Modelling of a hydraulic engine mount focusing on response to sinusoidal and composite excitations

Frequency response characteristics of a hydraulic engine mount are investigated. The mount studied is highly non-linear due to an amplitude-limited floating piston (the “decoupler”) which enables the response to large amplitude (typically road-induced) excitations to differ markedly from the response to small amplitude (typically engine-induced) excitations. The effect of the decoupler on frequency response as well as composite-input (sum of two sinusoids) response is considered. New experimental data for a production mount and several specially prepared mounts are presented and discussed. Two linear models, one for large amplitude excitations and one for small amplitude excitations, are developed and shown to be effective over a 5-200 Hz frequency range. The latter model explains a moderately high frequency (~ 120 Hz) resonance which is often observed in the data, but which has not previously been described in physical terms. A piecewise linear simulation and an equivalent linearization technique are used to explain the amplitude-dependence of frequency response, as well as the composite-input response. The applicability of equivalent linearization is justified by demonstrating that high order harmonics contribute very little to the transmitted force. Moreover, this technique is found to be computationally efficient and to provide insight into decoupler dynamics.