This review focuses on studying passive vibration isolation techniques and their applications. Advantages and disadvantages of different vibration isolation techniques will be compared in order to find an innovative method to reduce seating suspension system vibration and improve the ride comfort of vehicles’ drivers. Quasi-zero stiffness (QZS) isolators of high-static–low-dynamic stiffness are found to have good application prospects in low-frequency vibration isolation. In order to improve the isolation performance of the seating suspension system, a specially made seat cushion will be studied where a quasi-zero stiffness (QZS) isolator such as a double-diamond isolator is selected as one of the cells/units/elements of the seat cushion mattress. The double-diamond isolator structure does not represent the whole seating suspension system. The transmissibility ratio of the double-diamond isolator is evaluated by analytical and simulation models and compared to that of a conventional linear spring isolator. Although the performance of the passive vibration isolation/control system is usually worse than that of the active or semi-active control system, the cost of the passive vibration isolation/control system is lower than that of the active and semi-active control system, and the relative simplicity of adding a vibration isolation cushion mattress in an existing passive seating suspension system makes it low in cost, easy to implement, and more attractive than the active and semi-active vibration control systems.

With the further development of the automotive industry, the traditional vibration isolation method is difficult to meet the requirements for wide frequency bands under multiple operating conditions, the active control mount (ACM) is gradually paid attentions, and the control algorithm plays a decisive role. In this paper, the ACM with oscillating coil actuator (OCA) is taken as the object, and the comparative study of the control algorithms is performed to select the optimal one for ACM. Through the modelling of ACM, the design of controller and the system simulations, the force transmission rate is used to compare the vibration isolation performance of the nine control algorithms, which are least mean square (LMS) adaptive feedforward control, recursive least square (RLS) adaptive feedforward control, filtered reference signal LMS (FxLMS) adaptive control, linear quadratic regulator (LQR) optimal control, H₂ control, H_∞ control, proportional integral derivative (PID) feedback control, fuzzy control and fuzzy PID control. In summary, the FxLMS adaptive control algorithm has the better performance and the advantage of easier hardware implementation, and it can apply in ACMs.

The active hydraulic mount with solenoid actuator (AHM-SNA) does not require permanent magnets, is of low cost, and has attracted wide attention. This paper focuses on each link of the secondary path in AHM-SNA, the transfer functions (TFs) were studied one by one, and a simple and efficient expression for the total secondary path is discussed. First, based on the mathematical model of the hydraulic mount with inertia track and decoupling membrane, the TF from actuator active force to output force at frame side was analyzed, the results show that the TF was constant in the mid-frequency band. Second, based on the geometric parameters and cone air gap of solenoid actuator, it was obtained that the TF from the square of current to actuator active force is also constant; based on the relationship that the active force frequency is twice of the harmonic current frequency, the full-wave-rectified current was introduced. Utilizing the fact that the second harmonic component of the current is the main component, it was concluded that the total TF of the secondary path from current to active force and then to output force at frame side was constant in the mid-frequency band. Finally, two sets of experiments with full-wave-rectified current as the excitation were carried out, and the analytical conclusion was verified that the TF of the secondary path was constant as a proportional link and was convenient for the active control algorithms.

Active hydraulic mounts with an inertia track, decoupler membrane, and oscillating coil actuator (AHM-IT-DM-OCAs) have been studied extensively due their compact structure and large damping in the low-frequency band. This paper focuses on a comprehensive analysis of the active and passive dynamics and their fixed points in mid-low-frequency bands, which will be helpful for parameter identification. A unified lumped parameter mechanical model with two degrees-of-freedom is established. The inertia and damping forces of the decoupler/actuator mover may be neglected, and a nonlinear mathematical model can be obtained for mid-low-frequency bands. Theoretical analysis of active and passive dynamics for fluid-filled state reveals the amplitude dependence and a fixed point in passive dynamic stiffness in-phase or active real-frequency characteristics. The amplitude dependence of local loss at the fluid channel entrance and outlet induces the amplitude-dependent dynamics. The amplitude-dependent dynamics constitute a precondition for fixed points. A single fixed point in passive dynamics is experimentally validated, and a pair of fixed points in active dynamics for an AHM-IT-DM-OCA is newly revealed in an experiment, which presents a new issue for further analysis.

Active hydraulic mounts (AHMs) provide an effective solution for refining ride comfort noise and vibration in passenger cars. AHMs with inertia tracks, decoupler membranes, and oscillating coil actuators (AHM-IT-DM-OCAs) have been extensively studied owing to their compact structures and strong damping characteristics in the low-frequency band. This study focuses on the full parameter identification based on the distinct features of external dynamics, which can be used to obtain an accurate and reliable estimate of the transfer functions required for active control algorithms. A lumped parameter model was established for the AHM-IT-DM-OCAs, and the analytical frequency bands were defined by the two resonance frequencies of the fluid channel and actuator mover. Methods for nonlinear model simplification were proposed in different bands and verified theoretically. Based on the simplified models, the distinct features of the active and passive dynamics are successively revealed, which include three resonances and seven horizontal segments. Subsequently, a series of experimental studies on the distinct features were carried out, which agreed well with the theoretical results. However, owing to the limitations of the test equipment and fixture modalities, only the distinct features of one fixed point, two resonance peaks, and three horizontal segments can be used for parameter identification. Based on the validated distinct features, a procedure for full parameter identification is proposed, and all six key parameters are identified. The obtained results showed good consistency and rationality, indicating that this approach can be used for the transfer function estimation of the primary and secondary paths of the AHM-IT-DM-OCAs.

Based on the third generation of hydraulic engine mounts (HEMs), which has three types of hydraulic mechanisms such as inertia track, decoupler and disturbing plate, the influences of the three different hydraulic mechanisms on the dynamic properties were studied experimentally. The working principles of the three hydraulic mechanisms and the relationship between the dynamic properties of the three generations of HEMs were revealed clearly, these experimental results will be helpful for HEM design selection. It was discovered experimentally that the frequency-dependent dynamic properties of HEM with inertia track or orifice have fixed points under different excitation displacement amplitudes. Based on the facts that the analytical results matched well with the experimental ones, a new parameter-identification-method for HEM is presented, which is clear in theory and is time- and cost-saving, the identified results were reliable.