Design optimization of a diesel engine connecting rod

Abstract

Rotary motion is generated from a crankshaft’s piston alternating motion using a connecting rod. The engine combustion gases and components motion of inertia exert pressures that induces compressive and tensile stress in the connecting rod respectively [1], [2]. Connecting rods fail due to its overloading, bearing failure, irregular adjustments of the bolts and faulty assembly or fatigue [3]. It is important for connecting rods to be able to withstand the complex high tensile loads that acts on them. As a result, numerous design technology, material selection, working and fatigue test of a connecting rod have been studied and presented [4]. Mechanical properties (such as hardness, tensile strength, rigidity and fatigue resistivity) of the materials used in the manufacture of a connecting rod need vehicles depends on the design of the connecting rod. Failure of connecting rod is attributed to the in availability of much strength needed to hold the load. This can be overcome with the life cycle extended by increasing the strength [5].

Finite element analysis of connecting rod have been conducted and presented by a lot of researchers. In [6], theoretical and FEA of an IC engine connecting rod was conducted. The result of the analysis obtained shows the causes of failure at the fillet of both ends due to the induced stress. In [7] static FEA for fatigue, deformation and weight optimization of a connecting rod using ANSYS workbench is carried out and presented. From the suggested design changes obtained from the weight optimization result, the failure result is further updated to achieve a better result. In a paper by Bansal, dynamic stress analysis was carried out on a single cylinder four stroke diesel engine connecting rod of Aluminum material using FEA. The optimization was also done under dynamic loading with the boundary conditions and inputs determined from the pressure-volume diagram and engine specification chart respectively are carried out with different meshing size for an accurate result. [8].

FEA is the commonly employed computational tool for testing and modifying engineering structures within certain design limit.  It involves diving in to small units known as ‘elements’ for static and dynamic analysis of simple to complex model under different design constraints. Further investigation can also be done to improve the design for optimal performance and lifespan with regards to design failure [9].

Many kinds of literature have worked on weight optimization. Gaikwad in his paper modifies a roller conveyor by performing weight optimization after carrying out static analysis on the roller conveyor [10] In another paper by [10] the weight of a roller conveyor was reduced thereby saving the materials under specific load constraints using finite element method.

In this paper shape optimization with target weight reduction rate of 20 to 60% with an interval of 10 under a static loading of 100N. Further analysis for structural optimization is also done to determine a new optimized structure with new deformation and stress values respectively. The analysis is carried out in ANSYS static structural, mechanical solver with a tensile force of 100N acting on its larger end.