Abstract
The torsional vibration damping of diesel engines is assumed to consist of viscous friction damping and hysteresis damping. Their damping ratios are divided into two kinds of non-dimensional functions, respectively; that is φ1 (cr, D), φ1 (dc, D) composed mainly of engine size, and φ2 (n, p), φ2 (n, p) composed of natural frequency and number of equivalent masses. The characteristics of engine damping have been discussed in this paper by investigating the tendency of these nondimensional functions. The obtained results are as follows:
1) The torsional vibration damping of an engine ζecan be expressed by the following equation,
ζe=ζr+ζh=φ1 (cr, D) ⋅φ2 (n, p) +φ1 (dcD) ⋅φ2 (n, p)
where, ζr =φ1 (cr, D) . φ2 (n, p) ; damping ratio due to viscous friction damping, ζh=φ1 (dc, D) . φ2 (n, p) ; damping ratio due to hysteresis damping, cr =viscous damping coefficient for one cylinder, dc= mean diameter of crankshaft, D= cylinder bore, n= number of equivalent masses, p= frequency ratio.
2) It is difficult to estimate accurately the value of the non-dimensional equivalent damping function φ1 (cr, D), because any equation cannot calculate the value of crwith high precision. The value of φ2 (n, p) is greatly dependent on natural frequency.
3) As the formulae of Lewis has been adopted to estimate the hysteresis damping energy, the damping ratio due to hysteresis damping ζhis proportional to θ0.310 (where, θ10; angular displacement) . The value ofφ1 (dc, D) varies from 5×10-3to 10×10-3, independent of engine size. The value of φ2 (n, p) for all torsional vibration is less than unity. Then, ζhhas values of the order of 10-3.
