IMA rpm vs. efficiency

[crx_rogus]

Folks -

At what rpm do the AC motor windings' resistance equal its impedance, or at least where induced back-EMF from rpm equals voltage across the windings from simple resistance? I ask because below that you're converting pack energy more into heat than propulsion. I'm assuming for the MT it's 3000 rpm, because that's its power peak (from a promotional poster for an '06 MT), and for a motor's power peak rpm = point where IR = E. (Of course there's also inverter resistance, which I'll assume equals motor winding resistance.)

Sometimes I try to maximize mpg by maximizing MAP and minimizing rpm, the traditional approach to maximizing ICE efficiency, but I don't want to throw away Assist kW via excess heat generation at really low rpm, and if that means no sustained Assist below 3000 rpm, then the shifter gets more use. With the torque peak at 2000 rpm, can I assume any Assist below that is wasting at least 2/3rds of the used wattage, if not much more?

(And yes, I'm starting to realize lean burn with some manifold vacuum at a higher rpm could be more efficient than stoichiometric or certainly rich at a lower rpm with insignificant manifold vacuum.)

Thanks,
Roger
Silver 2000 Insight #4047

[IamIan]

I would first say there is a significant difference between the efficiency operating conditions of the ICE and the IMA motor.

But as far as the IMA motor goes... it has been mapped.

The center most point of darkest red is the point of highest IMA electric motor efficiency... not just a product of RPMs.

Also remember even if you combine the efficiency point of the ICE and the IMA ... vehicle techniques of maximizing conservation of momentum also still apply as well.

Also remember Lean Burn can increase ICE efficiency up to ~20%.. while decreasing ICE friction by up to ~8%.... The varaible Air to Fuel Ratio Aspect of the Insight's ICE makes some of the conventional methods of maximizing ICE efficiency less effective.... the Efficiency map of the RPMs vs load will change each time the air to fuel ratio changes.

[retepsnikrep]

I must admit I err on the side of minimum revs to get the most out of the car mpg wise.

But I do notice the revs need to be a minimum of about 2000rpm to allow full assist.

I could be wasting some electrical energy by using lots of assist at very low revs but I do have some to spare. I also like the max mpg so avoid the ice as much as possible.

[crx_rogus]

Originally Posted by IamIan

... But as far as the IMA motor goes... it has been mapped.

The center most point of darkest red is the point of highest IMA electric motor efficiency... not just a product of RPMs.

Wow... Excellent data source, thanks. I was going by general principles governing DC and induction motors, figuring there were probably some additional complicating variables with the IMA motor + drive circuitry and control. It's truly great to see high efficiency all the way from basement level to 3700 or so, with decent efficiency out to 4500 or so. Just out of curiosity, can you point me to where that's from?

Originally Posted by IamIan

Also remember even if you combine the efficiency point of the ICE and the IMA ... vehicle techniques of maximizing conservation of momentum also still apply as well.

I'm still figuring out when pulse and glide works best and when gradual normal acceleration with lean burn works best, with a significant distance between myself and whoever's ahead of me being a golden thing. I'm finding the car's generally fine maintaining a high SOC, gradually rebuilding it if I find a way to pull it down, but using the IMA to really boost mpg is where I can easily see MIMA or MIMA-L as being something needed in that regard. IMA works great as a form of rechargeable supercharging as Honda intended, but it would be nice to have a little more EV functionality as appropriate, to help maintain lean burn conditions while keeping up with traffic but without overheating any subpacks etc.

Originally Posted by IamIan

Also remember Lean Burn can increase ICE efficiency up to ~20%.. while decreasing ICE friction by up to ~8%.... The varaible Air to Fuel Ratio Aspect of the Insight's ICE makes some of the conventional methods of maximizing ICE efficiency less effective.... the Efficiency map of the RPMs vs load will change each time the air to fuel ratio changes.

In WWII the basic technique of maximizing ICE efficiency of maximizing manifold pressure while minimizing prop/crankshaft rpm was established, but as you point out, and I'm finding, using slightly higher revs with some manifold vacuum to get lean burn in/around its sweet spot does work a bit better. (Nothing in WWII did any form of lean burn I'm familiar with.)

Re:

Originally Posted by retepsnikrep

I could be wasting some electrical energy by using lots of assist at very low revs but I do have some to spare. I also like the max mpg so avoid the ice as much as possible.

From that graph it looks like absolute peak efficiency for available power extends from idle to about 2600 rpm, so winding resistance and therefor one assumes inverter resistance must both be negligible so low-rpm efficiency is basically a non-issue, and yes, you have some to spare [cackle cackle].

Regards,
Roger

[crx_rogus]

I found the graph source via a Google search that pointed to a pdf of the SAE paper right here on Insight Central. It seems to have everything Insight-related.

[IamIan]

Originally Posted by crx_rogus

Wow... Excellent data source, thanks. I was going by general principles governing DC and induction motors, figuring there were probably some additional complicating variables with the IMA motor + drive circuitry and control. It's truly great to see high efficiency all the way from basement level to 3700 or so, with decent efficiency out to 4500 or so. Just out of curiosity, can you point me to where that's from?

As you found.
It is also shown as one of the Gen-I Insight Resource Library Links... among many other interesting articles to read.

Remember that is a general model / guide ... actual IMA electric motor efficiency will also vary with other variables other than RPMs and load... temperature and others which are not shown.

That picture is only depicting the IMA electric motor ... not the ICE gasoline engine ... not the MDM control electronics ... not the IMA batteries themselves... etc.

The batteries for instance due to Peukert effects will always yield better Ah out at lower Amp discharge rates... I'll post my IMA battery Peukert k value in a few days... a few more tests to do on that and the Rate of Self Discharge tests.

Originally Posted by crx_rogus

but it would be nice to have a little more EV functionality as appropriate, to help maintain lean burn conditions while keeping up with traffic but without overheating any subpacks etc.

That's why Peter an others have done PHEV / booster battery Mods.