With the continuous development of road traffic, the speed of car has been greatly improved, so the requirement for automobile suspension is also higher and higher. The suspension system is one of the most important assemblies of the car, which connects the body and the car elastically. The automobile suspension is the general term of all the force connecting devices between the body and the wheel. It is usually composed of elastic elements, shock absorbers and guide elements. In the process of moving vehicle's suspension is elastically connected with a frame and axle, slow moving vehicle impact force caused by uneven pavement, ensure the ride comfort and the goods, due to the rapid decay caused by the vibration of elastic system, vertical, longitudinal and lateral force and torque, and play a leading role, so that the wheels according to a certain trajectory relative to body movement. The roughness of the road is one of the most important incentives for the vehicle to drive, which has a direct impact on the driving performance of the vehicle. Suspension determines the stability, comfort and safety of the automobile. It is one of the most important parts of modern automobile. If there is no suspension, it will greatly affect the stability and smoothness of the vehicle. Suspension has an important impact on the performance of the whole vehicle. Therefore, the improvement of vehicle handling stability and smoothness has become the consensus of the major automobile manufacturers. The suspension system, which is closely related to this, has been constantly improved, and the application of the active semi-active suspension and other electronic control systems with feedback in the high end vehicles is becoming more and more widely. No manufacturer dares to ignore the suspension system and its role in the whole vehicle, whether a large commercial vehicle or an economic car of a common family. All this is because the suspension system is closely related to the subjective feelings of the occupants. The suspension system is good and bad, the crew can feel immediately on the car.

Research status at home and abroad: 1. passive suspension is a traditional mechanical structure, stiffness and damping are not adjustable. According to random vibration theory, it can only guarantee a good effect under certain road conditions. At the present stage of our country, there is still a high value of research. The research of the 2. semi-active suspension is focused on two aspects: the research of executive strategy; the research of the actuator. There are two main damping dampers, one is to adjust the damping by changing the size of the throttle, and the other is to change the viscous damping by changing the damping fluid. 3. active suspension research is also focused on two aspects: reliability,actuator. Because active suspension adopts a large number of sensors, singlechip, output and input circuit and various interfaces, because of the large number of components and reducing the reliability of suspension, increasing the integration level of components is an insurmountable stage. The main research of the actuator is the use of electric devices instead of hydraulic devices. The linear servo motor and permanent magnet DC linear servo motor in the electric power system have many advantages, which will replace the hydraulic actuator in the future.

Although China has become the world's largest automobile production and sales, but China auto market most foreign brands occupy, the brand's market share is not high, the main reason is the independent brand development ability is relatively weak, the level of product technology is not fully recognized by consumers. Now many independent brand manufacturers have been able to develop their body and shape independently. However, most of the chassis are imported from abroad, or are invited to be developed by famous foreign design companies, and their independent development capability is weak. In the western developed countries, semi-active suspension became mature in the late 1980s. Ford Motor Co and Nissan first applied on cars, and achieved good results. Active suspension, although early starting, has been difficult to break through because of its complex control and involving many disciplines. In 1990s, it was still applied to luxury cars with a large amount of exhaust. There is no report on the use of this technology in domestic automobile products. Only a few research institutions, such as Beijing Institute of Technology and Tongji University, do research on active suspension.

In the aspect of theory research, the most recent topic of papers and works mainly focus on the control strategy and controller design, its fundamental purpose is to adapt to the premise of improving the vehicle speed, how to improve the response speed of the system, to achieve optimal control, to adapt to the external excitation frequency increasing trend. Han Bo and so on have studied the strategy and algorithm of adaptive and self correcting control of vehicle active suspension. The design of controller has adopted stochastic linear optimal control theory, and adaptive algorithm and self correction algorithm have been put forward on control algorithm.

According to the basic structure of automobile semi-active suspension, the system model of Jia Xiaoping and V.Gavriloski is established by mechanical analysis. In order to overcome the dynamic behavior of the actual control system uncertainty, Li Yinong of Chongqing University, using the adaptive control strategy, through the use of model parameter recursive identification, two indicators consisting of vertical acceleration of the body and the control signal, realized the automotive semi-active suspension frame adaptive stochastic optimal control.

In the control strategy, different methods are proposed for different problems. The adaptive control strategy is proposed by Miao Zan, and the intelligent control strategy is put forward by Liu Hua and so on. These control strategies effectively improve the performance of the control and the ride comfort of the vehicle. Zhou Jiming and others used the 1/4 vehicle model to analyze the dynamic characteristics of canopy damper and active suspension, and discussed the application of differential geometry method and feedback linearization method. Shu Hongyu et al. Used a simple two degree of freedom vehicle model to analyze the active suspension numerically. Because the damping coefficient in the continuous system is not as sensitive as that in the switched semi-active suspension system, the continuous semi-active suspension can improve the stability time of the transient response.

2. 研究的基本内容与方案

This graduation project takes Dongfeng K74M as the object, and researches its special requirements for suspension and relevant national standards. According to the special requirements of the suspension and the national standard, we use basic knowledge such as theoretical mechanics, material mechanics, mechanical principle and vehicle design to design the suspension and determine the size and material of each component.

The basic contents are as follows: 1. complete the design and selection of the components of the suspension system; 2. complete the checking calculation of the ride comfort and so on; 3. complete the structure design of the suspension parts

It includes structural analysis of suspension, selection of front and rear suspension schemes, selection of suspension performance parameters, calculation of elastic elements and design of shock absorbers.

The basic technical scheme is as follows: The structure and layout of the suspension (independent suspension), →Selection of suspension performance parameters (the frequency of partial suspension and static deflection and dynamic deflection, stroke, elastic properties, rear suspension main auxiliary spring stiffness distribution, suspension stiffness), →Calculation of elastic element (calculation of main dimensions the parameters of leaf spring, spring) →The design of un independent suspension guiding mechanism (front wheel alignment angle and guide mechanism of size selection, on the lower arm in the lateral plane inclination and tilt direction, upper and lower arm axis inclination selection), →Shock absorber design (main choices of performance parameters, including the relative damping coefficient, damping coefficient, maximum load; main dimensions data check).