After making my post #59, I decided that it would make sense to compute the power split between the "direct" mechanical path to/from the ICE and the indirect path through the two MGs in all the basically different modes of operation that I had illustrated in my posts #27 and 34. This turned out to be a very interesting and instructive exercise (well, to me at least!). I'll repeat the information from my post #59 again here for completeness.

I shall assume, as I did before, that no battery charging is taking place (it's "full" say), and that the MGs are 100% efficient in their energy conversion (this isn't seriously wrong — they are apparently ~95% efficient at each conversion between mechanical and electrical energy, so that their back-to-back conversion efficiency is ~90%). Then I can calculate the energy flow and split using the following formula:

Pe = Ne . Te = (0.7222 Nr + 0.2778 Ns) . Te

which can be derived from the Formulas page in my earlier posting. Here: Pe is the ICE power (positive if the ICE is supplying power to the wheels, and negative if the ICE is absorbing power from the wheels during fuel-cut engine braking); Te is the ICE's output shaft torque (positive if the ICE is supplying power to the wheels, and negative if the ICE is absorbing power from the wheels during fuel-cut engine braking) — we don't need to know the value of Te, only its sign which we can read off the nomograms; Nr is the ring-gear speed in rpm (positive if the car is moving forwards, and negative if it's moving backwards); and Ns is the sun-gear speed in rpm (positive if MG1 is rotating forwards, and negative if it's rotating backwards).

I will examine the following four scenarios using data from my Table:

1. Figure B — "Normal" mode: Transmission in 'D'
   RS = 120 km/h (~75 miles per hour) (this is the Road Speed)
   Ne = 3000 rpm
   Te > 0
   Nr = +3386 rpm
   Ns = +1995 rpm
   Pe = 3000 . Te = (2446 + 554) . Te > 0 (81.5% + 18.5% = 100%)
2. Figure C — "Heretical" mode: Transmission in 'D'
   RS = 120 km/h (~75 miles per hour)
   Ne = 2000 rpm
   Te > 0
   Nr = +3386 rpm
   Ns = -1605 rpm
   Pe = 2000 . Te = (2446 - 446) . Te > 0 (122.3% - 22.3% = 100%)
3. Figure G — "Fuel-cut" coasting: Transmission in 'D'
   RS = 120 km/h (~75 miles per hour)
   Ne = 1000 rpm
   Te < 0
   Nr = +3386 rpm
   Ns = -5205 rpm
   Pe = 1000 . Te = (2446 - 1446) . Te < 0 (-244.6% + 144.6% = -100%)
4. Figure I — "Fuel-cut" engine braking: Transmission in 'B'
   RS = 100 km/h (~62 miles per hour)
   Ne = 3000 rpm
   Te < 0
   Nr = +2822 rpm
   Ns = +3463 rpm
   Pe = 3000 . Te = (2038 + 962) . Te < 0 (-67.9% - 32.1% = -100%)

In each case I show in parentheses two percentages: (a) the percentage of the total ICE power that flows to the wheels mechanically directly through the planetary-gear set from the planetary-carrier (i.e., the ICE) to the ring-gear (or vice versa); and (b) the percentage that flows electrically from the sun-gear (i.e., MG1) to the ring-gear (i.e., MG2) (or vice versa). Negative percentages represent reverse power flow.

We see:

1. Figure B — "Normal" mode: Transmission in 'D'
   Here power flows from the ICE to the wheels, 81.5% of it mechanically and 18.5% of it electrically.
2. Figure C — "Heretical" mode: Transmission in 'D'
   Here 22.3% of the mechanical power flows back into the planetary-gear set electrically from MG2 to MG1, leaving, of course, a net total of 100% at the wheels. That's why it was dubbed "heretical" mode!
3. Figure G — "Fuel-cut" coasting: Transmission in 'D'
   Here 244.6% of the engine braking power flows directly from the wheels to the ICE through the planetary-gear set, while interestingly 144.6% of the power actually flows forwards electrically from MG1 to MG2, leaving, of course, a net total of -100% at the wheels. MG1 acts as a generator and MG2 as a motor here.
4. Figure I — "Fuel-cut" engine braking: Transmission in 'B'
   Here 67.9% of the engine braking power flows directly from the wheels to the ICE through the planetary-gear set, while 32.1% of the power flows electrically from MG2 to MG1, leaving, of course, a net total of -100% at the wheels. MG2 acts as a generator and MG1 as a motor here.

Notice how all sign possibilities are accounted for in these four cases: +/+; +/-; -/+; -/- respectively (recall that Te is negative in the last two cases!).

Stan

 

I've been attempting to follow this thread as it morphs into a rather technical analysis.

But my take-home lesson from all this (plus playing with the simulator) is that I can get max fuel economy by getting on a flat, no-traffic stretch of road and easing along at 48-55 miles per hour, while attempting to minimize the accelerator inputs.

 

We have a 8 mile mile highway to town. It has a very slight upgrade most would not notice. No cars were coming so I slowly accelerated keeping a eye on the on the scan gauge mpg readout. I noticed as the car accelerated the mpg kept climbing. It seemed to peak at 54 mph by the speedometer. I took it up to 56 but it lost a few mpg. I went back to 54 and it read higher again. Thats many trips to town in the two months I have owned the car. I think this was the highest reading I have seen on the highway to town.

In a few days I have a doctors appointment in Las Cruces, NM about 75 miles from Alamogordo. I'm thinking I may drive 55 or the 54 with the cruise and see how it does.

My favorite is watching the scan gauge mpg and engine lod. More important is trying to see if the mpg needle is on 60 with the engine at low rpm at cruising speed.

 

Yes, I cruise at about 54-60 miles per hour between Socorro and Albuquerque and get good results.

Traffic is almost never a problem, people can pass with no trouble. If there's more traffic I'll get in the "pack" in the slow lane and we generally mosey along at 60-65 MPH. That's a different operating regime entirely.

Curiously, I get worse results "drafting" large trucks at 65-70 MPH than I do in cruising without traffic at 54-65 MPH. Drafting requires "formation flying" technique, which means I'm constantly adjusting power input and the hybrid system is all over the place trying to keep up. It's never worth it for fuel economy, and makes me tired in a hurry to pay such close attention.

I think that I see this heretical mode on the trip home from Albuquerque, rolling downhill most of the way, at 54-60 miles per hour. The car indicates 50-60 MPG on the fuel economy gauge for much of that 75 mile stretch.

Does anyone see heretical mode with the cruise control? Or better results without it?

To cruise control or not?

 

I tried 60 miles per hour on the first round trip to Las Cruces. I had to go back a few days later so I drove 55. I saw little difference. I went up some really steep grades when in the city.

I did try a fill up of Chevron gas. I would not think that was the reason for loosing near 3 mpg. It was sunny with no wind on the first trip. There was some higher slightly gusty wind the second trip. It as also overcast that day.

I ran that tank down and refilled with phillips 66 which I have had good luck with. Conoco has a lot of new stations here in town. I understand its the same gas and company.

We eat sometimes in Mescalero near Ruidoso. Coming back it's a long downgrade to Tularosa. I usually set the cruise to 60. The car usually coast from 62 to 70 miles per hour. There is one place it will get up to 80 for half minute. I have tried putting the car in neutral or turning off the cruise. The engine stays running and the gallons per hour and rpm stay the same either way.

I have not tried that in about a month. I may give it another try the next time we go there.

 

Here are a couple of useful tables that allow one to easily determine when the TCH is in heretical mode, as a function of the car's speed and the ICE's speed (rpm, as determined by ScanGauge say). I'm assuming that the ICE is actually providing power to the wheels. This is the case whenever the ICE icon appears in the Multi-Functional Display on the dashboard. The following two tables are for vehicle speed in km/h and miles per hour respectively. They show as a function of Road Speed (RS) the ICE rpm (Ne) below which the car will be in heretical mode:


RS ; Ne
[km/h] ; [rpm]
50 ; 1019
60 ; 1223
70 ; 1427
80 ; 1630
90 ; 1834
100 ; 2038
110 ; 2242
120 ; 2446
130 ; 2649
140 ; 2853
150 ; 3057
160 ; 3261
170 ; 3465
180 ; 3669
190 ; 3872
200 ; 4076


RS ; Ne
[m p h] ; [rpm]
30 ; 984
40 ; 1312
50 ; 1640
60 ; 1968
70 ; 2296
80 ; 2624
90 ; 2952
100 ; 3280
110 ; 3608
120 ; 3936


Bear in mind that the car's top speed (governor limited) is nominally 185 km/h (~116 miles per hour). {Of course, speedometer calibration errors will also affect the indicated speed.}

Stan

 

Here are updated tables to replace those I gave in post #66. I have updated them by using the more accurate number given for the tires' rolling radius in the Oak Ridge National Laboratory's report on the TCH. The computed numbers change only slightly. For reference, the formulas relating the engine speed Ne (in rpm) to the car's road speed RS at the borderline between normal mode and heretical mode is:
3.60 Ne = 78.37 RS [for RS in km/h] = 126.13 RS [for RS in m p h].
One can use these formulas to calculate values for Ne at road speeds other than those given in the tables.

RS ; Ne
[km/h] ; [rpm]
50 ; 1088
60 ; 1306
70 ; 1524
80 ; 1742
90 ; 1959
100 ; 2177
110 ; 2395
120 ; 2612
130 ; 2830
140 ; 3048
150 ; 3265
160 ; 3483
170 ; 3701
180 ; 3919
190 ; 4136
200 ; 4354

RS ; Ne
[m p h] ; [rpm]
30 ; 1051
40 ; 1401
50 ; 1752
60 ; 2102
70 ; 2452
80 ; 2803
90 ; 3153
100 ; 3504
110 ; 3854
120 ; 4204

Stan

 

Exactly: I have been getting VERY good MPG with my TCH and I really take note of when I'm in this mode and try and keep it there. Use of Cruise Control kills MPG in my experience because it manages speed and not drive mode. I use a combination of pulse and glide and mode management to keep the car in the most efficient drive mode possible at all time (a fact that drives my wife absolutely bat-**** crazy).

In short, when climbing a medium size hill I allow the car to stay in E-Recirc as long as possible while shedding speed until I get to about 50MPH. I then smoothly pulse the engine into accelerate while climbing the hill (being careful not to look at the real-time MPG needle sitting at about 15MPG). At the top of the hill, I'll be going 68-70MPH and drop my foot off the gas to regain E-Recirc mode. There is a lot of electric humming noise when I do this. If the highway is level at this point, the car will likely not stay in E-Recirc mode for long if I try to maintain the speed. If so, I allow speed to decay once again and pulse back up if it drops to below 60MPH. On down-hills, I keep the car in E-Recirc which requires that I keep a demand for slight acceleration ON accelerating speed to well over 70MPH. I bank this kinetic energy into the next long-level or hill and repeat this all over again. I get a fairly consistent 41MPG highway when I do this as compared to 38 if I leave it on cruise control.

I think you are right about sustained use of E-Recirc for highway efficiency; but the electric overdrive is too tall to sustain the car at 65MPH in the flatlands.

 

Stan,

I have some quick questions for you. Forgive me if I DON'T get something in your nomenclature... And the simulator I'm about to site is a Prius PSD; but...

When I go to the PSD Simulator and plug in your ring-gear (Nr) and ICE (Ne) speeds, I get a sun-gear (Ns) speed of -7853 for the first case (75MPH fuel-cut coasting) and +1336 for the second case (62MPH fuel-cut B-mode). Also, at these stated vehicle speeds (75 and 62MPH) the ring-gear speeds are different as well. Is this due to the PSD simulator being a Prius vs a TCH?

If you respond to this question, I have a follow-up .

BB