General Overview of BMW automotive Universal Joint Driveshafts
BMW driveshafts, with few exceptions, are of the two-piece design. This design of driveline completely eliminates natural frequency vibrations commonly found in many one piece driveshafts.
Most BMW driveline designs use a rubber flex disc to connect the transmission to the driveline. This flex disc absorbs torsional vibrations from the engine/transmission and reduces shock load to the driveshaft and rear axle. The driveshaft is supported by a ball bearing, encased in a soft rubber cushion. This cushion also dampens unwanted driveshaft vibrations, and to some extent both the flex disc and the support cushion can be "tuned" to the specific arrangement of chassis, transmission and rear axle.
The front half of a BMW driveshaft, (excepting early 1600's) is connected to the rear driveshaft with a universal joint and either a fixed or sliding spline. A universal joint is a precision bearing, which allows for small angle changes from engine/transmission movement. BMW driveshafts use an extremely precise design of universal joint with considerable torque carrying capacity for its size.
The BMW universal joint is quite interesting. Unlike most designs, the roller bearings are contained in a thin shell, stamped from an exotic alloy sheet metal 1 mm thick. It is formed accurately enough to not require subsequent machining and is heat treated sufficiently by the force of the stamping to not require subsequent heat treating. The thinness of this bearing cap allows a large cross and larger roller bearings to be utilized, greatly increasing both strength and bearing life, while keeping size and weight low.
The rear of a BMW driveline (again, excepting early 1600's) uses either another universal joint or a constant velocity joint. They both serve the same purpose, to take up small angle changes, and the constant velocity joint furthermore allows for small length changes in the driveshaft.
BMW driveshafts also utilize an extremely strong tubular section. It is made from a special steel and cold-worked for additional strength, which saves weight compared to other designs of drivelines. The tubing is inertia, or friction welded, to the ends allowing very fast and accurate manufacturing of BMW driveshafts.
Just the type of sophisticated design BMW is noted for!
Another interesting feature of the most common BMW driveshaft design is that the front driveline is usually centered directly off the transmission main shaft. This driveline design causes BMW driveshafts to rotate with the smallest amount of radial run-out possible. Additionally the rear part of a BMW driveshaft is centered with the next most accurate means, a precision piloted fit flange.
In summary, BMW takes great advantage of state of the art techniques and designs in the manufacturing of their driveshafts. If you would like more information about BMW driveshafts or Driveline Service of Portland's line of remanufactured driveshafts for BMW automobiles please contact us by any means below.