Mitsubishi iMiEV vs. Honda FitEV EPA Ratings

[JoeS]

The purpose of this thread is to ask how exactly is the electric vehicle testing performed when trying to conform to the EPA test cycle. I'm concerned that our iMiEV is not getting a fair shake.

INTRODUCTION

For the last 6000 miles that I have carefully measured on my iMiEV, my average energy consumption is 4.24 miles/kWh = 236Wh/mile = 23.6kWh/100mi = 142.9MPGe using EPA's 33.7kWh/gal equivalency. This is a helluva lot better than the Monroney sticker of 112MPGe (combined city/highway)... but the last paragraph below perhaps explains the discrepancy. That's not the issue, but raises a flag.

I've always considered our iMiEV as having a pretty advanced drivetrain from an efficiency standpoint, noting that Mitsubishi had also put some effort into low rolling resistance (e.g., LRR tires and special wheel bearings and presumably non-dragging brakes).

Yesterday I attended an EV meeting wherein Honda gave a nice presentation about their FIT EV (they touted its refined and very-efficient drivetrain based on the Clarity), and after the meeting I had a chance to test-drive it. Briefly, from an operational standpoint it has three pushbutton-modes to play with: Sport, Normal, Econ AND two shift-lever positions D and B, with B giving the increased regeneration braking. I have no idea how to quantify their regeneration in B, but it 'felt' similar to our iMiEV. Incidentally, Sport mode makes that car indeed very lively.

Just to make sure we're on the same page, let's compare the two cars:

iMiEV
Engine 47kW
Weight 2579lbs
EPA City 126MPGe
EPA Highway 99MPGe
EPA Combined 112MPGe

Honda FIT EV
Engine 92kW
Weight 3252lbs
EPA City 132MPGe
EPA Highway 105MPGe
EPA Combined 118MPGe

I don't have a problem with the highway numbers as I presume the FitEV is slightly more aerodynamic than our iMiEV (Honda has not published the Cd, but says that it is low) and we all know how our iMiEV range suffers at higher speeds.

PROBLEM STATEMENT

The problem that I have is that the Honda FIT EV is 26% heavier than our iMiEV, yet scores almost 5% better than our iMiEV in the City test cycle. The EPA City cycle is a series of starts and stops with an average speed of 21.2mph for the 11.04 mile drive (we had a chart of this cycle on this forum but now I can't find it), with only two short excursions into speeds above 35mph. Starting and stopping simply involves accelerating and decelerating our car mass. I would have expected the FitEV to score significantly worse than the iMiEV in this test, if nothing else, based simply on the weight of the vehicle. Surely, the drivetrain efficiency is not that much better for the Honda to warrant such a significant difference in the end results? Something is wrong here, IMO!

SPECULATION

Unlike an ICE, I don't think engine size has much to do with the efficiency numbers, but I may be wrong. My own speculation is that perhaps Honda's setup for testing was more advantageous than Mitsubishi's. For example, was regeneration fully utilized in the iMiEV test? What modes were the cars in for this crucial testing? For example, I'd suggest that if the repetitive start/stop cycling were conducted in B instead of D (thus minimizing use of the brakes) the results would perhaps be more favorable for B.

I have no idea how they measured the energy consumed for the test, but I assume it was fairly sophisticated and identical for both cars.

QUESTION ON THE TABLE

Does anyone have any insight into the EPA EV testing procedures and did both Honda and Mitsubishi optimize their driving modes for this test and what were they?

EXTRANEOUS ASSOCIATED INFORMATION

Here is some additional information that I dug up that I don't want to lose again, gleaned from an early iMiEV review. Shows what an absurd arbitrary skewing of the data takes place after sophisticated datataking in order to compensate for the consumers' inability to drive efficiently. Quoting from -
http://www.autoblog.com/2011/10/26/2012-mitsubishi-i-first-drive-review/

How does that work? Well, the EPA measures electric vehicles using a two-cycle (city/highway) test and then subtracts 30 percent from these numbers to approximate "real world" driving. 70 percent of the i's city range (98 miles) is 69 miles. 70 percent of the car's highway range (78 miles) is 55 miles. In calculating a combined (city/highway) driving range, the EPA weighs the formula slightly more in the favor of the city range (55 percent) versus the highway range (45 percent), thus: (98 miles at 55 percent) + (78 miles at 45 percent) x 70 percent = 62 miles. That may make some sort of regulatory sense, but there should no longer be any doubt that your mileage may vary when it comes to EV range estimates.

 

[FiddlerJohn]

we had a chart of this cycle on this forum but now I can't find it)...
QUESTION ON THE TABLE Does anyone have any insight into the EPA EV testing procedures and did both Honda and Mitsubishi optimize their driving modes for this test and what were they?

 

[MLucas]

Shouldn't the larger motor take more juice as well? JoeS you mentioned that you are unsure if the motor size works the same as an ICE. I don't know either but I'm thinking a larger motor would require more electricity to run and to move the heavier car. I wasn't so sure about this or these numbers, I'm suspecting something isn't quite right either - I felt this when I started reading the reviews about the eFIT. At least it makes me feel good that they couldn't figure out how to keep their 'magic seat'. I guess they had a problem like the Leaf trying to fit in all the pieces as well.

I'm getting tired of the press treating our i MiEV's as the Red Headed Step Child. Most of the published reviews make the reviewer sound like they are talking out their hind ends.

 

[NeilBlanchard]

The EPA tests take the total drag into account, and the Fit EV definitely has lower aerodynamic drag than the i MiEV. The Fit EV also has less "aggressive" regenerative braking in the Normal mode; and none in the Eco mode. I believe all the EPA testing uses the Normal mode on all EV's.

 

[Jon]

I read a Fit EV review that said that Honda used the engine from their fuel cell car that they have been experimenting with for years. Maybe they have better more efficient system. I would love to drive one; 700 lbs heavier but twice the power.

 

[Don]

Shouldn't the larger motor take more juice as well?

I don't think so. With an ICE you take a small hit for the extra cubic inches even when you aren't using the extra power they can generate, but with electric motors using 20 HP from a big motor should consume about the same energy as using that same power from a smaller motor. It could even be that the larger motor is actually more efficient than the smaller one, so getting the same power out of it could consume even less energy than using the small one

I can see the Cd making the Fit more efficient on the freeway, but it shouldn't effect the City mileage much - Getting the 700 pound heavier car moving from a stop should take more energy than the lighter car though, all other things being equal

Don

 

[MLucas]

Thanks, Don. But, this car is 700 lbs heavier than the i, so on the same surface and conditions the Fit EV would consume more power to maintain the same speed as the i, wouldn't it? They also are lugging around more batteries as well. The Cd does help but 700 lbs is a lot heavier.

 

[Vike]

The Fit EV also has less "aggressive" regenerative braking in the Normal mode; and none in the Eco mode. I believe all the EPA testing uses the Normal mode on all EV's.

I think Neil's on to something here. It's interesting that Mitsu has MORE aggressive regen in Eco, and still some regen in Drive; this could well be hurting it in the EPA city tests. I don't know how much coasting they do, but the drag of the i-MiEV's "default" regen means the Fit would do it more efficiently. It's always worth remembering that ALL braking is bad for range - regen's way better than friction, but best of all is coasting, so I think Honda's right to have no regen on coast in Eco mode.

Regardless, I remain unimpressed by Honda's EV offering, as are they apparently. Lease only, restricted to a few states, 1100 total cars in 3 years? At least Mitsu's committed to build and sell the i-MiEVs in volume (funny as that sounds given current sales levels). So get as excited about the FitEV as you like - but you'll never own one, you're unlikely to drive one even if you're in California, and if you live in flyover country, you'll never even see one. Like Toyota/Tesla's RAV4-EV, this is no more than a thinly disguised field test at EV enthusiasts' expense.

 

[JoeS]

The EPA City Cycle has a lot of sharp starting and stopping. I agree that coasting is better than regen in highway driving situations and I wish we had that option in the iMiEV (instead of constantly shifting into N); however, if stopping or slowing is required (e.g., EPA city cycle), then using regen is preferable to using brakes as some energy is indeed being stuffed back into the batteries (I measured peak regen current of over 100A in our iMiEV). That is, unless the vehicle is unnecessarily over-slowed and then needs to add power to bring it back up to speed. A lot depends on the 'driver', as, if I understand correctly, indeed real human drivers are used to try to maintain the test profile. As with ICE vehicles, a 'good' driver can very easily beat EPA ratings by a large margin.

I agree that the FitEV's aerodynamics are better than the iMiEVs and thus I have no problem acknowledging the FitEV's superiority in the highway test; however, that and perhaps a slightly more efficient drivetrain does not explain the 5% advantage it appears to have in the EPA City Cycle despite being 30% heavier. Once rolling, I believe the additional vehicle weight does not exact much of a penalty on level ground.

 

[NeilBlanchard]

At 35-40mph, the aerodynamic drag is about 50% of the load. At 65mph and above it is about 75% of the load; so it does matter even at lower speeds. I don't know what the Cd of the stock Fit is, but the Fit EV has several significant tweaks, so it is likely under 0.30. That is ~20% better than the i MiEV -- and areo drag is a total loss.

I think that since EV's have such efficient drivetrains, that weight is less of a burden. In other words losing 10-15% is so much less than losing 80-85% (ICE's are pretty bad under heavy load) and then you can use the kinetic energy to coast if you need to carry speed, or use regen to slow down.

Once you accelerate a given mass, you get a given level of kinetic energy, so if you can coast farther, you accelerate for less time. The Fit still have regen on the brake pedal, so you can drive with a lighter foot. Also, being front wheel drive, there is a slight advantage for getting more regen out of the Fit EV.