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:
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…
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.
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.
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.