Beyond the first 40 miles driven, which can be provided by only battery power, the energy to power the Volt comes only from the ICE. How can such a car have any performance at all when such a small engine is driving it? Am I missing something or is this car being powered only by a 1 liter ICE beyond 40 miles. This seems unbelievably small.
I'm not an expert here, but I'll try to share what little I know. I've seen various figures out there about the specs of the electric motor and genset, but let's just assume this is accurate:
Electric Motor: 100 kW
According to that, yes, it is conceivable that while on genset power, performance will be significantly weaker. But consider this: You will rarely go above 53kW when driving. That means while you are below 53kW (or not accelerating), the batteries will be charging (and from a 30% charge at that). You will also get additional charge from regenerative braking as well (when slowing). So if you do need occasional extra performance (even with the genset active), the batteries are still there, and are willing to provide what they have (to a point).
So, yes, the Volt will still have performance even when the genset is active. But you probably can't expect the Volt to deliver peak performance constantly.
GM has stated that their intent is to create a global car that has full performance under all reasonable driving conditions. They have spoken about starting the genset at 30% but have shown the battery will be allowed to discharge below this point when exrra power is needed. The car must still be able to perform even when starting a long inclining drive at 30% SOC. While the full power of the traction (driving) motor may be utilized for hard accelerations. These are only short term loads that require high power but not a lot of energy. The battery can easily supply the full power needs even when at 30% SOC and a bit below that.
The 1L engine runs at constant speed to charge the battery. Automotive engines usually run at a fraction of peak power, which is only used for hard acceleration. The battery in the Volt, not the internal combustion engine, can provide peak power to the electric motor for hard acceleration.
Thanks. The responses makes sense. However, below is a section copied from the Other FAQs written by the readers section. Is it incorrect?
Q: When the battery is depleted down to 30% SOC (state of charge)after 40 miles, why is it maintained there instead of the generator recharging it?
A: Powering the electric motor directly from the generator is more efficient than repeatedly charging and discharging the battery.
All batteries have some internal electrical resistance. Whenever the battery is charged or discharged, some energy is lost in the form of heat due to this resistance. By powering the motor directly from the generator, this resistance is bypassed. Energy is lost in this manner when charging the battery and when utilizing the electric range, but this is unavoidable and the energy loss is small compared to the energy wasted by an internal combustion engine.
A: If the generator recharged the battery, this would prevent taking advantage of the main feature of the Volt, which is to recharge it with grid electricity.
A: Cycling the battery more often would reduce its lifetime.
The first answer may or may not be accurate, but neither contradicts what we are saying. The generator's power will either flow completely through the battery or the generator, motor, and battery power control module will share the same bus. I have heard the Volt described both ways by GM personnel. Perhaps Lyle could get a clarification from the GM engineering team on this. In any case, the battery is capable of supplying full power to the motor.
The second Q&A is only referring to how the intend to control the genset under "charge sustaining". Since the genset is more than large enough to power the average needs of the car, it could also charge the battery to 100% if desired. GM wants to maximize the benefit of plugging-in (since this what makes the Volt so special), so the want to keep it as close to the lower side of the discharge cycle as practically possible. The genset will be optimized to run at about 25KW. This is more than enough for normal driving conditions. This will allow the battery to cycle between something like 25-40% during charge sustaining mode and always reach an electric with the battery in this range of charge.
I'm more than a little confused by what I'm reading here.
I understand the points the GM spokesperson made.
But there are a few things not mentioned:
--regenerative braking will charge the battery
--the ICE will be most efficient at a higher power output than the car will need to cruise
--battery power will be needed for peak acceleration
So it would seem that under at least some conditions it would make sense to cycle the ICE on and off as needed, and run from the battery. Yes, there are some losses going through the battery, but there would also be losses running the ICE continuously at a lower than optimal load.
They wouldn't want to charge the battery anywhere near 100%, for the reason GM gave. But maybe to 40 or 50?
The major reason this might not work: the longevity of the battery. But the pack in the Prius appears capable of a very large number of cycles.
I've posted this in some of the other forums, but I think I've found the Volt's engine. Warning: big pic.
Its a 1.0 liter, 3 cylinder 12 valve-Ecotec engine. This motor is slated to be turbocharged & flex-fuel capable. http://media.gm-powertrain.at/powert...8200001_01.jpg