Stability and Energy Efficiency Improvement of Hydraulic Excavator Arm Control System With a Novel Asymmetric Pump

Pump controlled hydraulic circuit is an energy efficient alternative to valve controlled system, as they eliminate the throttling loss and require less cooling power. In all pump controlled systems, the internal and external leakages of the pump and actuator, especially the unequal flow rates of the single rod cylinder must be compensated. In presently existing solutions, an additional pump or some valves are used to compensate the unequal flow rates, leakages and to pressurize the system. However, these approaches increase the system complexity and complex control strategies are required to improve the overall system dynamic performances. Also, some of them suffer from undesired and uncontrolled pressure and velocity oscillations when the load force is small or its direction changes. This paper addresses the unequal flow rates compensation problem and stability problem of pump controlled single rod cylinder system, and proposes a novel solution for it. The system under consideration utilizes a new designed asymmetric pump which can match the unequal flow rates of the single rod cylinder basically. The feasibility of the new circuit is validated by both mathematics and multi-body simulation model. The results show that the undesired velocity oscillations can be removed up. Furthermore, the operating characteristics and energy efficiency of the arm cylinder with the new scheme based on the designed open-loop and closed-loop strategies are studied on a real excavator. The results show that there is no obvious velocity fluctuation with the asymmetric pump and the position controlled precision is satisfied. Compared with the independent metering circuit, the energy-saving ratio reaches to 57% during a working cycle.

Experimental Validation of Flow Force Models for Fast Switching Valves

This paper comprises a detailed study of the forces acting on a Fast Switching Valve (FSV) plunger. The objective is to investigate to what extend different models are valid to be used for design purposes. These models depend on the geometry of the moving plunger and the properties of the surrounding medium. A few analytic expressions have been suggested in the literature and these have been supported by CFD simulations, yielding accurate coherence for a large part of the fluid domain. However, when a moving body approaches a stationary body, squeeze film effects will occur if the plunger velocity is non-zero. This is the case in FSVs, where it results in an additional dampening effect, which is of relevance when analyzing contact-impact. Experimental data from different tests cases of a FSV has been gathered, with the plunger moving through a medium of either oil or air. This data is used to compare and validate different models, where an effort is directed towards capturing the fluid squeeze effect just before material on material contact. The test data is compared with simulation data relying solely on analytic formulations. The general dynamics of the plunger is validated for the established models, but an additional investigation of the dampening force is necessary. Therefore, numerical analyses are introduced to enhance the knowledge of the hydrodynamic end dampening. This has a visible effect on the velocity profile at the end-stop. This profile represents the measurements more accurately, but it is not possible to verify the velocity profile at the valve seat end-stop due to measurement uncertainties.

Design of a Velocity Control System Using an Inlet Metered Pump

This work introduces a new way to control hydraulic cylinder velocity using an inlet metering pump system to control the hydraulic flow entering the cylinder. The inlet metering system consists of a fixed displacement pump and an inlet metering valve that adjusts the hydraulic fluid flow entering the pump as required. The energy losses associated with flow metering in the system are reduced because the pressure drop across the inlet metering valve can be arbitrarily small. The fluid is supplied to the inlet metering valve at a fixed pressure using a charge pump. A velocity control system is designed using the inlet metering system as means to control the fluid flow to a hydraulic cylinder. In addition to the inlet metering system, the velocity control system designed in this work includes a four-way directional valve to set the fluid flow direction according to the desired direction of the hydraulic cylinder velocity. Open-loop and closed-loop proportional and proportional derivative (P and PD) controllers are designed. Designs with the goals of stability and performance of the system are studied so that a precise and smooth velocity control system for the hydraulic cylinder is achieved. In addition to potentially high efficiency of this system, there is potential for other benefits including low cost, fast response, and less complicated dynamics compared to other systems. The results presented in this work show that the inlet metering velocity control system can be designed so that the system is stable, there is zero overshoot and no oscillation.

Research on Sealing Performance in High Pressure Oil-Free Miniature Air Compressor

High pressure oil-free miniature air compressor has an irreplaceable role in some high demand areas such as cooling, scuba diving and pneumatic catapult due to its remarkable advantages such as compacted size, lightened weight and clean output gas. As the important sealing component in the high pressure oil-free miniature air compressor, piston rings hold the properties such as tiny diameter (less than 10mm), high sealing pressure (up to 410 bar) and high surrounding temperature (up to 500K), which make them distinctive from conventional piston rings. A mathematical model was established to simulate the pressure distribution of the compressor chamber, as well as the gap between the sealing rings. Sensitive parameters were considered to investigate their effects on the sealing performance such as the number and the cut size of the piston rings, the suction and discharge pressure and the rotary speed. The mathematical model was verified by comparing to published experimental research work. These work help to reveal the severe non-uniformity of the pressure distribution of different chambers, which were suggested be the primary cause of the premature failure of the sealing rings, thus improving the sealing performance and the service life of the air compressor.

Kinematic Multi-Objective Optimization of Circular-Toothed Gerotor Pumps by Genetic Algorithm

A gerotor gear generation algorithm has been developed that evaluates key performance objective functions to be minimized or maximized, and then an optimization algorithm is applied to determine the best design. Because of their popularity, circular-toothed gerotors are the focus of this study, and future work can extend this procedure to other gear forms. Parametric equations defining the circular-toothed gear set have been derived and implemented. Two objective functions were used in this kinematic optimization: maximize the ratio of displacement to pump radius, which is a measure of compactness, and minimize the kinematic flow ripple, which can have a negative effect on system dynamics and could be a major source of noise. Designs were constrained to ensure drivability, so the need for additional synchronization gearing is eliminated. The NSGA-II genetic algorithm was then applied to the gear generation algorithm in modeFRONTIER, a commercial software that integrates multi-objective optimization with third-party engineering software. A clear Pareto front was identified, and a multi-criteria decision-making genetic algorithm was used to select three optimal designs with varying priorities of compactness vs low flow variation. In addition, three pumps used in industry were scaled and evaluated with the gear generation algorithm for comparison. The scaled industry pumps were all close to the Pareto curve, but the optimized designs offer a slight kinematic advantage, which demonstrates the usefulness of the proposed gerotor design method.

Application of an Analytical Model for Simulating Hydraulic Systems Containing Internal Lines With Turbulent Flow

It is not uncommon for simulation models for the dynamics of hydraulic systems to contain fluid lines with turbulent flow. This paper demonstrates applications of an analytical model for pressure transients in lines with turbulent flow for lines with boundary conditions defined by hydraulic components such as pumps, valves, actuators, and restrictions; the model can be simplified for cases of laminar flow. The equations for conducting simulations with time varying inputs and for calculating eigenvalues of systems in which fluid lines are internal components are formulated. For an example demonstrating application of the equations, the model is used to simulate and optimize the performance of a hydraulic fracking system which involves the pumping of large volumes of water with additives through pipes under turbulent flow conditions into rock fissures. Specifically, the model is used to generate the frequency response of the flow transients in the pipe resulting from pump flow pulsations. This frequency response is then used to compute the eigenvalues of the system. The model is then used to conduct time domain simulations to determine the potential flow amplifications into rock fissures associated with pulsing the flow from the pump at the resonant frequency of the pressure transients in the pipe. The results reveal flow amplifications into the fissures of up to 22 times depending on the pulse shape of the input flow, the Reynolds number of the mean flow, the fluid properties of the slurry, and the length and diameter of the pipe.

Cavitation Erosion in the Portion of an Oil Passage Through Which Bubbles Pass

Cavitation erosion is a serious problem in the hydraulic system of construction machinery. In particular, the erosion which occurs even when cavitation bubbles only pass through oil passages, occurs at a connecting portion between the hydraulic components and piping, and the erosion causes oil leakage, which is a serious problem for hydraulic systems. However, it is difficult to predict the eroded area and to prevent the erosion because of a lack of research findings. The present study investigated erosion in the portion through which cavitation bubbles passes using a basic experimental apparatus that simulates an oil passage of hydraulic components, and by conducting a computational fluid dynamics simulation. The following results were obtained. Erosion occurs near the outlet of the oil passage, cavitation bubbles frequently disappear rapidly near the area of erosion, and the cause of bubble disappearance is the pressure distribution and amplification of the pressure wave of cavitation jets at the outlet of the oil passage. These results help explain the erosion generation mechanism and the characteristics of erosion in oil passages of hydraulic components, and can be used to design methods of reducing erosion.

Modeling and Simulation of a Hydraulic Drill for Control System Design Purposes

In rock excavation processes, hydraulic rotary-percussive drilling is used for drilling and blasting in both surface and underground drilling operations. A hydraulic percussive drilling system is composed of percussion, rotation, feed, and flushing functions. In this paper, we detail the interaction of feed and rotation functions using a rock model. The feed actuator is a cylinder drive and a hydraulic motor actuator rotates the drill bit. The feed is force controlled and rotation is torque controlled by a feed reduction valve acting on the pressure compensator of the mobile hydraulic proportional directional control valve. In addition, in this work an individual load sensing variable displacement pump is used for both hydraulic functions. A suitable rock model is developed and verified against a measurement set. The inputs of the rock model are percussion drill flow rate, percussion pressure, feed force, and rotation torque, and the outputs are drill bit penetration rate and rotational speed. The modeling work is carried out to enable intelligent rock drilling control system development for changing rock conditions. The simulation results obtained verify that the simple rock model emulates various rock characteristics ranging from extremely hard rock like granite to softer minerals and that the changes in drilling parameters were as expected.

Hydraulic Damper Concept for Thruster Ice Impact Load Reduction

Steerable thrusters are used to maneuver a vessel in open sea environment. The harsh environment of arctic seas introduces certain challenges with propellers hitting ice and decreasing lifetime of the system, as the loads generated by ice impacts are significantly higher than nominal loads. Damping of an ice impact load is a difficult task since the impacts have high torsional loads and they occur only in a fraction of the lifetime of the system. Commercial dampers are hard to find since they do not generally have the capacity for damping such high loads. The proposed active hydraulic damper reduces ice impact loads by accelerating and decelerating the shaft line. The lack of space and commercial components narrow down the possibilities but simulation results with the system show some positive effects in typical ice impact scenario. The system also recuperates most of the used energy and stores it to accumulator.