The Drive-a-Toyota Act

The word "dive" needs some context. Resetting the trip meter in my
Escape at the start of a crawl, the MPG indicated 99mpg for a few miles,
while the engine was stopped. Then it cycled on for 30-45 seconds with no
change in the indicated mpg. That cycle repeated a few times, and the MPG
dropped to 65MPG over the course of 7 miles. As traffic cleared up, the
mileage dropped off to 38 for a 10-12 mile stretch overall.

 

As I indicated, I'm not surprised. I would call itr an educatred guess
rather than a lucky guess on my part.

I was just making sure you understood that point that there was nothing
inherent about a d.c. generator being direct drive and an "alternator"
(now called generator) being non-direct drive and therefore less efficient.

Yes - due to the forward bias voltage drop (on the order of .7 to 1.5
volts depending on instantaneous current level) - inefficiency (waste
heat) there would equal that voltage drop times the current.

Regarding Toyota's having gotten around that as you speculate, very
likely there are no passive diodes for the rectification. As the
article you linked said, it apparently is a synchronous electronic
control. Very likely, the switching components (under electronic
control rather than the passive action of current reversal as in a
diode) are what are called power MOSFETs. These are a special kind of
"transistor" that do not have a non-linear voltage drop when turned on
(conducting). When turned on, they look like a resistor. The beefier
you make them, the lower the resistance that they have when turned on.
SO - make them stout enough, and you can get that (resistive) voltage
drop *way* below the typical .7 to 1.5 volts of a silicone diode.
*THAT'S* how you pick up efficiency there for a.c. to d.c. rectification.

Also, the control leg of a MOSFET (called the "gate") takes almost no
current to keep it in the turned-on state (unlike a transistor that
requires continuous current on the base to stay on). There is a second
order efficiency gain afforded by use of MOSFETS. (For accuracy, I will
say here that the gates do have some drive current requirements when
switching from one state to the other, but essentially zero current is
required once the switching has occurred. So at lower frequencies of
these generators, those switching losses are pretty small.)


Let me take this opportunity to correct what appears to be a
misconception on your part about "d.c. generators" and their efficiency
compared to alternators (with diode rectification): There is a good deal
of inefficiency in the commutation (constant switching going on at the
brushes) in a traditional d.c. generator. I don't have the numbers, but
I would not expect a d.c. generator to have any more efficiency than an
a.c. alternator with its rectifiers (I don't have the numbers on me, so
I could be wrong about that - but keep reading...).

Here's a basic piece of info. to keep in mind:
A rotating generator (stator or permanent magnet and moving coil) - in
the simplest form possible *IS* an a.c. device. The simplest is with
slip rings (or, as in the link you posted, with a stator coil and
permanent magnets on the armature - which requires *no* brushes, no slip
rings, no commutator - but that *IS* an a.c. device).

*SO* - and this is very important for you to understand: To get d.c.
power out of *ANY* rotating generator *SOMETHING* has to be added to
turn it into d.c. (i.e., to rectify it). The traditional d.c. generator
does that by its commutation to switch the current in the armature coil
*while* the power is being generated. The a.c. alternator with diode
rectification does the job *after* the a.c. power is generated without
commutation (slip ring instead). Both have their inherent inefficiencies.

So you can't just ding the a.c. alternator for inefficiency for its
rectifier losses without being fair and recognizing the commutation
losses in the d.c. generator.

Here's something to think about: What does it do to a d.c. generator's
efficiency when the brushes are passing over the gap between one
commutator segment and the next? There is a part of that transition
period in which the brushes are shorting those two segments together.
What about tolerance variation in the widths of those gaps between
segments and their relative angular locations around the circle of
commutation?

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

My experience is a bit different in this traffic jam crawl on a hot day
scenario. The battery will run down after a while, and then the ICE comes
on to provide recharge. This does indeed sap gas, and we have seen our
MPG dive under this situation.[/QUOTE]

Well, that's what's supposed to happen.

Obviously, your MPG "dives" in that situation--but consider a standard
car in that situation, where the engine is ALWAYS running, very
inefficiently, solely to allow you to creep along and to drive the air
conditioner.

So you can have moments of the ICE running on your hybrid, or you can
have the ICE run continuously on a standard car.

The difference is, you had no feedback mechanism on your standard car to
tell you what your MPG was. It was incredibly lower. Just do the math.

Had you seen what your actual MPG was in your standard car while you
crawled through downtown with the AC on, you'd be furious. But you
didn't see any instantaneous feedback on the instant MPG; all you saw
was the average for the whole tank the next time you filled up.

Do this: turn off your MPG display for a whole tank, drive like you
normally do, then turn it on right before you fill the tank the next
time.

You'll be a very happy man.

Or, stare at the MPG display every moment you're in the car, and obssess
over an instant number going down to 12mpg or something, and be a very
unhappy man.

You can't worry about instantaneous MPG numbers. The whole purpose of
the hybrid is that the engine will run as it needs to, which sometimes
is very hard. Then it can not run, or barely run. Overall, efficiency
is very high compared to a traditional car where the engine is always
running no matter what and where the engine must handle the entire range
of duties, from off the line to highway cruising, from a very small
electrical load to a very large one. No ICE can be as well tuned to
handle that range of duties all by itself. Decouple the ICE from the
wheels, stick the motor/generators and battery pack in there, and let
the software manage it all--you let each piece maximize its efficiency
independent of the other pieces and independent of what the driver is
asking of the whole system.

Staring at instantaneous MPG numbers while crawling through a hot
downtown with the engine suddenly starting in order to charge the
battery is like watching your retirement investments minute by minute.
You will go crazy watching the downturns, and your euphoria during the
radical upturns will be short lived as the system corrects itself.

Watch the average number over a large number of miles.

 

Ford, Dodge? Same thing. ;-)

Thanks.

 

If you add in the cost of a new set of batteries every 100K miles, your
savings of $4162 is actually more than $9000. When those hybrids are
traded in at 80,000 miles, I think the value of the batteries will
likely be prorated and the net depreciation will be greater than
anticipated.

Just say no to hybrids. There are electric cars out there that will go
80 MPH, 0-60 in 6 seconds, and run over 200 miles on a charge. For me
that means recharging it once every two weeks which I feel is very
reasonable.

--
Gyz

07 Saturn Sky
98 Dodge Status ES
94 Mitsubishi Eclipse GST

 

The proponents here are saying that Toyota says they have never had a
single battery failure outside the warranty period, and that the
batteries will last the life of the car, implying that if you push the
car to 250k miles over a typical consumer usage lifetime of, say, 15
years, it will still be running fine on its original batteries. ANd
further, assuming that you were to get 250k miles out of the car, not
only would the typical one still have the original batteries, but 100%
of those 250k mile cars would be.

The ulitmate implication of all that is that the public and dealers will
learn quickly that there is no need to subtract value from the used
Prius for anticipation of battery replacment.

Sounds like pie in the sky to me. I predict that reality will be a bitch.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Look into the Toyota Highlander Hybrid and the Lexus RX 400h, which
offer 4WD. It's a newer version of the e-Four design that was on the
Estima hybrid.

 

On the NHW20 2004-current Prius, yes, the variable-speed AC is
electrically-driven. (Prius models prior to this used a conventional
belt-driven off of the ICE for the AC compressor.)

 

Toyota Highlander Hybrid.

 

Oh yeah, one can play games with that reset button and get very odd,
statistically insignificant results. It resets itself every time one
refills the tank in the Prius, something that used to annoy me, but I have
now become used to it.

In this case the dive went from what was about 55 MPG for half a tank down
to 49 over a very slow, hot 10 miles or so.
Tomes

 

"Elmo P. Shagnasty" om...

Yep, I agree with all this. It sounds like you inferred that I was basing
this on the instantaneous number, lol. My dive was not watching the
instantaneous number. We both have been around the block enough now to
understand what you are saying. Instantaneous number is just that, for
that moment only, and is used for foot positioning purposes. My dive was
in the cumulative number for that tankful, about half a tank at that
point.
Tomes

 

I do not know about the NHW10 Prius...
The Classic NHW11 Prius (2001-2003 model years) will only reset the
Consumption Screen odometer/MPG if you manually hit the Reset button.
(I have well over 30,000 miles on my consumption screen odometer at
the moment. I keep missing the "roll-over" at the 9999.9 miles
mark...)
The 2004-2005 NWH20 Prius will reset the Consumption Screen odometer/
MPG at each fillup (more than about 3 gallons) automatically (one full
revolution of the wheel?), or if you manually hit the Reset button.
The 2006-current NHW20 Prius will only reset the Consumption Screen
odometer at each fillup automatically (same conditions as 2004-2005).
The Consumption Screen odometer/MPG will reset if you manually hit the
Reset button. (The cumulative MPG will only reset if you press the
Reset button.)

(The Consumption Screen odometer/MPG may also reset if you disconnect
12v power for a long enough period of time, as well...)

 

"dive". 49/55=10% drop. That in itself doesn't sound like a dive, and even
if it were, 49mpg is still far too good to say "the mileage took a dive" to
someone who is only getting 25mpg on a good day, and probably thinks of a
dive as dropping to 10mpg.

10 miles weighted against "1/2 a tank". That might suggest that the
mileage during that 10 mile stretch was 13mpg. That would be a dive.
But my experience over a 10 mile stretch of stop and go would suggest that
your example must have been far more stop than go. You might still have
gotten phenomenal mileage compared to the Toyota Corolla in the lane next
to you over those same ten miles.

 

So why does that excuse you from backing up yours?

Ed

 

Bump

 

"George Orwell" ...

Why?

 

:

Yep, I agree with all of this. 'Dive' is indeed a relative term. It was
noticeable enough for all of us to really take it as a learning point in
the car.
Cheers,
Tomes

 

He is a Troll.

 

This is now OT, but according to a 2004 US GAO report, between 1996
and 2000, 61% of American corporations and 70% of foreign-owned
corporations paid no US federal income taxes. For the 2000 tax year,
93.9% of US-controled companies paid less than 5% of its income in
taxes.
http://www.fool.com/investing/general/2004/04/08/most-companies-paid-no-taxes.aspx
http://www.boston.com/business/globe/articles/2004/04/11/most_us_firms_paid_no_income_taxes_in_90s/
original/full GAO report:
http://www.gao.gov/new.items/d04358.pdf

So, although I haven't found a site that publicizes US tax records,
since the majority of companies owned or operated in the US did not
pay US federal income taxes in 1996-2000, that the odds are in your
favor for truth if you say that corporation X didn't pay federal
taxes...

(I could not find data on individual firms' taxes paid, nor on state/
local income or property taxes, nor employment taxes...)

 

Are there not other taxes (besides income taxes) and fees that
corporations do pay that allow a little sleight of hand in the picture
that's painted when quoting such figures (i.e., just income tax)? Also,
ignoring that, the very people that would be in favor of hitting up
businesses with more taxes, costs, and penalties would be the very ones
who complained after the fact that businesses are moving off shore and
would blame, instead of themsleves, the people who were in favor of
giving businesses incenctives for staying here and keeping business
costs low.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')