Floating Ring Bearings Research Articles

On the dynamics of a nonlinear rotor‐floating ring bearing system

AbstractToday, in high speed applications the rotors are commonly supported by hydrodynamic journal bearings. One typical configuration of journal bearings incorporated in automotive turbochargers is the floating ring bearing. Rotors supported by floating ring bearings have many advantages, regarding costs and power consumption for example. However, they might become unstable with increasing speed of rotation. At the onset of instability both the perfectly balanced and unbalanced rotor undergo self‐excited vibrations which could cause the mechanical breakdown of the system. The “oil whip”‐phenomenon, very well known from the investigations of the plain journal bearing occurs here in a different form. At the stability limit the rotor begins either oscillating with about the half of the ring speed or the half of the ring speed plus the half of the journal speed depending on the system parameters.For this reason a rotor‐floating ring bearing model is presented showing the mentioned characteristics. By applying the nonlinear equations of motion the limit cycles of the system are determined and its loss of stability is investigated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Rotordynamics of Small Turbochargers Supported on Floating Ring Bearings—Highlights in Bearing Analysis and Experimental Validation

Turbochargers (TCs) improve performance in internal combustion engines. Due to low production costs, TC assemblies are supported on floating ring bearings (FRBs). TCs show subsynchronous motions of significant amplitudes over a wide speed range. However, the subsynchronous whirl motions generally reach a limit cycle enabling continuous operation. The paper advances progress on the validation against measurements of linear and nonlinear rotordynamic models for predicting shaft motions of automotive TCs. A comprehensive thermohydrodynamic model predicts the floating ring speeds, inner and outer film temperatures and lubricant viscosity changes, clearances thermal growth, operating eccentricities for the floating ring and journal, and linearized force coefficients. A nonlinear rotordynamics program integrates the FRB lubrication model for prediction of system time responses under actual operating conditions. Measurements of shaft motion in a TC unit driven by pressurized air demonstrate typical oil-whirl induced instabilities and, due to poor lubricant conditions, locking of the floating rings at high shaft speeds. Nonlinear predictions are in good agreement with the measured total amplitude and subsynchronous frequencies when implementing the measured ring speeds into the computational model. The computational tools aid to accelerate TC prototype development and product troubleshooting.

A Virtual Tool for Prediction of Turbocharger Nonlinear Dynamic Response: Validation Against Test Data

Advances on the modeling of nonlinear rotor-bearing models for prediction of the dynamic shaft response of automotive turbochargers (TCs) supported on floating ring bearings (FRBs) are presented. Comprehensive test data for a TC unit operating at a top speed of 65krpm serves to validate the model predictions. The static forced performance of the support FRBs considers lubricant thermal effects, thermal expansion of the shaft and bearings, and entrance pressure losses due to centrifugal flow effects. The bearing analysis also yields linearized rotordynamic force coefficients for the inner and outer lubricant films. These coefficients are used with the rotor model to predict the synchronous response to imbalance and the system natural frequencies and stability. A method renders an accurate estimation of the test rotor imbalance by using the actual vibration measurements and influence coefficients derived from predictions using linearized bearing force coefficients. Predicted ring rotational speeds, operating radial clearances, and lubricant viscosities for the inner and outer films are the main input to the nonlinear time transient analysis. The nonlinear response model predicts the total shaft motion, with fast Fourier transforms showing the synchronous response, and amplitudes and whirl frequencies of subsynchronous motions. The predicted synchronous amplitudes are in good agreement with the measurements, in particular at high shaft speeds. The nonlinear analysis predicts multiple frequency subsynchronous motions for speeds ranging from 10krpmto55krpm (maximum speed 70krpm), with amplitudes and frequencies that correlate well with the test data. The comparisons validate the comprehensive rotor-bearings model whose ultimate aim is to save TC design time and accelerate product development.

Test Response and Nonlinear Analysis of a Turbocharger Supported on Floating Ring Bearings

Measurements of casing acceleration on an automotive turbocharger running to a top speed of 115 krpm and driven by ambient temperature pressurized air are reported. Waterfall acceleration spectra versus rotor speed show the effects of increasing lubricant inlet pressure and temperature on turbocharger rotordynamic response. A comprehensive analysis of the test data shows regimes of speed operation with two subsynchronous whirl motions (rotordynamic instabilities). Increasing the lubricant feed pressure delays the onset speed of instability for the most severe subsynchronous motion. However, increasing the lubricant feed pressure also produces larger synchronous displacements. The effect of lubricant feed temperature is minimal on the onset and end speeds of rotordynamic instability. Nevertheless, operation with a cold lubricant exhibits lower amplitudes of motion, synchronous and subsynchronous. The experimental results show the subsynchronous frequencies of motion do not lock (whip) at system natural frequencies but continuously track the rotor speed. No instabilities (subsynchronous whirl) remain for operating speeds above 90 krpm. Linear and nonlinear analysis results for the operation of a small automotive turbocharger supported on floating ring bearings are presented. A comprehensive fluid film bearing model predicting the forced response of floating ring bearings is also described. The linear rotordynamic model predicts well the rotor free–free modes and onset speed of instability using linearized bearing force coefficients. The nonlinear model incorporating instantaneous bearing reaction forces in the numerical integration of the rotor equations of motion predicts the limit cycle amplitudes with two fundamental subsynchronous whirl frequencies. Comparisons of both models to experimental results follow. The predictions evidence two unstable whirl ratios at approximately 12 ring speed and 12 ring speed plus 12 journal speed. The transient nonlinear responses reveal the importance of rotor imbalance in suppressing the subsynchronous instabilities at large rotor speeds as also observed in the experiments.

Thermal effects on the performance of floating ring bearings for turbochargers

Physical models and fast computational programs aim to improve the design and performance of turbocharger (TC) rotordynamics. Most commercial automotive TCs incorporate floating ring bearings (FRBs) owing to their low cost and reduced power losses. However, persistent subsynchronous motions afflict this type of rotor/bearing system, albeit reaching limit cycles that enable their continuous operation. FRBs comprise two fluid films in series and are prone to show one or two subsynchronous instabilities over extended speed ranges of operation. A flow model for prediction of FRB forced response is detailed here. The model incorporates a lumped-parameter thermal energy balance for estimation of the lubricant viscosity and thermal growth of the rotor, bearing and floating ring. The FRB model, fully integrated into a non-linear rotordynamics computational program, predicts the floating ring speed, journal and ring eccentricities, power loss and the rotordynamic force coefficients of the inner and outer films as a function of the load applied at a given rotor speed. Knowledge of the actual load conditions, static and dynamic, and the changes in operating clearance and effective lubricant viscosity are most important for accurate estimation of a TC dynamic forced response. Predictions for the exit lubricant temperature, power losses and floating ring speeds agree well with measurements obtained in an automotive turbocharger test rig. The rotordynamic stability characteristics of the test TC are also highlighted.

A Steady-State Model of a Floating Ring Bearing, Including Thermal Effects

A steady-state model of a conventional floating ring bearing is presented, specifically, to assess the feasibility of its use in the power generating industry. It necessitates the numerical solution of the Reynolds and energy equations for both inner and outer lubricant films. Oil recirculation and heat and mass transfer between the films are included. For the application considered, the oil temperatures and eccentricity ratios encountered are not excessive.

Experimental and Analytical Research on Floating-Ring Bearings for Engine Applications

This study deals with whether floating-ring journal bearings can be applied to engine bearings or not. The performance of floating-ring journal bearings with nonstationary load is analyzed. The main bearings of a S195 4-stroke diesel engine are replaced by floating-ring bearings and an experiment is carried out with success. After the engine starting, the ring lifts off when crankshaft speeds approach seven hundred and forty rpm. The ring maintains its rotation until crankshaft speeds decrease to two hundred rpm, during its deceleration to a stop. Once the ring lifts off it remains in normal working order. It is possible for floating-ring bearings to be used in engines where the load is nonstationary. It is hoped that a further reduction in the ring starting speed will be provided by lessening the difference between dynamic and static frictional coefficients in friction pair and an increase in lifetime will be provided by the floating-ring journal bearing.

An Analysis of the Steady-State Performance of the Cylindrical-Spherical Floating Ring Bearing

A steady-state analysis based on the short bearing approximation is presented for the cylindrical-spherical floating ring bearing, where the inner surface of the ring is cylindrical whilst the outer is spherical. Performance characteristics are compared with Li and Rohde’s theoretical work on the conventional cylindrical-cylindrical bearing. Excellent agreement is obtained, especially for (L/D) = 0.5. The present analysis of both the inner and outer lubricant films, the thickness of the latter varying axially, takes account of striated flow downstream of cavitation inception. The importance of this is demonstrated when considering power loss prediction.

Externally-Pressurized Gas-Lubricated Floating-Ring Porous Journal Bearings Part 2: Dynamical State Analysis

Theoretical stability characteristics of a new type of floating-ring bearing, proposed in an earlier paper, are presented. The results bring out the essential features of dynamical behaviour of the proposed bearing against the externally-pressurized plain porous journal bearing. The numerical scheme for the computation of the stability margin adopted in this work is different, yet simple and very efficient.

Externally-Pressurized Gas-Lubricated Floating-Ring Porous Journal Bearings: Part 1: Steady State Analysis

A new type of gas-lubricated floating-ring journal bearing in which the fixed bearing and the ring are both porous, has been conceived and analysed, theoretically, for the steady state characteristics. Bearing characteristics are presented against two design parameters, namely, clearances ratio and permeability parameter. The comparison of these characteristics with those of externally-pressurized plain porous journal bearings shows that the new bearing represents, with its steady state performance, a distinctly advanced bearing design.

High-Speed Floating-Ring Bearing Test and Analysis

Testing of small high-speed floating-ring bearings, typical of those used in automotive turbochargers, revealed a discrepancy between ring speed measurements and ring speed prediction using isothermal bearing analysis. As bearing stability, energy loss, and load capacity are dependent on ring speed, an experimental program was undertaken to determine the effects of various bearing parameters on ring speed. The program results show that none of the 16 bearing parameters investigated increased the bearing ring speeds to those values predicted by the isothermal bearing analysis. In parallel with the experimental program, a thermal analysis was developed in which the effects of lubricant and bearing temperature on the ring speed of a floating-ring bearing way investigated. The ring speed predictions from this thermal floating-ring bearing model agree with the measured values except at the lowest and highest speeds tested. Therefore, for the type of floating-ring bearing design described in this paper, it is concluded that thermal heating can contribute significantly to ring-speed reduction.

Dynamic Characteristics and Stability of a Helical-Grooved Floating-Ring Bearing Operated in Turbulent Regime

The performance of a helical-grooved floating-ring bearing operated in turbulent regime has been studied. The load capacity of this type of bearing is proportional to the sum of speeds of journal and ring whereas the power loss is approximately proportional to the difference of these speeds. This gives a considerable advantage in terms of power loss and lubricant cooling requirement. Stabilities are analyzed. It is found that both the stability and load can be enhanced by pressurization of lubricant supply. This would avoid possible cavitation damage from applications with liquid metal as lubricant, for instance. Numerical results of dynamic stiffness and damping, the critical mass plus the static performance are presented in graphical forms or tables to facilitate design of this type of bearing. Performance comparisons are made with respect to those of a single journal bearing.

Load Carrying Efficiency of Floating Ring Journal Bearings

Floating ring bearings are compared to single film journal bearings over the full range from laminar to turbulent conditions in the films. Isothermal conditions are assumed. Assuming each type carries the same external load and operates at the same eccentricity ratio as determined by the Capacity Number, reductions in the power loss required range from 31 to 64 percent when the clearance ratio C0/(C1 + C2) is held constant and the length is shortened, and from 42 to 63 percent when the length ratio L0/L is held constant and the clearance ratio C0/(C1 + C2) is reduced. Equilibrium ring speeds range from ω0/3 to 0.45 ω0.

Dynamics of Rotor Bearing Systems Supported by Floating Ring Bearings

A general analysis and computational method is presented for calculating the unbalance and self-excited response of high-speed rotor-bearing systems. The analysis is applied to the calculation of the transient response of a rotor supported by two floating ring bearings. Included in the analysis are rotor gyroscopic moments as well as the flexibility of the shaft. Emphasis is placed on determining rotor whirl orbits as influenced by rotor unbalance, the phase angle of the unbalance masses, the clearances of the bearings, the viscosity of the lubricant, and the shock loads that the rotor may be subjected to. It is found that the rotor-bearing system normally operates in an unstable mode in the linear stability sense. However, the nonlinear forces developed by the fluid films of the floating ring bearing will bring the rotor-bearing system to whirl at a limit cycle well within the clearance circles. It is also shown that the rotor assembly will undergo a conical motion when the rotor and wheel configuration is asymmetrical.

Closure to “Discussion of ‘Dynamics of Rotor Bearing Systems Supported by Floating Ring Bearings’” (1982, ASME J. Lubr. Technol., 104, p. 476)

Closure to “Discussion of ‘Dynamics of Rotor Bearing Systems Supported by Floating Ring Bearings’” (1982, ASME J. Lubr. Technol., 104, p. 476)

Discussion: “Dynamics of Rotor Bearing Systems Supported by Floating Ring Bearings” (Li, Chin-Hsiu, 1982, ASME J. Lubr. Technol., 104, pp. 469–476)

Discussion: “Dynamics of Rotor Bearing Systems Supported by Floating Ring Bearings” (Li, Chin-Hsiu, 1982, ASME J. Lubr. Technol., 104, pp. 469–476)

Closure to “Discussion of ‘On The Steady State and Dynamic Performance Characteristics of Floating Ring Bearings’” (1981, ASME J. Lubr. Technol., 103, p. 397)

Closure to “Discussion of ‘On The Steady State and Dynamic Performance Characteristics of Floating Ring Bearings’” (1981, ASME J. Lubr. Technol., 103, p. 397)

On The Steady State and Dynamic Performance Characteristics of Floating Ring Bearings

An analysis of the steady state and dynamic characteristics of floating ring journal bearings has been performed. The stability characteristics of the bearing, based on linear theory, are given. The transient problem, in which the equations of motion for the bearing system are integrated in real time was studied. The effect of using finite bearing theory rather than the short bearing assumption was examined. Among the significant findings of this study is the existence of limit cycles in the regions of instability predicted by linear theory. Such results explain the superior stability characteristics of the floating ring bearing in high speed applications. An understanding of this nonlinear behavior, serves as the basis for new and rational criteria for the design of floating ring bearings.

Floating ring journal bearings: theory, design and optimization

The performance characteristics and design data for journal bearings with a precise floating ring inserted between the rotating journal and a rigid housing are investigated theoretically. Based on convenient boundary conditions, a theory has been developed to predict the floating ring behaviour. Performance charts are presented with curves provided with optimum design areas to help in practical design applications. Induced ring speed, hydrodynamic behaviour, oil film variation, load capacity and frictional drag could thus be analytically or graphically determined. Results indicate that the ring dimensions are a dominant factor in deciding the final bearing behaviour and that the oil film thickness between the ring and the housing is much thinner than that between the journal and the ring. The floating ring bearing showed less frictional power loss than a fixed sleeve bearing, but this may have been achieved at the expense of the load capacity.

Analysis of Dynamically Loaded Floating-Ring Bearings for Automotive Applications

This study deals with the frictional performance of dynamically loaded floating-ring journal bearings and investigates their feasibility for automotive applications. An analysis of the performance of floating-ring journal bearings in conducted. The bearing loads and speeds considered simulate those experienced in automotive engines. The potential contribution of the floating-ring design concept to reduced engine friction is assessed, and its compliance with current bearing durability criteria is evaluated. The results indicate that the adoption of the floating-ring design concept has the potential for reducing power loss in automotive engine bearings. It is shown that this can be accomplished without violating minimum film thickness constraints currently accepted as criteria for successful engine bearing operation.