wammers said:

IF THE VCU SIEZES UP THERE IS NO DIFFERENTIAL ACTION POSSIBLE.

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That goes without saying really, seizing being the same in effect as locking, just on a permanent basis.

Seeing as I'm not about to tempt fate by stripping down my working transfer box, I'm off to raid the grandkids lego technic and see if I can build this mythical diff

kernowdragon said:

I'm off to raid the grandkids lego technic and see if I can build this mythical diff

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i know a few FL1 owners who might be interested in that as an upgrade

Sean said:

i know a few FL1 owners who might be interested in that as an upgrade

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:hysterically_laughi

wammers said:

But forget the Land Rover description of the gear set as the differential unit. That is NOT a stand alone differential gear set, it only becomes so when coupled to the VCU. Please try to understand the gear set in conjunction with the vcu gives a differential effect.

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I agree.

Please bare with me.

The chain wheel supplies the power and transfers it to the rear output flange/prop shaft via a direct fixed mechanical link.

There is no fixed (locked) mechanical connection between the front and rear output shafts, only via the Viscous Material in the VCU which allows slippage or if a rear or front wheel loses grip the VCU locks (and controls slippage) to provide drive to the axle with both wheel in contact with the ground.

If the VCU seizes a transmission wind up occurs, removing a prop (this could be the front or rear prop) will remove this possibility.

If the the VCU fails to a condition where it is unable to transmit any drive (ie:a no lock up condition), if a wheel then loses grip the VCU will not lock allowing the wheel to continue to spin, all the drive power will be transmitted to that wheel.

So the VCU is used to allow/control/stop rotational speed differences between the prop shafts if wheel slippage occurs via the planetary gearbox.

Now if the vehicle is always on a level hard surface and no wheel loses grip and the vehicles VCU has failed to a condition where it will not lock up or control slippage.

1. Drive to the rear output is via the chain wheel>spline between the chain wheel carrier and output shaft.

2. The drive to the front wheels will be via the chain wheel>planetary gears> outer front drive tube>outer casing of the VCU>front output>to the prop shaft.

3. If the VCU has failed (unable to lock up), provided there is no lose of grip all four wheels will drive.

4. If a rear wheel loses grip and the VCU cannot control slippage (lock up), the rear wheel will continue to spin, no drive will be transmitted to the front axle. If a front wheel spins again the VCU will not lock, but because of the fixed mechanical linkage via the chainwheel>spline> rear prop the vehicle will have rear wheel drive only.

I've roughly drawn what I believe to be the way the VCU/Planetary gearbox is set up to act as a limited slip diff unit.

hth.....possibly......:behindsofa:

zzr

kernowdragon said:

That goes without saying really, seizing being the same in effect as locking, just on a permanent basis.

Seeing as I'm not about to tempt fate by stripping down my working transfer box, I'm off to raid the grandkids lego technic and see if I can build this mythical diff

Click to expand...

If you accept that statement, then what are you arguing about. A servicable VCU is needed to give differential gearing. You will accept then that the slipping action of the VCU instigates differential effect by allowing the planet gears to rotate around the sun gear as opposed to being locked in position on it as they are if the diff is locked. OR siezed.

zzr1200 said:

Please bare with me.

The chain wheel supplies the power and transfers it to the rear output flange/prop shaft via a direct fixed mechanical link.

There is no fixed (locked) mechanical connection between the front and rear output shafts, only via the Viscous Material in the VCU which allows slippage or if a rear or front wheel loses grip the VCU locks (and controls slippage) to provide drive to the axle with both wheel in contact with the ground.

If the VCU seizes a transmission wind up occurs, removing a prop (this could be the front or rear prop) will remove this possibility.

If the the VCU fails to a condition where it is unable to transmit any drive (ie:a no lock up condition), if a wheel then loses grip the VCU will not lock allowing the wheel to continue to spin, all the drive power will be transmitted to that wheel.

So the VCU is used to allow/control/stop rotational speed differences between the prop shafts if wheel slippage occurs via the planetary gearbox.

Now if the vehicle is always on a level hard surface and no wheel loses grip and the vehicles VCU has failed to a condition where it will not lock up or control slippage.

1. Drive to the rear output is via the chain wheel>spline between the chain wheel carrier and output shaft.

2. The drive to the front wheels will be via the chain wheel>planetary gears> outer front drive tube>outer casing of the VCU>front output>to the prop shaft.

3. If the VCU has failed (unable to lock up), provided there is no lose of grip all four wheels will drive.

4. If a rear wheel loses grip and the VCU cannot control slippage (lock up), the rear wheel will continue to spin, no drive will be transmitted to the front axle. If a front wheel spins again the VCU will not lock, but because of the fixed mechanical linkage via the chainwheel>spline> rear prop the vehicle will have rear wheel drive only.

I've roughly drawn what I believe to be the way the VCU/Planetary gearbox is set up to act as a limited slip diff unit.

hth.....possibly......:behindsofa:

zzr

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Not quite correct but to late tonight to start over. The drawing that is.

zzr1200 said:

The chain wheel supplies the power and transfers it to the rear output flange/prop shaft via a direct fixed mechanical link.

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Sorry zzr1200 that doesn't fit the official drawings or description. the rear output is feed by the carrier for the planetary gears, not the outer casing, and is therefore free to rotate at a different speed.

Taken from BW Overhaul Manual...

"The differential unit is driven from the intermediate shaft through a Morse chain. The outer casing of the differential unit is the differential input, while the sun gear provides the front output and the planet carrier the rear output. The planet carrier contains three sets of gears which mesh in pairs to maintain the correct directional relationship between the front and rear differential outputs. The rear output shaft passes through the differential unit, engaging with the planet carrier and protruding through the sun gear shaft to locate to the VCU inner splaine. The sun gear shaft(front output) locates to the VCU outer spline."

Hope this makes it clearer.

wammers said:

If you accept that statement, then what are you arguing about. A servicable VCU is needed to give differential gearing. You will accept then that the slipping action of the VCU instigates differential effect by allowing the planet gears to rotate around the sun gear as opposed to being locked in position on it as they are if the diff is locked. OR siezed.

Click to expand...

There is a subtle difference between what your saying and I'm saying. I'm saying a serviceable VCU is needed to allow the differential to differentiate, otherwise it will be locked,not that it instigates the differential effect as you are saying, because the VCU's function is to allow slippage whilst the two input shaft speeds are within certain limits of each other and it plays no part in transfering drive anywhere while it remains that way.

It is only when the two input shaft speeds move outside this range that the sheering forces within the VCU cause it to lock, at which point it effectively binds the two shafts together, forcing the rear input to function as an output and the rear to turn at the same speed as the front.

The only way the two input shafts can be rotating at different speeds if is the 'diff' truly is a differential, if as you suggested the diff mearly provides a front/rear split with no capacity for differing speeds then there will never be any sheering action within the VCU to cause it to lock!

In a locked state you have to think of the path of drive to the rear actually going forwards to the VCU which then transmits it back via the diffs rear output shaft.

kernowdragon said:

There is a subtle difference between what your saying and I'm saying. I'm saying a serviceable VCU is needed to allow the differential to differentiate, otherwise it will be locked,not that it instigates the differential effect as you are saying, because the VCU's function is to allow slippage whilst the two input shaft speeds are within certain limits of each other and it plays no part in transfering drive anywhere while it remains that way.

It is only when the two input shaft speeds move outside this range that the sheering forces within the VCU cause it to lock, at which point it effectively binds the two shafts together, forcing the rear input to function as an output and the rear to turn at the same speed as the front.

The only way the two input shafts can be rotating at different speeds if is the 'diff' truly is a differential, if as you suggested the diff mearly provides a front/rear split with no capacity for differing speeds then there will never be any sheering action within the VCU to cause it to lock!

In a locked state you have to think of the path of drive to the rear actually going forwards to the VCU which then transmits it back via the diffs rear output shaft.

Click to expand...

OK that is then what you are not grasping. There is no differential action when the diff is locked. Just as there is no differential action when the VCU is siezed. The VCU needs to be servicable and have movement in it for the gear set to act as a diff. This allows the planet gears to rotate around the sun gear to give that differential effect, without that movement there can be no differential. Please do not look at the gear set and think that all the gears revolve around each other in normal operation, they do not. All the assembly revolves en-mass to give drive, only when differential is needed does any rotation occur. Try to trace the power flow through the gear set and VCU you will see that the VCU is a link between front and rear drive, a link with variable resistance is the way to look at it. With the VCU working you have a flexible link with it siezed or locked the link is solid. And no differential effect can take place.

kernowdragon said:

Sorry zzr1200 that doesn't fit the official drawings or description. the rear output is feed by the carrier for the planetary gears, not the outer casing, and is therefore free to rotate at a different speed.

Taken from BW Overhaul Manual...

"The differential unit is driven from the intermediate shaft through a Morse chain. The outer casing of the differential unit is the differential input, while the sun gear provides the front output and the planet carrier the rear output. The planet carrier contains three sets of gears which mesh in pairs to maintain the correct directional relationship between the front and rear differential outputs. The rear output shaft passes through the differential unit, engaging with the planet carrier and protruding through the sun gear shaft to locate to the VCU inner splaine. The sun gear shaft(front output) locates to the VCU outer spline."

Hope this makes it clearer.

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You forget i know how it works it you who are having problems grasping the concept. The two splines at the front are coupled to the VCU this connects the planet gears driving the rear prop and the sun gear driving the front prop together through the VCU and prevents them from just revolving around each other. The movement available in the VCU coupling these two shafts give the differential effect as the planet gears can revolve around the sun gear. Thus adjusting for rotational differences front to rear.

wammers said:

There is no differential action when the diff is locked.

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TRUE

wammers said:

Just as there is no differential action when the VCU is siezed.

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TRUE

wammers said:

The VCU needs to be servicable and have movement in it for the gear set to act as a diff.

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TRUE: however if the VCU were replaced with a solid link between front output shaft and front prop you would still get differential action, just no locking.

wammers said:

This allows the planet gears to rotate around the sun gear to give that differential effect, without that movement there can be no differential.

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TRUE

wammers said:

you will see that the VCU is a link between front and rear drive, a link with variable resistance is the way to look at it.

Click to expand...

TRUE

wammers said:

With the VCU working you have a flexible link with it siezed or locked the link is solid. And no differential effect can take place.

Click to expand...

TRUE

wammers said:

The two splines at the front are coupled to the VCU this connects the planet gears driving the rear prop and the sun gear driving the front prop together through the VCU and prevents them from just revolving around each other.

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At normal shaft speeds the VCU does nothing, it is only when slipage between front and rear is 'sensed' that it locks front and rear shafts together.

wammers said:

The movement available in the VCU coupling these two shafts give the differential effect as the planet gears can revolve around the sun gear. Thus adjusting for rotational differences front to rear.

Click to expand...

The VCU cannot provide the differential effect, it's very locking/unlocking operation depends on the already present difference in rotational speeds between the input and output shafts. The difference in speeds can only be achived if the two shafts are already free to move at differing speeds via a true differential.


At the start of this discussion I must profess to almost total ignorance on the workings of my transferbox, it did what it did and I was thankful for it. Reading others posts and not being able to explain some of their comments was what lead me to go away and read up and attempt to understand it, for example being able to remove the front prop and retain drive, which would be impossible under the conditions some stated previously that the VCU only acted between the diff and front prop.

I wouldn't claim to be an engineer or have better than average mechanical understanding; however I am quite good at analysis and logic and the idea that the VCU PROVIDES the central differential effect simply doesn't stand up, the essence of it's operation relies on the heat generated through the sheering of the gel between the plates attached to the two input shafts. In order for there to be sheering and heat the two shafts MUST be travelling at different speeds (the actual speed required to initiate locking being dependent on the properties of the gel used). In order for the two shafts to be travelling at different speeds they MUST be free to do so within the disputed differential.

Maybe approaching this from a non-engineering prespective has allowed me the freedom to think less ridgidly about the transfer box operation, and accept that just because the diff doesn't llok like a traditional diff doesn't mean it isn't.

kernowdragon said:

TRUE
TRUE
TRUE: however if the VCU were replaced with a solid link between front output shaft and front prop you would still get differential action, just no locking.
TRUE
TRUE
At normal shaft speeds the VCU does nothing, it is only when slipage between front and rear is 'sensed' that it locks front and rear shafts together.
The VCU cannot provide the differential effect, it's very locking/unlocking operation depends on the already present difference in rotational speeds between the input and output shafts. The difference in speeds can only be achived if the two shafts are already free to move at differing speeds via a true differential.


At the start of this discussion I must profess to almost total ignorance on the workings of my transferbox, it did what it did and I was thankful for it. Reading others posts and not being able to explain some of their comments was what lead me to go away and read up and attempt to understand it, for example being able to remove the front prop and retain drive, which would be impossible under the conditions some stated previously that the VCU only acted between the diff and front prop.

I wouldn't claim to be an engineer or have better than average mechanical understanding; however I am quite good at analysis and logic and the idea that the VCU PROVIDES the central differential effect simply doesn't stand up, the essence of it's operation relies on the heat generated through the sheering of the gel between the plates attached to the two input shafts. In order for there to be sheering and heat the two shafts MUST be travelling at different speeds (the actual speed required to initiate locking being dependent on the properties of the gel used). In order for the two shafts to be travelling at different speeds they MUST be free to do so within the disputed differential.

Maybe approaching this from a non-engineering prespective has allowed me the freedom to think less ridgidly about the transfer box operation, and accept that just because the diff doesn't llok like a traditional diff doesn't mean it isn't.

Click to expand...

The gear set up cannot operate as a differential WITHOUT the flexible link which is the VCU. End of story.

Above a standard epicyclic differential design, yes?

The only difference between this and the RR one is the addition of paired planetary gears, which simply preserve rotational direction, and the use of the outside of the ring to provide the input via the chain.

This diagram functions as a differential without any link between the shafts from a VCU, however if you seated a VCU across the output shafts, as per RR, you'd effectively get an auto locking diff, just like RR.

How can this one work, yet the RR one can't possibly??

kernowdragon said:

Sorry zzr1200 that doesn't fit the official drawings or description. the rear output is feed by the carrier for the planetary gears, not the outer casing, and is therefore free to rotate at a different speed.

Taken from BW Overhaul Manual...

"The differential unit is driven from the intermediate shaft through a Morse chain. The outer casing of the differential unit is the differential input, while the sun gear provides the front output and the planet carrier the rear output. The planet carrier contains three sets of gears which mesh in pairs to maintain the correct directional relationship between the front and rear differential outputs. The rear output shaft passes through the differential unit, engaging with the planet carrier and protruding through the sun gear shaft to locate to the VCU inner splaine. The sun gear shaft(front output) locates to the VCU outer spline."

Hope this makes it clearer.

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Damm, back to the drawing board then.....:doh:

Is this better???

zzr1200 said:

Is this better???

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Yes that's fine.

zzr1200 said:

Is this better???

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That's pretty much it! which drawing package is that?

kernowdragon said:

That's pretty much it! which drawing package is that?

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Google sketchup 7

Never tried that one, how do you find it?