26-11-2012, 11:42 AM
Stress Analysis of Connecting Rod of Nissan Z24 Engine by the Finite Elements Method
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Abstract:
Nissan Z24 is one of the numerous vehicles in Iran. MegaMotor's reports show high rate
damaging in the crankshaft and connecting rod of this engine vehicle. So it is necessary doing a
complete research about slider-crank mechanism because of high expensive repair and replacement of
these parts and their effect on the other parts like cylinder block and piston. Result of initial researches
show that the important reason of these parts damaging is using of downshifting in driving. In this
research, we concerned on analysis of kinematics and kinetic of slider-crank mechanism in engine
maximum power, maximum torque and downshifting situation and also stress analyze of connecting
rod. For this purpose the engine was simulated in MSC/ADAMS/Engine software and forces acting on
different parts of crank mechanism were extracted after that connecting rod was simulated in
SolidWorks software, meshed in ANSYS software and critical loads were exerted on it finally stress
analysis was done.
INTRODUCTION
The automobile engine connecting rod is a high volume production, critical component. It connects
reciprocating piston to rotating crankshaft, transmitting the thrust of the piston to the crankshaft. Every vehicle
that uses an internal combustion engine requires at least one connecting rod depending upon the number of
cylinders in the engine. Beside these points Nissan Z24 is one of numerous vehicles of Iran and MegaMotor's
reports show high rate damaging in the crankshaft and connecting rod of this engine vehicle. So it is necessary
doing a complete research about slider-crank mechanism because of high expensive repair and replacement of
these parts and their effect on the other parts like cylinder block and piston. Cinematic and kinetic analysis of
slider-crank mechanism and stress analyze of connecting rod is done in this project.
The connecting rod is subjected to a complex state of loading. It undergoes high cyclic loads of the order of
108 to 109 cycles, which range from high compressive loads due to combustion, to high tensile loads due to
inertia. Therefore, durability of this component is of critical importance. Due to these factors, the connecting rod
has been the topic of research for different aspects such as production technology, materials, performance
simulation, fatigue, etc. For the current study, it was necessary to investigate finite element modeling
techniques, optimization techniques, developments in production technology, new materials, fatigue modeling,
and manufacturing cost analysis. This brief literature survey reviews some of these aspects.
Webster et al., (1983) performed three dimensional finite element analysis of a high-speed diesel engine
connecting rod. For this analysis they used the maximum compressive load which was measured
experimentally, and the maximum tensile load which is essentially the inertia load of the piston assembly mass.
The load distributions on the piston pin end and crank end were determined experimentally. They modeled the
connecting rod cap separately, and also modeled the bolt pretension using beam elements and multi point
constraint equations (Afzal, A. and A. Fatemi, 2004).
Methods:
A- Kinematics And Kinetic Analysis:
There is different ways for kinematics and kinetic analysis for example this job can be done by Newton's
lows and different computer's software (Meriam, J.L. and L.G., Kraige. 1998; Shigley, J.E. and C.R. Mischke,
2001). In this project MSC.ADAMS/Engine software was used to kinematics and kinetic analysis of slidercrank
mechanism. For obtaining to this purpose crank mechanism was simulated in ADAMS/Engine software.
Figure 1 shows dynamic model of Samand engine in ADAMS/Engine software.
Conclusions:
The following conclusions can be drawn from this study:
1. The maximum pressure stress was obtained between pin end and rod of connecting rod.
2. The maximum tensile stress was obtained in pin end.
3. The factor of safety for pressure stress was obtained 2.869 and for tensile stress was obtained 3.362.
Because of factor of safety for pressure stress was a little critical also according to this point that stresses on
connecting rod vary (from maximum pressure stress to maximum tensile stress) it is necessary fatigue analysis
of this part so fatigue analysis of connecting rod is proposed.