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BMW's xDrive all wheel drive system

Pro-active automatic all wheel drive system. The rear wheels are powered at all times. Torque can be transferred to the front wheels via electronically controlled multi plate clutch that is located in the transfer case. XDrive does not have a center differential. Most of the time, the clutch is partially locked and power is transferred to both axles in proportion 40/60 front to rear. The power distribution can be altered to continuously variable levels (from 50/50 to 0/100). For example, when driving at high speed, or when parking, the clutch is disengaged and all power goes to the rear wheels.
XDrive is linked to DSC (Dynamic Stability Control) - when the vehicle understeers, the clutch is disengaged thus transferring more torque to the rear wheels (0/100 torque split). When oversteering is detected, the clutch locks fully transferring more power to the front wheels (50/50 torque split).
DSC (Dynamic Stability Control) also brakes wheels individually to regain traction and to help cornering.
XDrive intervenes before the car becomes unstable and is unnoticeable by the driver.

xdrive bmw

x5 xdrive transfer case

Last updated: 16-Jan-2010 23:21

There are 6 comments
matt
February 14, 2009 - 19:24
Subject:

sounds crappy.. needs to be taken care of - clutch + it is reactive: it acts after the wheelspin has already occurred. torsen based 4wd is proactive - it acts BEFORE wheelspin occurs + there's not much to wear out!

Reply to matt
George
October 02, 2009 - 22:45
Subject: xDrive

This system doesn't have to be reactive. There can be initial pre-load on the coupling (easily changeable via software) and that can be variable depending on steering angle. (more if the front wheels are straight)
Seeing as BMW (and almost everyone) use throttle-by-wire, if the software detects that you have 'floored' the throttle, the clamp load can go to maximum, resulting in no rear wheelspin-maybe both tires on the same side, then traction control will brake those two.

Under extreme conditions, when you operating outside the torque bias ration, this can be better than a torsen differential.

hassan
February 08, 2009 - 14:02
Subject: BMW Hill Decent Control

I could not understand how HDC works and where is it located in the vehicle? (hill descent control) this is on a automatic transmission.

Reply to hassan
awd.ee
February 08, 2009 - 14:15
Subject: BMW Hill Decent Control

Hi Hassan. You can find HDC description on the BMW web site
http://www.bmw.com/com/en/insights/technology/technology_guide/articles/hill_descent_control.html

See youtube video:

http://www.youtube.com/watch?v=YUMi_O7Ojqk

WISSAM
January 05, 2009 - 13:52
Subject:

DEAR SIR
AT WHAT VEHCILE SPEED X-DRIVE STRAT ACTIVE

Reply to WISSAM
awd.ee
January 06, 2009 - 10:54
Subject:

Hi,
I am sure the x-drive four wheel drive is active right from 0 kph.
http://www.youtube.com/watch?v=dGWsogAlZLE

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