Abstract
In a quest to reduce fuel consumption and emissions of automotive combustion engines, friction losses from many different sources need to be minimized. For modern designs of turbochargers commonly used in the automotive industry, reduction of friction losses results in better efficiency and also contributes to a faster transient response. The thrust bearing is one of the main contributors to the mechanical losses of a turbocharger. Therefore, it is crucial to optimize the design of the thrust bearing so that it has minimum friction losses while keeping sufficient thrust carrying capacity. One of the main challenges of turbocharger thrust bearing design, is that rotation speed is not fixed: the turbocharger may have a rotation speed which varies between 0 to as much as 250 kRPM. Moreover, the thrust bearing generates considerable heat, which changes the temperature of the oil film and its surroundings. In the present work, the design of the thrust bearing of an automotive turbocharger has been optimized. A CFD-based Thermohydrodynamic (THD) computational approach has been developed, taking into consideration heat dissipation, conjugate heat transfer throughout the bearing domain including the surrounding parts, as well as shear thinning and cavitation in the lubricant domain. An optimizer has been coupled to the CFD solver, with the aim of identifying bearing designs with reduced friction losses. Two bearing concepts have been evaluated: a taper-land design—which is a commonly applied thrust bearing concept—as well as a pocket bearing design. The resulting optimum pocket designs exhibit improved performance, in comparison to the optimum taper-land design. The present results indicate that (a) the pocket design concept can substantially contribute to further reducing the friction losses of a turbocharger, and (b) optimal design parameters of pocket bearings depend on the specific application (size, operating conditions), therefore detailed calculations should be performed to verify optimum performance.
Highlights
Turbochargers have enabled combustion engines to become smaller and more efficient while remaining powerful
The results demonstrate that shear thinning substantially affects speed of 250 kRPM
The present study was concerned with the design optimization of the thrust bearing of an
Summary
Turbochargers have enabled combustion engines to become smaller and more efficient while remaining powerful. The amount of turbocharged gasoline passenger vehicles has grown considerably the past decades. Almost all diesel engines for passenger vehicles are nowadays equipped with turbochargers [1]. A turbocharger is basically a rotor that features a turbine on one Lubricants 2018, 6, 21; doi:10.3390/lubricants6010021 www.mdpi.com/journal/lubricants. Lubricants 2018, 6, x FOR PEER REVIEW on one side and a compressor on the other side (Figure 1). The turbine scavenges energy from the exhaust gas flow and delivers it to the compressor, which compresses ambient air and feeds it to the engine. As the density of the air is increased by compression, more air can be admitted at each combustion stroke and more power can be made [2]
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