HSI details

[hobbit]

I need some community help on a new document: Tao of HSI
.
Since my time at the helm of the 2010 is somewhat limited and I'm not
planning on buying one any time soon, I can't verify a few things myself
but as I was driving those of a couple of other new owners, I noticed quite
a few parallels to the states I see in my own '04 with the additional
instruments. So it seems like we need an official "proper use of the
HSI" document available to everyone since there could be a lot of good
information behind its simple status bar.
.
Post feedback here so we can all see the development process, and I'll
try to do timely updates.
.
_H*

[hobbit]

I've updated this file a bit, added a shot of the owner's manual
proving how Toyota acknowledges the existence of pulse & glide,
and thrown in Ken1784's suggested operation regions as well. Still
need some verification of various facts/parameters from actual
owners of the 2010, please. They're in bold, marked with XXX.
.
_H*

[cpatch]

Haven't tested mine enough to help you out with the XXX facts, but one thing I've noticed that you don't mention is that the center line is "sticky"...there is a little bit of play in the accelerator once the center line is hit before the bar moves to the right and the engine lights.

[fuzzy1]

... Still need some verification of various facts/parameters from actual owners of the 2010, please. They're in bold, marked with XXX.

From Hobbit's page:

As the HSI reaches up into the area shaded green here, engine load as reported by the ECM rises to about 80% and pushes toward 85% by the top end of that range.

Coming from a guzzling Subaru, it is very pleasant to see ScanGauge showing low RPM and high manifold pressure while operating in this green zone, indicating much reduced pumping loss.

I've been dropping into the lower Red zone too much and seeing the manifold pressure fall, indicating the return of pumping losses. At least RPM is very low. This seems to be a hint that I should be breaking into Pulse & Glide, at least at speeds where Stealth is available. More practice is needed.

[XXX: not yet known how fast holding the high end of this range will carry the car on the windless flat -- someone please test and report! In the second-gen it's around 65 - 70 MPH, ~2000 RPM, 6.2 ms injection, but with the marginally bigger and "thumpier" jugs in the third-gen it might be quite different.]

Will try to test and report back at the end of the week, if no one else has done so by then. But if it gets significantly higher than Gen2, I'll wimp out.

Pressing the "ECO" mode button by the shifter provides instant access to the HSI in the display, for those who would rather not have to punch the steering-wheel DISP button some variable number of times.

I wasn't able to confirm this, at least while sitting in the driveway. More detail in my next report.

However, the ECO mode may not be suitable for most normal driving as its output response curve is almost annoyingly "slow-bottom".

My foot has adapted to leaving this mode engaged permanently. I leave it on partly to cover the rough spots in my style, partly to gain the more efficient AC mode, partly to make cruise control (when I'm lazy) less aggressive. Most full time Gen3 drivers are likely to similarly adapt, though it should be turned off for test drives by folks accustomed to "vroom vroom".

As with the second-gen, the "B" shift position should be avoided unless descending long steep downhills where simply throwing away excess energy becomes needed for safety.

For shorter and shallower hills, where the 'fake engine drag' regeneration is not enough to prevent undesired acceleration but B is too much, I've taken to temporarily setting Cruise Control to increase regeneration to hold the car at a constant speed. This is very effective, until the traction battery fills, at which point the ICE starts whining as a high powered vacuum cleaner (high RPM and strong manifold vacuum) for real engine braking.

The thread that first mentioned this suggested that it is a new feature in Gen3.

[bwilson4web]

Will this help?

Near as I can tell, the HSI is a simple power requested indicator. One of the interesting but seldom used data points the Graham Mini-scanner reports is 'requested power.' My testing suggests the HSI behaves like a 'requested power meter.'

Bob Wilson

[fuzzy1]

I was able to test a few things on a road trip the past few days.

From Hobbit's "Tao of Hsi":

Pressing the "ECO" mode button by the shifter provides instant access to the HSI in the display, for those who would rather not have to punch the steering-wheel DISP button some variable number of times. [XXX: someone please verify that, I only noted it in the OM]

Confirmed. It worked fine for me this afternoon, on each of several tries.

Regarding HSI display ECO area:

[XXX: not yet known how fast holding the high end of this range will carry the car on the windless flat -- someone please test and report! In the second-gen it's around 65 - 70 MPH, ~2000 RPM, 6.2 ms injection, but with the marginally bigger and "thumpier" jugs in the third-gen it might be quite different.]

Unfortunately, the nearly ideal road section for this test, a known level section along a reservoir, had potential witnesses, so no go. I did try it in twice on other stretches, aborting both runs at 79 mph without having reached a steady speed. Unfortunately the GPS betrayed 25-30 foot descents.

Max RPM while still in this ECO area varies with speed -- 1660 rpm at slow street speed of about 20-25 mph, about 2400 rpm at 60 mph, and a solid 3200 rpm at 79 mph.

This trip included descending 6 mountain grades long enough to completely fill the traction battery on regeneration (CC and B modes) and automatically revert to pure compression braking, spinning up as high as 4700 rpm. If doing it again, I'd keep track of how much elevation loss was thrown away without regeneration, but it was almost certainly more than 5000 feet. That represents about a half gallon of gas spent climbing that could not be recovered by later downhill glides or regenerations. Despite this loss, mpg was 58.8 (displayed) or 57.2 (simple pump calculation) or 56.0 (pump including slight overfill on previous refill).

[royrose]

Hobbit,

I don't have my Prius yet, 20 days and counting, but I found your Tao of HSI to be very informative.

Could you please clarify your statement "As always, working engine-run times into upcoming road elevation changes generally gives the best results"? I think I have a general idea of what you are talking about, but some more specifics would help.

I am sure that you are right that pressing the ECO mode button brings up the HSI scree. When we did a test drive, I engaged ECO mode and the HSI screen popped up. The salesman was completely surprised.

Thanks.

[a priori]

Originally Posted by cpatch

. . . [O]ne thing I've noticed that you don't mention is that the center line is "sticky"...there is a little bit of play in the accelerator once the center line is hit before the bar moves to the right and the engine lights.

I'd agree with the "sticky" concept at the center line (when it exists) on the HSI. This was one of the first things I noticed after driving my new 2010, and I commented on it through this thread: Got the "Feel" of the HV/ICE Line!.

One benefit of the HSI is that you can see whether your demand/draw on or from the HV battery/electric motor(s) is too high to justify keeping the car in EV.

[hobbit]

Cool, thanks for the additional bits of input. I've updated
the file again, adding a section near the end all about the mode
buttons as I've seen a bit of confusion about them in some other
threads already.
.
I've removed a couple of the "XXX:" questions as they've been
answered [and confirmed the "ECO brings up HSI" thing myself too
at the Cincy meeting last weekend], but now have a couple of
different questions! Look again for "XXX" in the 090809 version.
.
I'm leaving the "terminal speed on windless flat" thing open for
now even though fuzzy's observations are really useful; the high
end sounds like it's *awfully* fast on the road and I'm more curious
what the result is by staying just shy of where the right-half
tapers off into the upward final triangle. I suppose expecting
a faster efficient highway cruise is reasonable, since with the
bigger engine and "earlier" BSFC curves it's clear that Toyota's
going up against the "autobahn cruiser" market or whatever.
.
The downhill behavior, going to more engine-braking automatically
regardless of "B" or "D", is exactly like the second-gen behavior.
Nice to hear of other people seeing the same thing, and it really
does take some of those big descents to be able to study it.
.
_H*

[fuzzy1]

. I'm leaving the "terminal speed on windless flat" thing open for now even though fuzzy's observations are really useful; the high end sounds like it's *awfully* fast on the road and I'm more curious
what the result is by staying just shy of where the right-half
tapers off into the upward final triangle.

Definitely leave this open, as I found only the neighborhood of the answer, not the actual answer. Though it is probably in the low 80s, I did have the bar well into the triangle, almost to the point where the ECO label turns off, and the road was providing a slightly gravity assist. The descent was visible only on the GPS, not visually from the terrain, but Prius certainly makes good use of gravity when it is available.

No wind was seen, but the very low vegetation was not good for displaying it.