How Much Does the IMA actually help?

[Lafter]

The other day I was trying to break my mpg record and I noticed I hardly every used the battery assist.

It got me thinking that our cars are just plain fuel efficient especially when in lean burn .. other then acceleration do these cars even use the battery?

And that got me thinking .. what if I just took the battery out?


I am not planing on doing anything like that to my car .. but I am curious.

[Willie Williford]

Numerous posts about that senerio. Search, Search is your best tool.
HTH
Willie

[Lafter]

Originally Posted by Willie Williford

Numerous posts about that senerio. Search, Search is your best tool.
HTH
Willie

Sorry .. I don't really care enough to search through numerous posts & spend hours reading about it.

I was just striking up a conversation with fellow insight enthusiasts .. figured any of the more knowledgeable people on these boards who were bored would not mind talking about the subject.

once again .. sorry if my post offended you .. It was not intended to .. I do know how to use the search feature so no need to point that out in the future.

[Eli]

It makes no difference on the flat, open highway as far as MPG goes.

It helps in the city and if you encounter hills.

What it really helps with is acceleration. The Insight's engine is almost scary gutless below 2500RPM without assist.

[Jivko57]

Right on the spot , that's my perception too... our engines are small and the missing part is needed only when accelerating, so thats the purpose of the IMA. Once up to speed they have more than enough power to keep the momentum so thats when we are benefiting of having a smaller engine...

[racer26]

Generally speaking though, its more efficient to accelerate VERY slowly, and not use the assist, because the reclaiming process that reclaims some of the energy lost to slowing down (normally converted to heat by brake pads in normal cars), while significantly more efficient than 0%, is nowhere even close to 100% efficient. Its better to not use the HV battery, than to have to recharge it later, in most cases.

[Lafter]

Ive found when driving at highway speeds 70mph-90mph my car uses the assist & drains the battery if I leave it in 5th gear.

When driving at them speeds I tend to keep my car in 3rd / 4th gear .. On days when I have to drive like that I only average 45mpg

[IamIan]

Originally Posted by racer26

Its better to not use the HV battery, than to have to recharge it later, in most cases.

Just expanding a bit on some of the exceptions to the 'most cases' context.

#1> First exception is easy ... if their is no recharge FE penalty ... which is possible with a PHEV / grid charger.

#2>Second Exception is also fairly easy without Plug-In .... which is just a variation on the no FE penalty for IMA Assist , but without a Plug-In ... it needs three things together.

• IMA battery energy comes from regenerative braking.
• The above braking energy is used when needed ... conservation of momentum is more efficient where it is safe to do so ... but even the most efficient driver might need to use the brakes from time to time ... down long steep hills , and such.
• Making use of this IMA energy does not put the ICE in too low of an operating efficiency ... not an issue if you have non-OEM control of the IMA ... anything that gives basic MIMA like control... without this it is possible but more limited.

#3> The third exception has to do with the most efficient path ... and is more a bit more complicated.

Based on the non-Lean Burn BSFC chart ... in it's non-Lean Burn state the Gen-1 Insight ICE varies between about ~26% efficiency and about ~39% Efficiency ... depending on Load and RPM ... the difference between getting 26wh output vs 39wh output from the same 100wh input means I get up to 50% more energy out at the higher 39wh peak ( non-Lean Burn ) state than in the lower state ~26wh state ... any time the IMA circle is more than 50% efficient it is more efficient to use the IMA circle and keep the ICE up at the ~39% point than it is to not use the IMA and drop to the ~26% point.

If your given speed you did not need / want so much power that you would drop all the way down to ~26% than there is a smaller gap ... and the IMA path would have to be more efficient than 50% .... if the given speed does not allow for peak ~39% efficiency no matter gear you are in or what amount of power you want than there is an even smaller gap... which also would mean the IMA path would have to be more efficient to break even or be better.

Of Course Lean Burn is even better than the peak non-Lean Burn ... so if you are choosing between Lean Burn and non-Lean Burn there will be a larger gap and the cycle efficiency of the IMA path can be smaller and still have a better net efficiency.

The IMA motor & electronics combined vary between about ~70% and ~92% efficient depending on the load and RPM ... if your conditions allow for the peak of ~92% ... than you have ~92% efficiency getting to the batteries and ~92% efficiency putting it back in use ... or a maximum of ~84.6% efficiency both ways ... the minimum ~70% efficiency would be ~49% both ways.

There will also be additional cycle losses in the battery ... In my own testing I've seen as our NiMH batteries cycle up into the mid 90% cycle efficiency range ... but this too will also vary considerably depending on the conditions ... to be conservative we can say a peak of ~90% Battery Cycle Efficiency ... it varies but not quiet the way allot of people expect ... things like Peukert effects are not really lost energy or significantly lower efficiency ... a lot of the energy is still there , it just might not be available at higher current rates ... and supposedly out BCM prevents any significant amounts of over wasted energy in over changing.

So the IMA cycle path will vary depending on conditions between as good as a peak of about ~76% efficiency ... to as low as about ~30% efficient.

Even without Lean Burn ... there are conditions where the more efficient path is to use the IMA energy stored from a higher ICE efficiency state than it is to lower the ICE efficiency to provde the additional power desired.

With Lean Burn added in to further widen the gap between peak ICE efficiency and minimum low point ICE efficiency ... there are even more conditions / contexts in which the IMA path is the net more efficient path.

- - - - - - -

Of course YMMV just as much if not more based on the nut behind the wheel who's driving style , and route conditions can increase or decrease the required about of energy needed.

[Eli]

I need to search IamIan's posts and read every one. Your posts are always so.. Insightful. I love numbers, and you seem to have a lot of them!

I'm a little surprised by 39% efficiency in non-lean burn. What does it go up to with lean burn, any ideas? Must be close to 50%? Very, very impressive for a gasoline engine.

Can I get a pic of the BSFC chart? I guess one doesn't exist for lean burn? Shame.

[IamIan]

Originally Posted by Eli

I need to search IamIan's posts and read every one. Your posts are always so.. Insightful. I love numbers, and you seem to have a lot of them!

I'm a little surprised by 39% efficiency in non-lean burn. What does it go up to with lean burn, any ideas? Must be close to 50%? Very, very impressive for a gasoline engine.

Can I get a pic of the BSFC chart? I guess one doesn't exist for lean burn? Shame.

Thanks for the compliment
I frequent this forum because I feel similarly about many other very helpful and informed members ... I've learned a great deal from this forum over the years and interacting with all the great people here.

I find myself numbers can help clarify things that can be missed otherwise ... or are too small of a variation to get different people to agree on ... so yeah numbers are my firend ... although sometimes I spend to much time with the numbers / details / theory , and not enough time doing more hands on real world stuff... oh well never enough time in a week.

We do have a very impressive ICE ... even putting all the other HEV .. aerodynamics , Aluminum stuff aside ...

• Gen-1 Honda Insight Engine awards
  
  The Insight Engine won the International Engine of the Year award for 2000.
  
  The Insight Engine won the International Engine of the Year Award subcategory for Best Fuel economy / Green engine in 2000,2001, & 2002.
  
  The Insight Engine won the International Engine of the Year award subcategory for sub 1.0 L Engine every single year it was produced 2000, 2001 , 2002 , 2003 , 2004 , 2005 , 2006

Attached non-LeanBurn BSFC Chart bellow.

We know some quantified things about the Gen-1 Insight's Lean Burn Function ... EPA quote from their testing attached bellow ... but there has been some debate about the phrasing they used ... 8% friction improvement is a direct and obvious ICE efficiency boost ... the 20% improvement phrasing is a bit less clear ... it could mean a 20% wide operating window to get the ~39% efficiency in + the additional ~8% efficiency bonus on top ... or it could mean a 20% higher peak efficiency ... and if it is the later does that mean ~59% peak ( would be unheard of crazy high ) ... or 20% higher than ~39% which would be ~46% ... ~46% efficiency + 8% less friction ... is still crazy good ... that would be better than some diesel engines... but the unknown here is kind of why I would eventually like to get it better defined with some real numbers.... the worst case I see is something like a 20% wide band of the ~39% efficiency +8% reduced friction.

Given the wording that they used about the PERE modeling it at ~0.48 ... that seems to suggest to me they did not just a 20% wider state of ~39%.

Which more directly in context of this thread ... I can do ~77% more work at the higher ~46% point than I can at the ~26% point with the same amount of chemical energy input .... that much variation would allow the IMA path to be much lower efficient and it would still be a net better energy efficiency than pulling the ICE down from it's maximum peak to its minimum low... but the Exact Lean Burn BSFC chart is still not really defined... so that is much more supposition / theory than what we do know from the existing non-lean burn BSFC chart.

46% ICE ~76% IMA = ~35% Net Efficiency.
Any IMA cycle efficiency above ~57% would be better than dropping the ICE from a peak of ~46% to a low of ~26%.

Any BSFC chart g/kwh numbers can be converted to a basic engine efficiency % using the average energy density for gasoline of 13kwh/kg ... of course Gasoline is not a stable product nor is it 100% standardized even at the same octane grade and of course different brand additives can change this as well ... and of course E5 or E10 etc also have different average kwh/kg energy densities.

So take the peak efficiency number from the BSFC chart ... 200g/kwh for the non-LeanBurn Gen-1 Insight invert it to 0.005 kwh/g x1,000 = 5kwh/kg ... then devide by your fuel energy density ~13 kwh/kg * 100 = ~38.46%... repeat for any different BSFC g/kwh number or different known fuel kwh/kg energy density.

Just Keep in mind the conditions the BSFC chart you are using was made under ... if it was made under 100% gasoline ... there will be a slight difference in combustion properties with a E10 fuel instead ... so not only does the E10 have a slightly different energy density , it does not burn 100% exactly the same as 100% gasoline does ... this can be a good thing or a bad thing ... of course depending on how the different fuel burns differently.

Getting a good BSFC of our Lean Burn Engines is on my list of things to do ... there are of course always a few issues to get worked out...

• An accurate real time A/F ratio meter that can be logged / synchronized with other sensor readings / data happening at the same time.
  • A lot of Dyno Shops have these linked up to their stuff ... but I haven't found one that does the unusually wide A/F ratios our Gen-1 Insight operates under ... I suspect as the A/F ratio drifts the BSFC chart will change shape slightly with it ... so I expect 15:1 to be slightly different than 16:1 slightly different from 17:1 etc ... and I've seen reports of people using more accurate celebrated A/F ratio meters finding our Gen-1 Insights ranging from as low as 12.5:1 Rich and as lean as 25.8:1 ... that is an unusually wide A/F ratio range ... and when I've called around , beyond the abilities of most dyno A/F ratio sensors.
  • I hope to eventually find a correlation between out OEM wide band O2 sensors and specific A/F ratios ... I know the O2 sensors are not linear responses ... and I know the change with operating temperature as well as A/F ratio ... and they have a finite limited response time to changes.
• An accurate real time fuel flow rate meter that can be logged / synchronized with other sensor readings / data happening at the same time... ideally I'd like to exploit some of the OEM stuff already in the car and it would be a standard others could use as well.
• The Dyno needs to be equipped to accurately do the lower power ranges we expect to see ... I'm suspecting down as low as ~5 HP will be needed... many Dyno Shops are designed for hundreds of HP and with the majority of their business coming from the high power 0-60 crowd ... I've had a hard time finding one that is setup to do what I want to do.
  • One solution to that I've been looking into is that the key piece the Dyno shop offers that I would need is to have a known torque and RPM not only measured ... but also controlled ... while I like the idea of a Dyno shop for a lot of reasons ... even if I ever did manage to find one equipped to do what I want to do ... by the time I pay for several full days doing all this testing ... I will have spent a good size chunk of money ... and if that good size chunk of money is reasonably close to what it would cost to go other routes and just have my own garage type Dyno that meets my needs , I would be better off having my own type device.
  • There are some nice torque and RPM sensors out there that can be shaft mounted ... I think that would be a nice way to gather lots of real world data ... and it would remove the need for a garage which I do not have ... but those are pretty expensive.