J
John M.
Amen. And that is my exact experience with my Subaru.
John
John
P
Paul Pedersen
Andy Mason writes :
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.
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 therear 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.
J
John Varela
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.
J
John M.
I just don't see the advantage of dragging around all this
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
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
P
Paul Pedersen
:
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.
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.
M
Michael P. Smith
You are right, maybe my cars do not worth stealing
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
M
Michael P. Smith
John M. said:
You know, THAT is the first thing that i have heard that DOES make sence.
Mike
P
Peter Berkey
John said:
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
D
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'texplain a good idea in five minutes or less, I don't understand it or it's
not a good idea.
J
John M.
Absolutely true... that's why it takes all types to make the world go 'roundLaughing my as* off..... said:marketing
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
and things are best when you are part of a great team.
<smile>
John
J
Jim Stewart
Dominic said:As a GREAT engineering myself
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.
J
John M.
Jim
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
R
Rocketman
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).
vern....
science that needs to take the square root of -1 to make it work is
witchcraft! (It's Halloween).
vern....
C
Carl 1 Lucky Texan
this is from the NASIOC faq;
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
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
T
Tony Hwang
Hi,Rocketman said:
Sq root of -1 is an i. LOL.
Tony
T
TransFixed
Under 5 minutes each:John said:
(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.
D
Dominic Richens
Jim Stewart said:
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
idea.
S
Staffan Nilsson
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
E
Edward Hayes
I think you are misinformed and you need to investigate some more. Start
with the Subaru shop manual. I believe most of your statement is incorrect.
eddie
with the Subaru shop manual. I believe most of your statement is incorrect.
eddie