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.

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.

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.

Predictive Pressure Control of a Monopropellant Powered Actuator

This work presents a model-based predictive control methodology applicable to systems with discrete input values (on/off) subject to a pure time delay. Specifically, the goal of this work is to develop a controller that will track a desired pressure for a monopropellant-powered pneumatic system with binary on/off input valves. The pneumatic actuator is pressurized by the catalytic decomposition of the liquid monopropellant hydrogen peroxide. The challenge is tracking a proportional output with a binary input, which means the output amplitude is not proportional to the input amplitude, but is proportional in time. This requires the controller to predict the future states for each of the two input candidates, on or off. The error between the predicted future states and the current desired states is calculated for each of the inputs. The control candidate that produces the smallest predicted Lyapunov function value is chosen. This results in the controller tracking a time delayed version of the desired pressure signal. Experimental results of the predictive controller demonstrate the effectiveness of this idea.

Static and Dynamic Analysis of HIL Simulator for Fluid Power Driven Machines

A Hardware-in-the-loop (HIL) simulation based method for designing and testing of fluid power driven machines has recently been studied in [1], [2] and [3]. In those papers the method has successfully been tested for driving physical prototypes with simulation models of various hydraulic circuits. Although the results of the tested method have appeared to be reasonable the critical boundary conditions of the system has not yet been studied. In this paper a simple hydraulic system is modeled and used for driving the simulator. The simulated system is then built from real components and measured. The measured and simulated results are compared. One of the main goals of this paper is to find answer to the following question: What is the maximum bandwidth that can be put out from the simulator with sufficient accuracy. The answer demonstrates the applicability of the developed HIL-simulator. Also different sizes of time steps are studied.

Design and Evaluation of a Pneumatic Gantry Robot for the Grinding of Steel Blanks

This paper describes the design and evaluation of a pneumatic gantry robot that is used to grind the edges of steel blanks as part of a finishing operation prior to being stamped. The objective of this research project is to automate the grinding process in order to reduce the frequency of cracking. The required force and degree of precision needed were thought to be within the capabilities of a pneumatically actuated robot. This would keep the cost of the apparatus down, which was important given the low capital cost of the manual operation. Furthermore, given that manipulation of the air pressure is the mechanism used to move a pneumatic actuator, the combined control of force and position is inherent to the system. A number of different pneumatic circuit configurations were examined before adopting a design that uses a combination of directional solenoid and flow control valves controlled by a Programmable Logic Controller (PLC). Pressure transducers and analog linear potentiometers are used for data acquisition. Laboratory test results are presented as well as a discussion of additional work that must be completed with the pneumatic gantry robot before field tests are conducted.