This is a demonstration of the hybrid transaxle of a second-generation Toyota Prius. The
second-generation Prius was the model years 2004 through 2009 the transaxle has several parts in it
and what makes it most unique is that it uses two electric motors we have motor-generator number two
which drives the wheels and motor-generator number one which is both the starter motor for the engine
and the generator to replace the alternator on the vehicle these electric motors are made of
very powerful magnets if we were to take this thing apart like I've taken this one apart if
we pull the cap off of it you can see that there's the slots in the laminated iron there where there
are some very powerful magnets with north and south poles that fit down into each of these
slots and the magnetic field produced by those permanent magnets is repelled are attracted to
the electromagnetic field created by this stator assembly, this is very much like an
alternator of any other vehicle this would be the rotor spinning inside of the stator and it
generate power three-phase power the AC power that goes to the rectifier is changed to DC and
charges the high voltage battery well this acts just like that when this is spinning when powered
by the engine but it can also be reversed to where we apply three-phase power to the
stator windings and it forces the electric motor MG1 to rotate MG2 that is connected
ultimately to the front tires has a giant stator this except of course much much larger
now the Toyota hybrid system that uses these two electric motors in the Prius is connected
to a standard planetary gearset and a standard planetary gearset has a ring gear this is the
ring gear right here sometimes it's called an internal gear sometimes it's called an
annulus gear toyota calls it a ring gear it will also have a Sun gear the Sun gear like
the Sun in our solar system will be in the center of our planetary gear set and then
we have a planet carrier also that has four planet pinion gears as part of the drive for
this vehicle now regular automatic transmission has at least one set of planetary gears these
three components for each two forward gears that the transmission has so if it's a two-speed the
old two-speed transmissions then it had one set of planetary gears if it's a four-speed
it has two sets of these if it's a six-speed as three eight-speed has four well the Toyota
hybrid transaxle that's in the Prius and very similar in the camera and the Highlander is an
electronic variable racial transmission CVT continuously variable transmission
as a matter of fact, they call it an eCVT for electronic continuously variable transmission
and what makes it continuously variable even though we're using a planetary gearset is that
unlike a standard automatic transmission with the ring gear planet carrier and a Sun gear
in those transmissions, we would hold one part drive another part and the third piece would
be the responding component, and then for a different gear we would hold another piece
turn another piece, and get a different gear ratio well that the Toyota Prius transaxle
doesn't hold anything solid of these three planetary gear cities so what we have is
motor-generator one that starts the engine and acts as the generator actually connects
to the Sun gear of this planetary gearset motor-generator two which drives the front
tires actually connects to the ring so if the ring gear moves at all more to generate
our two moves and it drives to the wheels if motor-generator one moves at all then
it drives the sun gear of the planetary gear set and then the planet carrier that has the
pinion gears in it is connected to the internal combustion engine I've got you to scoot this over
the equivalent of a torque damper this replaces a torque converter this automatic continuously
variable transmission has no torque converter but we've got a flywheel it's very similar
to a manual transmission that bolts to the crankshaft we have a pressure plate there's
a bevel pressure plate that is going to keep constant pressure on the clutch disk and this
clutch disc is always applied, it is engine driven and it drives the planet gears,
as a matter of fact, this planet carrier splines right in and if the engine rotates at all so does
the planet carrier so once again we've got the planet carrier that's connected to the engine
we've got the Sun gear that's connected to motor-generator one and we've got the ring gear that's
connected to motor generator-number two, so now I'm going to get this flywheel out of the way
and let's put this assembly together and see if we can figure out how we get forward
and reverse gear ratios so what we're going to take motor-generator number two right here and
we're going to connect the planet carrier to it just like that, we're going to take the Sun gear
with motor-generator number one connected to it and slide it into place and then there's an oil
pump there's a little miniature oil pump in this transaxle that's driven off the planet carrier and
I'm going to slide that into this other side so that we've got everything lined up just like it
is in the transaxle motor-generator two connected to the ring gear that drives the vehicle these
little logs right here connect to a drive gear of a chain that goes to the final drive we've
got the motor-generator one the hooks to the Sun gear and then we've got the planet carrier
that connects to the engine now I'm going to attempt to set this up in these B blocks here
it's very heavy and then I'm going to bring the clutch disc the damper disc from the engine over
here and connect it to the planet carrier so what we've got is the clutch disc represents the engine
we've got motor-generator one that's our starter and our alternator and we have motor-generator two
that drives the vehicle down the road so with the let's go through the different modes of operation
with the vehicle stopped motor-generator two is always going to turn with the tires,
so if the vehicle is stopped, motor-generator two is stopped if our high voltage battery is low
on charge we need to charge it up then we can turn motor-generator one, notice as I turn motor
-generator one it turns the engine we've got the disc for the engine it will start the engine and
then as the engine starts and continues to run notice that the engine turns motor-generator one
and makes it be a generator alternator ok so that will charge the battery we're going to take the AC
voltage created by motor-generator one convert it to DC and sent it back to our 201-volt battery
now the engine can start and stop as is necessary to charge the battery without motor-generator two
doing anything now let's say the engine is off and we want to start driving down the road if
the engine is off then motor-generator one is stopped motor-generator two is stopped and as we start to
drive down the road I'm going to hold the engine from turning motor-generator two, is going to start
to rotate because we're going to apply a magnetic field electromagnetic field to its field coil and
make it start to turn so notice as we start to turn motor-generator two that forces motor-generator
one to spin in the opposite direction at this time as you're driving on electric motor power only
motor-generator one even though it could act as an alternator at this point they turn the charge rate
way down to where it doesn't charge very much at all and we're just running on electric power
we're taking the DC voltage from the battery we're converting it to AC and turning motor-generator
number two now we reach a point where we've reached a vehicle speed that to run any faster on motor
generator two'w power, if we rotate this any faster we're really going to over-rev motor-generator
number one because it's actually a 2.6:1 gear ratio, for every 1 turn of this we're going to get
2.6 terms of the generator, and it turns out that around 37 to 40 miles an hour motor-generator two
reaches a speed where motor-generator one is spinning too fast to spin any faster
it's limited at 6500 rpm so at that point with modern-generator two spinning in motor-generator
one another spinning what we do is we slow down with electromagnetic field motor-generator one and
watch what that does to the engine as we start slow down motor-generator one we still allow it
to spin backward, but notice now the engine is turning creaks after the engine is turning and
the engine will start so now the engine is turning clockwise just as the motor-generator two driving
the vehicle is and we're driving down the road as we drive down the road if the engine speed and
motor-generator two speed were the same like they are now motor-generator one also spins the same
speed but typically the engine is going to spin a little faster than motor generator - and so motor
generator two spins faster becomes a charging unit generator and as the engine is running it forces
motor-generator one to become a generator that feeds power back to the battery it can also feed it to
motor-generator two through our electronics to continue driving the vehicle at higher speeds so
at the higher speeds, we still have motor-generator two rotating, we have motor-generator one rotating,
but only because the engine is spinning it at a faster speed and in being a generator, now that's
as we're driving down the road we still have motor generator - propelling the vehicle the
engine is assisting in the propulsion but I want you to notice that the engine is not connected to
motor-generator two there is no direct mechanical connection so at no time does the engine all by
itself propel the vehicle it can only assist motor generator two in propelling the vehicle and by doing
that it causes motor-generator one to become the generator or alternator is as we like to call it
sometimes now if we come to a complete stop and we want to back up then what we do is with the we
can do it two ways we can stop the engine which holds the planet carrier from rotating and we
can turn motor-generator one use it as an electric motor and notice that causes motor-generator two to
spin in the reverse direction and that backs us up but if the engine needs to be running we can still
have the engine run but we'd have to spin motor -generator one much faster to still get reverse.