The technologies of hybridization of vehicles have been proven to significantly improve the fuel economy and reduce the environmental pollution. These technologies combine additional power sources with a traditional internal combustion engine. In some other modern vehicles, advanced cylinder management is the means to reduce fuel consumption and emissions. While these advanced technologies aim at energy savings and preserving the environment they create additional noise, vibration and harshness (NVH) problem.
The noise, vibration and harshness problem has been a major area of research in the automotive industry. Vibration is the main cause for noise. With the advent of alternative energy and hybrid vehicles come new vibration problems and challenges that require nontraditional solutions. Semi-active vibration isolation devices are preferred to address the problem due to their effectiveness and affordability. A magnetorheological (MR) fluid mount can provide effective vibration isolation for applications such as hybrid vehicles. The MR fluid can produce different levels of damping when exposed to different levels of magnetic field. The fluid can be working in three modes which are the flow mode, shear mode and squeeze mode. A mixed mode MR fluid mount was designed to operate in a combination of the flow mode and the squeeze mode. Each of the working modes and the combined working mode has been studied. The mount's performance has been verified in simulation and experiments.
The focus of the current study is on the design of a control system for the mixed mode MR fluid mount. Based on a model for the uni-axial MR mount a controller has been designed to achieve the lowest possible vibration transmissibility. Furthermore, the MR mount in two degree of freedom structure has been modeled. Displacement transmissibility and force transmissibility are considered in this scenario. It is desirable to minimize both transmissibilities. The controllers to achieve the lowest value for each type of transmissibility were designed. Moreover, a hierarchical controller for realizing the tradeoff between these two types of transmissibility was also constructed. At last, a fuzzy logic controller is devised to closely reproduce the effect of the hierarchical controller. The experiments are set up to realize the hardware-in-the-loop tests. Results from the experiments show that the mixed mode MR fluid mount is able to achieve desired dynamic stiffness which is directly related to vibration transmissibility.
This study provided a fundamental understanding on the behavior of MR fluid mount in a single degree of freedom model and a two degree of freedom model. The significantly reduced transmissibility demonstrates effectiveness of the designed control system. The results of this research can shed some light on developing the control system for other effective isolation devices.