Damping of horizontal motion to suspension air bellows in heavy commercial vehicles

Suspension systems constitute one of the most critical subsystems in modern vehicles, acting as an intermediary between the chassis and the ground. Their fundamental purpose is to regulate the interaction between the vehicle body and road surface by absorbing shocks and vibrations caused by road irregularities. Through this function, suspension systems contribute not only to passenger comfort but also to cargo safety, vehicle stability, and road-handling performance. Over time, advancements in vehicle design and material technologies have led to the evolution of suspension systems with diverse structural configurations and material compositions. While metallic coil and leaf springs have historically been dominant due to their simplicity and robustness, the increasing demand for weight reduction, improved comfort, and adaptability has accelerated the adoption of composite springs and, most prominently, pneumatic (air) suspension systems. In this thesis, the types of suspension systems used in heavy commercial vehicles, their design criteria, operating principles, advantages, and disadvantages will be examined in detail. In addition, the effects of suspension systems on vehicle performance, as well as the key parameters related to road safety and driving comfort, will be addressed. This study aims to serve as a guide particularly for engineers engaged in the design and development of heavy commercial vehicles. The proposed design aims to extend the service life of air springs. To minimize frequent failures such as air spring ruptures, design improvements have been introduced at the connection points of the springs, and various optimizations have been presented. By reducing unexpected loads, or loads that are inevitable due to design constraints, this design is expected to provide significant advantages in terms of safety, cost, comfort, and driving performance. Air suspension systems, which utilize air springs as the primary elastic element, are particularly valued for their ability to provide adjustable stiffness, maintain ride height under varying load conditions, and enhance both ride comfort and handling characteristics. Nevertheless, despite their advantages, air springs are inherently designed to resist vertical loads, while operational scenarios often subject them to additional non-ideal loading conditions. Events such as sudden acceleration, braking, or lateral maneuvers introduce horizontal and angular forces that deviate from the intended design parameters. Temporary exposure to such lateral forces may not cause immediate failure; however, prolonged and repeated exposure leads to premature material fatigue, reduced durability, and eventually a shorter service life of the air spring. Addressing this issue has become a crucial engineering challenge in the optimization of heavy-duty and passenger vehicle suspension systems. The primary objective of this thesis is to develop, analyze, and validate a novel design approach that minimizes the detrimental effects of horizontal loads acting on air springs. The central hypothesis of this research is that the incorporation of controlled flexibility in the supporting components can provide an effective mechanism for mitigating undesired lateral stresses without compromising the vertical load-bearing capacity of the suspension system. To this end, a design innovation was proposed in the carrier element: instead of a conventional rigid fixed joint, a channel-based connection was developed. This channel configuration provides a defined allowance for movement under horizontal forces, thereby redistributing the stress flow, reducing direct lateral impact on the air spring, and extending its service life. The research methodology adopted in this study integrates parametric design exploration, finite element analysis (FEA), and iterative optimization techniques. Three-dimensional models of the proposed suspension components were created using advanced computer-aided design (CAD) software. Multiple design iterations with varying dimensions and geometrical parameters were generated, with particular focus placed on the length and angular orientation of the movement channel in the control arm. These parameters were identified as critical in determining the ability of the system to accommodate horizontal displacements while maintaining vertical stiffness. To ensure computational accuracy, mesh convergence studies were systematically conducted. Various mesh sizes and element types were applied to the models, and sensitivity analyses were performed to identify the optimal mesh configuration. Static structural analyses were initially performed to evaluate the strength and deformation characteristics of the redesigned components under representative loading conditions. Subsequently, rigid body dynamics analyses were carried out, with boundary conditions carefully defined to replicate realistic operating environments. The integration of static and dynamic analyses provided a holistic assessment of the proposed design's performance. The comparative evaluation between the reference (conventional) suspension model and the newly proposed design revealed substantial improvements. In the reference model, the air spring was directly subjected to significant horizontal forces, which could lead to accelerated wear and fatigue. In contrast, the proposed design successfully minimized the magnitude of lateral loads transferred to the air spring. The results demonstrated that the channel-based design redistributed these forces within the supporting structure, thus effectively safeguarding the air spring against premature failure. Additionally, the redesigned components exhibited sufficient strength and stability to withstand operational loads, as confirmed by static and dynamic simulations. Beyond demonstrating technical feasibility, the outcomes of this study highlight the broader implications of incorporating design flexibility into suspension systems. By reducing the detrimental influence of non-ideal loading conditions, the proposed design not only extends the lifespan of air springs but also enhances overall vehicle reliability, safety, and operational efficiency. The approach contributes to reducing maintenance costs and downtime, which are critical factors in both passenger and commercial vehicle sectors. In conclusion, this thesis presents a novel design strategy that addresses a long-standing limitation of air suspension systems by minimizing the exposure of air springs to horizontal loads. The integration of advanced CAD modeling, finite element simulations, and iterative optimization provides a robust methodological framework for suspension design enhancement. The findings underscore the importance of designing suspension systems that are not only structurally strong but also dynamically adaptable to real-world operating conditions. Future research will focus on experimental validation of the proposed design through prototype development and physical testing under laboratory and field conditions. Furthermore, the scalability of the concept to different vehicle classes and its potential integration with active and semi-active suspension technologies present promising directions for continued investigation. To mitigate the impact of sudden lateral loads, a controlled allowance for movement was introduced into the system, thereby reducing the horizontal force directly transmitted to the air spring. Through iterative studies focusing on the correct boundary conditions, a design configuration was achieved in which lateral forces were minimized. Static analyses of the components confirmed that the existing geometries possessed sufficient structural strength. Further optimization is possible by considering additional factors such as manufacturing methods, weight reduction, and cost efficiency. Moreover, since the proposed system has been compared with a specific reference product group, future studies may extend the analysis to other product groups with higher load-carrying capacities. In addition to the improvements introduced by the proposed system, there are also certain aspects that require further development. Since relative motion will occur within the channel, noise and vibration are expected to be observed. The magnitude and effects of these phenomena will become clearer following experimental investigations. It is evident that, compared to the conventional system, higher levels of noise and vibration may arise. Moreover, the machining of the channel will require a more detailed manufacturing process, which is likely to result in additional production costs. Other aspects that need to be refined and improved will also become more evident after experimental validation. In the proposed design, deformation within the channel hole of the carrier component, particularly at the connection between the air spring lower mounting part and the carrier, poses a potential risk. This indicates a possible need for design improvement in the connection region. Conducting a more detailed study of the design in this area would be beneficial. Furthermore, the dimensions of the connection pin inside the channel hole should also be examined and optimized accordingly. The optimization study will be further expanded by considering all system components in detail. Based on the weight of the parts and the loads to which they are subjected, modifications in the manufacturing method may be required. Although cast parts are more economical, forging may be considered if a more robust component is needed. Additionally, certain geometrical modifications should be investigated to ensure better compatibility and integration among system components. In particular, the distance between the axle on the carrier part and the air springs is critical from a design perspective, as it generates a moment that directly influences the operational characteristics of the air springs. Another important aspect is the selection of air spring types. While the present study was conducted using identical air springs as the reference configuration, future studies could explore the application of different air spring types with similar performance characteristics. Experimental validation will be highly beneficial to verify the results of the computer-aided analyses and to identify any unforeseen issues. The production of system prototypes is planned in order to obtain real-world performance data. By comparing the prototypes with the existing product, it will be possible to evaluate the suspension system both from a hysteretic behavior perspective and to assess the impact of the proposed improvements on the service life of the air springs. The contributions of this study will become clearer with the support of experimental data. Following the experimental results, any potential need for design revisions can be identified, enabling further optimization of the system.