Method for most efficient acceleration

[xqqqme]

After less than a week of living with our "new" 2001 Insight, I have a quesiton that reflects not what I know about this car but, rather, what I know about our Prius.

With the Toyota, the general consensus among hybrid "enthusiasts" is that energy conversion into and out of the battery is inefficient and is, therefore, to be minimized. When moving on a level stretch of ground at a speed under 41 mph (which is about the point that the Prius' CVT is going to start the gas engine due to planetary gearing) there is actually a mode you can find (and observe on the MFD) where no energy is flowing in either direction.

Similarly, there are methods of acceleration that promise greater efficiency (though they all seem to work equally well). And that leads me to my Insight question:

According to the manual, shifting with the greeen "upshift" light is the most efficient. However, in actual use, this feels like serious short-shifting. In order to attain acceleration any faster than glacial, I find I am really stepping into the throttle. In any other car, it would be lugging to beat the band. But with the Insight, the battery assist cuts in to provide the "oomph" I'm lacking.

When I rev it out to what feels to be a more productive engine speed (not more than 3000 rpm), the upshift light will have been glowing for quite a few seconds, quietly urging me to get into another gear. When I do this, from what I can see, there is no charging and no assist. If this is an accurate indication, I'm simply utilizing the ICE and not converting any energy within the IMA system.

So, overall, which is more efficient in terms of mpg -- getting into the IMA and letting the electric motor add some torque (energy for which will have to be replaced in the battery by additional running of the ICE)...or asking the ICE to act just a tiny bit more like it would in an Si model Honda?

[Dougie]

If you're trying to maximize economy, and don't care about performance, the best approach seems to be to short shift--perhaps even more aggressively than the upshift light suggests--and to stay out of assist. I am in 5th gear at 30 mph, for example. But staying out of assist seems to be the most important thing, because in the mountains I rev the engine quite high in order to make progress at 30 or 40 mph, frequently in 2nd gear at 4000 rpm. That seems to work better than lugging the engine with lots of assist, as the lights suggest...

[Fred]

I have an idea of what your asking about and can offer the following for what it may be worth.

.1. I have a 2006 CVT; aka "The Silver Bullet"

.2. On any given run on a relatively level road, if I gradually take the car up to about 45 to 50 MPH (2000 RPM) over a 1 mile run I can get significantly better milage than I can if I purposely "step on it" in order to have the IMA kick in and help the gasoline engine accellerate the vehicle to to the same speeds over the same distance.

.3. This is not to say that I do 10 MPH or so when starting out. On the contrary, experience has shown me that such lower speed ranges consume an inordinate volume of fuel for the performance delivered but if I get the vehicle up to forty or fifty MPH rather quickly (without "stepping on it!") so that I don't become a traffice hazzard (in some cases, going too slow for current road conditions and traffice flow can be just as deadly as going too fast) the ratio between MPH and MPG achieved by this method of driving is such that I'm satisfied with the results and there is a doubt here that others with a CVT can do much better - but then again, I could be wrong about this.

.3. While not an automotive engineer, experience has shown me so far that these little cars aren't "racers" as such but they really excell at long range running, provided you are prepared to keep your speed somewhere between the mid-forties to the mid-fifties.

Hope this helps

Fred :-)



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[xqqqme]

Thanks for the replies...I guess, as everyone discovers, that it's just going to take a lot of trial and error (and observation). I filled up yesterday and reset the MPG meter for Trip and took off for the better part of the day on a lot of errand-running in city driving conditions (lots of traffic signals and speeds not exceeding 40-45 mph. After about 30 miles I was really bummed that I was showing something like 43 mpg and thought "Heck, I can do better than that in the Prius under the very same conditions." I ended the day, however, with some highway driving (60-65 mph) and that brought things up. Today, I did more of the same (both types) and between the end of the day yesterday and today's running I got the avg up to 53.

I've always been pleased that my Prius results have always come from driving with the flow of traffic and never impeding anyone. I'm not at all sure, however, that I can drive the Insight by the upshift light and say the same thing. It feels like I'm holding up the show.

[minako]

xqqqme, I understand what you mean about not wanting to hold up traffic. I tend to ignore the upshift light (yes, I know, blasphemy!). Here is my rough estimate of shifting patterns while driving in the city:

1st to 2nd ~13 mph
2nd to 3rd ~27 mph
3rd to 4th ~34 mph
4th to 5th ~43 mph

My daily commute is roughly 70 miles a day. I estimate that about 10 of those miles is actual driving in the city (i.e. traffic signals and stop signs). This would probably explain why my average mpg is in the low 70s. I think that the Prius really shines in city driving but the Insight is designed more for highway driving to really maximize fuel performance.

The most important thing, though, is to try and anticipate stops - and avoid them. For instance, if you see that you are coming up on a red light and there are already cars waiting, let off the gas and coast to the stoplight. A little trick I do is take the car out of gear and step on the brake gently until I hit auto-stop (when you drop to 19 mph or lower). When auto-stop occurs, I push in the clutch (DO NOT put it into gear) and let go of the brake, thus coasting the rest of the way to the stop light while still in auto-stop. If you take your foot off the brake without having the clutch pushed in, or if you put the car back into gear (even with the clutch pushed in) the car will turn back on. As long as you gauge the distance and speed correctly, you'll be able to maximize these situations without pissing off the other people on the road. If they are too impatient and cut out from behind you, that's alright. More than likely, they will still be waiting at the stoplight by the time you reach it.

[psuinsight]

Technique is everything when it comes to driving Insights for maximum gas mileage. I sometimes log 48 mpg on the same route where I have logged 72 mpg. I find it critical to observe the FCD closely and I often ignore the upshift light. I have a hilly commute and I do use the IMA frequently. Sometimes I suddenly realize I have been criusing along in 2nd when I should be up in 4th. I feel that I get my better mileage when I get my speed up to a bit over the posted limit (usually 35 mph) and then drive with the pulse and glide technique.
The Insight always presents a challenge to improve my driving and thus improve my mileage. So far 95% of my driving has been on slow speed rural roads (lucky me ) however this weekend I will be travelling to Philly via the PA Turnpike .
I can't wait to see what kind of highway mileage I will get.

[xqqqme]

Originally Posted by psuinsight

Sometimes I suddenly realize I have been criusing along in 2nd when I should be up in 4th. I feel that I get my better mileage when I get my speed up to a bit over the posted limit (usually 35 mph) and then drive with the pulse and glide technique.

Pulse and glide I am familiar with from the Prius...though our Insight is a 5-speed and I'm still becoming familiar with how that state appears with the Honda. But, yeah, as far as the shifting...I've already caught myself in lower gears, causing no harm other than lower mpg. But years of wanting to stay a bit "up" in the revs for the cut-and-thrust of city driving means that I have my ears out for the sound of the engine more than I have my eyes trained on an upshift light!

[xqqqme]

minako, one of the key secrets to Prius mileage is, indeed, coast...a lot! The tip about anticipating stops (and other clogs and obstacles in the traffic ahead) reaps significant gain with the Prius. But, fact is, it's helpful with *any* car, not just hybrids.

What I'm fascinated to see on the instantaneous fuel use display is when -- at a point at which I am cruising along at, say, 45 mph and the street levels out and/or I lift up on the throttle and all of a sudden the display shoots up past 100 mpg or even higher. This, I gather from what I've read here, is the "lean burn" state, correct? Whatever it is, I can see where sustaining that mode as long as possible could be as helpful in boosting mpg as the equally desirable "glide" mode in the Prius when no energy is going into or out of the batteries and, similarly, instantaneous mileage shoots up to 99.9 (the highest that can be displayed).

[minako]

I, myself, do not really understand 'lean burn' even though I've done a few shallow searches for it on the site. However - yes! When you are at that mode in which you are neither charging nor draining the battery, and you sustain that FCD readout to show over 100 mpg as much as possible, you will reap the mileage like crazy!

Another note on shifting with the MT Insight. In first and second, don't expect to get much more than 25 mpg on the FCD if you're wanting to get going in a decent time (i.e. you don't want the guy behind you to slam into you). As you shift into the higher gears, however, pay attention to the FCD. When I'm accelerating, I usually aim to keep that FCD somewhere between 50 and 75 mpg. Then I 'glide' as much as possible to sustain that 150 mpg readout. If I start dipping below 100 mpg, I sometimes give it a little bit of gas to get my momentum up again. I find that if I downshift, I usually end up losing more on the FCD than if I had just stepped on the gas a little harder.

[Dougie]

No, when the instantaneous mileage jumps up to 150 that's just because you're coasting and the fuel injection is shut off.

Lean burn is fairly difficult to observe. You need to be going about 50 mph (go too fast and it won't go into lean burn), and everything needs to be nicely warmed up, and it needs to be level terrain. Then you just go along and gradually lift your foot so that the car is cruising along smoothly.

If you do it right, the instantaneous mileage will go up to about 100. This seems pretty normal at first, but then suddenly (maybe once a minute or even more often), without anything changing hill-wise or gas-pedal-wise, the instantaneous mileage will drop down to maybe 50 or so for a few seconds, then jump back up to 100. This is the purge cycle of the lean burn mode, and when you see it doing this then you know you are in lean burn.

I suspect that the engine goes into lean burn more frequently than people think, in other scenarios than the above, but unless conditions are right you can't really tell whether you're in it or not.