The other night I was driving the 8 miles from town out to our house. The highway has a ever so slight downgrade. Leaving town, I accelerated up to 45. During acceleration the FE readout was showing both the motor and ICE to the wheels at the same time. I eased off at 45 putting on the cruise. The EV shut off and only the ICE was running. It ran all the way to the turnoff to our house. I had plenty of time to watch the scan gauge. The gallons per hour was down to .4 and the rpm were rather low at about 1250 rpm. The engine load was something like 60.

I'm new to this and was curious what mode I was in. I forgot to mention, the whole 8 miles the mpg needle was sitting at 59 or 60 . I checked and the scan gauge mpg read the same thing. I thought to myself, at certain throttles this can be a really lean burn engine.

 

rburt07 — I believe that you were in "heretical" mode. From your data (72 km/h, 1250 rpm) I compute (using the Formulas in post #34 of the thread "Heretical Mode") that MG2 was spinning at 2032 rpm and MG1 was spinning backwards at -783 rpm under electrical power from MG2. That's an indication of heretical mode. From your fuel consumption figure of 0.4 gal/h (~1.5 L/h) we can also compute that your FE should have been ~2.1 L/100 km (~112 mpg). For some reason, though, this doesn't seem to agree with what you say SG said (~60 mpg).

Stan

 

Thanks Stan for your input.

I will have plenty of times to view the readings as its our daily 8 mile route to town and back. This time was very similar to the other night. While cruising at 45 mph, the scan gauge engine readings were:
gph = .5
lod = 65
rpm = 1235

Again the mpg indicator was sitting right next to the 60 mpg mark and never moved till we tuned off the highway. I did notice the total mpg had improved only .2 mpg.

Evidently the traction battery was up enough the charge arrow never came on. The indicator shows only the ice running. The EV was not on at all during the whole 8 miles.

 

rburt07 — These new numbers are pretty much the same as your previous ones — still "heretical" mode, of course. This time I compute that you were achieving ~90 mpg. I'd be curious to know what ScanGauge gives for your mpg during these runs, since it seemed (unless I misread your original post) to disagree with my computed mpg. By the way, the ICE isn't a lean-burn engine to my knowledge. It's just that, in heretical mode, it's being forced by MG1 to provide the needed power at lower rpm (and consequently higher LOD) than would otherwise be the case. This has two benefits: (1) greater ICE efficiency since the Atkinson-cycle engine is now being operated closer to its peak efficiency at that power; and (2) lower ICE noise due to the lower rpm. The extra conversion losses (caused by shuttling some of the ICE's output power back from MG2 to MG1) are less than the extra efficiency gains.

Stan

 

I think you'll find the engine spinning at 1250-1280rpm over a wide range of cruising speeds. This is where the engine seems to settle at under small load conditions. Speaking of engine load, I haven't seen such a high engine load (60) while in the heretical mode. Fifty-five seems to be the upper limit for me. It's usually somewhere in the 40's. I agree with Stan about the fuel consumption. Your ScanGauge should have read somewhere near 90mpg. At 45mph with an engine load of 60, I would expect the SG to read something like 1.0gph not .5gph. I think you were just cruising really efficiently based on your engine load and fuel consumption numbers.

 

Today coming home on the 8 miles stretch, I sped up to cruise at 50 mph. The load went up to 80 and stayed there much of the way. It would go to 85 occasionally. The gph had went up to 1.1 and did not vary much. The mph on the scan gauge II and the FE mph were both again were right at 60. Occasionally it would drop to 56 due to highway imperfections.

I paid more attention to the rpm today. I went from a 40 to 45 zone for near a mile. Then the main highway were I took it up to 50 mph. The rpm did settled back down to about 1285.

This new engine has only 300 miles on it. Could that be the reason my lod reads 80. With my last two cars it would read, 40/45 lod on the same scan gauge and the 8 miles of highway. One was a '03 Corolla 1.8 liter, VVT engine. The last was a '06 Ford 500 with a Duratec 203 hp V6. I was driving at 45 mph at the time.

The highway has a very slight upgrade when we drive back to town. I have tried driving at 40, 45 and 50. It seems this atkinson engine likes 50 mph better than the slower speeds right now for efficiency. I found at 37 mph and below, the traction battery likes to power the wheels.

I only see the 90 to 120 mph on the scan gauge when I let off the gas.

Burt

 

LOL TCH — If the ICE is burning fuel and providing motive power, then its torque vector is positive (upward in my diagrams). This means that the MG1 torque vector is downward (negative), since they must balance (Newton's third law: action = reaction). Then whenever MG1 is spinning backward (negative rpm) its power (torque x rpm) is positive, and so it is acting as a motor. This makes it "heretical" mode operation. See my Fig. C. In normal-mode driving, MG1 would be spinning positively, and then its power would be negative, making it a generator. See my Fig. B. Yes, heretical mode is only somewhat more efficient — you still use gas!

rburt07 — Some cars report LOD as a percentage of available power at that rpm. The TCH does this, I believe. Some report LOD as a percentage of maximum power at any rpm; i.e., % of the ICE's maximum power output specification. The LOD numbers of such cars would thus appear to be lower. Your previous cars might have fallen into the latter category. The rpm, Ns, of MG1 (the sun-gear) is related to the ICE's rpm, Ne, and the road speed, RS, by the formula:

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

so you can easily compute whether Ns is positive (normal mode) or negative (heretical mode) as long as the ICE is providing power. The sign depends crucially on the interplay between Ne and RS. Small changes can flip you between "normal" mode and "heretical" mode. You need to be sure to take all your speed readings at the same moment. If your speed slips below ~40 mph in 'D' you go into pure-EV mode, and the ICE is then "off" — all power coming from the battery. I don't believe that the newness of your car has anything to do with any of this.

Stan

 

Thanks, SPL and LOL TCH for your input to my question. A little update here. Going to town with no AC at 50 mph:
67 mpg, .7 gph, 72 lod, 1216 rpm, with battery aid.

On the way back near that same area at 50 mph. It was dark and was hard to tell.
67 mpg, .7gph, 76 lod, 1216 rpm.

I'm improving on going up the overpass and using the accelerator. I taper off enough to keep it at 30 mpg and usually on EV power.

At 450 miles i'm already feeling more comfortable with the hybrid mpg. I picked up a full mpg driving a 45 minute trip up in the mountains and back home. We did make one stop in town then came home. Speed for the trip was 50 with a few minutes at 55 to check the readings.

I really like the way the computer looks at the load. If it's a rather level highway, then it lowers the rpm. Then the gph falls to a nice reading.

I'm looking forward to starting off with a full tank in about a week to see if I can improve.

Burt

 

Two corrections. First, the torques from the ICE, MG1, and the combination of MG1/wheels must balance. MG1 and the ICE can both be negative, as may be the case on a steep downhill in the B transmission setting. That is, this is a three way balance of torques through the planetary gear set, and not a two way as stated.

Second, motors are generators when the RPM times the motor constant Kv is greater than the voltage ***in either direction***. (Kv is reasonably constant over most of the operational speeds of any given motor, but I doubt that MG1 and MG2 have the same Kv value.) For example, at -1000 RPM with a Kv of 1000, if the voltage is less than (more negative) -1 volt (say -3.8 volts), then the motor is sucking current trying to go faster (towards a larger negative RPM, up to -3800 RPM at -3.8V). If the voltage is more than -1V (say, +2.5V), then the motor is generating current (and would continue to do so up to +2500 RPM, in this case). Neither the direction of rotation, nor the polarity of the voltage alone determines whether the motor is acting as a torque producing/current consuming motor or a torque consuming/current producing generator. That is determined by the simple relationship of the voltage to the product of the speed time the motor constant. (This assumes the phasing of the voltage on the three phase motor is always being maintained, as the inverter does, just as an armature does on a brushed DC motor.) The greater the difference between the RPM times Kv and the applied voltage, the greater the current flow.

The hybrid inverter controls whether MG1 and MG2 are acting as motors or generators by controlling the voltage applied to them, from -600V to +600V (I'm not sure what the voltage range of the inverters are, but I understand the motors are rated at up to 600V). It similarly controls whether the batteries are suppling current to power (one or both) motors, or being charged by the motors (generators) by raising or lowering the voltage applied to the batteries to be above (to charge) or below (to drain) the voltage of the batteries (which vary with the state of charge). The combined current flows to the two motors and battery pack must total zero.

-- Alan

 

Huh?