| One of the characteristics that define the quality of a vehicle is the amount of noise-vibration-harshness (NVH) in the cabin. An automobile's engine, body, and chassis system are susceptible to undesirable vibrations, due to two sources of excitation:the inherent unbalance of the reciprocating engine, and the disturbances transmitted through the suspension system from the road. Therefore, the increase in fuel economy and decrease in price of the automobile comes at a price:more NVH and less comfort. For improving the ride comfort, reducing noise levels and increasing the whole quality of an automobile, high performance engine mount has been becoming a hot topic since the increase in fuel economy and decrease in price of the automobile comes at a price.Magneto-rheological (MR) fluids are materials that respond to an applied magnetic field with a change in rheological behavior. Typically, this change is manifested by the development of a yield stress that monotonically increases with applied field. Interest in magnetorheological fluids derives from their ability to provide simple, quiet, rapid-response interfaces between electronic controls and mechanical systems.That magneto-rheological fluids have the potential to radically change the way electromechanical devices are designed and operated has long been recognized.Magneto-rheological fluid squeeze mode investigations at Center for Vehicle Systems and Safety (CVeSS) at Viginia Tech have shown that MR fluids show large force capabilities in squeeze mode.A MR squeeze mount test result shows the equivalent damping is the function of the excitation frequency, the excitation amplitude, initial gap, and it also can be controlled by the applied current early. A variant engine mount based MR squeeze mount was proposed and studied in this dissertation. It can be tuned between the'hard'mount and 'soft'mount which is to obtain a compromise between engine isolation and engine bounce easier than a traditional elastormeric mount. It will improve the ride comfort, reducing noise levels and increasing the whole quality of an automobile.Chapter 1 is the introduction. The motivation, objectives, the approach and the outline of this disseretation was introducted. The literatures about engine mount, tuned vibration absorbers, Magneto-rheological fluid and squeeze mode were reviewed in this chapter.In this research, a MR squeeze mount used for dynamic test was designed in Chapter 2 firstly, which is always bulging out and has a uniform and regular shape.This mount and magnet system was then validated using the FEMM software.Parts of parameters of magnet system are studied and optimization by Co-simulation of the FEMM and Matlab. It's found that an efficient return path will reduce the power dissipate,in other word,there will be a much stronger magnetic field with a better return path with the same power input. A semi-empirical model of the magnetic intensity is derived depending on the FEMM simulate results.The semi-empirical model matches the FEMM model very well, which will be used to reverse the control current from the desired magnetic field intensity.Secondly, the experiment rig was set up for the steady state tests in Chapter 3,four factors are considered in each test such as applied current, initial gap size, frequency and amplitude of the displacement on MR squeeze mount. Experimental results emphasized that the compressive force of the MR squeeze mount was strongly affected by the applied current, the initial gap size and the displacement amplitude. The compressive force and hysteresis loops of the force-displacement curves of the MR squeeze mount increased with increasing the applied current, increasing the displacement amplitude or decreasing the initial gap size. However, the rebound force is much smaller than compressive force. On the compression side of the curve, the maximum compressive force attained dropped with increasing the frequency. This could be attributed to the fact that as the MR squeeze mount is compressed, the distance between the two plates decrease and the magnetic density inside the MR squeeze mount increase. The chains of the MR fluid tend to become thicker increasing the strength of the MR squeeze mount. The chains have more time to thicker at lower frequency than the higher frequency. The force jump, when the velocity change the direction, will increase as increasing the frequency since the acceleration increases as the speed of the square of the frequency and the inertia effect becomes more significant. The equivalent damping of the MR squeeze mount increased with increasing the applied current, or decreasing the initial gap size and it will decrease with increasing the displacement amplitude, especially with increasing the frequency.Then, a mathematical model based on Bingham model for the compress processor was droved and it was validated by the test data in Chapter 4. The squeeze force for a Newtomian fluid was studied first, and then, the MR behaviors was analyzed, in which the effect of the pressure on the yield stress was considered, additional, the membrane stiffness was test and added to the mathematical model. At last, the inertial effect was included into the model. The mathematical model match the test data very well during the compress processor and it also shows the inertia effect becomes more significant at higher displacement frequencies. The radius of the MR squeeze mount is an important design parameter. Hence, a simulation of a MR squeeze mount with the double size radius based on the mathematical model has been done. Compared with the normal one, it shows increasing the radius will increase the vertical force tempestuously and the inertial effect also increased extremity at the high frequency. A semi-empirical model, which is fast, robust, have enough precision and considering the whole hysteresis loop of MR squeeze mount, was built based on the test data. The semi-empirical model matches the test data very well and it could be used for more operation conditions since it matches the initial conditions and the boundary conditions of the first derivative.Finally, a simulation of the MR squeeze mount used to isolate a passenger car engine vibration is stuied in Chapter5. The excitation from the single cylinder was studied first, and then is the disturbances from the four cylinder inline engine, in which shows the second order reciprocating inertia force, roll moment and pitch moment will be the main excitation to the vehicle body. Considering the compress vertical force is much bigger than the rebound vertical force, a variant engine mount with the one degree-of-freedom system was studied. The uncertainties in the elastormeric mount stiffness and elastormeric mount damping (±10%) were considered. The obtained model is more practical from an application perspective. With a new partition technique, the uncertainties are depicted by a polytope with eight vertices. The transmissibility is converted into the transfer function of the derived closed-loop system. Thus, the optimization of the transmissibility is transferred to the optimization of the infinity norm of the transfer function, and the optimization problem is converted into a robust Hx controller design problem. In order to reduce the conservativeness of the conditions of a robust Ha control, a new sufficient condition for robust Hm output-feedback control was droved and a new iterative algorithm to solve the BMI-based problem. The displacement transmissibility is smaller than 1.05 with this controller. It shows the large force range of an MR squeeze mount to be suitable for use for the isolation of the modeled engine vibration. And then, the engine is considered as a 3 degree-of-freedom system as the last of this chapter, which is assembled with a 10 degree-of-freedom vehicle system, in which the vehicle body and the engine are assumed as rigid body, which both have freedom of vertical, roll and the pitch motions.The vehicle body is connected with four unsprung mass, the tires were assumed as linear springs and tire damping are neglected. An H∞controller is designed to reduce the vertical force transmissibility, the roll moment transmissibility and the pitch moment transmissibility at the same time. The dynamic stiffness of the MR squeeze engine mount can be tuned in an area, between the'soft'mount for the high frequency and the'hard'mount for the low frequency, instead of a line for a passive elastormeric mount. It is easier to obtain a compromise between engine isolation and engine bounce easier than a traditional elastormeric mount. It will improve the ride comfort, reducing noise levels and increasing the whole quality of an automobile.Main innovations of this dissertation:1)An MR squeeze mount was designed for dynamic test, which is always bulging out and has a uniform and regular shape,and then parts of parameters of magnet system are studied and optimization by Co-simulation of the FEMM and Matlab. A semi-empirical model of the magnetic intensity is derived depending on the FEMM simulate results, which will be used to reverse the control current from the desired magnetic field intensity, and the dynamic properties of the MR squeeze mount were testedup to 50Hz.2) A mathematic model was development for the MR squeeze mount dynamics behavior, in which the fluid viscous, the applied current, effect of the pressure on the yield stress, the membrane stiffness and inertial effect were included. A variant engine mount with the one degree-of-freedom system was studied. The uncertainties in the elastormeric mount stiffness and elastormeric mount damping (±10%)were considered. With a new partition technique, the uncertainties are depicted by a polytope with eight vertices. In order to reduce the conservativeness of the conditions of a robust H∞control, the new sufficient conditions for robust H∞output-feedback control was droved and a new iterative algorithm to solve the BMI-based problem.3) A semi-empirical model, which is fast, robust, have enough precision and considering the whole hysteresis loop of MR squeeze mount, was built based on the test data. The engine is considered as a 3 degree-of-freedom system, which is assembled a 10 degree-of-freedom vehicle system. An H∞controller is designed to reduce the vertical force transmissibility, the roll moment transmissibility and the pitch moment transmissibility at the same time. The dynamic stiffness of the MR squeeze engine mount can be tuned in an area instead of a line for a passive elastormeric mount. It is easier to obtain a compromise between engine isolation and engine bounce easier than a traditional elastormeric mount.
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