This master thesis was conducted during the spring of 2014 at Atlas Copco Rock Drills AB in Örebro. The purpose of the thesis was to develop a simulation model of the rotation system for a hydraulic rock drill. In the future, the model will be used to investigate the phenomena called “jerky rotation”. In order to validate the simulation model a test bench was designed and tests were made. The main focus was to model the gerotor motor that is used to propel the rotation of the drill string. The model shows the pressure and flow variations that occur due to the geometry of the motor. Simple models of the rock and drill steel were developed to simulate the entire rock drill. Those models were also validated with test results. The results from the model of the motor are considered to be good enough to be used for future simulations of the rotation of the rock drill. However, in order to see the cause of “jerky rotation”, a better model of the hydraulic supply system for the gerotor is needed. A better model of the rock might also be needed. / Detta examensarbete genomfördes under våren 2014 på Atlas Copco Rock Drills AB i Örebro. Syftet var att ta fram en simuleringsmodell av rotationssystemet för en hydraulisk bergborrmaskin. Modellen ska i framtiden användas för att undersöka fenomenet ”jerky rotation”. Under arbetet konstruerades en provbänk och mätningar gjordes för att validera simuleringsmodellen. Tyngden i arbetet lades på att göra en modell av den gerotormotor som används för att driva rotationen av borrsträngen. Modellen återger de variationer i tryck och flöde som uppstår på grund av motorns geometri. Enkla modeller för berg och borrstål konstruerades för att simulera hela borrmaskinen. Även dessa modeller validerades mot mätningar. Resultaten från motormodellen bedöms vara tillräckligt bra för att i framtiden kunna användas för att simulera rotationen vid bergborrning. För att kunna se vad som orsakar ”jerky rotation” behövs dock bättre simuleringsmodeller av det hydrauliska försörjningssystemet som driver gerotormotorn. Eventuellt behövs också en bättre bergmodell.

This PhD thesis experimentally studies the volumetric efficiency of gerotor pumps in aero-engine gas turbine oil systems. This efficiency is the ratio of the effective measured flow rate and the theoretical flow rate computed based on pump displacement. In case of low inlet pressure and high rotational speed, which is often the case in aeronautical applications, the pump performance is severely affected by cavitation. This phase change from liquid to vapour causes a large portion of the flow to be occupied by gas, reducing the volume available for the liquid and reducing the overall mass flow rate. Due to its nature, the lubrication oil used in gas turbine engines is subjected to aeration which is the dissolution of air in oil. The air is dissolved in the liquid at high ambient pressure and released at lower pressure causing more air to occupy the cavities inside the pump. The change in liquid aeration is a relatively slower phenomenon causing the variation of aeration to be delayed with respect to the actual pressure and therefore varying also accordingly to the previous oil condition.The essential part of the work presented in this thesis is based on experimental research realised at the ATM department. This was conducted on a dedicated oil system test rig. This rig is build to reproduce the complete set of operating conditions encountered in a flying embedded oil system. This test rig was modified and equipped with several specific measurement systems to acquire data on pump performance and oil aeration. Precisely, a series of single-phase performance characterisations and transients have been recorded. The oil aeration was measured with two density-based instruments. The pump outlet pressure was recorded with a high-frequency pressure transducer. A new set-up of the test rig was also developed to allow the testing of pumps in two-phase flows conditions. Two-phase flows performance characterisations and transients have then also been studied.The data processing provided information necessary to build empirical models and to understand pump and cavitation behaviours. The focus is on pump performance in cavitation. This justify the extensive use of the cavitation number indicating the tendency of a flow to experience cavitation in given conditions. The base models can be used to determine if a given condition leads to cavitation or not, and predict the pump efficiency in both cases. The high-frequency pressure measurements provided an efficient tool to detect cavitation. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

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This paper presents a numerical model for the evaluation of the actual torque in Gerotor units. The model consists of two major modules: the pre-processor module and the HYGESim module. The preprocessor module consists of the geometric and the mechanical module. The geometric pre-processor module considers the CAD geometry of Gerotor with tolerances as input and it provides as output the geometric features needed to evaluate the rotor loading and the flow features. The mechanical preprocessor module evaluates the forces of interaction at the contact points between the rotors. The flow displaced by the unit is evaluated using a lumped parameter model whereas the lubricating gaps are evaluated by solving the Reynolds Equation. The main novel aspects consist of the evaluation of the frictional losses at various interfaces. An Elasto-Hydrodynamic Lubrication (EHL) approach is used to evaluate the frictional losses at the contact points between the rotors. Tests on a prototype Gerotor unit are performed for the model validation, particularly as pertains to the features of the shaft torque. Additionally, the paper comments on the distribution of the different torque loss contributions associated with the operation of the unit taken as reference.

This paper describes a high fidelity simulation model for GEROTOR pumps. The simulation approach is based on the coupling of different models: a geometric model used to evaluate the instantaneous volumes and flow areas inside the unit, a lumped parameter fluid dynamic model for the evaluation of the displacing action inside the unit and mechanical models for the evaluation of the internal micro-motions of the rotors axes. This paper particularly details the geometrical approach, which takes into account the actual geometry of the rotors, given as input as CAD files. This model can take into account the actual location of the points of contact between the rotors as well for the actual clearances between the rotors. The potentials of the model are shown by considering a particular GEROTOR design. A specific test set-up was developed within this research for the model validation, and comparisons in terms of steady-state pressure versus flow curves and instantaneous pressure ripples are shown for the reference pump.

<div>Gerotor units are widely used in low-pressure (up to 30 bar) </div><div>fluid power applications, injection and lubrication systems, due to their compact package and low cost. Their performance in terms of volumetric efficiency, flow pulsations, internal pressure peaks or localized cavitation depends on many parameters, such as the rotors profiles and the manufacturing tolerances. In this work, a multi-domain simulation approach for the numerical analysis of the performance of Gerotor units is proposed. The model can be used for analysis and virtual prototyping of units considering the actual geometry of the rotors, their geometrical tolerances and the properties of the working fluid and materials.</div><div><br></div><div><div>The approach is based on the coupling of different models: a numerical geometric model evaluating the instantaneous volumes and flow areas inside the unit; a lumped parameter fluid dynamic model describing the displacing process of the tooth space volumes; and a mechanical model evaluating the internal micro-motions of the rotors axes according to their tolerances. In this way, the model determines the actual loading of the rotors, considering also the actual location of the points of contact. Advanced 2D CFD models for the analysis of lubricated interfaces have been developed to study the axial and the radial gaps. This approach allows an accurate prediction of the power losses and radial micro-motion of the rotors taking into account fluidstructure interaction effects. A line contact model is used to describe the contact interface using an elastohydrodynamic approach and non-Newtonian fluid behavior for the prediction of the friction between the rotors.</div></div><div><br></div><div><div>Specic experiments were performed by connecting the pump outlet to a variable loading orifice and by measuring the delivered flow, pressure ripple and required torque under dfferent operating conditions of speed and outlet pressure. These experiments allowed a detailed model validation through the comparisons with simulation data in terms of signicant steady-state as well as transient pressure, flow and torque features. After the model validation, gaps compensation solutions to minimize the volumetric losses are developed and studied showing the potential improvements on the performances of a prototype unit by reaching up to 55% volumetric effciency at high pressure (pmax > 100bar).</div><div><br></div><div>The approach used in the current work along with its proven accuracy through experiments can be considered a valuable tool when studying the impact of real-life technological clearances and gears geometry on the fluid-dynamic performance of the pump.</div></div>

<div>Gerotor pumps are positive displacement pumps that are frequently used in low-pressure applications such as lubrication and charge pumps. They are characterized by their unique gearset that is an internal gearset with one tooth difference that has continuous contact throughout the entire rotation. Recent trends especially in the automotive industry suggest an increased demand for greater performance from these pumps, e.g. operating with higher pressure, higher speed, lower viscosity fluid, less noise emission, and greater energy efficiency. The shape of the gears is one of the most important aspects of a gerotor pump, as it determines the pump's size and flow, affects its internal leakages, and influences its amount of wear. Although gerotors have been in operation for nearly 100 years, no design methodology has emerged in scientific literature that fully considers all the main performance aspects simultaneously and identifies the best designs. This problem is made more difficult, as gerotors can have an infinite number of different types of profiles. The main goals of this work are therefore to define a method to design gerotor gear geometry for several performance goals, identify the best designs for a given gear profile type, compare the best designs among the various profile types, and invent a new profile type that can offer improved performance over conventional designs.</div><div><br></div><div>Gerotor profile generation is described in the beginning, first for the conventional epitrochoidal, hypotrochoidal, and standard cycloidal profile types. Then a description of how to generate gerotors from an arbitrary curve is given and applied to elliptical, generalized cycloidal, cosine, and asymmetric elliptical gerotors. The generalized cycloidal profile type is new to this work.</div><div><br></div><div>Multi-objective optimization is used as the method to identify the best gear profiles for a given application considering seven performance metrics and ensuring a feasible gear profile. The seven performance goals to minimize are the radius of a pump for a given geometric displacement and face width, the kinematic flow ripple, the adhesive wear, the contact stress, the tooth tip leakage, the lateral gap leakage, and the mean displacement chamber inlet velocity. The conditions to generate feasible gerotor profiles without cusps or self-intersections are also given as constraints for the optimizations.</div><div> </div><div> Seven gerotor profiles were then optimized using a genetic algorithm to consider all the performance aspects. The design space for each profile type was thoroughly explored, and clear Pareto fronts were identified. The Pareto fronts from each profile type were then combined, and a new Pareto front was identified from the best designs of each profile type. No single profile type proves to be objectively better than the others, but the epitrochoidal, hypotrochoidal, elliptical, and generalized cycloidal profile types tend to produce the best designs. Two methods to select a design from the Pareto front that consider the relative importance of each performance goal were presented.</div><div> </div><div> The optimization strategy was then further validated by demonstrating significant possible performance improvement over state-of-the-art designs in industry and suggesting alternative designs to a specific gearset used in industry that were tested in simulation and experiment. Two generalized cycloidal profiles were selected as alternative designs: the first design matched the fluid dynamic performance of the reference design with significantly reduced contact stress, and the second is a profile that could reduce the outlet flow ripple while fitting within the same pump housing. The contact stress of the reference and alternative designs when including clearance between the gears was compared in finite element analysis. Prototypes of the alternative designs were then manufactured and tested in experiment. The experimental pressure ripples of the alternative designs were compared, and the second design showed a reduction in outlet pressure ripple that validates the proposed design methodology.</div><div> </div><div> This work has thoroughly explored the performance possibilities of the gerotor mechanism and presented a method to select an optimal profile geometry depending on the desired performance characteristics. It has therefore accomplished its goals in making a contribution toward improving the performance gerotor gear geometry.</div>

This paper describes a high fidelity simulation model for GEROTOR pumps. The simulation approach is based on the coupling of different models: a geometric model used to evaluate the instantaneous volumes and flow areas inside the unit, a lumped parameter fluid dynamic model for the evaluation of the displacing action inside the unit and mechanical models for the evaluation of the internal micro-motions of the rotors axes. This paper particularly details the geometrical approach, which takes into account the actual geometry of the rotors, given as input as CAD files. This model can take into account the actual location of the points of contact between the rotors as well for the actual clearances between the rotors. The potentials of the model are shown by considering a particular GEROTOR design. A specific test set-up was developed within this research for the model validation, and comparisons in terms of steady-state pressure versus flow curves and instantaneous pressure ripples are shown for the reference pump.

En los últimos años, los trabajos de investigación están muy motivados por todo aquello que contribuye a reducir el ruido emitido por los sistemas oleohidráulicos. Como ha sido demostrado por varios investigadores, el origen de estas perturbaciones hay que buscarlo en el proceso de generación de las pulsaciones de caudal como característica intrínseca del propio funcionamiento real de la bomba, y en consecuencia, cualquier avance en este terreno debe pasar ineludiblemente por la simulación del comportamiento dinámico de estas unidades.El presente trabajo de investigación se circunscribe al estudio de una bomba gerotor, con el fin disponer de un estudio global, coherente y unificado que comprende la geometría de los perfiles trocoidales del engranaje, la cinemática del engrane, las características volumétricas, las tensiones en los puntos de contacto y su comportamiento dinámico.La geometría y cinemática de engrane del engranaje trocoidal se han deducido analíticamente mediante las ecuaciones de los perfiles de los dientes y la línea de puntos de contacto en función de cuatro parámetros básicos, sentando la base para el desarrollo de los estudios posteriores. Las características volumétricas se han desarrollado, puesto a punto y comparado mediante dos métodos: uno numérico que se fundamenta en un análisis integral-derivativo, y el otro que se fundamenta en un análisis derivativo-integral en sus dos posibles versiones, la analítica y la numérica. La concordancia de resultados obtenidos utilizando estos métodos es muy satisfactoria. En el cálculo de las tensiones de contacto, también se han propuesto y desarrollado dos metodologías de cálculo. Un primer método parte de la teoría desarrollada por Colbourne, implementado con una variante para el cálculo de los puntos de contacto. Este método es adecuado para ruedas dentadas exteriores donde el perfil del lóbulo o diente es ajustable a un arco circular. Puesto que su aplicación es muy restrictiva, se ha creído oportuno proponer un método alternativo implementado con el Método de los Elementos Finitos mucho más genérico. Este último ha proporcionado los valores de la magnitud de la máxima tensión de contacto más fiables y ha demostrado un alto nivel de flexibilidad que facilita en gran medida el proceso de optimización de la forma geométrica de los perfiles de los dientes.El comportamiento fluidodinámico de la bomba gerotor se estudia proponiendo un método de simulación física (Método de BondGraph) que incida directamente en el cálculo de las pulsaciones de caudal. El modelo de simulación fluidodinámico presenta un análisis matemático que parte del submodelo de una cámara y se completa con la interacción engranaje-bomba y las fugas de caudal. Esta metodología numérica desarrollada se contrasta con una técnica experimental (Método de la 'Fuente Secundaria') que permite la comparación directa de los resultados obtenidos por ambas vías. Son dos los bancos de ensayo empleados y desarrollados de acuerdo con la norma ISO 10767, uno en el Fluid Power Centre de la University of Bath, y otro diseñado y construido específicamente para esta tesis en el laboratorio del centro LABSON. Se observa que las amplitudes (pico a pico) de las pulsaciones de caudal obtenidas por vía experimental en el Fluid Power Centre son inferiores y más regulares que las obtenidas en el laboratorio del centro LABSON.La comparativa de resultados de la pulsación de caudal 'ideal' obtenida de la simulación y la pulsación de caudal de los ensayos experimentales muestran ser muy precisos en su forma, a pesar de existir diferencias de amplitud. El modelo de simulación muestra que describe con gran grado de exactitud la interacción engranaje-bomba y las fugas de caudal de una bomba gerotor. / In recent years, there has been a growing awareness of the hazards of industrial noise and how to reduce it in hydraulic systems. A great number of studies have been carried out in the past in this field and it has been shown that the source of these perturbations has to be sought in the process of the generation of flow ripple as an intrinsic characteristic of the pump. As a consequence of this, any advance in this field has to inevitably pass the simulation of the dynamic behaviour of the pump.The investigation work presented in this thesis is concentrated on the performance analysis of a gerotor pump in order to develop a coherent and unified global study of the trochoidal profiles geometry of the gear, the kinematics of the mesh, the volumetric characteristics, the contact stress at the contact points and its fluid dynamic behaviour.The geometry and kinematics of the mesh of the trochoidal gear has been analytically deduced through the equations of the teeth profiles and the line of contact, which are in turn function of four basic parameters and were the basis for further studies. The volumetric characteristics have been developed and compared by using two approaches: the integral-derivative approach solved by a numerical differentiation and the derivative-integral approach solved by a numerical and analytical integration. The coherence of the results obtained by both approaches is very satisfactory.Contact stress calculation is also proposed and developed by using two methodologies. The first method is based on Colbourne's theory and it is implemented by a new approach to the calculation of the contact points. This method is only valid for external gears formed by circular-arc teeth. Because of the limitation of this method, an alternative and more generic method has been proposed by implementing the Finite Element Method. This last method provides more reliable magnitude values of the maximum contact stress and it has shown a high flexibility that aids the process of optimization of the teeth profiles geometry.The fluid dynamic behaviour of the gerotor pump study is based on a physical simulation method (BondGraph's Method) which is focused on the flow ripple calculation. The simulation model presents an analytical approach which starts with a submodel of a single chamber and it is completed by the interaction of gear-pump and leakage flows. This numerical methodology is contrasted with an experimental methodology (Secondary Source Method) which allows a direct comparison between results from both methodologies. Two test rigs have been employed and developed according to the ISO normative 10767-192/84247: one of the test rigs is at the Fluid Power Centre of the University of Bath and the other test rig is specifically designed and constructed for this thesis at the LABON Centre. A comparison of the experimental results has shown that the amplitude (peak to peak) of the flow ripple of the Fluid Power Centre is more accurate than those obtained at the LABSON Centre.The comparison between the 'ideal' flow ripple from the simulation and the 'real' flow ripple from the experimental work are shown to be very precise in shape and form, despite of the discrepancies observed between amplitudes. It has been proved that the simulation model describes with a high accuracy the interaction of gear-pump and leakage flows of the gerotor pump.

<p dir="ltr">Positive displacement machines are used in various industries spanning the power spectrum, from industrial robotics to heavy construction equipment to aviation. These machines should be highly efficient, compact, and reliable. It is very advantageous for designers to use virtual simulations to design and improve the performance of these units as they significantly reduce cost and downtime. The recent trends of electrification and the goal to increase power density force these units to work at higher pressures and higher rotational speeds while maintaining their efficiencies and reliability. This push means that the simulation models need to advance to account for various aspects during the operation of these machines. </p><p dir="ltr">These machines typically have several bodies in relative motion with each other. Quantifying these motions and solving for their effect on the fluid enclosed are vital as they influence the machine's performance. The push towards higher rotational speeds introduces unwanted cavitation and aeration in these units. To model these effects, keeping the design evaluation time low is key for a designer. The lumped parameter approach offers the benefit of computational speed, but a major drawback that comes along with it is that it typically assumes fluid inertia to be negligible. These effects cannot be ignored, as quantifying and making design considerations to negate these effects can be beneficial. Therefore, this thesis addresses these key challenges of cavitation dynamics, body dynamics, and accounting for fluid inertia effects using a lumped parameter formulation.</p><p dir="ltr">To account for dynamics features related to cavitation, this thesis proposes a novel approach combining the two types of cavitation, i.e., gaseous and vaporous, by considering that both vapor and undissolved gas co-occupy a spherical bubble. The size of the spherical bubble is solved using the Rayleigh-Plesset equation, and the transfer of gas through the bubble interface is solved using Henry's Law and diffusion of the dissolved gas in the liquid. These equations are coupled with a novel pressure derivative equation. To account for body dynamics, this thesis introduces a novel approach for solving the positions of the bodies of a hydraulic machine while introducing new methods to solve contact dynamics and the application of Elasto Hydrodynamic Lubrication (EHL) friction at those contact locations. This thesis also proposes strategies to account for fluid inertia effects in a lumped parameter-based approach, taking as a reference an External Gear Machine. This thesis proposes a method to study the effects of fluid inertia on the pressurization and depressurization of the tooth space volumes of these units. The approach is based on considering the fluid inertia in the pressurization grooves and inside the control volumes with a peculiar sub-division. Further, frequency-dependent friction is also modeled to provide realistic damping of the fluid inside these channels.</p><p dir="ltr">To show the validity of the proposed dynamic cavitation model, the instantaneous pressure of a closed fluid volume undergoing expansion/compression is compared with multiple experimental sources, showing an improvement in accuracy compared to existing models. This modeling is then further applied to a gerotor machine and validated with experiments. Integrating this modeling technique with current displacement chamber simulation can further improve the understanding of cavitation in hydraulic systems. Formulations for body dynamics are tested on a prototype Gerotor and Vane unit. For both gerotor and vane units, comparisons of simulation results to experimental results for various dynamic quantities, such as pressure ripple, volumetric, and hydromechanical efficiency for multiple operating conditions, have been done. Extensive validation is performed for the case of gerotors where shaft torque ripple and the motion of the outer gear is experimentally validated. The thesis also comments on the distribution of the different torque loss contributions. The model for fluid inertia effects has been validated by comparing the lumped parameter model with a full three-dimensional Navier Stokes solver. The quantities compared, such as tooth space volume pressures and outlet volumetric flow rate, show a good match between the two approaches for varying operating speeds. A comparison with the experiments supports the modeling approach as well. The thesis also discusses which operating conditions and geometries play a significant role that governs the necessity to model such fluid inertia effects in the first place.</p>