What is torsional vibration damper? (2023)

What is torsional vibration damper?

Torsional Vibration Dampers absorb rotational vibrations in internal combustion engines. The dampers are particularly effective in conjunction with decoupled pulleys, which keep crankshaft irregularities away from the belt drive and auxiliaries.

Torsional vibration is angular vibration of an object—commonly a shaft along its axis of rotation. Torsional vibration is often a concern in power transmission systems using rotating shafts or couplings where it can cause failures if not controlled. A second effect of torsional vibrations applies to passenger cars.

Vibration dampers are used to absorb vibration emanating from machinery, pedestrian traffic, etc. primarily to reduce the noise associated with such vibration and to procure a more comfortable environment.

In industrial applications, the most common equipment where torsional vibration testing is important is with variable frequency drive (VFD) motors driving large inertia fans and reciprocating engines/compressors. For VFD's, problems can occur due to tuning of the drive.

Torsional vibrations are an example of machinery vibrations and are caused by the superposition of angular oscillations along the whole propulsion shaft system including propeller shaft, engine crankshaft, engine, gearbox, flexible coupling and along the intermediate shafts.

Undamped torsional vibrations (rotations back and forth) of a wheel attached to a thin elastic rod or wire satisfy the differential equation I0θ″+kθ=0, where θ is the angle measured from the state of equilibrium, I0 is the polar moment of inertia of the wheel about its center, and k is the torsional stiffness of the ...

A vibrating motion can be oscillating, reciprocating, or periodic. Vibration can also be either harmonic or random. Harmonic vibration occurs when a vibration's frequency and magnitude are constant. A vibration is random when the frequency and magnitude vary with time.

A torsional natural frequency of a mechanical system is a frequency at which the inertia and stiffness torques are completely in balance (see App. C). In the absence of damping in the system, forcing the mechanical system at this frequency would generally result in a theoretical infinite vibration response.

Vibration isolation prevents vibration transmission. It keeps vibration energy from entering an object, such as a structure or piece of equipment. Vibration damping dissipates vibration energy. It absorbs or changes vibration energy, reducing the amount of energy transmitted through the equipment or structure.

A typical vibration absorber is a single-DOF spring/mass/dashpot system that is attached to a vibration body. The stiffness and mass of the absorber are designed in order to produce an "anti-resonance" in the total system response.

How do I reduce torsional vibration?

Torsional Vibration occurs in the crankshaft of the engine mainly because of the tangential forces acting on the crankshaft when rotating at some RPM. All the above vibrations may cause wear down of internal components, loosening of holding bolts, damage to the engine structure, and even failure of the crankshaft.

Taking a shaftline of a certain length, it is possible to modify its natural frequency of torsional vibration by adjusting the diameter: a small diameter results in a low natural frequency, a larger diameter in a high natural frequency. The introduction of a tuning wheel will also lower the natural frequency.

The excitation that causes torsional vibrations of crankshaft is the Gas firing pulse phasing in the cylinders of an engine. The Crankshaft natural frequencies get excited several times through out the operating speed of engine by different components of firing pulse harmonics, called orders of an engine.

The time for one complete vibration is called the period (T) and is measured in seconds. For example, if the period of a vibration is 0.1 second (one vibration takes 0.1 second), the frequency of the vibration is 10 vibrations per second or 10 hertz.

Often described as torque per unit deflection, torsional stiffness is significant in positional systems and describes a coupling's resistance to torsional deflection. Torsional deflection is the inverse of torsional stiffness and is defined by deflection per unit torque.

Torsional Vibration occurs in the crankshaft of the engine mainly because of the tangential forces acting on the crankshaft when rotating at some RPM. All the above vibrations may cause wear down of internal components, loosening of holding bolts, damage to the engine structure, and even failure of the crankshaft.

A balancer adds weight to help (externally) balance the lower rotating assembly of an engine, while a damper, quells the vibrations during crankshaft vibration which occur as a function of the combustion process. Keep in mind, while all harmonic balancers are dampers, all dampers are not balancers.

How do I reduce torsional vibration?

The dual-mass flywheel (DMF) is used between the combustion engine and the transmission as a standard measure for reducing engine torsional vibration.