External Gear Research Articles

A fault prognosis strategy for an external gear pump using Machine Learning algorithms and synthetic data generation methods

Fault prognosis is an important area of research that aims to predict and diagnose faults in complex systems. The sudden failure of industrial components can have adverse consequences for an organisation in terms of time, cost and workflow. It is, therefore, critical to ensure the maintenance of equipment components in optimal condition in order to avoid downtime that may cause significant disruption. Due to this reason, in recent years, there has been an increasing interest in creating innovative methods for fault prognosis that can increase system reliability and reduce maintenance costs. Gear pumps are widely utilised in a variety of industrial applications, and their reliability and effectiveness are crucial for achieving optimal system performance. Gear pumps, on the other hand, are prone to malfunctions and failures, which can result in substantial downtime and maintenance costs. The challenge is to develop a fault prognosis approach that is reliable and accurate enough to detect and diagnose defects in a gear pump before they cause system failures. This paper proposes a novel computational strategy for the fault prognosis of an external gear pump using Machine Learning (ML) approaches. Due to the unavailability of sufficient experimental data in the vicinity of failure mechanisms, a novel approach to generating a high-fidelity in-silico dataset via a Computational Fluid Dynamic (CFD) model of the gear pump in healthy and faulty working conditions is presented. However, considering the computational demand for rerunning the same CFD simulations, novel synthetic data generation techniques are implemented by perturbing the frequency content of the time series to recreate other working conditions and constructing degradation behaviour using linear and cubic interpolation methods for run-to-failure scenarios. The synthetically created datasets are used to train the underlying ML metamodel for fault prognosis. Two types of ML algorithms are employed for fault prognosis: Multilayer Perceptron (MLP) and Support Vector Machine (SVM) algorithms. A series of numerical examples are shown, allowing us to infer that the proposed modelling technique is feasible in an industrial setting and that employing the MLP algorithm delivers superior fault prognosis results when compared to SVM. Furthermore, datasets generated using the cubic interpolation method have lower prediction errors than datasets generated using the linear interpolation method due to the smoother degradation behaviour in the data.

Анализ конструктивных и технологических особенностей шестеренчатых насосов

The article presents the main design and technological features of gear pumps with a description of the contacts of the gear wheels during their interaction and manufacturing accuracy. The increase in contacts in the interdental space reduces the pulsation by 75%, the noise level by 5 decibels. The use of helical gears increases the efficiency of gear pumps and reduces pulsation. External gear pump with axial compensation with high precision and high quality materials resistant to fatigue. Internal gear pumps have a compact body and are less noisy. In practice, external gear pumps are most commonly used due to their simple design and low cost. The gear pump housing is subject to wear due to high pressure. During operation of the pump, uneven stresses occur, which leads to fatigue loads on the shaft in one direction. Additional pulsation entails oscillations of the structure. The gear pump’s own vibrations contribute to its failure, especially if the rotation speed is 100,000 cycles. During the operation of a gear pump, noise occurs that can be dampened with silencers or dampers, which increases the price of the pump. The interdental spaces of a gear pump are prone to cavitation during sudden pressure surges, which increases wear. To eliminate wear, pulsation, vibration, noise, a new design of the gear pump is proposed using various types of oils and methods for correcting the shape of the teeth.

Characteristics in hard conformal EHL line contacts

PurposeInternal gearings are commonly used in transmissions due to their advantages like high-power density. To ensure high efficiency, load-carrying capacity and good noise behavior, a profound knowledge of the local gear mesh is essential. The tooth contact of internal gears relates to a convex and concave surface that form a conformal contact. This is in contrast to external gears, where two convex surfaces form a contraformal contact. This paper aims at a better understanding of conformal contacts under elastohydrodynamic lubrication (EHL) to improve the design of internal gearings.Design/methodology/approachAn existing numerical EHL model is used for studying the characteristic properties of a hard conformal EHL line contact. A hard contraformal EHL line contact is studied as reference. Non-Newtonian fluid behavior and thermal effects are considered. By taking into account the local contact conformity and kinematics, the effects and relevance of the curvature of the lubricant gap and micro-slip are analyzed. In a parameter study, scale effects of the contact radii on film thickness, temperature rise and friction are examined.FindingsThe curvature of the lubricant gap and effects of micro-slip are small in hard conformal EHL line contacts. For high micro-slip, it can be neglected. Hence, the modeling of conformal contacts using an equivalent geometry of the contact problem is reasonable. The parameter study shows beneficial tribological aspects of the conformal contact compared to the contraformal contact. Higher film thickness and lower fluid coefficient of friction are observed for conformal contacts, which can be attributed to lower pressures for the case of the same external normal force, or to a higher contact temperature rise for the case of equivalent contact pressure.Originality/valueDespite its widespread existence, the local geometry and kinematics in hard conformal EHL line contacts like in internal gearings have been rarely studied. The findings help for a better understanding of local contact characteristics and its relevance. The quantified scale effects help to improve the efficiency and load-carrying capacity of machine elements with hard conformal EHL contacts, like internal gearings.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2022-0366/

Simulation Study on the Tribological Characteristics in the Meshing Contact in the Context of the Load Carrying Capacity Calculation of Internal Gears with Unbalanced Sliding Conditions

Planetary gearboxes are characterized by a high power density and a compact design with coaxial in- and output. Consequently, planetary gear units are frequently used in many practical applications, e.g. in wind energy and industrial transmission systems as well as in automotive applications such as automatic transmissions. As a result of the scaling-up of the required system power, the risk of flank damages increased during the last decade. Certain damage types, such as pitting and micropitting, occur predominantly in contact areas of negative specific sliding on the tooth flank surface. Unlike external gears, internal gears offer the possibility of positioning the pitch point C outside of the active profile. Depending on the gear design, this allows a complete avoidance of negative specific sliding either on the planet or on the ring gear. In contrast, the corresponding gear is subjected to negative specific sliding only. It can be assumed that the lifetime regarding flank damages of each meshing partner can be affected by different positions of the pitch point and the resulting differences in the specific sliding, which allows an optimization of the full gear system, taking into account e.g. the load carrying capacity reserves for different material pairings. It is to be noted that such gear designs are already part of some practical applications.However, the existing analytical approaches within standardized load carrying capacity calculation methods are typically based on investigations considering external gears with balanced sliding conditions. Systematic results on internal gear designs with pitch point positioned outside of the active profile are not available.Within this paper, extended theoretical studies on the tribological characteristics of different internal gear designs are presented. Therefore, a reference geometry with balanced sliding conditions is compared to internal gears with pitch point below respectively above the active profile. The focus of the studies is the analysis of the lubricant film thickness and the contact temperature in the meshing contact. Referring to this, a high-order TEHL contact simulation model was used. The results of the numerical analysis with the FZG calculation software TriboMesh are compared to different analytical approaches in the context of the calculation of load carrying capacity to derive recommendations for the design of internal gears.

Multidisciplinary design optimization of external engagement cylindrical gear flowmeter

Multidisciplinary design optimization of external engagement cylindrical gear flowmeter

Transform of parameter and teeth surface modification for non-standard planetary spur gear train with X-gears

In view of the lack of ready formulae for modification calculation of non-standard planetary spur gear trains, the paper is focused on new modification methods of non-standard planetary spur gear trains with X-gears. Firstly, a novelty transform method from the parameters on the pitch circle to the parameters on the reference circle for a non-standard planetary spur gear train with X-gears is proposed in order to study the modification method. Secondly, a scheme of teeth surface modification for non-standard planetary spur gear train with X-gears is put forward. Thirdly, the calculation method of loaded transmission error and flash temperature on the tooth surface under mixed elastohydrodynamic lubrication for external meshing spur gear pairs is proposed using tooth contact analysis as well as loaded tooth contact analysis. Then, a new modification optimization method for non-standard planetary spur gear train with X-gears is proposed, and formulae of the maximal modification length along the tooth height are derived. Finally, the effectiveness of the modification optimization method is confirmed by an example, and the transform formulae of the optimized modification parameters for sun gear are derived.

СТРУКТУРНЫЙ АНАЛИЗ И УРАВНОВЕШИВАНИЕ МЕХАНИЗМА ВОЗВРАТНО-ПОСТУПАТЕЛЬНОГО ДВИЖЕНИЯ

The paper presents new mechanisms of reciprocating motion, built on the basis of a two-row planetary gear with non-circular gearwheels with two external gears. The desired type of the output link motion is realized by converting the rotationally reciprocating movement of the planetary mechanism output shaft using the transmission “toothed wheel — toothed rack”. The proposed mechanisms are balanced on the example of three planetary gear schemes, with one, two and three satellites. Structural analysis of gears with multiple satellites has shown that the addition of each extra satellite takes away one degree of freedom from the mechanism, as a result of which it becomes immobile. It is proposed to use a counterweight on each additional satellite instead of one two-moving kinematic pair, which leads to the elimination of redundant links. The conditions of static equilibrium for the developed schemes of planetary mechanisms are obtained, which make it possible to locate the centers of mass of the mechanisms on the axis of rotation and thereby significantly reduce noise and vibration in the gear developed on its basis.

The mathematical model of non-circular crossed-axis gear

Non-circular crossed gear can be regarded as the general form of the single stage gear, which can be converted into hypoid gearing, non-circular bevel gearing, non-circular external gearing, and non-circular internal gearing with specific parameters. This paper established its mathematical model, deduced equation of its axode, and put forward a new method of tooth profile generation with introduction of relative velocity. In term of the theory above, the 3D model of a pair of conjugated gears was built, and its output angular velocity was obtained in analysis of ADAMS. Finally, the physical prototype of the gearing was developed and output angular velocity was measured as well. Both the simulation and measurement results show the motion is in good condition, which confirms the correctness of the theory and algorithm.

Virtual Design and Analysis of the Balancing Element of an External Gear Machine Considering Cavitation and Mixed Lubrication Effects

This paper presents a simulation based approach for sizing the axial balance elements of a pressure compensated external gear machine. The reference hydraulic unit must be able to guarantee operation in two quadrants, as either a pump or a motor. It also needs to operate in a wide operating range of speed and pressure, as it is to be used as primary hydraulic unit for an electro-hydraulic actuator (EHA). The design procedure builds upon past work at the author’s center, but it extends it to the case of multiple quadrant units. Also, a unique method for modeling of both mixed lubrication and cavitation that might occur in the lubricating film is used. After describing the design procedure, the paper discusses the features of the balancing of a reference unit, along with the effects of both cavitation and mixed lubrication.

ДИНАМИЧЕСКОЕ ИССЛЕДОВАНИЕ МЕХАНИЗМА ПЛАНЕТАРНОГО ПРИВОДА САДОВОЙ ПОЧВООБРАБАТЫВАЮЩЕЙ ФРЕЗЫ

The second article of the series considers the issues of inter-row and near-trunk land cultivation in orchards. As a result of the study and analysis of the literature, a classification and comparative evaluation of the existing machines intended for the cultivation of the mentioned areas was implemented. Both the advantages and disadvantages of rotary tillers with horizontal and vertical rotation axis were indicated. It has been stated that from the prospect of agro-technological and technical requirements of the mentioned machines, rotary tillers with vertical axis are preferable, which, anyhow, need to be upgraded. Based on the above stated, it has been recommended to select planetary mechanism with external gear as a transmission mechanism for the rotary tiller, which will enable to provide high rotation numbers for the disc of the tillers’ blade in case of relatively fewer rotation numbers of the rotor. It is theoretically justified and experimentally confirmed that from the point of view of effective tillage and a sharp decrease in the traction resistance of the unit, the optimal number of satellite cutters is three, located at an angle of 1200 to each other, and the number of knives is two, with a symmetrical arrangement. The expressions derived in the result of dynamic research on the recommended mechanism, enable to identify the optimal geometric parameters for the installation of the tillers’ disc knives, in case of which the resistance force factors of the cultivated medium, including the traction resistance force of the unit will assume the possible minimum values in conditions of the stated regime.

RESEARCH ON THE CHARACTERISTICS OF GEAR-CUTTING PROCESSES FOR EXTERNAL AND INTERNAL MESHING USING THE POWER SKIVING METHOD

The results of modelling and investigation of external and internal gear-cutting processes using the power skiving method are presented. The principles of constructing a geometric model of undistorted chip formation are described, based on parameters from which cutting forces are calculated. It is found that, under identical conditions, the cutting force is three times greater when internal gears are cut than when external gears are cut. The influence of this force on the machining error is determined by the gear pitch parameter. It is shown that the most rational way to reduce the machining error is to reduce the cutting force by reducing the axial feed rather than by increasing the number of passes.

Lightweight mechatronic system for humanoid robot

Abstract This paper presents the technical specifications of a lightweight humanoid robot platform named Robinion Sr. including its mechanical and electrical design. We describe a versatile and robust mechatronic system, efficient walking gait, and software architecture of the humanoid robot. The humanoid robot platform is targeted for use in a range of applications, including research and development, competitions, and the service industry. A reduced platform cost was an essential consideration in our design. We introduce a specialized and inexpensive mechanical design, which includes a parallel-kinematics leg design, external gears, and low-cost controllers and sensors. The humanoid robot is equipped with an efficient electronic structure and a tablet computer for task scheduling, control, and perception, as well as an embedded controller for solving forward & inverse kinematics and low-level actuator control. The perception system recognizes objects at real-time inference with Deep Learning-based detection algorithms without a dedicated GPU. We present and evaluate the capabilities of our newly developed advanced humanoid robot and believe it is a suitable platform for the academic and industrial robotics community.

Design and justification of hydrostatic transmission parameters for special transport vehicles

Traditionally, hydrostatic transmissions of specialised transport vehicles use piston hydraulic machines to move the vehicle, as well as to operate attachment systems and units. For a wide range of special vehicles used in agriculture and municipal services, movement requires the power of the drive motor, comparable to the power of gear hydraulic machines. Gear hydraulic machines are less demanding on the quality, viscosity, and purity of the working fluid, are cheaper, and are easier to operate. Regulation of speed of an output shaft of gear hydraulic motors, as a rule, is provided by the throttle method that considerably reduces the general efficiency of a hydraulic drive. In the article the project of hydrostatic transmission on the basis of gear hydraulic machines with "volumetric" way of regulation is offered, the basis of which is the combination of work of two hydraulic motors (gerotor and gear with external gearing) with connection of output shafts of hydraulic motors to axes of gear differential. The basic calculation dependencies for determining the operating parameters of transmission hydraulic machines are given.

Modeling of undeformed chip in power skiving gear cutting process

The method of cutting gear wheel by the Power skiving method is considered and the principle of creating non-deformed chip when cutting external spur gear is analyzed in detail in this paper. The task of this investigation is to develop an adequate model of chip formation and to analyze quantitative estimates of parameters of slices in Power skiving process. In order to solve this problem, complex system of grapho-analytical, mathematical and computer modeling of this process is developed. It takes into account its kinematics and reliably reproduces the regularities of cutting-forming processes. The grapho-analytical method developed by I. E. Hrytsai for worm tooth milling is used to model the parameters of the sections. The continuous movement of cutting and forming is presented in the form of successive discrete movements of the contour of the tooth, and its linear and angular positions relative to the processed gear wheel are easily described mathematically. This greatly simplifies the model and geometric constructions using existing CAD systems, unlike other known methods. In each position of the tooth, its contour in the front surface is combined with the contours of the teeth, which performed cutting in the previous positions both along the axial feed and on the helical line. The main condition for the accurate determination of the parameters of the cuts is the establishment of the shape and dimensions of the surface, which is formed in the process of steady cutting in each cavity of the gear wheel between the treated surfaces of the teeth and the raw surface of the workpiece for 1 revolution of the cutter. To investigate the parameters of the slices, the schematic arrangement of the gear wheel and the cutter is depicted and the process is divided into discrete states. The results of modeling according to the above mentioned parameters are given in the form of graphic dependencies: chip cross-sectional area, thickness depending on different axial feeds of the cutter and for different modules of the gear wheel. The dependence of the change in the geometric characteristics of the undeformed chip on the position of the cutter is obtained. In further research, it is possible to establish a number of other physical quantities and their interdependence during gear cutting using the Power skiving method.

OBJECTIVE FUNCTION OF PARAMETRIC OPTIMIZATION OF THE SPEED OF A CLOSED PLANETARY MECHANISM FORMED BY TWO SIMPLE JAMES PLANETARY MECHANISMS

The results of building а mathematical model of estimation the speed of the designed construction of the closed planetary mechanism formed from two simple planetary mechanisms of James are presented. The speed of the designed construction of the mechanism is estimated by the value of the equivalent moment of inertia of the mechanism links reduced to its input shaft. A model is a dimensionless function (analogue the equivalent moment of inertia) of two variables - transmission relations of simple planetary mechanisms, and set of numerical parameters. The parameters take into account the values of the coefficients that characterize the mass inertia models of gears and planet carriers, the design and strength limitations of external gears of simple planetary mechanisms of James, as well as the structure of these mechanisms. Set of values of parameters and range of varying of possible values of transmission relations of simple planetary mechanisms influence on position of a minimum of the analogue the equivalent moment of inertia. The influence of the number of planetary gears of simple planetary mechanisms and the moment of inertia of the planet carrier of the differential mechanism on the positions of the minima of the analogues of the reduced moment of inertia of a closed planetary gear was analyzed in calculations for contact strength and bending strength. Based on the function of the analogue of the equivalent moment of inertia, the objective function of parametric optimization of the project fast-acting of the design of a closed planetary mechanism is built. Keywords: simple James planetary mechanism (mechanisms type ); closed planetary mechanism; moment of inertia of gear-wheel; moment of inertia of the planet carrier; moment of inertia of the planetary mechanism; contact strength of the gearing; bending strength of the gearing; parametric optimization; parametric optimization of the equivalent moment of inertia of the planetary mechanism

Evaluating the Time-Varying Mesh Stiffness of Planetary Gear Set With Gear Crack Considering the Friction Force Under Mixed Elastohydrodynamic Lubrication Condition

Abstract The mesh stiffness calculation of the planetary gear system with gear crack is investigated, and gear crack is modeled into end-face and addendum extended crack. Furthermore, the mesh stiffnesses are calculated under the effect of friction force obtained under the mixed elastohydrodynamic lubrication (EHL) condition. The nonuniformly distributed gear cracks on external and internal gear pairs are comprehensively modeled and analyzed, which is rarely investigated in previous studies. Moreover, the influence of crack propagation conditions on the meshing stiffness of the planetary gear system is analyzed. The obtained results show that the mesh stiffnesses experience abrupt variation in the pitch area during meshing, the extent of change is determined by the amplitude of the friction coefficient; in addition, gear crack position and extent could cause mesh stiffness reduction at varying levels at different stages of gear meshing.

AN INVESTIGATION OF THE IMPACT OF PUMP DEFORMATIONS ON CIRCUMFERENTIAL GAP HEIGHT AS A FACTOR INFLUENCING VOLUMETRIC EFFICIENCY OF EXTERNAL GEAR PUMPS

Gear pumps are widely used in transport machines not only in hydraulic drive systems, but also in lubrication and fuel systems. A positive displacement pump converts mechanical energy into pressure energy stored in the liquid, which it transports to the hydraulic cylinder or motor. The efficiency of this process depends on the efficiency of the system components, including the efficiency of the pump, which depends on the amount of internal leakage through the gaps between the high and low pressure sides. The larger the gaps, the lower the volumetric efficiency. This article presents an investigations of impact of pump deformations on circumferential gap height. The article presents a three-dimensional model of an external gear pump using Finite Element Method (FEM) during operating conditions. The model reflects pumping operation at discharge pressures up to 32 MPa and it was validated against strain measurements of pump casing. The simulation results indicate that the pump casing becomes deformed due to pressure, causing a significant increase in the height of the circumferential gap. The increase of the discharge pressure from 8 to 32 MPa causes more than twofold local increase in the height of the circumferential gap. The obtained results indicate that for the correct modelling of the flow generated by gear pumps, it is necessary to consider the change in the size of the gaps resulting from the deformation of the pump.

A new three-stage gearbox concept for high reduction ratios: Use of a nested-cycloidal architecture to increase the power density

Increasing the Gear Ratio (GR) while decreasing the gearbox dimension is a contradiction that mechanical designers are challenged to solve. The increasing importance of fine-tuning high power density designs has led to the development of innovative solutions involving cycloidal and hypocycloidal gears. However, when the required GR increases and the number of the stages raises, the gearbox architecture plays a key role in minimizing the overall dimensions. In the present paper, an innovative gearbox architecture is presented. The new design combines three cycloidal and hypocycloidal gearing stages to achieve a higher GR with respect to a traditional two-stage cycloidal gearbox with the same overall dimension. This architecture is called Nested since it involves stages with internal and external gears arranged one inside the other. A comparison of the proposed solution with the more compact two-stage cycloidal architecture (Wolfrom) is shown. The GRs as a function of the total number of meshing features are discussed as well as the torques acting on each component. Eventually, a design solution is illustrated.

A numerical study of an external gear pump operating under different conditions

In this work, Computational Fluid Dynamics (C.F.D) analysis has been done using a commercial CFD solver FLUENT-6.2 to simulate the fluid flow in rotary pumps of positive displacement type, utilising an external gear pump as an illustration. The 3-D model of the fluid flow volume around the casing and gear teeth is created to represent the computational domain for analysis. To anticipate pump performance, a three-dimensional CFD approach was devised and deployed in terms of pressure field, velocity vectors, and the flow pattern to understand pump flow. The primary goal of this research is to examine how the number of teeth affects how a gear pump operates and to show the pressure profile in each intermittent teeth gap. It is observed increase in speed of gears increases the mass flow rate of the pump whereas the increase of the number of teeth keeping same pitch circle diagram, decreases the mass flow rate of the pump. The results found, gives a clear picture of the pressure rise across the teeth annulus of the pump. Therefore, another goal of this work is to predict the performance of the pump virtually and to verify with the analytical result of the pump with numerical result to establish the validation the model.

Numerical Study of the Hydrodynamics of an External Gear Pump

Numerical Study of the Hydrodynamics of an External Gear Pump