Using my dual ScanGauge II's on my 2007 TCH, I monitor the following gauges while driving: RPM, instantaneous MPG, coolant temp, air intake temp, fuel flow(gph), open/closed loop, miles per hour and throttle position seting.

With all of the above, i've noticed that when below 39 miles per hour and in ev mode, loop is open as 0 fuel is used(even though the SG displays 0.04gph) and 0 rpm.

Sometimes after driving on the highway for a bit, and exiting, I drop into ev mode usually at the end of the exit ramp. Loop changes from closed to open, perfectly normal. I can then go into and out of ev mode as I desire, within the constraining parameters we are all familiar with; speed, SOC, loop and coolant temperature. Every once in a while when being in ev mode for a brief time, the TCH goes out of ev mode when below 39mph as the loop indicates closed, fuel is being consumed as rpm, mpg and gph display varying amounts. Most of the time, the SOC is sufficient where I feel the ICE doesn't have to turn on. However, it doesn't go back into ev mode until I accelerate to 41mph and then let off the accelerator. As soon as I pass 41mph and drop back down to 39mph, loop then indicates open and I can go into ev mode once again. Why does this happen?

When going between 40mph and 60mph, loop can be either open or closed. Assume the SOC is sufficiently positive, not needing ICE recharging. When loop is open, rpm varies around 870; gph usually indicates 0.04(a known problem with the SGII);throttle position is at 15 and the TCH mpg indicator is at the 60 line. I assume that I am in fuel-cut mode. When loop is closed, rpm varies around 1000, gph indicates .25 or greater; throttle position is usually greater than 15.

Above 70 miles per hour, I hav observed that loop is always closed, even while coasting.
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I understand that when the oxygen sensor is being used to control the mixture it is closed loop and when it is not it is open loop. It is usually closed except when the engine is cold or under full throttle acceleration.

I don't understand what other constraining parameters affect loop status, which in turn does effect fuel consumption.

I hope that this question makes sense.

 

nyceshirtz — I believe that what you say about the TCH and ScanGauge is correct, and that you are correctly interpreting the TCH's operation. Quite why the TCH sometimes does not go into pure-EV mode at low speeds, when everything seems to be right for it to do so, is not known to me. The car has a mind of its own (or at least its ECUs do)! I'm sure there's a good reason, known only to Toyota.

I'll have a look at the question of open-loop operation when coasting at speeds above 70 miles per hour (~112 km/h). I thought that the ICE did go open-loop even at these speeds. Certainly the ICE must continue to spin, either in open-loop, fuel-cut mode (using MG1), or else continue to burn some fuel (closed-loop). If it reads closed-loop, it's burning fuel, that's for sure.

Stan

 

I think the answer may be in how other HSD drives work. I know much more about the Prius than the Camry and although the two are totally and completely different in practically every way, there are a few key similarities. One of these seem to effect glide entry (EV mode). There are 5 stages of Prius operation. These translate fairly directly to the TCH. As a corollary to this work it was discovered that there is "special thing" that happens at 80 degC. At this point the coolant loop opens and the engine is forced to run to pump the coolant through the entire system.

So every glide failure I found during my review was either do to being in stage S3 instead of stage S4 or the coolant loop opening.

Now as far as the SG problem goes. Its a SG software bug... clear and simple. To see this you need to look at a SG with FW rev 3.01 and another with FW rev 3.15. Take both units and set it to Liters instead of gallons. Start your Camry and shift to N before the engine lights. Note that on that on FW rev 3.01 LPH registers as 0.0 and on FW rev 3.15 LPH registers as 0.15 (I think). This is a clear example since it can't be attributed to rounding error. If the SW was in sync, v3.01 should register 0.1 LPH and v3.15 should register 0.15 or (preferably) both should register 0.0.

Now on to the OPEN / CLOSED loop question. Using the Prius as a not very appropriate analogy, there is a trick called "Warp Stealth". Basically if you have XGauge, you program up "gps" to show gas pedal pressure. Now on both cars at about 45 mph, you come off the gas and then re-apply till your pedal pressure reads 10%. In both the Prius and the TCH this will cut the injectors (IGN=5) set the car to OPEN loop and register all yellow lines (like your in EV) but the RPMs will read 900ish. What's happening is that the PSD is using the touque from the MG sets to pull the ICE around at at certain RPM. The reason it does this has to do with an RPM limiter on one of the MGs. Now as you go higher MPH this trick becomes more difficult to pull off. It can't be done at all in the TCH at 70 MPH and it can't be done at all in the Prius at 90 MPH. I suspect at a certain point the MG sets just can't keep pulling the ICE around, so just orders it to idle instead of allowing it to fuel-cut.

Now this doesn't mean you can't hit high numbers at high speed (assuming that is the nature of your question). If you start watching IGN you will see it serves as a precursor for when your MPG is about to jump. Over 50 MPH if the terrain allows, the RPM can drop below 1200 RPM and IGN can drop 19. You'll usually register between 50-90 MPH in this state and it can be maintained for miles.

Anyway... Hope that helps.

11011011

 

i have observed that the normal operating temperature of the coolant is in the range of 195f-205f (90c-95c). it appears that the ICE will almost always run to keep the coolant circulating. wouldnt it make more sense to have a separate electric circulator pump whose sole function in life would be to run INSTEAD of when the ICE runs just to circulate the coolant? this could further maximize FE at the expense of a few dollars for an electric curculator pump; much like the circulator pump used in baseboard heating in homes today.

 

Just verified that the Camry will not go into Open loop unless it reaches stage 4. Block temp can be any temperature at all... doesn't matter. Until the Camry is in S4 (as described in the 5 stages of prius operations) it won't cut fuel on decel. Pretty interesting. May not be 100% but I noticed it failed alot more often before I forced the S4 transition.

11011011

 

Dan - in stage 4/5, under 39mph is not a problem. it is over 39 miles per hour that i cannot figure out what alignment of planets and stars allow the tch to go into fuel cut mode when coasting, foot off the accelerator, on a straight road or even going downhill (not bringing wind speed or direction into play). For example, on the downstroke of the same bridge, at the same speed on different days, with the car running a coolant temp of 188-195, foot completely off the accelerator, sometimes i go into open-loop, more times than not, it stays in closed-loop. a few times it goes into open-loop and in middle of the downstroke, it goes into closed-loop. i would like it to go into open-loop as often ans for as long as possible in order to maximize FE. any suggestions you can supply are greatly appreciated.

 

"I hope this question makes sense.."

Not nearly as much as I hope the answer I'm about to type makes sense.

First, for most modern day engines, "open loop" insofar as controlling the A/F mixture, is not really.

With the engine idling or just cruising along at a relatively constant speed, "lightly loaded", the A/F mixture is controlled, fully optimized for lowest emissions, via the upstream oxygen sensor(s). When you depress the gas pedal enough, or start up an incline, requiring a level of torque that the engine cannot easily supply absent enriching (~12:1) the mixture, the engine A/F control switches over to MAF/IAT sensor module control, "open loop" only insofar as optimization of emissions level is concerned.

I'm not sure which A/F mixture feedback control loop might be appropriate when the ICE isn't running, or is stopped after running for some period. Perhaps the engineers simply ignored the issue and let the system remain in the previous feedback mode. Or since, seemingly, it matters not at all it may be purely random when the ICE isn't running, stops.

On the other hand if the ICE is not run for a fairly longish period the catalyst may not be up to operational temperature. In that case when the ICE is started, does restart, it would undoubtedly run in enriched, "open Loop" mode even while "idling".

Confused..??

 

Still!

The scenario I portrayed is on the downstroke of the bridge. After just going up the upstroke, the ICE was running to maintain the speed limit, so the catalytic converter should be at operating temperature. On the downstroke, when the planets and stars are aligned, the ICE idles at appx 960 rpm when in open loop mode. Conversely, when in closed loop mode, the ICE runs between 800 and 1100 rpm for the same downstroke, with my foot completely off the pedal. After having reread the prius chat Pulse and Glide technique for the umpteenth time, this excerpt from www.cleanmpg.com : http://www.cleanmpg.com/forums/showthread.php?t=1224 “Warp Stealth: a Prius driver's guide.” (http://techno-fandom.org/~hobbit/cars/warpstealth.html) stands out:


"The Prius does fuel-cut at higher speeds too, but several other useful things also happen when you take your foot off the accelerator:

Engine RPM drops to around 950, maintained by the motors
VVTi valve timing is retarded as far as possible
Regenerative "fake drag" comes into play, charging the battery and of course fuel injection ceases entirely.

This is the typical coasting/slowing mode, which feels just like it would in a conventional car. But once we're in this state, we can take better advantage of these low-consumption conditions. By feathering the accelerator back on just a *tiny* bit, a driver can eliminate the fake drag and actually bring the battery in, just a smidge, to help keep spinning the "dead engine" and push the car a little. Fuel-cut is maintained, and the retarded intake cam timing reduces the amount of air sucked in around the throttle flap and through the engine to almost zero. This is a very low-resistance state for the engine to be in, and it only takes a kilowatt or two to keep all that merrily turning. Since the regenerative drag is reduced or eliminated, the car will coast along a lot farther -- still losing speed on the flat, but fairly slowly, and one can easily maintain speed or accelerate going downhill. It's really the higher-speed equivalent of "glide" with perhaps a little more brought in from the battery to compensate for the spinning dead weight of the engine. If held long enough, the HV battery charge will begin dropping just like it would during gentle EV running at lower speed."

I guess I will try feathering the throttle and see if I can induce “Warp Stealth mode" at a spead greater than 39mph.

 

This is exactly what the TCH will do if a driver attemps to place the selector in "N" at a speed higher than 42 mph. It ratios the ICE back down to around 900 RPM, goes into fuel-cut and retards the timing. Becasue of the splash lubrication system, the PSD and drive train treats both actions exactly the same way. The drag produced by the regen system is removed and the car "coasts" better. The only difference I have been able to observe is that the regen drag is replaced by an ECU induced ICE drag (by introduction of an MG torque split) if the car is in "D" once the SOC is topped out. This does not happen in when the selector is in the "N" position.

 

I feathered the gas pedal when the stars and planet were aligned. i was able to travel appx 2 miles in open loop at appx 63mph in "Warp Stealth mode". Energy screen looked just like in EV mode under 39 miles per hour with the arrows traveling from the battery to the wheels. No ICE arrows at all. RPM was about 985 with 0.00 GPH. FE jumped higher by 2mph. I was also able to go into ""WARP STEALTH MODE"." for a shorter duration. This time the arrows travelled from the wheels to the battery, similar to regen braking. MPG also improved, but not as dramatic as the previous "WARP STEALTH MODE". But my biggest question remains: HOW DO I GET THE TCH TO GO INTO "Warp Stealth mode". WHAT ARE THE KEY PARAMETERS THAT EFFECT THE ECU'S DECISION ALGORITHM TO ALLOW "WARP STEALTH MODE".