ag4ever — You sound like an ideal person to participate in the FE test. Thanks for offering! (Having a few more people participating would also be great.) Your comments, and those of alan_in_tempe, are relevant for the significance of any results we might get from such a test. Yes, having the navigation package makes running the test easier. Yes, the variability and lack of control over driving conditions are indeed significant concerns, but I had hesitated to suggest even more onerous restrictions in order not to put everyone off! However, since you raise the issue, the following is what I would consider to be the IDEAL way to run the test (or, at least, the closest to ideal that we're likely to be able to achieve):

Choose a relatively low traffic density route of about 30 km (~20 miles) each way, with a terrain such that one can force pure-EV mode frequently and for long periods at a time. Find a day when you have the morning or afternoon free — probably on a weekend. Around mid-day might be best for stable temperatures and reduced wind. Have the TCH well warmed up. Run the same route back and forth repeatedly, using type-(i) driving there-and-back on one round trip, and then type-(ii) driving on the next round trip. Drive at least TWO round trips in each of modes (i) and (ii). To see if your data are meaningful: Do the two return trips of type (i) agree well with each other as far as FE is concerned? (And also, are the driving times for the two outbound legs comparable to each other, and similarly for the times of the two return legs?) Ditto for the two type-(ii) trips. If so, I think that you will indeed have obtained meaningful data!


What do you say ag4ever? Are there any other takers?


Stan

 

You also have to take into account some highway driving to recharge the batteries at a "high efficiency" drive time.


I will try to do some testing on my drive to work, logging the weather, wind, time of day, and time of trip. i might take a month or so to get 10 days worth of data since I don't have a regular set schedule. I am in construction, so one day I might go to the office, and have to leave early to go to an architect's office, then the next day I might be going to a job site for the day and not even go to the office, and other days i might go to an owner's office, so it might take a while to get some good data.

I have been "testing" some driving methods recently, and I have noticed that my most recent tank is one of my better tanks, and I have not force e-mode very much on this tank.

Houston is getting a cold front this PM, so winds might be very unpredictable for the next few days.

 

ag4ever — You're quite right that the state of battery charge at the end of each return trip MUST be the SAME as it was at the start of that same trip! I'm embarrassed actually that I omitted to mention this important requirement, since it WAS clearly stated in my original post that started this thread! So, yes indeed, add the requirement that at the start of each return trip the SOC of the NiMH battery must be noted down, and at the end of that return trip, one must make sure that the SOC is as close as feasible to being the SAME as it was at the beginning. This means that: (a) if it's lower, one must continue driving to recharge the battery to its original SOC; and (b) if it is apparent that it's going to be higher, one ought to have allowed more pure-EV mode to occur towards the end of the trip in order to bring it down to its original level. But this is getting overly complicated. I think that all one needs to do is to make sure that, at the start of each return trip, the battery is as close to being fully charged as it ever gets in normal driving. Then at the end of the return trip it WON'T be any higher than this, and so the (b) scenario won't occur. Then one only has to take the (a) scenario into account. I think that's feasible. Do you agree?

Stan

 

If you are doing two trips a day, "to work" and "return home" the SOC only really matters at the start of the day and the end of the day. This time at work should not matter as long as you don't drive the vehilce to lunch, then it might introduce some additional error into the test.

I think the best way to control the externals would be to devote a weekend and a couple tanks to controled rout driving. I don't plan to do that.

I did start my testing this moring on the way to work documenting most variables, but I did not note the SOC at the arrival to work, it was supprisingly at one purple bar when I started it this morning.

 

Everybody — We need more volunteers to join ag4ever in the experiment to assess the possible benefits of forced pure-EV mode. People with sizeable commutes, or the interest to run some controlled driving tests during a weekend, would be best. I explained the requirements for conducting a meaningful test in some recent posts, and ag4ever elaborated on them. You also need to know how to "force" pure-EV mode, of course. Please offer to participate!

Stan

 

ag4ever — Can you please let us know how your fuel efficiency experiments are going? Thanks.

Stan

 

Unfortunatly I have not been doing them yet.

Long story shortened:
We were living in my inlaws house since they were in South Africa and we sold our house.
Mother-In-Law decided she did not like South Africa so she moved back.
I decided I could not live with mother-in-law.
Wife and I decided to get our own house.
We started moving on 12/8/06.
Since then my drive to and from work has been very inconsistant (stopping at home improvement store for new house items, using truck b/c I needed to get stuff from storage, going gift shopping on the way home from work, etc...)

All in all, I just have been having a very hectic month, and hope that January will settle down some.

On a good note, the change in my drive to work has resulted in my average trip FE to go from 39 MPG to 44 MPG. I also have much less opportunity to use pure EV mode as we live much closer to road that allow me to drive above 50 MPH with very few stops. About my only EV mode driving I can do is in the neighborhood now. About 2-3 miles worth each way.

 

Dear All:

Introduction:
It’s now almost two months since I issued my challenge, earlier in this thread, for those Toyota Camry Hybrid owners (and any other model Toyota hybrid owners too), who believe that they have the ability to achieve better overall fuel efficiency (FE) than Toyota’s ECU can achieve, by forcing “pure EV-mode” operation (i.e., ICE “off” and car being propelled solely by the NiMH battery via MG2) as much as possible, to try to substantiate their claims with hard data. I even suggested a test procedure that I felt would be able to provide the sort of data needed. Not having heard of any such tests having been conducted yet, I reluctantly decided on December 14 last year to conduct just such a test myself. Why reluctantly? For two reasons: (i) I really feel that those who make such claims, not those who question their accuracy, have the responsibility to substantiate them; and (ii) because winter was settling in where I live in Ontario, Canada, and the opportunity to achieve substantial pure-EV mode driving was decreasing as the temperatures dropped. It was either now, or not until next spring.

The Experimental Procedure:
So, on December 14th I set out from Waterloo, Ontario for Wallenstein, to use the ~30-km (~19-mi) run from there to Listowel as my test track. [For convenience I’m going to report most of my data in SI units only, but I will also give some of the more relevant data in US units, and I will summarize my conclusions also in US units towards the end.] This stretch of road is straight, almost completely flat, with only minor undulations, and has no stops between these two cities. Traffic is also relatively light, but I will admit that my low-speed antics did annoy a number of other motorists and truck drivers, to whom I hereby apologize for slowing them down in the interests of scientific research! It’s not my habit to drive this way normally, and most of the other road users seemed to take it good naturedly. I drove the return trip from Wallenstein to Listowel four times, alternating forced pure-EV-mode driving (Trips 1 and 3) with normal driving (Trips 2 and 4). Including getting there and back, the total distance I covered that day was 312 km, and the overall fuel consumption was 15.5 L {according to my ScanGaugeII (SG)}, giving an overall FE of 5.0 L/100 km (48 mpgUS = 57 mpgImp). I started the experiments around 10:00, and finished around 14:00, and the ambient temperature slowly rose from 4°C to 7°C (39°F to 45°F) during the course of the experiments. My gas tank was an indicated ~1/2-full (87-octane fuel) to begin with, and ~1/4-full at the end. My tire pressures were the Toyota-recommended 220 kPa (32 psi). Other than the non-defeatable (in Canada) daytime running lights, the SG, and my Alpine “Blackbird” GPS system, no other electrical accessories were drawing power from the 12-V battery. The cabin heater was on in ECO mode, set to 21°C (70°F), and the ICE water temperature stayed around 89°C throughout. The wind was ~0 km/h until the second half of the last return trip, when it picked up to maybe ~20 km/h approximately perpendicular to the road.

I was surprised how easily I was able to achieve and maintain pure-EV mode operation when I wished to do so. I started with the NiMH battery at a 7/8ths State Of Charge (SOC), and was careful to return it to this SOC by continued driving at the end of each return trip if it happened to be different when I finished each of the four return runs. (It was indeed lower after each forced-pure-EV-mode trip, as expected.) In normal driving, I used the TCH’s cruise control to keep the speed around 65 km/h (~40 mph) whenever possible. During the forced pure-EV mode driving, I tried to maintain pure-EV mode at 60 km/h (~37mph) whenever possible, this being near the maximum possible without the ICE starting up. During normal driving, the SOC remained essentially constant at 7/8ths (7 bars), but during pure-EV mode, it dropped to as low as 2/8ths (2 bars) during pure-EV-mode segments. I found that it was extremely difficult to maintain a steady ~60 km/h in pure-EV mode; more so as the SOC dropped lower and lower. The result was that my speed generally tended to creep down towards 50 km/h when I was in pure-EV mode, after which the ICE would start up, and I would drive at around 60 km/h until the battery’s SOC had recovered sufficiently to allow me to force pure-EV mode again.

The Experimental Data:
(1) Trip 1 — Pure-EV-mode return trip #1:
Fuel used = 2.9 L
Return trip distance = 64.2 km
Return trip time = ~66 min
Time in pure-EV mode = ~22 min
Average speed = 58.4 km/h
Average FE = 4.5 L/100 km (52 mpgUS = 63 mpgImp)

(2) Trip 2 — Normal driving return trip #1:
Fuel used = 2.8 L
Return trip distance = 59.4 km
Return trip time = ~56 min
Time in pure-EV mode = ~1/2 min
Average speed = 63.6 km/h
Average FE = 4.7 L/100 km (50 mpgUS = 60 mpgImp)

(3) Trip 3 — Pure-EV-mode return trip #2:
Fuel used = 2.8 L
Return trip distance = 62.1 km
Return trip time = ~65 min
Time in pure-EV mode = ~27_3/4min
Average speed = 57.3 km/h
Average FE = 4.5 L/100 km (53 mpgUS = 63 mpgImp)

(4) Trip 4 — Normal driving return trip #2:
Fuel used = 2.6 L
Return trip distance = 56.8 km
Return trip time = ~53 min
Time in pure-EV mode = ~0 min
Average speed = 64.3 km/h
Average FE = 4.6 L/100 km (52 mpgUS = 62 mpgImp)

Interpretation of the Data:
These data are remarkably consistent between each of the two runs for each driving modality, and this convinces me that this was in fact a darn good experiment, even if I say so myself! But it wasn’t perfect (more on possible improvements to the experimental procedure below). Note how much time was spent in pure-EV mode in Trips 1 and 3 — fully 38% of the time on average! This is remarkable. (These are actually pretty impressive FE numbers at these steady and moderate speeds, and much better than EPA ratings, of course!) Nevertheless, the FE differences are so small as to be in the measurement noise:
Average FE in normal-mode driving = 4.6 L/100 km (51 mpgUS = 61 mpgImp)
Average FE in pure-EV-mode driving = 4.5 L/100 km (52 mpgUS = 63 mpgImp)
This is partly because ScanGaugeII reads fuel consumption to a precision of only 1 decimal place — namely ±0.1 L. Since I measured the fuel consumption separately for each half of each trip, this means that the fuel used for each return trip has a potential worst-case error of ± 0.2 L, but probably much less. A worst-case error of ±0.2 L per return trip would represent a potential worst-case error of ±0.3 L/100 km in the computed FE numbers. This is greater than the differences between the FE numbers for the different-mode trips! One must conclude from these data that there was no statistically significant difference between the FE numbers obtained for the two different driving modalities.

But, the average speeds were significantly different in the two driving modalities:
Average speed for normal-mode driving = 64 km/h (36 mph)
Average speed for pure-EV-mode driving = 58 km/h (40 mph)
Now, the FE inevitably drops as the speed goes up, largely due to the increasing losses caused by air resistance. From my calculations on the original Prius (given in Post #29 of this thread), I would expect an increase in fuel consumption of ~0.4 L/100 km at 64 km/h compared with 58 km/h due primarily to this cause. This means that, had I done the normal-mode driving at a nominal speed of 58 km/h instead of 65 km/h, the results would probably have looked more like this:
Average FE in normal-mode driving = 4.2 L/100 km (56 mpgUS = 68 mpgImp)
Average FE in pure-EV-mode driving = 4.5 L/100 km (52 mpgUS = 63 mpgImp)
And this would probably be statistically significant. (See my comments below on suggested improvements to the experimental procedure.)

Conclusions:
The fact that the data show no statistically significant difference between the two modalities of driving, given the significantly different average speeds used, actually does provide convincing (but not conclusive) evidence in support of my hypothesis — namely, that there is no benefit to forcing pure-EV mode when the TCH’s ECU doesn’t wish to switch to this mode. Indeed, there is most likely a loss of FE caused by doing so. This does not surprise me, as I have argued from the beginning of this thread that the laws of physics actually predict such an outcome. The results, however, are closer than I would have expected. And, this was with pure-EV mode occurring a very substantial fraction of the travel time too. For more usual pure-EV-mode forcing, which I assume would occur for a smaller fraction of the total travel time, the difference would be even smaller. So, don’t try to force pure-EV mode operation — it won’t benefit your FE, and will most likely worsen it.

Hindsight Thoughts About an Improved Test Procedure:
(a) It would have been better to have driven the normal-mode trips at a cruising speed of ~58 km/h and not 65 km/h. This would have made the two different modalities have approximately the same average speeds, and so have eliminated the effect of the differing wind resistance from the data. The TCH would probably have stayed predominantly out of pure-EV mode when run under cruise control at 58 km/h (even though this speed is low enough to allow it to drop into pure-EV mode), simply because the not-so-gentle throttle action of the cruise control would likely have quickly kicked the TCH out of pure-EV mode each time.
(b) It would have been better to read the combined return-trip fuel consumption rather than resetting SG’s trip meter after each lap. This could have yielded potentially greater accuracy in the fuel consumption numbers for each round trip. However, I did need to pause in order to gather and notate all the data accumulated during each lap, and I didn’t want any fuel consumed during this pause to appear in the total consumption. This is why I did reset SG each lap. If I had had a co-pilot to do all the note taking, it would have been better.

Challenge Re-issued:
If you don’t like or believe my results, please don’t hypothesize me wrong! The onus is on you to prove me either right or wrong by conducting at least as good a series of tests of your own, and reporting your results here. I’m confident that, if you do so, you’ll find that you will inevitably be led to the same conclusion as I.

Stan

 

Excellent work, Stan. Thanks for the great effort.

I would only add a very subtlety different conclusion. The difference between forced EV and ECU determined EV is virtually insignificant so as to suggest both sides of this argument are proven mostly wrong! Driving to force EV is a good way to improve FE, but not enough to matter much, and forces slower speeds to do so. That is, any FE improvement is mostly a function of speed, in spite of, and not a function of using EV mode, and your original hypothesis that EV mode harms FE is mostly validated, even if only barely so!

On the other hand, judicious use of forced EV may still be wise, even though the EV proponents haven't demonstrated when it is judicious to do so, and you have demonstrated that forced EV mode to the max is probably not optimal.

A modification to the experiment I would like to see would be to 1) not use cruise, but to allow a small variation in speed to better optimize FE when not forcing EV, perhaps as much as +/- 3 MPH, to take advantages of small changes in road conditions where the cruise reacts too quickly for best FE, in order to better optimize FE in the non-EV use part of the test (as my personal experience suggests), and 2) limit the forced EV to no less than half or 3/8ths SOC, and to some minimal speed, as I think a less aggressive forcing of EV would likewise better optimize the use of EV, even though result in significantly less total EV usage. The use of both protocol changes should increase FE for both modes, and will bring the average speed of the EV legs higher so that reducing the speed in the non EV legs will be less necessary for fair comparison.

My goal for the above changes in protocols would not be to prove forced EV is better/worse than non-EV, but to better understand how best to achieve hypermilage with the least effort, and perhaps gain a better understanding of how and when EV mode can contribute. I am sorry that I am not able to run these tests myself to further contribute to the cause.

My hope is that further experimentation may identify perhaps rare conditions where driver induced EV mode may be smarter than ECU chosen EV modes.

-- Alan

 

Challenge Re-issued:
If you don’t like or believe my results, please don’t hypothesize me wrong! The onus is on you to prove me either right or wrong by conducting at least as good a series of tests of your own, and reporting your results here. I’m confident that, if you do so, you’ll find that you will inevitably be led to the same conclusion as I.

Stan

Good job Stan!!! thanks