Another Positive Review for the Chevy Volt

[Slapshot28]

Here's a new Volt review from Conceivably Tech:

http://www.conceivablytech.com/6567/...chevrolet-volt

It starts right off with, "If there was ever a car we did not want to give back, it was this one."

One thing confused me: the low MPG quoted in the article. "It is tough to take the Volt into the 35-40 MPG area when on gasoline: I hit a maximum of 37 MPG in feather-footed driving, but was closer to 31 MPG in normal driving."

That must be city driving in Sport mode. That's all I can imagine.

On another recent long trip in the Volt (400 miles) I paid close attention to real-time mileage, as displayed by the Volt's Trip Odometer. Averaging about 65-70 mph I got 39 MPG consistently. If I dropped to 55-60 mpg, the mileage increased to 40 MPG right away. If I drove 75 mph for brief periods I got maybe 36 or 37 mpg.

It's amazing how precise and responsive the Volt measures real-time gasoline consumption. I'm guessing the Volt must use either a gasoline flow meter (likely), or a sensitive gas-tank weight measurement (unlikely). Certainly a conventional gas-tank level measurement would not provide sufficient precision.

The two boys in the back seat were in heaven for the whole trip. They love the rear bucket seats.

Chris
VIN '541
Berwyn, PA (and currently Corolla, NC)

[Steverino]

I liked "the Volt is very unique and gives a glimpse how many of our cars may function within 5 to 10 years."

Here's a CNET video review that is favorable overall, though less in depth. Oddly, at one point the reviewer suggested that charging the car is an "awful lot of hassle just to get 93MPGe" and most folks would probably be happy driving it as an ICE. Kind of like going to a great seafood restaurant and ordering a burger in my mind :-)

http://cnettv.cnet.com/2011-chevy-vo...-50102661.html

[adamsocb]

I agree this is generally a good review.

The MPG difference may do to cycle time. The article reads as though they did not take any long gasoline burning Charge Sustaining (CS) mode trips. I have never run in CS mode for more than about 30 miles, and most of my CS cycles are 10 miles or less. My CS MPG is down around 30 as well.

I think the reason is that an ICE will use more fuel when cold (lower air/fuel ratio), so short CS mode trips likely get worse MPG than long ones where the ICE is warm and the air/fuel ratio stays at stoichiometric, or optimal, efficiency.

[Slapshot28]

The MPG difference may do to cycle time. I think the reason is that an ICE will use more fuel when cold (lower air/fuel ratio), so short CS mode trips likely get worse MPG than long ones where the ICE is warm and the air/fuel ratio stays at stoichiometric, or optimal, efficiency.

That makes a lot of sense. I wonder if, in the first minute or two of CS mode, the ICE also is recharging the battery a bit, just to assure sufficient electrical power buffer. I can imagine that the ICE control logic might operate that way.

Chris

[Rusty]

I wonder if, in the first minute or two of CS mode, the ICE also is recharging the battery a bit

That has absolutely been my impression. It sucks when I just have a mile or two to drive in CS because I don't quite have enough CD range. The ICE comes on hard and strong. I think that's because the end of CD range SOC is below where they want the CS SOC to be. So, as you say, they spend gas to make up the difference. From an engineering sense, it makes sense. It'd be nice if we could tell the car "Look, I know I'm going over my CD range - go to CS earlier at the CS SOC point."

[Slapshot28]

One of the simplest kinds of controllers uses a "dead band" to turn on and off the device. Home heating systems typify dead-band controllers. (Those of us old enough may have marveled at mercury rheostats in our youth. In contrast, cruise control is not a dead-band controller; it's a proportional band controller. It cranks up and down, an analog action, rather than on and off, a discrete action.)

Almost always a dead-band controller turns on at the bottom of the dead band (the low setpoint). Then it stays on until it reaches the top of the dead-band (the high setpoint). Surely the Volt is a bit more complex, since it also can decide how "hard" to push the ICE when it turns on. Nevertheless, I agree with you.

It seems like an accurate determination of MPG would require careful study and repeated experiments over a relatively long period of time in varying conditions. A few quick looks at the Trip Odometer, especially at the start of CS mode, might give a misleadingly low answer.

[adamsocb]

I agree this is generally a good review.

The MPG difference may do to cycle time. The article reads as though they did not take any long gasoline burning Charge Sustaining (CS) mode trips. I have never run in CS mode for more than about 30 miles, and most of my CS cycles are 10 miles or less. My CS MPG is down around 30 as well.

I think the reason is that an ICE will use more fuel when cold (lower air/fuel ratio), so short CS mode trips likely get worse MPG than long ones where the ICE is warm and the air/fuel ratio stays at stoichiometric, or optimal, efficiency.

I just got a Thunderbolt Android phone so I can access MyLink. My total miles is 1507 and my EV miles is 1350. By subtracting EV from total I get 157 CS or “gas” miles. My total fuel burned is 4.6 gallons. This makes my “gas” MPG about 34, so it is better than I thought.