The power train normally consists of:

  • Driving element (prime mover)
  • Coupling element (coupling, gearing, etc,)
  • Driven element (driven machine)

The power train transmits mechanical power which can be calculated from speed and torque. In the area of mobile hydraulics, mainly used are prime movers that employ the piston principle (diesel engine). These engines do not transmit their power uniformly to the crankshaft during a revolution. The torque induced in the crankshaft by the cylinder varies significantly, but can be reduced by increasing the number of cylinders through larger centrifugal masses. The driven machines frequently used in this area are pumps, compressors or generators.

Vibrations are caused by the firing order of the engine on account of the frequency. Since the material (steel) has an elastic behaviour with a specific weight, these vibrations are transmitted, producing an oscillatory system with a specific frequency. If this system is excited with natural frequency and not damped, this could cause resonance as the oscillation amplitude increases dependent upon the excitation amplitude, resulting in failure of the system.

To prevent this happening, highly elastic torsional vibration dampers (couplings) are normally used that serve not only for amplitude damping, but also set the first natural frequency to an uncritical state.

Used in these torsional vibration dampers are special elastomers with highly elastic and damping properties. The materials used are natural rubber or temperature-resistant silicon based. These couplings can nonetheless fail due to high dynamic loads attributed to different causes.

Failure cases:

  • Fatigue (fatigue fracture)
  • Thermal destruction (reversal)
  • Forced rupture
  • Ageing

The most frequent cases of damage can be attributed to failure as a result of fatigue and thermal destruction. The high damping work gives rise to heat development which has a negative effect on the elastomer material, whereby the molecule chains are split and the material hardens.

There are now no specific vibrating damping properties and the vibrations produced by the diesel engine are transmitted via the coupling into the gearbox where they are also liable to cause damage.