This paper introduces an approach to study a valve's internal fluid dynamics. During operation, the flow causes forces on the spool. These forces must be correctly balanced. Since these forces cannot be measured, a three-dimensional (3D) computational fluid dynamic (CFD) modeling approach is needed. A case study has been undertaken to verify the approach on a two-way pressure compensated flow control valve. Since forces vary during operation, the analysis must be transient. From the initial zero spool position, the flow goes through the valve causing a spool shift inside the valve's housing until the spool stops at its final position. Forces depend on the spring reaction, the inlet pressure force, the pressure force of the fluid inside the spool, and the spring holder volumes, and the balance of forces influences the outlet flow rate at the final spool position. First, the initial case geometry was modeled, prototyped, and tested, and this geometry was studied to verify the model accuracy compared to experimental data. The comparison shows good agreement with a maximum error of 3%. With the same approach, several other geometries were designed, but only the best geometry was prototyped and tested. The model was adopted to make several analyses of velocity contouring, streamlines trends, and pressure distribution in the fluid volume. The modeled and tested results achieved the expected performance confirming the effectiveness of the methodology.

High power density, good controllability and low cost are the most appealing characteristics that make hydraulic systems the best choice for many applications. Current state of the art hydraulic variable displacement pumps show high efficiency at high displacement while they have poor efficiencies at low displacement. This paper proposes a novel alternating flow (AF) variable displacement hydraulic pump to 1) eliminate metering losses by acting as a high-bandwidth pump for displacement control, 2) achieve high efficiency across a wide range of operating conditions and displacements, and 3) allow multiple units to be easily common-shaft mounted for a compact multi-actuator displacement control system from a single prime-mover. A dynamic model using first principles describes the cylinder pressure, flows between pairs of cylinders, and net inlet and outlet flows as a function of the pump's phase shift angle. The model captures hydraulic check valve dynamics, the effective bulk modulus, leakage flows, and viscous friction. Piston kinematics and dynamics are discussed and energy loss models are presented. A first prototype of the AF pump was constructed from two inline triplex pumps that were modified so that three piston pairs were created. Experiment tests were conducted and used to validate the model. After model validation, simulation results from the model can offer an initial evaluation of this novel pump concept and potential applications and can be used to guide the design for future prototype of the AF hydraulic pump.

This research presents a lumped parameter numerical model aimed at designing and optimizing an axial piston pump. For the first time, it has been shown that a lumped parameter model can accurately model axial piston pump dynamics based on a comparison with computational fluid dynamic (CFD) models and experimental results. Since the method is much more efficient than CFD, it can optimize the design. Both steady-state and dynamic behaviors have been analyzed. The model results have been compared with experimental data, showing a good capacity in predicting the pump performance, including pressure ripple. The swashplate dynamics have been investigated experimentally, measuring the dynamic pressure which controls the pump displacement; a comparison with the numerical model results confirmed the high accuracy. An optimization process has been conducted on the valve-plate geometry to control fluid-born noise by flow ripple reduction. The nonlinear programming by quadratic Lagrangian (NLPQL) algorithm is used since it is suitable for this study. The objective function to minimize is the well-known function, the nonuniformity grade (NUG), a parameter directly correlated with flow ripple. A prototype of the best design has been realized and tested, confirming a reduction in the pressure ripple. An endurance test was also conducted. As predicted from the numerical model, a significant reduction of cavitation erosion was observed.

In this study we present a procedure for the design and implementation of a control strategy to optimize energy use within a light weight hydraulic hybrid passenger vehicle. The hydraulic hybrid utilizes a high pressure accumulator for energy storage which has superior power density than conventional battery technology. This makes fluid power attractive for urban driving applications in which there are frequent starts and stops and large startup power demands. A dynamic model of a series hydraulic hybrid powertrain is presented along with the design of a model predictive control based energy management strategy. Model predictive control was chosen for this study because it uses no future information about the drive cycle in its design. This increases the flexibility of the controller allowing it to be directly applied to a variety of drive cycles. Using the model predictive framework, a holistic view of the powertrain was taken in the design of the control strategy, and the impact of each actuator’s efficiency on overall efficiency was evaluated. A hardware-in-the-loop experiment using an electro-hydraulic powertrain testbed was then used to validate the dynamic model and control performance. Through a simulation study in which each actuator’s efficiency was given varying levels of priority in the objective function, it was found that overall system efficiency could be improved by allowing for small sacrifices in individual component performance. In fact, the conventional wisdom of using the additional degrees of freedom within a hybrid powertrain to optimize engine efficiency was found to yield the lowest overall powertrain efficiency. In this work we present a rigorous framework for the design of an energy management strategy. The design method improves the powertrain’s operational efficiency by finding the best balance between optimizing individual component efficiencies. Furthermore, since the design of the control strategy is built upon an analysis of individual components, it can be readily extended to other architectures employing different actuators.

In this paper, a three-dimensional (3D) computational fluid dynamics (CFD) methodology to improve the performance of hydraulic components will be shown, highlighting the importance that a study in the fluid mechanics field has for their optimization. As known, the valve internal geometry influences proportional spool valve hydraulic performance, axial flow forces, and spin effects on the spool. Axial flow forces and spin effects interact directly with the position control performance of a direct actuating closed-loop control valve, reducing its capability. The goal of this activity is the study of the torque on the spool induced by the flow and using a CFD 3D methodology to identify causes of this phenomenon and to find a general mathematical solution to minimize the spool spin effect. The baseline configuration and the new ones of the proportional four-way three-position closed-loop control spool valve have been studied with a mathematical model. The models were also validated by the experimental data performed in the Hydraulic Lab of the University of Naples. In particular, the tests allowed to measure the torque on the spool varying the oil flow rate, using a dedicated test bench layout where the spool was directly connected to a torque meter. Several geometries have been analyzed to find the best one to minimize spool spin behavior while maintaining an acceptable pressure drop. The study results confirmed the significant improvement of overall component performance.