Prop-shaft Dog Clutch required 200-300BHP

[TheMadHatMan]

Hi Guys
Sorry if this a daft Q, but I am looking for a dog clutch (pref 12V electrically operated) that I could fit in the drive train (prop shaft) of a permanent 4wd vehicle, to disable drive to the rear wheels, or to enable 4wd.

I have looked around on the internet and cant seem to find anything suitable. Can you advise?

best regards
Richard

 

[GregLocock]

You will destroy the centre diff.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[TheMadHatMan]

Interesting response. Thank you.

It is common practice on a particular 4wd vehicle to remove the propshaft drive to the rear wheels, to reduce fuel consumption and to improve performance on-road. However if off-roading is required, then the prop (obviously needs to be re-connected first. I am thinking of connecting some form of dog-clutch to save having to remove the prop-shaft. Apart from balancing the new rotating mass, what other problems do you envisage?
Who do you think it would destroy the diff? I am fairly sure it doesnt have a centre diff.

 

[GregLocock]

Fair enough, if it doesn't have a centre diff then you won't destroy it.

Why are you being coy about the vehicle model?

Sorry I don't have any leads.


Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[TheMadHatMan]

On an allied note....
If an engine produces 300BHP(say), would the coupling need to handle all 300 BHP or, because it is only in the drive to the rear wheels, half of that? I understand there may well be losses in the gearbox.

ps I am not being really cagey - just dont think it is important at this stage...

 

[patprimmer]

If the details required to form a reasonable opinion are secret, so is my response. I expect most professionals here will have a similar attitude.

Good luck.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[TheMadHatMan]

if its that important - its a Land Rover Freelander

 

[TheMadHatMan]

Hey guys - I was asking for help here - you dont seem very friendly - I wasn't expecting the Rack and thumb-screws. As I said it aint secret - just didnt think it was relevant. No point in cluttering up the post unnecessarily - is there?

 

[patprimmer]

http://www.landrover.com/gb/en/Vehi...r_Freelander_overview@__link__InfoBlockLink_5

The above link shows the Freelander does have a viscous coupling type centre differential.

I imagine with one end having no load at all and the other end fully loaded, the diff would be very inclined to work the fluid in the coupling very hard, and it would get very hot.

If you could mechanically lock the diff when you disengaged one drive axle, it could work.

Where I was bought up, if you ask someone to do you a favour, for free, it was considered plain good manners to offer them any co-operation you could. Apart from being "the right thing to do" it was also much more effective in gaining help.

I have never thought that plain basic good manners could be considered as being equivalent to torture.

Without this unnecessary information, I could not have found the information that indicates you were lacking in fact in your second statement, and therefore could not have advised you.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[TheMadHatMan]

sorry if i offended - that was not the intention.

I was going to put the device before the vcu, its a bit tight - bit that would of course depend on the unit. So far I haven't found any unit that would be suitable, so bar designing and making one, I didnt realise that the vehicle would be significant. I also no of several people who already have removed the propshaft with no apparent ill effect.

pax vobiscum

 

[Fabrico]

It is common on other makes to disconnect the front drive, not the rear. It is also questionable that FWD on an SUV will improve on-road performance or mileage.

Caution is advised on the project as the "center differential" is a computer controlled viscous coupling. You will be at least doubling it's intended duty. If you fry it, you will have a repair bill far exceeding any fuel savings.

 

[TheMadHatMan]

oops - i dont think i can have explained myself well.
The idea is to remove traction from the rear wheels, thereby making a 4wd into 2wd. This isn't anything new. As I said before, I am aware that it is common practice to remove the propshaft from the rear diff to disconnect the drive to the rear. The problem is having to reconnect the propshaft every time you want 4wd. I am just trying to make this a bit easier by trying to devise a system to enable/disable the drive without crawling under the vehicle with spanners etc. The initial thought was a simple dog-clutch to connect/disconnect the drive. There would obviously need to be some interlocks for safety. I just couldnt find a dog-clutch that could take 300bhp - or for that matter a dog-clutch other than by Meccano (lol). The purpose of this thread was to see if anyone could point me in the direction of a suitable dogclutch, however it seems to have grown since then. To keep costs down a proprietory device is preferable. I am not sure how other manufacturers (such as on the Nissan X-trail) achieve this.
I bow to your collective wisdom - any help is appreciated. I apologise again if I have ruffled any feathers, this is due to my ignorance on this subject, not because I wish to offend.

 

[Tads3]

If you manage to install a dog clutch and assuming you don't engage it on hard surfaces, why can't you just do away with the viscous coupling? AFAIK on a Freelander the VCU is constantly acting partly locked up as Land Rover deliberately made the front and rear differential ratios different to generate some RWD on road to allow them to make the claim it is "permanent 4WD" like their other vehicles. I don't think there is any computer controlled.

 

[TheMadHatMan]

the idea is to enable AND disable the drive to the rear when required, without unscrewing parts (such as the prop shaft already mentioned. Ideally by the flick of a switch.

 

[patprimmer]

With a dog clutch, you will still be turning almost all the 4WD drive train, it will just be disengaged from the engine, but it will still absorb about the same amount of power. Turning the axles and especially the differential will consume some power. Not having to try to drive both axles at slightly different speeds should save some power.


Freewheeling hubs as used on OEM part time 4WDs saves more as the second diff is not being turned.


I can't offer any more advice without a thorough understanding of the exact drive train involved.

This was not obvious from the website.


Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

When Audi introduced the Quattro they claimed that the reduced drag from the wheels more or less compensated for the increased drivetrain loss, so the fuel consumption was not hit by the AWD.

If the intention is to save fuel then the /maximum/ benefit would be of the same order as the difference between a 2wd and 4wd version of the same vehicle.

Well funnily enough, we make one.

The six-speed model meanwhile is rated at 12.2 litres/100km for RWD and 12.8 litres/100km for AWD.

However, the AWD weighs 90 kg more, from 1995 for the 2wd, and I suspect that about half that fuel saving is due to the weight change.

My guess then is that you would save a maximum of 0.3 litres/100 km, and if we believe Audi it will be less than that. At today's fuel costs in the UK (taking a wild stab) that is 0.6p/mile for which you have to install this thing and risk blowing up your transmission. That's 60 pounds a year.




Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[TheMadHatMan]

Hi Guys
Thanks for the feedback.

Doesnt sound too good an idea eh? lol

 

[NickE]

How about a Transfer Case and front freewheeling hubs like the rest of the 4WD (as opposed to AWD) I've seen and driven....

(Heck my 1981 AMC Eagle SX/4 had vaccumn motors on the front axle and the transfer case to shift btw RWD/4WD-- by hitting a switch in the cabin -- You might have to fab up some things to make it work but these things do exist -- though it wont be cheap.)

 

[Fabrico]

Tads3, my bad, you are correct on the no-computer-control on this one.

Yes, the whole thing sounds like a not so good idea for several reasons.