On Dec 18, 2008, at 1:13 PM, Jed Rothwell wrote:
Furthermore, the Prius ICE is specially designed for hybrid use,
and it is more efficient than an off-the-shelf ordinary ICE would
be. I am sure the new Chinese car will also have a specially
designed ICE.
This engine would not work effectively in an ordinary car. It is
designed to be run at one speed, with a constant load.
- Jed
Most motors have some range of effective RPMs, even small turbines.
This is why I have suggested the possibility of use of a direct
drive, i.e. "overdrive" connection for small gas engine hybrids for
use on long trips. Following are some miscellaneous thoughts about
all this.
If I were to build an amateurish hybrid for my own use, and thought
I'd be taking long trips, I'd probably use a clutch to direct connect
a fixed gear ratio drive from the engine to the electric drive
motor's drive shaft in an "overdrive" mode. When the clutch engages
this direct drive it high speed, i.e. "overdrive", the generator
would be electrically shut off and freewheel except for breaking,
unless excess power and needed minimum RPMs were available and the
battery needed charging. This would provide the efficiency of
cruising purely on the gas engine power with direct drive, which
could be as efficient as a stick shift. Some vehicles can cruise at
55 on flat terrain with a mere 5 hp. A very small motor might work
well for long trips in flat country, but not in mountainous regions,
so the best design depends on the conditions. Here is a diagram:
turbine/generator-->clutch-------
|
electric_motor-->transmission---+--->wheels
If needed, a second clutch could be used to disengage the
transmission. A patented version of this uses a two input
differential transmission to take power from either source in any
quantity available. It seems to me more efficient to use the engine
in direct drive mode on long trips, and that avoids some patent
infringement problems.
Here is a fairly simple variation of the above that runs everything
through an ordinary transmission.:
turbine/generator-->clutch-->electric_motor-->
transmission--->wheels
This has the disadvantage of incurring the efficiency loss of running
the "overdrive" power through a transmission, and it can not kick in
until up to cruising speed.
Here's a 2 clutch variation small turbine design:
turbine-->step down gears-->clutch1-->generator-->clutch2-->
electric_motor-->transmission-->wheels.
Everything is essentially aligned, or could be aligned, on one shaft.
The generator is clutched in to the drive chain for breaking using
clutch2. Overdrive is cut in using clutch1. Generating separate from
drive operation is achieved by engaging clutch1 and disengaging clutch2.
The above designs have to run the regenerative breaking though the
transmission in reverse.
Here is another version requiring two types of generators:
turbine-->step down gears-->generator-->clutch-->
electric_motor-->transmission-->breaking generator-->wheels
This requires two generator types, which might actually be an
advantage since their operating conditions and RPMs might differ
dramatically (and control can then be independent), but only requires
one simple overdrive clutch. The breaking generator can be on either
side of the transmission, but more efficiently located direct connect
to the wheel drive chain.
In all cases the battery is engaged with the electric motor to a
degree depending on driving demands, and charged based on battery
need, excess available turbine power, and minimum turbine RPMs.
The following might be a better diagram:
turbine/generator-->clutch-->electric_motor-->transmission--+-->wheels
|
breaking generator(s)------------
In this version it is clear the breaking generator can be eliminated
if the electric motor can also serve to do the breaking.
Here turbine/generator includes any necessary step down gearing.
When in overdrive mode the electric motor can simply freewheel unless
extra demand exists for hill climbing, acceleration, etc. I know
that some electric vehicles work without a geared transmission,
purely electronically, using a separate motor/gen set on each wheel.
The above would simply have to clutch in the turbine to a couple
wheels for long (non electric) trips in overdrive mode and turn off
the motor drive current. Switching to pure battery mode for shorter
trips is simple too.
Some other issues regarding the "overdrive" method were discussed
here earlier on vortex:
On Mar 30, 2005, at 3:31 PM, Horace Heffner wrote:
At 4:29 PM 3/30/5, Stephen A. Lawrence wrote:
Why is it not better to use a gutsy electric motor, a small
gasoline or
diesel engine, and a battery pack? That always seemed like the
"reasonable" way to build a hybrid -- take a tip from diesel electric
locomotives, that run the diesel engine at a very efficient constant
RPM, and use the electric wheel motors with their very wide dynamic
range to do the "impedence match" to the terrain. The battery
pack gets
you onto the expressway and up the hills, and the petroleum based
motor/generator provides all the electricity that you need while
cruising.
Obviously my intuition here is wrong. Is there a 20 word
explanation of
why?
I'm no expert on this, but I'll give it a shot. However 20 words
is a bit
too little. Here's a short answer:
If big energy batteries weighed nothing, cost nothing, and had no
bulk, you
would need no gas motor.
A longer answer is size, cost and weight of electric motor,
control, and
battery must be balanced to savings achieved by reduction in these
parameters due to transmission and fueled motor size reduction and
regenerative breaking. Optimizing depends on the driving
conditions for
the design. It appears a good match for present battery systems is
roughly
even sizes for the power of the two systems. In this way a
combined gas
motor/battery combination is available for big hill climbs or charging
while driving. The motor does not need to be on while idling or
even at
all times when cruising. If you have a 30 hp gas motor and cruise
at 60
mpg you have about 2/3 the motor output available for charging when
cruising, so can cruise more than half the time without the gas motor
running at all. The vehicle can perform at half power on either pure
electric or pure gas motor. When stopped in traffic no motor need
run at
all.
The answer also depends on what kind of transmission is used for
the gas
motor "impedence matching". If no shifting transmission is used
for the
gas motor, i.e. no gas power is put through a shifting
transmission, but it
can direct connect in high gear for hill climbs or high speed
driving, then
this doubles the hill climb horsepower without beefing up the
transmission
or incurring the overhead for electric power generation from gas
during the
cruise. This overdrive type connection doesn't help low speed
acceleration, but low speed acceleration using electric motors is
pretty
good anyway. Acceleration could be improved using a fluidized or
electronic clutch connection between the gas motor and the overdrive
connection, or just by beefing up the transmission, but this is a
cost/benefit trade-off.
Another short answer: the gas motor doesn't need to run when you are
cruising unless you need to charge or to go uphill.
Regards,
Horace Heffner
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
