Grietas

ADVANCED DESIGN FOR CRANKSHAFTS AND SLIDING
BEARINGS IN RECIPROCATING ENGINES
Elena Galindo
R&D and Product Engineering Department, COJINETES DE FRICCION, S. A. Ctra. de
Andalucía, km 13.6, 28906 GETAFE, Madrid, Spain. Tel: +34-1-6653200.
Fax: +34-1-6829198
Manuel Valdés
José María López
INSIA (Instituto Universitario de Investigación del Automóvil - University Automobile
ResearchInstitute). c/ José Gutiérrez Abascal, 2. 28006 Madrid, Spain. Tel: +34-13363156. Fax: +34-1-3363006.
e-mail: mval@ccupm.upm.es

Abstract: This paper describes two methods for predicting crankshaft loading and
bearing performance in multicylinder engines. The first, the so-called statically
determinate method, has been employed in the motor industry for the last three
decades. The second, known asthe statically indeterminate method, is based on a
sequential solution to the hydrodynamic and structural FEM equations. This method
allows for more accurate calculation, owing to the smaller number of assumptions upon
which it is based. Similarly, by enabling detailed analysis of crankshaft stresses and
calculation of the influence of crankshaft flexibility on engine performance, design oflighter crankshafts is also rendered possible.

1 INTRODUCTION
Of all the components involved in the lubrication system of an automotive engine, it is
big-end and main bearings that have probably been most researched and analyzed. Most
bearing and engine manufacturers use calculation programs in tandem with hands-on
experience to set design objectives as regards minimum oil-film thicknessand pressure.
In recent years, major efforts have been made to come up with a more accurate
expression of real bearing performance, by incorporating state-of-the-art structural
analysis techniques into the calculation process and reducing the number of simplifying
hypotheses employed. Indeed, this has been the target of ongoing research in the form
of successive collaboration agreements betweenCojinetes de Fricción S. A.’s R&D
Department and the Madrid Polytechnic University’s Automobile Research Institute
(Instituto Universitario de Investigación del Automóvil - INSIA). Said collaboration has
led to the joint development of a number of models for the calculation and design of
sliding bearings.
The model that forms the topic of this paper allows for computation, not only of thebearing as an isolated component, but also of the integrated performance of the
crankshaft-bearing unit under dynamic conditions. The model can be used in diverse
applications, such as the study of main bearing edge loading or the calculation of the
fatigue safety factor in the case of a multicylinder engine crankshaft.

2 HYDRODYNAMIC ASSESSMENT
The point of departure for any study onlubrication is the solution to the Reynolds
equation /1/, proposed by Sir Osborne Reynolds in 1886. There is no single general
analytic solution to the Reynolds equation. Partial analytic solutions have been obtained
by using analogies with electricity or numerical and graphical methods. One of the most
interesting approaches is the Mobility Method, the premises of which were first
formulated byBooker /2/ and which has since served as the basis for other solutions put
forward by authors, such as Goenka /3/.
In essence, the Mobility Method is based on ascertainment of the bearing’s polar load
diagram and allows for calculation of the journal orbit diagram, oil film pressure diagram
and other associated variables such as the required volume of oil flow or friction
horsepower loss. Thepolar load diagram (Figure l) represents the variation in the
resulting load which acts on the bearing during the course of one complete engine cycle.

Fig. 1: Polar load diagram for connecting rod big-end bearing
The journal orbit diagram (Figure 2) depicts the path traced by the journal center on
displacement within the bearing clearance during one complete engine cycle and
furnishes...