4EAT Line Pressure control.
 

The oil pressures that act in the Auto box are a number of different pressures that are all derived from the oil pump pressure that is called the Line Pressure. The engine drives the oil pump, and its output varies with the engine speed. To prevent the pressure from becoming too high at high engine speeds, the Pressure Regulator valve controls the line pressure.

This valve is not just a pressure bleed off type. It is a valve that controls the pumps output, by moving the pumps cam ring to change the volume output, from full output, to no output. As the pump pressure builds up, the Regulator valve sends more pressure to the cam ring to reduce the pumps output. In this way the maximum line pressure is held to about 215 psi, but as the engine speed varies, so does the line pressure, reducing to about 70 psi at idle. The Regulator valve also adjusts for the sudden variations in Line pressure caused by the application of clutches, bands and valve action.

As the Line pressure varies with engine speed, so does the engines torque, so it is not a problem to have the pressure low with low engine speeds. As the engine speed and torque increases, the pressure increases. If the engine is at part throttle and at high speed, there is no need for a high Line pressure as the torque is low. To save power the Line pressure is adjusted to suit the throttle position. This is performed by the Duty solenoid A.

The A solenoid is a controllable valve that can vary a Pilot pressure applied to the Regulator valve, to alter the Line pressure, under the control of The Transmission Control Unit. The TCU controls the pressure for oil temp, throttle position and gear shifting. The TCU turns the Throttle Position Sensors 0 to 12V signal, into a 12V Duty Cycle signal that varies the current sent to the Solenoid, in line with the throttle position. When full throttle is used, the solenoid stays as an open drain, and the pressure is held high. As the throttle is closed the Throttle Duty Cycle current, is increased to reduce the solenoids drain on the Pilot pressure that acts on the Regulator Pressure Modifier valve and Line pressure is reduced.

http://www.subaru-svx.net/photos/files/oab_au/39645.jpg

The way the TCU controls the Line Pressure for oil temp or gear shifting, is done by the A solenoid valve, through a different wire that connects directly to the A solenoid, without going through the Dropping resistor. As the Throttle Position Duty Cycle is a 12V signal and the A Solenoids resistance is only 3 ohms, the Dropping resistor is used to drop the current to a level that the solenoid can use. The other signal from the TCU is a 5V Duty Cycle that is fed in to the line, between the dropping resistor and the solenoid. This forms a voltage divider circuit, so that both signals can be sent to the Solenoid at the same time. So that when the throttle is wide full open and the line pressure is high, the TCU can send a signal through the other line to reduce the line pressure while the box changes gear, or for a number of other conditions.

This is what the circuit looks like with both TCU signals feed to the solenoid.

http://www.subaru-svx.net/photos/files/oab_au/39636.JPG

So while the Throttle pressure is controlled by the throttle pedal position. The Line Pressure is modified by the TCU to suit the operating conditions that apply at the time.

Harvey.;)

Interesting.

Are the two duty cycles the same frequency, and if so, are they in phase or out of phase?

Hi Phil, good to see you back on the job.:D
I would think that they are at the same frequency, as they are working the same armature, and would be in phase. Other wise they would cancel each other out.

Harvey.;)

Didn't explain that very well Phil.
 

As usual I didn't explain that very well.:confused:

The signal coming from the TCU G/R, pin c8 to the dropping resistor is a zero to 12 volt Duty Cycle. The signal coming from the TCU G/Y, pin c7, is a zero to 5 volt Duty Cycle. The two can be in phase, as by the time the two signals meet, between the resistor and the solenoid, the dropping resistor has reduced the 0v to 12v to the same, zero to 5V, for the other TCU line.

I would imagine that this line would always have a 'driving' current on it. to close the solenoid and reduce the line pressure. I can't see a reason for it to have a 'no drive' signal that might conflict with a 'drive' signal on the Throttle line. So it would always only have to raise the current level, regardless of the throttle level.

Harvey.;)

Harvey,

Your unsolicited post has no other purpose than to instruct. Therefore members should take heed with much caution.

You are stating explicitly that when the resistor circuit is disconnected, the only control signal present is at a maximum potential of five volts.

What you outline would indicate that you also continue to believe that the A solenoid is held stationary at intermediate positions in order to control pressure. Is this so ?

You state :-

So while the Throttle pressure is controlled by the throttle pedal position. The Line Pressure is modified by the TCU to suit the operating conditions that apply at the time.

Please clarify exactly what is "throttle pressure".

Your opening statements suggest that you believe the major duty in respect of line pressure control is carried out hydraulically/mechanically in line with earlier designs and control via the A solenoid valve is a secondary feature. But here you agree line pressure is modified by the TCU, to suite operating conditions.

I contend that the transmission is designed such that line pressure, is in all operative modes, electrically / electronically controlled via the TCU, fail safe features accepted.

The idea put forward is confusing to the extent that straightening out what is a strange proposal could be exceedingly time consuming or impossible. This may be the intent.

Surely if "drive" does exist it can be defined. I would gather. reference is endeavouring to be being made in some way, towards the the main control signal.

In fact there is but one control signal, on one control line. Any control via the TPS is via the TCU. There is no such animal as a "Throttle line". The resistor circuit has an independent auxiliary function, as I have clearly defined.

Information put forward by way of instruction, based on that which is "imagined", is surely questionable.

If the intent of the original post here is to open a technical debate, in deference to what I have set down, it is clear that nothing will be "explained very well", or statements adhered to, much less confirmed. Another magic solenoid in limbo. ;)

Trevor,

I don't intend to get in the middle of your 'pissin' match, so please don't dump on me, but this seems to be Harvey's thread. It would seem in fact, that it is your post that is 'unsolicited'.

I'm not aware that one need be 'solicited' to begin a thread, as Harvey has done here. Perhaps it best for all that you initiate a separate thread to discuss your views.

It all depends on your definition of what "is" is......
I did not have svx with that woman!!!!
She had svx with me!!!!

Harvey...;)

I define ‘drive’ as an increased percentage of Duty Cycle current, and ‘no drive’ as a decreasing percentage of Duty Cycle current applied to the Solenoid.

Harvey.;)

No problem Ron, if Trevor doesn't understand, there may be others that don't also. So I don't mind explaining or expanding anything that I have said.
Harvey.;)

What you are saying is that a member can own a thread, that this is not an open forum and statements made therein can not be queried. I therefore leave it to you to believe in what you will, including that a simple solenoid, as characterised by the A solenoid valve, is held stationary part open or closed, by means of an electrical signal.

Go to it Harvey, spin your thread for those who wish to trip on it. :p

Trevor,

I said no such thing, please don't rephrase my words.

I believe my post was clear, I questioned your statement that one's post could be 'unsolicited' on a thread initiated by that same one.

[QUOTE=NeedForSpeed] It would seem in fact, that it is your post that is 'unsolicited'.

I'm not aware that one need be 'solicited' to begin a thread, as Harvey has done here. QUOTE]

Isn't the first statement here is a direct contradiction of the second? Any post in an open forum is by definition a solicitation.

Stephen,

You could be right about that. Apologies to all.

[QUOTE=elninoalex]