Stress Analysis of Connecting Rod of Nissan Z24 Engine by the Finite Elements Method

Transcription

1 Australian Journal of Basic and Applied Sciences, 5(12): , 2011 ISSN Stress Analysis of Connecting Rod of Nissan Z24 Engine by the Finite Elements Method 1 Mohammad Ranjbarkohan, 1 Mohammad Reza Asadi and 1 Behnam Nilforooshan Dardashti 1 Department of Mechanical Engineering, Islamic Azad University, Buinzahra branch, Qazwin, Iran. 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. Key words: Nissan Z24, Engine, Connecting rod, Cinematic, Kinetic, Stress, Analysis. 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 10 8 to 10 9 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). In a study reported by Repgen (1998), based on fatigue tests carried out on identical components made of powder metal and C-70 steel (fracture splitting steel), he notes that the fatigue strength of the forged steel part is 21% higher than that of the powder metal component. He also notes that using the fracture splitting technology results in a 25% cost reduction over the conventional steel forging process. These factors suggest that a fracture splitting material would be the material of choice for steel forged connecting rods. He also mentions two other steels that are being tested, a modified micro-alloyed steel and a modified carbon steel. Other issues discussed by Repgen are the necessity to avoid jig spots along the parting line of the rod and the cap, need of consistency in the chemical composition and manufacturing process to reduce variance in microstructure and production of near net shape rough part (Repgen, B., 1998). El-Sayed and Lund (1990) presented a method to consider fatigue life as a constraint in optimal design of structures. They also demonstrated the concept on a SAE key hole specimen. In this approach a routine calculates the life and in addition to the stress limit, limits are imposed on the life of the component as calculated using FEA results (El-Sayed, M.E.M. and Lund, E.H., 1990). Corresponding Author: Mohammad Ranjbarkohan, Department of Mechanical Engineering, Islamic Azad University, Buinzahra branch, Qazwin, Iran. 2084

2 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.. Fig. 1: Dynamic Model of Engine in ADAMS/Engine. Combustion chamber pressure curve was measured in mega motor's power test lab. These experimental data have been shown in Figure 2. Data of these curves were exerted on piston in modeled mechanism. 6 Combustion pressure on 2800 Rpm(Full load) Combustion pressure on 2400 Rpm(Full load) Combustion pressure(idel) 5 Pressure (Mpa) Crank angle (Deg) Fig. 2: Combustion Pressure in Different RPM and Load. B- Modeling, Meshing And Loading Forces On Connecting Rod: For stress analysis of connecting rod it was modeled in SolidWorks software, SolidWorks software has more tools for modeling and we can make complicated models with more care and less time in this software. Figure 3 shows modeled connecting rod in SolidWorks software. Meshing and stress analysis of connecting rod was done in ANSYS software. Figure 4 shows meshed connecting rod in ANSYS software. Solid92 element was considered to carry analyzing. This element is three dimensional with 10 nods. Also, this element related to Solid72 is better specially, in problems with curve bounds had more accuracy, but it increases time need to solve problems (Jahed Motlagh, H., 2003). Total nodes used for model were and total elements used to carry analyzing was The process for manufacturing Nissan Z24 connecting rod is forging. Material qualification of CK45 steel (used for Nissan Z24 engine connecting rod) has been shown in table 1 (Anonymous, 2008). 2085

3 Fig. 3: Modeled connecting rod in SolidWorks software. Fig. 4: Meshed connecting rod in ANSYS ver9 software. Table 1: Material qualification of steel used in connecting rod. Cr C Si Mn S P 0.2/Max 0.4/ / / / 0.035/ Max Max Poisson Ratio Modulus of Elasticit (Gpa) S / Max YTS UTS (N/mm 2 ) (N/mm 2 ) To calculate stress, forces was exerted on corresponding parts in modeled connecting rod in ANSYS software s medium considering following notes: 1. Inertia forces were evenly exerted on pin end inner level (figure 5) (Kolchin, A. and V. Demidov, 1984). The value of these forces was calculated using following formula: Fig. 5: Inertia force distribution on pin end. Fi 2 Pi ( N / m ) (1) 2Rml s Where P i is force per unit area (N/m 2 ), l s is pin end width (m), F i is inertia force and Rm is pin end mean radius (m). 2086

4 2. The force resulted from combustion pressure were sinusicaly exerted on pin end inner level (figure 6) (Kolchin, A. and V. Demidov, 1984; Afzal, A. and A. Fatemi, 2004). The value of this force was calculated using following formula: Fig. 6: pressure force distribution on pin end. 2Fg 2 Pg ( )sin ( N / m ) (2) Rmls Where P g is force per unit area (N/m 2 ) and F g is force resulted from combustion (N). 3. The force resulted from falsifying of pin end s linier and also from friction between linier and piston pin were evenly exerted on pin end inner level all situations. These forces cause pressure stress in linier and tensile stress in connecting rod. This pressure was calculated using following formula (Kolchin, A. and V. Demidov, 1984): (3) tot Pb ( d dsi )( dsu dsi ) U su ( dsu dsi )/( dsa dsi ) U dsu ES Eb Where tot is sum of initial diameter differences and diameter differences resulted from friction (m), dsu is pin end s outer diameter (m), dsi is pin end s inner diameter (m), U is Poisson ratio and E s, Eb is elasticity module of connecting rod and linier (Pa). This pressure is evenly exerted on pin end level (Kolchin, A. and V. Demidov, 1984). RESULTS AND DISCUSSION Kinetic analysis was done for different rotational speeds. These speeds were 1500 RPM, 2800 RPM, 3500 RPM, 4800 RPM and 6000 RPM. Figure 7 shows exerted forces on connecting rod in mentioned speeds. Pin end of connecting rod(newton) 1500 Rpm 2800 Rpm 3500 Rpm 4800 Rpm 6000 Rpm Cranck angle(rpm) Fig. 7: Exerted forces on connecting rod in different speeds. 2087

5 As shown in figure 7 the maximum pressure force is (N) and it occurs at 2800 RPM rotational speed (in 375 degree of crank angle) and the maximum tensile force is 9333 (N) and it occurs at 6000 RPM rotational speed (in 1 degree of crank angle). For calculating pressure and tensile stresses above forces were used. The maximum pressure stress was obtained between pin end and rod of connecting rod (in node 53717). The value of this stress was 202 MPa (Fig. 8). The maximum tensile stress was obtained in pin end (in node 2726). The value of this stress was 174 MPa (Fig. 9). According to table 1, ultimate strength ( u ) CK45 steel (used for this connecting rod) is 585 MPa. So factor of safety (F.S.) will be: u 585 F. S. pressure stress all 202 u 585 F. S. tensile stress all 174 Fair factor of safety for mechanical tools is about 2 to 3 (Khanali, M., 2006), so calculated factor of safety is fair for connecting rod under tensile loads but for pressure loads it is a little critical. Fig. 8: Stress distribution in connecting rod, resulted from maximum pressure force considering Van Misses. Fig. 9: Stress distribution in connecting rod, resulted from maximum tensile force considering Van Misses. 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 and for tensile stress was obtained

6 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. REFERENCES Afzal, A. and A. Fatemi, "A comparative study of fatigue behaviour and life predictions of forged steel and PM connecting rods". SAE Technical Paper, 1: Anonymous, "Nissan Z24engine Maintenance and Repayments catalogue". Megamotor Co,. Chen, N., L. Han, W. Zhang and X. Hao, "Enhancing Mechanical Properties and Avoiding Cracks by Simulation of Quenching Connecting Rod". Material Letters, 61: El-Sayed, M.E.M. and E.H. Lund, Structural optimization with fatigue life constraints, Engineering Fracture Mechanics, 37(6): Jahed Motlagh, H., M. Nouban and M.H. Ashraghi, "Finite Element ANSYS". University of Tehran Publication, PP: 990. Khanali, M., "Stress analysis of frontal axle of JD 955 combine". M.Sc.thesis. Thran University, 124. Kolchin, A. and V. Demidov, "design of Automotive Engines". MIR Publication. Meriam, J.L. and L.G. Kraige., Engineering Mechanics, 5th Edition, New York, john willey, 712. Repgen, B., Optimized Connecting Rods to Enable Higher Engine Performance and Cost Reduction, SAE Technical Paper Series, Paper No Shigley, J.E. and C.R. Mischke, "Mechanical Engineering Design", McGraw-Hill, New York, 776. Webster, W.D., R. Coffell and D. Alfaro, A Three Dimensional Finite Element Analysis of a High Speed Diesel Engine Connecting Rod, SAE Technical Paper Series, Paper No