To respond to your replies:

Droid13 — Those are interesting comments, and I basically agree with you. Indeed, I think that Toyota has tried to optimize FE by adopting just your scheme (amongst other strategies, no doubt). You aren't disagreeing with me so much as suggesting that fuel-efficient driving habits DO actually increase FE, and this is true for both hybrids and non-hybrids. The point of my posts, however, was to point out to those people trying to FORCE pure-EV mode that this is counter-productive.

Pete4 — A similar point was made by earlier posters. This is not a fair comparison, however, because on a FLAT road at a CONSTANT lower speed, the TCH will NOT keep switching between pure-ICE and pure-EV modes. It would be using the ICE alone, or in combination with electricity generated by MG1 and immediately used by MG2. The battery would not be involved at all — it cannot be, as its capacity is inadequate to provide CONTINUOUS power to help propel the vehicle. At higher speeds, the electrical power flow is actually in the reverse direction, from MG2 to drive MG1 backwards (the so-called "heretical" mode — see e.g. www.ecrostech.com/prius/original/PriusFrames.htm) in order to keep the ICE closer to its optimal efficiency region, and to prevent it from over-revving. I disagree with you about the effect of ICE losses, however. They will affect ALL power (mechanical and mechanical-to-electrical) generated by it. The only power NOT affected by such losses would be kinetic energy regenerated during braking.

Regarding the ScanGaugeII, I first heard about it on this Newsgroup, I believe (try searching for "ScanGauge"). In addition to its ability (like all scan gauges) to read conventional OBDII engine error codes and the "freeze-frame" data relating to them, it also has the unique ability to display various running sensor readings like ICE rpm, ICE load factor, instantaneous fuel consumption in L/100 km (or in mpg for our U.S. friends, including the range above 30 L/100 km and above 60 mpg), ICE water temperature, vehicle speed, etc. It's a very nice product, and it is helping me to understand better how my TCH works. It would be REALLY nice if the ScanGaugeII could also display hybrid-specific data like NiMH and 12-V battery voltages, NiMH battery temperature, NiMH battery current, transaxle water temperature, MG1 and MG2 rpm's, etc., but in its current incarnation it can't. Perhaps, if like me you think that this would be of interest to you, you could drop the manufacturer an e-mail to this effect (the capability for feedback is on their Web site). I have!

wcmack — One further comment about the first scenario you proposed in your earlier posting to this thread: The TCH's FE may actually be LOWER than the ICE-only Atkinson-cycle vehicle, because if there's electricity being shuttled between MG1 and MG2 (as does occur in certain speed ranges), there will be a loss associated therewith (0.9 x 0.9 = 0.81, i.e., ~19% loss in my example) which doesn't occur in the ICE-only vehicle. This assumes that the ICE-only vehicle has a gearbox that allows it to select a gear ratio that makes its ICE run at the SAME rpm as the hybrid's ICE.

Stan

 

But... you force pure-EV by attempting to reduce the car's energy consumption to absolute bare minimums, thus being very productive. We are talking about two different things in theory which happen to be the same thing in reality.

 

So your point, SPL, is simply that the ICE can provide a better FE than the HSD, but only given constant velocity, elevation, an imaginary transmission, etc...? With the proof being simply that since all motive energy must derive from the ICE and the ICE delivers power without suffering the inefficiencies of the various energy conversions required to support electric-only power?

To support this proof, you're neglecting exactly those synergies(!) that occur in the HSD which make it shine (regenerative braking, shutting off the ICE when stopped or under limited acceleration, eCVT, 40 extra horsepower).

That's like suggesting a Kia outshines a BMW if you take away all the things that the BMW does better. An obvious conclusion, but the comparison's been rigged!

In any case, while your deduction might be correct in an academic sense, its certainly not in an empirical sense. An apples-to-apples comparison of the ICE/electric HSD to a comparably-powered Atkinson-cycle ICE would demonstrate that the HSD clearly provides superlative FE in real world driving.

(That said, this is a fun thread and I commend you for starting it.)

 

I don't know where everyone is on agreeing or disagreeing with SPL's contentions, but it seems some of us are of the opinion that he is arguing that the HSD system is no more fuel-efficient than an Atkinson cycle engine operating in a region of high efficiency. IMHO, this is not his point (sorry SPL, I don't mean to be trying to restate your very detailed presentations).

I think SPL would agree that an system HSD can operate more efficiently (at higher FE) than a "similar" Atkinson-cycle engine on its own, under many real-world conditions. At the same time, I would agree that, drop for drop of gasoline, powering the drive shaft of the TCH directly from combustion of gasoline in the ICE is more "efficient" than converting that mechanical energy into electrical energy in MG1/2, then storing it as chemical energy in the traction battery, then reconverting it to electrical energy and thence mechanical energy in MG1/2. But, as many have pointed out, these conclusions don't really get us to the real issue I think is in play here - how to operate the HSD system in the real world to get maximum FE.

I don't think that the "thought experiments" we have been conducting in this thread will get us a clear answer. These mental exercises have helped frame good questions, but it our intuition that is supplying the answers, not solid science or math. I certainly don't feel I have enough data (and enough knowledge) to do the serious calculations I believe are necessary to get to a more precise and convincing answer.

I also fear that this issue will not be settled by empirical experiment. As anyone can see by going to the Real Mileage Database, each of us gets a little different FE. Each of us drives differently from all the others, on different roads with different ambient conditions (altitude, air temperature, humidity, etc). So even if we wanted to compare different driving styles to guage their impact on FE, we could not eliminate all these other variables.

While this is certainly fun and informative, will we ever do more than battle with our beliefs? I doubt it.

 

Some Prius hypermilers believe that they can get better FE without using pure EV mode. They claim that energy conversion losses during charge/discharge cycles are bigger than penalty of keeping the engine running at all times while driving. This is, under some circumstances correct. There is a way to keep Atkinson engine in some kind of superlean mode, which is very fuel efficient and keeping the engine in that mode requires batteries to be fully charged since if you were using EV mode, subsequent battery charging would take the ICE out of the superlean mode and lower FE. During FE competitions some Prius drivers can achieve up to 99 mpg to prove their point. Based on that some people jumped to conclusion that Prius and in this case TCH can be even more efficient than it is now, if it didn't have extra 100 pounds of batteries and did away with all that hybrid system. IMO this is pure fantasy but it would require whole bunch of data and very technical analysis to prove it. If it was so simple how come top FE cars are hybrids? And how come for example GM won't use Atkinson type engine without using hybrid system but with hybrid FE? Instead they came up with some marketing gimmick called mild hybrid but nowhere the fuel economy of THSII. I think there was thread about that few days ago. I believe hybrid system will always be more efficient than ICE only powertrain, due to battery loading and unloading the ICE and therefore keeping it in efficient range regardless of varying power demand, overcoming the energy conversion loss. I also believe Toyota uses Atkinson cycle engine in its hybrid system not only for fuel efficiency. I think much bigger benefit of using Atkinson is it's freewheeling capability with minimum loss of energy which helps with quick start and also lowers fuel usage at highway speeds. Even at 70 mph, when ICE needs to be spinning at all time it can do so without burning any fuel if there is little power demand, being powered by electric motor. Anyway, interesting thread with a lot of new info even if we don't agree on the principle.

 

This is exactly the idea between pulse and glide. Use the ICE to accelerate up to 42 mph, the max speed at which the ICE will shut off. Then keep it in glide mode, where neither the regen is charging the batteries nor the batteries driving the car. That allows the car to coast further than if regen were taking place and eliminates the inefficiencies of energy conversion.

That's a little confusing. When you refer to "lean" burning of an engine you're referring to an engine with an air to fuel ratio of greater than the ideal (14.3 to 1). What you're referring to is the efficiency of the engine under a particular load. The pulse portion of pulse and glide is supposed to keep the ICE in an efficient mode, although I'm not sure if it's any more efficient than when the car is holding a steady speed.

Well, removing the batteries and hybrid system would make the car pulse and glide more efficiently. But that would just cause it to be a regular car with the ability to turn off the engine when power is not required; for instance when sitting at a light or coasting. Don't know why a company would develop a car to simply pulse and glide. I tried pulse and glide once. I guestimated my TCH was getting above 60 mpg while maintaining it's SOC, so I wasn't getting an artificially high FE by draining down my batteries. Yes it works, but with all due respect to those that do this, it's about as much fun as root canal without anesthetia.

 

Dear All:

Well, there have been further interesting comments posted on this thread, and even some good-spirited disagreement amongst us. That's fine! Here are my comments on those posts that relate directly to my arguments:

Droid13 — But, after such forced pure-EV mode, the traction battery has to be recharged to its initial state-of-charge before one can conclude that there's been a net benefit! If this recharge energy comes from the ICE at a lower net efficiency than had the ICE just powered the car directly on its own (because of the multiple conversion losses involved), then one has LOST efficiency by forcing pure-EV mode.

turk — I fear that you're missing the point. My arguments do NOT imply that regenerative energy recovery during coasting, deceleration, and braking, and switching off of the ICE aren't beneficial. They are ESSENTIAL to making a sensible hybrid. I'm taking these aspects FOR GRANTED, and assuming that they are always present. I'm also assuming that MG2 will be used to provide extra torque from the battery during acceleration, as it usually does. Pure-EV mode CANNOT occur during these scenarios. This basically leaves ONLY the constant-speed portions of vehicle operation to be analyzed from an incremental fuel-efficiency-gain point of view, and that's why this was what I addressed in my post. I'm questioning whether trying to FORCE pure-EV mode (i.e., trying to get the TCH to go into EV mode when it wouldn't normally have done so by itself) can actually benefit us in this one remaining regime.

wcmack — No need for concern, as I'm quite happy with your paraphrasing of my main points. Thanks! But, I do believe that my thought experiments CAN lead us to a clear answer. If you agree with what I have said above in response to turk, then ALL we need to analyze IS the constant-speed portions of vehicle operation, and the question is: "Can we do better than Toyota's ECU programming?" To do this, we must have pure-EV mode when it is more efficient (taking energy reconversion losses into account) than the ICE but Toyota doesn't give it to us, and use the ICE when IT is more efficient than pure-EV mode would be. That's the only way to beat Toyota in this game. Are people actually succeeding in doing this? Some hard FE data could convince me.

Pete4 — Interesting comments! Yes, a hybrid system should always be more efficient than a non-hybrid one.

Stan

 

And this occurs when I check my FE after using a tank of gas maximizing Emode vs "don't care" mode.

The key word being "IF". Fortunately the design of the system optimizes battery charging during high ICE efficiency and optimizes battery usage during low ICE efficiciency. That, coupled with the fact that Emode is a low energy requirement state to begin with, more than offset power conversion losses.

If battery charging was performed based on much simpler logic, for instance if charging occurred when charge level falls to a certain point regardless of any other variables like vehicle speed, acceleration, etc. then I think your theory might actually show up in real world experiences.

 

Maybe somebody already said it - it is hard to stay awake and read all this stuff - but ICE is NOT the only source of energy. I have a daily commute that involves 1500 ft of net downhill over 20 miles. Gravity --> regen braking --> battery --> drive moter. Don't need ICE at all - yet it tries to help.

 

Dear Tedpark,

Well, no, actually the ICE is the only source of energy for the TCH (except perhaps for the first charge in the traction battery). How did your car get to the high point from which you could coast when going to work? You had to use either the ICE or the traction battery running MG1/2. The battery receives its charge from recovery of mechanical (motive) energy while the car is moving and the conversion and storage of that energy as chemical energy. The car gains that mechanical energy only because the ICE is converting gasoline (chemical energy) into motive energy through combustion.

Think about your round trip to and from work. Although you descend 1500 net feet in the morning, you have to climb that 1500 feet in the evening to get back to the same point. To do that, the ICE has to run.

SPL's original point was correct.