X drive enquiry

[bigwave2255]

hi just an enquiry for thoughts / info.

i understand in a more conventional vehicle the purpose of a centre diff.

(i have a Jeep Cherokee , so am comfortable with how centre diffs work, when to lock and unlock and when to use low range, and the effects of axle wind up if you get it wrong)

i also understand that X drive doesn't have a centre diff, but use,s clutches and that the clutch is motor activated, i read some where that there is drive to all wheels, so this could mean that there has to be slippage at that clutch pack where the centre diff would normally be.

so if that is the case what happens about wear, is there a life expectancy?

when i think of clutch packs i think of an auto trans, but in a trans the clutches only slip a little on engagement / disengagement so the wear is minimal, relatively speaking.

but if you have a centre clutch pack taking the place of a centre diff, i would think that these clutches are constantly slipping / engaging as the need arises, and controlled by the actuator motor / via computer inputs.

am i getting this right?? any knowledgable people want to educate me

Ewen

[X5Sport]

The E53 is indeed permannt four-wheel drive with a 40:60 front:rear default ratio. The X-Drive unit uses a wet multi-plate clutch controlled by an electric servo and is on the front drive output in the earlier versions. It only activates when the system detects a loss of drive on one pair of wheels so it then shifts the power to the other pair, and in extreme cases brings the ABS into play to control single wheel spin. The DSC system also uses it if you drive it like you stole it around corners to control under/over steer.

I've never heard of one wearing out, and given that it is not operating all of the time I would be surprised if it did unless the particular vehicle was used on loose surfaces all of the time - so needing a lot of traction shifting.

Under normal circumstances the slippage is going to be minimal which the wet multi-plate clutch will have been designed to cope with.

There's a detailed article here:

http://share.qclt.com/bmw资&#2...3%20xDrive.pdf

[bigwave2255]

wow thanks for that article, very informative

lots of stuff going on while im sitting back enjoying the drive

hehe

[Martin-C]

Thanks so much for this exchange of ideas and info. I have been looking for info about the working of the transfer box. I was told that my actuator needs changing and when I did some research, I found that there is a plastic gear that is actually a weak point in the system. The actuator costs about $800 USD and about $9600TT (that's my home currency in Trinidad and Tobago)