Power Distribution

March 15, 2012 | By | Reply More

The E30 chassis was the first to sport four-wheel-drive here in America, and the original X5 (E53 chassis) was released in 2000 with a 4.4L V8 that produced 282 horsepower. In 2002, the 4.6L M62TU was added, which brought the horsepower up to 340, and this trend has continued.

transfer case id

Sometimes a physical inspection is all you need to identify the transfer case model. Look at the top line and you can see this is a New Process NV125. This means it has a planetary gearset that is full-time 4WD, and a 32% front/68% rear torque split.

So, how is all this horsepower translated into acceleration without simply burning up the tires?  The logical answer is through 4WD, which feature has grown in numbers at BMW. In 2001, the E46 chassis 325xi Sport wagon and the 325xi and 330xi sedans received the 4WD treatment. In 2004, the new xDrive system  was introduced in the X3 (E83 chassis), and in 2006 the 5 series E60 (Sedan) and E61 (Wagon) chassis  were offered with the xDrive system. That is quite an extensive offering of 4WD vehicles, and more have been added every production year.  Of course, besides harnessing huge amounts of horsepower on pavement, this feature keeps you going in snow, or off-road, and improves weight distribution and stability control.

The X5 in particular was designed to handle well in on-road and off-road situations. There are many technological advancements that come standard on the X5. ABS (Antilock Braking System) and ASR (Anti-Slip Regulation) are standard, with DSC (Dynamic Stability Control) available as an option.  All of these systems are specifically tailored to the E53 chassis.  They also work with the newer BMW xDrive system. The combination of these various systems helps enhance traction and improve vehicle control. Now it’s our job to maintain  their performance.

How does  4WD work?

The first transfer case used in 4WD BMWs was the New Process NV125 unit. The main component of the NV125 is the planetary gear set. This is what divides the torque to the front and rear differentials.

ATCcomponents

Here are the key components of the ATC transfer case. The input shaft directly drives the rear output shaft. The servo motor can engage or disengage the clutch that drives the front axle. This VTG system has a control unit with self-diagnostic capability.

Here’s how it works: The transmission output shaft drives the entire planetary carrier, which provides a 68% rear/32% front torque split between the drive shafts. An annulus gear driven by the carrier directs power to the rear drive shaft. Sun gears in the planetary gearset transmit torque to a drive chain that then drives the front axle drive shaft. This is a very strong design that is usually trouble-free. A key benefit is the ability to split torque under varying conditions thanks to the ADB (Automatic Differential Brake). When the DSC control unit senses a loss of traction based on input from the wheel speed sensors, the brakes are pulsed on the wheel that

 

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Category: Steering + Suspension, the bimmer pub

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