On the Effect of Thermal Energy Transport to the Performance of (Semi)Floating Ring Bearing Systems for Automotive Turbochargers

Abstract

Bearing systems in engine-oil lubricated turbochargers (TCs) must operate reliably over a wide range of shaft speeds and withstanding severe axial and radial thermal gradients. An engineered thermal management of the energy flows into and out of the bearing system is paramount to ensure the components mechanical integrity and the robustness of the bearing system. The bearings, radial and thrust type, act both as a load bearing and low friction support with the lubricant carrying away a large fraction of the thermal energy generated by rotational drag and the heat flow disposed from a hot shaft. The paper introduces a thermohydrodynamic analysis for prediction of the pressure and temperature fields in a (semi) floating ring bearing system. The analysis solves simultaneously the Reynolds equation with variable oil viscosity and the thermal energy transport equation in the inner and outer films of the bearing system. Flow conditions in both films are coupled to the temperature distribution and heat flow thru the (semi)floating ring. Other constraints include calculating the fluid films’ forces reacting to the externally applied load and to determine the operating journal and ring eccentricities. Predictions of performance for a unique realistic (S)FRB configuration at typical TC operating conditions reveal distinct knowledge: (a) the heat flow from the shaft into the inner film is overwhelming, in particular at the inlet lubricant plane where the temperature difference with the cold oil is largest; (b) the inner film temperature increases quickly as soon as the (cold) lubricant enters the film and due to the large amount of energy generated by shear drag and the heat transfer from the shaft; (c) a floating ring develops a significant radial temperature gradient; (d) at all shaft speeds, low and high, the thermal energy carried away by the lubricant streams is no less that 70% of the total energy input; the rest is conducted through the TC casing. To warrant this thermal energy distribution, enough lubricant flow must be supplied to the bearing system. The efficient computational model offers a distinct advantage over existing lumped parameters thermal models and with no penalty in execution time.

Rotordynamic and Friction Loss Measurements on a High Speed Laval Rotor Supported by Floating Ring Bearings

“…It is well-known that unbalance plays an important role in determining both the synchronous as well as the sub-synchronous response [6,8,13]. Furthermore, when using hot gas to drive the rotor, a considerable amount of heat is conducted from the turbine to the bearing system [10], which changes the oil viscosity and thus the bearing properties [5,9]. Moreover, the non-axisymmetric air pressure distribution around the compressor wheel and the turbine wheel can cause significant radial rotor loads [14].…”

“…[1][2][3][4][5][6][7][8][9][10][11][12]), particularly because the complex interaction between the oil films and the rotor can lead to self-excited vibrations, resulting in excessive audible noise, wear and possibly even failure of the bearings [3]. Many recent studies on the dynamics of rotors supported by floating ring bearings have focused on automotive turbocharger applications, often with the goal to replace expensive experimental testing by numerical simulation tools [1,[4][5][6][7].…”

A review of heat transfer in turbochargers

“…Increasing number of researches on heat transport in turbochargers is studied through CHT [34,35]. Individual components such as turbine, compressor and bearing housing along with full turbocharger analyses are also done using CHT [35,36]. This shows the interest of many researchers to increase the level of complexity in 3-D analysis to better model the heat transfer process.…”

“…The bearing system is carefully designed to accommodate the thermal flow between the turbine and compressor. Andres et al [36] developed a thermohydrodynamic computational model of the turbocharger bearing system (floating-ring) that carefully documents the pressure and thermal profile of each component including the lubricant. Shaaban and Seume [5] showed that the heat energy transfer to the oil is 30% of the total heat transfer from the turbine.…”

Modelling the thermal state of a turbocharger bearing housing when calculating the rotor dynamics at transient modes

“…This thermal imbalance affects the amplitude of the synchronous oscillations. San Andres et al (2012) presented a thermohydrodynamic computational analysis that simulates the transfer of thermal energy in a floating annular bearing system. The paper presents the pressure and temperature fields in the inner and outer films, the radial temperatures of the ring, as well as calculating the working clearances gaps in the film and the eccentricities of the neck and ring, etc.…”