Study On The Key Technology In Active Vibration Control Of Automobile Power-train

Automobile power-train is the dominant source of noise and vibration in automobiles, and the vibration isolation of automobile power-train is crucial to the improvement of NVH (Noise, Vibration and Harshness) characteristics.In order to reduce the power-train vibration's impact on the passenger-comfort, the main methods have been disturbance attenuation, anti-resonance and vibration isolation. The vibration isolation system is the flexible connection device between the power-train and chassis. A sound system of vibration isolation can reduce the vibration of automobiles, vibration power from the power-train to the chassis and the noise induced. As a result, durability and passenger-comfort of automobiles are improved.At present, the power-train vibration isolation systems in most cars are rubber mounts and hydraulic damping mounts, which perform the function of vibration isolation and reducing noise to a great extent. Because of the problems of energy and environment protection, cars are being designed to be even lighter in weight. With the wide application of former driving motors, most cars use four-cylinder engines with poor performance in balancing, which make the problem of vibration in power-trains more obvious.Research indicates that the feature of ideal dynamical force in the mount system is that the system has a high static stiffness to hold weight of power-train and the output torque. When in low frequency, it should have a high stiffness with large damping to reduce large-amplitude vibrations caused by torque variations of engines when starting, braking, shifting and quick accelerating and decelerating. When in high frequency, it should have a low stiffness with small damping to reduce the transmitting of vibrations and improve the effect on reducing the noise. Ideal stiffness and damping of mount system should vary with the frequencies and amplitude of vibrations, which is hard to realize in real project. Although hydraulic damping mounts performed much better than the rubber mounts did in vibration isolation, there still exist some shortcomings, such as the stiffness not being big enough in low frequency and a phenomenon of hardening in high frequency.Active mounts system of power-train is an efficient way for vibration isolation of the automobile power-train. Active control technique should be applied to the vibration isolation system in the power-train with active mount system and proper control strategies. In this way vibration amplitude of chassis will be reduced greatly. This paper focuses on the key techniques of actuator selection, structure design of active mount, modeling of the control system and selection of control strategy. Content of the paper is as follows:Literatures about the research of active mount system are systematically reviwed, including both domestic and foreign development. Some foreign active and semi-active mount systems are mainly introduced. Different sensors and control algorithms for active control of vibration are summarized. Previous techniques in active control of vibration in automobile power-train are analyzed, and the problems in each situation are pointed out.According to the requirements for mount performance of the automobile power-train, two conditions which should be considered for design of active mount are proposed. Two active mount structures based on piezo-actuator and electromagnetic actuator are respectively designed. Dynamical models of the two active mounts are established. Performance of vibration-isolation with the piezo-actuator is discussed under different control schemes, which provides theoretical foundation for the design of active mount in power-train.Experimental platform of active mount in power-train is designed and the mathematical model with 10 DOF (degree of freedom) is established, which will facilitate the research. Performances of vibration isolation without control and with a linear quadratic regulator are analyzed by simulation experiments. The results indicated that performance of vibration isolation with active control scheme was better than passive control. A simplified mathematical model of active mount in power-train system with 5 DOF is built to reduce the cost of control and the complexity of actual control system in automobiles. Simulation results showed that the simplified model could capture dynamics of the complicated 10 DOF model well.Active vibration isolation system of power-train is designed by means of feedforward control and feedback control schemes respectively. As signals correlated with disturbance could be obtained by rotation speed of engines, feedforward control with adaptive x-LMS filter could eliminate vibration better than feedback control. In addition, the essence of active vibration in power-train is the problem of noise attenuation. The target of H∞optimal robust control is to minimize disturbance's influence to system output. Considering the conclusions above, H∞output feedback control system is designed with LMI method. In order to improve the performance of vibration isolation in low-speed section, starting and stopping section, frequency between 1Hz and 50Hz is taken into consideration in the selection of weighting function. The results of experiment in simulation indicate that H∞output feedback control scheme can better restrain the influence caused by power-train to the body of the car.Adaptive inverse compensation is adopted to eliminate the hysteresis nonlinearity of piezo-actuator in active control system. The adaptive control law based on grads method is obtained with Prandtl-Ishlinskii model. It is proved that when Prandtl-Ishlinskii model is used, results of compensation have no contact with slopes under the assumption that backlash model has a symmetry structure and backlashes as well as slopes are all proportional with each other. As only proportion of reference input and output is related with slopes, the estimated parameters are reduced to only one. The results of simulation indicated that compensation effect of adaptive inverse control to hysteresis nonlinearity was much better when signal frequency was low ( less than 25Hz). The technology of active vibration isolation on power-train in China is still in the earlier phase of development. There are only few relevant reports abroad. The problem of the key technologies that are involved in active vibration isolation on power-train are not solved properly, which restricts the development of active vibration isolation in power-train. The study of this paper is helpful for the research and design of power-train vibration control system. It can also provide valuable reference for engineering design related with active vibration control system.