LSD

No, not the drug or the money!

Having had AWD made clear to me, perhaps you all could oblige over
limited slip differential.

What is it? Is it better/worse than a locking differential, or just
different?

--

R
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"Rooney" <[email protected]> wrote in message
news:[email protected]...
> No, not the drug or the money!
>
> Having had AWD made clear to me, perhaps you all could oblige over
> limited slip differential.
>
> What is it? Is it better/worse than a locking differential, or just
> different?
>

Limited slip differentials have clutch packs which are engaged by a
difference in torque across the diff. In effect they provide a limited
amount of difference to allow turning etc.
In practice I have found LSD to be crude and next to useless. In cars they
have now been largely superseded by other forms of diff control or diff
design or electronic traction control acting on the braking system.

Huw

On Sun, 9 Jan 2005 20:56:39 -0000, "Huw"
<hedydd[nospam]@tiscali.co.uk> wrote:

>Limited slip differentials have clutch packs which are engaged by a
>difference in torque across the diff. In effect they provide a limited
>amount of difference to allow turning etc.


Sorry, Huw, but can you put that into terms a technopeasant like me
can understand?

--

R
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y

"Rooney" <[email protected]> wrote in message
news[email protected]...
> On Sun, 9 Jan 2005 20:56:39 -0000, "Huw"
> <hedydd[nospam]@tiscali.co.uk> wrote:
>
>>Limited slip differentials have clutch packs which are engaged by a
>>difference in torque across the diff. In effect they provide a limited
>>amount of difference to allow turning etc.
>
>
> Sorry, Huw, but can you put that into terms a technopeasant like me
> can understand?
>

I can only point you to a web site called 'How stuff works' on the web. If
you have not grasped the fundamentals of differential operation then you
will have difficulty with control systems. I dare say the site also explains
limited slip diffs, torsen diffs, no-spin, fully locking by various methods,
and all kind of other weird and wondrous patents.

Huw

On Sun, 09 Jan 2005 19:59:42 +0000, Rooney <[email protected]> wrote:

>Having had AWD made clear to me, perhaps you all could oblige over
>limited slip differential.
>
>What is it?

When a car goes around a bend the outside wheel travels further than
the inside. So that drive may be maintained to both wheels a
differential gear is put between them. This puts exactly the same
amount of torque (sort of rotational effort) into each wheel whilst
allowing one to travel further than the other.

This is great when there is a lot of grip but if one wheel loses grip
the maximum torque that can be applied is that which goes to the wheel
which is slipping or spinning. So there are various devices for
maintaining torque to the wheel that still has some grip. The
simplest, locking differentials, have mechanical (dog) clutches that
lock both output shafts together. Plainly once locked the differential
effect is gone and both wheels rotate the same amount on a bend, so
they make driving on firm ground again difficult, not to mention they
accelerate tyre wear.

So a number of more automatic systems are offered. In the racing world
where the spinning is caused by huge amounts of horsepower as the cars
accelerate out of corners it is best to maintain some differential
effect, so as not to foul up the steering, they tend to use limited
slip versions, I am not sure of current types but in the 60s these
would be sprung loaded clutch packs which were forced together by a
ball ann ramp affair which was moved by the relative movement between
the two output shafts.

For your off road driving the lockable type is more useful. A drawback
of locking diffs is that all the drive effort then gets concentrated
on one output shaft, which means these often need beefing up with a
locking diff.

There are other types and ways of doing this, one is by having a
viscous coupling (this was commonly used on the differential between
front and back axles on range rovers), another is by using back to
back one way clutches (no spin diffs) and another is a traction
control that works like ABS brakes. As soon as one wheel starts
spinning a sensor on the wheel notices it is rotating faster than the
others and momentarily applies the brake to that wheel only.


> Is it better/worse than a locking differential, or just
>different?

Well from my limited experience for off road use I would say limited
slip is less use than locking which is slightly less good at winding
you out of a hole than "no spin diffs". No spin diffs and articulated
steering work well together but not seen outside construction plant.

IME once you need to lock the diffs you don't get much further than
when you started getting into trouble.

AJH

<[email protected]> wrote in message >
> IME once you need to lock the diffs you don't get much further than
> when you started getting into trouble.
>

Depends on the type and condition of the terrain.
If one side of your vehicle is on a soft verge at this time of year then a
form of traction control gives a distinct advantage though a LSD is next to
useless IME being eclipsed by traction control.
For rock crawling while driving very slowly with high axle articulation,
then ABS type traction control is a poor choice while you need a true
locking diff. Which is why traction control equipped Land Rovers now have
the option of a locking diff on at least the back axle.

Huw

"Huw" Which is why traction control equipped Land Rovers now have
> the option of a locking diff on at least the back axle.
>
> Huw
>

In case you were wondering, I am thinking of the new Discovery.

Huw

On Sun, 09 Jan 2005 21:43:54 +0000, [email protected] wrote:

<snip>.
>
>IME once you need to lock the diffs you don't get much further than
>when you started getting into trouble.
>
>AJH
>


Thanks - and to you, huw.

I'm a bit more enlightened now.

--

R
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Rooney <[email protected]> wrote:

> What is it? Is it better/worse than a locking differential, or just
> different?

Different.

LSD locks the diff once one wheel has slipped more than seemed
reasonable to the designers. Locking diffs are controleld by the driver,
they don't lock until you command them to lock.

I have both on my 4x4 (Ford Exploder), it has a choice of "Auto" which
is normal driving where the drive is 100% to the rears. The rear diff is
a LSD so if one wheel slips the other will take up the drive sooner or
later. The centre diff also has limited slip as does the front diff.
Eventually if enough slipp happens all the diffs lockup and all wheels
are drive at the same speed.

Sounds good, but in practice it's a PITA as when it does cut in, it cuts
in with a bang and is likely to cause a four wheel skid. The better
option is to dial the required setting in using the dashboard selector,
as 4x4 High ot 4x4 low which works pretty much like the Land Rover
(Series III) lever. Drive to all wheels, all diffs locked.

--
"They that can give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."

-- Benjamin Franklin, 1759

"Huw" <hedydd[nospam]@tiscali.co.uk> wrote:

> a LSD is next to useless IME being eclipsed by traction control.

Ewwww no, not on the slippy stuff. I tried to take a Vectra with
traction control up a (mild) slope with a slippy (wet clay) surface. The
4xFord with LSD sails up it in all weathers. The Vectra sarted to flash
the traction control light, backed off the throttle and stalled. Over
and over again.

--
"They that can give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."

-- Benjamin Franklin, 1759

On Mon, 10 Jan 2005 00:40:35 +0000, %steve%@malloc.co.uk (Steve Firth)
wrote:

>Rooney <[email protected]> wrote:
>
>> What is it? Is it better/worse than a locking differential, or just
>> different?
>
>Different.
>
>LSD locks the diff once one wheel has slipped more than seemed
>reasonable to the designers. Locking diffs are controleld by the driver,
>they don't lock until you command them to lock.
>
>I have both on my 4x4 (Ford Exploder), it has a choice of "Auto" which
>is normal driving where the drive is 100% to the rears. The rear diff is
>a LSD so if one wheel slips the other will take up the drive sooner or
>later. The centre diff also has limited slip as does the front diff.
>Eventually if enough slipp happens all the diffs lockup and all wheels
>are drive at the same speed.
>
>Sounds good, but in practice it's a PITA as when it does cut in, it cuts
>in with a bang and is likely to cause a four wheel skid. The better
>option is to dial the required setting in using the dashboard selector,
>as 4x4 High ot 4x4 low which works pretty much like the Land Rover
>(Series III) lever. Drive to all wheels, all diffs locked.


Thanks, Steve.

--

R
o
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Steve Firth wrote:

> "Huw" <hedydd[nospam]@tiscali.co.uk> wrote:
>
>> a LSD is next to useless IME being eclipsed by traction control.
>
> Ewwww no, not on the slippy stuff. I tried to take a Vectra with
> traction control up a (mild) slope with a slippy (wet clay) surface. The
> 4xFord with LSD sails up it in all weathers. The Vectra sarted to flash
> the traction control light, backed off the throttle and stalled. Over
> and over again.
>

Vectras traction control is achieved by backing off the power - it's
supposed to stop you going into an uncontrolled skid by detecting when
you're about to break away and backing the power off.

The ETC on most 4x4s works by pulsing the brakes on the slipping wheel to
make sure that the diff doesn't go fully open and just sits there spinning
the wheel with no traction.

It's a different thing - don't judge 4x4 ETC by what a Vectra can do - they
are different things.


P.

"Steve Firth" <%steve%@malloc.co.uk> wrote in message
news:1gq5dmi.1wes1au1pbo5eyN%%steve%@malloc.co.uk...
> "Huw" <hedydd[nospam]@tiscali.co.uk> wrote:
>
>> a LSD is next to useless IME being eclipsed by traction control.
>
> Ewwww no, not on the slippy stuff. I tried to take a Vectra with
> traction control up a (mild) slope with a slippy (wet clay) surface. The
> 4xFord with LSD sails up it in all weathers. The Vectra sarted to flash
> the traction control light, backed off the throttle and stalled. Over
> and over again.
>

1. The Vectra is not a 4x4.

2. I still have three 4x4's with LSD and whether comparing them with each
other or with any other 4x4, the LSD's in the rear axle don't make a blind
bit of difference.

Huw

"Huw" <hedydd[nospam]@tiscali.co.uk> wrote:

> 1. The Vectra is not a 4x4.

Didn't say it was, but IME 4x4 traction control is just as bad.

> 2. I still have three 4x4's with LSD and whether comparing them with each
> other or with any other 4x4, the LSD's in the rear axle don't make a blind
> bit of difference.

So three 4x4s with LSD are the same as each other? Why am I not
surprised?

--
"They that can give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."

-- Benjamin Franklin, 1759

"Huw" <hedydd[nospam]@tiscali.co.uk> wrote in message
news:[email protected]...
>
> "Steve Firth" <%steve%@malloc.co.uk> wrote in message
> news:1gq5dmi.1wes1au1pbo5eyN%%steve%@malloc.co.uk...
>> "Huw" <hedydd[nospam]@tiscali.co.uk> wrote:
>>
>>> a LSD is next to useless IME being eclipsed by traction control.
>>
>> Ewwww no, not on the slippy stuff. I tried to take a Vectra with
>> traction control up a (mild) slope with a slippy (wet clay) surface. The
>> 4xFord with LSD sails up it in all weathers. The Vectra sarted to flash
>> the traction control light, backed off the throttle and stalled. Over
>> and over again.
>>
>
> 1. The Vectra is not a 4x4.
>
> 2. I still have three 4x4's with LSD and whether comparing them with each
> other or with any other 4x4, the LSD's in the rear axle don't make a blind
> bit of difference.

Well, I've a 2000 3.0D Trooper with a LSD - and I can't say I've noticed
it's effect on tarmac or off.

Cheers
Andrew Kay.

"Steve Firth" <%steve%@malloc.co.uk> wrote in message
news:1gq73iu.151ehh7s9789gN%%steve%@malloc.co.uk...
> "Huw" <hedydd[nospam]@tiscali.co.uk> wrote:
>
>> 1. The Vectra is not a 4x4.
>
> Didn't say it was, but IME 4x4 traction control is just as bad.
>
>> 2. I still have three 4x4's with LSD and whether comparing them with each
>> other or with any other 4x4, the LSD's in the rear axle don't make a
>> blind
>> bit of difference.
>
> So three 4x4s with LSD are the same as each other? Why am I not
> surprised?
>

You shouldn't be. I have owned around seven 4x4's with LSD over the years
and the remaining three, a Nissan, Isuzu and Mitsubishi, amply demonstrate
the futility of the design. On wet mud or slippery grass as well as mixed
terrain such as one side on tarmac and one in mud, my various traction
controlled devices **** all over them, tyres allowing.

I have one with full time four wheel drive and three diff locks but frankly
it is not as good in most conditions as my LR110 with open axles, mainly due
to having over wide tyre equipment. The diff locks do not sway the balance.
In my extensive experience, diff locks provide the most advantage when slow
rock crawling. Traction control is good in slippery stuff taken at a good
walking pace or faster and LSD's might as well not exist for all the
advantage they convey to the vehicle and user.

Huw

"Andrew Kay" <[email protected]> wrote in message
news:[email protected]...
> "Huw" <hedydd[nospam]@tiscali.co.uk> wrote in message
> news:[email protected]...
>>
>> "Steve Firth" <%steve%@malloc.co.uk> wrote in message
>> news:1gq5dmi.1wes1au1pbo5eyN%%steve%@malloc.co.uk...
>>> "Huw" <hedydd[nospam]@tiscali.co.uk> wrote:
>>>
>>>> a LSD is next to useless IME being eclipsed by traction control.
>>>
>>> Ewwww no, not on the slippy stuff. I tried to take a Vectra with
>>> traction control up a (mild) slope with a slippy (wet clay) surface. The
>>> 4xFord with LSD sails up it in all weathers. The Vectra sarted to flash
>>> the traction control light, backed off the throttle and stalled. Over
>>> and over again.
>>>
>>
>> 1. The Vectra is not a 4x4.
>>
>> 2. I still have three 4x4's with LSD and whether comparing them with each
>> other or with any other 4x4, the LSD's in the rear axle don't make a
>> blind bit of difference.
>
> Well, I've a 2000 3.0D Trooper with a LSD - and I can't say I've noticed
> it's effect on tarmac or off.
>

Slippery smooth tarmac may actually show the greatest effect so it is
telling that you have not noticed an effect. In my Trooper I can say that it
stops one wheel spinning wildly when accelerating in first and second gear
2wd in such conditions. Instead, both wheels lose traction and the back end
tries to overtake the front in a violent spin. If one tries ;-)
LSD's also tend to lose stiffness as they wear. I did once have an unit with
a particularly stiff setting which had some peculiar effects including quite
severe tyre wear.

Huw
Huw

"Huw" <hedydd[nospam]@tiscali.co.uk> wrote in message
news:[email protected]...
>
> "Andrew Kay" <[email protected]> wrote in message
> news:[email protected]...

>> Well, I've a 2000 3.0D Trooper with a LSD - and I can't say I've noticed
>> it's effect on tarmac or off.
>>
>
> Slippery smooth tarmac may actually show the greatest effect so it is
> telling that you have not noticed an effect.

Maybe we'll get some more snow this winter. If we do, I'll see if I can
find a way of telling whether it is doing anything useful.

Cheers
Andrew Kay

On Sun, 9 Jan 2005 21:29:05 -0000, Huw
<hedydd>
was popularly supposed to have said:

>
> "Rooney" <[email protected]> wrote in message
> news[email protected]...
>> On Sun, 9 Jan 2005 20:56:39 -0000, "Huw"
>> <hedydd[nospam]@tiscali.co.uk> wrote:
>>
>>>Limited slip differentials have clutch packs which are engaged by a
>>>difference in torque across the diff. In effect they provide a limited
>>>amount of difference to allow turning etc.
>>
>>
>> Sorry, Huw, but can you put that into terms a technopeasant like me
>> can understand?
>>
>
> I can only point you to a web site called 'How stuff works' on the web. If
> you have not grasped the fundamentals of differential operation then you
> will have difficulty with control systems. I dare say the site also explains
> limited slip diffs, torsen diffs, no-spin, fully locking by various methods,
> and all kind of other weird and wondrous patents.

I'll have a go, if you like.

A bog-standard diff drives the fastest-moving wheel. Drive into mud, and
get one wheel spinning, and that wheel will spin and spin, and the other
one won't get any drive at all.

There are a few ways round this problem.

Firstly, a locking diff. Lock the thing solid so both wheels get drive.
Works great in mud, but you get wind-up on bends when one wheel's going
further/faster than the other, hence over-run front hubs on some
machines.

Secondly, a Detroit Locker, which drives the slowest-moving wheel. More
complicated to build, lower volume production but if done properly works
OK.

Thirdly, traction control. You stick a sensor on the drivetrain, and on
each wheel. The computer knows how fast the wheels should be going, how
much power is going to 'em, and if one wheel seems to be spinning, it
hits the brakes on just that wheel to force the diff to give thoe other
wheel some power.

Fourthly, LSDs. The amount one wheel can slip compared to the other
wheel is set, using a clutch mechanism and some mechanical trickery to
detect when the limit is exceeded, and a clutch to link the two wheels
together. Tends to engage and disengage with a bang, especially on
bigger, beefier, more agricultural units. As seen up-thread, considered
the province of boy racers and techno-****wits.

Finally, stick a honking great electric motor on each wheel and computer
control all four of 'em with reference to steering, etc. Power off a
diesel-electric generator, or your favourite automagical power-making
thingie. Said to work OK, defintely works on big quarry wagons, is being
used by the US Army for a prototype stealth vehicle (turn off motor, run
on batteries and nobody can see/shoot at your exhaust heat).

May or may not get used, especially given that the height of
technological sophistication for America's enemies these days seems to
either be a suicidal god-bothering ****wit or a Toyota-load of armed
morons.

--
Dan Holdsworth PhD [email protected]
By caffeine alone I set my mind in motion, By the beans of Java
do thoughts acquire speed, hands acquire shaking, the shaking
becomes a warning, By caffeine alone do I set my mind in motion

Huw wrote:
> LSD's might as well not exist for all the advantage they convey to
> the vehicle and user.

Interesting notes there Huw. I have read (but never tried)
that LSDs can sometimes be helped by tweaking the handbrake
a little - assuming that it is the normal sort that acts
on the rear brakes. Any truth to that in your experience?

-- Steve