1. Purpose and Significance (including domestic and foreign research status analysis)

   Due to the increasing requirements for comfort and safety of modern automobile , designing a suspension with good overall performance has become an important issue for modern vehicle research.

   As the vehicle parameters and driving conditions change, the requirements for the performance of the suspension system are different. For the traditional mechanical structure of passive suspension, the stiffness and damping are not adjustable, according to the theory of random vibration, it can only ensure good results under specific conditions. But its theoretical maturity, simple structure , Reliable performance, relatively low cost and no additional energy, and thus the most widely used. At this stage in our country, there is still a higher research value. The study of passive suspension performance mainly focuses on three aspects: (1) through the car After stress analysis, establish a mathematical model, and then use computer simulation technology or finite element method to find the optimal parameters of the suspension; (2) study the variable stiffness of the spring (3) research guide mechanism

   Due to the rapid development of computer technology and various new control methods, people have continuously improved the level of control of various vibrations and noises, providing a new way to essentially improve the performance of automotive suspension systems. With the rapid development of control theory, electronic technology, computer technology, measurement and control technology, mechanical dynamics and other disciplines, intelligent suspension system came into being, namely the intelligent suspension system based on electronic control - active suspension system has been rapidly developed And gradually apply on the car.

   In recent years, research on semi-active suspension has focused on two aspects: (1) research on implementation strategy; (2) study on actuators.one of damping adjustable damper is to adjust damping by changing the viscosity of damping fluid. By changing the viscosity of the damping fluid to change the damping coefficient, it has the characteristics of simple structure, low cost, no noise and impact, and is therefore the main direction of development at present.

   Research on active suspension has also focused on two aspects: (1) reliability; (2) actuators. Since the active suspension employs a large number of sensors, single-chip microcomputers, input and output circuits, and various interfaces, the increase of components reduces the number of suspensions. The reliability of the frame, so increase the degree of integration of components is an insurmountable stage. The study of actuators is mainly used to replace hydraulic devices with electric devices. Linear servo motors and permanent magnet DC linear servo motors in the electric power system have a The advantages of many will replace hydraulic actuators in the future. Using electromagnetic energy storage principle, combined with parameter estimation self-tuning controller, it is expected to design a high-performance, low-power electromagnetic energy-storage adaptive active suspension to make the active suspension. From theory to practical application

   the important obstacle to sustained development of suspension technology and the healthy development of Chinese auto industry, is its own research and quality requirements. For example, there are more than 160 domestic automobile suspension spring production enterprises, and more than 80 professional production enterprises (with a production scale of 0.8 million tons or more) across the country, and the product quality level has just reached the level of foreign advanced countries in the 1990s. Most of the companies are small in scale, low in production concentration, and the problem of scatter is relatively serious. There are only a few companies that have truly formed large-scale, high-volume production. Most of them still remain at the level of simple production processes. The higher product costs make it difficult to participate in international market competition. Second, there are only four companies that can produce high-end automotive steel suspension springs in China. After half a century of development, Chinese auto industry has begun to take shape, but it is facing pressure from energy shortages, technological backwardness, a serious lack of independent brands, and increased international competition. Chinese auto industry needs to accelerate, sustain and develop healthily, and it has become a pillar industry of China's national economy. It must adhere to industrial innovation, choose to develop its own industry innovation model with Chinese characteristics, and promote the upgrading of the automobile industry structure, technological progress, And the rise of national brands.

   Therefore, in order to design a reasonable limousine suspension structure, in order to adapt to the auto industry's independent development path, it is particularly important to carry out design and strength calculation of the suspension and to conduct research and promotion.

   This time for the luxury car suspension design, the selected model is the imported BMW X5, and its front suspension type is a double wishbone independent suspension. Firstly, for unequal double wishbone suspensions, as long as the lengths of the upper and lower cross-arms are properly selected and optimized, and through reasonable arrangement, the change in the wheelbase and front wheel positioning parameters can be within acceptable limits. The car has good operational stability and good ride comfort, and is a relatively advanced suspension, which largely satisfies the performance and ride requirements of high-class cars. The double-wishbone independent suspension can be said to be an upgraded version of it. First of all, for the precise control of the positioning parameters, the wheel can be closely attached to the ground, and the strong lateral rigidity provides good lateral support. The superiority of this structure is obvious for the control ability of the vehicle, but the use of the structure of the upper and lower control arms also leads to an increase in the lateral installation space of the suspension, so it is often applied to large luxury cars with a large body. on. The purpose of the entire suspension design process will be gradually achieved through the design, calculation and verification of important components in the suspension system Also,we need to figure out the meaning of each positioning parameter and the analysis of its impact on the vehicle's performance.

2. 研究的基本内容与方案

2 Basic content, goals, proposed technical solutions and measures