K. Jones said:
Ummm, no. AFAIK, less than 1/2 dozen specific vehicles currently being
manufactured have, "questionable" HP ratings.
Don't take that as all or most. I simply stated there are a _few_
instanses.
Either you didn't read anything I wrote earlier, or we have a comprehension
problem.
HP=HP. Stating a continious duty number (and saying so), and stating a peak
number (and saying so), isn't "rating them differently".
That is almost the entire problem - They don't say so.
There is one other thing about torque, which I will try to explain better
below.
Thirteen seconds+fraction, or 1/4 mile at a time, to be more specific
*smile*
Exactly. Good time! I managed to get into the high 14's once with a 2.8 L
MPFI 5 speed Camaro. Those little engines really like a lot more fuel and
ign timing then when delivered stock.
I never claimed it took 275 HP to drive down the highway, why would you
imply that?
Just to show that that 275 HP is not used much! Same as the full (peak)
power of an electric motor.
You intall controllers, and wire/fuse at 20HP electric motor for 60/80HP
duty??
There is a grammical error in there, but assuming you meant "wire a 20 HP
motor up for 60 to 80 HP", they, yes, that's what I mean. The motor can
handle that power for short duty cycles without damage, then backing it off
to the 20 HP level. This is easily done with PWM (Pulse Width Modulation)
techniques, which at full PWM duty cycle (duty cycle, as in the % that high
frequency electrical control pulses are on) is at full power. At 20% PWM
duty cycle, the motor is at approx 20% power. The controller is the key to
making this work. A AC motor using a simular setup just uses 3 PWM
controllers to generate the required 3 phase electrical needs.
Exactly. The only difference is, auto manufactures don't give a "continious
rating", which would be much lower than the peak HP rating.
Now your understanding what I'm trying to say
"They" are not comparing
apples to apples.
It's called "de-tuning". Many ice's are "de-tuned" at the factory for
various reasons. That's what keeps various "performance chip" manufactures
in business.
A big chunk of those performance chips often suck! Some just tell the engine
it's running cold, and it goes into open loop operation with cold fuel
enrichment, screwing up the fuel injection system. All at a cost of $400 or
more, for a $4 chip. The other thing is it is set up to someone's test
engine, not your setup. Speed density systems (map sensor based) are very
sensitive to variations, unlike MAF based systems which are not that common
anymore due to expensive sensors. Of course there are exceptions, and most
brands seem to be getting better. I'd rather program my own to my engine and
parts, not someone else's "test" engine. check out
www.diy-efi.org however
they experienced a huge crash a few months ago and are not fully up and
running again. Sorry for the off topic stuff - but you may enjoy it.
I suspect the reason cited above would be marketing. Don't wanna piss the
guys who are buying your "premium" sports car (the vette) off, by offering
as "powerful" a plant in the "cheapie" sports package now, do you? *smile*
Exactly - the programming in both computers was compared to be the same, and
the dyno results showed very close HP ratings, but the Corvette was always
rated at least 15 HP higher (Not really that significant anyway at 285 HP +,
unless racing). The Corvette is much lighter anyway, which does make a huge
difference.
You didn't answer the question.
"What kind of electric motor is always in it's peak power, regardless of
speed or load?"
Perhaps a bad choice of words - the torque of a electric motor (somewhat
dependant on motor design also) is VERY high at 0 RPM, and slowly decreases
with speed. This is perfect for accelerating a vehicle. With constant power
input, a torque curve output would basically look like a straight, sloping
down line on a graph of torque VS RPM. This is why that Tzero car can
accelerate faster then much higher powered cars. Torque is what moves a car,
the more you have, the faster you can accelerate ( Newton's law F = MA).
When bringing in RPM's with the torque, HP is produced.
What I meant (putting motor losses aside) when I said a electric motor is
always in it's peak power, was that if you dump 150 kW, or 200 HP into it,
you get 200 HP out regardless of speed, etc. When was the last time you saw
a gasoline engine start of at 0 RPM, and produce full HP until it's red
line? A general performance gasoline engine has a high power range in the
2500 to 5500 RPM range. It therefore needs to keep shifting into new gears
that bring the RPM's down, and thus the torque at the wheels. An electric
motor can produce full power (or close to it in reality) from 0 to 10,000's
of RPM's That is the difference with an electric motor and how a smaller
electric motor can beat a larger gas motor.
Because of this torque relationship, large diesel trains are not
mechanically powered! Large electric motors turn the wheels and a generator
is on the output of the engine!
acceleration.
????????
Torque: Something which produces or tends to produce rotation or torsion and
whos effectiveness is measured by the product of the force and the
perpendicular distance from the line of action of the force to the axis of
rotation.
Yes, I'm well aware of the definition. See above, maybe I straightened it
out a little. Don't forget the wheels turn the torque into linear force.
Did I mention that it's HP limited due to traction problems?
Are you talking about that messed up "tractive effort per vehicle weight"
graph?
What the hell is that?
The force that accelerates the car. Force is what matters in acceleration,
since A = F/M (rearranged F = MA). The torque is transformed into force
from the wheels. Smaller wheels = more force (at the expense of higher wheel
speed as the car speeds up). The distance from the bottom of the graph to a
line is proportional to the vehicle's acceleration.The electric motor is
accelerating at a constant rate when the traction control is on. When the
traction control is no longer needed, the electric motor is in a constant
power mode. With heavy, continuous acceleration, the total acceleration is
very high after several seconds. With the gas motor, acceleration starts off
slow, has a nice peak in the "power range" of the electric motor, then needs
to shift, greatly limiting the available torque at the wheels, and thus
greatly limiting acceleration.
"A gasoline engine produces a high amount of torque over a small rpm
range"???
Here are some _real_ engine dynographs
http://www.v8sho.com/SHO/dynographs.html
(I used to own a gen III V8SHO, what a fun car to drive!)
Sweet! I always wanted something with a TPI 350 in it, now I want something
with a LT1 or LT4. With the performance of that Tzero, I may want to go with
electric soon!
You can derive torque from HP and rpm, right?
Yes, and you can then turn the torque into force, if the drive train
reduction is known along with the wheel size. Wheel RPM, wheel size and HP,
or HP and speed would also work. Acceleration can be calculated from that if
the weight of the vehicle is given. Interesting they recorded the peak HP
much higher then the real peak. The HP peak does not count where the
transmission shifts and causes the stored up energy in the flywheel (shown
in the big dips) to be dumped all at once into the drive train, and thus the
spike.The net hp betwen the dip and spike is about equivalent to a
horizontal line, if that. The real peak is almost 50 HP lower then the
recorded peak HP because of this on the red line, first graph. I'm not sure
what those little spikes are from, perhaps a resonance in the air flow?
