Jump to content


Welcome to Ultimate Subaru Message Board, my lurker friend!

Welcome to Ultimate Subaru Message Board, an unparalleled Subaru community full of the greatest Subaru gurus and modders on the planet! We offer technical information and discussion about all things Subaru, the best and most popular all wheel drive vehicles ever created.

We offer all this information for free to everyone, even lurkers like you! All we ask in return is that you sign up and give back some of what you get out - without our awesome registered users none of this would be possible! Plus, you get way more great stuff as a member! Lurk to lose, participate to WIN*!
  • Say hello and join the conversation
  • Subscribe to topics and forums to get automatic updates
  • Get your own profile and make new friends
  • Classifieds with all sorts of Subaru goodies
  • Photo hosting in our gallery
  • Meet other cool people with cool cars
Seriously, what are you waiting for? Make your life more fulfilling and join today! You and your Subaru won't regret it, we guarantee** it.

* The joy of participation and being generally awesome constitutes winning
** Not an actual guarantee, but seriously, you probably won't regret it!

Serving the Subaru Community since May 18th, 1998!

Guest Message by DevFuse
 

Photo
- - - - -

How does it all fit tougher for ( 4eat auto ? 062.5i impreza auto wagon and related?)


  • Please log in to reply
7 replies to this topic

#1 subaruplatt

subaruplatt

    Eat, Live, Breath Subaru

  • Members
  • 320 posts
  • Toronto

Posted 02 September 2007 - 08:03 PM

Weight distribution ( not sure )
Tire pressure ( factory is the only guide there are no charts for greater pressures )
Electronic clutch when does it act? 60/40 ?
Wheel diameter pressure vrs weight deflection vrs temperature and expansion
Open differentials?

It is clear to me that with factory tire pressures 33/30 the front ones seem to have an effective diameter which is less than the rear do to greater compression and because of greater frontal load ( weight balance).

Doesn't this cause the front tires to spin a little faster than the back ones and upon take off effectively bias the all wheel drive system to kick in quicker?
Does throttle position effect the all wheel lockup?

Do the centrifugal forces tend to equal the varying diameters after a certain speed?
Do increased temperatures exist up front that work to equalize the difference front to back diameters?

Once again how does it all work together?

#2 GeneralDisorder

GeneralDisorder

    Elite Master of the Subaru

  • Members
  • 20,280 posts
  • Portland

Posted 03 September 2007 - 04:42 AM

Weight distribution?


Put it on a scale and find out

Tire pressure ( factory is the only guide there are no charts for greater pressures )


Contact patch test is the best way to figure out proper pressure for various applications. Black paint and white butcher paper.

Electronic clutch when does it act? 60/40 ?


It starts as like 90/10, and has a MAX of 50/50 depending on conditions.

Wheel diameter pressure vrs weight deflection vrs temperature and expansion
Open differentials?


Some were open, and some were LSD rear diff. Depends on year. But the Viscous Coupler acts like an LSD for the 4EAT. Temp expansion would be equal in all tires so isn't a concern.

It is clear to me that with factory tire pressures 33/30 the front ones seem to have an effective diameter which is less than the rear do to greater compression and because of greater frontal load ( weight balance).


That's not clear at all - the larger pressure in the front is designed to offset the extra weight in the front of the vehicle.

Doesn't this cause the front tires to spin a little faster than the back ones and upon take off effectively bias the all wheel drive system to kick in quicker?


Maybe under hard braking - but that's what the VC is for - to allow different rotational speeds of the wheels.

Does throttle position effect the all wheel lockup?


I doubt it - not neccesary to lockup anything unless there's a loss of traction. The wheel sensors are all that's needed to bias the torque. Why complicate it with throttle posistion. Besides I happen to know the 4EAT doesn't have a TPS signal.

Do the centrifugal forces tend to equal the varying diameters after a certain speed?
Do increased temperatures exist up front that work to equalize the difference front to back diameters?


You aren't making any sense. Stop making it complicated - it's not.

Once again how does it all work together?


Pretty simple really - if a wheel sensor indicates a loss of traction it biases the torque to the opposite end of the car till they equalize in speed.

GD

#3 ron917

ron917

    Subaru Fanatic!

  • Members
  • 431 posts

Posted 03 September 2007 - 08:34 AM


Why complicate it with throttle posistion. Besides I happen to know the 4EAT doesn't have a TPS signal.


The 4EAT does have a TPS input, and it is one of the inputs used to control front/rear power distribution. See the Subaru factory service manual for the vehicle in question. Also see the Endwrench article at http://endwrench.com.../VarNov06EW.pdf

Quote from the Endwrench article, a couple of paragraphs from the Active AWD section which describes the NA 4 cylinder with 4EAT:

The TCM monitors input from speed
sensors on the front and rear drive shafts and also takes
input from the throttle position and the transmission. All
of these factors cause the TCM to select a software
strategy that determines how aggressively it adjusts the
power distribution.
Active All-Wheel Drive varies the power distribution
according to driving conditions. When throttle input
signals acceleration, the system responds by transferring
more power to the rear wheels to account for rearward
weight transfer. When releasing the throttle indicates
deceleration, power transfers to the front wheels to
enhance braking performance.



#4 GeneralDisorder

GeneralDisorder

    Elite Master of the Subaru

  • Members
  • 20,280 posts
  • Portland

Posted 03 September 2007 - 09:49 AM

Ah yes - I was thinking of the EA series 4EAT I think. But I forget..... Ah well at any rate it's not as complex as he thinks.

GD

#5 subaruplatt

subaruplatt

    Eat, Live, Breath Subaru

  • Members
  • 320 posts
  • Toronto

Posted 03 September 2007 - 11:32 PM

That's not clear at all - the larger pressure in the front is designed to offset the extra weight in the front of the vehicle.

With 33/30 there is still more compression on the front set than on the rear.
It's not like they are making the tires equal in diameter via air pressure.
At least they are not the same diameter when the car is at rest.
Then I wondered if centrifugal forces had an effect and what effect they might have on wheel diameter.

#6 jamal

jamal

    1000+ Super USER!

  • Members
  • 1,015 posts
  • Los Angeles

Posted 04 September 2007 - 05:02 AM

Put it on a scale and find out

Contact patch test is the best way to figure out proper pressure for various applications. Black paint and white butcher paper.

It starts as like 90/10, and has a MAX of 50/50 depending on conditions.

Some were open, and some were LSD rear diff. Depends on year. But the Viscous Coupler acts like an LSD for the 4EAT. Temp expansion would be equal in all tires so isn't a concern.

That's not clear at all - the larger pressure in the front is designed to offset the extra weight in the front of the vehicle.

Maybe under hard braking - but that's what the VC is for - to allow different rotational speeds of the wheels.

I doubt it - not neccesary to lockup anything unless there's a loss of traction. The wheel sensors are all that's needed to bias the torque. Why complicate it with throttle posistion. Besides I happen to know the 4EAT doesn't have a TPS signal.

You aren't making any sense. Stop making it complicated - it's not.

Pretty simple really - if a wheel sensor indicates a loss of traction it biases the torque to the opposite end of the car till they equalize in speed.

Hey good work on that long drawn out post that is mostly wrong. Lets start out with the fact that no Subaru automatic has a viscous coupling, and only the vtd cars have an actual center diff. They primarily use clutch packs.

Then you say that the 4eat doesn't have a tps signal. The TCU does use the tcu signal, and clutch pack lockup is very dependent on throttle position.

On top of that, many automatics do not even have wheel speed sensors. VSS1 and VSS2 are really all there is, but the 4eat awd system is proactive and will activate the center clutch before any difference between the two VSS signals. That's because the TCU reads more than the speed sensors to determine what to do with solenoid C.

Next time you should at least read an endwrench article or two, and maybe parts of the FSM, before you start posting about how things work. Here's a nice list of the things the TCU monitors to control center clutch pack lockup that took me all of 30 seconds to look up on endwrench:

Throttle sensor
Idle switch
VSS 1
VSS 2
Tach signal
Inhibitor switch
Cruise control signal
ATF temp
Ignition/battery voltage
1-hold/selector position/manual mode
FWD mode

source

Oh, and please explain how "if a wheel sensor indicates a loss of traction it biases the torque to the opposite end of the car till they equalize in speed"

#7 GeneralDisorder

GeneralDisorder

    Elite Master of the Subaru

  • Members
  • 20,280 posts
  • Portland

Posted 04 September 2007 - 05:34 AM

Yeah - I meant clutch pack, not viscous coupling. I was thinking of the 5MT's.

As for the rest, I was mostly going off my experience with the EA82 4EAT's which were considerably less advanced. In the ariticle you linked to it mentioned that they have undergone "continuous development and improvment" which I should have realized but wasn't really thinking too hard about. The newer ones are much more "nannyfied". The endwrench articles deal almost exclusively with Legacy's and beyond - the 4EAT was quite a bit less advanced when it first arrived.

I frankly despise auto's in the first place and wouldn't consider owning one except for some very narrow applications where they make sense.... and for people who never learned to clutch.

GD

#8 subaruplatt

subaruplatt

    Eat, Live, Breath Subaru

  • Members
  • 320 posts
  • Toronto

Posted 04 September 2007 - 11:43 AM

" the 4eat awd system is proactive and will activate the center clutch before any difference between the two VSS signals."

It's like the car is always ready to climb a hill!
The car is set up to do a couple of mph without depressing the gas pedal.
I feel the awd pushing against all 4 wheels when holding it back in drive.
The cooling system has to work harder to cool the transmission as the car is literally fighting itself stopped and in drive.
I readily shift the car into neutral when I am stopped at long lights.
I hear that the new model actually throws the transmission into neutral itself after the car is stopped and the brakes have been depressed for a matter of time.




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users