zilspeed
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| posted on 26/7/08 at 06:47 PM |
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Locost reverse box - using locking diff...
I've been applying my limited brain power to this and reckon I might be onto something.
This is for front engined cars mounted longitudinally like most non midis.
Anyway, the theory.
Take one small diff - like this midget one. Mount it in the transmission tunne with the output shafts facing the engine and the rear of the car. Power
goes in one and out the other. No crown wheel, no pinion.
As we all know, the two output shafts are linked via the spider gears and rotate either in tandem or in opposite directions.
So (stick with me here).
Engine power is applied to the output flange on the left, the diff cage is allowed to rotate freely, therefore power is transmitted unaltered to the
other output shaft. The fact that the diff cage rotates means that the spider gears simply operate in a stationary fashion.
Reverse ?
Lock the diff cage to prevent it from rotating by means of either mechanical lock or small hydraulic caliper.
The power which enters the assembly cannot rotate the diff cage, so the spider gears transmit the power to the other output shaft - in reverse
direction.
Bingo - reverse gear.
Discuss ?
(An oil can, and pillow blocks a la chain diff would of course be required, but that's relaitvely simple. )
Doesn't seem like terribly difficult engineering.
[Edited on 26/7/08 by zilspeed]
EDITED TO ADD THAT THE ABOVE WILL NOT WORK WITHOUT A LOCKING DIFF FOR FORWARD MOTION. HOW I COULDN'T SEE THAT, HEAVEN ONLY KNOWS.
THREAD STILL WORTH READING THOUGH 
[Edited on 27/7/08 by zilspeed]
[Edited on 27/7/08 by zilspeed]
[Edited on 27/7/08 by zilspeed]
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theconrodkid
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| posted on 26/7/08 at 06:57 PM |
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good idea but i think you will have to lock the planet gears to go forward and unlock/lock the casing to go in reverse?only one way to find out
who cares who wins
pass the pork pies
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adithorp
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| posted on 26/7/08 at 07:00 PM |
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Remember what happens when you have one wheel spining in the mud?
When you let the clutch out the cage would just spin (very fast) and you'd not move. You'd have to be able to lock the planet wheels in
order to move forward.
adrian
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zilspeed
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| posted on 26/7/08 at 07:01 PM |
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Locking and unlocking the casing is a doddle.
Machine it down to resemble a brake disc and use a caliper.
Job done.
But I completely take your point on the forward motion bit. It will 100% work in reverse, that's not in doubt. But, I guess forward motion is
sort of important as well.
Regarding the reverse function, I already have a very very elegant solution worked out involving nothing more than a hydraulic line lock and the
car's existing brake pedal. 
No mechanical linkages whatsoever.
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zilspeed
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| posted on 26/7/08 at 07:07 PM |
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quote:
Originally posted by adithorp
Remember what happens when you have one wheel spining in the mud?
When you let the clutch out the cage would just spin (very fast) and you'd not move. You'd have to be able to lock the planet wheels in
order to move forward.
adrian
Point taken Adi.
One difference though. In your example, you are applying power to the ring gear via the pinion gear.
Remember, my idea uses this diff mounted in the transmission tunnel behind the engine and longitudinally.
In my theory (that's all it is at the moment), if power is applied to one of the output shafts from the engine, the other output shaft will
rotate in tandem unless the cage is locked.
Or
You would shoot off backwards. But I don't think that's the case.
One things for sure, you would definitely move - that's a certainty.
Having said the above, I'm not convinced 100% yet myself. Not until I try it.
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Gerhard
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| posted on 26/7/08 at 07:43 PM |
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"One difference though. In your example, you are applying power to the ring gear via the pinion gear"
It's no diffrent if you applaying power to ring gear or drive shaft.
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zilspeed
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| posted on 26/7/08 at 07:57 PM |
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quote:
Originally posted by Gerhard
"One difference though. In your example, you are applying power to the ring gear via the pinion gear"
It's no diffrent if you applaying power to ring gear or drive shaft.
Ok, fair enough.
But I see a crucial difference.
In normal usage of a diff, the output shafts rotate due to a happy coincidence betwixt spider gears and diff cage . The power was actually applied
elsewhere within the assembly. The spider gears transmit the power to the output shafts.
In my idea, the power is directly applied to an output shaft. It is 100% definitely going to get to the other output shaft and transmit everything
except bearing loss directly to it. The only doubt is whether the unrestrained diff cage causes the output to be reversed. Locking the cage will
definitely cause it to be reversed. That being the case, a reverse gear is an absolute certainty. As said above, losless forward motion without
locking the two shafts has to be confirmed.
Please also remember that the assembly will be mounted on two pillow blocks and will rotate freely. Other than input and output shafts, there are no
other influencing factors.
I can see that I'm going to have to demonstrate this. :-)
This will either result in the theory being proven or me looking like a total tool.
I can live with either result
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adithorp
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| posted on 26/7/08 at 08:10 PM |
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"I can see that I'm going to have to demonstrate this. :-) "
Just keep your fingers clear of the cage. I predict it will spin at twice the shaft speed (once there's load on the other shaft).
adrian
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zilspeed
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| posted on 26/7/08 at 08:16 PM |
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And I predict that everyting will rotate at exactly the same speed and in the same direction.
When I lock the cage, the output shaft will rotate in the opposite direction to the input shaft, at the same speed.
(It's a good job I'm not a betting man )
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blakep82
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| posted on 26/7/08 at 09:03 PM |
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consider what happens if you have your car in gear, jack one wheel off the ground and leave the other on the deck, you can turn the wheel. it
won't work 
________________________
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don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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mark chandler
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| posted on 26/7/08 at 09:40 PM |
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I thought about this and have the perfect donor, just lost interest really.
Range rover transfer box diff, nice tidy package already, especially if you can find an old 4 speed box as these are smaller.
Already has an option for locking the diff, for reverse you just clamp the outer with diff lock out.
As they come in a machined tail unit on the transfer box in so you already have a housing, just need to machine an end plate with bearing to replace
the lump that the transfer gearbox sits in.
Here's a pic of the diff, about 3" across if mt memory serves me well.
regards Mark
 
Rescued attachment 220199297253_1.jpeg
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blakep82
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| posted on 26/7/08 at 09:43 PM |
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an lsd might do it, right enough...
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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blakep82
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| posted on 26/7/08 at 09:45 PM |
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but an lsd doesn't have planet gears does it? so would that just burn the clutches out if you try to lock the diff case?
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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zilspeed
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| posted on 26/7/08 at 09:50 PM |
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quote:
Originally posted by mark chandler
I thought about this and have the perfect donor, just lost interest really.
Range rover transfer box diff, nice tidy package already, especially if you can find an old 4 speed box as these are smaller.
Already has an option for locking the diff, for reverse you just clamp the outer with diff lock out.
As they come in a machined tail unit on the transfer box in so you already have a housing, just need to machine an end plate with bearing to replace
the lump that the transfer gearbox sits in.
Here's a pic of the diff, about 3" across if mt memory serves me well.
regards Mark
Well, it appears although I may be mental, I may not be the only one.
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daviep
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| posted on 26/7/08 at 10:29 PM |
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quote:
Originally posted by blakep82
consider what happens if you have your car in gear, jack one wheel off the ground and leave the other on the deck, you can turn the wheel. it
won't work
No you can't!!!!
However I still don't think it will work either, the cage will spin, you need to be able to lock the gears to the cage.
Just my tuppence worth
Davie
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zilspeed
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| posted on 26/7/08 at 10:36 PM |
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quote:
Originally posted by daviep
quote:
Originally posted by blakep82
consider what happens if you have your car in gear, jack one wheel off the ground and leave the other on the deck, you can turn the wheel. it
won't work
No you can't!!!!
However I still don't think it will work either, the cage will spin, you need to be able to lock the gears to the cage.
Just my tuppence worth
Davie
The cage must spin for it to work.
If the cage doesn't spin, it gives you reverse. That's the whole point.
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mark chandler
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| posted on 26/7/08 at 10:42 PM |
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Classic range rovers up to about 93 with an lt230 transfer box have open diffs with diff locks, later ones have viscous diffs.
The picture is of an open diff, they are made from a machined lump or metal which all bolts together, just because you cannot see the gears does not
mean they are not there !
If you machined a couple of oil seals each end then it would be a self contained unit.
The output shafts slip in either side with spline that locates in the planet gears within. The diff lock simply locks one of the output shafts to the
housing with dog teeth.
 
Rescued attachment Gbox_diff_in_bits.jpeg
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mark chandler
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| posted on 26/7/08 at 10:43 PM |
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Nearly bolted up
 
Rescued attachment Gbox_diff_part_assem.jpeg
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mark chandler
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| posted on 26/7/08 at 10:45 PM |
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where it all lives! left hand housing, the gears live in the bit to the right.
The 3 bolt plate is the diff lock level, the open hole goes across to the transfer box proper to operate the hig/low gears. but these all unbolt so
can be discarded.
You can tell the size of the diff by the size of the prop flange, this is the same size as a sierra diff flange, PCD on bolts may even be the same.
Regards Mark
[Edited on 26/7/08 by mark chandler]
 
Rescued attachment gbox_diff_housing.jpeg
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blakep82
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| posted on 26/7/08 at 11:39 PM |
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quote:
Originally posted by daviep
quote:
Originally posted by blakep82
consider what happens if you have your car in gear, jack one wheel off the ground and leave the other on the deck, you can turn the wheel. it
won't work
No you can't!!!!
Davie
oh yeah, i got that wrong, it would lock everything up...
anyway, point is, the differential was designed to allow one wheel to turn faster than the other. its deisgned so that the cage turns instead of the
other wheel when cornering.
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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Bob C
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| posted on 27/7/08 at 07:58 AM |
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Mark Chandler is right.
I'm loving the range rover locking diff idea & have a suggestion to take it further..... get this:
1)diff unlocked, cage loose = no drive
2)diff unlocked cage clamped = reverse
3) diff locked cage loose = normal forward drive
4) diff locked cage clamped = parking brake!!!
Yes it's a combined reverse and handbrake, allowing the use of lightweight hydraulic- only calipers on the rear wheels!
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zilspeed
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| posted on 27/7/08 at 09:34 AM |
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quote:
Originally posted by Bob C
Mark Chandler is right.
I'm loving the range rover locking diff idea & have a suggestion to take it further..... get this:
1)diff unlocked, cage loose = no drive
2)diff unlocked cage clamped = reverse
3) diff locked cage loose = normal forward drive
4) diff locked cage clamped = parking brake!!!
Yes it's a combined reverse and handbrake, allowing the use of lightweight hydraulic- only calipers on the rear wheels!
I'm with you Bob.
Only one question for you.
You say "1)diff unlocked, cage loose = no drive"
So if that were the case, where does the power go to ? The power can only go straight through or be reversed. There is no third way, ever. Not even
remotely possible.
If the input goes to one side of the spider gear, it goes to the other side too. It really isn't like the normal use of a diff where in an
unloaded state the pinion gear can remain stationary and the output shafts can counter rotate.
Anyway, I'm going to shut up now and go and do it.
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blue2cv
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| posted on 27/7/08 at 10:25 AM |
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Zil your idea will work, was something i was mulling over ages ago.
[Edited on 27/7/08 by blue2cv]
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zilspeed
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| posted on 27/7/08 at 10:57 AM |
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quote:
Originally posted by blue2cv
Zil your idea will work, was something i was mulling over ages ago.
[Edited on 27/7/08 by blue2cv]
Well, I reckon so too
It does occur to me that in hill start conditions with the diff in the normal free state, that if the car were to roll backwards and engine power was
applied then it would definitely be powered backwards. Clearly this is no use to us. It really does need to have the output flange locked to the cage
to ensure this doesn't happen.
So, either use a locking diff, or one which can be modified to lock.
Reverse is easy to engineer.
Is suspect that once this has been finalised, it's going to be a real goer.
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iiyama
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| posted on 27/7/08 at 12:18 PM |
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Watching with interest...lots of it! 
If its broke, fix it. If it aint broke, take it apart and find out how it works!
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