Continuously Variable Transaxle (CVT) Operation

Continuously Variable Transaxle (CVT) Operation


This is a
demonstration of a continuously variable
transmission
a belt-driven continuously variable
transmission. This is a General Motors
VT25 transaxle
it has a drive pulley
right here and driven pulley over here
it has a steel belt that seems to be the
weak point in these transmissions
because the steel belts tend to break at times. we have an input shaft
from the torque converter which is
connected to the engine, so our power
comes in
we have the reverse clutch
if we hold this solid with the
engine turning
the drive pulley would turn backwards, we
have a forward clutch
when it applies with the engine turning
it will connect the forward clutch to the
drive pulley
and turn the drive pulley causing the
driven pulley
over here to also rotate
connected to the driven pulley is our
output shaft with this
gear right here, this gear connects to
file drive and
propels the the front tires, so
the way a CVT, which is continuously variable transmission,
the way that works is to continuously vary the gear ratio
of the input to the output. The
gear ratio in the low range that we’re
in right now
is about 2.6 to 1 (2.6:1)
takes about 2.6 turns of the input shaft
equal one turn
up the output shaft, but we can control
width of this pulley and the width of this other pulley
which makes this steel built shift
positions and we can have
gear ratios that go anywhere from that 2.6 to 1
all the way up to an overdrive gear
ratio of, clear up to about
.4 to 1 (0.4:1) which I will demonstrate here
in just a moment, so we’re going to have
power coming in,
we want to move forward, we apply the
forward clutch, and
turn the drive pulley, in this
demonstration were actually going to hook a
socket to the
output and turn the driven pulley, but
that’s not really how it’s done
in the vehicle, but we’re doing that in this
demonstration
to show you the different gear ratios
as we change it with a compressed air on
the Pistons
that are in these housings
so, we’ve got a very large socket
new drill motor we are going to hook up to the
driven pulley, let’s go ahead and start
turning that,
notice that
as the drive pulley turns very quickly
the driven pulley is turning very slowly
and it is a gear ratio of about 2.6 to 1
now, if I come in and want to change the gear ratio
i am going to apply hydraulic pressure
to the piston that controls this pulley, and i am going to use air pressure in this demonstration
and it’s going to be noisy, but you’ll see the pulley
come down to a smaller width and its
going to
cause the driven pulley to go wider, so I am going to do that right now
notice now the input
is turning really slow
the output is turning fast, that is overdrive

we are in overdrive right now, the engine is turning really slow
but the output shaft is turning really
fast, now we are going to come in and
change ratio back to an under drive
situation
Okay, now we’ve got the engine turning really fast and
and the wheels,
the output, turning really slow. and those are the two
extremes of a CVT transmission
and what is cool is that we can very the
vary the gear ratio anywhere between this
low and the high
the we had, we can even have a 1 to 1
gear ratio of
direct-drive, so once again this is a
continuously variable transaxle
CVT, this particular one is out for
general motors
product, a Saturn, but a Honda
Nissan, Chrysler, all used continuously
variable
belt driven transmissions, transaxles,
The hybrid electric vehicles use an
electronic
continuously variable transaxle that uses
electric motors and planetary gear set
in place in these pulleys


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