A spring system that achieves a low spring constant can be designed by incorporating an auxiliary air chamber. When combined with a height control valve, this design ensures consistent suspension height in railway vehicles. Unlike traditional coil springs, the platform and vehicle hook heights remain stable regardless of passenger load, maintaining a higher overall vehicle body height. This stability is crucial for smooth operation and comfort.
To maintain the vehicle body within a specific range relative to the platform and side hook, an air spring system is more effective than a coil spring, which cannot easily reduce its spring constant. In an air spring equipped with a height control valve, the spring height remains constant through controlled air pressure, allowing for the use of a low spring constant while keeping the vehicle at the desired height.
Air springs also excel in suppressing high-frequency vibrations. Unlike coil springs, which transmit high-frequency oscillations due to their mass, air springs support the vehicle using compressed air, eliminating pulsation. This results in a lower natural frequency of vertical motion, improving vibration isolation. Additionally, the spring constant of an air spring increases with load, but the change in natural frequency is minimal compared to coil springs. Practical applications have shown that designing an air spring with a low spring constant via an auxiliary air chamber significantly reduces vehicle body acceleration and vibration.
The use of air spring bogies began in the U.S., with the Budd Company pioneering the first commercial air spring vehicle. Their design featured a two-layer airbag that utilized lateral stiffness, making it a distinctive innovation. The Japanese air spring development was influenced by these early designs. A notable example was the all-stainless steel air spring vehicle introduced by Tokyu Vehicle Manufacturing Plant, which showcased technological advancements for private railways.
After World War II, as rail transport revived, there was a growing need for faster and more comfortable trains. Air spring bogies were developed with assistance from rubber manufacturers. The bogie described here features a lateral vibration linkage mechanism called a "pillar boom," replacing traditional metal coil springs. It uses a three-layer airbag structure that functions only in the vertical direction, with the auxiliary air chamber located inside the upper bolster beam.
Initially, air spring systems included an orifice between the main air spring and the auxiliary chamber to create damping through airflow resistance. However, because the flow characteristics of air through the orifice are non-linear, adjusting the orifice size directly affects the spring constant. To ensure adequate damping, hydraulic dampers were initially used alongside air springs. Later, some designs eliminated oil dampers entirely, relying on optimized orifice sizes determined through vibration testing. This approach led to the development of self-damping air spring bogies, improving ride quality without additional components.
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