[Tim603]

Ive been trying to find a video or a good write up of how our xdrive transfer cases actually work. Ive done research on how different AWD systems work and 4x4 but I know our Xdrive is a little different.

Anyone know of any videos or write ups of how our transfer case works? (engages/ disengages/ transfers power, etc)

Thanks!

[floydarogers]

Google "xdrive transfer case"

Gives

as the first result.

[gtaccord]

As the video shows it works exactly like a t case in a 4x4 truck except it has a motor to infinitely control front lock up and only one ratio instead of a lever or button that says 4 hi 4 lo etc.

[Tim603]

I was on youtube and that video wouldn't load so I gave up, well it works now apparently

So the servo motor basically engages/disengages the front drive shaft by using a clutch, interesting

[gtaccord]

Correct.

[floydarogers]

Originally Posted by Tim603

I was on youtube and that video wouldn't load so I gave up, well it works now apparently

So the servo motor basically engages/disengages the front drive shaft by using a clutch, interesting

Originally Posted by gtaccord

Correct.

It also can complete disconnect the REAR drive shaft, sending everything to the front.

[jwzimm]

Originally Posted by floydarogers

It also can complete disconnect the REAR drive shaft, sending everything to the front.

Nope. The most it can do is send 50% of the power forward. The rear driveshaft is always powered.

[gtaccord]

Originally Posted by floydarogers

It also can complete disconnect the REAR drive shaft, sending everything to the front.

This is incorrect. It cannot do that. The bmw literature is misleading.

[floydarogers]

Originally Posted by jwzimm

Nope. The most it can do is send 50% of the power forward. The rear driveshaft is always powered.

The video (not that anyone should completely trust one source) says that 100% can go to the front. This statement: "However, this can be altered in one tenth of a second, with almost 100% of engine torque being applied to the front or rear axle." is contained within this article: http://www.carmagazine.co.uk/News/Se...ut-BMW-xDrive/
In this video (

), the guy says "100% to the front..." near the end.
And finally, this tech page on BMW's site says 100% front or rear: http://www.bmw.com/com/en/insights/t...echnology.html

[ajsalida]

Originally Posted by floydarogers

It also can complete disconnect the REAR drive shaft, sending everything to the front.

Complete bullshit. Please do some research for the system on e9x cars. The rear drive shaft is solidly connected to the transmission, no breaks. The transfer case hangs off of it, and clutches can engage the front drive shaft up to at most the same rate of rotation as the rear.

The stuff you are referring to is marketing BS by BMW to hide the fact that this is a particularly simple system. It works well but it CANNOT transfer 100% of anything to the front. The only thing it could do is if the rears were on ice (or up in the air), it locks up the TC and if the fronts have traction, technically 100% of drive goes to the front, but that is only because the rears have zero traction. The front driveshaft can turn no faster than the rear and therefore outside of artificial situations like the one I mention, no more than 50% of TQ can go to front wheels.

Said another way if the rears are not turning the front can't get any power at all, ever, under any normal circumstances with all four wheels on the ground. The rear cannot be disengaged, period.

edit: the video you first posted is either completely wrong, or it is referring to a newer xdrive system not available on e9x cars that I am not familiar with.

edit2: BMW marketing has been very sleazy with describing the xdrive system. They are doing everything they can to draw attention away from the fact that xdrive does not have a true center differential like some premium AWD systems of competitors. It is not a bad system, basically add-on to a RWD platform.

[floydarogers]

Originally Posted by gtaccord

This is incorrect. It cannot do that. The bmw literature is misleading.

Originally Posted by ajsalida

Complete bullshit. Please do some research for the system on e9x cars.

edit: the video you first posted is either completely wrong, or it is referring to a newer xdrive system not available on e9x cars that I am not familiar with.

Alrighty, but I've posted links to lots of people saying 100%. Post something that disputes it, please. (I'm guessing that you can't, but I remain open-minded about that.)

If "the literature is misleading", then it's misled plenty of people (journalists) who would love to find errors in BMW's statements - money for them!

[ajsalida]

Originally Posted by floydarogers

Alrighty, but I've posted links to lots of people saying 100%. Post something that disputes it, please. (I'm guessing that you can't, but I remain open-minded about that.)

If "the literature is misleading", then it's misled plenty of people (journalists) who would love to find errors in BMW's statements - money for them!

You are wrong, sorry. Look inside a diagram for the TC, this gets discussed and shot down every year or so on this forum. Better yet get under your car and look at the TC, work it out in your head (if you can, I remain open minded about that). Hell look at the beginning of the second video you posted. Notice where the drive shaft comes out of the tranny?

Please understand that 100% just refers to power being put to the ground, this is where the weasel-speak is. The rear axle cannot be disconnected, so the only way 100% of drive power gets put to the ground in front is if the rears have zero traction and the front has traction. But they still turn at the same rate, get it?

[ajsalida]

Here stare at this for a while. Part #8 is the solid Rear drive shaft connecting the tranny through the TC to the rear end. It cannot be disengaged. The clutches, fork, etc. hang off of this and engage/disengage front drive shaft (connected to #42) via control of the electric motor, #27.

[wdeerfield]

it keeps me on the road with my snow tires on the way to the mountain. who cares if it cant send all the power to the front and disconnect the rear, it works just fine as is. i do like that it can send all the power to the back though, thats nice for highway commuting.

[ajsalida]

Just to complete the explanation, 12 & 14 are the clutch and "flywheel". 14 slips onto splines on the rear driveshaft, it is locked to it. The motor 27 pulls 12 towards 14 to engage the clutch and pushes it away to disengage.

42 is connected to the gear 44 on a short splined shaft. It rotates at whatever the rate the front driveshaft rotates. 44 is always meshed with the gear 33, which is always meshed with the gear on 12. 12 slides forward or back depending on the electric motor 27, engaging or disengaging the whole assembly with the rear driveshaft.

QED

[Hobbs64]

Not to bring an old thread back to life, but I'm wondering how complicated it would be to create a control module (like a rheostat) that would allow for manual selection of the amount the servo motor engages the clutch in the t-case? I only ask because I want to put an S62 in my E90 and keep the AWD. If I can manually control torques split then I can install the engine in stand-alone. Any thoughts anyone?

[nsjames]

it's a stepper motor, so you'd need a driver. and you'd have to figure out how much current to drive it with and how many steps it has.

[blueloco]

Ditch the motor and put a cable on it. Drive it from a handbrake lever or something similar.. In all seriousness the X drive system is pretty good from BMW. Taking manual control really doesn't make any sense unless you want full lock or off modes. No way you can modulate a friction clutch pack fast enough to keep up with changing conditions.
From a performance and handling perspective I think it is better than conventional truck & SUV systems, and better than the open diff brake assisted stuff that cheap AWD cars seem to be getting. Better than viscous coupling systems for many reasons. Never driven a torsen center diff AWD car, hear they are good but they seem to have fallen out of favor by the makers. Overall I can't see messing with it helping in any way unless you wanted to make a rock crawler from on E90, which might actually be a cool project. But at that point?? Weld it up and make it permanent 4x4 or put in a 4x4 truck frame.

The front diff bolts to the pan and there is a tunnel through the oil pan. Did the S62 come in an X-drive car?

[carguy138]

Blueloco: here's my experience of torsen vs xdrive.

Drove a quattro A4 (torsen center differential) for 5 years and it is quite awesome in snow/gravel/mud. Big step above xdrive or the systems most crossover AWD cars use these days (i.e. transverse motor with clutch pack to rear driveshaft). The upside with xdrive is that it feels more like a RWD car and allows you to briefly kick the rear end out on wet/dry roads.

Doing donuts in a parking lot with summer tires on snow/ice won't really show the difference. It starts to become much more apparent with good tires at higher speeds. Most people will never experience the below and that is why manufacturers are moving away from them. Heavier and more expensive to produce.

When I say better, I mean in terms of predictably at higher speeds. In the torsen based AWD (Audi Quattro A4 and bigger, or some subarus), they respond the same way-every time. Take for instance powersliding in 3rd/4th gear on snow, or 2nd/3rd on gravel/mud. With the torsen based system you get an unbelieveable amount of confidence and ability to hold a slide under power. You also have that feeling that if you stay on the gas, it will straighten out predictably.

With the other systems, such as xdrive, it becomes very unpredictable and apparent that the ECU doesn't want you sliding. Here is the best explanation from my experience.

On an xdrive, say 3rd gear in snow with Blizzaks, and traction control fully off. Once you initiate the powerslide, all feels well. Then at some point the computer starts reacting by trying to lock up the center transfer case to reduce the slip angle. It just feels very reactionary and unpredictable. Dangerous when you are loading up the suspension with a significant slip angle.

For blasting around back roads in the winter (think northern NH or VT), torsen based systems are much better due to the consistency.

[nsjames]

Originally Posted by carguy138

Blueloco: here's my experience of torsen vs xdrive.

Drove a quattro A4 (torsen center differential) for 5 years and it is quite awesome in snow/gravel/mud. Big step above xdrive or the systems most crossover AWD cars use these days (i.e. transverse motor with clutch pack to rear driveshaft). The upside with xdrive is that it feels more like a RWD car and allows you to briefly kick the rear end out on wet/dry roads.

Doing donuts in a parking lot with summer tires on snow/ice won't really show the difference. It starts to become much more apparent with good tires at higher speeds. Most people will never experience the below and that is why manufacturers are moving away from them. Heavier and more expensive to produce.

When I say better, I mean in terms of predictably at higher speeds. In the torsen based AWD (Audi Quattro A4 and bigger, or some subarus), they respond the same way-every time. Take for instance powersliding in 3rd/4th gear on snow, or 2nd/3rd on gravel/mud. With the torsen based system you get an unbelieveable amount of confidence and ability to hold a slide under power. You also have that feeling that if you stay on the gas, it will straighten out predictably.

With the other systems, such as xdrive, it becomes very unpredictable and apparent that the ECU doesn't want you sliding. Here is the best explanation from my experience.

On an xdrive, say 3rd gear in snow with Blizzaks, and traction control fully off. Once you initiate the powerslide, all feels well. Then at some point the computer starts reacting by trying to lock up the center transfer case to reduce the slip angle. It just feels very reactionary and unpredictable. Dangerous when you are loading up the suspension with a significant slip angle.

For blasting around back roads in the winter (think northern NH or VT), torsen based systems are much better due to the consistency.

I would say this greatly depends on the manufacturer and the programming.

You are correct that the xdrive is fun police, and freaks out if you slide the car.
My wife's Volvo, yes, the "safe" car, will do slides completely controlled at 40 MPH in 3rd gear with the motor high in the rev range all day long. It is a haldex clutch pack on the rear pinion system.

I assume BMW has programmed the xdrive like this because their reasoning is "If you want a fun car, buy a RWD one."