This research examines different techniques and proposes a Computational Fluid Dynamics (CFD) model as a robust tool for flow characterization of load leveling valves. The load leveling valve is a critical component of an air suspension system since it manages air spring pressure, a key function that directly impacts vehicle dynamic performance in addition to maintaining a static ride height. Efficiency of operation of a load leveling valve is established by its flow characteristics, a metric useful in determining suitability of the valve for application in a truck-suspension configuration and for comparison among similar products. The disk-slot type load leveling valve was chosen as the subject of this study due to its popularity in the heavy truck industry. Three distinct methods are presented to model and evaluate flow characteristics of a disk-slot valve. First is a theoretical formulation based on gas dynamic behavior through an orifice; second is an experimental technique in which a full pneumatic apparatus is used to collect instantaneous pressure data to estimate air discharge; and third is a CFD approach. Significant discrepancies observed between theoretically estimated results and experimental data suggest that the theoretical model is incapable of accurately capturing losses that occur during air flow. These variations diminish as the magnitude of discharge coefficient is altered. A detailed CFD model is submitted as an effective tool for load leveling valve flow characterization/analysis. This model overcomes the deficiencies of the theoretical model and improves the accuracy of simulations. A 2-D axisymmetric approximation of the real fluid domain is analyzed for flow characteristics using a Realizable k-ϵ turbulence model, scalable wall functions, and a pressure-based coupled algorithm with a second order discretization function. The CFD-generated results were observed to be in agreement with the experimental findings. CFD is found to be advantageous in the evaluation of flow characteristics as it furnishes precise data without the need to experimentally evaluate a physical model/prototype of the valve, thereby benefitting suspension engineers involved in the development and testing of load leveling valve designs. This document concludes with a sample case study which uses CFD to characterize flow in a modified disk-slot load leveling valve, and discusses the results in light of application on a heavy truck. / MS / A majority of heavy trucks in North America equipped with air suspensions use a device known as a load leveling valve. This is a mechanical control system which manages pressure in air springs to maintain a preset/constant static ride height irrespective of the payload, doing so by sensing the distance between the truck frame and the axle. The rate of airflow to/from air springs in response to a road disturbance or load shift is critical to the stability of the truck when on the road. This rate of airflow for a given set of conditions constitutes flow characteristics of a load leveling valve. Accurate measurement of flow characteristics is necessary to understand the actual effect of the use of a particular valve on a truck-suspension configuration. This research addresses that requirement by presenting three distinct methods to model and evaluate flow characteristics of a load leveling valve, conducted on the disk-slot valve for its popularity in the heavy truck industry. First is a theoretical formulation based on flow of gas through an orifice; second is an experimental technique in which a full pneumatic apparatus is used to collect instantaneous pressure data to estimate air discharge; and third is a Computational Fluid Dynamics (CFD) approach. Significant discrepancies observed between theoretically estimated results and experimental data suggest that the theoretical model is incapable of accurately capturing losses that occur during air flow. The disparities also justify the adoption of CFD as an alternate method. A comprehensive CFD model is proposed as a capable tool for load leveling valve flow analysis/characterization. This model overcomes the deficiencies of the theoretical model and improves the accuracy of simulations. CFD-generated results are found to be in agreement with the experimental findings, highlighting its effectiveness at flow characterization. The ability of a CFD model to furnish precise data without the need to experimentally evaluate a physical model/prototype of the valve promises to benefit suspension engineers involved in the development and testing of load leveling valve designs. This document concludes with a sample case study which uses CFD to characterize flow in a modified disk-slot valve, and discusses the results in light of application on a heavy truck.

This research provides a thorough flow characterization study to compare the functionality of two types of load-leveling valves that are commonly used for air suspension systems of commercial trucks. The first valve features a simple disk/slot design and is relatively compact for installation. The second type is larger and has a sophisticated, chambered design, which allows for considerably quicker fill and exhaust response times in the transient region. A new approach is introduced to estimate the transient mass flow rate of a load-leveling valve under different suspension pressures, without requiring a mass flow meter. An extensive series of dynamic tests are conducted to characterize and compare the two load-leveling valves. A generic heavy-truck pneumatic suspension, consisting of load-leveling valves, airspring, air tank, and air-hose fittings, is configured for testing. The test setup is used to evaluate the transient performance of each type of load-leveling valve in a typical truck suspension. The flow behavior of the system is validated by the force/pressure responses of the air spring due to various displacement excitations. The experimental results describe the detailed flow behavior of both valves. The flow characterization results can be incorporated as one of the most critical parameters for future model development of pneumatic systems. The tests indicate that the leveling valve with chambered design has a far faster transient flow response than the disk valve, although it is more complicated in its mechanical design and therefore costs more. To take advantage of the design simplicity of the disk valve, while also enabling it to have a faster transient response (compared with the chambered design), it is re-designed with larger flow openings and other elements to match the performance of the chambered valve for transient flow. A comparison of the experimental results and simulations validates that the re-designed rotary disk valve performs nearly the same as the chambered valve, but is simpler and costs less. The study's results are directly applicable to improving the transient dynamics of heavy truck air suspensions by providing a better understanding of how load-leveling valves can be used not only to provide ride-height control, but also to influence the roll and pitch dynamics of heavy trucks. / Master of Science / Heavy trucks are balanced using air suspension systems. These pneumatic controls provide stability when a truck undergoes a turn or other change in movement, including roll and pitch. As a truck experiences these changes, air is supplied or purged from the system to balance the truck. Load leveling valves control this flow of air that provides stability and are considered crucial elements in the overall design of a heavy truck. This study evaluates many different types of valves, namely a "chambered" valve and a "disk" valve. The chambered valve is large and has many parts, resulting in a heavy expense but high performance. The disk valve is a simpler design, making it much cheaper but at the expense of performance. The quality of performance that is evaluated here is the time it takes to fill or purge the air suspension, which is related to the mass flow. These characteristics were experimentally obtained and compared. The results showed the disk valve taking more time and having a lower flow rate, making its performance lower when compared to the chambered valve. The next aspect of this study is the modification of this disk valve design that is commercially available to make its performance comparable to the chambered valve. After a series of experiments, the modified design was verified to perform as well as the chambered valve. Overall, these results are important for the future design of heavy truck load leveling valves and clarify important characteristics to consider when designing them. The results from this study can lead to lower costs for heavy truck companies and a better ride for truck drivers.