Subaru Automatic AWD isn't really, in most models
Paul Pedersen
I've been spending a lot of time lately studying Subarus
and am starting to see clear through the misleading text
by Subaru and others on the subject of AWD and automatic
transmissions. Personally I drive a manual but I've been
so bothered by the incomprehensible descriptions of the
automatics that I wanted to find out what was really going
on.
With manual transmissions there isn't much confusion.
Most if not all AWD manuals use three conventional
differentials : one to split the power front to back,
then one at each end to split the power side to side.
There is usually something to block the center differential
so if one wheel spins power will get sent to the other
end of the car just the same. Most Subarus use a
viscous coupling in the center differential which locks
up if there's too much of a difference between front and
rear.
My Corolla AWD wagon has an electrically lockable
center differential which is operated at the push of a
button (as does the current Subaru STi). A much better
idea, in my mind, in that the spinning wheel doesn't
get to dig a hole before the differential locks up.
With automatic transmissions the subject should be as
simple, but the literature describes things in such a
was as to make things almost incomprehensible.
The only difference between a manual and an automatic
should be that the clutch is replaced by a torque
converter and the gears and shifted automatically.
An automatic AWD Corolla is like this and the power
out of the automatic transmission goes to three
differentials like the manual. The only difference
is the locking of the center differential is automatic
if speed differences are detected.
Things are not the same with Subaru automatics. First,
there are two kinds : the MPT and VTD. The VTD is on
the higher end models like the WRX and Outback H6.
The VTD is true AWD in that it has a center differential.
But : the MPT, used in most models, does not have a center
differential. As far as I can tell power always goes to
the front unless the system detects a difference between
wheel speeds (using sensors) at which point it will engage
a multi-plate clutch (like in a motorcycle) to send power
to the rear. What Subaru doesn't say is that this will
only happen in the case that one of the front wheels is
spinning.
I've seen lots of complaints about the Honda automatic
CR-V being like this, but I haven't seen anywhere that
the non VTD Subarus are also like this.
In my mind, then, these automatics are front wheel drive
vehicles unless some very particular circumstances are
met.
AWD, in my mind, is much more than something to help
getting unstuck. It's a matter of balance, both in
power application and engine braking, with everything
distributed to all four wheels, each doing 25% of the
work. There is less chance of a wheel spinning during
acceleration, or of a wheel locking up if you engine
break in slippery conditions.
If you read texts by Subaru and Honda on their automatics
you get the idea that the system is constantly adjusting
things front to back depending on conditions. Well, it
may be monitoring things constantly, but it isn't doing
anything most of the time.
So if you're looking at AWD for safety and fun, either
go with a manual, or make sure you get an automatic with
a center differential.
Subie25l
50:50 max rear
The can also adjust to 95:5 front:rear.
I found this info at http://subaru.com.au/awd/ in the shockwave animation
I do agree thought that it is not as good as the manual. But it is alot
better than the CRV
"Paul Pedersen" <a...@def.com> wrote in message
news:3F9511AF...@def.com...
Rob Munach
are describing (so I have been told - anyhow). It is my understanding
that it is tied into the engine computer so that it can proactively send
torque to the rear wheels when you get accelerate - to reduce wheel spin
and in other sitiations. I agreewith you , however, that I would rather
have the manual transmission.
Edward Hayes
Forester AUTOMATIC has a default ratio of 60 front/40 rear until wheel
Torque difference is detected. The AT is almost always in a state of flux
and is always activated unlike the locking center differential on the MT
models. The 60/40 default ratio is fixed by the transfer gear set as shown
in the Subaru Factory Manual. Power is transferred by a "continuously
variable clutch pack" behind the transfer gear set in the transmission. The
same gear set is reversed to obtain a default ratio of 40/60 for the Impresa
GT ? To quote Subaru literature "to give a more sporting feel in spirited
driving" I think the "old" Subarus that were front or all wheel drive
depending on whether the system was activated may be where the 90/10 or
100/0 idea came from. The AT system even in the base Subaru is a far more
advanced AWD system. In fact Subaru called it the thinking mans transmission
for its almost instantaneous reaction to wheel torque compared to the
locking differential which is locked until wheels slip and then the silicone
oil heats and then power is transferred. Subaru factory racers have a switch
to deactivate the locked center differential so as to bypass the much
delayed power transfer. Let us get our facts in line before typing.
"Subie25l" <subi...@hotmail.com> wrote in message
news:3f95255b$0$23615$5a62...@freenews.iinet.net.au...
TransFixed
Yes, you are basically correct here (and this has been discussed several
times in this news group). But as Rob says, even Subaru's inexpensive
AT AWD is a bit more proactive, e.g., when you start driving, or under
strong acceleration. However, it does not have the full set of sensors
that the VTD/VCD has, and does not give you the benefits a set-up with
~50-50 default has.
As I have said before here, for technical reasons and given the lack of
a center diff, the clutch pack can basically only work in an on-off
mode. That is, when it is off, the distribution by definition must be
almost 100:0. When it is on, it can be anything because with an
(almost) locked differential, the torque goes to where the traction is.
That is, the torque distribution then is variable not due to variable
clutch pressure, but because traction to the ends varies due to surface
conditions.
This is a trick that is used by several manufacturers to reduce fuel
consumption. So, Subaru can claim that the AT rquires as little
gasoline as the MT. (Wether this is true under practical circumstances,
I don't want to get into).
- D.
Etienne
> and am starting to see clear through the misleading text
> by Subaru and others on the subject of AWD and automatic
> transmissions. Personally I drive a manual but I've been
> so bothered by the incomprehensible descriptions of the
> automatics that I wanted to find out what was really going
> on.
>
> CR-V being like this, but I haven't seen anywhere that
> the non VTD Subarus are also like this.
>
> In my mind, then, these automatics are front wheel drive
> vehicles unless some very particular circumstances are
> met.
>
> AWD, in my mind, is much more than something to help
> getting unstuck. It's a matter of balance, both in
> power application and engine braking, with everything
> distributed to all four wheels, each doing 25% of the
> work. There is less chance of a wheel spinning during
> acceleration, or of a wheel locking up if you engine
> break in slippery conditions.
>
> If you read texts by Subaru and Honda on their automatics
> you get the idea that the system is constantly adjusting
> things front to back depending on conditions. Well, it
> may be monitoring things constantly, but it isn't doing
> anything most of the time.
>
> So if you're looking at AWD for safety and fun, either
> go with a manual, or make sure you get an automatic with
> a center differential.
The Suburu Auto AWD is not the same as the Honda and should not be
compared. The Subuaru system is a proactive system. I see little or no
disadvantage with the Auto AWD when compared to the manual AWD. It is
a proactive system. I have tested this out, and it is very difficult
if not impossible to generate wheel spin.
Case #1: Raining Day. Flooring gas pedal from a traffic light. The AWD
system automatically shift power to rear wheels to compensate for the
weight transfer. In fact in this case, I think it is better than the
50/50 in the manual system, since the manual system waits to slip
before transfer power!!!!
Case #2: Ice Storm. Again same as above flooring from a traffic light.
No slippage what so ever. AWD system already compensates for weight
transfer to rear wheels!!!
Etienne
Edward Hayes
"TransFixed" <ey...@2003forester.jp> wrote in message
news:S%qlb.80555$Ms2.71022@fed1read03...
bilgab
For what i have read, all AT subaru are now full-time AWD. Some models
used to be part time AWD, but not anymore. In fact, the AT AWD is more
advanced than the MT AWD. The automatic transmission pump pressure
allows the design of this more advance AWD. It is the same system as
the Audi A8. In 1st and 2nd gear the power distribution is 60/40. To
reduce gas consumption, the distribution goes to 80/20 or 90/10 in 3rd
and 4th gear.
For the MT AWD, when there is slippage, the center differential which
is normally open, locks to 50/50.
For the AT AWD, when there is slippage torque is sent to the axel with
less slippage, hence torque on each axel is adjusted dynamically,
which make the AT AWD better. Of course, it doesn't mean the the MT
AWD doesn't do the job well. In fact it is a good system also, it is
just less advanced and adaptative.
quote from "http://home.comcast.net/~eliot_www/awd.html"
"Subaru deserves mention here because in the automatic version of the
Legacy and Impreza (including the Outback variants), it uses a
computer controlled system much like those found in the Mercedes
4Matic, automatic Audi A8/V8 and the earlier Porsches. Subaru has been
offering this sophisticated system for a long time in a relatively
inexpensive car."
http://home.comcast.net/~eliot_www/awd.html is a very interesting
document on AWD.
Good going Subaru !
bilgab
Paul Pedersen
Edward Hayes writes :
> Subaru of America (tech dept) and Subaru of Australia claim
> that my 2000 Forester AUTOMATIC has a default ratio of
> 60 front/40 rear until wheel Torque difference is detected.
Funny, I was talking to a Subaru salesman and he claimed
50-50 for the non-VTD automatic. Due to my disagreement
we went to the mechanic and he said 80-20.
It would be so nice if Subaru cleared all this up for those
of us who like to understand things. Here are the different
numbers I've come across, all from Subaru :
Off the Subaru Canada website
-----------------------------
http://www.subaru.ca/interface/Subaru02/WebPage.asp?WebPageID=4768&WebSiteID=282
-> "Click to view our AWD demo"
"The different Subaru AWD systems are matched to each
vehicle's character. A 60% front 40% rear torque
transfer on our basic system prioritizes safety while
a 36% front 64% rear torque transfer on our STI helps
maximize performance where sporty driving is the
priority."
[--> no mention made of which transmission this might apply to]
Out of the Outback 2003/4 brochure
----------------------------------
"Manual transmission models split engine power
50/50 between front and rear wheels. Automatic
transmission models use Active All-Wheel Drive,
an electronically controlled multiplate transfer
clutch. VDC model uses a Variable Torque
Distribution System."
[--> no problem, except it violates the previous ]
Off the Subaru Global website
-----------------------------
http://www.subaru-global.com/about/awd/2321.html
[manual transmissions]
"Normally, the centre differential distributes the torque at a
ratio of 50:50 to the front and rear wheels for extremely
stable driving and maximum traction. Where the balance of
traction is lost when front or rear wheels slip, viscous
LSD automatically redistributes torque to maximise grip,
so full traction and driveability are always available."
[automatic transmissions]
[--> no values for the MPT trnasmission]
http://www.subaru-global.com/about/awd/2323.html
[--> ie WRX ]
"V-T-D AWD is an AWD system for automatic transmission vehicles
that provides positive, sporty driving by making improvements
in turning-in while maintaining the basic driving safety
performance of Subaru AWD. The system uses complex planetary
gear type centre differentials that distribute the basic torque
at a ratio of 35 for the front wheels and 65 for the rear.
Distributing more torque to the rear wheels reduces the
tendency to understeer when accelerating while cornering to
provide smoother, more confident handling."
[--> here are the gear reductions for the VTD WRX :
front : 4.111 rear : 4.111 ]
"Torque distribution is also optimally controlled to suit road
conditions. This system provides both sporty driving and
stability under any road conditions by automatically
equalizing the front and rear wheel torque distribution to a
maximum ratio of 50:50."
Out of the Impreza 2004 Service Manual (Mechanism and function)
---------------------------------------------------------------
Automatic Transmission : Transmission Control Module (TCM)
AWD transfer clutch control - Ordinary transfer control
Input signals :
Throttle position sensor
Rear vehicle speed sensor
Front vehicle speed sensor
Inhibitor switch
ATF temperature sensor
FWD switch
[--> there aren't any 'torque sensors']
Automatic Transmission : AWD Transfer System
A: MPT MODELS
"This all-wheel-drive (AWD) transfer system uses an
electronically controlled multi-plate type transfer
clutch. The clutch is controlled by the TCM through
the transfer hydraulic pressure control unit which
consists of a duty-cycle-controlled solenoid valve
and is located at the rear of the automatic
transmission section together with the vehicle speed
sensor.
The TCM has in its memory a set of duty ratio data,
each defining at what ratio the transfer clutch should
transmit the torque for a particular driving condition.
Based on the driving condition information it receives
from the corresponding sensors (vehicle speed, throttle
opening, gear range, slip of wheels, etc.), the TCM
selects an appropriate duty ratio from the memory and
uses it to control the solenoid valve. The solenoid
valve then regulates the pilot pressure of the transfer
control valve which creates the pressure to the clutch
from the line pressure. The clutch is engaged to a
degree determined by the transfer clutch pressure
thus created. Through this process, the torque from the
engine is distributed to the rear wheels optimally
according to driving conditions.
B: VTD MODELS [ie WRX]
The center differential performs the differential functions
of absorbing the speed difference between the front and rear
wheels and also distributes drive forces to the front and
rear wheels at a predetermined ratio. In normal conditions
(when there is almost no difference in the speed between the
front and rear wheels), the drive force distribution ratio
is 45.5 % to the front wheels and 54.5 % to the rear wheels.
The hydraulic multi-plate clutch connected in parallel with
the center differential between the carrier and 2nd sun gear
functions as a differential action limiting device (LSD) and
also as a device that controls torque distribution according
to driving conditions."
From Subaru's Drive magazine
----------------------------
http://www.drivesubaru.com/SubaruTakesSafe.html
"The VDC system first uses the transmission’s VTD AWD to help
maintain control of the vehicle by transferring power between
the front and rear wheels. Under normal driving conditions
the VTD AWD system directs 45% of the engine power to the
front wheels and 55% to the rear wheels. This slight rear-wheel
bias produces a more neutral balance by reducing understeer
and providing more of a performance driving feel."
For another non-Subaru description see :
http://www.autoworld.com/news/Subaru/Subaru_All-Wheel.htm
(this article mentions 90%-10%)
> The AT is almost always in a state of flux
> and is always activated unlike the locking center differential on the MT
> models. The 60/40 default ratio is fixed by the transfer gear set as shown
> in the Subaru Factory Manual.
At least for the 2004 non-turbo Impreza (and Forester ?)
the gear reductions are the same front and back 4.111
so any torque difference must come from the viscous
coupling in the transfer clutch, which under normal
conditions is mostly disengaged. The 90-10 figures I've
seen look sensible for this condition.
With the transfer clutch fully engaged (locked) the
distribution will be 50-50. An interesting thing here
is that I don't beleive it's possible to spin a rear
wheel without a front wheel also being in the spinning
state.
Another thing, I don't see a transfer clutch as a
replacement for a center differential. There's no
balancing function. When the clutch is disengaged
there is little going to the rear, then as the
clutch closes, there is more and more going to the
rear - but - there is never anything to handle the
difference in wheel speeds front and back and
vehicle handling must go out the window. (Just try
driving a car with a locked center differential).
My personal vote is for 90-10 (if not 100-0) unless
conditions dictate a shift to the rear, which can
go to a max of 50-50.
It would seem that Subaru shies away from numbers
when they talk about the MPT transmission...
Paul Pedersen
TransFixed writes :
> As I have said before here, for technical reasons and given the lack of
> a center diff, the clutch pack can basically only work in an on-off
> mode. That is, when it is off, the distribution by definition must be
> almost 100:0. When it is on, it can be anything because with an
> (almost) locked differential, the torque goes to where the traction is.
> That is, the torque distribution then is variable not due to variable
> clutch pressure, but because traction to the ends varies due to surface
> conditions.
>
Thanks for the confirmation, TransFixed. I should have read
your post before writing my last one.
If I may pick a nit, in the above I'd replace the "where the
traction is" with "where the traction isn't" since torque is
being forcibly split front to back, but then the diffentials
at the ends have to take care of things and unless they're
limited slip, the torque will go to the wheel with the least
traction (while not affecting what is happening at the other
end of the car).
The VTD models are neat in that they can apply the brakes
individually to prevent wheelspin and send the torque
elsewhere.
Tony Hwang
Etienne wrote:
Hi,
I don't think you really don't know yourself. I have Honda, Subaru
and Mitsu in my family manual and auto, all AWD. They do things it
suppose to do all the time. It does it ALMOST real time.
You're wrong saying it isn't doing anything most of the time.
How old are you and how many years have you been driving?
I am 63, drivivng for ~50 years. In those years one flat tire on the
road, one broken steady bearing on my tow truck pulling trailer
which stranded me until I got the new bearing. No other break downs. I
maintain my vehcile very well
and know how things work inside out.
Tony
Vlad
> TransFixed writes :
Nice research. You got it right.
Funny, when I came here I learned that most americans are unable to drive
stick, and Subaru had to take this fact into consideration as well, since
they want to sell cars on the biggest market, so, from my point of view,
they came up with an obvious solution: make a subaru a honda like, and apply
as much marketing BS as possible, so consumers start spending their $$ on
subarus. But since Subaru in a AWD business, they could not give up the idea
completely, and market their ATs as very advanced to those who listen, but
in fact a few people from this group reported that this (very advanced)
tranny can be vary dangerous on slippery turns, when the back kicks in
causing tremendous oversteering, but who cares, cars must be sold anyway.
On a funny note, I never lock my cars, they are equipped with a natural
anti theft device - an MT. Never had a problem for years.
vlad
Tony Hwang
Vlad wrote:
Hi, Vlad
Maybe your car is not worth stealing. MT has nothing to do with it.
Maybe you'are driving a rust bucket or wrecker, LOL.
Don't be so sure. You think thieves steal only whole car? They steal
tires, trims, stereo, etc. Even in America serious drivers drive
manual and most older people know how to drive manual. In old days there
was no automatic shift. Automatic is for just conevenience. Try to drive
in a rush hour traffic in a city like N.Y. or LA.
When you say, I never lock my car, it sounds STUPID to me. Just like
guys who don't wear seat belt(I hope you do). Or you live in a small
town where people know everyone each other. There are still places like that
even nowadays.
Tony
P.S. What kind of dummy is going around slippery corner in high speed?
Only people doing winter rally here. I live in cold Alberta.
Alan
to year (some years we don't get any to speak of), so the first snowfall
always produces more accidents than subsequent snows. The second snow,
everyone is driving real carefully after seeing the results of the first
snow- if they even see any snow on the road, they slow to a crawl. After
the third anow, drivers start to drive more reasonably- if you can see the
road under the snow, then drive a bit faster. Unfortunately, that's also
when the morons with the SUVs start driving too fast for conditions. They
can go, but they can't stop. If they go fast enough (ka-boom), I refer to it
as "natural selection".
"Tony Hwang" <drag...@shaw.ca> wrote in message
news:B9zlb.147760$9l5.145318@pd7tw2no...
Vlad
> Vlad wrote:
You are right, maybe my cars do not worth stealing ;) But if a thief wants your
stereo, he will take it anyway, the point here is what you end up with - a
broken window, or in my case a slashed rug top, which is more expensive to
replace then a stereo. You can call this STUPID, I call this WISE, up to you.
I drive stick in rush hour traffic, and think that it is safer then an AT,
because drivers behind me tend to keep safe distance for obvious reasons.
(hint - I rarely use brakes), but this is out of topic.
I do not know how those drivers went into a heavy oversteering condition,
I only pointed that I saw such postings in this group. My previous post was
about 'advanced AT' as some people think. The point here, regardless how
advanced you auto tranny is, a simple stick is still far more advanced,
and regardless how much marketing BS you absorbed the things will remain the
same.
vlad
PS. Convenience is a marketing term I think, helps to steal your money
Tony Hwang
Hi,
Okay, I respect your onw personal opinion. But the gap between MT and
smart AT is narrowing. Some day in the future, most cars won't have MT.
You don't even have to steer it, it'll be all automatic.
With high power micro procesor and AI, why not? Just my personal
opinion. Anyhow, I park my car inside garage at home/work.
Tony
null_p...@nowhere.com.net.edu.gov.de
>when the morons with the SUVs start driving too fast for conditions. They
>can go, but they can't stop. If they go fast enough (ka-boom), I refer to it
>as "natural selection".
Unfortunately that can also be natural selection in reverse: When the
hugh SUV goes KA-BOOM into a small car whose driver was driving with a
high level of intelligence.....
TransFixed
Read the above posts carefully. You are dscribing the advanced VTD/VDC
AT AWD in the more expensive models. The cheaper Subarus (including the
FOrester and Impreza) don't have that.
- D.
TransFixed
> Glad to hear from you Transfixed. Ed
> "TransFixed" <ey...@2003forester.jp> wrote in message
> news:S%qlb.80555$Ms2.71022@fed1read03...
...
I guess we still disagree... :)
- D.
TransFixed
Perhaps I did not make myself clear. Forget about the wheels and
presence / no presence of a rear/front LSD for a moment. If you lock
the center, or almost lock it, then torque will go to the axle with the
most traction. No computer, differential, or other gizmo necessary.
Think of a toy car with locked center diff. Place the front wheels on
fine sand paper, the back on wet ice. All wheels will turn at the same
rate, the car will move forward. Where did the torque go? 99.9%
magically went to the front. The back wheels did not do any work.
So when (almost) locking the center, a manufacturer can claim automatic
torque distribution. Nifty, isn't it? Of course that 'almost' can get
you, depending on the design, e.g., when trying to get up a wet boat
ramp with a trailer, when almost all static and dynamic weight is on the
back, but your car is a FWD vehicle with just a clutch pack to the
back... (remember it needs to slip a little to compensate for different
wheel spin during driving).
- D.
TransFixed
I think it is very difficult to get a wheel to spin just on a wet
surface if you start from 50-50. Remember, each wheel only needs ~1/2
the traction it requires with FWD or BWD, now. If you have the rear
LSD, you are even better off due to the dynamic weight distribution.
So in this case, the AT tries hard to be about as good as the manual.
>
> Case #2: Ice Storm. Again same as above flooring from a traffic light.
> No slippage what so ever. AWD system already compensates for weight
> transfer to rear wheels!!!
This example I give to you. But then I can come up with plenty other
examples of real world driving, where it is better to be 50-50 from the
outset during driving (not from a dead stop).
Also, once you are a bit up to speed in the AT, it will basically turn
into FWD until it senses or comes into the next problem situation.
Then the rear kicks in, and if you happen to be in a turn at that time,
you will probably say "Whoa! Where did this come from?".
When it is ~ continuosly slippery, the fluid in the MT will be thick all
the time, so it is pretty much locked, no sudden changes there.
- D.
>
> Etienne
Paul Pedersen
TransFixed a écrit :
> Think of a toy car with locked center diff. Place the front
> wheels on fine sand paper, the back on wet ice. All wheels
> will turn at the same rate, the car will move forward. Where
> did the torque go? 99.9% magically went to the front. The
> back wheels did not do any work.
Ok. I can see what you're saying, though like the rest of
this subject, it'll take me a while to digest it. (I don't
like magic :-)
My apologies for putting your words in doubt.
bilgab
Actually, most of the above post are wrong. I'm describing the basic
system AT subaru have. VTD and VDC are different things. Subaru really
have an full-time AWD. The belief that the AWD on MT is better is
erroneous. And like other posters said, CRV AWD cannot be compared to
the subaru.
The basic system can only make distribution from 95/5 to 60/40. VTD
allows to do distribution from 95/5 to 5/95. When there is no slippage
VTD give a distribution of 40/60 to be more like a sport car.
VDC on the other hand use the ABS system instead of torsens to
distribute torque lateraly.
That MT AWD is better is a myth.
Edward Hayes
the Subaru techs here in the US and Australia. eddie
"bilgab" <bil...@yahoo.com> wrote in message
news:2325a276.03102...@posting.google.com...
Alan
pole.
<null_p...@nowhere.com.net.edu.gov.de> wrote in message
news:viqdpv8p49f3q5hjj...@4ax.com...
Etienne
> Etienne wrote:
>
>
> I think it is very difficult to get a wheel to spin just on a wet
> surface if you start from 50-50. Remember, each wheel only needs ~1/2
> the traction it requires with FWD or BWD, now. If you have the rear
> LSD, you are even better off due to the dynamic weight distribution.
>
> So in this case, the AT tries hard to be about as good as the manual.
>
with a 50/50 it is very hard to get a wheel spin.
John M.
> into FWD until it senses or comes into the next problem situation.
> Then the rear kicks in, and if you happen to be in a turn at that time,
> you will probably say "Whoa! Where did this come from?".
>
I feel always firmly in control. Never have I felt the need to say "Whoa!
Where did this come from?".
In any case, my car is not 'basically FWD until it senses a problem'. It's
intelligent AWD that constantly puts the torque where it's needed... no
muss, no fuss.
Regards,
John
Stu Hedith
The AT tranny is not dangerous. Many factors go into a spin. I had a
'98 GT sedan with the AT that is refferred to here and it was VERY
controllable. Under accel it would send power to the rear and create a
SLIGHT oversteer, helping to point the nose where you want it. If you
don't want it, don't hammer the gas. On dry pavement, you could do some
pretty awesome power slides on highway interchanges. Once you hit the
apex, punch it and the rear would hang out a little and go where you
told it. In the snow it would allow for some control of direction when
the front tires were sliding. The only thing i wished i had on the '98
was a rear LSD. I lit up an inside rear tire a few times starting from
a stop under hard accelleration and turning sharply. VCD may provide
for more traction, but I would prefer the vehicle control. VCD aims to
remove oversteer. I prefer oversteer to understeer any day of the week.
I've lost control of various cars suffering from both and once the
under steer kicks in, there's nothing you can do.
Stu
TransFixed
...
-snip
...
Nice research, of course some of us have been frustrated for years by
this jumble of true tidbits and useless marketing speech.
The only thing I would add to the above is that 50:50 for a locked
center only applies in the case of same traction front and back. If the
traction is different, the torque applied is different since the axle
with the most grip will do most of the work.
- D.
TransFixed
You are absolutely right. You have the better AWD of the two AT AWDs.
We were talking about the cheapo AWD in the lower cost AT Subarus (that
are not VTD/VDC). I should have made that clearer.
- D.
Tony Hwang
Hi,
You're looking at only mechanical part, there is electronics involved.
Not as simple as one might think.
Tony
Paul Pedersen
TransFixed writes :
> The only thing I would add to the above is that 50:50 for a
> locked center only applies in the case of same traction front
> and back. If the traction is different, the torque applied
> is different since the axle with the most grip will do most
> of the work.
I originally thought that it wasn't possible to transfer
more than 50% to the rear, with an MPT automatic. I now
see that if the front is slipping and the transfer clutch
is locked, 100% will go to the rear, so anything in between
is possible, though perhaps hard on the transfer clutch.
I think the misleading description of the MPT automatic
is most harmful to buyers of Foresters. There are no
Foresters with VTD transmissions. If I were buying a
Forester for true AWD and then found out that it's
really only a FWD with (fancy) rear backup, I'd be kind
of peaved. (There are manual Foresters, with true AWD).
A few corrections :
I mentioned that the system didn't have any torque
sensors, only wheel speed sensors (and only front
and back, no left and right). I believe it's possible
to deduce torque :differences: from the speed differences,
though I didn't manage to figure out the formula after
a bit of trying. I'm too rusty, I guess. Figuring
out the actual torque would have to take into account
the power output of the engine, not just the state of
the throttle.
I also said that I wanted balanced AWD during engine
braking to prevent a wheel from locking. After further
review this doesn't really happen. It may feel like a
wheel is locked but it's probably only turning less
fast than the other wheels, (still sliding so little
traction). The wheel may stop moving at some point
but that would only be a particular case. In fact
(if I understand things correctly) the slipping wheel
may end up going backwards, like the other three
wheels are trying to get it to do.
Finally, I said that there wasn't a balancing function
with a transfer clutch, compared to a differential. I
now believe that there is, as long as the clutch is
slipping. Not the same kind of balancing, but probably
effective. With the MPT the front is connected directly
to the engine so the front will always get the same or
more torque as the rear (unless the front is slipping)
but I saw somewhere that the front never turns less than
the rear anyway (not sure about this last bit, I haven't
worked it out).
Thanks again TransFixed for your help in my understanding
of things. It's all quite mind-boggling.
Ned Pike
news:bn8p1g$uh8tp$1...@ID-114862.news.uni-berlin.de...
Up here in Vermont, the first sign of true winter is a Grand Cherokee with
Massachusetts plates upside-down in the Interstate median.
Tony Hwang
Hi,
Some Jeep(SUV) drivers are real dumbass. In the middle of summer, a
woman rolled a Jeep making a turn in the intersection downtown here
knocking down mom and kid waiting at the sidewalk to cross the street.
Does not have to be winter. Go figure.
Tony
Alan
got a subie. Wanted 4/AWD without the rollover risk.
"Tony Hwang" <drag...@shaw.ca> wrote in message
news:Etbmb.166710$9l5.144582@pd7tw2no...
Greg Reed
Tony Hwang wrote:
<snip>
> Hi,
> You're looking at only mechanical part, there is electronics involved.
> Not as simple as one might think.
> Tony
Actually, in the case of a viscous-coupled differential or just a plain-old
viscous coupling (and I'm not clear myself which Subaru uses to distribute
power between the front and rear axles in its manual transmission cars -- it
sounds like they might use both depending on the application), there are
absolutely no electronics involved at all. The lockup is accomplished
entirely by differences in clutch plate speed heating up the fluid in the
clutch pack, which changes its viscosity.
FWIW, Volkswagen's old "Synchro" system (circa 1986 or so) uses a
non-differential viscous coupling. It has only two shafts going into it --
one from the front differential and one from the actual drivetrain. As long
as the front wheels are turning the same speed as the rear wheels, the unit
is "open" and no torque is transferred to the idling axle. When the viscous
coupling unit experiences a difference in speeds between the axles, it
"locks up", transferring torque to the idle axle. A friend who is a devoted
fan of old VW Synchro Vanagons tells me that lockup of this unit takes less
than a second in that application.
A viscous-coupled differential employs the same concept but between the two
output shafts of the differential -- some wheel speed difference is
tolerated, but too much and the unit locks up. I'm pretty sure that this is
what Subaru employs in the rear differentials that are advertised as
"limited slip" such as on my new Forester XT or on the WRX. But as I stated
earlier, I'm not certain whether manual-transmission Scoobies use a center
differential with viscous-coupled limited slip or a plain old viscous torque
transfer unit, like in the old VW Synchro application. The salespeople to
whom I've talked about it know way less about the functioning of the various
AWD systems currently on the market than I do, and can't tell me any more
about Subaru's systems than what's printed in the brochures. They seem to
neither know nor care how their cars' AWD systems work. All they know is
"the wheels that slip to the wheels that grip" -- a catchy line but not
terribly informative.
To Subaru's credit, they've been in the AWD business since long before it
became sheik. They share this proud heritage with just a few other
companies -- most notably, Audi and Volkswagen. These companies were AWD
when AWD wasn't cool, to paraphrase a particularly annoying song. But when
it comes right down to it, I still think that Audi's Quattro is the best AWD
system available. Simple, cheap, and light as viscous coupling units are,
they just can't hold a candle to the Torsen differential that has become
Audi's trademark. Torsens are instantaneous where viscous units don't
engage until *after* wheel spin is occurring. And Torsens can handle
driving with different output shaft speeds all day long, where viscous units
will lock up and cause potentially serious handling and tire wear problems
if both output shafts are not turning at exactly the same speed (as with
slightly different diameter tires on the front and rear axles).
- Greg
--
1976 Cadillac Fleetwood 9-passenger sedan
(for sale: http://www.dataspire.com/caddy)
1989 Audi 200 Turbo Quattro 5-speed sedan
2000 Oldsmobile Intrigue
2001 Chevy Astro AWD (wife's)
2004 Subaru Forester XT (turbo) 5-speed (coming soon!)
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Bobby
news:3F9511AF...@def.com...
|
| I've been spending a lot of time lately studying Subarus
| and am starting to see clear through the misleading text
| by Subaru and others on the subject of AWD and automatic
| transmissions. Personally I drive a manual but I've been
| so bothered by the incomprehensible descriptions of the
| automatics that I wanted to find out what was really going
| on.
|
| CR-V being like this, but I haven't seen anywhere that
| the non VTD Subarus are also like this.
|
| In my mind, then, these automatics are front wheel drive
| vehicles unless some very particular circumstances are
| met.
|
| AWD, in my mind, is much more than something to help
| getting unstuck. It's a matter of balance, both in
| power application and engine braking, with everything
| distributed to all four wheels, each doing 25% of the
| work. There is less chance of a wheel spinning during
| acceleration, or of a wheel locking up if you engine
| break in slippery conditions.
|
| If you read texts by Subaru and Honda on their automatics
| you get the idea that the system is constantly adjusting
| things front to back depending on conditions. Well, it
| may be monitoring things constantly, but it isn't doing
| anything most of the time.
|
| So if you're looking at AWD for safety and fun, either
| go with a manual, or make sure you get an automatic with
| a center differential.
|
Been a lot said on this topic by now... I say who cares! AWD on my 02 OBW
with an automatic tranny works just fine when it counts. While I rarely
take my car to it's limits, when I have it hasn't let me down. If I punch
it from a stop light while turning 90 degree's it has yet to slip (even in
wet conditions). Studded tires are Hell on the roads up here (Alaska) and
when it rains there is an extremely bad hydroplaning problem, but not with
my Subie. When I bought my car (in FWB Florida) I test drove it on the
beach, I couldn't get it stuck in the sand...
60/40 or whatever, my tires seem to grip to what's underneath them period.
Andy Mason
news:3f9c...@post.newsfeed.com...
>
> Tony Hwang wrote:
>
> <snip>
>
> > Hi,
> > You're looking at only mechanical part, there is electronics involved.
> > Not as simple as one might think.
> > Tony
>
> Actually, in the case of a viscous-coupled differential or just a
plain-old
> viscous coupling (and I'm not clear myself which Subaru uses to distribute
> power between the front and rear axles in its manual transmission cars --
it
> sounds like they might use both depending on the application), there are
> absolutely no electronics involved at all. The lockup is accomplished
> entirely by differences in clutch plate speed heating up the fluid in the
> clutch pack, which changes its viscosity.
Tony was referring to the automatic version. You're right that the manual
has no electronics involved. It's a viscous-coupled differential for the
center diff.
I think someone already posted this, but it's really worth the read if
you're interested in AWD systems:
http://home.comcast.net/~eliot_www/awd.html
> it comes right down to it, I still think that Audi's Quattro is the best
AWD
> system available. Simple, cheap, and light as viscous coupling units are,
> they just can't hold a candle to the Torsen differential that has become
Remember that you can't assume that Quattro = Torsen anymore. Torsens are
used in Audi Quattro's (and VW 4Motions) with longitudinally mounted
engines. Haldex's are used in Quattro's and 4motions with transverse
engines.
Andy
(perfectly happy with the AWD in my manual WRX...)
John M.
> Been a lot said on this topic by now... I say who cares! AWD on my 02
OBW
> with an automatic tranny works just fine when it counts. While I rarely
> take my car to it's limits, when I have it hasn't let me down. If I punch
> it from a stop light while turning 90 degree's it has yet to slip (even in
> wet conditions). Studded tires are Hell on the roads up here (Alaska) and
> when it rains there is an extremely bad hydroplaning problem, but not with
> my Subie. When I bought my car (in FWB Florida) I test drove it on the
> beach, I couldn't get it stuck in the sand...
>
> 60/40 or whatever, my tires seem to grip to what's underneath them period.
>
John
Paul Pedersen
Andy Mason writes :
> I think someone already posted this, but it's really worth the
> read if you're interested in AWD systems:
>
> http://home.comcast.net/~eliot_www/awd.html
Thanks for this link, nice article. It points out something
that occurred to me since my last attempt at reducing
confusion.
In the case of Subaru's MPT automatic transmission, the front
is 'hard wired' to the transmission, whereas the rear goes
through the transfer clutch. Since the clutch is (almost ?)
always slipping, there can be no transfer of power to the
rear because the body of the car will pull the rear wheels
into turning faster than the transfer clutch can, because
it's slipping relative to the front. So under normal
circumstances, the rear is actually applying drag to the
system (so maybe the transfer ratio is 105% front / -5% rear :-)
The rear can't be anything greater than 0%.
For the (slipping) clutch pack to act as a center differential,
and transfer something to the rear it would have to be turning
faster than the front, to make up for the slippage. This
is mentioned in the above article. However, on Subaru MPT
vehicles, the gearing is the same front and rear, and the
transfer is 1:1 so this can't be happening.
So, although I've been trying to shine some light on the
Subaru MPT automatics, it turns out they're even worse
than I originally thought :-) I now can't see how the
rear would ever be engaged at all unless a front wheel
is slipping. So this business of the rear kicking in, in
the middle of a turn, can't apply unless you're also
spinning a front wheel (and thereby are at the limits
of safety anyway). Not something that happens in everyday
driving.
I just don't see the advantage of dragging around all this
AWD stuff if it's only ever going to be used when you're
stopped on ice, or when you floor it on a gravel road,
or when you turn a corner so fast that you're sliding
anyway. None of these hardly ever happen and none of them
are related to safety (the last is actually kind of
frightening to me). Might as well go with a FWD vehicle
(and a set of chains) and save many thousands of dollars.
I have no problem with Subarus, only marketing bullshit.
I have yet to meet a Subaru representative that knew how
their systems work.
John Varela
> I just don't see the advantage of dragging around all this
> AWD stuff
It's extremely likely that the Subaru engineers feel the same way and have so
arranged things that the car doesn't operate the way you theorize. Sheesh.
--
John Varela
(Trade "OLD" lamps for "NEW" for email.)
I apologize for munging the address but the spam is too much.
John M.
> > AWD stuff
>
> It's extremely likely that the Subaru engineers feel the same way and have
so
> arranged things that the car doesn't operate the way you theorize.
Sheesh.
>
> --
> John Varela
> (Trade "OLD" lamps for "NEW" for email.)
> I apologize for munging the address but the spam is too much.
Laughing my as* off. It's amazing how much people will try to think away
something many engineers have spent many hours designing and putting
together. Additionally, if that doesn't work for you think about this: all
of that AWD 'stuff' cost money. Do you think managment is going to pay for
'stuff' just for the hell of it? To try and trick people into thinking it's
a technological marvel? There are much cheaper ways to do such a thing.
Simply because they can't understand it, it must be marketing bullsh*t!
Subarus have the best vehicle control systems on the road. Anything else is
just so much wishing. Just because a dealer or 'marketing person' can't
explain it means nothing. When have you ever met a dealer or marketing
person that could explain something technical?
John
Greg Reed
Andy Mason wrote:
<snip>
> Remember that you can't assume that Quattro = Torsen anymore.
> Torsens are used in Audi Quattro's (and VW 4Motions) with
> longitudinally mounted engines. Haldex's are used in Quattro's and
> 4motions with transverse engines.
>
> Andy
> (perfectly happy with the AWD in my manual WRX...)
Point taken. I'd actually completely forgotten about the Haldex system,
which I perceive as being used by VAG to implement AWD in platforms
originally designed to be FWD only. The specific arrangement to which I was
referring was the use of a Torsen center diff, as is used in all of Audi's 4
and 6 models, and was used in my old '89 200 sedan, as well as the original
Quattro, and most every other Quattro car that Audi released before about
1998 or so. (One notable exception is the old V8 Quattro Automatic, which
used a computer-locked center diff.)
And while I'm planning to purchase a Subaru that AFAIK doesn't have a Torsen
anywhere in it, I still think that the best AWD system ever commercially
produced was that in the Audi V8 Quattro 5-speed, which had Torsen diffs in
both the center and rear axle locations. The perfect AWD system would have
*three* of 'em. (Note that some of the more powerful FWD cars are now
offering Torsens in front to limit the torque steer that results from
violent front-wheel spin in a FWD car. I've never driven one of these cars,
and the torque steer-limiting effect of a Torsen seems counter-intuitive to
me. I'm trusting Car and Driver magazine's editors that the application
really does work.) I guess I'm just a big fan of the Torsen -- much more so
than of viscous coupled differentials.
- Greg Reed
--
1976 Cadillac Fleetwood 9-passenger sedan
(for sale: http://www.dataspire.com/caddy)
1989 Audi 200 Turbo Quattro 5-speed sedan
2000 Oldsmobile Intrigue
2001 Chevy Astro AWD (wife's)
2004 Subaru Forester XT 5-speed (coming soon!)
Paul Pedersen
"John M." writes :
> Laughing my as* off. It's amazing how much people will try to think away
> something many engineers have spent many hours designing and putting
> together. Additionally, if that doesn't work for you think about this: all
> of that AWD 'stuff' cost money. Do you think managment is going to pay for
> 'stuff' just for the hell of it? To try and trick people into thinking it's
> a technological marvel? There are much cheaper ways to do such a thing.
> Simply because they can't understand it, it must be marketing bullsh*t!
> Subarus have the best vehicle control systems on the road. Anything else is
> just so much wishing. Just because a dealer or 'marketing person' can't
> explain it means nothing. When have you ever met a dealer or marketing
> person that could explain something technical?
Hey, if you know how the MPT automatic works please tell me.
There's nothing I'd like more than fully understanding what's
going on.
I'm a mechanic, have read most of the Impreza shop manuals,
and scoured the Internet for weeks now trying to piece together
some reliable understanding of the MPT system. I've presented
what I've learned in as clear a fashion as I could in case
the subject might be interesting to someone else. Is it really
possible that :no one: is interested in the mechanical aspects
of their car or the one they're about to buy ?
BTW, it took me about 5 minutes to understand how a Corolla
AWD automatic works.
Michael P. Smith
> You are right, maybe my cars do not worth stealing ;) But if a thief wants your
> stereo, he will take it anyway, the point here is what you end up with - a
> broken window, or in my case a slashed rug top, which is more expensive to
> replace then a stereo. You can call this STUPID, I call this WISE, up to you.
Like the other guy's MT theft derterant, i use the Stock radio theft derterant
Mikke
Michael P. Smith
> something many engineers have spent many hours designing and putting
> together. Additionally, if that doesn't work for you think about this: all
> of that AWD 'stuff' cost money. Do you think managment is going to pay for
> 'stuff' just for the hell of it? To try and trick people into thinking it's
> a technological marvel? There are much cheaper ways to do such a thing.
> Simply because they can't understand it, it must be marketing bullsh*t!
> Subarus have the best vehicle control systems on the road. Anything else is
> just so much wishing. Just because a dealer or 'marketing person' can't
> explain it means nothing. When have you ever met a dealer or marketing
> person that could explain something technical?
>
> John
You know, THAT is the first thing that i have heard that DOES make sence.
Mike
>
>
Peter Berkey
> Laughing my as* off..... <snip>.... When have you ever met a dealer or
marketing
> person that could explain something technical?
OTOH, have you ever met a GREAT engineer who could sell you on something
extremely technical?? I've found that some of the greatest minds on the
planet sometimes go around tripping over their own shoe laces ;)
John M.
and things are best when you are part of a great team.
<smile>
John
Dominic Richens
>
> OTOH, have you ever met a GREAT engineer who could sell you on
> something extremely technical?? I've found that some of the
> greatest minds on the planet sometimes go around tripping over their
> own shoe laces ;)
As a GREAT engineering myself :-) my rule of thumb is that if I can't
explain a good idea in five minutes or less, I don't understand it or it's
not a good idea.
--
Dominic Richens | dom...@alumni.uottawa.ca
"If you're not *outraged*, you're not paying attention!"
Jim Stewart
> <Peter Berkey> wrote:
>
>>OTOH, have you ever met a GREAT engineer who could sell you on
>>something extremely technical?? I've found that some of the
>>greatest minds on the planet sometimes go around tripping over their
>>own shoe laces ;)
>
>
> As a GREAT engineering myself :-) my rule of thumb is that if I can't
> explain a good idea in five minutes or less, I don't understand it or it's
> not a good idea.
I don't understand what you're trying to say. Do you mean that
you can expain any good idea in 5 minutes *if* you understand it?
I think there is a vast quantity of ideas that can't be explained
in 5 minutes whether you understand them or not. Fast fourier
transforms, error correcting codes and single sideband come to
mind off of the top of my head.
John M.
> > As a GREAT engineering myself :-) my rule of thumb is that if I can't
> > explain a good idea in five minutes or less, I don't understand it or
it's
> > not a good idea.
>
> I don't understand what you're trying to say. Do you mean that
> you can expain any good idea in 5 minutes *if* you understand it?
>
> I think there is a vast quantity of ideas that can't be explained
> in 5 minutes whether you understand them or not. Fast fourier
> transforms, error correcting codes and single sideband come to
> mind off of the top of my head.
>
I agree with you... there are so many things that can't be explained
quickly.
There are many things that most of us will never understand or be able to
reverse engineer to our way of thinking.
How many people understand Einstein and Theory of Relativity? If you don't
quite understand the theory and you study it to try and understand it... and
you are unsuccessful, do you then say the theory must have a fault?
Just because someone can't understand how Subaru AWD systems work does not
mean they do not work. It just means that that person is not qualified to
make a judgement on what system is better; unless they have practical
experience to guide them.
John
Rocketman
science that needs to take the square root of -1 to make it work is
witchcraft! (It's Halloween).
vern....
"Jim Stewart" <jste...@jkmicro.com> wrote in message
news:bnu4du$7...@library2.airnews.net...
Carl 1 Lucky Texan
Q: What is the AWD difference between the AT and MT Impreza's?
A: Lets talk about MT cars first. If you think about the way a viscous
limited slip works, it's obvious that "50/50" is a huge
oversimplification. Put the car up on a lift and run the engine (not
recommended). Now put a brake on the rear driveshaft (i.e., both rear
wheels), and measure the torque there. Initially, there will be very
little torque as the rear end slows down due to the braking force. 50%
of the engine's torque is obviously not going there right now. Only
after the rear shaft has slowed down, and the fluid heated up causing
viscous drag, does torque begin to be delivered there. In other words,
some amount of slip must occur before the torque "transfer" occurs.
Now let's take AT cars with the MPT (multi-plate transfer clutch)
system. This is a very sophisticated system similar to the one used on
the WRC (but built for MUCH lighter duty use of course). TCU, or
Transmission Control Unit, does indeed "anticipate" slip by applying
clutch lock-up depending on throttle, speed, and gear position. So when
you accelerate from a stop at WOT, the TCU always sends torque to the
rear, regardless of wheel slip condition. Note that the Haldex center
diff used on VW's is mechanically identical to our MPT, however by not
being connected to the TCU it is lacking this very powerful feature --
like the viscous coupling, the Haldex must sense slip before lock-up occurs.
So the "90/10" myth is exactly that. With the MPT clutch fully
disengaged (low throttle or braking at highway speeds), maybe this is
somewhat accurate, but at every other situation, it is not.
Note that you can force fully locked 4WD ("50/50") on the autotrans by
putting the selector in "1".
fyi
Carl
1 Lucky Texan
--
to reply, change ( .not) to ( .net)
Tony Hwang
Rocketman wrote:
> Yeah, but you're talking wireless communications which is a black art. Any
> science that needs to take the square root of -1 to make it work is
> witchcraft! (It's Halloween).
>
Hi,
Sq root of -1 is an i. LOL.
Tony
TransFixed
Under 5 minutes each:
(1) The special theory of relatively recognizes that the predominance of
the velocity of light in the equations that describe electromagnetism is
not a fluke. Instead, it is there because the equations are valid for
any observer who ("in any frame that") is moving with a constant
velocity. Therefore, this idea should be generalized to all of physics.
Making the "other" physics of the time, classical dynamics, invariant
against such frame transformations required Einstein to accept a
then-known mathematical modification to space-time and apply it properly
to the physics that describes the motion of bodies. This modification
is not apparent in daily life; it only becomes important at very large
velocities. An equivalent way of saying this is that the velocity of
light is the largest possible velocity. Looking at the mass/energy of
accelerated bodies, he quickly distilled E = mc^2 from that. In
essence, this latter equation means that (because of the huge factor
velocity-of-light-squared in it) even a small piece of mass contains
huge energy, if you can set it free. From that derives the large energy
of nuclear reactions.
(2) Einstein realized that the description of gravitation did not yet
fit his new view. For one thing, Newton's gravitation acts
instantaneously at a distance - a flaw even Newton recognized. In
addition, the classical theory does not explain why we don’t feel a
difference between acceleration (e.g., in an elevator or on a rocket)
and gravitation. Einstein's general theory of relativity fixes this by
generalizing space-time once more. This time, the generalization to
accelerated frames means space-time must be intrinsically curved. Its
local curvature is caused by the mass of bodies and at the same time
forces other bodies (and even light) not to move in straight lines.
This is a "geometrification" of the force of gravitation, a beautiful,
powerful idea that has many consequences meanwhile observed in
astronomical contexts (e.g., black holes, red shift of remote galaxies).
Even Einstein’s cosmological constant, which he originally introduced
to enable static universes (and then withdrew as his biggest blunder
when confronted with observations of the expanding Universe), has earned
a new place to describe the as-yet-little-understood repulsive energy
that appears to accelerate the expansion of the Universe.
The above "geometrification" on the other hand has been the biggest
problem in attempts to unify all forces of nature now known. Perhaps,
string theory will resolve this issue. See current Nova programs on PBS
for that.
- D.
Dominic Richens
>
>> As a GREAT engineering myself :-) my rule of thumb is that if I
>> can't explain a good idea in five minutes or less, I don't
>> understand it or it's not a good idea.
>
> I don't understand what you're trying to say. Do you mean that
> you can expain any good idea in 5 minutes *if* you understand it?
>
> I think there is a vast quantity of ideas that can't be explained
> in 5 minutes whether you understand them or not. Fast fourier
> transforms, error correcting codes and single sideband come to
> mind off of the top of my head.
You are right. The flaw in my analogy is that it involved one subject
matter expert talking to another.
The typical context of the "5 minute rule" is two or more peer engineers
working on the same problem, brain storming ideas. If after 5 minutes I
still have a room full of blank stares, it's time to move on to the next
Staffan Nilsson
>
> Now let's take AT cars with the MPT (multi-plate transfer clutch)
> system. This is a very sophisticated system similar to the one used on
> the WRC (but built for MUCH lighter duty use of course). TCU, or
> Transmission Control Unit, does indeed "anticipate" slip by applying
> clutch lock-up depending on throttle, speed, and gear position. So when
> you accelerate from a stop at WOT, the TCU always sends torque to the
> rear, regardless of wheel slip condition. Note that the Haldex center
> diff used on VW's is mechanically identical to our MPT, however by not
> being connected to the TCU it is lacking this very powerful feature --
> like the viscous coupling, the Haldex must sense slip before lock-up
> occurs.
>
Incorrect. The Haldex works in the same way as you describe for the MPT
above, applying lock (transfering torque) depending on things like
engine torque, gas pedal position and so on. No difference there.
/Staffan
Edward Hayes
with the Subaru shop manual. I believe most of your statement is incorrect.
eddie
"Staffan Nilsson" <staf...@algonet.se> wrote in message
news:brdef2$9bg$1...@green.tninet.se...