Harvey - Solenoid Fault Checking ?

[Trevor]

There is an additional important fact regarding automatic transmissions, which it would appear has not seen previously mentioned here. This in spite of continual self acclaiming, expletive announcements by Harvey, who audaciously claims utmost superiority in respect of both knowledge and class status.

The SVX transmission was designed to be both couth and smooth, rather than suitable for traffic light drag racing and components are incorporated accordingly. It would appear that the major factors given prominence in threads, have been confined to overall line pressure. There is another issue in this respect, which can be raised with advantage.

When a column of high pressure fluid (incompressible), is started or stopped by a valve, in order to control a device which terminates the line, a pressure spike is created. This spike, unless suppressed will cause not intended, extreme and sudden, operation of the controlled device, e.g. clutch or band. Pressure waves, in the form of what is in effect, high frequency water hammer, can also be generated with destructive results,

In order to combat these problems, the SVX transmission incorporates pressure accumulators to protect the shift circuits. These operate broadly as has been previously described in regard to line pressure control. Each accumulator is set up to provide appropriate dynamic response and so dampen the associated high pressure spike.

A worthy guess is that one of the modifications carried out by “Level 10”, as their best kept secret, is to modify the action of the pressure accumulators by changing the control springs from standard, so as to provide harder shifting. The proper way to test the results, would be to hook up a transducer and oscilloscope to view the pressure waves. Whether “Level 10” would have gone to these ends, is a matter of conjecture.

[Trevor]

Was it gelded

[TomsSVX]

Originally Posted by Trevor

It is obvious that the trouble sensing circuitry can monitor cuurent, but why is it that a mechanical fault can not be detected ?

Trevor.

Mechanical fault can be detected. My Sol. C. is working fine but due to a clog in the transfer vavle or somewhere else, it is still contantly engaging AWD. svxfiles has sent me an entire rear tailshaft that will be installed as soon as it gets here. All I wanted to say is that I am throwing a Sol C code but I can hear it working properly.

Tom

[oab_au]

Originally Posted by Trevor

I commiserate with those who have become impatient as a result of my adversaries lack of intestinal fortitude such that he remains in hiding. Artistic talents thus displayed are associated with that which I hold in contempt. BS is BS and moire particularly so when garnished with insults by way of a sour condiment.

Some years back a thread including opposition to Harvey’s senseless theory, was typically concluded with insults towards me. This thread included my comments exactly as follows :-
________________________________

As there appears to be confusion as to exactly what is occurring in the resistor and solenoid circuits I have hooked up my scope and had a look at things.

N.B. Harvey, The findings are COMPLETELY at odds with what you have stated, therefore could you please advise as to where you got your information. (CURRENT NOTE - This information was typically never provided.)

Unfortunately I was on my own, so was unable to run the car in drive against the brakes as I had hoped to do. I admit being chicken as I was conscious of the garage wall and shelves containing valuable stuff in front of the car, as well as my own neck ! As a result the car was run in neutral and I could do no more than increase revs while checking the scope trace and taking measurements.

Static, all voltage measurements coincided with specifications.
The resistor measured 12.3 ohms and the solenoid 3.4 ohms.

With the engine running and the resistor in circuit the output from C7, i.e. before the resistor, showed a pulsed signal at a constant approximate 13.5 volts and at a rate of around 50 hertz . This was not in effect a square wave as the voltage fell to zero between pulses and the solenoid EMF was completely disrupted resulting in a substantial reverse spike. The frequency remained constant as did the voltage, but the length of the pulses became shorter as the revs rose.

Tested as above, the output from C 8, i.e. the direct circuit to the solenoid, showed a similar signal but with shorter pulses. The pulse length did not vary with throttle opening and increased revs. Once again a significant negative spike was observed. It was noted that the resistor ran extremely hot .

With the resistor open circuit, the same pattern was registered showing that feed back had not effected the individual circuit measurements.
______________________________________

FAQs

For those who can sort fact from fiction, I set out the former in broad and simple terms:-

DUTY SOLENOID A.

A pulse width modulated duty solenoid valve, ( Sometimes known as a pulsoid), as is incorporated in the SVX transmission control system, adjusts pressure in the following manner :-

The fluid line is provided with a bleed or bypass via an on/off device, in the form of an electrically operated valve. This solenoid valve is opened and closed repeatedly, in a rhythmical manner by a control current which is turned on and off by the transmission control unit (TCU). The valve is a normally closed device, and remains closed in the event of the loss off a control current.

After passing through this modulated solenoid valve, the continually interrupted pressure is in the form of a pulsed flow. When the peaks level off with the troughs there is a resulting overall steady reduced pressure. The level of this pressure is adjusted by varying the on/off intervals. Most often the length of the on time is adjusted and the number of on/off pulses per second is kept constant. The usual rate is around 50 cycles per second.

The resulting adjusted output pressure is therefore delivered as a rapidly fluctuating stream. The system incorporates an expansion chamber as a smoothing element, which works as a sort of cushion. This device is usually in the form of a cylinder and piston or diaphragm, backed by a coil spring. In the SVX system the component is described as a Pressure Modifier Accumulator. The high pressure peaks in the stream press the piston outwards and become rounded off, while the low pressure troughs are filled in as a result of the piston moving inwards under spring pressure. The end result is a smoother level of pressure, such that controlled devices are not materially affected.

An increase in the volume of fluid controlled, is achieved by transferring the solenoid regulated pressure, to a pressure modifier valve and a regulator valve.

It should be clear that by “chopping” the fluid supply in an adjustable way, pressure control is achieved economically using a simple poppet type solenoid valve, with few mechanical or electrical complications. However the valve remains in a continuos cycling mode, which can impose rather arduous mechanical stresses.

THE DROPPING RESISTOR CIRCUIT.

It will be immediately apparent that a sudden on off cycle tends to cause what could be called a hammering of the valve seat, even though this is largely checked by the controlled fluid flow. The dropping resistor introduces a second series of current pulses applied in parallel with the control signal. These shorter pulses are applied during the off cycles and timed to check the travel of the armature as it reaches the closed position, thus reducing both shock and noise.

These secondary parallel signals in effect, “round off” the closing period and reduce the closing shock. This arrangement can be made even more sophisticated and configured so as to soften the the opening cycle, as well as the closing of the valve.

It will be appreciated that reducing the resistance in the circuit, or opening the circuit by omitting the dropping resistor, has two outcomes. Firstly the relative electrical off time is increased thus increasing the line pressure. Importantly as a second issue, increased shock loads are applied to the valve.

SOLENOID C

The same principals apply, but the duty is less arduous and therefore no parallel circuit is incorporated.

By way of preserving accuracy, I reserve copy rights.

I conclude by noting the lack of supportive response regarding the insults directed towards me and by directing towards your one armed paper hanger and all other BS artists, my two fingers! Any complaints should be directed towards the moderators. I stand by my words. *<)

There is reason to believe this post to be inaccurate and misleading. Further info can be found in this thread.
http://www.subaru-svx.net/forum/showthread.php?t=35942

Harvey.

[Trevor]

Originally Posted by oab_au

There is reason to believe this post to be inaccurate and misleading. Further info can be found in this thread.
http://www.subaru-svx.net/forum/showthread.php?t=35942

Harvey.

As expected and as is usual, a side step and bluff, rather than a direct reply.

There is very good reason to understand that all I have said is accurate.

Exact information can be found in this thread.

http://www.subaru-svx.net/forum/show...306#post442306