1,721,016 research outputs found
On the relation between vane geometry and theoretical flow ripple in balanced vane pumps
No full textAdvancements related to the correlation between pump design parameters and the kinematic flow ripple in balanced vane pumps are addressed in the present work. In particular, the study focuses the attention on the influence of the vane geometry on the oscillations of the flow rate produced by the volume variation of both under-vane pockets and displaced chambers, that is known as one of the most relevant sources of noise in hydraulic systems. The working principle of the machine is detailed and used as starting point to deduce analytical correlations describing both vane kinematics and delivery flow rate ripple. The set of results that can be achieved with the obtained formulation is evaluated by means of a nondimensional parametric study including the two main design parameters defining the vane geometry, i.e. thickness and tip radius. The resulting trends demonstrate that the theoretical delivery flow ripple is closely related to the vane design and the cam ring shape profile
Analytical determination of the vane radial loads in balanced vane pumps
No full textThe present study proposes an analytical methodology to estimate the variable loads applied to the vanes of balanced vane pumps. The dissertation is adopted to detail the nature of the different time-varying excitations that load the machine and to define their analytical calculation on the basis of vane geometry, cam ring profile and working conditions. In this context, a dimensional reduction is proposed in order to highlight how the pump geometrical parameters affect each single force component and how they may be used to modify the ratio between each load contribution. A comprehensive overview of the mutual interconnections between time-varying loads and the pump design is provided by means of a parametric study involving vane design parameters, pump displacement and cam ring shape. Admissibility of the pump geometry is verified throughout the entire study. The results show that, given the cam ring shape, the vane design significantly influences the radial loads, which may also reach negative values and promote the vane detachment
On the assessment of lumped parameter models for gear pump performance prediction
No full textThe present work describes a statistical approach for the assessment of discrete models for gear pump efficiency prediction. A critical discussion is performed on the input data assumptions that are commonly adopted to carry out the analysis, with particular regards to the actual bearing clearances and casing radial clearances. The proposed model adopts well-established techniques for simulating the pump fluid-dynamics in association with a novel approach, which allows us to take into account the effects produced by the gearpair micromotions. Moreover, the possibility to study both spur and helical gears, as well as non-unitary transmission ratio gearpairs, has been included, in order to ensure the wide applicability of the model in modern design solutions. Measured data obtained from an extended experimental campaign, involving 20 nominally identical samples of the same pump design, are used to establish the assessment procedure. Each sample is geometrically characterized by measuring the actual clearances at the end of the production process and then tested at 14 different working conditions, leading to 280 tests. The entire set of test conditions is then adopted to carry out a trace-driven simulation analysis, showing that the lumped parameter approach may reach different levels of accuracy depending on both the analyzed working conditions and the simulated pump samples. The results underline that reliability and accuracy of this kind of model should be evaluated with respect to a population of pumps, defined on the basis of a statistical approach, since referring to a single pump sample may easily lead to an over/under-estimate of the quality of the proposed model. In addition, they also demonstrate that real clearance values need to be included in the model to obtain high fidelity estimations
Influence of different design parameters on the theoretical flow ripple in balanced vane pumps
No full textThe present study focuses the attention on the correlation between the cam ring design and the kinematic flow ripple in balanced vane pumps. In particular, the work addresses the influence of the main pump design parameters on the oscillations of the flow rate produced by the volume variation of both under-vane pockets and displaced chambers, which is considered as one of the main sources of excessive noise and vibration. The pump operating principle is firstly defined and the design philosophy is presented, together with the theoretical approach used to determine both then vane motion and resulting flow ripple. The proposed methodology is evaluated by means of a parametric study involving design parameters such as vane thickness and tip radius. The analysis suggests that these geometrical parameters, together with the cam ring shape, affect the pump dynamic behavior due to their correlation with the fluid-dynamics of the machine
An iterated local search algorithm for the Travelling Salesman Problem with Pickups and Deliveries
No full textThe Travelling Salesman Problem with Pickups and Deliveries (TSPPD) consists in designing a minimum cost tour that starts at the depot, provides either a pickup or delivery service to each of the customers and returns to the depot, in such a way that the vehicle capacity is not exceeded in any part of the tour. In this paper, the TSPPD is solved by considering a metaheuristic algorithm based on Iterated Local Search with Variable Neighbourhood Descent and Random neighbourhood ordering. Our aim is to propose a fast, flexible and easy to code algorithm, also capable of producing high quality solutions. The results of our computational experience show that the algorithm finds or improves the best known results reported in the literature within reasonable computational time
Assessment of the finger contact surface to promote the spin motion in finger follower mechanisms
No full textThis work describes the kinematic properties of finger-follower mechanisms in the spatial domain in relation to the spin motion of the follower. In this framework, the effectiveness of the cylinder-on-sphere coupling as contact condition between finger and follower is assessed in relation to the classical cone-on-sphere coupling, showing the capability of the former to achieve a satisfactory valve spin pivoting radius. An analytical study is performed by taking advantage of a geometrical approach which allows to evaluate 3D layouts, demonstrating that the cylinder-on-sphere coupling requires a higher number of design parameters to fully determine the mechanism. This characteristic increases the complexity of the system, but it adds freedom and flexibility to the design procedure. Several design configurations are evaluated to highlight this aspect thanks to a dedicated parametric study, where the declivity of the contact surface is shown to represent the key parameter controlling the spin pivoting radius. In this context, the possibility to control the cylinder surface declivity on multiple planes may be adopted to improve the stability of the mechanism behavior with respect to the production tolerances
Detecting cavitation inception in external gear pumps by means of vibro-acoustic measurements
No full textThe present work investigates cavitation in external gear machines by means of a dedicated experimental campaign. Four different pump prototypes have been designed and manufactured to perform this research, one of them specifically built up to not be affected by such a phenomenon. Vibro-acoustic measurements performed by a hydrophone and a high-frequency accelerometer are put in comparison with measurements of inlet and outlet pressure ripple, in order to enlighten their capability to follow the development of the phenomenon. Waterfall spectra are investigated and later Root Mean Square (RMS) values of the filtered signals are shown with respect to the cavitation number and compared with efficiency measurements. Results demonstrate that vibro-acoustic measurements associated to a dedicated signal processing procedure represent a powerful tool to detect cavitation inception in gear pumps. In addition, effect of oil temperature is investigated, showing its contribution in spreading the phenomenon on a wider speed range
The role of gear layout and meshing phase for whine noise reduction in ordinary geartrains
No full textWhine noise is one of major concern within geared system dynamics. The time-varying bearing forces are transmitted to the gearbox case, which coupled with the whole system assembly provokes an undesired noise emission. The paper proposes an analytical formulation able to forecast the main overall direction and magnitude of bearing reaction forces on idler gear when the geartrain works under quasi-static condition. Moreover, a parametric study is conducted by evaluating the influence of geartrain layout, the meshing phase shift and the amplitudes of meshing forces. Finally, numerical experiments are performed in order to evaluate discrepancies and similarities when the inertial effects become relevant
Kinematics of a balanced vane pump with circular tip vanes
No full textThis paper analyzes the kinematics of the vane-cam ring mechanism in balanced vane pumps, by considering both vanes with centered and not-centered circular tip. The motion of the vane, the position of the contact point and the evolution of the pressure angle are analytically determined in reference to a generic cam ring profile. The results of the kinematic analysis are used to obtain the constraints defining the admissibility of the vane geometry, which is described in terms of tip radius, vane thickness and tip center eccentricity. A parametric study is performed to show the capabilities of the proposed formulation and the influence of the vane design parameters on its kinematics. The analysis demonstrates that the vane kinematic motion in balanced vane pumps is mainly controlled by the tip radius and the tip center eccentricity, as long as the cam ring profile is defined. The tip radius is mainly responsible for the shape of the vane motion, while the tip center eccentricity has a major influence on its timing. Furthermore the effect of the cam ring profile is evaluated by demonstrating that shape and extension of the rise and fall phases influence on the vane geometry admissibility. (c) 2019 Elsevier Ltd. All rights reserved
Kinematics and geometrical admissibility conditions of balanced vane pumps with twin lip vanes
No full textThe present work is devoted to analyze the kinematics of twin lip vanes adopted in balanced vane pumps. The work provides the analytical description of the vane motion according to its geometrical parameters and the cam ring profile. Attention is given to the duality of the solution, an intrinsic property of twin lip vanes that may be considered as followers with two symmetrical half-circular tips. Based on the linkage kinematics, the analytical dissertation is further deepened to define the geometrical admissibility of the vane design and its mathematical domain. In order to evaluate the proposed approach, an extended parametric study is performed on the basis of the Buckingham theorem, detailing how the twin lip configuration affects the machine kinematics. Additional calculations are proposed to determine the vane design configurations that satisfy the fundamental law of cam design and to highlight how this requirement dramatically reduces the subset of available choices in presence of cam ring with a precompression profile. Finally, design guidelines are proposed in order to overcome these drawbacks and expand the admissibility domain
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