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Hello, I'm Professor john Kelly and this is the WeberAuto YouTube channel. Today we are
going to look at the amazing hybrid transmission used in the Acura MDX and RLX sport hybrid
vehicles. Now this is a very unique transaxle transmission with the front axle built into
it, because it has an electric motor built into a seven speed dual clutch automatic transmission.
And so it has all the benefits of a dual clutch transmission, such as quick shifting, but
also it has the extra power added by an electric motor. This electric motor is rated at 35
kilowatts, or 47 horsepower. And this is just one of three motors on the RL export hybrid.
It has two more electric motors in the rear drive unit, one for the left rear wheel and
one for the right rear wheel, and then combine that with a 3.5 liter engine. It's a high
performance hybrid. And so let's take a look at how this thing works. Because it's not
enough that it's a dual clutch transmission. This is a wet dual clutch transmission. Unlike
some other Dual Clutch transmissions like this one here that came in the Ford Focus,
it had a dual dry clutch transmission. This is a dual wet clutch transmission. And it
seems to be a lot more reliable than the dual dry clutch. So there are several things we
want to do here, we want to explore the dual clutch features, we want to see how power
is transferred through the strands. And we want to see the three modes of operation that
this transaxle and those vehicles are capable of. So let's start with an empty transmission
case. Okay, now that I've removed all the parts from the transmission case on this side,
except for this one idler gear, we can put it together and see what is unique about the
dual clutch assembly. And then what is unique about the electric motor being added to that,
and then discuss the three overall modes of operation. So just like any other transaxle
we need a differential to allow the right front left front tires to turn different speeds
when you drive down the road and turn corners. This is a high performance differential, it
is some sort of a limited slip or heavily pre loaded differential to try to keep the
wheels from slipping. And a lot of high performance cars have these Limited Slip differentials.
This differential has a ring gear on it that has 68 teeth, and it is driven by a counter
shaft just like any other manual transmission, there's a counter shaft that drives the the
ring gear, this counter shaft has a gear on the bottom of it the equivalent of a pinion
gear on a rear axle and it has 19 teeth on it. And so, this 19 tooth gear comes in and
meshes with the ring gear. And now if we turn this countershaft we have 19 gear teeth driving
68 gear teeth, that gives us a final drive gear ratio of 3.579 to one so 3.579 rotations
of our counter shaft to get run one rotation of the tires. Now this counter shaft has some
extra gears on it. So these other gears so these three gears total will allow power to
be transferred in certain gears. So for example, on the backside over here, there is a shaft
called the secondary shaft right here, and it has gears four six and two on it and it
will come in and mess with the counter shaft only in gears four six and two or two, four
and six the even gears and then there's another shaft right here called the main shaft and
the main shaft is what connects to the dual clutch assembly and it comes in on this side
of the counter gear and provides power to the counter gear in first, third, fifth and
seventh gears. And so this same counter gear receives power from two different gear shafts,
the main shaft and the secondary shaft. Now to make that happen, we have to get into the
dual clutch and see how the dual clutch system works. So let me push this transaxle out of
the way for a moment the case now on this main shaft if I take off all of the pieces except for these two, then we can finally
get in and start looking at dual clutch. What Dual Clutch means Dual Clutch operation. So
this is the main input shaft the main shaft that provides power from the engine on this
side into this transaxle. And most manual transmissions over the years just had one
input shaft most automatic transmissions just have one input shaft, but this one has an
additional gear shaft. And notice it's it is a hollow shaft has a gear has a gear on
the end of it. And it provides power in all the even gears so two, four and six, where
the main shaft only provides power in first, second, third and seventh. And so we have
two different input shafts that feed power to our two different gear stack ups the secondary
shaft and the main shaft here. And then both of those provide power to the countershaft
at the appropriate time to send power to our differential to make the vehicle go down the
road. So let's take a look at the dual clutches the dual clutch operation. Okay, instead of
having a torque converter, like any other automatic transmission, this has a dual clutch
assembly and the dual clutch assembly. If you open it up like I've done already. inside
of it, you will find two sets of multi plate clutches. So this great big set of clutches,
which is a set of steel plates, fiber plates, steel plate fiber plate, alternating back
and forth. There are six fiber plates in here. All of these clutch plates go down inside
of here and are used to transfer power in all the odd gears. So these sit down inside
of this housing. These clutches right here, which there are six more fiber plates, supply
power in the even numbered gears, and they sit inside of this housing, so we have two
housings, a large one on a small one, two sets of clutch discs a large one on a and
a smaller one, but the smaller one, the clutch discs are a little bit wider, so it evens
out as far as how much torque they can handle. There are two clutch disc assemblies clutch
packs that can be applied or released. And what that does is it will connect or disconnect
one of these two shafts for the odd gears or the even gears to the engine or not. So
when both clutch packs are released, there's no power from the engine into the transmission.
But if we apply this great big clutch pack, then power from the engine will be connected
to the main shaft right there. And if we apply the small clutch pack, then power from the
engine will be connected to this hollow shaft right here for all of the even numbered gears.
So if we put these two together just like this, when I turn the large clutch
pack housing, notice the center main shaft rotates and that's the same as applying it
and getting power from the engine. If I rotate the inner clutch housing here, it rotates
the hollow input shaft to the transmission and that sends power through the idler gear
to our secondary shaft for all of the even numbered gears. So a dual clutch transmission
really means that it has two clutches in it, and unlike the standard manual transmission
single clutch disc that you might have with a manual transmission that's dry or like the
Ford Focus getrag six speed transmission with a dual dry clutches. This assembly is always
bathed in transmission fluid The Honda dw one transmission fluid. And it allows for
these to apply and release a nice smooth apply and release and stay cool over time, which
is a problem the dry dual clutches had to deal with. So we've got two input shafts,
we've got two clutches in a big housing that almost looks like a torque converter, but
it's not. It just has two different clutches on it. Those clutches are applied hydraulically.
This dual clutch assembly is made by Luke at a Germany I believe, but it has two bearings
in it, released bearings except they're actually applied bearings. And so there's one in the
middle here, that if I were to put compressed air pressurized fluid to it, it would push
it up and apply the small clutch pack. There's the larger one here on the outside, that if
I were to apply pressure to the inlet port, it would apply the large clutch pack back
here and send power to the main shaft for all of the odd numbered gears. So on the back
of this housing, we've got these two ports right here. One is for the small piston with
the bearing on it. The other ones for the the large one, I'm going to try to just gently
push them forward, let's see what happens I don't want to pop them out too far. There
we go. Looks like a pop it all the way out. That's alright, it just has a lip seal on
it. But this piston, as you can see, can move forward, it can move up and squish those clutch
plates and apply them and that transfers power from the engine to the small clutch pack,
which is our even numbered gears. And then if I hit power to or hit hydraulic pressure
to the the larger one now There we go, we pop it out. And you can see it comes out just
has a double lip seal seal you can see there's just a cavity that it sits down in. And so
this is a piston that moves up and down and applies the clutch pack will move side to
side and applies the clutch back in the vehicle but as a bearing on the top of it to allow
the apply plate for those clutches to rotate with the engine running. So just to wrap up
on what Dual Clutch means. It physically means we have two sets of clutches in in this housing
here, a clutch or a set of clutch discs for the even Gears of clutch or a set of clutch
discs for the odd gears, depending on the vehicle manufacturer transmission manufacturer.
Alright, well on this one, it's a wet dual clutch transmission. They've seemed to be
very reliable, I haven't read or heard about any issues with them. Okay, now that we've
learned about the dual clutches themselves and the two different input shafts, let's
take a look at how power is transferred into the even numbered gears. So we have our counter
shaft right here, let me just lift that up for a moment because we are going to bring
in the secondary shaft that has gears four, six and two, four right here, six right here
and two right here. And then we just have a power transfer gear down to the bottom here.
But these gears are going to mash with these gears just like that, and then they're going
to sit right down in the transaxle just like that. So here's our counter shaft. Here are
our even numbered gears. Okay, so once again, we have gears four, six and two, numbered
right there. And if we want to transfer power into the trans for gear itself, then all we
have to do is come in with some shift forks, like a y piece of metal and lift up on the
synchronizer ring for fourth gear, and that's going to transfer power from this bottom gear
into the Top Gear into the counter gear into the little final drive gear. Gear into the
final driven gear. To give us the gear ratio in fourth gear, we'll take a look at that
here in a moment. So we can transfer with synchronizers, we still have synchronizers
synchronizer rings, shift forks. As you can see here in this folder, there's a whole bunch
of shift forks. The shift forks in this automatic transmission are computer controlled. And
so yes, this is a manual transmission, but it's automatically shifted. So you could call
it an automatic transmission. But all Dual Clutch transmissions that I'm aware of are
automatically shifted for you. And the big advantage there is that we while you're in
one gear, we can physically move the gear into the ready position on the other gear
shaft and then just swap clutches, the even clutch for the odd clutch, and that actually
shifts the transmission, not the physical moving of the sleeve, the synchronizer sleeve.
And by the way, if you're not familiar synchronizers. As the word implies, it synchronizes something.
So we have gears, if you look at this shaft right here, if I keep it keep the base gear
from rotating, if I turn the final drive gear right here, here we go. Notice that there
are gears on this shaft here that rotate. And that's because those gears are tied to
a vehicle speed. But then this bottom gear right here, and all the synchronizer hubs
are tied to the engine. So we have engine speed versus vehicle speed, controlling the
rotational speed of these gears here. And in order to shift from one gear to the next,
those speeds have to be synchronized, they have to be the same so that the synchronizer
can easily move up and complete the shift. Now how did power Get over here to the secondary
shaft, there's a gear right here, called the reverse idler, as you can see, and it connects
directly to the hollow input shaft from the small clutches in the dual clutch assembly.
So now if I were to reach underneath here in the bellhousing and rotate that hollow
shaft, it transfers power to the reverse idler and then over here to the bottom of our secondary
shaft and then when the computer decides that you need second fourth or sixth gear, it will
shift it automatically and transfer power into the transfer shaft and then into the
the final drive differential. So that's the even geared portion. So we have an input shaft
just for the even gears in this secondary shaft. Now let's let's do the odd gears. Okay,
I've got the main shaft put together, it has gears five seven and three, this is fifth
This is seventh, this is third. This is reverse idler and this is our even geared power input
and it also is going to mesh with the counter gear. So put it down in with the counter gear
just like that. Okay, now for power flow from the solid input shaft underneath the bellhousing.
Here, when I turn it, notice the the upper shaft and the synchronizer sleeves and our
reverse idler gear, all rotate, but none of the other gears. The fifth, seventh and third
gears don't have any power to them until we move a synchronizer with a shift fork computer
controlled shift fork to transfer power and now this is seventh gear here right I've applied
we transfer power up the shaft into the seventh gear into the counter gear into the final
drive gear into the final driven gear and our differential and make the tires rotate.
So now the tricky part about this whole thing is getting all three shafts in together. It's
easy to put two of them in at the same time but to get all three in at the same time.
Without a special holding fixture that I don't even know exists. It probably does but I don't
Don't think I don't think Acura or Honda even lets you or authorizes any diving into this
transmission or any type of repairs on it. But that's what I like to do is dig into things
that nobody else does or you're not supposed to. So now, let me put the even numbered gears,
the secondary shaft in with these all at the same time. And then we'll come back and add
first gear, because notice, up to this point, we've talked about gears, four, six and two
on the secondary shaft, and gears, five, seven and three on the primary shaft. Where's first
gear? Well, oh, and where's reverse first gear comes through and from the electric motor,
and a planetary gear set that we'll look at. So let me put this together, then we'll come
back and look at the planetary gear set and the electric motor next. Alright, now that
I've got this transaxle, the three gear stacks I'll put together, the the main shaft, the
counter shaft and the secondary shaft are all matched and put in and the hard part is
you got to put all three in at once, which is a lot harder than it sounds. Now I told
you that we get first gear from the electric motor. So I've got the electric motor rotor
right here, very strong permanent magnets. It's its internal, permanent magnet rotor.
And it has a set of splines right there in the center that connect to the input shaft
or the main shaft of the transaxle. So just like that, and if all we did was rotate the
motor, it would turn that main odd numbered gears, main shaft, but we need it to work
in more than just the odd gears, we needed to work in the even gears as well. And so
there's a planetary gear set involved and it also gives us some additional gear reduction.
So it's not just a one to one gear ratio here. Like you might think so let's take a look
at the planetary gear set that it connects to. Okay, so here's the planetary gear set
that the electric motor drives the sun Giro. So every planetary gear set has the sun gear,
a planet carrier, this piece that rotates right here, and then a ring gear or internal
gear, or annulus gear depending on on which book you look in. So let me get this put back
together here. The ring gear has 111 teeth in it, the sun gear has 39 and the planet
gears have 36 so if you do the math on the planetary gearset we are holding the ring
gear and preventing it from rotating in first gear, which means we turn the sun gear which
makes the planet carrier turn at a reduced speed and the gear ratio is 3.8461. So it
takes 3.8461 rotations of the electric motor and the main shaft to get one rotation of
the planet carrier and these splines right here, connect right here. Here's our sun gear.
Just like that. For now let's go through first through seventh gears. For first gear, we
use our planetary gearset and we get our 3.846 to one gear reduction that turns fifth gear
and fifth gear has 42 teeth. It drives the 48 teeth of the counter gear which drives
the 19 teeth of the final drive gear and the 68 teeth of the final driven gear. And if
you do the math on that the overall gear ratio from the main shaft to the counter shaft is
4.3959 to the final drive unit, and then you've got that additional 3.579 to one gear reduction.
Alright, so that's first gear and that can be electric assisted So now if I bring in
the, the rotor of our electric motor, it sits right up here on top, and drives that main
shaft and the sun gear of the planetary gear set. So we can get first gear through electric
motor operation or we can get it through the odd numbered clutches on the main shaft, turning
that same gear. So while we are in first gear, the computer has to predict which gear we
will want to go into next, chances are it's going to be second gear since we're in first,
however, it could be neutral, we could go to park, there's a couple options there, we
might want to go back go to reverse. So if we want to prepare to go to second gear, remember
we only have power coming in on that main shaft through one of the two clutches in that
dual clutch assembly. So now to go to second gear. While we're still in first, we prepositions
the second gear sleeve, this bottom gear is second. So we command with our shift fork,
we shift down into second gear. But since there's no power to the secondary shaft here,
we aren't actually in second, we're still in first. So actually, to shift from first
gear to second gear, all you have to do is in that dual clutch assembly is release the
large clutch and apply the small clutch. And you can adjust the timing of that to make
it very quick, we can just go first second, just like that without having to synchronize
gears, or anything like that, because it's already been synchronized while you were in
first gear. So when we apply the small clutch and the dual clutch pack, we apply power to
this bottom gear right here or hollow shaft, nas 30 14th, the drive 5014 of the reverse
idler that drive 46 teeth at the bottom of our secondary gear shaft. And then second
gear itself has 29 teeth that drive 59 teeth on our transfer gear. So if you do the math
on all of those not counting the final drive, then we get a second gear ratio of 2.754 to
one. So it was kind of a roundabout way to get over here to second gear, but it that
gives us second gear. All right. While we are in second gear, we can prepare to shift
into third. So we're still in second gear with power on the small clutch pack in the
dual clutch assembly. But now we can prepare to go to third gear. Well third gear is this
very bottom gear right here on the main shaft. So we'll come in with the shift forks. Push
down on that shift sleeve. And now to shift from second to third gear we released the
small clutch pack in the dual clutch assembly, apply the large clutch pack and now power
comes right up the main shaft to third gear which has 29 teeth also and it drives this
the same 59 teeth on the counter gear that second gear did. And that gives us a third
gear ratio of 2.034 to one. So an interesting thing I picked up here. As I was exploring
both of these shafts the main shaft and the secondary shaft have the exact same number
of gear teeth. For example, second, third gear both have 29 gear teeth, sixth and seventh
gear both have 53 gear teeth and fifth and fourth gears both have 42 gear teeth. The
difference there that sets them apart is that the secondary shaft back here has to go through
the reverse idler which gives it an additional gear reduction here from the hollow input
shaft through the reverse idler and then to the secondary shaft. So identical numbers
of teeth, which allows them to mess with the same transfer gear. Alright, so now we're
in third we can prepare to go to fourth. So over here on the even numbered gears, we can
come out of third and then fourth is this very Top Gear here. So now we'll come in with
our shift fork, lift up going into fourth gear and now once again power comes in on
our hollow input shaft with 34 teeth, driving the 54 teeth of the reverse idler, driving
the 46 teeth of the secondary shaft and then driving 42 teeth here in fourth gear to drive
48 teeth on the counter shaft. And so in fourth gear, we get a gear ratio of 1.5476 to one.
Alright, so now we're in fourth gear, we can prepare to go to fifth gear and we're just
swapping which clutch, the clutch or the odd clutch to actually shift the gears, we just
prepare before the shift takes place. So we're in fourth, let's figure out how to go to fifth,
fifth, this is very Top Gear right here. So we need to come out of third gear on the bottom.
So we'll move this shift sleeve up just like that. And then we'll move this shift sleeve
up also into fifth gear just like that. And now we swap from the even numbered clutch
to the odd numbered clutch. In the dual clutch assembly power comes right in on our main
shaft and drives fifth gear, which has 42 teeth driving 48 teeth of the counter gear
and that gives us a fifth gear ratio of 1.14321. Now while we are in fifth gear, we can prepare
to go to sixth gear. So over here, sixth gear is this big one right here. So we will move
from fourth which is up to the top here down to sixth. And then we swap which clutch we
apply we release the odd number clutch we apply the even number clutch, we have power
come in on our hollow shaft right here. They're even numbered shaft 3040 driving 5014 I know
I'm getting sick of it to driving 40 16th. But now we drive 53 teeth in sixth gear which
drives a much smaller gear on the the counter shaft here with only 33 teeth. And that gives
us a gear ratio in sixth gear, an overdrive gear ratio of 0.8435 to one so now we're in
overdrive territory. And this is a seven speed transmission. So while we're in sixth gear,
we can prepare to go to seventh. So back over here on the other side we had the transmission
in fifth gear with a shift leave. Seventh gear is this great big gear right here. So
we just move our shift sleeve down to seventh gear. And now power comes in from our odd
numbered clutch in the dual clutch pack into the main shaft drives 53 teeth just the same
as the secondary one, which drives the 33 teeth on the counter shaft. And that gives
us a seventh gear ratio of 0.623 to one, which is a pretty good overdrive. Now how does the
electric motor fit in to all the all of the gears above first? Well, it's already connected
to the main shaft so that it can help rotate in third, fifth and seventh gears and to go
into or to help supply power for the even gears through the planetary gear set. It actually
drives fifth gear, the fifth gear teeth all of the time, even though the shift sleeve
isn't engaged, which sends power to this upper gear on the counter shaft. So in doesn't matter
if we're in the odd number gears or the even number gears. When this electric motor rotates
it supplies power in both odd and even numbered gears. All right, that's a that's a pretty
involved transmission. The only gear left that we haven't discussed is reverse and reverse.
And what's that magnet versus right here. Okay, so there is a reverse synchronizer to
go into reverse. When we want reverse, we'd simply move a shift fork up and that changes
the direction of our counter gear. And then I believe we apply third gear. However there's
somewhat of a mystery with this transmission and reverse as far as my abilities to figure
this thing out. The published gear ratio for reverse on this transmission is 3.66 to one,
but I can't get 3.66 to one no matter what path I choose and what gear combination I
pick to get reverse. I must be missing something because I'm probably the one that's that's
got it wrong here, but I cannot figure out how to get 3.66 in reverse. So if any of you
know, let me know what mistake I'm making but I can't figure figure that one out. All
right, so we've got a seven speed dual clutch wet dual clutch transmission with an integrated
electric motor that can help in all four gears. This motor can also act as a generator because
the vehicle that this is in the Acura RL x and the MDX but the Acura RL X has a rear
electric motor setup with two electric motors one one for each rear wheel. And this can
generate power as you're driving for a rear wheel drive mode in which is one of the three
modes of operation. There's another mode which is a front wheel drive mode and then there's
all wheel drive mode where all the motors and the internal combustion engine are working
together for maximum acceleration. You can see the stater here behind me where the rotor
sits and spins inside. There are all kinds of little cooling tubes and pipes to keep
that rotor cool. There is a engine driven oil pump that circulates fluid throughout
this transaxle for cooling and for lubrication. Okay, as you've seen this is a fairly complex
transmission. All Dual Clutch transmissions are but the neat thing about it is this the
addition of this electric motor to give us extra power under certain situations. So there's
an all wheel drive, a super handling all wheel drive version in the accurate rlms sport hybrid
and then a front wheel drive version in the accurate MDX sport hybrid SUV. All right,
well, it's been quite a quite a lot of work. A lot of study into try to figure this thing
out and it's still kicked my butt with trying to figure out reverse, I just just can't do
it. I've wasted too much time trying to figure it out. So once again, let me know if you
know otherwise. Look forward to some more videos coming up. We've got several Tesla
power trains that we're going to be looking at very soon so hope to see you then. Have
a good day.
