This reprint features 12 research articles that contribute to the research on lubricated bearings. The articles focus on the latest steps in understanding bearing operating behavior, its interaction ...with lubricants, and its role as a component in the drive train. In addition to the description of novel modeling approaches, a variety of experimental data are presented to provide interesting identification results as well as validation data for the research and engineering community.
The analysis of turbocharger rotordynamics has been conducted so far focusing solely on the effect of radial bearings on the non-linear oscillations of the rotor-bearing system. It is well known that ...the oil-film concentrated in the rotor's journal bearings is the root cause of the system's occurring nonlinear vibrations. Nevertheless, the rotor-assembly requires to be supported in the axial direction as well in order to compensate the various thrust load effects occurring during operation. This paper investigates the influence of hydrodynamic thrust bearings on the nonlinear oscillations and bifurcations of the rotor system in terms of the thrust- and radial bearing interaction during run-ups. For that purpose the conventional rotordynamics environment is extended by integrating a nonlinear hydrodynamics thrust bearing model suited for transient run-up simulations. Focus is set on the impact of two major parameters that drive the virtual prototype process of new rotor-assemblies: the shaft diameter and the thrust bearing's position along the shaft. It is shown that for a given set of boundaries the thrust bearing's position along the shaft can have either positive, neutral or negative influence on shaft motion. Furthermore, certain combinations of shaft diameter and thrust bearing positions could occur that may have a negative impact on the thrust bearing itself, for example by means of the associated load capacity. In this regard, it is demonstrated that simulating the thrust and radial bearing interaction during run-ups is mandatory not only for shaft motion purposes, but for designing a robust thrust bearing as well. Finally, with the help of correlation coefficients and response surface methods, trends are identified that set guidelines while designing a new turbocharger center section.
The journal and thrust bearing design process remains a key aspect while developing an automotive turbocharger center section. The rotor assembly has to be supported in both the radial and axial ...direction assuring a safe operation with increased life time span. Both bearing types have to be developed sufficing multiple restrictions. Journal bearings are designed with focus on shifting undesired critical frequencies outside the range of operation while supporting various types of nonlinear vibrations. Thrust bearings are configured aiming at a balanced ratio of load capacity and friction losses. In general, both bearing types are treated as two distinct entities during development even when coping with the same center section. This paper investigates the journal and thrust bearing cross-influence effects during the design process of thrust bearing pads. It is conducted by accounting for the thrust- and journal bearing interaction during transient nonlinear run-up simulations. Focus is set on pad designs with different geometrical dimensions, which based on stationary calculations have nearly identical load capacity and friction loss properties. It is shown that thrust bearings consisting of such pads do no necessarily have the same impact on the rotor assembly's nonlinear vibrations during run-ups. In addition, the inherited thrust- and journal bearing interaction ends up with transient hydrodynamic pad properties that do no longer match stationary predictions. Furthermore, it is demonstrated that thrust bearings equipped with geometrically identical pads, but differently allocated along the circumference, interact with the rotor assembly in a different manner depending on the nature of the radial bearing. A semi- or a fully-floating journal bearing combined with a thrust bearing having a symmetric or an asymmetric pad allocation can have either positive or negative influence on shaft motion and load capacity. As a result, the associated friction losses obtained by stationary calculations are either over- or under predicted.
•The dynamic model of the planetary gear set-rolling bearing-rotor system is established.•A nonlinear restoring force model for ball bearing with misalignment is proposed.•The influence of bearing ...misalignment on system dynamic characteristics is analyzed.•The evaluation indexes of bearing misalignment are given.
Bearing misalignment may be one of the causes of cage fracture fault. However, the research of bearing misalignment on vibration characteristics of the rotating machinery system has not been paid enough attention. In this paper, the effects of axial, radial and tilt misalignments of the rotor support bearing on the dynamic characteristics of the planetary gear set-rotor system are analyzed. Firstly, based on the Hertz contact theory, a nonlinear restoring force model of the ball bearing is proposed under axial, radial, and inner/outer ring tilt misalignments. Secondly, taking the planetary gear transmission system of a tracked vehicle as the research object. The dynamic model of the planetary gear set is established through the lumped parameter method. The rotor is established by the Timoshenko beam element. Finally, the dynamic model of the planetary gear set-ball bearing-rotor system is obtained by coupling these three parts. Based on the proposed model, the dynamic responses are analyzed considering bearing misalignment. The results showed that the three types of misalignments reduce the vibration amplitude due to the strengthened constraint of the bearing on the system, but increase the load-bearing area and contact load. Radial and tilt misalignments increase the varying compliance (VC) frequency amplitude of the bearing. On the contrary, axial misalignment reduces the VC frequency amplitude. The sensitive evaluation indexes of three misalignment states are given. The research results can provide a theoretical basis for fault diagnosis and identification of bearing misalignment in complex rotating machinery system.
Rolling bearings are widely used in rotary machinery systems. The measured vibration signal of any part linked to rolling bearings contains fault information when failure occurs, differing only by ...energy levels. Bearing failure will cause the vibration of other components, and therefore the collected bearing vibration signals are mixed with vibration signal of other parts and noise. Using multiple sensors to collect signals at different locations on the machine to obtain multivariate signal can avoid the loss of local information. Subsequently using the multivariate empirical mode decomposition (multivariate EMD) to simultaneously analyze the multivariate signal is beneficial to extract fault information, especially for weak fault characteristics during the period of early failure. This paper proposes a novel method for fault feature extraction of rolling bearing based on multivariate EMD. The nonlocal means (NL-means) denoising method is used to preprocess the multivariate signal and the correlation analysis is employed to calculate fault correlation factors to select effective intrinsic mode functions (IMFs). Finally characteristic frequencies are extracted from the selected IMFs by spectrum analysis. The numerical simulations and applications to bearing monitoring verify the effectiveness of the proposed method and indicate that this novel method is promising in the field of signal decomposition and fault diagnosis.
•Multiple sensors are used to collect signals at different locations on the machine.•Multivariate EMD is used to simultaneously analyze multivariate signal.•The correlation analysis between matrixes is employed to determine effective IMFs.•The NL-means denoising method is used to preprocess the multivariate signals.
Vibration-based rolling element bearing diagnostics is a very well-developed field, yet researchers continue to develop new diagnostic algorithms quite frequently. Over the last decade, data from the ...Case Western Reserve University (CWRU) Bearing Data Center has become a standard reference used to test these algorithms, yet without any recognised benchmark it is difficult to properly assess the performance of any proposed diagnostic methods. There is, then, a clear need to examine the data thoroughly and to categorise it appropriately, and this paper intends to fulfil that objective. To do so, three established diagnostic techniques are applied to the entire CWRU data set, and the diagnostic outcomes are provided and discussed in detail. Recommendations are given as to how the data might best be used, and also on how any future benchmark data should be generated. Though intended primarily as a benchmark to aid in testing new diagnostic algorithms, it is also hoped that much of the discussion will have broader applicability to other bearing diagnostics cases.
•We provide a thorough benchmark analysis of the CWRU Bearing Data.•Three established diagnostic techniques are applied.•We provide the diagnostic outcomes for all data sets as a benchmark reference.•We discuss the records at length and identify data problems and anomalies.•We give recommendations as to how best to use the data for algorithm development.
•A bearing dynamics model with a lumped-mass flexible cage is established.•Cage is compressed in the loaded region while stretched in the unloaded region.•Appropriate radial load and acceleration of ...inner race could attenuate skidding.•Increasing connecting stiffness of cage could alleviate the roller skidding.
Rolling bearings are widely used in rotating machinery and its dynamic performance plays a significant effect on the stability, reliability and even safety of the machine. Presence of the skidding is likely to cause damages to the surfaces of the inner race, the outer race, the rolling elements, and/or the cage. In this paper, a skidding dynamics model of a rolling bearing is established to reveal the skidding characteristics. In the dynamics model, the cage is discretized into several segments having the same number of the rolling elements so as to introduce the flexibility of the cage represented by springs connecting the adjacent segments. And the nonlinear contact forces between the rolling elements and inner\outer races and the cage, the corresponding friction forces, and the gravity and centrifugal forces of the rolling elements are considered comprehensively. The simulation results are compared with the traditional dynamics model with rigid cage. By using the dynamics model, effects of the radial load, the inner ring acceleration, and the connect stiffness between the mass blocks of the cage on the bearing skidding are investigated. The results indicate that the rolling element skidding generally happens at the time instant that the rolling element is entering or leaving the loaded region. The smaller radial load or the higher angular acceleration of inner ring are the primary causes of the bearing skidding. In addition, increasing the connect stiffness could effectively alleviate the skidding phenomenon. Therefore, the proposed bearing dynamics model is proven to be capable of making a reasonable prediction on the bearing skidding with a more realistic flexible cage.
•The duration of natural frequency perturbations is found informative of spall size.•The WVS is utilized to identify the cyclic behaviour of natural frequencies.•This approach overcomes the ...limitation of entry/exit-based methods for natural spalls.•The new approach is validated and compared with existing methods in three tests.
Spalling caused by fatigue is the most common reason for rolling element bearing failure, and spall size can be a good indicator to predict the remaining useful life of the bearing. Previous studies reported that, in the acceleration signal, a low-frequency step response is caused by de-stressing or re-stressing of the rolling element during its entry into and exit from the spall zone, and a high-frequency impact response is often induced when the roller hits the trailing edge of the spall. The conventional spall size estimation methods thus attempt to capture these events (entry, impact, and exit) and use their time difference to estimate the spall size. But the limitation of these methods is that they were mostly built on artificial spalls and have proved scarcely effective in dealing with natural ones. A recent study investigated the effect of these events on bearing stiffness and reported that the stiffness of the bearing structure decreases when the rolling element traverses the spall zone. Inspired by the study, a novel approach is proposed in this paper, which utilises the duration of natural frequency perturbations (induced by stiffness variation) of the bearing structure to perform spall-size estimation. Compared to the existing methods, this approach investigates the instantaneous resonance frequency variation during the spall span instead of the signal events at the entry and exit points. This novel approach along with three other representative existing methods are tested on three experimental datasets: one obtained by an artificially induced spall and the other two by naturally extended spalls. The performance analysis results reveal that all the methods are effective for artificial spalls, but only the proposed approach is effective for naturally extended spalls.
This book focuses on the modelling and the design process of gas bearings, on the experimental validation of such models, and on their applications. In particular, recent developments about foil ...bearings, aerostatic bearings, porous bearings, and non-contact precision positioning systems are shown.
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