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  #16  
Old 12-06-2007, 01:35 PM
NiftySVX NiftySVX is offline
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Quote:
Originally Posted by b3lha View Post
I don't think a resistor will do the trick. The solenoid will still pulse open and closed at the same rate.

I think you need a circuit like this to generate your own duty cycle. Then you need a switch to select whether the transmission uses the TCU's duty cycle or the one from your circuit.
This is correct. The valve is just a normal electronic solenoid, it works like any other on/off valve, only the signal turning it on and off happens very quickly, allowing it to modulate line pressure to the transfer clutch. The pulse width and/or frequency is what allows it to vary the pressure. One would think that a resistor would, in a sense, depress the wave pattern sent out by the TCU (i.e instead of cycling from 0-12v it would cycle from 0-6 or so) which may or may not cause the valve to only partially open( not in a good way, either, it would be like it didn't move fast enough to the open position before it went back to close). This would almost certainly cause rapid failure. As for the effect on actual transfer pressure... I think it would have either no effect (if the valve is still able to fully open) or an effect of making the torque split even less (the more time the valve spends closed, the less fluid pressure the clutch gets).

I am, and have been for years, waiting in eager anticipation for someone to crack the TCU and then we can really start to have fun. I think that a combination of revising the map for the duty c solenoid and shift map will make the car really come alive. The only problem I worry about with modifications to the transfer map like is increased clutch wear if we increase the rear bias too much. I hypothesize that this is why it is conservative from the factory. With Subaru's overall goal of preventing wheel spin from occurring in the first place, it makes sense that they would want as even of a torque split as possible, all other things being equal.

The difference in the JDM and other versions is that it has the Variable Torque Distribution (VTD) type transfer system that includes a mechanical planetary center diff that defaults the torque split to the 35-65. The US SVX would have had this system (it was introduced to the world on the SVX) but at the time the government required that the vehicle be able to operate in 2WD for emissions testing which is not possible with the VTD system. This VTD system didn't come our way until the outback VTD of only a few years back.
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  #17  
Old 12-06-2007, 02:13 PM
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Quote:
Originally Posted by NiftySVX View Post
(the more time the valve spends closed, the less fluid pressure the clutch gets).
Please confirm and advise the evidence which indicates this as fact. As I understand it the C solenoid acts as a bleed and therefore reduces pressure to the clutch when open.

Can you definitely confirm that pressure engages the clutch?
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  #18  
Old 12-06-2007, 11:24 PM
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Quote:
Originally Posted by Tuck View Post
Did I not read somewhere here that the JDM transmission and TCU provided an initial 35-65 torque split? If so what makes them different?

Who needs throttle steering?
The JDM transmission (swapping to a JDM TCU will only cause problems, not create the effect you're looking for) is based on the VTD-4WD design which was introduced in 2001 on the automatic WRX here in the states. It's something like a 36/64 split normally. The transfer clutch mechanism is designed differently.
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  #19  
Old 12-06-2007, 11:29 PM
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Quote:
Originally Posted by Trevor View Post
Please confirm and advise the evidence which indicates this as fact. As I understand it the C solenoid acts as a bleed and therefore reduces pressure to the clutch when open.

Can you definitely confirm that pressure engages the clutch?
When there is 0v supplied to the sol. there is full pressure on the transfer clutches. When there is 12.v supplied it applies little to no pressure on the transfer clutches. Thats why I figured a weaker signal would create less of a front bias yet not bind in turns... just an idea

Tom
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  #20  
Old 12-07-2007, 12:04 AM
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Originally Posted by TomsSVX View Post
When there is 0v supplied to the sol. there is full pressure on the transfer clutches. (*because the solenoid is a normally closed device.) When there is 12.v supplied it applies little to no pressure on the transfer clutches. (*because the solenoid opens and pressure is bled off.)

Thats why I figured a weaker signal would create less of a front bias yet not bind in turns... just an idea

Tom
* Inserted by me as a simple means of explanation.

Exactly as I see it and why I accept your idea in principle, but not without reservations.
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  #21  
Old 12-07-2007, 12:12 AM
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Quote:
Originally Posted by Trevor View Post
Please confirm and advise the evidence which indicates this as fact. As I understand it the C solenoid acts as a bleed and therefore reduces pressure to the clutch when open.

Can you definitely confirm that pressure engages the clutch?
Actually you are correct, it does "bleed" pressure off of line to reduce clutch pressure. Fully open at 12v dumps the fluid and there is FWD. I'm not sure why i seemed to have forgotten that fact earlier
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  #22  
Old 12-07-2007, 12:17 AM
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Trevor,

trust me you don't even want to waste your time with this one as the people providing you information are providing you even worse information than usual/average.

There are a several things of importance which are well beyond their reckoning. First of all as is typical of most automotive transmission fluid circuits what you are actually dealing with is a play of pilot pressure versus line pressure not simply the control of one fluid pressure. Secondly the friction materials in an automatic transmission have a coeficient of friction which varies wildly according to the torque applied. Thirdly the atf used has a friction profile (on a side note many of the problems with heat/performance complained about on the 4eat are a result of users using a fluid with an inapropriate friction profile) which is far from linear.


Quote:
Originally Posted by Trevor View Post
Tom, I do not have data on the US system incorporating a clutch and have read confusing comments. Is the clutch engaged or is it released, when fluid pressure is applied.

When I can be absolutely sure in this regard, I will comment further.

Thanks, Trevor.
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  #23  
Old 12-07-2007, 12:49 AM
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WOW that's not very nice. I don't see the need to make assumptions about facts that are beyond other people's reckoning. All of that is true, and it is not hard to see that the pressure is actually pilot pressure. I mean, there is a pilot valve... and there is a transfer control valve... but those don't appear relevant when discussing a resistor to the duty solenoid c...

This reminds me of what is wrong with this board

People calling other people stupid, making statements like "There are a several things of importance which are well beyond their reckoning"

If you would like to explain, in detail, including all of these things that are beyond reckoning, that modification to the control circuit in this fashion is a bad idea, then be my guest. Maybe you think it's a good idea? I look forward to you explaining, in full detail, exactly what the effect of this might be, such a wealth of knowledge should not be lost to the world.

Don't forget to include:

The pilot pressure and why it is important to consider that in this context.

The coefficient (that's 2 f's, mind you) of friction which varies wildly according to the torque applied. (keep in mind coefficient means number so an equation would be relevant, since you brought it up)

Oh, and the friction profile of the fluid. This one may need a graph. Oh, and don't forget to include the equation.

Gee, seems like that would take an awful lot of writing to say that increasing transfer pressure could cause clutch wear and modifying the solenoid could cause, among other things, its failure?
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  #24  
Old 12-07-2007, 01:02 AM
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Nifty,

My appologies. I wasn't trying to insult you in fact my comments were not directed towarards anything you said.

I was simply addressing the "reservations" which Trevor was rightfully reserving. Any condescendeing tone was my bad and just an admission of frequency in which the information given to Trevor as rock solid fact is in fact wrong, wrong, wrong, wrong.

I really wouldn't like to explain in detail the play of pilot pressure vs line pressure, or the coefficient of friction vs torque, or the friction profile of the fluid. That was the whole point of my comment. Trying to apply a linear modification to a circuit with two non linear inputs and a non linear control..........well, you get the picture.


Quote:
Originally Posted by NiftySVX View Post
WOW that's not very nice. I don't see the need to make assumptions about facts that are beyond other people's reckoning. All of that is true, and it is not hard to see that the pressure is actually pilot pressure. I mean, there is a pilot valve... and there is a transfer control valve... but those don't appear relevant when discussing a resistor to the duty solenoid c...

This reminds me of what is wrong with this board

People calling other people stupid, making statements like "There are a several things of importance which are well beyond their reckoning"

If you would like to explain, in detail, including all of these things that are beyond reckoning, that modification to the control circuit in this fashion is a bad idea, then be my guest. Maybe you think it's a good idea? I look forward to you explaining, in full detail, exactly what the effect of this might be, such a wealth of knowledge should not be lost to the world.

Don't forget to include:

The pilot pressure and why it is important to consider that in this context.

The coefficient (that's 2 f's, mind you) of friction which varies wildly according to the torque applied. (keep in mind coefficient means number so an equation would be relevant, since you brought it up)

Oh, and the friction profile of the fluid. This one may need a graph. Oh, and don't forget to include the equation.

Gee, seems like that would take an awful lot of writing to say that increasing transfer pressure could cause clutch wear and modifying the solenoid could cause, among other things, its failure?
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  #25  
Old 12-07-2007, 01:04 AM
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I also admit my spelling has gotten really bad as of late
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  #26  
Old 12-07-2007, 01:31 AM
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Quote:
Originally Posted by longassname View Post
Trevor,

trust me you don't even want to waste your time with this one as the people providing you information are providing you even worse information than usual/average.

There are a several things of importance which are well beyond their reckoning. First of all as is typical of most automotive transmission fluid circuits what you are actually dealing with is a play of pilot pressure versus line pressure not simply the control of one fluid pressure. Secondly the friction materials in an automatic transmission have a coeficient of friction which varies wildly according to the torque applied. Thirdly the atf used has a friction profile (on a side note many of the problems with heat/performance complained about on the 4eat are a result of users using a fluid with an inapropriate friction profile) which is far from linear.
Rest assured I am well able to analyse information which has been provided to me and it is my prerogative should I seek additional confirmation.

I require no instruction in regard to fluid mechanics or associated control systems. I can find nothing within your text which makes any form of logical statement in regard to the topic at issue.
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  #27  
Old 12-07-2007, 01:46 AM
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Ok, my bad. You go about adding resistors to solenoid c then.

Quote:
Originally Posted by Trevor View Post
Rest assured I am well able to analyse information which has been provided to me and it is my prerogative should I seek additional confirmation.

I require no instruction in regard to fluid mechanics or associated control systems. I can find nothing within your text which makes any form of logical statement in regard to the topic at issue.
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  #28  
Old 12-07-2007, 02:15 AM
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Originally Posted by longassname View Post
Ok, my bad. You go about adding resistors to solenoid c then.
I nor anyone else intends to rush into anything and there are other options. That is why an interesting discussion is under way.
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  #29  
Old 12-07-2007, 03:22 AM
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What about my idea of a variable tone generator? Would that not cycle the Duty C in a user controllable fashion?
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  #30  
Old 12-07-2007, 03:42 AM
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God I wish I knew Assembly. I'd tackle that TCU code we have sitting around and do this damn test to prove once and for all what our duty cycles are.

Until then I'll leave it to the mechanical guys...
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