Design Analysis of Connecting rod of 4 strokes Single Cylinder Petrol Engine

Transcription

1 Design Analysis of Connecting rod of 4 strokes Single Cylinder Petrol Engine Amit B.Solanki #1, Mr.Bhoraniya Abhishek *2 Asst. Professor, Mechanical Engg.Deptt B.E.Student, Mechanical Engg.Deptt, C.U.Shah University, Wadhwan city, Gujarat Gujarat Technological University, Solanki.foru@yahoo.com Ahmadabad, Gujarat Abstract - Connecting rod is a major component of I.C. Engine which connects piston and the crankshaft and converts reciprocating motion of piston into rotary motion of crank shaft. Here, the force on the connecting rod is equal to the forces due to the maximum gas pressure. The inertia forces are neglected but bending stress due to the inertia forces is checked during designing of connecting rod. In this paper study is performed on a steel connecting rod achieved by change in material, is a significant factor in manufacturing cost reduction. A static analysis is conducted on a connecting rod of a single cylinder 4-stroke petrol engine. The model is developed using Pro/ENGINEER. Further Analysis is done to determine the von-misses stresses shear stress, strains for the given loading conditions and improving engine performance. minimum weight. The material mostly used for connecting rods varies from mild carbon steels (having 0.35 to 0.45 percent carbon) to alloy steels (chrome-nickel or chromemolybdenum steels). The carbon steel having 0.35 percent carbon has an ultimate tensile strength of about 650 MPa when properly heat treated and carbon steel with 0.45 percent carbon has ultimate tensile strength of 750 MPa. These steels are used for connecting rods of industrial engines. The alloy steels have an ultimate tensile strength of about 1050 MPa and are used for connecting rods of aero engines and automobile engines. Keywords - Connecting rod, Pro/ENGINEER Pro/E Mechanica. 1. INTRODUCTION The connecting rod is the intermediate member between the piston and the crankshaft. Its primary function is to transmit the push and pull from the piston pin to the crankpin and thus convert the reciprocating motion of the piston into the rotary motion of the crank. It consists of a long shank, a small end and a big end. It joins the piston pin with the crankpin; small end of the connecting rod is connected to the piston and big end to the crank pin. The cross-section of the shank may be rectangular, circular, tubular, I-section or H-section. Generally circular section is used for low speed engines while I-section is preferred for high speed engines. The lighter connecting rod and the piston greater than resulting power and less the vibration because of the reciprocating weight is less. The connecting rod carries the power thrust from piston to the crank pin and hence it must be very strong, rigid and also as light as possible. 1.1 Material and Manufacture of Connecting Rod The connecting rods are usually manufactured by drop forging process and it should have adequate strength, stiffness and Fig. 1.1 connecting rod 1.2 Forces acting on the Connecting Rod The various forces acting on the connecting rod are as follows: 1. Force on the piston due to gas pressure and inertia of the reciprocating parts, 2. Force due to inertia of the connecting rod or inertia bending forces, 3. Force due to friction of the piston rings and of the piston, and 4. Force due to friction of the piston pin bearing and the crankpin bearing. 108

2 Here, the forces due to the inertia of the reciprocating parts and force due to friction of the piston rings and of the piston is very low. Thus these forces are neglected while designing of connecting rod. The force on the connecting rod is equal to the forces due to the maximum gas pressure. The inertia forces is neglected but bending stress due to the inertia forces (i.e. whipping stress) is checked during designing of connecting rod. Maximum force on the piston due to pressure, F L =π/4 D 2 P = π/4 (57) 2 2 = N Since the connecting rod is design by taking the force in the connecting rod (F C ) equal to the max. Force on the piston due to gas pressure (F L ), therefore force in the connecting rod, F C = F L = N 2. DESIGN OF CONNECTING ROD In the design of connecting rod we choose the 150 cc engine. in the existing material is carbon steel while we chose other two material which are 20CrMo 4340 steel and Aluminium 7075-T6. 150cc engine specification: Engine type: air cooled 4-stroke Specification Bore stroke(mm) Displacement 149.5cc Maximum power 13.8bhp@8500rpm Maximum torque 13.4bhp@6000rpm Compression ration 9.35/1 Length of connecting rod(l) Maximum gas pressure 2MPa Table 2.1 engine specification Thickness of flange & web of section = t Width of section B = 4t The standard dimension of I-section Fig 2.1 I-section of connecting rod Height of section H = 5t Area of section A = 2(4t 2 ) + (3t 2 ) = 11t 2 Moment of inertia about X-axis: I xx =1/12(4t(5t 3 )-3t(3t 3 ) =419t 4 /12 I yy = 1/12(2 1/12(4t 3 )+1/12(3t)t 3 ) =131t 4 /12 I xx /I yy = 3.2 Radius of gyration, K xx =(I xx /A) 0.5 Maximum angular speed, ω max =2πN max /60 =2π8500/60 = rad/s The connecting rod is design for buckling about X-axis (i.e. in a plane of motion of connecting rod),assuming both ends hinged. Taking factor of safety as 6, the buckling load, W CR = F C 6 = = N 2.1 Design Calculation For Carbon Steel σ c = Compressive stress = 415 N/mm 2 a = 1/7500 σ c A Now, buckling load W CR = 1+a(L/K xx ) t = 1+1/7500(117.2/1.78t) 2 t t =0 t 2 = - (-36.89)±( (1)(-21.32)) 0.5 /2(1) t = 6.12 mm say 6.5 mm Thus dimension of cross section of connecting rod are Height = 5t = = 32.5 mm Width = 4t = = 26 mm Thickness t = 6.5 mm The mass of connecting rod Mass, m = volume density = A l ρ = 11t 2 l ρ = 11 (0.0065) = Kg Max. Bending moment, M max = mrω 2 l/9(3) 1/2 = /9(3) 0.5 = Nm And section modulus, Z xx = I xx /5t/2 =419 t 3 /30 = m 3 Max. Bending or whipping stress due to inertia bending forces, σ b(max) = M max /Z XX = N/m 2 109

3 These dimensions are at the middle of the connecting rod. The width (B) is kept constant throughout the length of the rod, but the depth (H) varies. The depth near the big end or crank end is kept as 1.1H to 1.25H and the depth near the small end or piston end is kept as 0.75H to 0.9H.Let us take Depth near the big end, H1=1.2H= =39 mm Depth near the small end, H2=0.85H= = mm say 28 mm Dimension of section near the big end, =39 mm 26 mm Dimension of section near the small end, =28 mm 26 mm 2.2 Design Calculation for 20crmo 4340 Steel: σ c = Compressive stress = 685 N/mm 2 a = 1/7500 σ c A Now, buckling load W CR = 1+a(L/K xx ) t = 1+1/7500(117.2/1.78t) 2 t =0 t 2 = -(-22.35)±( (1)(-12.92)) 0.5 / 2(1) t=4.79 mm say 5 mm Thus dimension of cross section of connecting rod are Height = 5t=5 5=25 mm Width =4t=4 5= 20 mm Thickness t= 5 mm The mass of connecting rod Mass, m = volume density =A l ρ = 11t 2 l ρ =11 (0.005) =0.251Kg Max. bending moment, M max = mrω 2 l/9(3) 1/2 = /9(3) 0.5 = Nm And section modulus, Z xx = I xx /5t/2 =419 t 3 /30 = m 3 Max. Bending or whipping stress due to inertia bending forces, σ b(max) = M max /Z XX = N/m 2 These dimensions are at the middle of the connecting rod. The width (B) is kept constant throughout the length of the rod, but the depth (H) varies. The depth near the big end or crank end is kept as 1.1H to 1.25H and the depth near the small end or piston end is kept as 0.75H to 0.9H.Let us take Depth near the big end, H1=1.2H=1.2 25=30 mm Depth near the small end, H2=0.85H= = mm say 22 mm Dimension of section near the big end, =30 mm 20 mm Dimension of section near the small end, =22 mm 20 mm 2.3 Design Calculation For Aluminum 7075-T6: σ c = Compressive stress = 434 N/mm 2 a = 1/7500 σ c A Now, buckling load W CR = 1+a(L/K xx ) t = 1+1/7500(117.2/1.78t) 2 t t =0 t 2 = -(-35.27)±( (1)(-20.39)) 0.5 / 2(1) t=5.98 mm say 6 mm Thus dimension of cross section of connecting rod are Height = 5t=5 6=30 mm Width =4t=4 6= 24 mm Thickness t= 6 mm The mass of connecting rod Mass, m=volume density =A l ρ = 11t 2 l ρ =11 (0.006) =0.130Kg Max. Bending moment, M max = mrω 2 l/9(3) 1/2 = /9(3) 0.5 = Nm And section modulus, Z xx = I xx /5t/2 =419 t 3 /30 = m 3 110

4 Max. Bending or whipping stress due to inertia bending forces, σ b(max) = M max /Z XX = N/m 2 These dimensions are at the middle of the connecting rod. The width (B) is kept constant throughout the length of the rod, but the depth (H) varies. The depth near the big end or crank end is kept as 1.1H to 1.25H and the depth near the small end or piston end is kept as 0.75H to 0.9H.Let us take Depth near the big end, H1=1.2H=1.2 30=36 mm Depth near the small end, H2=0.85H= =25.5 mm Dimension of section near the big end, =36 mm 24 mm Dimension of section near the small end, =25.5 mm 24 mm Height Width Depth near the big end Depth near the small end Dimension of section near the big end Dimension of section near the small end Weight of connecting rod Kg 0.251Kg 0.130Kg Table 2.2 Comparison for different Material [Crank end] Big diameter = 42 mm [Piston end] Small diameter = 31 mm Length of connecting rod is mm 2.4 Dimension of Crank Pin And Piston Pin [9] Crank pin: F L = projected area bearing pressure = d c l c P bc = d c 1.3d c P bc = d c 2 d c = mm say 42 mm l c =1.3 d c =54.6 mm Piston pin: F L = projected area bearing pressure 3. MODEL OF CONNECTING ROD After calculating manual design of connecting rod we conclude the design data as shown in above table by considering above calculated dimension of connecting rod we make a model of connecting rod in Pro-E. 3.1 Carbon Steel Connecting Rod: The orthographic view of carbon steel connecting rod is shown below: = d p l p P bc = dp 2d p P bc = 2 15 d p 2 d p = mm say 31 mm l p =2 d p =62 mm The dimensions of connecting rod for three materials which are obtained from design are as below: All the parameter in mm [millimeter] PARAMETER Dimension of cross section Thickness of flange CARBON STEEL 20CrMo 4340 STEEL ALUMI- NIUM7075 -T6 I section I section I section Fig.3.1 Dimension of carbon steel connecting rod 111

5 4.ANALYSIS OF CONNECTING ROD After preparing the model of connecting rod for 20CrMo 4340 STEEL, and ALUMINIUM7075-T6 in Pro-E we applied boundary condition and analysis is using Pro-E. 4.1 Analysis of 20crmo 4340 Steel Connecting Rod Property Density 7800 kg/m 3 Young s modulus 210 Gpa Poisson s ratio 0.29 Yield stress 1240 Mpa Thermal expansion /C Material Property 4.1 Material property of 20CrMo 4340 steel Fig.4.1 Analysis of 20CrMo 4340 steel connecting rod 112

6 Result of Analysis Parameter Maximum von misses stress Maximum displacement 1150 Mpa e-06 in 4.2 Result of analysis of 20CrMo 4340 steel connecting rod Checking For Von Misses Stress Maximum von misses stress = 1150 Mpa Yield stress for 20CrMo 4340 steel = 1240 Mpa Von misses stress < yield stress Thus, our connecting rod is safe. 4.2 Analysis of 20crmo 4340 Steel Connecting Rod Material Property Property Density 2700 kg/m 3 Young s modulus 70 Gpa Poisson s ratio 0.34 Yield stress 500 Mpa Thermal expansion /C 4.3 Material property of aluminium 7075-T6 Result of Analysis Parameter Maximum von misses stress Maximum displacement 470 Mpa e-05in 4.4 Result of analysis of aluminium 7075-T6 connecting rod CHECKING FOR VON MISSES STRESS: Maximum von misses stress = 470 Mpa Yield stress for aluminium 7075 T6 = 500 Mpa Von misses stress < yield stress Thus, our connecting rod is safe. Fig 4.2 Analysis of aluminium 7075-T6 connecting rod 113

7 5. CONCLUSIONS For a Connecting rod following are the major consideration. Cost of Material Material Carbon steel(existing material) 20CrMo 4340 steel Aluminium 7075-t6 material Cost of Material Per Piece Cost in Cost in Cost in $/tone $/kg rs/kg 800 $/tone 0.8 $/kg 49.6 rs/kg 1100 $/tone 1.1 $/kg 68.2 rs/kg 2700 $/tone 2.7 $/kg rs/kg 5.1 Cost of material Material Cost Carbon steel(existing material) rs/piece 20CrMo 4340 steel rs/piece Aluminium 7075-t6 material rs/piece 5.2 Cost of material per piece From above comparison we conclude that we should choose 20CrMo 4340 material for connecting rod. [8] Pravardhan S. Shenoy, "Dynamic load analysis and optimization of connecting rod", 2004, Master"s thesis, University of Toledo. [9] optimization of steel connecting rod by aluminium connecting rod using finite element analysis by Tukaram S. Sarkate, Sachin P. Washimkar, Sachin S. Dhulekar BOOKS: [10] "Machine design" by R.S.Khurmi and J.K.Gupta chapter to chapter from page no 1144 to page no [11] "Design of machine element" by V.B.Bhandari design of connecting rod from chapter internal combustion engine REFERENCES [ 1 ] "Fatigue analysis and optimization of connecting rod using finite element analysis" by Prof. Pushpendra Kumar Sharma1, Borse Rajendra R.2,1Head Department Mechanical Engineering NRI-IST, RGPV University, Bhopal, 2Research Scholar M.tech. NRI-IST, RGPV University, Bhopal. [2] "Connecting rod optimization for weight and cost reduction" by Pravardhan S. Shenoy and Ali Fatemi, The University of Toledo. [3] Repgen, B., "Optimized Connecting Rods to Enable Higher Engine Performance and Cost Reduction," SAE Technical Paper Series, Paper No ,1998. [4] Park, H., Ko, Y. S., Jung, S. C., Song, B. T., Jun, Y.H., Lee, B. C., and Lim, J. D., "Development of Fracture Split Steel Connecting Rods," SAE Technical Paper Series, Paper No ,2003. [5] Design and finite element analysis of aluminium-6351 connecting rod by Priyank D. Toliya, Ravi C. Trivedi, Prof. Nikhil J. Chotai Department of Mechanical Engineering Marwadi education foundation's group of institutions, Rajkot, , Gujarat, India [6] James R. Dale, "Connecting Rod Evaluation", January [7] Suraj Pal, Sunil kumar, "Design Evaluation and Optimization of Connecting Rod Parameters Using FEM". International Journal of Engineering and Management Research, Vol.-2, Issue-6, December ISSN No.: