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Hydraulic Control Systems

This paper describes the design and prototyping of a new high-performance actuation system that combines the benefits of conventional hydraulic systems and direct-drive electrical actuators, namely high torque/mass ratio and modularity. It is referred to as the electrohydraulic actuator (EHA) and results from the fusion of the above-mentioned technologies. The EHA is a unique device with its own characteristics and requires hydraulic components that are specifically tailored to its needs and requirements. Based on a mathematical model of the EHA, the requirements for its components are determined. These requirements are used as a basis for component selection, component modification, and design of a customized new symmetrical linear actuator. The analysis of the EHA presented is supported by experimental data and explains the extremely high level of performance attained by a prototype of the EHA.

Design of a new high-performance electrohydraulic actuator

The importance of sensitivity analysis in engineering design cannot be over-emphasized. In design under uncertainty, sensitivity analysis is performed with respect to the probabilistic characteristics. Global sensitivity analysis (GSA), in particular, is used to study the impact of variations in input variables on the variation of a model output. One of the most challenging issues for GSA is the intensive computational demand for assessing the impact of probabilistic variations. Existing variance-based GSA methods are developed for general functional relationships but require a large number of samples. In this work, we develop an efficient and accurate approach to GSA that employs analytic formulations derived from metamodels of engineering simulation models. We examine the types of GSA needed for design under uncertainty and derive generalized analytical formulations of GSA based on a variety of metamodels commonly used in engineering applications. The benefits of our proposed techniques are demonstrated and verified through both illustrative mathematical examples and the robust design for improving vehicle handling performance.Copyright © 2004 by ASME

Analytical Variance-Based Global Sensitivity Analysis in Simulation-Based Design Under Uncertainty

This paper describes the design and prototyping of a new high performance actuation system that combines the benefits of conventional hydraulic systems and direct drive electrical actuators, namely high torque/mass ratio and modularity. It is referred to as the electrohydraulic actuator (EHA) and results from the fusion of the above mentioned technologies. EHA is a unique device with its own characteristics and requires hydraulic components that are specifically tailored to its needs and requirements. Based on a mathematical model of EHA, the requirements for its components are determined. These requirements are used as a basis for component selection, component modification, and design of a customized new symmetrical linear actuator. The analysis of EHA is supported by experimental data, and explains the extremely high level of performance attained by a prototype of EHA.

Design of a new high performance electrohydraulic actuator

A complete analysis of axial piston pump leakage and output flow ripples

Preface. Introduction. I. FUNDAMENTALS. 1 Fluid Properties. 1.1 Introduction. 1.2 Fluid Mass Density. 1.3 Fluid Bulk Modulus. 1.4 Thermal Fluid Properties. 1.5 Fluid Viscosity. 1.6 Vapor Pressure. 1.7 Chemical Properties. 1.8 Fluid Types and Selection. 1.9 Conclusion. 1.10 References. 1.11 Homework Problems. 2 Fluid Mechanics. 2.1 Introduction. 2.2 Governing Equations. 2.3 Fluid Flow. 2.4 Pressure Losses. 2.5 Pressure Transients. 2.6 Hydraulic Energy and Power. 2.7 Lubrication Theory. 2.8 Conclusion. 2.9 References. 2.10 Homework Problems. 3 Dynamic Systems and Controls. 3.1 Introduction. 3.2 Modeling. 3.3 Linearization. 3.4 Dynamic Behavior. 3.5 State-Space Analysis. 3.6 Block Diagrams and the Laplace Transform. 3.7 Stability. 3.8 Compensation. 3.9 Conclusion. 3.10 References. 3.11 Homework Problems. II HYDRAULIC COMPONENTS. 4 Hydraulic Control Valves. 4.1 Introduction. 4.2 Valve Flow Coefficients. 4.3 Two-Way Spool Valves. 4.4 Three-Way Spool Valves. 4.5 Four-Way Spool Valves. 4.6 Poppet Valves. 4.7 Flapper Nozzle Valves. 4.8 Conclusion. 4.9 References. 4.10 Homework Problems. 5 Hydraulic Pumps. 5.1 Introduction. 5.2 Pump Efficiency. 5.3 Gear Pumps. 5.4 Axial-Piston Swash-Plate Pumps. 5.5 Conclusion. 5.6 References. 5.7 Homework Problems. 6 Hydraulic Actuators. 6.1 Introduction. 6.2 Actuator Types. 6.3 Linear Actuators. 6.4 Rotary Actuators. 6.5 Conclusion. 6.6 References. 6.7 Homework Problems. III HYDRAULIC CONTROL SYSTEMS. 7 Valve-Controlled Hydraulic Systems. 7.1 Introduction. 7.2 Four-Way Valve Control of a Linear Actuator. 7.3 Three-Way Valve Control of a Linear Actuator. 7.4 Four-Way Valve Control of a Rotary Actuator. 7.5 Conclusion. 7.6 References. 7.7 Homework Problems. 8 Pump-Controlled Hydraulic Systems. 8.1 Introduction. 8.2 Fixed-Displacement Pump Control of a Linear Actuator. 8.3 Variable-Displacement Pump Control of a Rotary Actuator. 8.4 Conclusion. 8.5 References. 8.6 Homework Problems. INDEX.

Hydraulic control systems

In this paper, the theoretical flow ripple of an external gear pump is studied for pumps of similar size using different numbers of teeth on the driving and driven gears. In this work, the flow ripple equation is derived based upon the flow of incompressible fluid across the changing boundaries of a control volume. From this method, it is shown that the instantaneous length of action within the gear mesh determines the instantaneous flow ripple. A numerical and a closed-form approximation are presented for the instantaneous length of action and it is shown that the difference between these two solutions is negligible. Fast Fourier transform analysis is employed for identifying the harmonic frequencies and amplitudes of the flow pulse and these results are compared for 16 different pump designs. In summary, the results of this study show that the driving gear dictates the flow ripple characteristics of the pump while the driven gear dictates the pump size. As a result, it may be advantageous to design an external gear pump with a large number of teeth on the driving gear and a fewer number of teeth on the driven gear This design configuration will tend to reduce both the physical pump size (without reducing the volumetric displacement of the pump) and the amplitude of the flow pulsation, while increasing the natural harmonic frequencies of the machine.

The Theoretical Flow Ripple of an External Gear Pump

This research examines the idealized and actual flow-ripple of an axial-piston swash-plate type hydrostatic pump. For the idealized case, a perfect pump is examined in which the leakage is considered to be zero and the fluid is considered to be incompressible. Based upon these assumptions, closed-form expressions which describe the characteristics of the idealized flow-ripple are derived. Both the ripple height and the pulse frequency of the ripple are described for a pump with an even and an odd number of pistons. Next, the actual flow-ripple of the pump is examined by considering the pump leakage and the fluid compressibility and for computing these results a numerical program is used. For both the idealized case and the actual case-a comparison is made between a nine-piston, an eight-piston, and a seven-piston pump. From the idealized analysis it is quantitatively shown that the eight-piston design is less attractive than the nine or seven-piston design; however, the analysis of the actual pump flow reveals that the qualitative difference between all three designs may not be too significant. From a flow ripple point of view, the numerical results of this research show that a pump designed with an even number of pistons may be as feasible as one that is designed with an odd number of pistons. This is an unexpected conclusion.

The Discharge Flow Ripple of an Axial-Piston Swash-Plate Type Hydrostatic Pump

This study develops closed-form equations that may be used to guide the up-front design of a variable-displacement pump. In particular, the initial design of the control actuation system and the controller flow-gain is considered. A dynamic model of the pumping system is also presented and the dynamic effect of parameter variations such as actuator volume, discharge-hose volume, controller flow-gain and system leakage is discussed.

Modeling and designing a variable-displacement open-loop pump

The objectives of this research are to investigate the principal advantages of using various valve-plate slot geometries within an axial piston pump. In particular, three types of geometries are considered: a constant area slot geometry, a linearly varying slot geometry, and a quadratically varying slot geometry. By analyzing the pressure transients that are associated with each design at low pump displacements, it is shown that the magnitude of the pressure transition itself and the maximum pressure time rate-of-change may be specified for each design. In conclusion, it is shown that the constant area slot design exhibits the principal advantage of minimizing the required discharge area of the slot, the linearly varying slot design exhibits the principal advantage of utilizing the shortest slot length, while the quadratically varying slot design exhibits no principal advantage over either of the other two designs. The results of this research suggest that the use of quadratically varying slot geometry is not justified since it offers no obvious performance improvement.

Noah D. Manring

Papers

Hydraulic control systems

The Theoretical Flow Ripple of an External Gear Pump

The Discharge Flow Ripple of an Axial-Piston Swash-Plate Type Hydrostatic Pump

Modeling and designing a variable-displacement open-loop pump

Valve-Plate Design for an Axial Piston Pump Operating at Low Displacements