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  #736  
Old 05-07-2008, 06:56 AM
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Quote:
Originally Posted by Nomake Wan View Post
That makes no sense. "Open center diff?" In all the diagrams I've seen, it's clearly labeled as a limited-slip differential.

I'm lost, here. The VTD clutch does what, exactly? If it is fully disengaged, then what? It makes absolutely no sense, from an engineering standpoint, to have a setup so that failure of the VTD clutch to engage results in front or rear wheels rotating arbitrarily. A design in which the failure of the clutch (or disengagement of it on purpose) results in one or the other rotating every time, on the other hand, makes infinitely more sense. Such as Nissan's ATTESA-ETS.
Nomake,

You are no doubt confused by Harvey’s statement,”The clutch plays no part in driving either end.” Think on what he is effectively saying. The centre differential has a fixed front rear ratio when the clutch is not engaged.

The complete picture:-

In respect of the JDM box with VTD clutch, a signal providing maximum energised time and current to the normally open solenoid “C”, will increase transfer control pressure by closing a bleed. This causes the LSD clutch to be engaged, resulting in front rear drive virtual lock up. This can proven by inserting the control fuse.
Failure of solenoid valve “C”, will result in the clutch not becoming engaged and therefore drive in accordance with the mechanical ratio, i.e. front 36.4%, rear 63.6%.

The US arrangement incorporates a normally closed solenoid “C”, so that a similar control signal, reduces control pressure by opening the solenoid and creating a bleed. Consequently the clutch is not operated and there is no rear wheel drive.
Failure of solenoid valve “C”, will result in the clutch operating and front rear binding.

These alternative arrangements in respect of solenoid valve configuration, prevents the need for mechanical alterations in respect of the hydraulics used in the two systems, as has been proposed by Harvey.

Cheers, Trevor.
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  #737  
Old 05-07-2008, 07:14 AM
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Actually, Trevor, I was more confused by the statement, "If the VTD clutch does not work, we just have a open center diff that will spin one set of wheels or the other."

So all right, I'm back to my original understanding that there is a fixed mechanical ratio between the front and rear for VTD-4WD. But then what I don't understand is the functioning of the actual clutch mechanism. If the ratio front:rear is mechanical, then where does a clutch fit into that system, and how does it allow for more torque to be transferred to the front differential?
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  #738  
Old 05-07-2008, 07:16 AM
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Quote:
Originally Posted by Trevor View Post

In respect of the JDM box with VTD clutch, a signal providing maximum energised time and current to the normally open solenoid “C”, will increase transfer control pressure by closing a bleed. This causes the LSD clutch to be engaged, resulting in front rear drive virtual lock up. This can proven by inserting the control fuse.

Failure of solenoid valve “C”, will result in the clutch not becoming engaged and therefore drive in accordance with the mechanical ratio, i.e. front 36.4%, rear 63.6%.

The US arrangement incorporates a normally closed solenoid “C”, so that a similar control signal, reduces control pressure by opening the solenoid and creating a bleed. Consequently the clutch is not operated and there is no rear wheel drive.
Failure of solenoid valve “C”, will result in the clutch operating and front rear binding.

These alternative arrangements in respect of solenoid valve configuration, prevents the need for mechanical alterations in respect of the hydraulics used in the two systems, as has been proposed by Harvey.

Cheers, Trevor.
Thanks for expanding on these points Trevor.

Between yourself and Harvey I am at last beginning to see how the power is transferred in the two different transmission types.

Regards :
In respect of the JDM box with VTD clutch, a signal providing maximum energised time and current to the normally open solenoid “C”, will increase transfer control pressure by closing a bleed. This causes the LSD clutch to be engaged, resulting in front rear drive virtual lock up. This can proven by inserting the control fuse.
I am unsure still what exactly the phrase "resulting in front rear drive virtual lockup" By this do you mean that the LSD clutch is fully engaged, and the resulting front to rear drive/torque distribution is 50/50?

So if Solenoid C on a VTD car fails, it defaults to the mechanical 36/64 distribution?

And if a Solenoid C fails on the US type transmission, the default will be 90% or 100% Front Wheel Drive?

Joe
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  #739  
Old 05-07-2008, 07:38 AM
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Sounds like we've nearly come to some agreement about how sol C works.

I added logging to the tcuscan program and took a 10 minute drive at lunchtime. Unfortunately I behind traffic the whole time and didn't find an empty bit of road where I could get up some speed.

The CSV file can be loaded into any spreadsheet and graphs can be plotted.

It takes 3 seconds to read all of the parameters from the TCU. About 0.2 seconds per parameter. This leads to a problem with consistency because the parameters are not being read at the same time. If you compare the "gear" column with the "sol 1" and "sol 2" columns then you will see what I mean. I could improve things a little by changing the order so that related items are read one after another. But in order to increase the resolution it will be necessary to read fewer parameters.
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File Type: zip new.zip (52.3 KB, 409 views)
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Last edited by b3lha; 05-07-2008 at 07:47 AM.
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  #740  
Old 05-07-2008, 07:43 AM
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Quote:
Originally Posted by Nomake Wan View Post
Actually, Trevor, I was more confused by the statement, "If the VTD clutch does not work, we just have a open center diff that will spin one set of wheels or the other."

So all right, I'm back to my original understanding that there is a fixed mechanical ratio between the front and rear for VTD-4WD. But then what I don't understand is the functioning of the actual clutch mechanism. If the ratio front:rear is mechanical, then where does a clutch fit into that system, and how does it allow for more torque to be transferred to the front differential?
I'm not sure but I equate it to this;
In a rear wheel drive car with an open rear diff, if one of the wheels has no traction (in the air or on ice) that wheel will spin and the one with traction will do nothing. If you gently apply the brakes that will sometimes provide enough resistance to the spinning wheel to cause the diff to divert power to the wheel with traction.

Is the VTD clutch acting like the brake???
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  #741  
Old 05-07-2008, 08:04 AM
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Quote:
Originally Posted by svxistentialist View Post
And if a Solenoid C fails on the US type transmission, the default will be 90% or 100% Front Wheel Drive?

Joe
Nah, on a US car, inserting the control fuse (energizing the solenoid completely) will result in 95% duty cycle, or 100% Front Wheel Drive. A failure of the solenoid (0% duty, since there's no power at all?) will result in full lockup of the transfer clutch, or 50/50. This is why a Solenoid C failure in a USDM car will cause binding issues.

Quote:
Originally Posted by hocrest
I'm not sure but I equate it to this;
In a rear wheel drive car with an open rear diff, if one of the wheels has no traction (in the air or on ice) that wheel will spin and the one with traction will do nothing. If you gently apply the brakes that will sometimes provide enough resistance to the spinning wheel to cause the diff to divert power to the wheel with traction.

Is the VTD clutch acting like the brake???
But that assumes that the center differential in a VTD box is an open differential, which has been proven to be false by Trevor's statement that there's a constant mechanical ratio between the front and rear drives. About 35/65 front/rear.

I just don't get it. What's connected when the clutch isn't? Something has to be connecting the front and rear propeller shafts to result in a 35/65 ratio when the clutch isn't there to influence it. And when the clutch does come into play, how does it take torque away from that gear set and send it to the front propeller shaft?
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  #742  
Old 05-07-2008, 08:42 AM
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Quote:
Originally Posted by Nomake Wan View Post

I just don't get it. What's connected when the clutch isn't? Something has to be connecting the front and rear propeller shafts to result in a 35/65 ratio when the clutch isn't there to influence it. And when the clutch does come into play, how does it take torque away from that gear set and send it to the front propeller shaft?
In Harvey's sketch to me the red shaft appears to drive the rear green shaft through the sun gears turning the blue planetaries. Direct mechanical connection.

The VTD clutch is in yellow and must be connected to the yellow transfer gear. By energising this clutch some of the 64% power going to the rear green drive shaft is transferred to the forward drive shaft via the yellow transfer gear.

Is this a correct interpretation?
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  #743  
Old 05-07-2008, 08:58 AM
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Aha...I think...I'm starting to get it. Assisted by this diagram from Subaru:

http://img241.imageshack.us/img241/2...diagramiv7.jpg

As well as Harvey's illustration, I think that's right... the planetary gears have the ratio for the front and rear. Connected through to the front sun gear is the clutch, which essentially "overrides" the planetary gear ratio by introducing a load onto the rear output shaft. That load from the rear output shaft is fed through to the front transfer gear, where it is added to the torque already gained from the front via the planetary gears.

It all makes sense if the front transfer gear (front, in yellow) is connected to the input shaft (in green). This way, when the clutch (rear, in yellow) disconnects from the rear shaft (in red), torque is still fed to the front via the transfer gear (front, in yellow), but more is fed to the rear through the planetary gears' (blue) ratio.

Sorry if that sounds overly complicated, but if I don't get really deep down into specifics, I won't be able to wrap my head around it. I'm trying to hold a 3D model of the mechanism in my head, and then move the gears and clutch... so yeah...
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  #744  
Old 05-07-2008, 05:58 PM
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Quote:
Originally Posted by Nomake Wan View Post
Actually, Trevor, I was more confused by the statement, "If the VTD clutch does not work, we just have a open center diff that will spin one set of wheels or the other."

So all right, I'm back to my original understanding that there is a fixed mechanical ratio between the front and rear for VTD-4WD. But then what I don't understand is the functioning of the actual clutch mechanism. If the ratio front:rear is mechanical, then where does a clutch fit into that system, and how does it allow for more torque to be transferred to the front differential?
Nomake,

Put simply, the clutch limits the slip of the differential in a controlled manner, rather than in an uncontrolled manner, as with the usual form of limited slip differential.

P.S. A normal unrestrained differential will distribute torque in a variable fashion left/right, depending on load. The transfer system also does so front/rear, and the uncontrolled the transfer ratio, is governed by the inbuilt uneven differential ratio.
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Last edited by Trevor; 05-07-2008 at 06:20 PM. Reason: P.S.
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  #745  
Old 05-07-2008, 06:04 PM
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Quote:
Originally Posted by Nomake Wan View Post
Aha...I think...I'm starting to get it. Assisted by this diagram from Subaru:

http://img241.imageshack.us/img241/2...diagramiv7.jpg

As well as Harvey's illustration, I think that's right... the planetary gears have the ratio for the front and rear. Connected through to the front sun gear is the clutch, which essentially "overrides" the planetary gear ratio by introducing a load onto the rear output shaft. That load from the rear output shaft is fed through to the front transfer gear, where it is added to the torque already gained from the front via the planetary gears.

It all makes sense if the front transfer gear (front, in yellow) is connected to the input shaft (in green). This way, when the clutch (rear, in yellow) disconnects from the rear shaft (in red), torque is still fed to the front via the transfer gear (front, in yellow), but more is fed to the rear through the planetary gears' (blue) ratio.

Sorry if that sounds overly complicated, but if I don't get really deep down into specifics, I won't be able to wrap my head around it. I'm trying to hold a 3D model of the mechanism in my head, and then move the gears and clutch... so yeah...
I think we are getting there.

Dave is right, as to the term"open diff", Our front diff is 'open' the rear diff is 'limited slip'. So the center diff in the VTD is 'limited' when the clutch works. 'Open' when the clutch does not work.

The principal is the same. In our rear diff the side/sun gears are meshed with the pinion/planetary gears. the whole assembly rotates as a unit, it is only when one axle loses grip that the sun and planetary gears work to drive the other wheel. The Viscous clutch in the rear spans the two axles to prevent wheel spin.

The VTD is the same, the sun and planetary gears just rotate as a unit. The only time that they rotate against each other is when the front or rear drive looses grip, the gears will work to drive the other end.
This is when the clutch works to "limit the slip", as it just spans the two drive shafts to limit the spin.

The difference is. In the rear diff, the ratio for the sun to planet gear is the same on both sides. In the VTD the ratio of the sun to planet gears are different, to produce the torque difference.

Nomake Wan says,
< It all makes sense if the front transfer gear (front, in yellow) is connected to the input shaft (in green). This way, when the clutch (rear, in yellow) disconnects from the rear shaft (in red), torque is still fed to the front via the transfer gear (front, in yellow), but more is fed to the rear through the planetary gears' (blue) ratio.>

The drawing is a bit small, if you blow it up a bit, you can see that the (yellow) carrier that the planet gears are mounted on, the top transfer gear, and the clutch housing, are a solid unit. The top transfer gear (yellow) is free to rotate on the mainshaft (green). If it was a solid connection, we would be back to the US. Transfer system, with the front permanently driven. Not so.

The other thing that may not be obvious is that the two (blue) planet gears are one piece with the two sets of teeth cut on the one lump. This gear meshing with the two sun gears, forms the solid connection between the two ends.

Harvey.
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  #746  
Old 05-07-2008, 11:05 PM
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Quote:
Originally Posted by oab_au View Post
I think we are getting there.

Dave is right, as to the term"open diff", Our front diff is 'open' the rear diff is 'limited slip'. So the center diff in the VTD is 'limited' when the clutch works. 'Open' when the clutch does not work.

The principal is the same. In our rear diff the side/sun gears are meshed with the pinion/planetary gears. the whole assembly rotates as a unit, it is only when one axle loses grip that the sun and planetary gears work to drive the other wheel. The Viscous clutch in the rear spans the two axles to prevent wheel spin.

The VTD is the same, the sun and planetary gears just rotate as a unit. The only time that they rotate against each other is when the front or rear drive looses grip, the gears will work to drive the other end.
This is when the clutch works to "limit the slip", as it just spans the two drive shafts to limit the spin.

The difference is. In the rear diff, the ratio for the sun to planet gear is the same on both sides. In the VTD the ratio of the sun to planet gears are different, to produce the torque difference.

Nomake Wan says,
< It all makes sense if the front transfer gear (front, in yellow) is connected to the input shaft (in green). This way, when the clutch (rear, in yellow) disconnects from the rear shaft (in red), torque is still fed to the front via the transfer gear (front, in yellow), but more is fed to the rear through the planetary gears' (blue) ratio.>

The drawing is a bit small, if you blow it up a bit, you can see that the (yellow) carrier that the planet gears are mounted on, the top transfer gear, and the clutch housing, are a solid unit. The top transfer gear (yellow) is free to rotate on the mainshaft (green). If it was a solid connection, we would be back to the US. Transfer system, with the front permanently driven. Not so.
Ahhhh, I get it now. Yeah, that's complicated! But I finally get it.
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  #747  
Old 05-09-2008, 05:01 AM
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Oh, something interesting. A friend of mine went and got himself a Skyline GT-R32, and I've been doing some testing with it. While pondering an interface for his car, I went researching CONSULT and stumbled onto this post on a Nissan Q45 forum. Ah, blast from the past.

Quote:
Originally Posted by Q45 Forum
The output of the ECU is open collector, which requires an external pull-up resistor(provided by the board). On some of the DIY boards, you'll see this signal going straight into the RS232 converter. The MAX232's can be picky about their voltage hi/low signal thresholds, so this is where you run into problems. The problem is the 'low' signal is too high, and the MAX232 registers it as a 'hi'. My boards don't use a MAX232, because it isn't serial, but the same applies to the CP2102 also... there are hi/low thresholds you have to look out for.

I attempt to circumvent this by running the ECU signal into an op-amp comparator. Anything above a set threshold is output as a 'hi', otherwise it's a nice clean 'low'. FWIW, the comparator has an inherently very high input impedance. The only thing that could possibly be done is tweak the pull-up resistor value, but that may keep it from working on other ECUs.
Sounds kinda familiar, doesn't it?
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  #748  
Old 05-09-2008, 05:28 AM
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Quote:
Originally Posted by Nomake Wan View Post
Oh, something interesting. A friend of mine went and got himself a Skyline GT-R32, and I've been doing some testing with it. While pondering an interface for his car, I went researching CONSULT and stumbled onto this post on a Nissan Q45 forum. Ah, blast from the past.


Sounds kinda familiar, doesn't it?
Yeah. We would probably still be trying to figure it out if Calum hadn't come over from Nissan land and shown us the light.


Here's something that might help you (note the author)
http://www.sr20forum.com/rom-ecu-tun...ester-box.html
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  #749  
Old 05-12-2008, 10:45 AM
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Phil, the ECU and the TCU arrived safely, thank you.

I did not yet get time to fit the TCU this weekend, but I hope to next Saturday. I had to strip the rear calipers on Saturday, one was binding, and I managed to fix it and put on replacement pads [they are Ferodo, I had them in stock so I said I might as well use them.]

I'm looking forward to seeing if the mod works well for the Power mode.

Ta

Joe
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  #750  
Old 05-19-2008, 12:38 PM
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more on the ECU communication

hi all - just a note about the ECU communication - i have the same issue that nomake has reported where i read the ROM ID no problem, and the parameters start reading fine. however, it loses sync with the ECU and reads garbage (0's, -128's) for a few parameters, then regains sync, on and off.

here's what i hope is of use to you guys - yesterday i tried running a port monitor from sysinternals.com while running the vwrx software, and to my surprise whatever extra load (or buffering) on the port makes it stays sync'ed 80% of the time.

i have not tried building b3lha's "'92 problem" comparator yet. do you all think that is necessary even though the port monitor software seems to effect the problem?
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