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From: Ike on 8 Oct 2008 10:36
In a week, I'll have had my 2004 for exactly five years
- the longest by far that I've owned any car. When I
bought this rolling innovation, the distinctive shape
made it a recognizable rarity on the highway, in parking
lots, and in the neighborhood, so over the years I've
been called upon to explain its workings many hundreds
of times. Today, the popular Prius is everywhere, but
it's evident that most people - including Prius owners -
do not understand what the car is about. I've even given
presentation to Prius clubs and found that most people
there think they're driving an electric car the battery
of which is kept charged by a gas engine. That will be
true when the Volt is released, but the Prius is far
more conventional.

This is a gas-powered car and NOT an electric car. It
has a four cylinder internal combustion engine modeled
after the Echo, with many parts in common. However, the
valve timing, cooling system, and electronics have been
modified to provide excellent efficiency. The valve
timing change makes it an "Atkinson/Miller-cycle"
engine, as opposed to less efficient "Otto-cycle"
engines that power every other car except the Wankel.

Though a Miller cycle engine is thermodynamically
efficient (read "low fuel consumed per unit work"), one
unfortunate characteristic of such valve timing is very
poor low RPM torque (read "acceleration from a start").

Toyota's brilliant solution was to build one of the
world's most efficient engine-car combinations, and then
augment initial acceleration with an electric motor
system that has maximum torque at zero RPM. The rest of
the features, like electric cruise, regenerative
braking, and efficient (but the Kammback shape seemed
odd) aerodynamics, are just enhancements of the basic model.

The only time the electric motor system matters is when
accelerating from zero. New, the traction battery
capacity was equivalent to ~3 ounces of gasoline, which
was far in excess of that needed for the designed
purpose. Over time that capacity diminishes, but should
remain sufficient for the purpose over the car's
lifetime (decades?). Nice design.

Ike
From: fred seaver on 8 Oct 2008 16:36
The owners manual for the 2008 Prius has it all.
"Ike" <binarydotike(a)gmail.com> wrote in message
news:gcigha$p6c$1(a)registered.motzarella.org...
> In a week, I'll have had my 2004 for exactly five years - the longest by
> far that I've owned any car. When I bought this rolling innovation, the
> distinctive shape made it a recognizable rarity on the highway, in parking
> lots, and in the neighborhood, so over the years I've been called upon to
> explain its workings many hundreds of times. Today, the popular Prius is
> everywhere, but it's evident that most people - including Prius owners -
> do not understand what the car is about. I've even given presentation to
> Prius clubs and found that most people there think they're driving an
> electric car the battery of which is kept charged by a gas engine. That
> will be true when the Volt is released, but the Prius is far more
> conventional.
>
> This is a gas-powered car and NOT an electric car. It has a four cylinder
> internal combustion engine modeled after the Echo, with many parts in
> common. However, the valve timing, cooling system, and electronics have
> been modified to provide excellent efficiency. The valve timing change
> makes it an "Atkinson/Miller-cycle" engine, as opposed to less efficient
> "Otto-cycle" engines that power every other car except the Wankel.
>
> Though a Miller cycle engine is thermodynamically efficient (read "low
> fuel consumed per unit work"), one unfortunate characteristic of such
> valve timing is very poor low RPM torque (read "acceleration from a
> start").
>
> Toyota's brilliant solution was to build one of the world's most efficient
> engine-car combinations, and then augment initial acceleration with an
> electric motor system that has maximum torque at zero RPM. The rest of the
> features, like electric cruise, regenerative braking, and efficient (but
> the Kammback shape seemed odd) aerodynamics, are just enhancements of the
> basic model.
>
> The only time the electric motor system matters is when accelerating from
> zero. New, the traction battery capacity was equivalent to ~3 ounces of
> gasoline, which was far in excess of that needed for the designed purpose.
> Over time that capacity diminishes, but should remain sufficient for the
> purpose over the car's lifetime (decades?). Nice design.
>
> Ike


From: Kirsty Wursty on 9 Oct 2008 03:22

"Ike" <binarydotike(a)gmail.com> wrote in message
news:gcigha$p6c$1(a)registered.motzarella.org...
> In a week, I'll have had my 2004 for exactly five years - the longest by
> far that I've owned any car. When I bought this rolling innovation, the
> distinctive shape made it a recognizable rarity on the highway, in parking
> lots, and in the neighborhood, so over the years I've been called upon to
> explain its workings many hundreds of times. Today, the popular Prius is
> everywhere, but it's evident that most people - including Prius owners -
> do not understand what the car is about. I've even given presentation to
> Prius clubs and found that most people there think they're driving an
> electric car the battery of which is kept charged by a gas engine. That
> will be true when the Volt is released, but the Prius is far more
> conventional.
snip
> Ike

Thanks Ike,
I know this information is available but the way you explain it is easier
to understand. I had thought the electric motor assisted at higher speeds
as well.

Kirsten

From: "Michelle Vadeboncoeur mrv on 9 Oct 2008 08:52
On Oct 8, 10:36 am, Ike <binarydot...(a)gmail.com> wrote:

> It
> has a four cylinder internal combustion engine modeled
> after the Echo, with many parts in common. However, the
> valve timing, cooling system, and electronics have been
> modified to provide excellent efficiency. The valve
> timing change makes it an "Atkinson/Miller-cycle"
> engine, as opposed to less efficient "Otto-cycle"
> engines that power every other car except the Wankel.

Actually, you have it backwards. The Prius pre-dates the Echo/Yaris,
so the Echo/Yaris has a conventional Otto-cycle version of the Prius'
engine. (Outside of the US, the Echo was called the Yaris. The
current US Yaris is the newer redesign of the Yaris.)
From: Ike on 9 Oct 2008 10:24
Elmo P. Shagnasty wrote:
> In article <Pc2dnf8okqLeLHDVRVnzvQA(a)telenor.com>,
> "Kirsty Wursty" <kurstywursty(a)myob.net> wrote:
>
>> I had thought the electric motor assisted at higher speeds
>> as well.
>
> It does.

The term "assisted" is not quite correct - you've been
misled. According to my onboard bus monitor, if engine
load is low enough the car will cruise for a couple of
miles on electrics alone - at up to 35 or even 38 mph.
But that limited capability has little to do with the
basic concept, and is deceiving because overall fuel
used will increase when using electrics alone. It burns
more gas to do that than it does to do the same path at
the same speed on the engine alone. Here's why:

When the engine spins a generator that charges the
battery that powers the motor system that propels the
car, that is a less efficient process than when the
engine alone propels the car. Each intermediate step has
less than 100% efficiency, so there are losses when the
generator is spun, the battery is charged, the motor is
powered, etc. Engine power alone is therefore more
efficient than electric motors alone.

A Prius doesn't need a ScanGauge to show evidence of
this. With a charged traction battery, drive at 35mph on
engine alone, on a flat road. Get perfectly stable, and
you should see more than 80mpg. Then enter into the same
conditions with a depleted traction battery, and the
displayed mpg will be lower.

My car's LOAD readout shows a much higher figure when
the battery is low. At that point, the engine must
propel the car AND recharge the battery, and that need
to accommodate varying load means compromises on engine
efficiency.

Ike
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