1．目的及意义
Comfort is one of the most important performance of a car. Comfort is related to the inherent vibration characteristics of the body, and the inherent vibration characteristics of the body are related to the characteristics of the suspension. Therefore, vehicle suspension is an important component to ensure ride comfort. At the same time, vehicle suspension is an important component to ensure the safety of vehicle driving as a force transmission device connecting the frame (or body) and axle (or wheel). Therefore, automobile suspension is often listed as an important part in the technical specifications of cars, as one of the indicators to measure the quality of cars.
If the car frame (or body) is directly mounted on the bridge (or wheel), the goods and people will feel very uncomfortable because of the uneven road and ground impact, which is due to the lack of suspension devices. Vehicle suspension is a general term for the elastic coupling device between the frame (or body) and axle (or wheel). Its function is to elastically connect the axle and frame (or body) to ease the impact on the vehicle during driving. To ensure the intact goods and comfortable personnel; to attenuate the vibration introduced by the elastic system, so that the vehicle can maintain a stable posture and improve the handling stability; at the same time, the suspension system bears the transmission of vertical reaction force, longitudinal reaction force (traction and braking force) and lateral reaction force, and the torque caused by these forces acts on the frame (or body) to ensure the smooth driving of the vehicle; And when the wheels jump relative to the frame, especially when steering, the wheel trajectory must meet certain requirements, so the suspension also plays a guiding role in making the wheels jump relative to the body according to a certain trajectory.

Whether the suspension structure and performance parameters are reasonable or not directly affects the ride comfort, handling stability and comfort of the vehicle. So the suspension system is one of the most important assemblies in modern automobiles.

During the more than 100 years since the automobile was born at the end of the 19th century, the automobile industry has developed at an alarming speed, which has written an important chapter in the history of modern human civilization. Automobile is the most numerous, most popular, the most extensive range of activities, the largest volume of transportation of modern means of transport. It can be asserted that no mechanical product has such a wide and far-reaching impact on society as automobiles. The development of modern automobile suspension is very fast, and new suspension devices are constantly appearing. According to the different types of suspension of automobile steering mechanism, it can be divided into independent suspension and non-independent suspension. The characteristic of non-independent suspension is that wheels on both sides are mounted on an integral axle. When one side of the wheel is impacted, it will directly affect the other side of the wheel. When the wheel bounces up and down, the positioning parameters change little. If the leaf spring is used as an elastic element, it can play a guiding role, simplify the structure greatly and reduce the cost. At present, it is widely used in trucks and buses, and some rear suspensions of cars are also used. Although automotive suspension has been evolving from structure type to working principle for more than one hundred years, it is composed of three parts: elastic element, vibration absorber and guiding mechanism.

For example, the front suspension of FAW Audi 100 sedan. The cylindrical shock absorber is installed in the sliding column barrel, which is rigidly connected with the steering knuckle. The spiral spring is installed in the support seat of the upper end of the sliding column barrel and the steering knuckle assembly. The upper end of the spring is supported in the front spring seat connected with the body by cushion. The lower end of the sliding column barrel is connected with the sway arm of the suspension through the ball hinge. When the wheel moves up and down, the sliding column barrel and steering knuckle assembly move along the piston motion axis of the shock absorber. At the same time, the lower fulcrum of the sliding column barrel also swings with the yaw arm. As an elastic element, coil spring can only bear vertical load, so its suspension system should be equipped with guide mechanism and shock absorber. Shock absorber and elastic components undertake the task of cushioning and vibration reduction. Excessive damping force will deteriorate the suspension elasticity and even damage the connecting parts of shock absorber. Therefore, the contradiction between elastic elements and shock absorbers should be adjusted.
(1) During the compression stroke (the bridge and frame are close to each other), the damper has a smaller damping force, so as to give full play to the elastic role of the elastic elements and mitigate the impact. At this time, elastic elements play a major role.
(2) During the suspension stretching journey (the bridge and frame are far away from each other), the damper force should be large and the vibration should be reduced rapidly.
(3) When the relative speed between the axle (or wheel) and the axle is too large, the shock absorber is required to automatically increase the liquid flow, so that the damping force is always within a certain limit, in order to avoid bearing excessive impact load.

The function of the shock absorber is to absorb the vibration of the vehicle when the leaf spring takes off and lands, so as to restore the stable state quickly and improve the driving stability of the vehicle. Hydraulic dampers are widely used in McPherson suspension systems. Its principle is to use the resistance of liquid flow to consume the energy of vibration. When the frame moves relative to the bridge, the piston moves up and down in the cylinder, and the oil in the shock absorber shell flows repeatedly from one chamber to another through some narrow holes. At this time, the friction between the hole wall and the oil and the internal friction of the liquid molecules will form a damping to the vibration, so that the vibration energy of the car body and frame can be converted into heat energy and absorbed by the oil and shock absorber shell, and finally dispersed into the atmosphere. Damping force of shock absorber increases and decreases with the increase or decrease of relative moving speed of frame and bridge, and is related to oil viscosity.

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2. 研究的基本内容与方案

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2.1 Basic Contents and Objectives of Design

(1) Select appropriate design parameters of independent suspension.
(2) The independent suspension model is established by using CATIA software, and the three-dimensional model is transformed into two-dimensional plan. Then the drawings are processed with AutoCAD software.
(3) Optimize the designed independent suspension and complete the design instructions.
2.2 Technical scheme and measures to be adopted

(1) The flow chart of the technical scheme is as follows:

Figure1：Flow chart of technical scheme

(2) Measures: The suspension model is built in CATIA and the two-dimensional drawing is completed in AutoCAD.

3. 参考文献

[1]Lapusan, C.,Chiroiu, V.,Munteanu, L.,Bara, L.,Brisan, C.. Development of an avatar for a vehicle with independent suspensions[P]. Automation, Quality and Testing, Robotics, 2014 IEEE International Conference on,2014.