen 1 Volt could be described as an electric car that extends its range by generating more electricity as needed. The gas engine, whose primary function is to crank the smaller motor as a generator, can run full throttle, taking advantage of the benefits of premium gas to create the electricity that allows the car to continue operating as an electric car even when the battery is depleted.

The Gen 2 Volt, on the other hand, extends its range using a gas hybrid configuration to propel the car. Under moderate speeds and moderate torque demands (i.e., Fixed Ratio Extended Range Mode) the engine directly drives the wheels and the generator motor is off and locked.

Seems to me an engine operating as a generator and an engine operating as an automobile engine might have a different set of operating characteristics.
Gen2 is a hybrid engine configuration so it stays within a narrower range close to optimal as compared with a normal engine/transmission. The electric motor drains off the extra horsepower, or supplements with extra horsepower, to keep the engine near its optimal efficiency. So it might be a lot like the gen1 motor.
 

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Gen2 is a hybrid engine configuration so it stays within a narrower range close to optimal as compared with a normal engine/transmission. The electric motor drains off the extra horsepower, or supplements with extra horsepower, to keep the engine near its optimal efficiency. So it might be a lot like the gen1 motor.
The addition of the second planetary gear, allowing the engine to operate as the sole source of propulsion, surely makes keeping the engine at its most efficient operating point a more complex issue for the Gen 2 than it was for the Gen 1, but that is likely what the OP is trying to learn more about. Have you any links to further resources on the issues?

Someone posted this link some time ago to an article that appeared in this forum on the Gen 2 Volt transmission. Lots of discussion appears in the comments at the bottom of the article, too:

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