The self-attenuation of the air spring and the bogie without the bolster spring up and down are shown in Fig. 10. An orifice is provided between the air spring body and the auxiliary air chamber, and the spring is applied to the air spring by giving resistance to the air flow. At the same time, attenuation can also be given, which was already known in the development of air spring bogies. On the other hand, it is also known that the flow characteristics of the air passing through the orifice are non-linear, and if the orifice diameter of the orifice is reduced and the flow resistance is increased, the spring constant of the air spring increases.
Since it is not understood how much attenuation can be given by relying only on the orifice, for this purpose, in the initial stage of the air spring bogie, as with the conventional bogie, the hydraulic shock absorber is installed in parallel with the air spring. Sumitomo Metals has considered air spring bogies that do not have upper and lower hydraulic shock absorbers by considering the self-attenuating bogie design using only air springs.
The air spring bogie determines the throttle aperture size by running vibration test. In this running vibration test, the pressure changes of the air spring and the auxiliary air chamber were also measured. From the analysis result of the data, a linear spring-damper model of the self-attenuating air spring was deduced, as shown in this model. When the orifice diameter is reduced, the attenuation constant of the damper becomes large, and the spring constant k1 of the air spring increases.
On the other hand, if the aperture is properly sized, the attenuation value of the shock absorber becomes an appropriate size, and the spring constant of the air spring can become a low spring constant for the internal volume of the auxiliary air chamber. It is already sufficient to analyze the up and down vibration of the actual air spring vehicle. Based on this result, the design of the air spring was made to understand that even without the upper and lower dampers of the air spring bogie, necessary springs and attenuation characteristics can be given. The cradle-free boom bogies that were born later were air spring bogies without upper and lower dampers.