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lugging the engine for the best mpg

4834 Views 23 Replies 8 Participants Last post by  Insightful Trekker
Hi guys,

Please have mercy if you think this issue has already been covered: I pledge that I did have searched the forum, and haven't found a satisfactory answer, nor topic that is devoted to this.

In short wording, I am concerned that chasing the best mpg number could be damaging to the Insight's engine. (This obviously seems a bit paradoxical, right?) What I frequently find myself doing is driving around 1500 rpm, gas pedal floored to maximize the assist (like when my speed drops on a hill, and my battery is full).

Now every normal gas engine would suffer from this kind of lugging practice, loading it to the max at low rpm's. My question is purely technical: is Insight engine in any way designed to handle this abuse better? Perhaps the VTEC valve system helps a bit, or perhaps it is just tuned to work ok at low rpm's...

Does anyone feel competent to speak for the engine designers? I would be most thankful, and would sleep better too!

Thanks!
Predrag
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John correct me if I am wrong here:
I think the answer is that with modern Fuel Injected computer controlled engines, the issues with engine lugging are not the same as when pressing on the throttle at 1200rpm on the older carburated engines. The fuel management system in the Insight does not just dump more fuel in the engine to try and increase power, it does it in response to the feedback from the emission control system, so only gas that can be efficiently burned is delivered to the engine, to maintain low emission, so the negatives of engine lugging are not in play.
With MIMA, I sometimes find my self driving at 30MPH at 1200rpm in 5th. I maintain momentum with short pulses of IMA.
 

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Hi Guys
While pondering this question, and fulfilling my need for a 100 mile trip over a mostly rural rolling New England secondary highway this afternoon. (CT RT 12), I made the 100 mile round trip with 79.9MPG. Average speed 36 mph, max of 50. The road goes through several small to middle size towns, with lots of traffic and traffic lights, I hit some school busses on the way back, the road is never flat, with two hills that without MIMA, to maintain 40mph, you would need to be in 3rd. My speed was with traffic, and at the speed limit +- 10MPH.
Take off from a stop was always with gentle throttle, and full manual assist, to get to speed with minimal gas usage.
The technique I settled on for cruising was to be in 5th as much as possible, even down to 30 mph. RPM 1000 to 1400. I had PIMA tuned so that the assist setpoint was at ~95 MPG, and the regen setpoint at 115 MPG. Come to a hill, gently change the throttle so the MPG was down to 70, and I already had full assist. Over the hill, back off the throttle to 130-140 MPG, and I got from 10-30 A of regen, with 150mpg giving full regen.
All so intuitive that I forgot about it.
With the stock IMA, if you press down the throttle to get acceleration or to compensate for slowing down on a hill, with the RPM at 1000-2000RPM, you must push down to ~ 40MPG before full assist comes in if it ever does. One look at the torque curve for the IMA, and you will see that the ICE only puts out about 20HP down there, and the electric puts out 13.Therefore the need to down shift.
I could top all but the big hills never dropping my MPG much below 60, all in 5th. Dropped to 40 on the two big ones.
The battery SOC got to 2 bars, after the big hills, but was at 40% when I got back.
I would bet that if anyone of you got into a 5 speed MIMA equipped Insight, and did a MPG run over a familiar road without MIMA, then did a duplicate run with propertly tuned PIMA, that your MPG would go up 5-15 %. No special techniques needed, just go easier on the throttle that you would without MIMA.
The best part is that the speed range during the runs would be higher with MIMA, acceleration faster, pulses of power shorter, and speed closer to the speed of traffic flow while matching or improving on the straight IMA MPG.
The engine was down to <1000 rpm several times, it even stalled then restarted once at 22 MPH in 5th, abut the electric torque was able to accelerate right from there with no need to downshift.
MIMA really makes a difference, and I know that if mostInsight drivers tried it, they would want one.
IMBO (In My Biased Opinion)
:wink:
 

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With all discussions of comparitive MPG, the following things :
terrain, speed, traffic, stops, wind,weather,temperature, AC, and other factors would need to be comparable for a meaningfull comparison.
The minimum for me to feel comfortable with a comparison
would be average grade, average speed, max speed, number of stops, elevation change start to finish, round trip or not.
Why don't we come up with a standard way of defining a trip that will allow some good fair comparisons of terrain in particular.
Delorm topo usa allows a route to be plotted on a map, then a profile of the elevation changes can be plotted for the trip. it cost less than $100.
Here is one of my trip today:
http://pages.cthome.net/genesisone/Mikesouthrt12.pdf
what do you think?
 

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As I said, 22 in 5th was where I stalled, after that I kept it over 1300 most of the time.
The insight with full assist in the 3-6K power band of the ICE makes the car scary fast (by my standards). It will accelerate up a good grade at 90+ mph in 5th. In third at 3K + the Insight just blast off, with the full 13 electric ponies galoping right in there with the gas ones.
The normal IMA limits the assist to 6-7HP when you go that fast, not with MIMA. I can squeek the tires in first and second with out poping the clutch.
Too much fun at first, I had to work the lead out of my MIMA finger.
Now I am trying to get good mileage at normal commuting speed. :wink:
 

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The most interesting thing about MIMA is that you find out how much or the total torque actually comes from the electric. At <2000rpm, the electric produces a good% of the torque, at <1400 rpm, it producesmore than the gas. drive without IMA, and take a short spin, to see the difference.
TorqueHP graph:
http://pages.cthome.net/genesisone/torque.jpg
I plotted James commute:
home to lake, route 1:
http://pages.cthome.net/genesisone/Jamesreno1.pdf
lake to home, different route:
http://pages.cthome.net/genesisone/Jamesreno2.pdf
Now those are some "hills".
 
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