A Semi-Active Vibration Isolation System for the Low Frequency Excitation Region of Vehicle Seats

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Yazan Dabbas
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Human bodies are often exposed to vibrations, most commonly through a vehicle seat or while walking. Exposure to such vibrations for a prolonged period could have adverse effects on health and activities. These unwanted vibrations are generally distributed in the low-frequency range (0.5-25 Hz), which falls into the human body parts' resonant frequency. Many studies have shown that the essential parts of the human body vibration frequency are generally between (3-17) Hz, and the sensitive parts are located in (6-8) Hz. Thus, to avoid such frequencies transmitting to the human body while driving, in this project, a proper, effective, compact, low-dynamic, and high-static stiffness system that can fit under the seat of B-Segment and C-segment cars has to be designed. In doing so, an enhanced quasi-zero stiffness (EQZS) isolator is proposed in this project. The isolator consists of two oblique springs and a vertical spring to support a load to achieve quasi-zero stiffness at the equilibrium position. However, achieving the equilibrium position under a wide range of loads cannot be done with the typical quasi-zero stiffness isolator. Thus, two components are added to enhance the performance of the isolator. To support any additional load above the weight of the supported load by the vertical spring, a sleeve air spring is used; this is done by increasing the pressure delivered to the air spring, which increases the stiffness, thus supporting higher loads. However, increasing the stiffness in a system that depends on component values would cause a problem. Therefore, to overcome this situation, a horizontal adjustment mechanism is used to adjust the ratios. The main reason is that it was impossible to reach higher frequencies with the existed stroke when a heavy load is used, hence not reaching the equilibrium position which may be made the final result inaccurate.