Quote:
Originally Posted by wwest
"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..??
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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.