Coach's test drive of the Volt

Do you have any links or paper citations to back that up?

Both of those claims (clutching engine at lower speeds and high torque and using "two motor no ice" under high speed primarily to gain torque) are inconsistent with what I've read. My understanding is that the 2 motor configuration is used to gain efficiency by lower the RPM of the motors, not torque. I'll post my links tonight when I have more time.

 

Mgb does indeed gain efficiency at lower rpm. At 7000 rpm it can not generate as much power from the same battery power, which looks like a drop in torque on a dyno curve. The statements are consitant with each other. Motor trend looked at the torque curves which is where my point of view came from. If you are less efficient with battery power, then you will get less power to the wheels Going 80 the acceleration would get even worse.

The lower speed direct connection at higher loads came from a clarification from gm on the 70 mph motor trend had found. I can't find the source right now, and it could have been one of the marketing folks and not an engineer.

cool.

 

Here's a start. This is a quote from a GM-written blog for mechanics and what it says is consistent with other technical documents I've seen from GM engineering folks:

Voltec Electric Drive Unit and High Voltage Battery - GM Techlink

It is true, however, that at speeds above 75 mph or so these combined motor modes are generally used even under higher torque loads.

Another place to look is at the graphs posted at the following link. The actual paper may have addition useful textual quotes but I will have to look for them later. You can see from the graphs that single motor modes are preferred under higher torque demand at lower speeds.

http://gm-volt.com/forum/showthread...-RPM-then-quot-CD-mode-quot&p=67812#post67812

 

Thanks that was informative. Clearly what I read before about connecting the ice at lower speeds at higher power was wrong. The paper the graphs came from is a pay one. Figure 18 clearly shows that the ice is clutched in at lower torque. There is a curious region on this figure at the lower right, where the ice is off and both motors engaged at high speed lower power I would assume this is highly dependant on SOC of the battery. What do you think?

Figure 17 seems to have a region that tends to contradict what motor trend found in their testing. I wonder if this is pre production. That region has 1 motor at high speed high power. I can understand not changing the clutch during acceleration, but I would think once the second motor was clutched in it would stay clutched in, and allow for greater acceleration at these higher speeds. The only reason I can see for declutching is if the structural strength of the gears can not handle the torque.

 

I stand corrected that there are hybrids with worse FE than the Volt in CS mode. But those are bigger cars. The Volt, with its small 4-passenger size, has no excuse for its poor FE.

Oh, and entirely off topic: Isn't the PiP a liftback? The pictures look to me like a liftback. But everybody seems to be using "Prius liftback" to refer to the non-plug-in Prius. What's up with that?

 

The excuse is it weighs a lot. Haven't you seen all the wailing and gnashing of teeth about how it weighs nearly the same as an equinox? So it should have similar fuel economy in CS mode. Though aerodynamic drag is better. Anyway it has an excuse and in fact gets exactly the fuel economy one would predict based on the battery size. It is downright eerie how perfectly extrapolating smaller battery size PHEV simulations by Argonne come to exactly matching observed volt fuel economy.

 

All of those hybrids have larger displacement gas engine (V6 and V8 included!). Why are we focused on the highway MPG? The effectiveness of a hybrid system is in the city MPG. Highway is more to do with engine displacement, gearing, aerodynamic and vehicle frontal size.

Volt has the most powerful electric motor out of all those hybrid and the biggest battery to power it. Either the planetary setup is inferior or the battery weight worked against it, only the result matters. It is clear that Volt's hybrid system is ineffective at 35 MPG in the city.

 

From Sunday 11Mar2012:
My 2011 Volt with the famous 2011 software update which happened in the Fall when range was dropping anyway and people were concerned about it. Today it was 64F on my way to an event and I got 48.7 electric miles on the battery. No climate controls needed because of temp. 35-45 MPH with a lot of stoplight (which I don't think were good - stop/start acceleration kW usage)

Notice that my ICE/gas_generator mileage was pretty good as well. 39.7miles / 0.79 gal of gas = 50_MPGused. Yes, the ICE stopped/started multiple times.

 

You don't get how the volt is used. Who cares about the City CS? if you are doing mostly city you'll be in EV. If you drive more than 35-50 miles a day its likely a good chunk is on highway, which is where you can use the ICE. (Of course it would help if the EPA lets have an Hold mode like EU).

The comments on vehicle size (interms of interior room) does not really matter to efficiency, except as size impacts weight and aerodynamic.

The important this is that Volt's actual MPG (and MPGe) in normal use is way better than any of those hybrids. Real use is beating EPA on EV usage (and hence overall). The Volt's bigger battery help it avoid its ICE so its not that critical if the ICE CS milage is lower. How many PiPs are reporting 200+ MPG over thousands of miles? 220/598 people on Volt stats are. The median there is 150MPG!

So if you are worried about the MPG_CS, you are worrying about the wrong item interms of improving overall reduction of petrol usage.

 

Larger displacement does not always imply lower mpg as Toyota proved when they switched from 1.5L to 1.8L in the 2010 Liftback. Or, when they came out recently with the Prius C which is still 1.5L and smaller/lighter but only gets about the same mpg as the Prius Liftback. Likewise, the Honda Civic hybrid with 1.5L gets better mpg than the 1.3L Insight.

The primary reason for higher displacement is increased power for performance or to compensate for a heavier vehicle. The Volt is not notably slower or lighter than any of these cars.

All the vehicles listed below are 4 cylinder. I have noted cars with 1.8L or smaller displacement. The rest are 2.4/2.5L.

Code:

Gasoline 4 cylinder hybrids 40 mpg highway or less:

2012 Chevrolet Volt 1.4L (40)*
2012 Toyota Prius V 1.8L (40)
2012 Lexus CT 200h 1.8L (40)*
2012 Hyundai Sonata (40)
2012 Kia Optima (40)
2012 Toyota Camry (39)
2012 Honda CR-Z 1.5L (39)*
2012 Ford Fusion & Mercury Milan (36)
2012 Lexus HS 250h (34)*
2012 Ford Escape (31)

Gasoline 4 cylinder hybrids 37 mpg combined (city/highway) or less:
2012 Chevrolet Volt 1.4L (37)*
2012 Honda CR-Z 1.5L (37)*
2012 Hyundai Sonata (37)
2012 Kia Optima (37)
2012 Lexus HS 250h (35)*
2012 Ford Escape (32)

Gasoline 4 cylinder hybrids 35 mpg city or less:
2012 Chevrolet Volt 1.4L (35)*
2012 Honda CR-Z 1.5L (35)*
2012 Hyundai Sonata (35)
2012 Kia Optima (35)
2012 Lexus HS 250h (35)*
2012 Ford Escape (34)

* compact or 2-seater

I left off the Nissan Altima Hybrid (licensed variant of Camry HSD) since they discontinued it in 2012. It got 33/33/33.

I also left the 3 GM midsize "eAssist" mild hybrids off the list. They all got about 25/29/36 (city/combined/highway).

Highway is the most relevant comparison for the Volt because its larger battery pack will cover the large majority of the city driving. The Volt's gas engine will be primarily used on the highway during longer commutes and road trips. That will also be true for the PiP but to a lesser degree since its smaller pack is more likely to leave people driving significant city miles on gas even if they hold battery capacity by toggling the HV button on the highway.

 

Great results. You really know how to milk it.

Average CS MPG on Voltstats.net remains to be 35 MPG so you are in the extreme end of the spectrum.

 

Under those conditions I'll get about 310 miles of EV range. But if I have to go that far I'll drive the Prius and burn less gas than a Volt.

The Volt excels under a very narrow range of conditions. That's probably why so few people consider it worth the price tag.

 

You are driving the Volt like Prius PHV at 35-45 mph speed. What about the highly hyped Volt's superior features such as a full EV acceleration up a mountain or at very high speed?

 

You are complaining because he chose to drive efficiently?

 

They are mostly due to gearing and aerodynamic. Both GenIII Prius and Civic hybrid have better aerodynamic than GenII Prius and the Insight, respectively. The final gear ratios are also taller respectively.

I do acknowledge that Gen III Prius 1.8L gas engine is more efficient with better BSFC. It is not the only factor.

The comparison you did with Volt and all those hybrids have a huge variation. 2013 Fusion midsize hybrid with 2.0L is reported to get 47 MPG in the city while the compact Volt is rated at 35 MPG with 1.4L ICE.

Volt is designed to deplete the battery first, either highway or city and then use the gas engine as a range extender. What if one's city driving is at the end of the trip? The owner should pretend that there is a mountain to climb toward the end of his/her commute? Mountain mode is the only way to "hold" the battery charge.

Things complicate further if your commute is mixed with highway->city->highway->city. Volt will end up recharging the battery with the gas engine and may not use all the battery charge at the end of the trip when used with mountain mode.

What we can take away from this discussion is that using the right fuel for the right traffic condition good for efficiency. EV purity for any speed/condition is bad.

Another point I want to make (which I have in the past) is that, Volt was engineered with the best case in mind. Prius PHV was engineered with the worst case in mind. Volt's worse case is 35 MPG in the city on premium gas. It's best case is 35 EV miles at 94 MPGe. GM did a poor job minimizing the worse case but instead focused on the best case.

Prius PHV's worse case is 49 MPG with regular gas on the highway. Toyota bumped up 1 MPG over the no-plug liftback. The best case is 11 miles at 95 MPGe. To me, Prius PHV is a better balanced car with a much lower price (MSRP, not cost after tax credit) and superior refueling speed.

 

No, just pointing out that he isn't using the EV performance that he paid for. If he is driving the Volt like a Prius PHV, what was all the fuss about Prius PHV gas engine starting at full acceleration and all the braggings about Volt's high speed EV performance?

How was he accelerating in EV mode to get that kind of range? I bet Prius PHV 0-30 mph acceleration in 6 seconds is enough for that kind of driving.

 

Since the Ampera can go into hybrid mode whenever the driver chooses, this might be more of a regulation issue. My gen2 Prius didn't have an EV button or HID adjuster, but had the blanks for them on the dash.

 

If they can put the mountain mode, what could be the problem with the hold mode? Prius PHV has the EV/HV button to hold the battery charge so it can't be US specific regulation.

I think the real issue is, not to destroy the investment in the entire EREV campaign. It'll make the Volt operate the same way as Prius PHV but with more inefficient, less useful features that costs more and longer to recharge.

 

Umm he can drive more than 15 miles on electricity? That is kind of a reason to get the volt...

 

Its comments like these that come across as really opinionated, when I believe you were trying to be more objective.

I think your second sentence would be more objective if you had said "EV purity for any speed/condition is bad for efficiency". It would more closely parallel your first sentence and be less of an overall judgment on any other aspects of the design.

I completely agree the right fuel for the condition is generally good for efficiency, particularly if I am going to exceed the AER and burn gas later anyway. But what if the drive is just 15 miles, but requires heavy demand that will run the ICE in the Pip? For the Pip running the ICE is an efficient choice to save the limited battery capacity for when it will matter the most, but for the Volt it would mean dropping out of 94mpge when it is really not necessary to do so because the whole trip can be completed at that level, staying in EV in that case is more efficient (compared to if the Volt dropped out of EV to burn gas on the higher demand portions).

At the moment the cars can't properly factor in the trip duration when deciding when it will be efficient to run the ICE (maybe with nav advancements in the future they will). What is needed is driver intervention to make those decisions. The Pip lets you do that with the HV button or in Europe the EV city button, the Volt only has the limited ability you mention with the mountain mode.