1,721,032 research outputs found
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
Comparison of single-input single-output and multi-input multi-output control strategies for performing sequential single-axis random vibration control test
No full textThis study investigates the use of single-input single-output and multi-input multi-output control strategies for performing single-axis vibration control tests. In particular, the work addresses the problem of high-level cross-axis responses during those tests. To compare the two control strategies, the study presents a test campaign carried out on an automotive component by exploiting two different test facilities: a single-axis shaker and a three-degree-of-freedom shaker table. The analysis points out the limitations of the single-input single-output control strategy. The coupling between the excitation system and the test specimen causes cross-axis excitations that compromise the test validity. In some cases, the cross-axis vibration level even exceeds the acceptable threshold of 14 dB. The multi-input multi-output control strategy instead, besides the feedback control of the main axis, allows the simultaneous vibration control along the two cross axes, thus, improving the quality of the single-axis test. Moreover, the work provides a detailed study followed by practical examples on how to better exploit the evident potential of the multi-input multi-output control strategy for definitely avoiding cross-axis vibration control problems
Rattle detection in powertrain transmissions based on vibro-acoustical measurements
No full textThe sound of rattling is a common issue in gear transmissions, caused by the chattering of teeth
during specific operating conditions. Given the growing focus on Noise and Vibration Harshness
(NVH) issues in the automotive industry, identifying and explaining this phenomenon could
prove beneficial.
In this paper, three indices for rattle noise identification have been proposed, suitable for
mechanical transmissions with gears. These indices are based on the processing of microphone
signals and acceleration signals measured on the gearbox housing. The main advantage is that
the accelerometers and the microphones can be simply placed on the exterior of a mechanical
transmission and the experimental acquisition of these signals is accessible in a large number
of configurations.
Furthermore, a lumped parameter (LP) model of a transmission powertrain, capable of
reproducing the rattle features, has been employed to verify the proposed indices on numerical
data. Finally, an experimental campaign has been conducted, rattle and no rattle conditions
have been compared and the effectiveness of the proposed indices has been proved. These
techniques can be successfully used also for condition monitoring purposes
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
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
On the Fatigue Damage Estimation in Multi-axis and Single-Axis Vibration Testing
No full textRandom vibration testing is one of the most frequently employed procedures to ensure the durability of a component in operational conditions. Random vibration tests are commonly performed by means of single-axis tests. In particular, it is common practice to test the component multiple times, changing the loading direction. However, real working environments present, in general, multi-axis vibration, and single-axis loads are often incapable of reproducing the response of a component subjected to multi-axis vibration. In this work, the effects of sequential single-axis and multi-axis vibration are compared in terms of fatigue damage. A test campaign has been carried out, exploiting the triaxial shaker system available at the University of Ferrara. In particular, a specifically designed specimen has been tested until failure in different configurations under sequential single-axis and multi-axis uncorrelated vibration. The objective of the test campaign is to quantify the difference in terms of time to failure of the specimen when its dynamic behavior is activated differently. The tests performed with multi-axis vibration resulted always in a significant reduction of the time to failure, compared to sequential single-axis testing. Moreover, it has been found that the S–N curve of the specimen is heavily affected by the activation of the specimen dynamics, resulting in a different fatigue damage accumulation. Finally, the time to failure and the S–N curve of the specimen are used to define a correction factor that quantify the damage inflicted to the specimen by the multi-axis vibration, compared to sequential single-axis testing. The correction factor takes into account the different activation of the specimen dynamics, and it is capable of accurately estimating the time to failure of the specimen under multi-axis loading
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
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