Design of thermal mathematical model and 1D thermal analysis study of shock absorber internal and external temperatures for different shock absorber forces

In this thesis study, the thermal behavior of a shock absorber equipped with a Hydraulic Rebound Stop (HRS) system and operating under different damping forces is investigated. The primary focus of the study is to analyze the time-dependent temperature distribution of the hydraulic oil inside the shock absorber and the temperature of the outer tube. For this purpose, a comprehensive approach combining experimental investigations, thermal mathematical modeling, and one-dimensional (1D) numerical simulations has been adopted. The developed thermal model is validated through 1D simulations conducted using SimCenter Amesim software. Shock absorbers are critical suspension components that are subjected to continuous and long-term operation, particularly during durability and lifetime tests. During such tests, mechanical energy dissipated through damping forces is converted into thermal energy, leading to a significant increase in the temperature of the hydraulic oil. The rise in oil temperature directly affects the overall thermal behavior of the shock absorber and has a substantial impact on its performance, durability, and reliability. One of the most temperature-sensitive components in a shock absorber is the seal, which plays a vital role in preventing oil leakage and maintaining internal pressure. When the hydraulic oil temperature exceeds the allowable thermal limits of the seal material, degradation of material properties occurs. This degradation may result in seal deformation, loss of sealing performance, and eventually oil leakage. Such failures not only invalidate durability tests but also increase test duration, cost, and development time. Therefore, effective thermal management is a critical requirement during shock absorber lifetime testing. To prevent excessive temperature rise, an active cooling system is commonly employed during durability tests. In this system, a water jacket is mounted around the outer surface of the shock absorber. Temperature sensors placed on the outer tube continuously monitor the surface temperature, and the cooling system is activated or deactivated based on predefined upper and lower temperature limits. When the measured temperature exceeds the upper limit, cooling water flows through the jacket to reduce the external and internal temperatures. Once the temperature approaches the lower limit, the cooling system is stopped, and the test continues under normal operating conditions. For standard shock absorbers, these upper and lower temperature limits are generally well-defined based on established testing procedures and prior experience. However, in shock absorbers incorporating an HRS system, the determination of these temperature limits is not straightforward. The HRS system introduces additional flow restrictions, control elements, and valve mechanisms that significantly influence heat generation within the damper. As a result, temperature limits for HRS-equipped shock absorbers are often determined using a trial-and-error approach, which leads to extended test durations and increased testing costs. The main objective of this thesis is to develop a time-dependent thermal model that accurately describes the relationship between the hydraulic oil temperature and the outer tube temperature in a shock absorber equipped with an HRS system. By establishing this relationship, it becomes possible to predict internal oil temperature based on externally measured surface temperature, thereby enabling more efficient and reliable control of the cooling system during durability tests. To achieve this objective, the fundamental physical principles governing heat transfer within the shock absorber are first examined. The dominant heat transfer mechanisms, including conduction, convection, and thermal energy generation due to damping forces, are identified and modeled. Based on these principles, a thermal resistance network is established, and the corresponding heat balance equations are formulated for each component of the system. The shock absorber is modeled as a cylindrical structure composed of multiple concentric components. These components include the piston rod, hydraulic oil, sleeve, cylinder tube, reservoir, and outer tube. Each component is treated as a separate thermal node, and heat transfer interactions between adjacent components are described using equivalent thermal resistances. The influence of material properties, geometric dimensions, and convective heat transfer coefficients is incorporated into the model. An explicit numerical solution method is employed to solve the governing differential equations and calculate the transient temperature distribution within the shock absorber. This approach allows the temperature evolution of each component to be tracked over time under varying operating conditions. The numerical model is implemented and validated through 1D thermal simulations performed using SimCenter Amesim, which provides a reliable platform for system-level thermal analysis. The simulation results demonstrate that the shock absorber exhibits significant temperature variations when subjected to different impact and damping force levels. In particular, the hydraulic oil temperature shows a strong dependency on the damping force magnitude, operating frequency, and internal flow characteristics introduced by the HRS system. It is observed that the control ring geometry and valve system configuration, which are key subcomponents of the HRS system, play a crucial role in heat generation and temperature rise within the hydraulic oil. Furthermore, the thermal properties of the hydraulic oil, such as specific heat capacity and viscosity variation with temperature, are found to have a notable influence on the overall thermal response of the system. These effects highlight the importance of considering both mechanical and thermal characteristics in the design and analysis of HRS-equipped shock absorbers. The findings of this study emphasize the critical role of thermal management in shock absorber design and testing. The developed thermal model provides a valuable tool for predicting internal oil temperature based on measurable external parameters, thereby reducing reliance on trial-and-error methods. This approach has the potential to significantly shorten test durations, lower testing costs, and improve the reliability of durability tests for shock absorbers with advanced damping systems.In conclusion, this thesis contributes to the understanding of the thermal behavior of shock absorbers with HRS systems and offers a systematic methodology for thermal modeling and analysis. The results obtained serve as a solid foundation for future design improvements, optimization of cooling strategies, and development of more efficient and robust shock absorber testing procedures. Keywords: Shock Absorber, Thermal Mathematical Model, 1D Analysis, Heat Transfer, Numerical Analysis