When one is trying to recover the energy of a moving vehicle or
object slowing down one has a problem.  The energy is proportional
to the square of the axle RPM so at first there is a lot of energy
recovery and
braking effect. As the vehicle slows down the braking  energy rapidly
falls off.
If a generator is directly connected to the wheel the braking effect of
the
generator and energy recovery will fall off directly proportional to the
RPM.
This is not what is required to stop as quick as possible. The
conventional
brakes must be applied I suspect unless some way is found to rapidly
increase
the load on the generator such as changing gear ratios and/or by
electronic
means.  The same thing can be said about spinning up a flywheel to store
the
braking energy. This device, invented in the early seventeen hundreds,
might be
used to speed up the flywheel or generator as the vehicle comes to a
stop
then is reset to wait for the next stop.

http://www.sailtexas.com/long.html
http://www.antique-pocket-watch.com/sinclair-harding.html

It will be very interesting next year when KERS is implemented in
Formula
1
to see how the various teams achieve storing braking energy in a
flywheel.

Paul Lamar


Paul,

If the drive train is influenced by the motor cum generator, the duty
cycle can be increased as the car slows down.  Accelerometers are solid
state and cheap to provide the necessary signal to maintain the desire
rate.  The control circuit fits on a quarter. Same challenge encountered
in slowing a low mass wind turbine rotor that has been hit with a micro
gust.  I do agree that flywheels are a more logical way to store energy
however. More efficient than say, electro chemical batteries. They can
be  electro-magnetically or mechanically coupled through the use of
ferro fluids that change viscosity depending on the small amount of
current applied to them. Back in the late 1970s flywheel energy storage
systems were all the rage and then suddenly the technology dropped from
sight.  Perhaps the researchers got side tracked by the PacMan computer
game craze:) Since then stable homogenous ferro magnetic fluids and air
bearings have been perfected along with certain ceramics that will turn
to (super heated?) dust if the outer Kevlar protective casing is
breached.

The amount of energy a flywheel can store is both amazing and
frightening.  This percieved danger may be the reason the technology was
not accepted readily.  Witness the damage a truck wheel and tire can
cause when it comes off and hits a house.  I wonder if the gyroscopic
effects influence the handling of the vehicle?


Doug in Japan

Wait a minute...  Isn't the amount of energy available related to the
speed.  But, the acceleration is related to the braking force
available (traction on tires)?    If so, as a vehicle slows, the
energy available at a constant deceleration should diminish.  The
coefficient of friction on the tires won't noticeably change with
speed (ignoring aerodynamics).

I think this makes sense as slowing from 70-60 mph in 2 sec should
require transferring much more energy than slowing from 15-5 mph in
the same amount of time...

Ke = 1/2 * m * v^2

deltaKe = 1/2 * m * (v2^2 - v1^2) which is not equal to 1/2 * m * (v2 -
v1)^2

My point is that if you make the motor system large enough to put a
constant energy load on the tires, they will lock up.  In order to
maintain maximum braking force you may need gear up the motor for
adequate braking at very low speeds - due to motor inefficiency, but
not much.



Matt-

That was what I was trying to say but I think you mean generator
and not motor. Yes I know... same o same o but the motor is in generator
mode.

Paul Lamar

Still not sure we're on the same page.  I think having a single ratio
drive to the regen generator/motor is perfectly adequate - a cvt or
other variable ratio drive is not necessary.  The bulk of the energy
available is going to come from slowing from a high speed.  The regen
energy available from a slow speed is negligible.

Storing energy to a flywheel certainly requires a different approach -
accelerating the flywheel while decelerating the car.


Regards,

Matt-


Well You could be right. Maybe we don't have to change the ratio.
How do you propose speeding up the flywheel as the car slows?

Paul Lamar

Like I said..  The all mechanical storage system (flywheel) requires
something different.  If weight weren't a concern, I'll bet an
electric-electric system would be as efficient as anything else - the
wheel motors become generators while braking, driving a motor which
mechanically turns the flywheel - probably gear the flywheel to turn
faster than the motor.  It might be difficult to design a motor which
would survive at the RPM required to make the flywheel efficient
(v-squared term dominates).  It could be worth trying though as
integrating the motor into the flywheel would dramatically simplify
the system.

The electrical portion of the system is reversed to recover power from
the flywheel.


Matt-

Well we shall see as weight is everything in a Formula 1 car.

Paul Lamar