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Comment: Re:nope (Score 1) 426

by AikonMGB (#48806339) Attached to: Chevrolet Unveils 200-Mile Bolt EV At Detroit Auto Show

My understanding is that the Volt also shifts into the mechanical connection at very high speeds (in the area of 70mph / 110 KmPh) even when it has power in the battery. The ability to couple the engine to the drive wheels adds a lot of mechanical complexity to the transmission, which both adds weight to the car and creates a possible maintenance problem; I wouldn't be surprised if the next generation Volt does away with that and becomes a pure series hybrid.

If you are in charge deplete mode (i.e. running off the battery), the Volt will not turn on the ICE nor engage it to the wheels regardless of speed. It is the sources that led to that misunderstanding that I am trying to get to stop spreading false information =/ Sources: a) I own a Volt; b) GM's head of electric propulsion; c) Popular Mechanics; I could keep digging up more if you'd like.

If you watch the "Deep Dive" videos on YouTube, you'll see that the system is actually not that complicated: a fixed planetary gear set with three clutches that only mate when speed-matched. This is much simpler than the transmission in most vehicles, including automatics, standards, and CVTs, so it is disingenuous to say that it could be a maintenance problem. Is it more complicated than a single electrical motor connected only to the wheels? Yes. On the scale of possible automobile complexity is it really that complex? No, not really. Have a look inside a dual-clutch automated manual transmission.

Lastly, I would be very surprised if GM moved away from the Voltec drivetrain. They have invested a lot of money in designing it, and these very aspects that we're talking about are what make it stand apart from other parallel, series, and parallel+series hybrids out there. The fundamental decision is if you're committed to lugging around an ICE to drive a generator, how do you make the most efficient use of it across the full range of driving scenarios? The Cadillac ELR is based on the Voltec drivetrain (slightly different ICE, possibly slightly different motors, and certainly different software) and operates in the same fundamental way.

p.s. The next-generation Volt has already been unveiled, and the new generation of Voltec drive-train appears to operate in much the same manner; they even indicate that a key development is to couple the two motors together in even more driving scenarios

Comment: Re:Double nope (Score 1) 426

by AikonMGB (#48795095) Attached to: Chevrolet Unveils 200-Mile Bolt EV At Detroit Auto Show

Exactly right, but your sensible viewpoint doesn't belong anywhere on a blog site, apparently. No, you can't completely describe the Volt as a plug-in hybrid, EV, series or parallel hybrid, or whatever--it's a Volt and there's nothing else exactly like it.

Haha, +1 on that first point. Hurrah for nuanced opinions!

You are exactly right, the Volt cannot be described using the existing "hybrid" terminology. That is why GM fought to call it an "extended-range EV", but no one could get past the part where the engine drives the wheels (sometimes). It's a shame, really. They caved for the ELR; despite having the same basic drive-train (different ICE, probably slightly different motors/electronics, and definitely slightly different software) they are calling it a hybrid :(

Comment: Re: nope (Score 1) 426

by AikonMGB (#48794997) Attached to: Chevrolet Unveils 200-Mile Bolt EV At Detroit Auto Show

Please provide a citation for that being a pure series hybrid being the original intent. Please also provide a citation discussing how the one driving scenario we've discussed above prevents the range extender from being transitioned to a larger battery or a fuel cell. As a counter point, here's one that shows that it wouldn't be difficult at all. Since the ICE is not needed for maximum acceleration or vehicle speed, the Volt does not need that mechanical connection, it is simply an optimization of the equipment that they already had on board for the existing design. Replace the ICE with a battery and you get some higher EV range, but when it runs out it runs out. Replace it with a fuel cell and a Hydrogen tank and you can replenish the battery from that, but now you have to deal with the lack of Hydrogen infrastructure and the challenge of transporting it safely.

The Volt is not a series hybrid. It is not a parallel hybrid. It is not a pure battery-EV. It can be any one of those things depending on driving conditions and state of charge. If you peruse this website and sort by EV% (distance traveled in EV mode as a percentage of total distance traveled) you can see people using their Volts anywhere from nearly completely EV mode all of the time to nearly always series/parallel-hybrid. Obviously there is a use-case for the entire spectrum.

Comment: Re:nope (Score 4, Informative) 426

by AikonMGB (#48793491) Attached to: Chevrolet Unveils 200-Mile Bolt EV At Detroit Auto Show

The general problems are the design trade offs that occur any time when there is a direct mechanical linkage between the internal combustion engine and the drive train. The reason is because you are most likely forced to use an engine that has some greater variability in torque and rotational speed than would be necessary if there was no direct linkage.

Why does this matter? Because it likely reduces overall system efficiency. For maximal efficiency, you are better off having an engine that is custom paired to the generator, meaning that it runs at a very confined torque range and rotational speed to maximize generation of electricity since electrical generators generally work most efficiently at a specific rotational speed and fall off on either side of that speed.. This of course requires that the amount of electricity generated is enough to drive the electric motors alone (i.e. no battery support in the case that the battery is dead). By adding a direct mechanical linkage, the engine is likely to require operation over a wider range of speeds and torque and is less likely to be optimized.

Why all this "likely" talk? The video I linked to is the first in a series of presentations by Pamela Fletcher, the head of GM's electric drive train division. She talks about the trades and the systems design that led to what we have now; it's really pretty interesting. Basically they started out with exactly what you want: a traction motor driving the wheels directly, and a generator motor attached to an ICE, with only electricity flowing between them. Then they said "hey wait a second, electric motors are less efficient at higher RPM; can we use this second electric motor to reduce the speed of the first through a high gear ratio, thus improve overall efficiency at high speeds? By golly we can!". That is why the generator motor is able to couple to the traction motor at high speeds to drive the wheels together.

The fact that there is a mechanical linkage when you then enter charge deplete mode is actually a by-product of wanting the ICE connected to the generator motor, but also wanting the generator motor connected to the planetary gear set. It's not something that was baked in from the start as a "core ideal" or goal, it was something that came about as the result of a number of other trades.

The biggest downside to going this route is that there are intermediate periods of time where the ICE will be free-wheeling, which means they required a throttle assembly. If the generator motor were always attached to the ICE output shaft, you wouldn't need a throttle, because you could just cap the RPM using back torque from the generator motor.

Based on the specific conditions that you had indicated for when the mechanical linkage occurs (constrained torque scenario), it is possible that they were able to marry the best of both worlds in terms of efficient engine design, but I'm skeptical. Also, this setup would presumably mean that the individual drive wheels are not directly driven by electrical motors and that there is a drive shaft and differential of sorts in between the electric motor and the wheels. This likely also reduces overall efficiency than a direct drive scenario (i.e. electric motors directly connected to the individual drive wheels).

After warming up, the ICE is generally operating at wide-open throttle (peak efficiency for a given power output). Its RPM is capped by the torque put on it by the generator motor and, when in that situation, the planetary gear set. By adjusting the flow of current (and thus the torque) between the two motors, and using the battery as a buffer for transient events, they can adjust the output power of the engine simply by adjusting its output RPM. Keep in mind that the electric motors are not lossless and neither is charging/discharging the battery. Any power going from the ICE output shaft to the drive shaft mechanically is not subject to the losses of going through two electric motors (one to generate the electricity, then a second to turn that electricity back into mechanical energy).

In almost every vehicle, the wheels have independent half-shafts that are connected to each other and to the main drive shaft via a differential. The design of this differential is sometimes different (open vs limited slip vs Torsen, etc.). This applies for pretty much any mass-market vehicle you can think of. The Volt was never looking at individual drive motors for each wheel (neither did Tesla for the Roadster, S, D, or X; do you think there might be a reason for that?).

Comment: Re:nope (Score 5, Interesting) 426

by AikonMGB (#48792893) Attached to: Chevrolet Unveils 200-Mile Bolt EV At Detroit Auto Show

Take another re-read (and a chill pill, while you're at it). I never said it was a pure EV -- I said it operates as one when in charge deplete mode. While the systems are different than what we've been using with automatic and manual transmission gasoline cars for years, they are actually not that complex. Three clutches that only mate when speed-matched (which means low-wear, so they should last the life of the vehicle) and a fixed planetary gear set. Much simpler than an automatic transmission.

Comment: Re:nope (Score 4, Informative) 426

by AikonMGB (#48792637) Attached to: Chevrolet Unveils 200-Mile Bolt EV At Detroit Auto Show

Please stop spreading misinformation. There is a driving scenario where a) the vehicle is operating in "charge sustain" mode (i.e. battery is flat, or user has selected "Hold") and b) the vehicle is being operated at relatively high speeds (> ~50 km/hr) with low torque requirements (i.e. roughly constant speed). In this very specific driving scenario, you are correct, there is a mechanical connection between the gas engine and the wheels.

However, in all other driving conditions, there is no mechanical connection. In stop-and-go traffic around down or on the highway during rush hour, in charge sustain mode, the gas engine will drive a generator motor, the electricity from which feeds the traction motor and the battery -- this is a series hybrid configuration. Under any driving condition while in "charge deplete" mode (i.e. drawing from the battery), the gas engine never turns on, making it operate purely as an EV. An important point to note is that the vehicle is able to achieve is full performance capabilities -- acceleration, top speed, and braking -- under purely electric propulsion without the gas engine ever turning on. This is the distinction that makes it more than just a series+parallel hybrid.

Comment: Re:When the rocket is standing on the pad (Score 2) 67

Addendum: I don't know if this was mentioned in the article (yay laziness!), but most spacecraft are merely cleaned, not sterilized. Avoiding contamination is important for interplanetary missions, but not so much for something that's going to stay in Earth orbit or burn up in its atmosphere.

"Now here's something you're really going to like!" -- Rocket J. Squirrel

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