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Hi guys. I've been driving my gen 1 after recently disconnecting my IMA for battery related issues. I was surprised to see the efficiency hasn't really dropped at all. Ok so I probably wasn't getting the best performance from my dying battery pack, and maybe the engine was running more to charge it. But I started asking how much more efficient is the car with the IMA system fully functional?

Obviously the first thing I noticed is how much easier in gear coasting is without the regenerative brakes taking hold as soon as you lift off the accelerator. This means you can coast for longer and accelerate less often as you maintain more momentum. Pulse and glide techniques work far better with IMA disabled. The downside is poor acceleration meaning working the engine harder and using more fuel. But after a short 45 mile trip tonight, I still averaged over 72 MPG. So any long term users able to give a rough idea, maybe in percentage terms, what kind of increase do you get IMA fully functional V's IMA disabled?
 

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If you drive at constant speed most of the time, then the IMA is almost useless. IMA is needed in stop'n-go city driving.
 

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So any long term users able to give a rough idea, maybe in percentage terms, what kind of increase do you get IMA fully functional V's IMA disabled?
It has been discussed before, not sure which threads, and it kinda depends on a variety of factors. The driving mix is the key to any improved mileage from the IMA system. For example, hypermilers use the IMA system very little and very judiciously.

I'll just talk about the two driving EXTREME mixes and say that everything else lies in the middle. First, if you are driving at 52-55 mph on a fairly level, limited access highway with no stops, any use of the IMA will be a negative on the trip mpg. This is because the round trip for energy from the generator to battery and back to the electric motor-actually the same device- isn't 100% efficient. The electrical losses have to be made up by gasoline. There is no free energy - only transformations of type.

The other EXTREME is heavy urban/suburban driving with lots of speed changes, braking, and stop lights. This is the situation in which the IMA system really shines because it recaptures and reuses energy which would otherwise be dissipated as heat. In addition, the supplementary power provided by the Motor/Gen allows the use of a very small, very efficient engine running at an average large throttle opening (high BMEP) which is very efficient. So, yes the IMA improves mpg under these conditions.

Of course, the car benefits from other features including aerodynamics, light weight, LRR tires, and high gear ratios (promoting high BMEP).
 

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I'm not an expert on this, but chiming-in is preferable to watching batteries discharge...

I take it you mean 'fuel efficient' when you say "efficient." In general you can get the best fuel economy when you're going gas-only and you slow down a lot. The electric is mainly there to add power when you need it and to reduce emissions - without harming fuel economy. So if you never use/need that extra power, there's no benefit (or actually some harm). That's the rub, though - because most people just drive 'normally', in which case you do need/use that extra power and you do see better fuel economy. People who do mostly city driving will see the most benefit; people who do mostly highway driving will see little if any benefit...

Off the top of my head, holding driving style and terrain, etc. equal, and assuming 'normal' driving style - keeping up with traffic and such - I'd say one might see about a 10-20% fuel economy gain with the IMA functioning well, in a mix of city/highway driving... Not much more than a guess though. When I'm driving with the IMA disabled, yet trying to maintain acceleration and speed as I normally do, the difference might be like 10-20 mpg lower on the U.S. version of the instantaneous fuel consumption display...

One other thing: pretty sure lean burn is disabled when the IMA is disabled, and I'm not sure how much of a difference that can make during the highway driving part of a trip. Seems like I can usually just roll-off the throttle out of lean burn, maintain speed, yet not see much if any fuel economy hit...
 

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I have both:
2000 with IMA functioning well with 165,000miles EGR clean functioning. Lean burn works well.
2005 IMA Battery removed and both BCM MCM removed 235,000mi. Lean burn works well have not checked EGR yet.

I get 6 to 10 mpg better with No IMA.
I have tried very hard on the same 30mi route to work to get better mpg in the IMA car but, average best of both in summer is
no IMA 72mpg
IMA 64mpg

I got a good deal on the IMA and bought it after the no IMA hoping for better.
 

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no IMA 72mpg
IMA 64mpg

I got a good deal on the IMA and bought it after the no IMA hoping for better.
Keep your eye on the regen light on the IMA car and see how much background charging it is doing. Cars with marginal batteries, long before they throw the IMA light, do a lot of background charging so that could be your problem. Otherwise I'd suspect the engine of being down on power.
 

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jime
Overall the IMA car does see down on power more when it goes into the lean burn mode than the non IMA. It cannot maintain 70mph like the non IMA.

Plugs look good. EGR clean. Do you think it could be the cat-converters being plugged?
 

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There are a lot of things that can influence this. I agree with Jim that the IMA might be weak and causing a lot of background charging that you don't see. I've seen as much as 10A background charge without anything showing up on the dash.

How about doing a comparison by doing the same disconnect on the IMA car and compare both cars without the IMA in the system.

Make sure they have the same tires, same pressure, same AC use, and then start looking at other things.

Sam
 

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I've driven my car with no IMA vs working IMA.

- I LOVE IMA! Acceleration is MUCH faster, resulting in less time spent accelerating. When I get on onramps, I run at full WOT and shift at 6k with full assist, to get up to speed in the shortest time possible. This allows more time spent getting good MPG.

- Uphills on freeway. With working IMA, I can run leanburn uphills and at the very top of the hill if I'm losing speed, I can roll into the throttle to get a nice little boost over the crest of the hill. With non working IMA it just bogs and I keep losing speed, having to downshift and get the revs up and poor MPG.

I hate driving this car without boost. But yeah, it does seem to coast easier.
 

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How can I check this with an OBDIIC&C?

Ron
Select BAM ($0D) as one of the left side data displays on the screen.

When using assist a negative reading will be IMA battery discharge amps, a positive reading is charging amps into the battery.
 

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Discussion Starter #12
Thanks for the replies, its an interesting debate, I'm sure it's been discussed 1000 times before, but try searching "IMA" or "efficiency" on a forum of this type, you can imagine the results!

Had another little drive tonight yielding 76.5 MPG. I do miss the performance of course, I think the performance loss is noticed more than the economy.
 

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I have both:
2000 with IMA functioning well with 165,000miles EGR clean functioning. Lean burn works well.
2005 IMA Battery removed and both BCM MCM removed 235,000mi. Lean burn works well have not checked EGR yet.

I get 6 to 10 mpg better with No IMA.
I have tried very hard on the same 30mi route to work to get better mpg in the IMA car but, average best of both in summer is
no IMA 72mpg
IMA 64mpg

I got a good deal on the IMA and bought it after the no IMA hoping for better.


how does your 12v charge in the car without the bcm and mcm? I am very curious about this as I have heard a few people put alternators in their cars. I am still unclear on how exactly the 12v is charged with and without the ima functionalities.
 

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I'll agree with much of what has already been said by others.

Just to drop my own 2 bits .. veterans probably already know what I'm going to post.

Some things .. like Regenerative braking instead of friction brakes .. conservation of momentum .. etc .. those things are always a net energy efficiency benefit.

- - - - - -
I'll add one more of my own .. that historically has been more 'controversial'.

The efficiency of both the ICE and the IMA vary considerably .. to know which path will be the highest energy efficiency to wheel .. and by how much .. will vary with conditions .. It is not always the same answer set and unchanging in all conditions.

If you look at the efficiency curves for IMA and ICE .. and then do the math .. yes there are additional energy conversion loss steps .. but when you do the math .. there are conditions of net lower energy efficiency .. but other conditions for a net higher energy efficiency .. It isn't something the OEM system seems to have been programmed to take full advantage of .. so to get the most out of it would probably require manual control via IMAC&C (or MIMA) .. and it isn't always true in all conditions .. but it is there .. go math.

For example:
The combined IMA system (Motor+Controller+Batteries) is able to return to the shaft at most a maximum of about ~81% of the shaft energy it takes .. At worst it is a low of 0% when all IMA energy goes to the DC-DC .. and a shaft low of about ~50% .. The ICE's energy efficiency to the shaft varies from a low of near 0% (neutral idle) to low to the shaft of about ~25% .. a high of at least 38% (If you believe the 2003 PERE Models the maximum high in Lean Burn could possibly be up as high as about ~48%).

Soo .. the most extreme ideal case:
~48% through ~81% back to the shaft as much as ~38.8% of the energy.
When ICE conditions would otherwise force the ICE to operate bellow that ~38.8% point that ideal IMA path is a net benefit .. but if conditions allow for the ICE to operate above that ~38.8% point up to the 48% than the IMA path can not possibly offer any net improvement.

For the 38% ICE Peak .. the break even line shifts to ~30.7% ... Conditions that force ICE to operate below that ~30.7% and it is possible for the IMA path to be higher net efficient .. any ICE condition above that ~30.7% and it is not possible for the IMA path to offer any net improvement.

At the low end worst case IMA path .. ~48% @ ~50% is only ~24% ... and the ~38% is ~19% ... under either case the worst case shaft (not DC-DC) path the IMA would not ever offer any net energy efficiency improvement.

And if the worst case ICE (Shaft not idle) is combined with worst case IMA path (shaft not DC-DC) ... ~25% @ ~50% only gets you about ~12% net efficiency , really sucks.

And of course .. just for fun .. PHEV IMA energy is always a benefit to reduce/replace gasoline ICE usage .. even under ideal max ~48% or ~38% ICE conditions.
 

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how does your 12v charge in the car without the bcm and mcm? I am very curious about this as I have heard a few people put alternators in their cars. I am still unclear on how exactly the 12v is charged with and without the ima functionalities.
A DC-DC converter is used by the Insight to charge the 12v battery. With the IMA battery disabled or removed the DC-DC can be wired back into the remaining wiring and runs directly from the IMA motor/alternator.

The people that have added an normal alternator to the Insight are doing it for other reasons.
 

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In my driving experience, I would say the IMA gives me another 10% in gas mileage over a non-functional IMA, after driving with both.

My best tank with IMA was 117 mpg.

My best tank without IMA so far this year is 108 mpg.

This is under similar circumstances, time of year, roads, temperature, and so on.

For me, it's much easier to keep high MPG's with a good IMA, even on flat roads.

Jim.
 

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In my driving experience, I would say the IMA gives me another 10% in gas mileage over a non-functional IMA, after driving with both.

My best tank with IMA was 117 mpg.

My best tank without IMA so far this year is 108 mpg.

This is under similar circumstances, time of year, roads, temperature, and so on.

For me, it's much easier to keep high MPG's with a good IMA, even on flat roads.

Jim.
Hey Jim, was your IMA removed or just turned off?
 

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Hey Jim, was your IMA removed or just turned off?
I turned off the IMA about five months ago, because it was dying. I was very conservative with the IMA use, and tried to keep down excessive grid charging, but it happened anyway.

There are some distinction advantages to running without the IMA however. And I am still discovering what they are. The biggest one? No more hassling over that state of battery charge.

The biggest safety improvement without IMA? No worry about AutoStop stalling the engine at a fast moving intersection, only discover that the IMA will not restart the ICE. A very dangerous situation now avoided.

Jim.
 
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