CFRP Output shafts

Also known as: side waves

In the course of the electrification of vehicles, there are various engine concepts and variants for power transmission. However, the limitation of range in comparison to classic vehicles with combustion engines still poses a major challenge. In addition to the performance capacity of the battery storage cells, a vehicle weight that is as low as possible is the biggest adjusting screw for the urgently required range improvement. Which drive concepts will prevail in the future is still uncertain. One thing is certain, however: with the help of lightweight drive shafts and new lightweight output shafts, DYNEXA will and can make a contribution to the global mobility future even in the short term.

State of the art

For power transmission in vehicles, lightweight drive shafts with shaft tubes made of carbon fiber-reinforced or glass fiber-reinforced plastics and various joint technologies have been state of the art since the 1990s. The power transmission takes place in:

  • Classic” design: in the front engine from the manual transmission to the axle drive (2WD) or the two axle drives (4WD).
  • Transaxle” design: from the front engine to the rear manual transmission.

Due to the high stiffness and low density of the modern high-tech material, these fiber composite shafts are longer than metal shafts of the same outer diameter. To compensate for this, rear-wheel-drive vehicles with a metal construction often use two-piece shafts with intermediate bearings. Total lengths of approx. 1000 mm to approx. 3000 mm (in commercial vehicles) must be bridged. If fiber composite shafts are used, in addition to the primary weight saving through the lightweight shaft itself, the intermediate bearing components and the unfavorable acoustic bridge to the passenger compartment for acoustic reasons can also be omitted. In addition to the lightweight construction and the associated conservation of resources, the more direct response behavior of the one-piece composite fiber shafts during load changes improves both driving behavior and safety. This is offset by the additional costs of high-tech lightweight construction materials compared to the renowned solutions made of steel or aluminum.

But what about the significantly shorter output shafts or side shafts, which serve the final power transmission from axle drive(s) to drive wheels and road? There, it is only necessary to bridge lengths of approx. 200 mm to approx. 500 mm. Can the required torques be transmitted from the lightweight output shafts in the near-wheel installation space of the vehicles? Don’t possible bending and torsional vibrations pose any challenges at operating speeds? Are weight savings at all still possible with the aid of short fiber composite pipes compared to metallic competitor products? Many textbooks answer these questions with a clear “no”…

Antriebswellen BMW

New concept cfrp output shaft

In order to clarify the above questions in practice, DYNEXA has developed an output shaft concept with shaft tubes made of carbon fiber-reinforced plastics and compared it directly with its metallic competitors. In vehicle tests, the prototypes dimensioned and manufactured by DYNEXA were subjected to the toughest tests. The results and findings obtained made the audience sit up and take notice.

  • Installation space: Due to the mandatory suspension travel of the bike, installation space was available in sufficient form. This favored a dimensioning and design of the new DYNEXA product “Composite Output Shaft” suitable for fiber composites.
  • Torque transmission: The output shafts from DYNEXA in the vehicle were also convincing here and were in no way inferior to the metal competition in the transmission of up to 3000 Nm.
  • Vibration behavior at speed: Speed behavior and vibration behavior in torsional and bending direction proved to be good-natured and problem-free. 

– Weight: The elimination of the vibration absorbers, which are absolutely necessary for metal competition, contributed to weight savings: they did not have to be “dragged along” by the DYNEXA shafts as additional weights. If the perfectly suitable DYNEXA interference fit is used to transmit torque from both joint elements to the fiber composite shaft tube, a metallic hub overlaps both fiber composite tube ends inside. The joint pressures required for torque transmission there place additional stress on the components in comparison with the generally welded solid metal solution and require a local support ring overlapping the outer diameter of the pipe. Despite these additional components required in comparison to solid metal technology and the relatively short carbon-fiber-reinforced shaft tube with a diameter of approx. 250 mm, a weight saving of 20 to 25% compared to the steel solution could be achieved, among other things by using the integral carbon-fiber support rings used by DYNEXA.