Transmission Resistor-- Again.

[Trevor]

There have been no replies to my previous query regarding the transmission resistor and how it actually works particularly in respect of duty solenoid ÒAÓ and the control of line pressure. I trust that this does not mean that the resistor is being open circuited by many without positive knowledge of the effects on other components. I sincerely hope someone will come up with some information.

There has also been an interesting query from Brian Steel regarding a second parallel connected 78 ohm resistor fitted to a 96 transmission again with no information in reply. This information tends to confirm my suspicion that we may be dealing with a rather crude form of control but I hope I am wrong.

If someone has a wiring diagram which includes the resistor this would take me a long way towards diagnosing how and in what way it works.

Any leads of any sort would be appreciated. Trevor.

[Beav]

From what I've been reading the bypassing of the resistor increases the voltage and consequently the main line pressure.

Being a 'duty cycle' circuit, I'm sure you understand, this doesn't increase the pulse width, just the voltage per pulse. The reason I mention this is I think there is some misunderstanding here, for some, that a solenoid is capable of intermediate positioning by varying its voltage. Solenoids are purely on or off, there is no 'in between'. Duty cycle circuits can regulate pressure or flow by clicking on and off at a speed determined by a controlling device. This is known as 'pulse width' or 'duty cycle'. A simple voltage meter doesn't display fast enough to see the switching, an oscilloscope or a digital graphing meter is required. Once again, I just wanted to clear that up for those unaware.

I believe svx_commuter has probably done the most research into this, not counting the efforts of 'Level-10' or other similar transmission rebuilders. He has introduced a secondary resistor into his car in order to place the line pressure at OE specs. In other words, his pressure was too high and the additional resistor lowered it to spec.

Give me a couple minutes and I'll post a wiring diagram in my locker. I don't know if I have a hydraulic chart available, I'll post it if I can find one.

Beav

[Beav]

I posted the pertinent pages in my locker - sorry, the only hydraulic schematics I have are for the lock-up convertor.

Beav

[Trevor]

Thanks Beav, what you have said is exactly the reason for my interest.

The resistor is of relatively high wattage which made me suspect that it is direct circuit with the duty solenoid and your answer appears to confirm this as you refer to voltage measured at the solenoid. This is the point which made me unable to understand the logic of the resistor being any form of control device.

As you say a solenoid valve is in effect an on off device which can be modulated to control flow and as a result pressure but can not employed as voltage controlled valve so why the resistor? There are two possible answers as I see it.

(1) The correct resistance solenoid was not available and therefore the manufacturer compromised by adding a resistor. This I can not wear as a possibility.

(2) The resistor reduces the current passing through the solenoid and therefore its power so that the speed of closing is reduced and therefore the flow/pressure increased without varying the frequency of modulation.. This is the crude form of adjustment I alluded to in my post.

This is indeed a possibility but I would have thought that a means of varying the pulse width or off time and or modulation frequency would have been used. However modulation may be derived directly from R.P.M. rather than electronically generated so as to provide a simple direct method of varying pressure to align with transmission R.P.M. This could be a viable approach and the more I think about it could well be the way things work.

In this case we must assume that the manufacturers used the resistor as a means of fine tuning rather than altering the winding on the solenoid to arrive at the correct level of power. Hence my reference to a crude form of adjustment. We can also assume that Subaru do not have direct control over specifications for the transmission and we know that others also use it so that what we have may be the result of a commercial compromise.

All told option 2 could make sense and if what I have described is the principal of operation varying the resistor would be a valid method of fine tuning the system. The addition of a second resistor could also be used as a means of shall we say vernier adjustment if the correct stock value of main dropping resistor was not readily available. Also the parts specs. would not be effected in respect of older models.

It appears that Òpulling the resistor plugÓ increases line pressure rather than resulting in the solenoid being open circuited therefore the resistor would need to be in parallel with the solenoid. However this makes it hard to understand reference to a second 78 ohms being added with one side to ground when two wires run to the resistor indicating it is above ground. However I have seen mention of a three pin plug so that there are other possibilities.

A circuit diagram will either shoot me down or confirm and I wait in anticipation of viewing the contents of your locker.

Thanks again, Trevor.

[Trevor]

Thanks Beav for going to the trouble of providing the wiring diagram and data. I have noted the amount of time you must put in helping people and I hope you are appreciated to the degree you deserve.

As suspected the resistor is above ground and I now see that from within the control system it could be connected either in series or parallel with the solenoid as and when required. I now do not think that the resistor is a means of adjustment but comprises an integral part of a system which is very sophisticated, entirely electronically programmed and does a lot more than adjust line pressure in accordance with RPM, there being several inputs involved. This is quite a motor car we are dealing with and probably a first of its kind in very many respects.

Without having a schematic of the automatic transmission control unit, which I doubt is published by Subaru, it will be difficult to learn much more.
I have some ideas which involve the modulation of the solenoid and I could investigate further by hooking up my Ôscope and looking at the wave form with and without the resistor in circuit. However whether my interest in the subject will support the work involved is doubtful at this stage. A local car wrecker has stripped an SVX and may be good enough to let me have a look inside the A/T, but again considerable time is involved.

If by any chance a schematic of the A/T is available this would be an answer to a prayer and I will wait with bated breath as you appear to be a source of all things SVX.

It is nice to be working on this rather complicated subject with you, Trevor.

[Ron Mummert]

Uhhh...Trevor - Isn't it time for your dip in the ocean?
Glad I could help. Ron.

[oab_au]

Originally posted by Trevor
There have been no replies to my previous query regarding the transmission resistor and how it actually works particularly in respect of duty solenoid ÒAÓ and the control of line pressure. I trust that this does not mean that the resistor is being open circuited by many without positive knowledge of the effects on other components. I sincerely hope someone will come up with some information.

There has also been an interesting query from Brian Steel regarding a second parallel connected 78 ohm resistor fitted to a 96 transmission again with no information in reply. This information tends to confirm my suspicion that we may be dealing with a rather crude form of control but I hope I am wrong.

If someone has a wiring diagram which includes the resistor this would take me a long way towards diagnosing how and in what way it works.

Any leads of any sort would be appreciated. Trevor.

Giday.Trevor.

The function of the resistor,as far as I can see is. thus
The "A" solenoid is a magnetic driver for the line pressure by-pass valve, to regulate the pump output to suit operating conditions. This solenoid is run on a modulated square wave, at a frequency to suit the solenoid, The TCU varies the duty.cycle to vary the magnetic pull of the solenoid and thus the position of the regulator valve. The frequency that the duty cycle wave is run at is to keep the armature and the valve vibrating to prevent the units sticking in one position and to improve the sensitivity of the movement.

The resistor is a parallel feed to the "A" solenoid coil to prevent the valve from fully turning off. Holding the 12 volt duty cycle up on a pedestal of what ever voltage the resistor drops. I think it may have been fitted to prevent the armature and valve from sitting in the off position to prevent sticking, open to speculation ? Removing it allows the by-pass valve to turn off fully for a bit more line pressure.
I think what Brian Steel has done with the second resistor, is to form a voltage divider, to wary the standing voltage in the fully off position.
At lest that is the way I see it mate,
Harvey.

[Trevor]

Hi Harvey,

Sorry I am unable to agree with your assessment of the operation of the solenoid particularly regarding the idea that the vibration is designed to prevent the units sticking in one position. Modulation of the valve i believe is the basis of the means of flow control which bears a direct relationship to frequency and the on/off ratio. Refer to Beavs second message in this thread which backs this up. A solenoid valve is an on off device not a device with an opening which can be varied in accordance with applied voltage.

However I do agree with your theory regarding the application of a constant voltage via the resistor to ÒsoftenÓ its following of the modulated signal. I had this in mind when referring to possible parallel connection and reference to this by you and further deliberation makes me sure this is the answer, As you have said the resistor would have a definite effect on flow/pressure in such an arrangement and a second resistor connected in series would lower the constant voltage and increase the effect of the modulated signal.

From this I think that we can come to the conclusion that it would be unwise to simply open the resistor circuit as some have been doing, but adding a second to drop the voltage somewhat should be OK.

The arrangement described does not constitute a voltage divider but the addition of a resistor to ground results in a true voltage divider configuration which has advantages. This is a very likely answer to the reason for the additional resistor connected to ground reported as being fitted to late model cars.

You are starting to get me keen enough to remove the battery etc. from my car to get at the resistor, jumper lead the battery back into circuit and set up my Ôscope and observe and measure. However after a lifetime spent as an amateur mechanic, tuner, builder, driver, I find I am now not so keen on grazed knuckles, sore back, stiff neck and attendant grease and dirt.. We will see what interest we have raised.

While doing this I would like to check on the voltage drop alleged to take place in the very short length of cable connecting the alternator to the battery as I have my doubts regarding the merits of the so called up grade. In this regard. I think that the attention in respect of the ground return circuit which is also involved is the most likely source of any improvement.

Thanks Harvey. Trevor. *<)

[oab_au]

Originally posted by Trevor
Hi Harvey,

Sorry I am unable to agree with your assessment of the operation of the solenoid particularly regarding the idea that the vibration is designed to prevent the units sticking in one position. Modulation of the valve i believe is the basis of the means of flow control which bears a direct relationship to frequency and the on/off ratio. Refer to Beavs second message in this thread which backs this up. A solenoid valve is an on off device not a device with an opening which can be varied in accordance with applied voltage.

*<)

Ok Trevor, I'll try to explain it simpler.
First the solenoid IS a device that can be moved to any position, in accord with the applied current. If the current is turned on, the armature will start to move towards the full position, if the current is removed when it reaches halfway, the armature will stop before it reaches the end and start to move back under spring pressure, but before it moves back the current is applied again, which starts it moving towards the fully on position.
This way we can move the armature to any position we want and hold it there, to control the flow to the control valve. The mark space ratio of the duty cycle achieves this.

Secondly, the signal that is used to control this type of positioning valve is a mixture of two frequency. The square wave duty cycle that is used to position the valve is not a smooth DC signal, it is derived from a frequency of around 1 to 10khz. This frequency is chosen to suit the armature size and weight and is used to prevent the armature from sticking when it has to stay in one position, thus making it more sensitive to small movements signals. Thus when the duty cycle is turned on it is actually a DC voltage that is in turn, being turned on and off at the much higher frequency thus vibrating the valve. Has to be seen on a scope to see the duty cycle level when on, is actually a frequency. This is common practice in operating hydraulic valves of this type.

Thirdly. the resistor plays no part in the operation of the solenoid, the duty cycle does that. The resistor is an additional low level DC feed to the solenoid to prevent the duty cycle from turning it fully off. The reason for this is not clear but for some reason they did not want the solenoid to turn off or, it is to limit the maximum pump pressure. Open to speculation.
Hope this makes it clearer, very hard to explain without waving the arm about and drawing.

All the best
Harvey.

[svx_commuter]

Hi Trevor,

I am impressed with your verbage on this subject. Can you make it to the reading meet? I have leads connected to the TCU to measure the LINE VOLTAGE for the line pressure solenoid and also for the TRANSFER PRESSURE SOLENOID. I would be more than happy to give you a demo of how the voltage changes with throttle position.

[Ron Mummert]

Oy....By following Trevor & Harvey's uhh... debate? I now find myself illiterate in not only computer stuff, but in mechanical stuff as well. I guess you're never too old to learn about what you never learned in the first place.
Sigh... Ron.

[Beav]

Originally posted by svx_commuter
Hi Trevor,

I am impressed with your verbage on this subject. Can you make it to the reading meet? I have leads connected to the TCU to measure the LINE VOLTAGE for the line pressure solenoid and also for the TRANSFER PRESSURE SOLENOID. I would be more than happy to give you a demo of how the voltage changes with throttle position.

You can also hook a volt meter to a circuit and flick a switch on and off at different rates to vary the voltage reading. Problem is if the voltage changes too far is it the resistor, the transistor, the power relay, the....?

Beav

[Trevor]

Hi again Harvey,

The armature of a solenoid can not be moved to, or held in any given position against a load in accord with an applied constant current on the basis of practical criteria. The armature will move full travel or not move at all within the parameters of practical time constants.

But you are suggesting that if the control current is modulated in the form of a square wave ( between 1 cycle per second and 10,000 which is an extremely wide range ), it is possible to reliably adjust the frequency in accordance with the spring rate of a return spring so as to hold the armature in any position in relation to full travel. Furthermore that this is used to vary the aperture or flow path within a valve so as to control flow/pressure.

My company Relays N.Z. Pry Lid built a considerable number of industrial control systems which I designed and a component of this sort would have answered many problems. I would appreciate it if you could advise me where such a variable aperture solenoid valve and control module is available. or are you suggesting that this form of solenoid control is confined to the automotive industry?

The principle which both Beau and I describe results in a, shall we say ripple flow from the solenoid operated valve, which varies in volume according to the frequency ( i.e. the on off rate and ratio of the opening and closing of the valve ) and this would quickly return to a constant flow and pressure. If you relate this to the duty cycle and parallel constant feed from the resistor to which you refer, you will see that we are to a large extent on the same wave length ( No pun intended ).

Please read again BeavÕs authoritative comments at the beginning of this thread where he also firmly points out that a solenoid valve is purely an on off device. He has obviously studied their application in respect of his practical experience with automatic transmission systems.

There is no need to wave your arms about in order to explain! I am sure that I understand the theory which you have presented but cannot agree with the principle of a control valve with an orifice or flow path varied by means of a solenoid with controlled travel. Basically it is of necessity an on off device and flow/pressure control is achieved by modulating the on off ratio or frequency more likely the latter..

This is no personal argument and I enjoy your company even at so great a distance. Therefore we debate in good humour and with enjoyment! The next round will be awaited with interest. I will be away for a few days as it is Easter but will return to the fray. Meantime all the very best and I appreciate our discussion which will no doubt be off interest to others.

Trevor.

P.S. My spell check (US) does not go along with my British heritage but I am sticking with the Oxford dictionary. Shall we cross swords and have fun on that one for more fun and debate. Not likely I can not spell for sour apples and used to rely on my secretary for input on that score. What is more I wish I could type like any one of them.

[Trevor]

Hi Commuter,

Sorry I canÕt make the Reading meet ( I gather this is a meeting of enthusiasts in the US. )
as my SVX is not amphibious and even if it were I might run out of fuel! Sarcastic bugger arenÔt I , but please note my signature!

I am away right now for a few days over Easter but will come back to you re Line Voltage when I get back.

Also Hi Beav.

I am glad you are back into this debate as I have referred to your expert opinion.

If you flick a switch in a circuit connected to a meter as you say you may observe different readings but this will be due to a time delay in the meters response. The result will be a crude square wave with a constant peak voltage all things being equal. However you may be describing some other phenomenon, not sure.

Happy Easter all, ( I am not religious by the way ) Trevor.

[Beav]

Apparently I need to be a bit more verbose (I wonder if anyone here ever thought I needed to be that?) Flicking the switch on and off is still applying the entire given voltage with each cycle. The meter lag, eye/brain perception lag, etc. will cause it to appear as if the voltage was merely lower.

The solenoid is incapable of sustaining an intermediate position just by a specific constant voltage. The cycling or frequency of the voltage application combined with the dampening effect of the hydraulic fluid pressure causes the solenoid plunger to 'float' in an intermediate position and therefore regulate the pressure. This doesn't require the solenoid to actually fully open and close with each cycle.

The main reason I brought this up is that in some instances knowing the duty cycle, or frequency if you will, is necessary for accurate diagnosis.

Beav