Hydraulic Spool Valve Metering Notch Characterization Using CFD

This paper presents some results from an attempt to characterize hydraulic oil flow inside spool valves with different spool metering notches using Computational Fluid Dynamics (CFD). Hydraulic spool valve oil flow under different conditions has been simulated using a commercially available CFD software program. The fluid flow is assumed steady-state, incompressible, isothermal and normally in a turbulent mode. A complete simulation procedure is presented from parametric geometry creation with a 3-D solid CAD program through final post-processing of CFD results. Main focus of this study is to explore the effects of geometric parameters of notches on important hydraulic oil flow characteristics, such as flow force and discharge coefficients. Formulas, intended for predicting such flow forces and discharge coefficients at different stage of spool notch openings, have been generalized and summarized under certain conditions based on a CFD result database from groups of same types of notches. Results comparison to experimental data is also presented.

FE Approach: Electro-Mechanical-Fluid Interaction of Jet Pipe Electrohydraulic Flow Control Servovalve

Jet pipe electrohydraulic servovalve finds main application in feedback control system working on jet engine and fighter aircrafts. The analyzed jet pipe electrohydraulic servovalve is used in precise fuel control applications in gas turbine engine. This paper gives a new approach for servovalve modeling with the hydrostatic fluid elements in achieve steady state operation. The actual flow required to achieve the force balance is presented analytically. FE model gives the relationship between the spool and jet pipe position in achieving the steady state operation. The spool end cavity volume changes are presented.

Analysis and Optimization Design of Pressure Compensated Flow Control Valves

A pressure compensated valve (PC valve) is a type of flow control device that is a combination of a control orifice and a compensator (often called a hydrostat). The compensator orifice modulates its opening to maintain a constant pressure drop across the control orifice. In other words, the PC valve is so designed that the flow rate through the valve is governed only by the opening of the control orifice and is independent of the total pressure drop across the valve. Because of the high non-linearities associated with this type of valve, it is impossible, in practice, to design such a valve where the flow rate is completely unaffected by the pressure drop across the valve. In this paper, the effect of the non-linerities on the performance of the PC valve is investigated. First, a generic non-liner model of a PC valve is developed. Using this model, all possible operating conditions can be determined. Then a linearized model is developed and used to analyze the dynamic behavior of the PC valve. The model can then be used to optimize the design and operation of the valve for specific applications.

Determination of Discharge Coefficient for Ball Valves With Calibrated Inserts

The valve coefficient was measured for 1/2-, 3/4- and 1 nominal ball valves. It was desired to use a recently designed orifice insert with these valves to obtain smaller valve coefficients. Orifice inserts were placed into the body of a threaded ball valve just upstream of the spherical control element. The valve coefficient was measured for each insert, and an expression was determined to relate the orifice diameter to other pertinent flow parameters. Two groups were chosen to correlate the collected data, and a graph was developed. These results can be used as an aid in sizing the orifice insert needed to obtain the desired valve coefficient. The study has shown that a two parameter power law equation can be used as an aid in predicting the desired results. Knowing pipe size and schedule, the diameter of the orifice insert needed to obtain the desired valve coefficient can be approximated with minimum error. An error analysis performed on the collected data shows that the results are highly accurate, and that the experimental process is repeatable.

A Transient Hydrostatic Dynamometer for Single Cylinder Engine Research With Real Time Multi-Cylinder Dynamic Simulation

A new high-bandwidth transient hydrostatic dynamometer test system has been developed that accurately replicates multi-cylinder engine operation using a single-cylinder research engine. Single-cylinder engines are typically used for research because of their low cost and good cylinder accessibility for instrumentation and optics. This dynamometer maintains these advantages while dramatically improving transient and low speed testing capabilities. The system also incorporates hardware-in-the-loop models for simulation of other components that would typically be present in a vehicle application. These models include: adjoining cylinders and ancillary components in the engine, the transmission, driveline, and vehicle load. Utilizing these models it is possible to replicate actual driving cycles. This high-bandwidth transient dynamometer extends the test capabilities of single-cylinder research far beyond the traditional steady state regime, enabling transient speed single-cylinder engine research while providing single-cylinder engine operation that is comparable to the multi-cylinder engine.

Applicability of Pump Models for Varying Operational Conditions

It is commonly known that the characteristics of a fluid power pump depend on pump type, pressure, rotational speed and displacement. But in addition to these, also all the other parameters or factors associated with the operating conditions may have a significant effect on the characteristics. The most important of these are the pump construction and size, operating point temperature and the characteristics of the oil, which also depend on temperature and pressure. The aim of this study is to show the effects that the varying operational conditions have on the characteristics of a axial piston pump, to compare the measured characteristics with other published characteristics of axial piston pumps and to study the capability of pump models to represent these characteristics. The results include information of the effects of fluid temperature, type of fluid and the setting value of the displacement on the pump characteristics along with the effects of pressure and rotational speed. The sensitivity of the pump to each of the parameters is discussed. The effect of limited information of pump characteristics on the reliability of simulation results is studied using the Schlo¨sser models.

Robust Control of Oscillations in Agricultural Tractors

This paper relates to analyses and control of the oscillations occurring in many off road vehicles, which are designed without any suspension. Without suspension, the tire is the only elastic element acting between the vehicle and the ground but the suspension and damping properties of the tires cannot meet the demands for fast, safe and comfortable road transportation. In this paper the above-mentioned phenomenon is investigated with special focus on agricultural tractors. A control strategy is developed to make the implement counteract the movement of the tractor and thereby reducing the pitching oscillation. The control strategy is based on a linear plant model with constant or slowly varying parameters. Using a frequency-response approach the disturbance rejection is made effective over a significant portion of the system bandwidth. To improve robustness with respect to bounded disturbances (from the road) natural frequencies for the vehicle and implement is identified and the controller parameters tuned adaptively based on an optimization formulation.

Testing and Evaluation of Control Strategies for a Prototype Hydraulic Press

The work that this paper describes is the attempt to safely optimize, test and evaluate the performance of advanced strategies for the control of hydraulic systems. The method proposed is to use a computer model of a prototype hydraulic press to develop, optimize and test various controllers. The same tests are then repeated on the actual prototype of the press. The results of the experiments are compared to evaluate the accuracy of the model, the performance of the controllers, and the validity of the method.

Sensitivity Studies for the Shallow-Pocket Geometry of a Hydrostatic Thrust Bearing

Hydrostatic thrust bearings have been the object of considerable research for many years. The attention that these bearings have received is primarily due to the important role they play in the design and operation of heavy equipment. In this role, the hydrostatic thrust bearing is often considered to be the “Achilles heel” of the total machine system as failures result in catastrophic difficulties and expensive repairs. The objectives of this research are to examine the nuances of designing a hydorstatic thrust bearing using a shallow pocket as opposed to the more traditional deep pocket design. By using a two-dimensional model for this geometry, the basic features of the shallow pocket design are extracted in closed-form and behaviors that would be expected in the three-dimensional setting are identified. In this research, a single dimensionless parameter is used to describe the influence of the bearing speed under laminar flow conditions. The principal results of this research are closed-form expression that describe the load carrying capcity of the bearing, the tilting moment exerted on the bearing by a skewed pressure distribution, and the volumetric leakage of the bearing. Sensitivity studies are conducted using these results and the influence of small perturbations of the pocket depth are identified for bearings with different pocket widths. These results are discussed and conclusions are itemized in the final section of the paper.

H∞ Robust Control Design for Hydraulic Front Wheel Drive Speed Control of a Motor Grader

A dual-mode H∞ robust tracking controller design is presented to regulate the speed of a hydraulic front wheel drive system on a motor grader. The controller design uses a multiplicative unstructured uncertainty model to account for the un-modeled dynamics of the plant and parametric uncertainties such as variations in fluid temperature and air entrainment. The H∞ design is compared to a classical PI controller design, which is the existing industrial practice. It is shown that the H∞ design provides a higher level of stability robustness and better performance guarantees, which make it a viable candidate for motor grader application.