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E46 Xi Forum
The E46 XI was produced from 01-05 in sedan and touring body styles. Powered by either a 2.5L inline 6 in the 325xi or a 3.0L inline 6 330xi. Discuss all thing about BMW AWD E46 'Xi' here.

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Old 12-08-2010, 02:01 PM   #1
conv440
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60/40 Power Split

Maybe a stupid question but I've read that our XI AWD system transfers 60% power to the rear wheels and 40% power to the front. Ok fine, but how does this work? The front and rear wheels turn at the same speed. If you gear the fronts down through the transfer case to reduce the power won't that also make them turn at a slower speed? Maybe it's the definition of the word 'power' that is throwing me off. Can anyone enlighten me?
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Old 12-08-2010, 02:20 PM   #2
Capt1014
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The Computer
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Old 12-08-2010, 02:21 PM   #3
ProchaineStation
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usually all AWD systems are like that, even audi
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Old 12-08-2010, 02:28 PM   #4
conv440
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Say I have an electric vehicle with motors for the front and rear wheels. I can put a 40 HP motor on the front wheels and a 60 HP motor on the rears. They will have different horsepower at any given speed but both motors are turning at the same RPMs. How do you do that with a single engine and a transfer case?
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Old 12-08-2010, 02:42 PM   #5
SamDoe1
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Originally Posted by Capt1014 View Post
The Computer
Computer doesn't touch the transfer case.

It works through a planetary gearing system. Engine power comes out of the transmission and into the transfer case. Engine power goes to the front drive shaft through the sun gear of the planetary set the ring gear provides power to the rear wheels. The whole process is worked out so that the wheels turn at the same speed, it's all in how the gearing is set up in the system.

Google planetary gears for more info.
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Old 12-08-2010, 04:16 PM   #6
dephantn
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Our E46 xi use old style transfer case with planetary gear as SamDoe1 said to make Front & rear wheel same speed but 40/60 torque (all mechanical)
The new Xi & X5 use clutch and chain in transfer case , the clutch control by DTS/ABS to run the motor to press the clutch, so the torque can transfer to front or rear when it need, to 100 % .
The X5 even has the clutch ( option ) between two rear wheels to control & can sends the torque 100% to either rear wheel, all makes Bimmer xi the best slip handling.
It can go up hill with one side good road & other side icy , stop and go again.
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Old 12-08-2010, 04:18 PM   #7
GCoop
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62/38

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Old 12-09-2010, 07:17 AM   #8
Capt1014
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Originally Posted by SamDoe1 View Post
Computer doesn't touch the transfer case.

It works through a planetary gearing system. Engine power comes out of the transmission and into the transfer case. Engine power goes to the front drive shaft through the sun gear of the planetary set the ring gear provides power to the rear wheels. The whole process is worked out so that the wheels turn at the same speed, it's all in how the gearing is set up in the system.

Google planetary gears for more info.
Oh.
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Old 12-09-2010, 09:07 AM   #9
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So basically the newer XDrive is an electronic computer controlled version of the ix viscous coupled drive train.
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Old 12-09-2010, 09:40 AM   #10
SamDoe1
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So basically the newer XDrive is an electronic computer controlled version of the ix viscous coupled drive train.
Yes, but only to control torque split front and rear. Unlike what was said before, the xdrive system only does front to back. Any left to right slippage is still dealt with by the DSC system. There are no clutches in the differentials, both of them are normal open diffs with the DSC braking the slipping wheel to send power to the other wheel. The center diff does have a clutch system which sends power front or back as needed and is computer controlled.
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Old 12-09-2010, 10:18 AM   #11
latitude39
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Diagram for 60/40 power split

Quote:
Originally Posted by conv440 View Post
Say I have an electric vehicle with motors for the front and rear wheels. I can put a 40 HP motor on the front wheels and a 60 HP motor on the rears. They will have different horsepower at any given speed but both motors are turning at the same RPMs. How do you do that with a single engine and a transfer case?
I have done some research into the New Venture 124 transfer case that is on our e46 (2001-2005 325xi and 330xi) models. I hope this helps. Please note that I am not an authority on this--just an interested enthusiast.

I have asked the same question: what is going on in the transfer case to make the 60/40 split happen? I've attached two diagrams I found. The first diagram shows the planetary gears (ring gear, the 3 planet gears, and the sun gear). I summarized my understanding, in terms of input from the transmission and outputs to the front and rear driveshafts:

• Input from the transmission turns the planetary carrier—the housing that holds the 3 planetary gears together as a unit. The small planetary gears in the carrier are meshed with both the larger sun gear, and the surrounding ring gear.
• Output to the rear driveshaft comes directly from the ring gear, which is driven by the planetary gears.
• Output to the front driveshaft comes indirectly from the sun gear, which is driven by the planetary gears. The sun gear then turns the transfer gear(not shown on this diagram), which, in turn, turns the output gear that is connected to the front axle.

The second diagram shows a cutaway view of the TC with the planetary unit at the top, the "transfer gear" in the middle, which turns the front driveshaft.
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Old 12-09-2010, 09:40 PM   #12
pjaneiro
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Originally Posted by ProchaineStation View Post
usually all AWD systems are like that, even audi
Yes, But Audi is the reverse

68% front
32% rear

Bleh !!!
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Old 12-13-2010, 12:35 PM   #13
welcher330xi
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Audi used to be 50/50 until slippage but is now 40/60 (front/rear).

Excluding Haldex equipped models
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