A CFD Approach to the Optimization of Components in Fluid Power

Hydraulics has the highest energy density of any power transmission technology and is a very effective way to transfer power from a source to a user. The convenience of sharing a single power source with many users with high reliability, justifies the wide use of this technology. The recent development of new components and technologies especially the use of electronic sensors and controls on hydraulic components, makes hydraulic systems more flexible and efficient. Hydraulic systems can be used in niche application where electromagnetic effects must be avoided. But hydraulics has a few disadvantage including low efficiency, high costs, noise, leaks and complexity. Hydraulic systems capability of creating high forces with small electronic control devices has found wide application, and electro hydraulic components are widely used in applications that require precise actuator control or matching of variable working conditions. Hydraulic is widely used in many sectors. In this PhD Thesis the research has been focused on the optimization of hydraulic components used in the industrial fields and on engines for lubrication circuits. In recent years, many studies were initiated to improve the performance of hydraulic components. However, the scientific understanding of valves, pumps and transmissions operation is limited because of the lack of three-dimensional fluid dynamics computation capability. In this PhD thesis a 3D computational fluid dynamics (CFD) modeling technique developed by the Hydraulic Research Group of the University of Naples Federico II led by Professor Adolfo Senatore is presented. The methodology has been applied for the study of several different applications. Using a three-dimensional CFD approach it is possible to improve component performance and the understanding of the internal flow of each component. To achieve the goals, the hydraulic research group of University of Naples “Federico II” has worked in close collaboration with the Center for Compact and Efficient Fluid Power at the University of Minnesota led by the Professor Kim A. Stelson. The first chapter describes, in detail, the three-dimensional CFD modeling methodology proposed in this thesis. After an introduction to Computational Fluid Dynamics (CFD), the methodology will be shown along with all possible applications. Then, in the second chapter, each study will be presented. Research is focused on the optimization of hydraulic components. In particular, these applications were studied: 1) Hydro - Mechanical Transmission, 2) Variable Displacement Vane pump, 3) Gerotor Pumps, 4) Engine Lubrication Circuit, 5) Pumps as Turbine (PAT), 6) Directional Spool Valve, 7) Flow Control Valve. The results demonstrate that the technique achieves high accuracy for a wide variety of applications and components

Design and Analysis of Hydraulic Hybrid Passenger Vehicles

University of Minnesota Ph.D. dissertation. September 2015. Major: Mechanical Engineering. Advisors: Perry Li, Thomas Chase. 1 computer file (PDF); x, 305 pages.The research described in this dissertation focuses on the development of computationally efficient design methodology to optimize the hydraulic hybrid power-split transmission for fuel efficiency, acceleration performance and robustness against powertrain uncertainties. This research also involve experimental implementation of a three-level hierarchical control approach on two test beds, requiring powertrain control design and fine-tuning. Hybrid powertrains have the potential to benefit the fuel efficiency of highway and off-highway vehicles. Hydraulic hybrid has high power density. Hydraulic power-split architecture is chosen in this study for its flexibility in operation and combined advantage of series and parallel architecture. An approach for optimizing the configuration and sizing of a hydraulic hybrid power-split transmission is proposed. Instead of considering each mechanical configuration consisting of combinations of gear ratios, a generalized kinematic relation is used to avoid redundant computation. The Lagrange multiplier method for computing the optimal energy management control is shown to be 450 times more computationally efficient for use in transmission design iterations. To exploit the benefit of high power density of hydraulics, a classical multi-objective solver is utilized to incorporate the acceleration performance criteria into the transmission design optimization. By considering worst-case uncertainty, the transmission design is optimized to be robust against powertrain uncertainties and insensitive to operating condition variations, and yet fuel efficient. The Generation I and II vehicles are experimental platforms built to implement controls and to validate the fuel efficiency gain for power-split transmission. The powertrain for the platforms are modeled to predict the potential fuel efficiency improvement by different energy management strategies. Results show maximum of 74\% fuel efficiency gain by optimizing engine management from CVT to full optimal hybrid operation. The three-level control strategy is implemented on the Generation I vehicle. This control strategy segregates the tasks of the drive-train into three layers that respectively 1) manages the accumulator energy storage (high level); 2) performs vehicle level optimization (mid-level); and 3) attains the desired vehicle operating condition (low level). Results validated the modularity and effectiveness of this control structure

Robust Optimal Design of Unstable Valves

Abstract—This paper is concerned with the application of robust control design concepts for the physical geometric design of electrohydraulic valves. Currently, limitations of solenoid actuators have prevented single stage electrohydraulic valves which are simpler and more cost effective from being utilized in high flow rate and high bandwidth applications. Fluid flow force induced instability has been proposed as a means to alleviate the demand on the solenoid actuators. Previous research has demonstrated that simple changes in the valve geometry can be used to manipulate both the transient flow force as well as the steady flow force for this purpose. This paper considers the dimensional design of such “unstable ” valves to minimize the net steady flow force. The robust optimal design method, in which the design must be robust to uncertainties such as variations in operating pressure ranges and dynamic viscosity, etc., is proposed. By representing the original problem as a linear fractional transformation interconnection, the robust design problem is formulated into one of synthesizing an optimal controller for an appropriate static plant with a structured uncertainty. An algorithm for solving this design synthesis problem is proposed. A case study is conducted to compare the nominal optimal (without considering uncertainty) and the robust optimal designs. It is shown that viscosity effect is exclusively utilized in the nominal optimal design, whereas both the viscosity effect and the nonorifice flux effect are needed in the robust optimal design. The robust optimal design imposes smaller steady flow force on the spool than the nominal optimal design under perturbed situations. Based on the robust design method, an actual prototype design of the unstable valve has been developed. Index Terms—Electrohydraulics, flow force, linear fractional transformation (LFT), proportional valves, robust design, structured uncertainty, unstable valve. I