Hypermiling the i-MiEV

Hypermiling the iMiEV is a multi-faceted topic. In order to make sure we all start out on the same page, I'd like to refer to the following website, where hypermiling is explained and its implementation described by Wayne Gerdes, who coined the phrase. Don't be put off by it's discussions of liquid-fueled and hybrid vehicles, as the principles certainly apply to EVs.

Description: http://www.cleanmpg.com/cmps_index.php?page=hypermiling

How-To: http://www.cleanmpg.com/forums/showthread.php?t=1510

The iMiEV is very responsive to hypermiling techniques, and even though the EPA has rated the iMiEV's overall energy consumption at 30kWhr/100miles (the best of any vehicle), on my first long trip with the iMiEV I had little problem getting 21kWhr/100miles, and that was mostly on the Interstate!

Without one becoming obsessed about it, hypermiling is simply a good skill to know for driving any vehicle.

In future posts we'll be exploring the many variables that affect our iMiEV's mileage, and try to pinpoint and how to deal with the major contributors. There are a few How-To tricks that are fun to implement and to which the iMiEV is especially responsive.

JoeS, thanks for the links. I'm pretty familiar with the basic hypermiling techniques but haven't seen much focused specifically on EV's. Live in Hawaii so never use the heater and A/C very infrequently since the drives here tend to be very short in nature. Always drive in Eco mode unless a steep downhill at which time B mode is employed, fortunately speed limit on freeway is 55 mph on Oahu so rarely push Miev over that. One of the things I did with my previous ICE is to neutral on moderate declines but have not tried with Miev since my understanding is that braking while in neutral will not use regenerative braking and wear down brakes. Look forward to your future hypermiling posts!

oahumiev, stand by, as properly utilizing Neutral is a pivotal aspect of hypermiling the iMiEV. There are a number of considerations, including the warnings in the owner's manual. We'll be discussing this in time and I plan on starting a separate thread on just this topic.

In the meantime, have you quantified your needs for hypermiling? Do you need the extended range or do you need to save on energy costs? I was shocked by the Hawaiian electricity costs (noting that they have an EV rate) and can't help wondering if simple benefit/cost and payback analyses would lead to the conclusion that solar/wind is the way to go... NOW.

http://www.heco.com/portal/site/hec...mt=default&vgnextrefresh=1&level=0&ct=article

Sorry, that shouldn't be in this thread...

JoeS, those rates listed are from 2010 and have risen quite a bit since then, now Oahu is about 33 cents kw/h residential and much higher on the other islands. The time of use EV rates from the utility do help but even then, I knew solar was the way to go so I installed an additional 5 panels to my existing array just for my Miev about a month ago. Even so, I'm interested in hypermiling to extend range when visiting family on the opposite side of the island which is about a 50+ mile roundtrip. One of the main questions I had and I'm sure you've considered is over inflating our tires beyond the 36 psi recommendation. They are rated at 51 psi max and I currently have mine at 40. Sorry if I jumped the gun on one of your future posts regarding inflation pressure.

Hi oahumiev - congrats on the solar!

oahumiev said:

... I'm interested in hypermiling to extend range when visiting family on the opposite side of the island which is about a 50+ mile roundtrip.

Click to expand...

Ah, no problem: simply offer your family a couple of dollars to plug in when visiting them. Since you can keep your speed down without being shot at, 50-60 miles with the iMiEV should be no problem, anyway.

oahumiev said:

One of the main questions I had and I'm sure you've considered is over inflating our tires beyond the 36 psi recommendation. They are rated at 51 psi max and I currently have mine at 40...

Click to expand...

I've already touched upon this one here:
http://myimiev.com/forum/viewtopic.php?p=976#p976
In our litigious society (especially here in California), I'm walking gently in this area. As for myself, I've been running 60psi on my Honda Insight (max sidewall rated 44psi) for seven years. Negligible and even tire wear and very crisp handling. It's underinflation that's the primary safety culprit, IMO. Once again, I personally am not recommending anything other than what the manufacturer specifies.

At present, I'm trying to quantify the contribution of each drag component on the iMiEV in order to present a complete and cohesive picture.

I just finished a detailed post regarding hypermiling and the use of Neutral (Coasting), but it was pointed out to me that since it violates manufacturer's warnings, may have some safety ramifications, and may even describe an activity deemed illegal by the DMV, that I should not post it. :roll: I've saved the writing and if any iMiEV owner is interested please PM me with your email and I'll be happy to send it to you with all the disclaimers.

JoeS,

I'm going to play devil's advocate here…

I think that with a simple disclaimer that the practice of "coasting in neutral" is a
contentious issue and illegal in most states, your material should be postable.

The matter of coasting in neutral is presented on numerous vehicle sites;
muscle cars, sports cars, classic cars, eco cars, hybrid cars, automatic transmissions,
manual transmissions, cars, trucks, motor homes, motorcycles.

On most sites someone pipes up that the practice is "illegal in most/all states," and
immediately there is a discussion of why that might be. Typically it is posited that
the prohibition goes well backk in time to when manual transmissions did not have
synchromesh, and new style hydraulic drum brakes easily overheated and faded or
boiled the brake fluid --- before that brakes were cable operated -- and later
possible loss of power-assisted brakes and steering relying on the engine driven
pumps or vacuum.

Nobody really knows why, but lots of people have opinions yea and nay. The
reason why nobody knows is simple; it would take a massive effort to find out.
You'd have to research the history of the statute in each state. I doubt that the
records have been digitized as I suspectt that they go back to the 1930s, maybe
the '20s. (Sounds like a good topic for a university law school review article.)

I have not been able to find a list of states with cites to the prohibition of coasting
in neutral. Here is a link to a gassavers.com thread that has the most states identified…
and in a Google search I turned up Maine, Arizona, and California:
http://www.gassavers.org/showthread.php?t=9946&page=2

There remains a question as to whether these laws even apply to an EV where
neutral is an electrical condition as opposed to a mechanical state of the ICE
being disconnected from the drivetrain/wheels.

Here however is a pleasant bit of news. As of May 2011, Florida repealed its no
coasting in neutral law on the basis of its being obsolete:

TALLAHASSEE, Fla. — Florida Governor Scott signed into law a measure which repeals
obsolete provisions that prohibited a motor vehicle from coasting on a downgrade.
An old law that is still on the books prohibits Sunshine State drivers from travelling
downhill while in neutral or with the clutch disengaged.

“Gas prices are approaching $4 per gallon,” said Senator Evelyn Lynn, R-Daytona,
sponsor of the measure, Senate Bill 1630. “There is no logical reason for a law that
puts the brakes on commonsense practices such as efficient driving. It’s not that F
loridians want to scoot around in Flintstone-mobiles. We just don’t want or need a
mandate that prevents us from a safe and helpful tactic such as coasting.”
http://www.flsenate.gov/Media/PressRelease/Show/Senators/2010-2012/District7/PressRelease/PressRelease20110505145621542

Of course, YMMV

Is coasting in neutral specifically mentioned in the iMiEV owner's manual?
(I still find it a real or potential customer disservice that the manual isn't available
on the Inter-web. It creates the impression that Mitsubishi has something to hide.)

rokeby, thank you for the encouraging words and links. What follows is my discussion with disclaimers...

The following is a discussion of one small element of Hypermiling: Coasting in Neutral. I like to refer to this as a Hypermiler's second best friend.

The most efficient mode of travel for any vehicle is to have it move without consuming any energy (DUH). The only losses we should have to contend with are aerodynamic drag and rolling resistance.

Unless one needs to slow down, Regeneration is BAD, as it slows the vehicle down while resupplying the battery with less energy than it took to get it up to that speed (over time). Don't get me wrong, as I love our iMiEV's flexible ability to control Regen and properly handling this feature will be addressed in a follow-on discussion.

Now, there are two ways of achieving this zero-energy point:

1) Very carefully balancing one's foot on the accelerator to keep the Energy Usage Indicator (Mitsubishi's term) red needle exactly midway between the blue and green segments

2) Shifting the car into Neutral while it's moving. Another word for this is Coasting.

Personally, I am incapable of balancing my right foot on that go-pedal and achieving and consistently maintaining the zero-energy point while driving.

[As an aside, I am very unhappy that the EV manufacturers are not providing us with the option of zero regen as part of the normal D setting. In the middle of the last century vehicle manufacturers were providing a feature called Freewheel (or sometimes incorrectly called an Overdrive) as a fuel-saving measure. I've happily driven my 1967 Saab with this feature (actually a carry-over from when the Saab was a two-stroke) for the last 45 years! When using Freewheel, letting go the gas pedal results in the vehicle coasting - think of it as a uni-directional drive - with no engine braking at all.]

OK, given that the delicate foot-balancing act is so difficult, the only option available to us is to simply manually shift the car from D to Neutral while it's moving. Quick and easy, … but first let me repeat the WARNING in the Owner's Manual:

Never move the selector lever to the "N" (NEUTRAL) position while the vehicle is in motion. You will lose regenerative braking. In addition, a serious accident could occur if the selector lever were inadvertently moved into the "P" (PARK) position or "R" (REVERSE) position.

Since the manual made a specific point of this, I can't help wondering if there is something more to it than what they've stated. I have a question in to Mitsubishi via my salesman asking for further elaboration.

Heeding their warning I note that the normal brakes work just fine and when alternating betwen D and N I simply keep the shift lever pushed to the right to preclude an inadvertent shift into R.

There are three other considerations when Coasting:

1) Possible effect on the Active Stability System (ACS), discussed in this thread:
http://myimiev.com/forum/viewtopic.php?f=10&t=292
I believe the conslusion there is that the braking system is unaffected and power reduction to the drive wheels would be inapplicable, anyway.

2) For California (and perhaps other states), the following Vehicle Code Section 21710 might be applicable:
21710.  The driver of a motor vehicle when traveling on down grade upon any highway shall not coast with the gears of such vehicle in neutral.
I actually tried to get my local legislator to tackle changing this one, as I believe it dates back to early last century when braking systems were marginal.

3) With the vehicle coasting in neutral, there would be a slight time delay in an emergency if one needed to shift the car into D and accelerate away from a problem.

OK, with that out of the way and duly noted by you, here are some brief thoughts on Hypermiling and Neutral…

Any time you "ease up" on the accelerator, you can shift into N. The car continues at a slowly diminishing speed so you've accomplished this "ease up", but at zero-energy consumption. Examples of this are any downgrades, seeing a red traffic light a block away and simply coasting along with the car gradually slowing as one waits for the light to change, or simply when wanting to slightly back off in highway traffic. To repeat myself, the car is moving at traffic speed while consuming zero energy. What could be more efficient than that? Over the course of most trips, a not-insignificant portion of that travel can be coasting, with surrounding traffic not even realizing any change in your vehicle's behavior.

Every downhill I start off by shifting into N, and if I get going too fast I simply use D-ECO-B to modulate my speed. On some of the hills around here, this goes on for miles of travel, nicely staying with the flow of traffic while not only not consuming energy but feeding at least some of it back into the batteries with the regen.

Remember, while driving on the level in D, ECO, or B, "easing up" on the accelerator usually puts the car into Regen which inefficiently robs the vehicle of kinetic energy and vehicle speed which then needs to be made up by applying more power to get back up to speed plus some extra to regain the energy lost by regen.

OK, so the next time you go out for a drive, think in terms of keeping the car moving at the zero-energy point. You will soon discover the dozens of opportunities to do this during the course of the drive.

The proof is in the pudding: using this as one of my techniques, on the first measured round-trip I made with the iMiEV (which involved a number of hills), I was able to beat the average EPA rating of 30kWh/100mi with my own mostly-highway trip yielding 20.9kWh/100mi.
http://myimiev.com/forum/viewtopic.php?p=960#p960

Once again, I have to draw attention to the manufacturer's warning in the owner's manual as well as the three additional considerations and caution anyone who wants to try this technique to be aware of this and if you do so, you do it at your own risk. Finally, as a favor to all drivers (and to not give the iMiEV a bad name), please remember to always stay in the right lane if you are slower than prevailing traffic.

Nice write-up, Joe!

Jenn

Before we progress any further with this Hypermiling discussion, it might be suitable to briefly mention WHY we should learn to hypermile and perhaps WHY NOT bother implementing it on a daily basis...

WHY HYPERMILE

1. Hypermiling any car saves energy, and therefore extends the vehicle's driving range and saves on energy costs, be they $/gallon or $/kWhr

2. Hypermiling saves wear-and-tear on the car, as one drives the vehicle very gently.

3. Hypermiling extends battery life, as it avoids large discharge currents.

4. Finally, the primary reason to learn how to hypermile is that it is a good skill to know when, on the hopefully rare occasion, it is seriously needed.

Now, the converse is -

WHY NOT HYPERMILE

1. On some vehicles which have trip and lifetime efficiency readouts (e.g., Leaf or Honda Insight - but NOT the iMiEV), one can become obsessed with trying to optimize this number. With the iMiEV one has the added step of manually calculating mileage vs. kWhr consumed, so the gratification is not immediate and thus lessens the addiction...

2. It can drive your passengers nuts!

3. It can frustrate other (primarily clueless) drivers and, by extension, it can give the i-MiEV (and thus all electric cars) a bad name!

4. In my case, with my oversized solar array, it doesn't save me any energy $$

In later discussions I'll be talking about minimizing the impact on traffic and other drivers when hypermiling.

For myself, with a Jekyll and Hyde approach to driving - I'm still quite a leadfoot except in my Honda Insight where my present mileage stands at 77.5mpg over 80K miles - I've taken to simply tailoring my iMiEV driving to the distance I intend to drive: for short trips I drive normally and like to show off the fact that the iMiEV is no slouch, but if there's a considerable distance to cover and charging isn't assured along the way then I balance my driving to always have at least ten miles RR (Range Remaining) by the time I get to a destination with charging ability.

Surely the pressure would be properly set from your dealer, eh? Well, I neglected to check up on their prep, and sure enough, the tires were set to a cushy 32 psi when Mitsu recommends 36 psi. Since I had a challenging 50 mile uphill highway run planned with a newby passenger yesterday, I went ahead and raised 'em to 50 psi to forestall her "range anxiety". What a difference! Feels like forever for coast-down, without a noticeable increase in noise or roughening of the ride on concrete highway. On fresh asphalt? Better than rails.
So, I drove 51 miles uphill to a meeting and arrived with two bars and 7 projected miles remaining. After a full recharge (all day meeting), the downhill return left me with four bars and 14 remaining miles. ON the way up I intended to stay at 55 mph, but spent plenty of time over 60.
To follow up on yesterday's 101 miles o fun that used 26 kwh from the battery, I did 64 miles today of mostly street travel on a single charge, using only 14 kwh (14 bars o charge)! Now that 62 mile EPA figure is looking reasonable after all!
3300 miles and counting!
PS- We had over an inch of snow on the ground this morning, and I pushed the front end through a few cold wet corners to test the effect of higher pressure. Tire scrub was not noticeably worse.

Last I heard about anyone driving an iMiev in the snow was Mitsubishi's promotional video!

What's the max tire listed on the tires? Was it 50psi?

Maximum pressure shown on the sidewall is 51psi. Mitsubishi recommends 36psi, front and rear, for the iMiEV.

jray3 said:

So, I drove 51 miles uphill to a meeting and arrived with two bars and 7 projected miles remaining. After a full recharge (all day meeting), the downhill return left me with four bars and 14 remaining miles. ON the way up I intended to stay at 55 mph, but spent plenty of time over 60. To follow up on yesterday's 101 miles o fun that used 26 kwh from the battery, I did 64 miles today of mostly street travel on a single charge, using only 14 kwh (14 bars o charge)! Now that 62 mile EPA figure is looking reasonable after all!

Click to expand...

jray3, your uphill drive of 51 miles is corroborating that distance as a comfortable limit for highway-speed excursions. I personally don't want to drop below two bars. Surprised you didn't do better downhill, but I figure you may have been in a hurry to get home... 26kWh/101miles=0.257kWh/mi, but you say that was battery-to-wheel and not wall-to-wheel(?). Glad you caught the tire pressure before your trip.

Yep, that's battery-to-wheel from the guessometer. The ChargePoint station I used midday didn't output the kWh for some reason, only the elapsed time on charge. On the return trip I took a hillier, twistier route that was a mile shorter, but had more fun! The net elevation change was only 600 feet, but I'd wager several times that after the rolling hills.

Moving right along with the subject topic of hypermiling, let's talk about things that rob us of the small amount of energy we have...

Aerodynamics
Not much we can do here as it is designed-in. Mitsubishi tells us the Cd is 0.35 and they had not optimized this by, e.g., putting in a full-length underbody pan or wheel skirts or aerodynamic side mirror housings nor even building in a spoiler to keep the rear of the vehicle clean (see 1960s Saab station wagon). About all we can do is NOT put on a roofrack or bicycle rack ... I've been told that keeping the car clean and waxed does help.

Rolling Resistance
Again, this is designed-into the vehicle, with rolling friction hopefully minimized with appropriate bearings and zero-drag brakes and efficient low-friction motor and drivetrain. About all we can do is pump up the low-rolling-resistance tires, noting that the factory recommends 36psi and the maximum load noted on the sidewall is at 51psi. Even though I run higher, far be it for me to recommend anything other than what the manufacturer specifies.

Weight
Simple: keep it light and empty. DO NOT CARRY ANYTHING SUPERFLUOUS in the car. Trailer hitch falls into this category. Go on a diet yourself. Drive by yourself and want to be extreme? - take out the passenger seat, and you'll have more cargo room as well if you need it. What the heck, take out all the other seats as well. :roll:

Regeneration and Brakes
We already talked about this, but I feel I need to repeat it: use regen ONLY if you need to slow down; otherwise, regeneration sucks valuable kinetic energy from the vehicle. Applying the brakes is even worse: as an experiment, you might practice driving as though you had no brakes and simply apply them when you're down to 5mph.

Other Energy Consumers

HVAC - the onboard heater is a terrible waste of battery power, but if all you do is short trips and don't need to hypermile, then by all means stay comfortable. The seat heater is an excellent low-power alternative. I don't know how much energy the air conditioner consumes, so I don't know how much of a hit the battery pack takes with it, but it can't be good. Where I live I'm lucky and can get by with simply opening the windows (even though that is not good from an aerodynamic standpoint).

Lights - I haven't quantified how much the driving lights, headlights, etc. consume, but those are necessities anyway. About all I intend to do is remove the fuse from my driving light circuit once summer comes (unless someone can point out to me that they're legally needed). My car has the foglamp switch which doesn't work on the driving lights... or else I'm confused.

Radio and accessories - the one or two amps at 12V is probably negligible in the overall scheme of power consumers, so I wouldn't worry about it.

In the next installment I'll talk about what I believe to be the biggest range-limiting hit the iMiEV takes: aerodynamics - and what we can do about it safely while driving. Future topics will include acceleration/deceleration, cornering, dealing with hills, dealing with traffic, and simply examples of real-life driving situations.

SWOT, but my odometer just rolled 3400 miles while still a week short of 3 months of driving. This 'second car' has certainly proved to be our prime mover! :mrgreen:

A sensible firmware modification would set "D" mode driving to only regen when you touched the brakes. It would also be nice to have an indication when mechanical braking was applied, so you could train yourself to ride the edge of regenerative braking without wasting energy heating up the brake pads.

Of course, modifying the firmware of one's car would certainly void the warranty. It would be nice if Mitsubishi would allow some kind of hidden override switch to enable this feature, though.

Is there any difference between the zero pedal regenerative braking in the "D" and "Eco" modes already?

One tool for those trying to max their MPGs in a Prius is the ScanGauge II.
It plugs into the OBD II port and is easy to use.

Using custom programmable X-Gauges you can monitor HV battery in/out puts,
temps, and a bunch of other metrics.

Has anyone mounted a ScanGauge and got any of the X-Gauges to work?

I was coasting the other day and I moved the gearshift into "R" by mistake! I noticed the indicator on the dash and immediately moved it back to N, then D. I don't know if I actually put my foot on the accelerator at that time or not! Nothing happened, though, nothing at all. But I'm not going to try it again on purpose.

Jenn