How will the Chevrolet Volt be better than a Toyota Prius plug-in hybrid?

Excellent! Thanks for that info.

You wouldn't want to. The point is that in mountain driving the regular Prius will charge its battery to full and then regen stops. With the system described by usbseawolf, it would be able to store far more regen energy on long downhills before it ran out of space. That energy would then be available when you hit uphill or level terrain.

What happens with the Volt in CS mode on very long downhills? Is it capable of recharging the battery to full on a long enough downhill, if it was in CS mode before hitting the downhill?

I suppose that with 35 miles of range, it's unlikely you'd ever reach full, but my question is: Would it revert to EV mode, after having been in CS mode, if it hits a long enough downhill to charge the battery enough from regen?

 

I believe you have the right of it with regards to long down mountain runs, however I have seen some posters think this means the normal regen driving around town will somehow fill their EV range, which it wouldn't.

Truth be told I don't know the answer to your question about if there is an arbitrary cap on the amount of regen in the Volt. If there is I've never hit it (but I've never driven it on a mountain yet either).

Your question about whether it would revert to EV mode is a little easier to answer.

I have done tests where I use mountain mode after depletion to manually raise the charge level, then turn MM off so it floats back down to normal CS level. If I do that before AER indicated reaches zero, the gauges switch to Blue "gas" mode in MM and when I turn MM off they go back to green "EV" mode (showing about 14 EV miles). If I do the same thing after AER has reached 0 miles, then turn MM off the gauges will stay blue and not turn green again so no additional EV miles will be shown.

However, even though the gauges stay blue and miles are being tracked in the CS "gas" miles, I will not burn any gas for the next 14 miles. If instead I immediately stop the car and restart it, the computer checks the actual charge level and will reassess and display the true green EV miles left. Regardless of what is displayed or how they are tracked I am getting the EV range, regen appears to happen the same way.

If I get a lot of regen while still in CD mode, the green bar meter may go up and some additional range may be displayed. If I get the same regen in CS mode the green bar is unlikely to move and no additional EV range will be indicated but I will drive on electric only for the same amount of time.

Its a bit bothersome to deal with miles of electric driving being tracked as gas miles, but the alternative I suppose would be to track electric miles every single time the battery was supplying power in normal hybrid operation.

What I've seen is that to get that extra 14 miles I burn gas faster in MM mode, such that I may only get 25 miles to the gallon, which results in 1 gallon of gas propelling me 25 miles and then using the generated electricity for another 14 and still getting around 39 total miles out of that 1 gallon of gas.

 

Good question.

I don't drive often enough on long downhill mountain roads to be sure but my guess is that a Volt in CS mode would not switch back to CD (EV) mode even if the battery was significantly recharged going downhill. However, I suspect that if you were to stop, turn off the car and then restart it you would reboot back up into CD mode. These modes in the Volt are really just about driver perception and mileage display accounting and do not influence the actual behavior of the powertrain.

It's really all about the battery state of charge. As long as your battery is above a target level (around 22%, I think) the gas engine will stay off. Once the gas engine is on, it generally provides enough power to maintain the battery around 20% while supplying enough power to the electric drive motor (via either a series or series/parallel configuration).

If you regenerate power to the battery by driving downhill and raise its state of charge above around 22% then the gas engine will stay off until the charge level falls back down again. In theory, you could regen all the way back to a full battery and it might keep the gas level icon on the driver display and appear to remain in CS mode but the driving behavior would be identical to a Volt that had just been fully recharged from the grid. But since you were in CS mode, the mileage display would count these miles as CS rather than battery grid miles because it makes the simplistic assumption that your downhill regen was just recovering the potential energy from an earlier drive up the other side of the mountain using the gas engine.

The Volt behavior is different from a blended power split design like the PiP which has an "EV mode" button to tell it to avoid starting the gas engine under periods of higher torque demand. The Volt has a larger battery power capability so it doesn't need to implement a blended power output.

 

Thank you both, Gwmort and Jeff. So the Volt will accept as much regen as the battery can hold, and will then revert to EV mode. (I'm not concerned with the contradictory dashboard display. Just with the actual drivetrain operation.) That's good.

In the early days of the Prius, once people started installing the EV switch, there were some who thought it was a good idea to get the battery fully charged and then drive electric until it was depleted. Of course this was an inefficient way to drive. However, there were limited conditions under which the gas engine would keep running even when the battery was full or nearly full, and then judicious (and I stress judicious) use of the EV switch to bring the battery back down to 5 or 6 bars was beneficial.

I continue to believe that if you are going to burn gas, then Toyota's method of blending gas and electric is more efficient than the Volt's method of either-or. Of course, I prefer to leave the gas engine at home (Prius) and drive electric (whether Xebra or Tesla) whenever possible.

 

They do provide this information and more. You do need to divide as they provide kwh/100 miles. The prius phv will be a little different since its blended and will have a mpge number (toyota estimate 87 mpge in charge depletion mode) that requires more knowlege of the gasoline usage to figure gas/electric split. I'm sure some pc person will figure this out soon, and share the information.

While quite true, the porsche 918 with a much more powerfull engine allows a hybrid mode to be selected. This can be for more power, or an efficient blend. The mountain mode in the volt provides a partial switch to hybrid, but not as nice as allowing for ice+battery power, or ice+battery efficiency.

There is likely a top SOC in the PIP and volt that the engineers have determined for pack longevity. I'm sure its under 100%, but it is unlikely there is a road that could charge either car to 100% so this should not hurt the feature.

But you are changing cars to decide when you are burning gas. Why not go full EV when the route allows, and use gas when it is past the EV range. The only reason to go the prius route is cost and weight, this compromise is not intrinsically superior, simply an engineering trade off. PHEVs are in their infancy, I would expect to see a number of blended and ev + er before they get large market traction. We know nissan is looking to add a small generator as an option, but this range extender adds many CARB costs.

 

Of course, when I say "full" I mean as full as the design permits, as opposed to limiting regen to the charge-sustaining threshold.

Because it is inefficient to haul around an unused ICE, or an unused battery. The Prius will burn far less gas than a Volt on my long drives up to Canada for summer hiking. Also because the complexity of (e.g.) the Volt makes it IMO less reliable than the Prius, which is conceptually complex, but mechanically simple.

If cheap transportation were the issue, a used Civic or Corolla beats a Prius, Volt, or Tesla. And admittedly, it is in one sense wasteful for me as a single person, to own two cars. But many families have two or more cars, and it is (again, IMO) more efficient to use a pure EV where possible, and the most efficient gas car (Prius) for long trips. I believe that the majority of two-car families woud be better off with a Prius and a Leaf, than with a Volt and any other car, or with two gas cars. (Given that the Tesla is outside the price range of most Americans.) (Hopefully a time will come when quick-charging is as common as gas stations and EVs can replace gas entirely. I don't expect to live to see that day.)

 

I think it's confusing to describe mountain mode as a kind of hybrid variant. All it does is raise the minimum state of charge setpoint from 20-something percent to 40-something percent. Doing that only causes the gas engine to start up if your battery is below the new higher minimum target level.

I wouldn't be surprised to see an ice+battery power mode on the future Cadillac ELR Voltec since it seems doable and would fit with Cadillac marketing.

The ice+battery efficiency seems more dubious. I'm not sure how blending in burned gasoline is more efficient than driving full-power electric assuming you have enough battery power (and I'm surprised to see Daniel favors this). I can see how using electric power can help improve efficiency of a smaller gas engine during strong acceleration but that presumes you are burning gas and I don't want to be doing that when I have enough charge left to drive on electric alone.

 

Its not that inefficiency. The leaf uses 34kwh/100 miles the volt 36kwh/100 miles, and these differences are are mainly because of the design choices. If your going all the way to canada your likely doing mainly highway miles where the volt is 40mpg, your gen II prius 45mpg, not a huge difference either. Let's face it, it is less efficient to have materials, parking, registration, insurance, etc in 2 cars versus 1. You have a really cool car in the tesla roadster, which makes keeping the prius make sense, but for the bulk of those not able or wanting a tesla, the argument seems hollow. The volt is new, but not more complex than a prius, but time will have to tell on reliability. I would not bet on the gm being more reliable, but I already have rattles in my gen III.

tesla is an outlier because of its range and price. Some people can easily live with the limitations of an imev or leaf or future bev focus and rav4, but many more can drive partially electric and still handle all their trips in a phev like the volt or upcoming prius phv or cmax energi. Since this thread is about which is the better phev, I find it intellectually wrong to say you really need two cars a hv and a bev. Both people may need to drive further than an BEV, and families are unlikely to be replacing both cars so the gas car left will likely get worse mileage than the volts 35mpg city/40 mpg highway.

 

I favor pure electric, as I've said many times. But I also said that IF you must burn gasoline, because your trip is significantly beyond your electric range, then blending the way Toyota HSD does is better than first using all your electricity, and then burning your gasoline, the way Volt does.

My actual highway mileage in the 2004 Prius is consistently 51 mpg. That's on my trips to Canada (my only road trips for the past 2 or 3 years) which means it's summer, on secondary highways, with speed limits of 55 mph on some and 65 mph on others. That's about 16 mpg better than the Volt in gas mode.

In town my Prius does not do as well, but in town I drive pure electric, formerly in the Xebra, now in the Roadster.

 

To answer it simply. Once the Volt enters into CS mode with the gas engine running it will not revert back to "EV" mode... This is one thing that irritates me with the car. Even if you roll down a long enough hill, and say you get 0.3-0.5kwh back in to the car it will drive in EV mode until it re-depletes that charge. The caveat however is that the car will record those miles as gas miles even though the engine was not on. To me if the engine is off and not using gas they should be recorded as EV miles. It will even show you on the display that it is on battery power alone, then it will change over to battery/engine mode, and finally it will grey out the battery and go into engine only. So it will put energy back in to the battery. Your only indication of this though is to know how many kwh hours your battery depleted at, and then watch that counter run backwards. It will never put bars back on the battery icon like the Prius does unless you plug it in that I have seen. Granted on the Volt 1 bar = approx 1kwh, and that is a lot of juice to put back in by regen braking.

 

A non-plug Prius HSD isn't recharged from the grid and has a small battery with a narrow useful state of charge range of about 300-500 Wh. Studies have shown that increasing the battery buffer beyond that level does not significantly increase efficiency burning gasoline.

At highway speeds (40-45 mph+), the Volt operates in a serial/parallel mode effectively like the Prius except when it is briskly accelerating. The Volt manages to get the same EPA highway mileage rating of 40 mpg as the compact Lexus CT200h which uses the 3rd generation Prius 1.8L HSD powertrain even though the Volt weighs 500 pounds more mostly due to the larger battery pack.

I did a 2800 mile road trip in my Volt from California up through British Columbia on the TransCanada Highway and back and averaged 42 mpg gas-only driving similar speeds. I probably could have done better if I had increased the tire pressure beyond the GM-recommended 35 psi (51 max psi tire rating) and if the first 700 miles hadn't included 3 other adults and their luggage.

Weird coincidence -- I drive full electric back home also but I don't have to switch cars. I can also charge up along the way during long trips. On this trip to Canada my total average was 45 mpg due to charging at the homes of relatives and once at a parking lot in Vancouver, BC. Next time around I assume I'll be able to also charge conveniently at the hotels along the way and increase my total mileage to 48 mpg or better.

 

So this confirms what both Jeff and Mort have said: The Volt drive train works like it should: It accepts regen as long as the battery has room for it (within whatever charging limits the designers have programmed in) and then uses that regen energy for driving. So on a long mountain downhill it would charge all the way down, and then revert to electric operation. I give the car points for this.

Only the way it displays and calculates electric usage is screwy, which I can see is annoying to people who want to track their exact usage constantly, but which, frankly, I consider a secondary matter of minor importance. I don't take any points away from the car for this.

Again, for me, I prefer having the two cars, because I NEVER burn any gasoline unless the EV cannot do the trip. And with only minor exceptions (hauling big stuff on extremely rare occasions, and parking at the airport) those trips are so long that the Prius burns less gas than a Volt would, since I'm not going to stop every hundred miles for a multi-hour charge-up. And around town, rather than a 35-mile ideal EV range I have a 245 mile ideal range. Even with hard (fun) driving and the heater on full blast, I'll still never drive beyond my EV range except for the aforementioned road trips. A Volt right now in Spokane (using the heater) would have considerably less than 35 miles range and would probably burn gasoline every time I go downtown (roughly 30 miles round trip and no convenient place to plug in unless I make a special stop and sit around for a few hours).

Don't get me wrong: I'd have bought a Volt if it had come out before there was a full-on EV available. I just prefer a full-on EV now that such cars are available. And (JMO now) I expect better long-term reliability from the leaf, and even the Tesla, than from the Volt, because I simply do not trust GM's commitment to quality.

 

So far I am doing good as far as not burning gas.. I needed 0.2 gallons the other day cause I over did it (but then again that is what the 4 banger under there is for). I am always looking for the shortest way between point A and point B.. Really makes you re-think how you drive that is for sure. My first day driving to work yesterday was 17 miles.. Found a way today with the help of a co-worker and I am now down to 9.7mi.

Since you are on here Daniel a question for you since you have a Tesla.. I have noticed with the Volt going faster really depletes the battery charge rather quickly. Granted I am still over the EPA's 35 mile est, but not at the 44 mile range I was when I left Florida. Granted today I did got 40 miles with 3 left showing when I pulled in the driveway, but that is because of my new shorter (and lower speed) route.. Does the Tesla show any drastic kwh usage going 55mph over say 45mph. Everything I have read says 50-55mph is about the most efficient speed, but it would seem to me 45mph is better for getting the most range out of the battery and not being a nuisance to other traffic.

 

The most efficient speed for the Tesla and LEAF appears to be around 15-20 from what I've read. I haven't read any careful tests for the Volt but I'm guessing it is similar.

Electric Vehicle Range and Charging - Tom Saxton's Blog

 

Almost there, CT200h gets 41MPG EPA. Volt gets 40MPG. But that's highway only.
In city driving CT200h gets 42MPG while Volt gets 35MPG.

 

I have not noticed it myself, but I've never paid much attention. One of the great benefits of having more than twice the range I'll ever conceivably use, is that I don't need to worry about maximizing efficiency or finding the shortest route (as I did with the Zap Xebra).

However, the attached graph shows that, as Jeff says, the most efficient speed is around 15 to 20 mph. Just eyeballing the graph, it looks like the range is 240 miles at 55 mph, and 200 miles at 65 mph. That's a 17% loss going from 55 to 65. But when you have 240 miles of range, losing 40 is no big deal unless you're planning a 220 mile trip. And for me, the Roadster is not a road trip car.

Another way I lose range is jackrabbit starts. Before heating season arrived to further complicate matters, when I charge in Standard mode (charging to just under 90% SoC) it told me my ideal range was 188 miles but my range "the way I've been driving recently" was around 170 miles. But with both those figures, I can still access the bottom 10% of the battery if I want to, so add 10% to both; and if I'm planning a longer trip I can charge in Range mode and charge the battery to close to 100%.

So your only error is "most efficient speed." You are correct that faster driving uses more energy. The really huge battery is one of the reasons I decided to buy the car: So I would never have to worry about range. (The big battery also means I am using less of the battery capacity, and that should extend battery life. And in addition, I can tolerate a much greater loss of range before it becomes too short for my needs.)

This whole week, my trips have been short, with the heater full blast. I'd have turned the heater way down had I driven farther. So this is a worst-case scenario: Standard charge, jackrabbit starts, heater on full. I think it told me about 140 miles range. 70 mph on the freeway would be less efficient, but if I'm going that far I'd be using much less heat after the first five minutes.

 

Exactly why gas engine should be used for high speed. I like how PiP intelligently use the best fuel for the situation.

Volt has 1.4L gas engine so it should get better MPG on the highway. Weight does not matter much on the highway, aerodynamic does. Both cars are rated 0.28. Assuming cross-section areas are the same, Volt should get better mileage on the highway due to smaller gas engine.

Having said that, Prius v (wagon) also gets 40 MPG on the highway.

 

According to both fueleconomy.gov and Lexus.com, the CT200h gets an EPA estimated 40 mpg on the highway (43 mpg city, 42 mpg combined).

I drive almost all of my gasoline miles on the highway.

 

Why not the city as well?

 

I'm not sure why you think burning gasoline at high speed is inherently more efficient than driving electric.

Just because a Prius burns gasoline at high speed due to perfectly reasonable engineering compromises doesn't mean it's inherently a good idea for cars designed with different trade-offs. My fueling costs are lower driving electric on the highway along with my total well-to-tank CO2 emissions.

I do choose to burn gas on the highway when my driving distance significantly exceeds my battery range. I do that because burning gas is a bit more efficient cruising on the highway than in stop and go city driving in my Volt. That's not even true in a PiP which is equally or more efficient using gas in city driving.