From: dold on
In Mike Hunter <mikehunt2(a)> wrote:
> You are free to believe whatever you choose. A modern V8 will run quite
> efficiently at 1,500 RPMs, even on four cylinders, at 60 MPH. Most 4 cy
> engines need to run at nearly twice that number of RPMs at 60 MPH.

My Honda Civic and Ford Escape 4 cyl both run around 2000 RPM at 60MPH.

Clarence A Dold - Hidden Valley Lake, CA, USA GPS: 38.8,-122.5
From: dold on
In Jeff <kidsdoc2000(a)> wrote:
> There was talk of making some early hybrid SUVs (I think the early
> Escape hybrid - perhaps before Volvo got involved) front wheel drive,

That was the original Chrysler design, reviewed in Car and Driver, for the
Dodge Durango Hybrid, called "through the road" hybrid technology.

Clarence A Dold - Hidden Valley Lake, CA, USA GPS: 38.8,-122.5
From: dold on
In Tomes <askme(a)> wrote:
> The Prius uses a thermos to where it pumps a good percentage of the
> engine coolant when the vehicle is turned off (keeps it warm for when the
> car is restarted without much of a delay). That is what the whirring
> sound is at that point, and why there is about a 5 second delay upon
> turn-on before the engine turns on (it pumps the fluid back into the
> engine system). Once the car is running, it does not pump it to that
> thermos, as the engine must reengage instantly when needed. Tomes

I wondered what that was ;-) The neighbor has a Prius. I noticed that she
"started" with no engine, but as she was moving away, the engine came on.
I thought she had just pressed on the gas a little too hard. I presume
that the engine would have shut down again a few seconds later. The engine
is so quiet at low demand that it's hard to tell if it's running from a
distance of more than a few feet, another plus of hybrid technology for
little motors. The cars can ooze away from a stop, up to 20mph or more,
with the engine turning 1500rpm for nominal acceleration.

Clarence A Dold - Hidden Valley Lake, CA, USA GPS: 38.8,-122.5
From: Bill Putney on
Jeff wrote:
> Bill Putney wrote:
>> Jeff wrote:
>>> Bill Putney wrote:
>>>> Jeff wrote:
>>>>> Bill Putney wrote:
>>>>>> Jeff wrote:
>>>>>>> Cars can also have electrically powered water pumps, power
>>>>>>> steering pumps, valves, and compressors for the air conditioners,
>>>>>>> although I don't know if any do, yet.
>>>>>> An honest question: All those things suck energy whether
>>>>>> mechanically or electricaly powered (and the power has to
>>>>>> ultimately come from the IC engine). For each one, is the
>>>>>> electrical version inherently more efficient than a mechanically
>>>>>> powered (belt or gear driven) one?
>>>>> I think the electrically powered ones of these are usually more
>>>>> efficient, because they can be more efficiently shot off (even if
>>>>> you shut off the A/C, there still is loss from friction in the
>>>>> pulleys) and they operate at the proper speed (the A/C compressor
>>>>> in my car would run a lot fast if I drive in 3rd gear on the
>>>>> highway instead of 5th).
>>>> OK - makes sense.
>>>>> Plus, I think the generating mechanism on a hybrid means less
>>>>> wasted energy.
>>>> Assuming you're not meaning strictly the regenerative braking, can
>>>> you explain what you mean? You're saying that the mechanism it uses
>>>> to convert mechanical energy into electrical energy is more
>>>> efficient than the alternator (the auto mfgrs. are back to calling
>>>> them generators now) in a traditional car? How is it done?
>>> A generator converts mechanical energy to DC current, not A/C current.
>> Semantic technical point here: Yes - a generator converts mechanical
>> energy to electrical energy. It is only initial convention (before
>> portable alternators became practical with the development of compact
>> and efficient solid-state rectification means) that originally limited
>> the word generator to d.c. generating devices (basically from common
>> usage of the word in the context of the automobile).

> Well, the generator is A/C. I thought it would be D/C, but I was wrong.

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

>> Later, when the portable alternator was developed (or became practical
>> - and almost necessary due to the increasing current demands of cars),
>> just to distinguish the terminology, they came up with the term
>> "alternator" (which -yes - does suggest a.c. from a pure language
>> standpoint). However, there really is no reason the term generator -
>> from a pure language standpoint - could not mean alternator in that it
>> *generates* (i.e., no reason any device that generates *anything*
>> could not be referred to as a "generator").
>> NOW - having said that - one point I was making is that many of the
>> auto manufacturers have, within the last 5 or 10 years (not sure of
>> the exact time frame - they kind of snuck it in on us), in their
>> documentation (service manuals, etc.) gone back to the term
>> "generator" to mean what they had previously been calling (and you and
>> I still call out of habit) "alternators". And there's nothing wrong
>> with that. If you look at an alternator as a black box - ignoring
>> what's inside - it turns mechanical energy into d.c. voltage and
>> current. So - hey call it a generator if you want to. (And as I
>> pointed out - even if it's final output *were* a.c., from a pure
>> language perspective, there would be no reason no to call that too a
>> generator.)
>> Just wanted to get that fun point out of the way.
>> Now - let's go a little further (and I'm not sure how this will tie in
>> to the discussion of hybrid cars) - what you and I know as alternators
>> pushed the "generator" (meaning d.c. generator) aside in the
>> automotive world because it (the alternator) was inherently more
>> capable of high current output across a much wider useable rpm range
>> (i.e, the traditional d.c. generator could not supply the increasing
>> current demands that cars were requiring in sustained low speed and
>> stop and go driving unless they were geared up to spin faster at low
>> engine rpm to the point that they would fly apart on the upper end of
>> the rpm scale).
>>> Because Toyota is so concerned with efficiency with the Prius, having
>>> an efficient generator system must have been a priority. And the
>>> output doesn't have to be converted to D/C with a rectifier. There's
>>> power loss in the rectifier. (All automotive alternators have them.)
>> And perhaps there have been some technological developments that have
>> overcome the previous rpm range limitations of the (d.c.) generator.
>> Perhaps the engine is running at a more constant rpm with the drive
>> train used in the hybrid? I don't know.
>>> Plus, the drive to the generators is direct drive, not belt drive
>>> driven, so there is less friction loss with a generator than a
>>> belt-drive.
>> You may not have said that the way you intended to, but the way you
>> stated it, I don't buy that. There is nothing that says a (d.c.)
>> generator inherently has to be direct driven and that an alternator
>> has to be belt driven/cannot be direct driven. So unless I missed
>> something there, let's scratch that part of the explanation.
> When the belts go around the pulley, they flex. This results in some
> friction inside the belt. The pulleys are not friction free, either.
> This added friction, compared with direct drive, results in some power
> loss. By getting rid of the belts and pulleys, you decrease the
> friction, which increases efficiency.
> There is no reason why you can't have a DC generator or an A/C generator
> belt driven or direct drive.

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.

>> In reality, I would not be surprised to find out that what they use
>> and call a "generator" is actually more like what you and I commonly
>> refer to as an alternator. I would also suggest that there is a bit
>> of electronic processing done on the raw output of the waveform that
>> comes out of this spinning device as to muddy the difference between
>> what you and I think of as generators and alternators and their
>> traditional differences such that we might have trouble deciding which
>> category in traditional terms whatever is in the Prius really fits
>> into. In addition, it would blend with the manufacturers tendency to
>> now call alternators generators anyway.
> When you convert A/C to DC or vice versa, there is energy loss (as heat
> in the diodes). This leads to lower efficiency. Apparently, Toyota got
> over this, because the generator is A/C, not DC.

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

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')
From: Jeff on
dold(a) wrote:
> In Jeff <kidsdoc2000(a)> wrote:
>> There was talk of making some early hybrid SUVs (I think the early
>> Escape hybrid - perhaps before Volvo got involved) front wheel drive,
> That was the original Chrysler design, reviewed in Car and Driver, for the
> Dodge Durango Hybrid, called "through the road" hybrid technology.

Ford, Dodge? Same thing. ;-)