External Gear Research Articles

Improving the dependability of the servo drives of unmanned aerial vehicles through optimized operating modes

Aim. Improving the reliability of servo drives through partial redundancy of structural components. Methods. The paper uses methods of harmonic analysis, technical system dependability theory. Results. The mean times to failure of servo drives that differ in terms of the level of redundancy of structural elements (external connectors, feedback sensors, control boards, electric motors and load gears) were compared. It was shown that structural element redundancy along with the capability to switch to still-operable elements in the course of servo drive operation enable a triple increase of the failure tolerance. The authors suggested criteria for identifying the moment of time for decision-making regarding an electric servo’s structure modification before the moment of failure of the redundant element of such servo. Conclusion. The method suggested in the paper allows formalizing the process of electric servo structure modification for the purpose of ensuring the required level of failure tolerance.

An advanced pressure pulsation model for external gear pump

Pressure pulsation is the inherent characteristic of external gear pump. This paper presents a new pressure pulsation model by considering the lateral clearance and manufacturing error. Firstly, inspired by the Archard model, the maximum roughness peak of lateral bushing surface with or without wear are measured by laser confocal microscope, which is to obtain the change law of lateral clearance indirectly and construct the lateral clearance model. Then, the manufacturing error model is constructed based on the long and short period errors of the master-slave gear acquired by the gear measuring center. Meanwhile, according to the boundary constraints, the lateral clearance model and the manufacturing error model are embedded into the lumped parametric model of the pressure pulsation to realize updating. Finally, the robustness of the new pressure pulsation model under different working conditions is verified, and the nature of the influence of the lateral clearance model and manufacturing error model on pressure pulsation is revealed. Experimental results on an external gear pump validate the merits of the new model in both time domain and frequency domain. The results can provide helpful guidance to understand the mechanism of external gear pump pressure pulsation.

Inter-chamber leakage flow through the transition contacts in epitrochoid generated star and ring hydrostatic units

The current study examines the impact of tooth clearance on the flow performance at the location of transition contact of the internal positive displacement trochoidal gear pump. The aim is to enhance the volumetric efficiency, which is caused by internal leakage due to tooth clearance. Two clearance models, that is, form closed and interference (forced closed) models of the pump help to elucidate the leakage phenomenon through which optimal volumetric efficiency can be achieved. Finite element investigation comprises the static structural analysis followed by 3D CFD analysis carried out for the study. The CFD model includes the contact deformations of external trochoidal gear due to the application of maximum pressure, which increases the inter-chamber leakage. Fluid velocity and pressure inside the pump have been predicated to understand the flow dynamics inside the pump. The simulation results were matched to theoretical values, and this shows a very excellent match. The volumetric efficiency of 89% with less than 1 gm/s of leakage has been achieved at a speed of 2500 rpm. Moreover, the simulation results show an increase in discharge flow with the interference model. Further, an empirical relation is established between volumetric efficiency, fluid density, and rotor speed using partial least square regression analysis.

Characteristics of Ecological Energy Carriers Used in Agricultural Technology

This article focuses on the properties of ecological energy carriers, which are used in agricultural and forestry technology. The aim of the article is to describe the degradation of the working fluid from the point of view of the atomic emission spectrometer, which is used for the purpose of monitoring contaminants and additive elements. The working fluid examined was Shell Naturelle HF-E 46, a universal ecological transmission–hydraulic fluid, which was tested on laboratory test equipment. The laboratory measurement was performed for 200 h, during which the gear hydraulic pump with external gearing was cyclically loaded according to the Vickers standard. The analysis of the transmission–hydraulic fluid was performed after every 50 working hours, where the analysis of the working fluid showed that there were no significant changes in the properties of the working fluid and fluid is suitable for work in agricultural and forestry machines operating in environmentally sensitive environments.

Wear material determination and parameters optimization of an external gear pump by Taguchi technique

Wear of a material in gear pump is affected by many parameters like hardness of the material and other operating parameters such as discharge, pressure, RPM etc. The hardness of the gear pump casing and gear, as a material parameter while RPM and discharge pressure are assumed as working parameters in this work to correlate simulated wear volume determined. Experimentation on gear pump was performed to check the effect of various parameters like pressure, discharge, efficiency etc. on performance of gear pump at regular interval of time. Archard model is applied here to determine the wear volume of a material surface using ANSIS workbench. The maximum volume loss due to wear has been obtained for the casing of defined hardness running at selected rpm and working pressure. In the next part of the work Taguchi analysis was carried out to found out the most affecting parameter on the performance of gear pump. Investigation of the various parameters like discharge pressure, hardness of casing material of pump and operating RPM on the wear of the external gear pump were explored by Taguchi technique. Factors affecting on the process with their optimization are determined using this method. After experimentation it is evident that wear volume of a material is affected by these factors and Taguchi approach is successfully implemented to identify the optimum parameters combination for achieving the best wear conditions for the external gear pump.

An experimental and numerical investigation into using hydropower plant on oil transmission lines

AbstractReplacing control valves in the inlet lines of oil transmission stations with hydropower plants can be a logical solution to convert energy losses into useful power. In this regard, this paper carried out an experimental and numerical investigation to study the feasibility of applying a pump as turbine in a hydropower system and its performance on the oil transmission lines. An experimental platform, comprising a tank, hydropower, centrifugal pump, electromotor, and measuring instruments, was constructed. An external gear pump was employed regarding the high working pressure of the system, maximally 80 bar, as an actuator of the centrifugal pump. By comparing the efficiency of the electropump with the hydropower‐driven pump, it was observed that maximum efficiency, approximately 20.6%, occurred when the pump reached its best efficiency point. Furthermore, based on experiments on hydropower‐driven pump under different inlet pressures, an optimal point was observed for the system. This issue enhanced the system's efficiency by 19% as the flow rate increased by 1.9 L/s in the inlet pressure of 80 bar. According to the results, as the flow rate increases, there is a descending trend in outlet pressure. Besides this, there is an optimum condition for the maximum efficiency of hydropower plants and this crucial point should be determined by experimental or numerical studies to reach maximum performance. Furthermore, extracted values of power from the computational fluid dynamics model were compared with the experiments with less than 8% error in most cases. Therefore, a correlation was introduced for the prediction of power based on effective parameters of outlet pressure and volumetric flow rate for the off‐design condition in each inlet pressure with roughly 2% error.

The extrusion of EPDM using an external gear pump: experiments and simulations

Abstract External gear pumps are used in fluid transport systems because of their tight clearances and accurate flow control. These tight clearances are a challenge for numerical studies in terms of spatial discretization. In earlier work, the flow of a viscous fluid in an external gear pump is computed using the finite element method (FEM). An element size based on the respective distance between boundaries is proposed. In this study, results based on the earlier work are compared to extrusion experiments of EPDM. The aim of this study is not only to validate the numerical simulations, but also to determine what material characteristics need to be taken into account for an accurate output prediction of the external gear pump. Especially the introduction of shear-thinning behavior results in an improvement of the amplitude of the pressure difference fluctuation. Taking into account compressibility, alters the torque fluctuation in such a way that it mimics the experiments. Unfortunately, the fluctuation in torque still has a too high amplitude. Eventually, simulations are performed including shear-thinning behavior, a temperature- and pressure-dependent viscosity, and compressibility. The effect of measuring the material behavior using oscillatory or shear experiments is shown. Furthermore, the simulations are applied to a second EPDM. Finally, different processing conditions are tested. For the simulations, only qualitative agreement is found, possibly as a result of the no slip boundary condition.

Research on the mechanisms of internal gear honing by use of cone-shape honing wheel with tool tilt angle

Internal gear is an important transmission component. However, it is restricted by its ring−shaped structure, which hinders the finishing process of the tooth surfaces after the heat treatment. Honing is the most commonly used finishing technique for external gear, but it is inconvenient for internal gear. In this paper, a new type of cone−shape honing wheel is proposed and the honing mechanism for improving the honing performance of the internal gear is studied. First, the mathematical model of the honing technology that employs a cone−shape honing wheel is built, and the merits of the new honing method are discussed. Then, the contact conditions between the honing wheel and the internal gear are analyzed. It is established that the tool tilt angle of the honing wheel has a good effect on the honing velocity distributions. Finally, the simulations of honing and profile measuring of the internal gear by employing the cone−shape honing wheel are carried out, by which the feasibility of the new honing technique is verified.

The effect of non-Newtonian behavior on contact formation in an external gear pump

In an extrusion process, an external gear pump can be used to control the flow rate of the system. When extruding polymers, the viscosity is quite high, resulting in negligible inertia and thus laminar flow. The external gear pump contains two gears, one driven by a motor and one driven by means of contact with the other gear. In our previous work, the flow of a viscous fluid through an external gear pump was studied using the finite element method. Local mesh refinement was applied based on the respective distance between boundaries. Furthermore, the rotation of both gears was imposed. In this work, the rotation of one gear is imposed, whereas the other gear is freely rotating. However, the minimum distance between the gears is limited to a minimum value. When this value is reached, contact is assumed and also the rotation of second gear is imposed. A reversion of the torque on this gear results in a release of contact. In this manner, a quasi driver/driven situation is created in the numerical simulations. It is observed that contact is released periodically, and thus cannot be assumed present continuously, as is often prescribed. Non-Newtonian material properties, such as shear thinning and the pressure dependence of the density or the viscosity, alter how long contact is released during a tooth rotation.

Determination of the dynamic characteristics of a gear pump by the load variation method using special bench systems

Introduction. Some of the major factors in the occurrence of vibration of units, causing fatigue failure of the housings of elements, pipelines, and failure of pump elements, are pulsations of the working medium in the hydraulic systems of machine tools, fuel feed systems of aircraft engines and liquid-propellant engine supply. This study aimed at the implementation of a method for determining the dynamic characteristics of a volumetric pump using special bench systems, and the comparison of the calculation results to the experimental data. The stages of calculating the dynamic characteristics of a volumetric pump were described, taking into account the pre-developed special bench systems on the example of an external gear pump with a capacity of 14 cm3 /rev. The implementation of V. P. Shorin's load variation method using special bench systems developed by the authors with predetermined dynamic characteristics was shown. The main stages of the methodology for determining the dynamic characteristics of a gear pump were described.Materials and Methods. Methods of spectral analysis of pulsating pressure were applied in the work. Pulsations of fluid flow at the pump outlet were determined using the impedance method, the method of load variation, and special bench systems.Results. The paper implemented a technique for determining the dynamic characteristics of a gear pump in the drive shaft speed range of 500-2500 rpm for four harmonic components of the vibration spectrum in a wide range of dynamic loads (from inertial to capacitive nature). The bench systems yielding the calculation of the dynamic characteristics of the pump with a minimum error based on the condition of matching the dynamic load and the source of vibrations were analyzed. The developed approach to the evaluation of the dynamic characteristics of the pump was verified through comparing the calculated and experimental data of pressure pulsations in the bench systems with choke, cavity and an extended pipeline at the pump outlet.Discussion and Conclusions. The method for determining the dynamic characteristics of a volumetric pump was implemented using special bench systems developed by the authors. The research results show that the gear pump under study can be considered as an independent source of flow fluctuations, for which the deviation of its own dynamic characteristics from the average values does not exceed 10% for the first harmonic component.

Modeling the Meshing Procedure of the External Gear Fuel Pump Using a CFD Tool

In modern aircraft engine technology, there is a tendency to replace the mechanical drive of external gear fuel pumps with an electric one. This significantly reduces the integral energy consumption for pumping fuel (kerosene). On the other hand, in order to reduce the dimensions of the structure, it is reasonable to increase the rotation speed of the pumping unit gears. The above considerations make it advisable to study the problems that may arise in the design of pumping units. Analysis of the existing designs of external gear fuel pumps shows that the flow processes in the meshing zone have a significant impact on the pump performance and lifetime. Incorrect truss plate geometry and the compensation system lead to an increase in the velocities when opening and closing the cavity in the meshing zone, which causes intense cavitation. To understand the causes and factors which influence this phenomenon, it is necessary to study the fluid flow behavior in the meshing zone gaps. High-speed cameras are used to experimentally study the flow behavior. However, this approach gives only a qualitative result but does not allow for determining the absolute values of pressure and load in terms of the angle of rotation. Nevertheless, high-speed surveying can be used as a basis for fluid flow model verification. In this paper, the model of the fluid flow in a high-pressure external gear pump was proposed. The verification of the simulation results for HDZ 46 HLP 68 oil operation was carried out according to the results of experimental data visualization. The influence of rotation speed on the position of cavitation zones was revealed and confirmed by operational data. The analysis of the flow process in meshing for kerosene as a working fluid was carried out.

Geometry design, meshing analysis and error influences of face-hobbed cycloidal bevel gears with double circular-arc profile for a nutation drive

As the core components of nutation drive, the internal meshing pair of bevel gear must be delicately designed to achieve desirable operational performances for the transmission device. For this purpose, this paper designs a face-hobbed internal meshing pair of cycloidal bevel gears with double circular-arc profile (DCAP). First, a cutter head with DCAP cutting edges is designed to generate the tooth surface of internal gear pair. Then, the tooth geometry of the external and internal bevel gears are derived according to the meshing theory. Finally, a finite element model is developed to simulate the meshing characteristics of the gear pair. The simulation results reveal that the proposed face-hobbed cycloidal bevel gear pair with DCAP has higher contact/bending strength, better load sharing and smaller transmission error compared with the logarithmic spiral bevel gear pair with DCAP. The effects of four typical manufacturing errors on meshing characteristics of the proposed bevel gear pair are investigated to provide fundamental references for the tolerance design of cycloidal bevel gears.

A New Method of the Positioning and Analysis of the Roughness Deviation in Five-Axis Milling of External Cylindrical Gear

Abstract Five-axis milling is a modern, flexible and constantly developing manufacturing process, which can be used for the machining of external cylindrical gears by means of cylindrical end mills and special disc mills on universal multi-axis machining centres. The article presents a new method of positioning the tip and the axis of the end mill and the disc cutter in order to ensure a constant value of deviation of the theoretical roughness Rth along the entire length of the tooth profile. The first part presents a mathematical model of the five-axis milling process of the cylindrical gear and an algorithm for calculating the Rth deviation values. The next section describes the positioning of the end mill and the disc cutter. Then, a new method for the empirical determination of the distribution of the involute root angle Δui and the data description by means of the interpolation function are presented and described. In the conducted numerical tests, the influence of the geometrical parameters of the cylindrical gear on the deviation Rth is determined, assuming a constant Rth value in the five-axis milling process.

Computerized Design, Simulation of Meshing and Stress Analysis of External Helical Gear Drives Based on Critical Control Points

Helical gears are widely used in powertrain systems. The computerized design of a new type of non-generated external helical gears based on critical control points at the transverse tooth profile is presented. The entire tooth profile is divided into different parts including the active tooth profile and fillet by control points. Involutes, circular arcs and Hermite curves are defined between two critical control points and smoothly connected with each other at those control points. The parametric equations for the tooth surfaces are derived considering the position of the mentioned control points. The basic design parameters and equations of the geometric sizing are proposed. The contact patterns, variation of the maximum stresses and peak-to-peak level of loaded transmission errors for six cases of design of the proposed new geometry of helical gear drives are studied with two cases of traditional helical gear drives as a reference, including gears with and without micro-geometry modifications. One case of an external helical gear drive designed with a combination of a circular arc and an involute to form the active tooth profile for both the pinion and the gear shows a much lower maximum bending stress and similar lower peak-to-peak level of loaded transmission errors with respect to the other cases of design. The proposed design method of tooth profiles based on critical control points lays the foundation for the topological optimization of helical gear drives.

New Method to Determine the Dynamic Fluid Flow Rate at the Gear Pump Outlet

External gear pumps are among the most popular fluid power positive displacement pumps; however, they often suffer from excessive flow pulsation transmitted to the downstream circuit. To meet the increasing demand of quiet operation for modern fluid power systems, it is necessary to give a physically sound method of analyzing the operation of a volumetric pump. The analysis of the basic approach used by the majority of researchers for calculating the flow rate of a gear pump by E.M. Yudin is presented. The article presents a new method for analyzing the operation of volumetric pumps. The method is suitable for the pumps whose dynamic characteristics should be considered according to the model of an equivalent source of flow fluctuations by V.P. Shorin. The method is based on wave theory, the method of hydrodynamic analogies and the impedance method, where the pump is considered according to the model in lumped parameters. The method consists in determining the pressure pulsations at the pump output in bench systems with known dynamic characteristics and recalculating the pump flow rate in pulsations. Computational dynamic models of bench systems in lumped parameters are proposed for subsequent use in dynamic tests of pumps in the form of equivalent sources of fluid flow fluctuations. We give recommendations for the formation of test bench systems with a throttle, a cavity and a pipeline at the pump output. Using the example of an external gear pump with a working volume of 14 cm3/rev, the implementation of the proposed method is considered. The pump’s own pulsation characteristic of the flow rate in a bench system with an “infinitely long” pipeline along two harmonic components of the spectrum is determined, and a test of the method based on the method of determining the instantaneous flow rate by R.N. Starobinskiy is proposed. It is shown that, according to the proposed method and the method of R.N. Starobinskiy, the divergence of the amplitudes of flow pulsations does not exceed (5–10)%. The high degree of coincidence of the results confirms that the external gear pump in question should be considered according to the equivalent source of flow fluctuations model.

Influence of the Nitrided Layer Structure on the Micro-Pitting and Wear Behavior of Slow-Running Nitrided External Gears

Nitriding can significantly increase the load carrying properties of gears. While the diffusion layer is primarily responsible for improving the tooth root and flank load carrying capacity, the compound layer mainly determines the tribological properties of the gear surface. In the present work, the influence of the compound layer on the tribological load carrying capacity of nitrided gears in the N/N pairing was investigated. For this purpose, compound layers with different thickness, porosity and phase composition were produced and their micro-pitting and wear behavior were investigated in load stage and speed stage tests. The test results confirm that the properties of the compound layer are decisive for the micro-pitting and wear resistance of nitrided gears. For a high micro-pitting resistance, the presence of pores in the near-surface area of the compound layer is of high importance, since no micro-pitting occurred as long as pores were present. With regard to the wear behavior, no dependence on the compound layer thickness or the porous zone thickness was found while the phase composition of the compound layer shows a decisive influence.

Computational fluid dynamics investigation of a misaligned-phase parallel external gear pump

To clarify the flow characteristics of the misaligned-phase parallel external gear pump with different phases and rotational speeds, the flow pulsation and cavitation of the misaligned-phase parallel external gear pump under different working conditions were systematically studied by combining theoretical analysis with tridimensional numerical simulation. The flow pulsation characteristics of the misaligned-phase parallel external gear pump are analyzed. Compared with the same-phase gear pump, the flow pulsation of the misaligned-phase parallel external gear pump was reduced. When the phase angle is [Formula: see text], the pressure and flow pulsations of the parallel gear pump are minimum, the flow pulsation is less than 1/4 of the same-phase gear pump. The relationship between cavitation and phase angle of the misaligned-phase parallel external gear pump is verified. When the rotational speed is different, with the increase in the rotational speed, the amplitude of the pressure fluctuation increases, and the effect of pressure pulsation overlapping and counteracting each other in the misaligned phase is more ideal. The flow does not fluctuate with the rotational speed and is only related to the phase angle, the cavitation is aggravated with the increase in the rotational speed.

Contact Forces of Spur Gearing

In this paper, on the basis of the bending produced by the normal force which is applied in contact point of teeth flanks, the contact force of external spur gearing was determined. For the calculus methodology presented in this paper, a computer program has been developed.

Analysis of the influence of hydraulic fluid quality on external gear pump performance

The basis of every hydraulic system is based on energy transformations, which are realized through hydraulic working fluid. Hydraulic oils are certainly subject to changes within their structure, meaning the basic characteristics and parameters of hydraulic oil, such as density, viscosity, humidity. The oils that are exploited are exposed to the process of degradation, which largely leads to significantly poorer quality of hydraulic fluid. The paper deals with the influence of changes in the characteristics of the hydraulic fluid on the hydraulic operating parameters of the gear pump installed on the hydraulic press. The parameters refer to pressure, flow, and temperature, as well as the quality of hydraulic oil, which affects the volumetric efficiency of the pump, and the results presented in the conclusion are based on the measured values of parameters before and after corrective measures. The control of parameters aims to increase the efficiency and reliability of the hydraulic system, a way of modern detection of deviations of parameters from standard, required values.

Mesh relationship modeling and dynamic characteristic analysis of external spur gears with gear wear

Mesh relationship modeling and dynamic characteristic analysis of external spur gears with gear wear