1.Purpose and Significance

1.1 Function of Suspensions

Comfort is one of the most important performances 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. When the car is driving, the unevenness of the road will arouse the vibration of the car. When this vibration reaches a certain level. It will make the passenger feel uncomfortable or damage the carrying goods. At the same time, due to the dynamic load between the wheel and the road surface, it will also affect their adhesion, which will also affect the steering stability of the car. In addition, the car may cause changes in body posture (pitch and roll, etc.) due to acceleration, braking, steering, and the like. It can also make passengers feel uncomfortable. Therefore, it is of great significance to study the vibration and stress of the vehicle and take effective measures to control it to the lowest level, which is to improve the ride comfort and steering stability of the vehicle.

A car suspension is a general term for an elastic coupling between a frame and an axle. Its role is to elastically connect the axle and the frame to mitigate the impact of the vehicle while driving. To ensure the integrity of the goods and the comfort of the personnel; the attenuation is due to the vibration introduced by the elastic system, so that the vehicle maintains a stable posture during driving and improves the steering stability; at the same time, the suspension system bears the vertical reaction force, the longitudinal reaction force (traction force and braking force) and The lateral reaction forces and the moments caused by these forces act on the frame to ensure smooth running of the car; and when the wheels are beating relative to the frame, especially when steering, the wheel trajectory must meet certain requirements. Therefore, the suspension also serves as a guiding function for the wheels to jump relative to the body in a certain trajectory.

The choice of suspension structure and performance parameters is reasonable, which directly affects the ride comfort, handling stability and comfort of the car. This shows that the suspension system is one of the important assemblies in modern cars.

1.2 Research status at home and abroad

From the early multi-section equal-section to the today's gradual stiffness, the spring stiffness gradually evolves from linear to nonlinear.The gradient stiffness spring is an improvement of the typical passive suspension, which has a certain improvement on the performance of the passive suspension, but its structure is complex and the cost is high, which cannot fundamentally change the defects of the passive suspension.

In recent years, in the theory and technology of coil springs, there has been great development at home and abroad. In modern cars, coil springs are used the most, and it has a strong absorption capacity for impact loads, which can improve the ride comfort of the car, and it does not require lubrication and maintenance.

The torsion bar spring can achieve the external force of buffering by torsional deformation. The torsional stiffness of the torsion bar spring is generally constant. In order to make the torsion bar spring suspension have better nonlinear characteristics, Zhang Hongtao of Nanjing University of Aeronautics and Astronautics in 2007 proposed a two-stage torsion bar spring.

Silicone oil springs are a new type of suspension device that utilizes the compressibility of silicone oil to achieve elastic and stiffness changes. This variable stiffness suspension device was invented by Damon et al. in the United States and patented in 2010 (US 2010/0044978 A1). This patent proposes a damper scheme using silicone oil as the elastic and damping medium. It controls the throttle valve to achieve communication between the main cylinder and the sub-cylinder for stiffness adjustment. In this patent, the right owner focuses on the principle of the stiffness adjustment of the silicone oil spring and the method of semi-active control of the suspension. However, the intrinsic law of the stiffness change and the dynamic characteristics of the suspension are not studied in depth.