FastMover — But the car couldn't (shouldn't?) report open-loop if it's still burning fuel! Yet, ScanGauge does show open-loop whenever the FE gauge reads precisely 0 L/100 km. I'm pretty sure that it's using absolutely no fuel then.

alan_in_tempe — I'm glad that we're finally on the same wavelength now! Thanks for your complimentary remarks.

Stan

 

Then there is absolutely something different in the two cars. True that most of the time you state the condition accurately 60MPG == open-loop, but in some conditions, mostly when backing down slowly from a low fuel burn rate in the 40-55 MPG range the indication is 60MPG with a battery discharge indication and also a fuel flow. Incidently, both indications remain if you go from this state back to a 40-55 MPG range -- and the car is producing some very limited amount of acceleration when you do this, but more that it is capable of on MG2 alone. If there is an ICE start during this time, I do not see it on the fuel flow indicator or feel it, just a smooth, very slight acceleration and a small increase in fuel flow.

One other thing. When going into an open-loop condition the MPG needle moves quite abruptly to the 60MPG "pegged" indication from where ever it was. But when the state described above occurs, the needle movement is consistent with the same movement as when it was changing from some higher value, say 50 MPG down to 55 MPG, except down to 60.

Question for you: Can you sustain an indication of approximately 50 MPG (about 4.7L/100 km I think) whilst maintaining a speed of apprximately 50 MPH (80 km) with an indication of the ICE turning and also a battery discharge indication. I can sometimes do this for periods of up to ten minutes on reasonably level terrain during my daily commute. I would guess the very low end of heretical mode except for your statement about the battery discharge indication not present in this mode. The battery does not actually seem to discharge either as the battery "full" indication itself remains fairly static. IF the car was acccelerating on the battery alone and gradually increasing the ICE RPM in fuel-cut I would expect a discharge on the battery over that lentgth of time.

 

FastMover — To answer your question: Yes, I can sometimes get a battery discharge indication (i.e., battery power going to the wheels via MG2) while driving at 80 km/h (ICE "on" and providing power with ICE icon present on MFD). Fuel usage is ~5 L/100 km. I haven't seen this for a prolonged period, though, but perhaps this is just because of the lack of a suitable flat road without heavy traffic around here.

On the metric TCHs, the FE gauge's display is directly proportional to fuel consumption. On the US model, however, the indication is inversely proportional to fuel consumption (the higher the fuel consumption, the lower the number). The gauges appear to have similar scales, only the numbers associated with the tick marks being different. In the metric gauge the major tick marks are labelled (from bottom to top) 0, 10, 20, and 30 L/100 km. The US version labels these same tick marks as (from bottom to top) 60, 40, 20, and 0 mpg. Now, first, 0 L/100 km cannot equate to 60 mpg (it's actually infinite mpg). Second, 30 L/100 km isn't 0 mpg (it's actually 7.8 mpg). The same disparity applies to the intermediate markings. Here's an equivalence table:

0 L/100 km equals infinite mpgUS (0 L/h at 80 km/h)
1.0 L/100 km equals 235.2 mpgUS (0.8 L/h at 80 km/h)
1.5 L/100 km equals 156.8 mpgUS (1.2 L/h at 80 km/h)
2.5 L/100 km equals 94.1 mpgUS (2.0 L/h at 80 km/h)
5 L/100 km equals 47.0 mpgUS (4.0 L/h at 80 km/h)
10 L/100 km equals 23.5 mpgUS (8.0 L/h at 80 km/h)
20 L/100 km equals 11.8 mpgUS (16.0 L/h at 80 km/h)
30 L/100 km equals 7.8 mpgUS (24.0 L/h at 80 km/h)

So, the US FE display must have its drive signal altered by the display's ECU and electronics — it's not just a differently calibrated dial — if it's to be accurate. It's possible (but in my view unlikely) that it does not in fact indicate indicate 60 mpg when the vehicle is in fuel-cut mode. Even if it does indicate fuel-cut in this manner, it can't display the range of FEs that the metric gauge does. For example, I frequently get indications of 2.5 L/100 km or less, but these are outside the 0 - 60 mpg range of the US FE gauge's display. So, when you say that your FE gauge reads, say, 40 - 55 mpg, I'm not sure how to translate this into equivalent readings for my metric FE gauge. Moreover, I don't think that you can trust your FE gauge's readings, at least when it displays numbers in the range above 40 mpg.

Here's what I find when coasting in fuel-cut at ~80 km/h on a flat road:

• The FE gauge reads 0 L/100 km and SG says the ICE is open-loop and spinning at ~1000 rpm
• The ICE icon disappears from the MFD (it's always present when the ICE is supplying any power to the wheels)
• The battery arrow can be either => (MG2 charging the battery), absent (no battery involvement at all), or <= (supplying battery power to MG2) depending on the amount of pressure applied to the accelerator (very small in all cases, otherwise the ICE will fire up).
• When the battery arrow is <= I believe that the battery is supplying only modest battery power to MG2 due to slight accelerator demand, but that true fuel-cut is maintained; SG still says open-loop, ~1000 rpm. This battery usage is "cheaper" than restarting the ICE for mild demands, but it will eventually drain the battery, and so it cannot continue for a prolonged period.

I believe that when the ICE icon is shown on the MFD, fuel-cut is not in effect. But, conversely, the absence of the ICE icon does not guarantee fuel-cut (e.g., during ICE warm-up with battery charging, neither the ICE icon nor the battery charging arrow are shown; also see the example below). I have also noted the following different scenario while coasting at 80 km/h on a flat road with the ICE "on" and using fuel in closed-loop (not fuel-cut) according to SG:

• The FE gauge reads slightly above 0, say ~1.5 L/100 km. SG says fuel consumption rate is ~1.2 L/h, which would be ~157 mpg. No ICE icon is shown on the MFD, but SG says that the ICE is idling at ~900 rpm.

Now, Toyota's US Patents dealing with battery charging, SOC monitoring, and prevention of "memory effect" in the NiMH battery, discuss various methods. They include periodically discharging the battery somewhat below its normal SOC operating range, or charging the battery somewhat above its normal SOC operating range. Could some battery management of this sort be under way in some of these cases? I really don't know, but it's possible. I'm attaching two relevant Toyota battery-management patents to this post.

Stan

 

I'm attaching an improved version of my post #27, containing Figures with more accurately drawn torque vector lengths, and detailed improvements in the covering document. They are all bundled in the file Heretical_v2.zip.

Stan

 

Your table is pretty close to what I see if I convert km/h to miles/hr. I think you are correct with your earlier observation that the metric car's MPG is a more accurate indicator. The 60 MPG "parked" position in the US version would appear from my own experience to have some ambiguity with regard to operating state. They probably considered that 60 MPG would equate to infinity for practical purposes, but us picky types found situations where that is not the case and the car was getting 70 or even 80 mpg with the ICE near or at idle and a very low power demand on a mild downgrade that for appearances sake looks level.

 

There's a very interesting measurement of the actual SoC of the Prius's NiMH battery pack versus its dashboard's SoC display at:
http://privatenrg.com/
Their numbers won't apply directly to the TCH's NiMH battery, but the TCH's SoC display is likely similar in behavior. What I find most interesting is that, of the 40 - 80% usable range that's shown by the 8 bars of the car's SoC display, bars 6 and 7 alone account for fully 56% of the usable charge! It may be that Toyota doesn't want drivers to be alarmed by seeing the SoC display constantly going up and down. Or else it may simply be that the display is based solely on the voltage of the NiMH battery pack, which spends most of its time in this narrow range. [Certainly, as their patents show, they probably do much more sophisticated things to determine and control the battery's SoC.] But, I hadn't realized until now that the SoC display was slugged in this way. This makes it almost impossible to accurately know the true SoC of the NiMH battery when it's showing bars 6 or 7. This in turn makes conducting accurate FE measurements really problematical, since one needs to ensure that the battery is recharged to its original SoC before one can compute meaningful fuel-usage numbers. [See the thread "An Unpalatable Fact (with apologies to Al Gore!)" for much more about conducting such tests.]

FastMover — This could explain why you see no visible change in the SoC display while using battery power in fuel-cut mode.

Stan

 

Correct me if I'm wrong but it seems to me that SPL and FastMover are talking about two different things here. FastMover is talking about cruising at moderate speed and SPL is talking about coasting (fuel-cut). The only two situations I've seen the engine go into fuel-cut is by taking my foot off the pedal completely or else going into warp stealth. Even in warp stealth the car is slowing down, just not as fast as taking your foot off the gas completely. Either way, you can't cruise in fuel-cut but you can in the heretical mode. For those still wondering about this take a look at Graham Davies' web site(Understanding the Prius- What's going on as I drive) or hobbit's write-up on the subject.

 

LOL TCH — I don't think FastMover and I are talking at cross purposes. His question to me was about ICE powered driving, but some of his earlier comments in the same post were about fuel-cut mode. Sorry if my replies to both were confusing! I'm still not clear, however, on just how the US FE gauge's readings correspond to those of the metric FE gauge.

Stan

 

I think I do understand the difference now. In order to faithfully replicate the 0L/100km on the metric car, the scale in MPG would need to be [infinity symbol] MPG. Very hard to make anything like a linear scale that includes infinity, so Toyota settled on 60 MPG to represent infinite MPG on the US car. Hoiwever, this compromise did not foresee the case where in some conditions the TCH is capable of greather than 60 MPG with the ICE running (low power, high PSD ratio downslope or decelerating). The computer cannot show ECOmode in this condition and must stay out of the blue zone on the indicator, so it just goes directly to 60 MPG.

So 60 MPG is an ambigeous indication that can display: 1> a true 60 MPG indication with the ICE with or without electrical modes (as determined by the battery-wheel indications in either direction; 2: a somewhat false 60 MPG indication where a greater than 60 MPG FE is currently being acheived under the similar conditions to >1 above; or 3> the ICE at idle wile the vehicle is moving at some speed whether being used for warming up or in a state near 40 MPH where power demand from the ICE is not required yet but where the computer's rules for EV mode have been exceeded either due to throttle demand or speed.

Stan, I have discoved that a very interesting thing to do is to look at what MG1 is doing in the speed ranges from 50-57 -- especially if you suddenly remove what was just previously a fairly agressive throttle demand for power. Look at it and tell me what you think.

 

FastMover — Your explanations for the operation of the FE gauge in the US TCHs seems plausible to me. However, I'm not really sure how you want me to observe MG1's behavior, or what aspect you want me to look at. I don't have the ability to read its speed out directly (do you, and if so how?). All I can do is compute its speed from the other data. Your suggested speed of 50-57 mph corresponds to 80-92 km/h. So, here are two scenarios for the ICE speed dropping from high to low values (as would occur if the accelerator is suddenly released):

• At 80 km/h, the ring-gear speed Nr = 2258 rpm, and at engine speeds of Ne = 3000/2000/1000 rpm I calculate sun-gear speeds of Ns = +4930/+1330/-2270 rpm respectively (and Ns = 0 at Ne = 1630 rpm).
• At 92 km/h, the ring-gear speed Nr = 2596 rpm, and at engine speeds of Ne = 3000/2000/1000 rpm I calculate sun-gear speeds of Ns = +4050/+450/-3150 rpm respectively (and Ns = 0 at Ne = 1875 rpm).

Are you perhaps referring to the reversal of MG1's rotation direction as the ICE slows down? The formula relating Ns, Ne, and the road speed RS is as follows:

Ns = 3.60 Ne - 73.37 RS [for RS in km/h] = 3.60 Ne - 118.08 RS [for RS in mph]

You might try setting your ScanGauge to metric units (km and L). This way you'll get non-reciprocal fuel-usage readings in L/100 km (which are easier to interpret than mpg), and fuel-usage rate in L/h (which is more sensitive than gal/h). Don't forget that SG gives incorrect fuel-usage readings when the car is in fuel-cut.

Stan