During the movement of the oil and gas spring, the reaction force generated includes not only the elastic force, the friction force but also the damping force. Due to the action of the one-way valve, the damping forces of the oil and gas springs during the stretching and compression strokes are not equal. When the piston rod moves for one cycle, the area enclosed by the reaction force curve is the magnitude of the damping force, which indicates the energy consumed by the oil-gas spring for one cycle, and also reflects the ability of the oil-gas spring to attenuate the vehicle vibration. Stiffness frequency characteristics Since the high-pressure nitrogen gas filled in the accumulator acts as a gas spring, the elastic deformation of the high-pressure nitrogen gas can be used to bear the load and reduce the impact of the ground on the vehicle, which is the elastic characteristic of the oil-gas spring. When the elastic characteristics of the oil-gas spring are analyzed, the effect of the damping force is not considered, and the influence of the fluid compressibility on the elastic force Fg is ignored.
The nonlinear mathematical model and characteristics of the automobile oil and gas spring can be seen that the stiffness of the gas in the oil and gas spring accumulator decreases with the increase of the excitation frequency of the road surface, showing a certain nonlinear characteristic. Damping characteristics When the vehicle is running, the hydraulic cylinder and the accumulator oil chamber cause the oil to flow back and forth through the damping valve due to the pressure difference, which consumes vibration energy. This process forms the damping characteristics of the oil and gas spring. The damping effect of the oil-gas spring comes from three parts: the damping caused by the oil-air spring damping hole, which is the main damping; the friction between the piston and the hydraulic cylinder; the partial pressure loss at the outlet of the accumulator and the pressure loss along the pipeline Damping. The oil spring has a small damping force in the compression stroke, and the elastic force of the air spring plays a main role to alleviate the vibration shock from the road surface. When the oil and gas spring is stretched, the damping force is large, and the vibration can be quickly attenuated, indicating the oil spring damping. The force velocity characteristics are non-linear.
Damping valve flow characteristics In order to further analyze the damping force generated by the damping valve at a certain speed, the relationship between the oil flow and the pressure difference at the inlet and outlet of the damping valve is analyzed p=f(Q), which is the flow characteristic of the damping valve. During the stretching stroke, the check valve is closed, and the oil in the accumulator flows through the through hole to the hydraulic cylinder, and a large pressure change occurs at both ends of the damping valve; in the compression stroke, the check valve is opened, and the equivalent flow is The increase in area increases the flow of oil from the hydraulic cylinder into the accumulator at the same speed, resulting in a small pressure change across the damper valve. Taking the oil and gas springs for engineering vehicles as the research object, the nonlinear mathematical model of oil and gas springs is established by considering the compressibility of oil, the nonlinearity of stiffness and the dynamic friction between piston and cylinder wall. The experimental results are compared with the simulation results, and the two are basically consistent, thus verifying the correctness of the mathematical model. Through the established mathematical model of oil and gas spring, the elastic characteristics, damping characteristics and flow characteristics of the damper valve are simulated and analyzed, which plays a guiding role in the design and research of oil and gas springs.
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