Two-step dynamics of a semiactive hydraulic engine mount with four-chamber and three-fluid-channel

Abstract

Semiactive hydraulic engine mounts (HEMs) offer better noise, vibration and harshness (NVH) performance in a wider frequency band than passive HEMs and provide acoustic and vibrational comfort for passenger cars that rivals that of active engine mounts (AEMs); these advantages lead to the wider use of HEMs than AEMs. In limited control modes, broadening the vibration isolation band as much as possible is the fundamental purpose of semiactive HEMs. This paper focuses on an analytical and experimental study of a unique semiactive HEM with four-chamber and three-fluid-channel whose lengths shorten successively while the cross-sectional areas increase successively. The semiactive HEM presents dynamic characteristics in a two-step style and thus can offer good NVH performance in a relatively wider band. The first step is induced by the resonance of the longest fluid channel, and the second step is induced by the resonance of the shortest fluid channel corresponding to a separate decoupling membrane (DM) fluid chamber. The relationship of bulk stiffness between the DM and the main rubber spring is switched from an in-series connection for the first step to an in-parallel connection for the second step, which is an intrinsic reason for effectively widening the vibration isolation band. To better clarify the two-step dynamics, the influence of the DM is further investigated by introducing frequency-dependent bulk stiffness in-series and in-parallel. Moreover, two additional HEMs and their experimental two-step dynamics are illustrated to validate the frequency-dependent bulk stiffness. The ideal control strategies for semiactive HEMs with four-chamber and three-fluid-channel are developed and numerically verified by minimizing the force transmissibility in a wider frequency band. The findings of this paper can facilitate the design of dynamics for HEMs with a DM. Proper matching and relationship switching of the bulk stiffness between the DM and the main rubber spring can effectively improve NVH performance for passenger cars.