Paralever
In newer BMW motorcycles with cardan drive , the Paralever ensures that the disruptive reaction forces of the cardan drive are reduced.
Gimbal reaction forces
The drive via a longitudinally arranged cardan shaft requires a deflection of the drive torque by ninety degrees in order to drive the transversely arranged rear wheel. A bevel gear on the rear wheel, consisting of a housing, pinion on the cardan shaft and crown wheel to drive the rear wheel, is used for this.
For very many kardanwellengetriebenen motorcycles is the crown of the bevel gear inside the wheel, see sketch. This has been the case with BMW motorcycles since 1955; older BMWs still had the crown wheel on the outside.
With this type of power transmission, the acceleration of the motorcycle leads to the rear lifting. The reason: a more or less strong "climbing" of the pinion on the ring gear. When the accelerator is released, the rear of the machine lowers. This behavior, which is not unique to BMW motorcycles, led to instructions in books and magazine articles that it is better to accelerate slightly in curves for even more lateral inclination, in order to “climb” the parts of the motorcycle that would otherwise have touched down on the cardan - but in any case take off the accelerator Avoid tight bends “out of fear”.
When accelerating hard in a bend, the front wheel of the motorcycle rebounds. This changes the steering head angle and the motorcycle drives a larger radius (understeer). This effect is not welcome on very sporty machines. To reduce this, the stern should not plunge into the throttle, if necessary rebound a little. This is why a geometry is often chosen for the chain drive for very sporty motorcycles, which allows the rear to rebound slightly. This means that you no longer need a rear wheel suspension that is too hard to prevent the rear end from deflecting. The geometry chosen by BMW suits very sporty motorcycles. Touring motorcycles, however, are often built with a dipping rear swing arm.
Concept of a parallelogram of forces
The concept of a "constant-angle" rear suspension in connection with a cardan drive and two universal joints was used as early as 1909 in a Wilkinson TMC.
For the most part, the Paralever avoids these chassis reactions - which otherwise take a lot of getting used to for BMW motorcycle newbies: The bevel gear on the rear wheel is articulated to the swing arm. The drive torque is absorbed by an additional strut. The strut and the rear swing arm are the same length and the attachment points on the rear wheel and on the frame are the same distance apart. The resulting joint parallelogram prevents the axle housing from twisting and thus keeps the suspension free of drive forces.
Designs from other manufacturers
The Italian manufacturer Moto Guzzi introduced a similar but simpler construction with the CARC ( Cardano Reattivo Compatto ): like BMW, Moto Guzzi uses an additional strut to balance forces in a parallelogram, but without an articulated joint. The strut prevents the cardan tube from lifting as a reaction to the peripheral force of the pinion that occurs during acceleration . The complex articulation joint is a complication, some also refer to it as "over engineered" - as the result of idealized force calculations, which result in a shorter joint distance in the vehicle's longitudinal direction than the distance from the pivot point to the rear wheel axle. In order to guide the articulated joint in a stable manner, a wide and therefore heavy tube and additional, stable mounting are required.
Joint problems
With the rear articulated cardan shaft joint, BMW motorcycles showed some damage in the first few years after its introduction: some of the first examples failed early, sometimes after only 30,000 kilometers, with severe joint damage and even broken shafts. The cardan shafts of the Paralever BMWs ran dry again, as they did before 1955, and not in an oil bath as before. The more modern Paralever design of the second generation, with a sliding joint and a pivot point moved from the center of the cardan, turned out to be more reliable.
See also
Web links
Individual evidence
- ↑ Freely adapted from Gaetano Cocco: The balance of the motorcycle. In: Motorrad-Technik pur , translated by Waldemar Schwarz, 1st edition 2001, Motorbuch Verlag, from page 83.
- ↑ Freely adapted from Gaetano Cocco: The balance of the motorcycle. In: Motorrad-Technik pur , translated by Waldemar Schwarz, 1st edition 2001, Motorbuch Verlag, page 86.
- ^ Hugo Wilson: The Lexicon from the motorcycle. MotorbuchVerlag, ISBN 3-613-01719-9 , p. 197.
- ↑ Moto Guzzi Breva V1100 and Griso 1100. bikerszene.de, accessed on February 7, 2014 .