Powertrain friction reduction by synergistic optimization of the cylinder bore surface and lubricant - Part 1: Basic modelling and tribological tests Polytechnic School - USP

Format:

Book

Conference/Event

Author/Creator:

Tomanik, Eduardo, author.

Contributor:

Jiménez, Antonio J.

Profito, Francisco J.

Tormos, Bernardo

Zhmud, Boris

Conference Name:

SAE Powertrains, Fuels & Lubricants Digital Summit (2021-09-28 : Live Online, Pennsylvania, United States)

Language:

English

Physical Description:

1 online resource cm

Place of Publication:

Warrendale, PA SAE International 2021

Summary:

On urban and emission homologation cycles, automotive engines operate predominantly at low speeds and part loads. In such regimes, engine friction losses represent around 10% of the consumed fuel energy, but 25% of the fuel consumption since the losses occur after engine combustion, so combustion efficiency needs to be considered [1]. Under such mild conditions, engine and engine oil temperatures are also moderated, and the influence of oil viscosity on friction losses are even more significant. Therefore, by reducing lubricant viscosity, one can minimize engine friction, thus improving fuel economy and reducing vehicle emissions. The benefit of using low viscosity oils on reducing emissions is still higher than the associated fuel economy. Since both oil and catalysts are cold at the test and use start conditions, a larger share of emissions occurs when the engine and oil are still cold. Among the engine components, the piston assembly is the major source of tribological inefficiencies and is responsible for about 50% of the total engine friction losses, making such components the main target elements for the development of low-friction technological solutions. Being a reciprocating system, the piston assembly operates in boundary, mixed and hydrodynamic lubrication regimes. The hydrodynamic regime is more relevant for power losses and fuel consumption since it generally occurs at higher speeds. The boundary and mixed regimes occur predominantly at the reversal points and are directly related to excessive wear and failure.In this work, computer simulations [2,3] were used to investigate the synergistic effect of three engine oils with different viscosity grades (10W40, 5W20 and 0W16) and two-cylinder bore finishes (a regular plateau honing usually applied on grey cast iron and a mirror-like finish used in modern thermal spray coated bores) on the friction reduction of passenger car internal combustion engines (ICEs). First, the Reynolds equation and the Greenwood-Tripp model were used to investigate the hydrodynamic and asperity contact pressures in the top piston ring. It is well-known that the classical Reynolds model works well for barrel-shaped profiles and relatively thick oil film thickness but has limitations for predicting the lubrication behaviour of flat parallel surfaces, such as those of Oil Control Ring (OCR) outer lands. In these cases, a deterministic-based model was used to evaluate the role of surface roughness on the hydrodynamic pressure build-up and, hence, on the OCR' lubrication performance. Samples and results of piston ring/cylinder bore tribological tests were used as input data for the mathematical models and to discuss the simulation results. The basic modelling and discussions presented in this first paper are later used as a fundamental approach and enlarged in a second paper wherein commercial software were employed to simulate the total engine friction losses and evaluate its impact on fuel consumption. In the second paper, motored and operation engine tests will also be described. [1] Tomanik, E. and others "Combined lubricantsurface system approach for potential passenger car CO2 reduction on piston-ring-cylinder bore assembly, Tribology International, V. 149, 2020, 105514, ISSN 0301-679X.[2] Tomanik, E. et al. "Effect of the coated bore pores on the piston ring tribology through deterministic simulation" TAE - International Colloquium Tribology, Esslingen, Jan. 2020.[3] Profito, F.J. et al. "Effect of lubricant viscosity and friction modifier on reciprocating tests" SAE paper 2013-36-0155, 2013

Notes:

Vendor supplied data

Publisher Number:

2021-01-1214

Access Restriction:

Restricted for use by site license