A hypothesis: 75mph is the highway mpg sweet spot

[acdii]

 

I might have to start running some tests out on county roads. I still think that the instantaneous gauge isn't very useful because when you're recharging, the instantaneous plummets, so I still don't understand why people use that. The average or the trip computer is probably more telling since it does weighted averaging so when the instantaneous fuel economy plummets when it's charging, it'll get averaged out.

No charging if the SOC remains high. Trick i found is ~53 MPH I can keep the ICE balanced with no draw or charge to the pack. It only works on one 3 mile stretch of road thats about the flattest on my daily drive.

 

Does it help me get better MPG? Nope, the difference in MPG doing this and just letting the car do its things is in the .x range.

[alpha754293]

I'd be interested to see that when you have the time. I'm not an engineer so I have limited understanding of these concepts but I want to understand them better.

 

I want to know from the perspective of manipulating my pressure on the gas pedal to make the engine run most efficiently. Unlike your comment above I would rather drive to power and kind of do already. On long highway trips I'll set the cruise control, but as I've learned more about how the FFH works I've starting way more driving to power rather than to speed. Since I walk to work I'm rarely driving in traffic so it's not a big deal usually for me to vary my speed up and down when there are few other cars around. Since most of our terrain is rolling hills I try to drive in such a way that I pick up speed going down the hills. Since it's more efficient to turn this gravitational energy into kinetic energy than it is to turn it into electrical energy through regen I prefer to feather the throttle so that the current flow in/out of the HVB is minimal. This way I can minimize efficiency losses. When travelling up a hill I try to keep the power demand low and in EV for awhile and then once my speed drops too much I step on the pedal enough to engage the ICE to recharge and propel me up this hill.

 

It my ScanGauge thread I've started doing some calculations based on the HP reading of the SGII to figure out the kW to tie it to the graph. I've also been able to do that with the amps of current out of the HVB to calculate approximate kWs at certain spots on the car's display. If I had BSFC data of at what kWs the ICE is operating in the optimal BSFC region then I could correlate that data to spots on the display. That would then help me to make sure I keep the ICE operating in that region as often as possible.

 

I agree that you can't operate the car in its most optimum range without affecting speed, but I am willing to change my speed to optimize ICE efficiency. EcoCruise already does this to a certain degree on the highway. While the pedal position doesn't necessarily directly correlate to RPMs like in a gas-only car, it does correlate directly to power demand. If I know what level of power demand is best then I can make my foot work within that area.

 

I'm not really sure how to break up the quote block, but here goes: to your first point - I'll probably do it like a bunch of university lecture notes for what would typically/commonly be covered in about a Junior level (3rd year) university thermodynamics course. It will be calculus based since it's easier to get to the thermo bits with calculus otherwise I'd end up breaking down the calculus bit into its fundamentals and it's quite easy to get lost in that rather than the thermo bits (which is what we're really after). It'll also likely be a mixture of like hand drawn-then-scanned diagrams with powerpoint, and I'll probably post it on my Google drive or something like that for you.

 

It will also have some inherent (and perhaps unrealistic, and grandiose) assumptions for the idealized Otto cycle. Or at least I'll start there. (Then depend on how that goes, we may extend that over to the Atkinson cycle, which is how the FFH engine ACTUALLY works), but if we run into more fundamental roadblocks with the Otto cycle, it's better to fix those first before moving on. Keep in mind that this is normally a 3rd year level course, so normally, at this stage, you would have had about two years' worth of engineering material behind you (including all the maths, physics, chemistry, solid mechanics, statics, and maybe even a humanities coures here and there)- but in the interest of time and keeping you entertained/interested and getting straight to the point; I'm going to be going over the material as though it were a 3rd year level course. We can always tackle the fundamentals that lead up to it some other time (or you might be able to go to Harvard/MIT/Stanford open university courses and watch the undergraduate lectures that they've opened up or through the various open and online universities that's available now. They're an excellent resource!)

 

To your second point - driving to power (as you call it) isn't exactly new. I used to hold my pedal at a fixed or nearly fixed position so it's to let the speed vary (often with grade changes).

 

That works, mostly if either the grade changes are small, or the wild swings in speed isn't going to get you rear ended. (I do it sometimes on hilly roads as well, because cruise control (which is based on you speed like you said) can't take momentum into effect/consideration, and so the control logic often is playing catch up with it, which causes wild swings in acceleration (which gives me motion sickness)).

 

Again, that works for you because you have a hilly region where variations in speed doesn't matter so much for you. So, knowing the bsfc, you'd have to be able to try and see if you can drive in such a way that you're isolating the ICE from the HVB so that your power numbers make sense. And if you're able to get the amps and voltage output from the HVB simultaneously, then you can actually pretty accurately figure out what the ICE is doing.

 

So me, I don't have much in the way of hills per se, and it's VERY dangerous in Michigan to vary your speed wildly (unless you're talking more along the lines of like 90 mph +/- 10 mph, then you might be ok). The risk of being rear ended here is VERY high. And people here also have a nasty habit of tailgating you (cuz that's how a lot of Michiganders drive).

 

And the other thing is that roads close to where I live (and out in the county) is SUPER flat.

 

 

No charging if the SOC remains high. Trick i found is ~53 MPH I can keep the ICE balanced with no draw or charge to the pack. It only works on one 3 mile stretch of road thats about the flattest on my daily drive.

 

Does it help me get better MPG? Nope, the difference in MPG doing this and just letting the car do its things is in the .x range.

 

I didn't think it would (necessarily). Remember that you get the greatest benefit from being able to use the EV since your instantaneous fuel economy is technically +infinity (but shows up as 999.9 mpg) and it's a weighted average. So, it the sweet spot is probably what can make it cycle most.

 

Like I said, I'll probably have to run the tests out in the county to generate a second "master equation" for speeds < 90 km/h (since I have to use a different road). (And I'll probably need to update my original master equation since the PCM update).

[hybridbear]

Again, that works for you because you have a hilly region where variations in speed doesn't matter so much for you. So, knowing the bsfc, you'd have to be able to try and see if you can drive in such a way that you're isolating the ICE from the HVB so that your power numbers make sense. And if you're able to get the amps and voltage output from the HVB simultaneously, then you can actually pretty accurately figure out what the ICE is doing.

I'll take whatever data you can provide. I also want to understand the relationship between LOD on the ScanGauge and the BSFC graph. The components of a BSFC graph are ICE power (kW or HP), RPM and fuel consumption. The SGII allows me to monitor power and LOD. My goal would be to be able to use the LOD number to regulate my driving for the best efficiency. If I knew for example that a reading of 85<LOD>95 means the car is in its most efficient BSFC range then I could try to feather the pedal to keep the LOD above 85 as much as possible while keeping it below 95. That would be easier to me than trying to regulate RPM and power output to drive in the most efficient BSFC region.

[dkegel]

I used to hold my pedal at a fixed or nearly fixed position so it's to let the speed vary (often with grade changes).

No offense, but I hate when people do this, at least on the highway. One second you're going faster than someone, the next, slower. It is dangerous, and annoying to those around you. Pick a speed and stick to it.

 

My $.02

 

Dave

Edited October 8, 2013 by dkegel

[corncobs]

No offense, but I hate when people do this, at least on the highway. One second you're going faster than someone, the next, slower. It is dangerous, and annoying to those around you. Pick a speed and stick to it.

 

My $.02

 

Dave

That's what ECC is for it does it a little bit but not as much to piss people off.

[alpha754293]

No offense, but I hate when people do this, at least on the highway. One second you're going faster than someone, the next, slower. It is dangerous, and annoying to those around you. Pick a speed and stick to it.

 

My $.02

 

Dave

 

None taken. Oh yeah...I know. Me too. But that was also before I had cars that had cruise control (or I trained my right foot to be able to give VERY fine, precise, accelerator inputs). Now that I'm so used to driving in Southeast Michigan, where to get anywhere, it's hop on the highway and usually within 5 minutes, cruise will already be set and on; so it drives me nuts when I'm approaching Toronto or hopping on the highway in Toronto and people there DON'T use their cruise much. (Granted, usually, there's so much traffic, that it's no point anyways, but mehhh...)

 

Now, I set my cruise to 110 km/h (69 mph) and just leave it there. And then on the surface road going to work, I usually set it at 70 km/h (44 mph). Or any other city street where I can keep it and hold it at a certain speed.

 

But that's why I also said that it depends on traffic conditions. If there is traffic, it's usually best NOT to do that; which he says is the case with him. So...

 

That's what ECC is for it does it a little bit but not as much to piss people off.

Did you mean ACC? I've never played with that to be honest. I think that the system panic-braking would give me such a migraine. ugh....

[alpha754293]

I'll take whatever data you can provide. I also want to understand the relationship between LOD on the ScanGauge and the BSFC graph. The components of a BSFC graph are ICE power (kW or HP), RPM and fuel consumption. The SGII allows me to monitor power and LOD. My goal would be to be able to use the LOD number to regulate my driving for the best efficiency. If I knew for example that a reading of 85<LOD>95 means the car is in its most efficient BSFC range then I could try to feather the pedal to keep the LOD above 85 as much as possible while keeping it below 95. That would be easier to me than trying to regulate RPM and power output to drive in the most efficient BSFC region.

 

Sorry - just to clarify - LOD is...?

 

Well...yeah...like you said - the gas pedal now has less of a direct connection to rpm than it used to. Besides, the addition of the CVT also decouples that relationship as well.

 

Having said that though - and since you know that the x-axis of a bsfc chart is rpm, y-axis is usually power (or torque) and the contours are usually the actual bsfcs - it used to be that the most efficient was in like the 3000 rpm range or so. But since your gas pedal is highly decoupled from that, trying to get it into the 3000 rpm range is going to be quite difficult. I don't think that my cruising at 110 km/h - I can even get it to stay at or around 3000 rpm. (It's usually like 2000-something). Unless I'm going uphill, but then I'm also using/needing more power, so that changes the conditions or the inputs.

 

But yeah, I'll try and see if I can put something together for ya by like this weekend or something.

[Eddie Sessum]

ACC is nice, but if someone comes over merging in front of you too close it hits the brakes and keeps on them for about 3 seconds while they accelerate away. Thats my only gripe about it.

[corncobs]

 

Did you mean ACC? I've never played with that to be honest. I think that the system panic-braking would give me such a migraine. ugh....

No not ACC I meant ECC - EcoCruiseControl works very well. I think it has dramatically improved with the PCM update. Even on small rolling hills it stays in EV if it can which is really cool. Also on flat stretches at any speed it does a better job going and staying in EV then I can most at the time. Edited October 9, 2013 by corncobs

[hybridbear]

No offense, but I hate when people do this, at least on the highway. One second you're going faster than someone, the next, slower. It is dangerous, and annoying to those around you. Pick a speed and stick to it.

 

My $.02

 

Dave

I agree. That's why I only do this if there is minimal traffic where I won't be a pain to other motorists. However, most motorists don't set their cruise control and thus are varying their speed all over the place too. The difference is that they are doing it without a specific purpose in mind, unlike how I am.

Sorry - just to clarify - LOD is...?

 

Well...yeah...like you said - the gas pedal now has less of a direct connection to rpm than it used to. Besides, the addition of the CVT also decouples that relationship as well.

 

Having said that though - and since you know that the x-axis of a bsfc chart is rpm, y-axis is usually power (or torque) and the contours are usually the actual bsfcs - it used to be that the most efficient was in like the 3000 rpm range or so. But since your gas pedal is highly decoupled from that, trying to get it into the 3000 rpm range is going to be quite difficult. I don't think that my cruising at 110 km/h - I can even get it to stay at or around 3000 rpm. (It's usually like 2000-something). Unless I'm going uphill, but then I'm also using/needing more power, so that changes the conditions or the inputs.

 

But yeah, I'll try and see if I can put something together for ya by like this weekend or something.

That's a good question. I don't know exactly what LOD is. It's one of the functions built into the ScanGauge. From my results when googling it and what I've observed I believe LOD is the % of maximum torque output of the engine at that RPM. So if the LOD says 90 that means that the ICE is currently producing 90% of its maximum torque for that RPM.

[Wade Burtch]

Hi everybody. I came to this topic after repeatedly encountering the same phenomenon as Aquineas. On road trips, I get better mileage when I travel at around 75 mph than when I travel around 65. The first few times I figured it was a fluke. But time and time again, I do better above 70 than below.

 

I have a theory. Most of my travels are in Pennsylvania, where it is usually hilly. When going slower, generally the ICE charges the battery uphill, and the car is in EV mode downhill. When going faster, the the battery assists the ICE uphill (hybrid drive), and the ICE is more likely to remain running while going downhill. It uses this time to charge the battery. Could it be that the latter combo of ICE/battery charging and assisting is more efficient than going into EV mode down every hill, draining the battery so it can't assist while going back up the hill?

[mwr]

I'm late to this topic, but my experience (unscientific) is that the faster I go the less mpg I get. I've been stunned with the high mpg I get when in slowed-down traffic (30-50 mph, in the 50s mpg). CC at 70 mph, I expect 43 mpg displayed (about 41 actual). Faster means less mpg for me. I don't really care; I just drive how I drive and let the mpg take care of itself, very nicely I might add.

[hybridbear]

Hi everybody. I came to this topic after repeatedly encountering the same phenomenon as Aquineas. On road trips, I get better mileage when I travel at around 75 mph than when I travel around 65. The first few times I figured it was a fluke. But time and time again, I do better above 70 than below.

 

I have a theory. Most of my travels are in Pennsylvania, where it is usually hilly. When going slower, generally the ICE charges the battery uphill, and the car is in EV mode downhill. When going faster, the the battery assists the ICE uphill (hybrid drive), and the ICE is more likely to remain running while going downhill. It uses this time to charge the battery. Could it be that the latter combo of ICE/battery charging and assisting is more efficient than going into EV mode down every hill, draining the battery so it can't assist while going back up the hill?

You're right that the cycling of the ICE on & off at highway speeds is inefficient. This is exacerbated by the increase in max EV speed from 62 to 85 from summer 2013. MN is also very hilly and I'll still drive 65 but I'll use my foot on the accelerator to keep the ICE on when I don't want it cycling.

[wiscy67]

I've seen at least a couple posts from others that support your hypothesis. Unfortunately they all seem to be from folks who are doing road trips. Therefore the same highway trips can't be repeated under the same/similar conditions but at different speeds to really test the hypothesis. It would be useful to design a test for a daily commute on the highway.

 

What I've seen in my highway travels (80% driving) still seems to indicate to me that for the same commute the greater the number of EV miles logged for that leg the higher the mileage I get. This is true for me when comparing the results for that same leg under similar conditions but with fewer EV miles logged for it. The way I vary the EV miles is by varying my speed. What I see is the faster I go the fewer the EV miles I log and the worse my mileage (when all other conditions are equal).

Hi everybody. I came to this topic after repeatedly encountering the same phenomenon as Aquineas. On road trips, I get better mileage when I travel at around 75 mph than when I travel around 65. The first few times I figured it was a fluke. But time and time again, I do better above 70 than below.

 

I have a theory. Most of my travels are in Pennsylvania, where it is usually hilly. When going slower, generally the ICE charges the battery uphill, and the car is in EV mode downhill. When going faster, the the battery assists the ICE uphill (hybrid drive), and the ICE is more likely to remain running while going downhill. It uses this time to charge the battery. Could it be that the latter combo of ICE/battery charging and assisting is more efficient than going into EV mode down every hill, draining the battery so it can't assist while going back up the hill?