BW44-44 transfer case
I've been following this thread, and others like it since I bought my sport in Feb.
Out of curiosity and concern, I've done some testing and disassembly to try and figure out how this TC works. I have a mechanical engineering background, so the mechanicals are very simple. The electrical and computer controls took a little more effort.
The part of the system that seems to be questionable is a three part system, called, and patented by a BW engineer, the electromagnetic clutch with ball ramp actuator and torsion spring.
The ball ramp can simply be thought of as a type of big ratchet. This is why the system doesn't bind, the ball ramp acts as a ratcheting mechanism between the front and rear drive systems. When turning, and the front wheels are following a larger radius than the rear wheels, these ratcheting mechanism (ball ramp), allows the front wheels to rotate at a higher speed than the rear wheels. Simply put, if your in a turn and have good traction, then you're being pushed along by the rear wheels only. Should the rear wheels begin slipping such that their speed becomes = or > than the front wheels, the ball ramp will start driving the front wheels too.
Next I'll discuss the electromagnetic actuator, torsion spring and the clutch pack. I'll refer to the front drive system, it's associated clutch plates, shafts, wheels, etc, as the "driven" system. Also, I'll refer to rear wheels, clutch plates, ball ramp, etc as the "drive", system.
In a nutshell, the ball ramp is disabled, and no torque throughput allowed, unless the electromagnetic actuator is energized, thus enabling the ball ramp. When the electromagnetic actuator is energized, the ratcheting mechanism between the driven system and the drive system is engaged. So, regardless of the knob setting in the cab, the entire ball ramp clutch system can only exist in 2 possible states energized, and not energized.
The system doesn't use the typical pressure plates/springs found in common clutches, rather the ball ramp itself applies the compressive forces between the clutch's drive plates and driven plates. As the ball ramp, is a torsional ramp, like a screw, the more torque = more compressive forces on the clutch plates.
So, in a nutshell. When the electromagnetic actuator is off, the clutches are disengaged.
When the electromagnetic actuator is energized, the rear wheels will need to spin about 1/2 turn 180° ramp/ball arrangement, before the ball ramps apply sufficient axial force to the clutch plates to engage the front, driven system. If you let off the throttle, then the torque differential between the drive/driven systems dissapear and the torsion spring returns the ball ramp to it's unlocked position. If you then mash the throttle again, (assuming the electromagnetic actuator is still energized), the rear wheels and hence the drive portion of the ball ramp will rotate untill
it catches up the the driven portion of the ball ramp (within 180° of rotation (2 180°opposed balls/ramps). , like a ratchet, it will begin rotating the front, driven, system again.
Now, to the electricals:
Really simple, I isolated the circuit under the truck, that controls the electromagnetic actuator, and put my multimeters hall effect coil around it. Testing in mud and snow in the north Cascade mtns.
4 auto only shows current when the rear wheels slip. So, in 4 auto, when the rear wheels start slipping there is current flow to the electromagnetic actuator. As soon as the front wheels start spinning at the same speed as the rear, the current flow disappears. The front wheels continue to spin in the mud, even without the electromagnetic actuator powered. Obviously as long as there torque being applied to the ball ramp, they stay locked together. If I let off the gas then hit it again, same results. Rear wheels spin first, then the multimeter shows current flow and then front wheels spin. Front wheels reach the same speed as the rear the the multimeter shows the current turns off. All wheels continue to spin untill I let off the gas.
Now to 4 lock and 4 low:
The circuit to the electromagnetic actuator shows current flow. At idle, at all throttle settings, and with the steering wheel turned from lock to lock.
This means that in 4 lock or 4 low, the determinant factor will be torque applied to the 2 halves of the ball ramp. If there is sufficient torque to overcome the torsion spring, the front wheels will be driven. If there isn't, they won't.
The videos posted showing a vehicle at idle, in 4 low, with the rear wheels only turning are likely the result of the drive system not applying sufficient torque to the ball ramp, to overcome the torsion spring and engage the driven portion. It may be that so little torque is applied to the ball ramp under those conditions that it simply isn't engaging. If it took more than the smallest amount of throttle to get the front engaged, then likely there's a problem.
Possibly something out of adjustment or clearanced incorrectly.
So, in summary:
2wd:
no power to the ball ramp, only the rear wheels pushing.
4auto:
no power to the ball ramp unless, rear wheels spin faster than the front, computer momentarily energizes the ball ramp and the rear drive system engages the front, driven, system untill rear and front wheels speed match. Front system is driven untill front wheels rotate faster than the rear wheels, such as in a turn, thus allowing the balls to drop out of the ramps. And disengage the driven system.
4lock and 4 low:
Under all conditions the ball ramp is energized. Any time the rear wheels (drive system) rotate faster than the front wheels, the ball ramp will ratchet the front (driven system) along at the same speed. If the front begins tracking around a larger radius than the rear (all turns), the ratcheting nature of the system will allow it to do so freely, with no binding. (Theoretically, if you turn at a radius that advances the driven system 179° beyond the balls engaged position, the next time you encounter a slip situation the rear wheels will spin appx 1/2 turn before the front engages).
This little review shows only the facts. I have no opinion regarding the comparitive effectiveness of this system, as I'm not an off road enthusiast. I'm a nerd. This system could be the best thing since sliced bread or complete garbage and I wouldn't know either way. My truck is very pretty though��, in it, from a distance, I look kinda off-roadsey.
Hope this was helpful.
asking for a friend !!!!:********:
