That's weird, no more chuggle. Or Mountain Mode vs Hold Mode
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Thread: That's weird, no more chuggle. Or Mountain Mode vs Hold Mode

  1. #1
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    Default That's weird, no more chuggle. Or Mountain Mode vs Hold Mode

    As a new Volt Gen 2 owner I've been testing this gem in different ways. When I first put the car in Hold mode a while back, I noticed the slight hesitation known as chuggle. In later testing I noticed that Mountain Mode eliminated any chuggle I'd experienced in either Hold, or when the battery ran out in Normal mode.

    So here's the weird thing. On a recent highway trip on Hold mode, I noticed that the battery was being used in conjunction with the ICE....just like Mountain Mode. I was on Hold mode at 72 km of battery reserve and this wonderful little car was cruising and accelerating as smoothly as a pure EV, using both battery and ICE. It was the same highway and similar driving as the previous tests.

    So was I missing that before? Is that the way Hold mode should work? By both capping the battery reserve whenever Hold is activated, and then using the battery to assist like Mountain Mode? If that's the case, what's the difference between Mountain Mode and Hold Mode? Other than Mountain Mode reserving the battery at around 12-15 km.

  2. #2
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    Mountain Mode is essentially charge and hold at 40% or so state of charge (SoC), not sure of exact SoC on Gen 2. If you are above the 40% it wont start the engine until you drop to that level.

    Hold just prevents the battery from draining. At the 40% for mountain mode, hold is going to feel the same.

    The key difference is mountain mode can charge the battery back to 40%, hold wont charge at all.
    Last edited by viking79; 07-20-2016 at 11:55 PM.

  3. #3
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    Quote Originally Posted by viking79 View Post
    Mountain Mode is essentially charge and hold at 40% or so state of charge (SoC), not sure of exact SoC on Gen 2. If you are above the 40% it wont start the engine until you drop to that level.

    Hold just prevents the battery from draining. At the 40% for mountain mode, hold is going to feel the same.

    The key difference is mountain mode can charge the battery back to 40%, hold wont charge at all.
    Mountain Mode in Gen 2 is about 20%. The ICE generator is more powerful so not as much buffer is needed in the battery. And yes, the car is always propelled by the electric motors even if the ICE is running (the electricity coming from the generator). There are times when the car must dip into the battery because the generator doesn't have enough output for heavy acceleration or hill climbing. Then the battery is recharged back to the preset SOC. At times the ICE can "HELP" propel the car directly, when it is more efficient to do so, but the Volt is mostly an electric car.
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  6. #4
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    There are three Range Extending modes, Hold, Mountain Mode, and Fully Depleted Battery. I have yet, however, to read any documentation that points out any performance distinctions between these modes under any particular driving conditions.

    It is possible that Mountain Mode’s programming, which establishes a programmed soc "hold" point and if needed will recharge the battery to that point (~4 bars for Gen 1, ~2 bars for Gen 2), might be tweaked to maximize performance under high demands conditions (e.g., driving fast up steep mountain roads). It is also possible that when the battery soc has reached the programmed low point (i.e., fully depleted battery), the system operation would be tweaked to minimize any drop in soc below that minimum level. Hold mode, in contrast (once called "City Mode" because the intent was to enable the owner to preserve battery use for urban low emission zones), allows "at will" access to use of the ICE, can be switched on at any soc level, and might not be programmed with precautions used when operating at low battery soc levels or under high power demand needs.

    Perhaps all three modes have very similar behaviors, except under particular circumstances where the "tweaks" do matter. Or perhaps there is no difference except the soc hold point.

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    I would venture to guess that the one way clutch that locks the ICE to the planetary input (yes, gen 2 does this- it doesn't only run on the electric via the traction inverter) when you are in Hold mode, but in MM it is decoupled because the system requires a generation surplus to charge the battery over the current requirement for propulsion.
    Therefore the one way clutch that locks the ICE to the input shaft of the transmission will not work because the rpm requirement for MM would be a higher rpm.

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    I noticed the same. It seems it intenitionally uses some of the battery in hold mode and then replenishes it. ALso once out of hold mode often my miles continue to accumulate against the engine count not pure electric count.

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    Quote Originally Posted by imanjunk1963 View Post
    I noticed the same. It seems it intenitionally uses some of the battery in hold mode and then replenishes it. ALso once out of hold mode often my miles continue to accumulate against the engine count not pure electric count.
    I notice the same with our 2016 Volt I believe its due to the gas engine generating the electricity to power the car even after the gas engine goes silent into normal mode. The computer somehow knows this and calculates fuel burn and kwh usage this way.

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    Quote Originally Posted by mike100 View Post
    I would venture to guess that the one way clutch that locks the ICE to the planetary input (yes, gen 2 does this- it doesn't only run on the electric via the traction inverter) when you are in Hold mode, but in MM it is decoupled because the system requires a generation surplus to charge the battery over the current requirement for propulsion.
    Therefore the one way clutch that locks the ICE to the input shaft of the transmission will not work because the rpm requirement for MM would be a higher rpm.
    No, the one-way clutch is only relevant when the ICE is off and the car is running entirely on the electric motors and battery. The one-way clutch allows the smaller motor (the "generator") to help push the car forward. Without the one-way clutch it would end up pushing the ICE backwards because the ICE (ring gear) and the generator motor (Sun gear) are both on the same planetary gear set and their gears are meshed together. With the one-way locking up when the ICE is being pushed in reverse that redirects all of the power to instead spin the planetary carrier on that planetary gear set which is ultimately connected to the wheels. The one-way gear is irrelevant when the ICE is running because the ICE is spinning in its forward direction of rotation.
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    Quote Originally Posted by imanjunk1963 View Post
    I noticed the same. It seems it intenitionally uses some of the battery in hold mode and then replenishes it. ALso once out of hold mode often my miles continue to accumulate against the engine count not pure electric count.
    Hold Mode could instead be called Hybrid Mode because it just causes the Volt to operate within a narrow window of battery charge (roughly 0.3 - 0.5 kWh). This holds or preserves the overall level of battery charge while allowing the car to briefly run with the ICE off when that is more efficient and then recharge the battery with the ICE or through regenerative breaking to keep the battery within that window of charge level.
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  13. #10
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    Quote Originally Posted by TSquare View Post
    And yes, the car is always propelled by the electric motors even if the ICE is running (the electricity coming from the generator). There are times when the car must dip into the battery because the generator doesn't have enough output for heavy acceleration or hill climbing. Then the battery is recharged back to the preset SOC. At times the ICE can "HELP" propel the car directly, when it is more efficient to do so, but the Volt is mostly an electric car.
    This is a little misleading, especially for the new 2016+ generation Volts.

    The new generation Volt no longer has a series generator mode so the ICE always has a mechanical path to the wheels. When the ICE is running, a majority of the torque and power flows mechanically to the wheels with the generator used to help control the engine rpm in order to create the effect of a continuously variable gear ratio. In one clutch setting, the new Volt has a fixed ratio gear connection from the ICE to the wheels where the engine can drive the wheels entirely by itself without any motor and battery assistance (although this remains possible, if needed).

    Even in the original 2011-2015 Volt, the car typically spends most of the time with the clutch connecting the ICE so it has a mechanical path to the wheels when the car is above around 40 mph and the the ICE is running for whatever reason ("empty" battery, Hold Mode, etc).

    See:
    http://gm-volt.com/2015/02/20/gen-2-...des-explained/
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