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How come D mode consumes more energy on a given load?

Posted: Sat Apr 16, 2016 7:09 pm
by acensor
I thought i fully understood the difference betwee D and E, E and B.

But one puzzling thing/observation:

On a given stretch of road (ssme grade, surface, wind, etc) if I switch from E to D I see the power consumption needle jumps up about, say, 15% .
Makes no sense to me as the amount if energy needed must be identical.

Explainations? Speculations?

Re: How come D mode consumes more energy on a given load?

Posted: Sun Apr 17, 2016 4:00 am
by JoeS
D mode consumes more energy on a given load

Whoa! On the face of it, that is a FALSE statement.

First off, are you talking about energy or power?

acensor, you failed to identify all the paramaters surrounding this allegation or your methodology for controlling the variables. Did you use CaniOn to measure the voltage and current precisely? How was your power input controlled? Sorry, but just looking at the red needle without precise control over the input doesn't tell us anything. For example, for a given pedal position, D will consume more power than Eco, but will also generate more power and the car will accelerate faster and perhaps achieve a higher speed (remember, there is an accelerator pedal gain change between D/B and Eco). Recall the difficulty we all had before CaniOn in even establishing what the correlation was of vehicle speed to needle position?

Until all the applicable parameters are demonstratably controlled, discussing this might not be too productive.

Re: How come D mode consumes more energy on a given load?

Posted: Sun Apr 17, 2016 7:54 am
by acensor
Been trying yo post a reply, but keep getting

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Re: How come D mode consumes more energy on a given load?

Posted: Sun Apr 17, 2016 7:59 am
by acensor
Regarding the posting error message:

Below is the short version of what I tryed to post.

.....I think you likely alteady have explained to my satisfaction why the needle went up in my test with your statement..
"for a given pedal position, D will consume more power tha Eco.."
Because to the best of my ability I was deliberately contfolling THAT factor....holding pedal position constant while switching E to D.
But I did not notice the acceleration and speed increase that, based on that fact, should be expected in my tests the way I run them ...but it could well just have been too minor and subtle for me to notice.

Will try it again with paying special attention to acelleration, but even if I don't detect that will consider it case closed, as consuming more power at a given load did not make much sense.

By the way...has anyine ever determined exactly what the "power"* gauge is displaying? Watts?
Amps?

Re: How come D mode consumes more energy on a given load?

Posted: Sun Apr 17, 2016 8:19 am
by kiev
Both the pedal position and the rate of change of pedal position determine the torque (or power) requested by the pilot in a selected gear, and each gear has a different pedal response profile.

Holding the pedal and shifting between gears is not the same as holding a given load, but it is equivalent to requesting a different power level due to the pedal profiles.

The resulting speed is controlled by the operator and is determined at the balance point between the commanded torque and the resisting loads on the car (aero, rolling, incline, accel, etc).

E mode has a less responsive pedal profile so it takes a greater rate and position change to produce the same torque command as in D mode, and visa versa...

Holding the pedal and downshifting from D to E will result in decel; upshifting from E to D will result in accel.

Re: How come D mode consumes more energy on a given load?

Posted: Mon Apr 18, 2016 11:30 am
by bobakka
I always use B when I need all the power in the batteries.

It is just an impression, but I think B consumes less energy than D for a given trip. It is difficult to prove scientifically since a lot of parameters will vary between two different trips. But my - and other Norwegian iMiev drivers - impression is that B saves energy. And that applies even when regeneration is not a big deal.

How to explain this? For me it is almost unexplainable. The only think I can think about is that the drive train is optimized for B and somehow D waste more energy. That energy must be converted into heat somewhere.

Re: How come D mode consumes more energy on a given load?

Posted: Mon Apr 18, 2016 12:55 pm
by wmcbrine
bobakka wrote:It is just an impression, but I think B consumes less energy than D for a given trip.

What about B vs. E?

Re: How come D mode consumes more energy on a given load?

Posted: Tue Apr 19, 2016 7:56 am
by JoeS
At any given speed and identical wind and terrain conditions, the i-MiEV requires the same amount of power, irrespective of whether it's in D, Eco, or B.

For any given acceleration and identical wind and terrain conditions, the i-MiEV requires the same amount of power, irrespective of whether it's in D, Eco, or B.

Foot-off the accelerator pedal regeneration increases (and thus deceleration increases) in each of the three settings, with D being least and B being greatest.

Rate-of-change of accelerator pedal position is yet another variable - kiev addressed this above. My only perspective on this is that pumping the accelerator pedal is bad as it hits the battery with current spikes, and thus a gradual pedal depression is easier on the batteries for the same acceleration.

Accelerator pedal depression in Eco is different than D or B: the same amount of pedal depression results in lower power and acceleration in Eco than in D or B. Lower power means the car accelerates slower and thus consumes less energy. You could do the same thing by simply being gentler on the accelerator pedal in D or B.

I use Eco when driving in town and talking with a passenger, as I don't multitask well; otherwise, in both town and mountain driving I use B. I use D only on highway driving.

Associated with this topic, recall that regeneration when going down the highway is BAD unless you actually want to slow down: the speed lost by regen has to be made up by subsequently applying power, with a net loss of energy compared to having not let up on the accelerator and engaging regen in the first place. This is the reason I am an advocate of having a 'shift' setting that would provide zero regen when the pedal was released - one hypermiling technique is to constantly shift into N at every little downgrade and thus prevent dropping into regen when trying to maintain a constant speed.

Re: How come D mode consumes more energy on a given load?

Posted: Tue Apr 19, 2016 9:47 am
by bobakka
JoeS wrote:At any given speed and identical wind and terrain conditions, the i-MiEV requires the same amount of power, irrespective of whether it's in D, Eco, or B.

For any given acceleration and identical wind and terrain conditions, the i-MiEV requires the same amount of power, irrespective of whether it's in D, Eco, or B.

Joe, how do you know this?

Is it your own hypothesis based on assumptions on how the iMiev drivetrain is build, is it facts that is written somewhere which you can share with us or is it tested by someone and documented?

I am an electrical engineer myself and know all the physics around this.
I was surprised when somebody at the local myimiev forum claimed that B was better than D.
I have tried it myself and as I said "it is my impression that B consumes less energy than D for a given trip".
It is difficult to prove since it require a lot of spare time to set up a valid test, that I do not have..
I am open to my impression being wrong, but I would love some kind of documentation..

Re: How come D mode consumes more energy on a given load?

Posted: Tue Apr 19, 2016 10:49 am
by PV1
Simple physics suggests that it takes the same amount of power to propel the same car down a certain stretch of road with the same conditions. Shifting between the different drive modes doesn't change physics (unless there is some hidden power savings going on between the drive modes, which has yet to be found). With HVAC off, reducing heating or cooling power is not a factor.

Flooring the pedal in ECO still gives us max power, and shifting between the different drive modes with the pedal floored doesn't cause any change in acceleration. Driving down the road, I can hold 48 MPH with the needle on the C in ECO regardless of the drive mode I'm in (obviously re-adjusting how far I push the pedal between D/B and ECO modes due to the change in throttle pedal map.

Ultimately, any consumption differences we observe is likely due to our driving habits, local terrain, and performance tolerances of different batches of hardware. I know that after 3 years of driving electric, I find ECO mode is the easiest mode to control power output due to the extended pedal travel. I couldn't tell you if one mode nets better range as I only need to hypermile once or twice a year, but ECO is the most comfortable mode for me.

As for the OP, the different pedal maps explain why the car would suddenly use more power (and the resulting acceleration) when shifting from ECO to D. I even joke with passengers and call B my "Boost mode" because I can get a surge of power without moving my foot just by changing modes.

As for an overall decrease in energy usage in B, I'd be almost willing to bet it is due to the much more aggressive regen. Even when holding the brake pedal down, shifting to B from the other drive modes increases regen, and every once in a while with the correct timing of pressing the brake pedal and shifting to B, I can get near 45-50 kW of regen. My record stands at 45 kW of regen, which is only possible in B mode.