Design and Analysis of Engine and Chassis Mounting Bracket

Transcription

1 Design and Analysis of Engine and Chassis Mounting Bracket Vidyasagar Kadam 1, Prof.A.C.Mattikali 2 1 M.Tech.,Mechanical Engg. Dept., MMEC, Belagavi 2 Assistant Prof. Mechanical Engg. Dept. MMEC, Belagavi Abstract The objective of this project is to carry out the static analysis of front engine mounting bracket to calculate deformation and stress in the component for different load conditions along x, y, z- direction using numerical analysis. And even to carry out modal analysis of front engine mounting bracket using numerical model to determine natural frequency and different mode shapes. Weight and stiffness optimization of front engine mounting bracket on basis of stress build up in bracket. It was statically and dynamically analyzed using simulation software Altair Hypermesh and Ansys. Static analysis is to find out the total amount of stress and displacement of engine front engine mounting bracket. Dynamic analysis is to find out the natural frequency of front engine mounting bracket. Optimization is based on Ansys linear static and dynamic modal analysis results, which can be used to enhance the efficiency of design process. Considering the result obtained from optimization, geometric modal was modified and iterated until satisfactory results were achieved. The process is repeated until all specified criteria are met. The process helps in finding the optimized design for the front engine mounting bracket in which it has the best performance without any failure and with minimum loads acting on the front engine mounting bracket. After implementing optimization, weight of the front engine mounting bracket will be reduced. FEA also be carried out on optimized design of the front and rear engine mounting bracket check whether the optimized design is safe or not. Final results are more optimize than existing design. Keywords Front engine mounting bracket; Static and Modal analysis; G-force, FEA, Optimization, Hypermesh, Ansys, I. INTRODUCTION An engine mount is a connecting link between vehicle chassis and engine. The engine excitation forces arising from firing pulse and unbalanced forces are widely considered among the main vibration sources for the road vehicles. Correct positioning and geometry of the mount brackets on the chassis ensures a good performance and ride quality. The brackets on the frame that support the engine undergoes high static and dynamic stresses and even the huge amount of vibrations, as the vehicle intend to be high a performance vehicle. Hence, by careful designing and analysis of the mount bracket, dissipation of vibrational energy and keeping the stresses under a predetermined level, the safety could be achieved. There are two essential but conflicting criteria that engine must satisfy. First, to control the idle shake and engine mounting resonance, the engine should be stiff and highly damped. Also, the motion resulting from load conditions such as travel on bumpy roads must be controlled by it, like a shock absorber. And secondly, for a small amplitude excitation over the higher frequency range, a compliant but lightly damped mount is required for vibration isolation and passenger comfort. In an automotive vehicle, the engine rests on brackets which are connected to the main-frame or the skeleton of the car. Hence, during its operation, the undesired vibrations generated by the engine and road roughness can get directly transmitted to the frame through the brackets. This may cause discomfort to the passenger(s) or might even damage the chassis. When the operating frequency or disturbance approaches the natural frequency of a body, the amplitude of Vibrations gets magnified. This phenomenon is called as resonance. If the brackets have their resonance All Rights Reserved 19

2 close to the operating engine frequencies, then the large amplitude of vibration may cause its fatigue failure or breakage, thus reducing its estimated or desired life. The mounting of the engine should be well constrained and the mount brackets need to be lightweight and designed to safely bear the inertial loads and maximize vibration-transmission.fea has been done to check the frequency and loading response of the brackets before finalizing the design. Mass optimization has been carried out to save material and reduce the weight. The modified designed has been re-analyzed using FEA before finalization. II. OBJECTIVE Design and development of front engine mounting brackets. Carry out static analysis of front engine mounting bracket to calculate deformation and stress in the component for different load condition along x, y, z-direction using numerical analysis. Carry out modal analysis of front engine mounting bracket using a numerical model to determine natural frequency and different mode shape. Weight and stiffness optimization of front engine mounting bracket on basis of stress builds up in brackets. III. METHODOLOGY At first engine mounting brackets theoretical study is done. To sustain the vibrations caused by engine as well as bumps from tires due to uneven road surfaces and support the Engine and power train is the overall purpose of engine mounting bracket. Identified key areas for modification are. The 3-Dimensional model is prepared for Bracket, insulator with the help of constraints of the design and then assembly of mounting bracket and insulator at proper resting surfaces of chassis and power-train are carried out. In present work, Static analysis and modal analysis of the engine mounting brackets are carried out. The work is mainly focus on the weight optimization of the bracket, safety factor and sensitivity curve. The optimization of the brackets is based on the stress builds in brackets and value of the stress should be less than yield stress. IV. DESIGNING OF FRONT ENGINE MOUNTING BRACKET The front engine mounting bracket mainly support to engine of the vehicle and it takes 30% load of the total weight to manufacture the front engine mounting bracket casting manufacturing process is used. Figure 4.1 shows 2D drafting of front engine mounting bracket and developed 3D design model of the same, which shows to resting position engine and chassis resting position. The rubber pad is designed to absorb vibration induced by engine or road which is assembled in between mounting bracket and chassis. In the design of rubber pad taking care of there is no contact in between two metal sheets at emergency condition i.e. sudden break and acceleration for this stoppers are designed, studs are used for assembly purpose. The rubber insulator is sandwich in between the two metal sheets whose main function to absorb the shocks and vibration shown in figure 4.2 with the assembly of front engine mounting bracket is done by nut and bolts and washer for tightening All Rights Reserved 20

3 Figure D drafting and 3D model of front engine mounting bracket Figure 4.2. Rubber pad for mounting bracket and assembly of front engine mounting bracket V. STATIC ANALYSIS FOR FRONT ENGINE MOUNTING BRACKET 5.1 Static analysis for base model of front engine mounting bracket The front engine mounting brackets undertake 30% load of total weight of engine since it important to design bracket from the safe working point of view. Types of load cases: The engine mounting bracket is usually subjected to different loading conditions i.e. acceleration, breaking, jerk and torque so that this load cases are taken in static analysis at different co-ordinate axes which usually indicates dynamic effect. This condition are on X=4g load, Y=3g load and Z=6g load. 1. First Load case:- X=4g= N 2. Second load case:- Y=3g= N 3. Third load case:- Z=6g= N For first load case (X=4g): Type of analysis:-static structural. Expected output:-displacement & Stress. Software used:-ansys Workbench All Rights Reserved 21

4 Geometry is created by using CATIA V5R16.It is imported in igs format in ANSYS Workbench. Mesh size selected is 5mm. Material assigned:-sg IRON 450/10. Type of manufacturing bracket: Casting. 5 Material properties as:-modulus of Elasticity (E)= 1.7e MPa, Poisson s Ratio (µ)=0.275 & 7.1e 9 Density( )= tonnes /mm 3. Load on bracket at load condition x=4g: N Yield Stress:-310 Mpa. Meshing Type:-Tetrahedral meshing. No. of nodes: No. of elements: Weight of bracket: Kg. Boundary Conditions:-The one end of the bracket is fitted with the engine resting surface other end is fitted on chassis resting surface and bracket is assembles by nut and bolt since the washer is created at region A and it is fixed also load is applied along direction of x-co-ordinate on washer at region B shown in figure 5.1. Figure 5.1. Boundary condition for first load case (at x=4g) and meshing of front engine mounting bracket Figure 5.2. Displacement & von-mises stress plots for front engine mounting bracket (at All Rights Reserved 22

5 1. Maximum Deflection= mm 2. Maximum Von Mises stress= MPa. For second load case (Y=3g): Boundary Condition: The fixing location at region A of bracket is same as per previous but load is applied along direction of y-co-ordinate on washer at region B shown in figure 5.3. Figure 5.3. Boundary Condition for second load case (at y=3g) Figure 5.4. Displacement & Von-mises stress plots for front engine mounting bracket (at y=3g) 1. Maximum Deflection= mm 2. Maximum Von Mises stress= MPa. For third load case (Z=6g): Boundary Condition: The fixing location at region A of bracket is same as per previous but load is applied along direction of z-co-ordinate on washer at region B shown in figure All Rights Reserved 23

6 Figure 5.5. Boundary condition for third load case (at z=6g) Figure 5.6. Displacement & von-mises stress plots for front engine mounting bracket (at z=6g) 1. Maximum Deflection= mm 2. Maximum Von Mises stress= MPa. 5.2 Static analysis of first optimized front engine mounting bracket In first case, the maximum stress builds up in all three load condition is Mpa along z-co ordinate axes, this value is comparatively less than yield stress since we remove the material where the less stresses builds-up. For first modification we reduce the thickness of chassis resting portion of bracket by 5mm thickness which is shown in the figure All Rights Reserved 24

7 Figure 5.7. Structural optimization of front engine mounting bracket Weight of bracket: Due to reduce in thickness of region B the weight of bracket gets reduced by % of base model and which comes to 2.72 kg. In the boundary condition fixed the hole at region A and load applied on region B in direction of X co-ordinate as shown in figure 5.1. For first load case(x=4g): Figure 5.8. Displacement & von-mises stress plots for first iteration of front engine mounting bracket (at x=4g) 1. Maximum Deflection= mm 2. Maximum Von Mises stress= MPa. For second load case (y=3g): Boundary Condition: The fixing location at region A of bracket is same as per previous but load is applied along direction of y-co-ordinate on washer at region B shown in figure All Rights Reserved 25

8 Figure 5.9. Displacement & von-mises stress plots for first iteration of front engine mounting bracket (at y=3g) 1. Maximum Deflection= mm 2. Maximum Von Mises stress= MPa. For Third load case (Z=6g): Boundary Condition: The fixing location at region A of bracket is same as per previous but load is applied along direction of z-co-ordinate on washer at region B shown in figure 5.5. Figure Displacement & von-mises stress plots for first iteration of front engine mounting bracket (at z=6g) 1. Maximum Deflection= mm 2. Maximum Von Mises stress= MPa. 5.3 Static analysis of second optimized front engine mounting bracket: The maximum von-mises stress builds up in this analysis is Mpa and the yield stress is 310Mpa. The maximum stress value is less than the von-mises stress since we have option to optimized this bracket where the less von-mises stress builds up so we remove the thickness by 6mm of base model from region B and also remove the supporting member at region A which is shown in figure All Rights Reserved 26

9 Figure Structural optimization of front engine mounting bracket Weight of bracket: Due to reduce in thickness of region B and also remove the supporting member from region A the weight of bracket gets reduced by 13.7 % of base model and which comes to 2.64 kg. In the boundary condition fixed the hole at region A and load applied on region B in direction of X co-ordinate as shown in figure 5.1. For first load case(x=4g): Figure Displacement & von-mises stress plots for second iteration of front engine mounting bracket (at x=4g) 1. Maximum Deflection= mm 2. Maximum Von Mises stress= MPa. For second load case (y=3g): Boundary Condition: The fixing location at region A of bracket is same as per previous but load is applied along direction of y-co-ordinate on washer at region All Rights Reserved 27

10 Figure Displacement & von-mises stress plots for second iteration of front engine mounting bracket (at y=3g) 1. Maximum Deflection= mm 2. Maximum Von Mises stress= MPa. For Third load case (z=6g): Boundary Condition: The fixing location at region A of bracket is same as per previous but load is applied along direction of z-co-ordinate on washer at region B. Figure Displacement & von-mises stress plots for second iteration of front engine mounting bracket (at z=6g) 1. Maximum Deflection= mm 2. Maximum Von Mises stress= MPa. VI. MODAL ANALYSIS FOR FRONT ENGINE MOUNTING BRACKET The vibrations induced by the road or the engine at idle are typically at the frequencies in below 30 Hz or in range in between the Hz.Since to the engine mount bracket should be stiff and highly damped. Considering the other uncertain causes of vibrations during the actual vehicle and front and rear engine mounting bracket life cycle a factor of safety is considered and the Natural frequency above the 250Hz was decided as a target first natural frequency of both front and rear All Rights Reserved 28

11 mounting bracket. Factors deciding the natural frequency of Front and rear engine mounting bracket are given below, Vibrations induced by the road. Vibrations coming from engine. Figure 6.1. Natural frequencies for different made shapes of base modal of front engine mounting bracket. Figure st mode shape and 2 nd mode shape Figure rd mode shape and 4 th mode All Rights Reserved 29

12 Figure th mode shape and 6 th mode shape VII. RESULTS Table 7.1 Von-mises stress and deformation for front engine mounting bracket Table 7.2 Natural frequencies (hz) for front engine mounting bracket for different mode shapes for different All Rights Reserved 30

13 VIII. CONCLUSION Static analysis has been carried out for different load cases and it is observed that even under maximum loading condition the engine mounting brackets are safe. Since, the stress levels are below yield stress Also the maximum deformation developed by front engine mounting bracket is less than acceptable deformation i.e. 2mm hence it is safe bracket. Modal analysis of engine mounting brackets are performed and it is found that the minimum fundamental natural frequency among front engine mounting bracket is Hz which is greater than the excitation frequency i.e.250 Hz, hence the engine mounting brackets are safe. The design has been successfully optimized from its preliminary stage which gives high quality engine mounting brackets at a lower cost. IX. AKNOWLEDGEMENT I would like to express my deep gratitude and sincere regards to all who helped me a lot to submit this dissertation work on Design and analysis of engine and chassis mounting bracket. And I would like to express my sincere regards and gratitude to the entire staff members in Mechanical Department of MMEC, Belagavi for their excellent, valuable suggestions and encouragement to take up this project and complete this project work successfully. REFERENCES 1. Zhang Junhong, Han Jun CAE process to simulate and optimize engine noise and vibration Mechanical Systems and Signal Processing 20 (2006) Gabriel-Petru Anton, Mihai Paval, Fabien Sorel, Application on an updated finite element model of an engine in the automotive industry Sisom 2011 and Session of the Commission of Acoustics, Bucharest May. 3. Senthilnathan Subbiah, O.P. Singh, Effect of muffler mounting bracket designs on durability, Engineering Failure Analysis 18 (2011) Youngwoo Choia, Dohyun Jungb, Kyoungchun Hamc, A study on the accelerated vibration endurance tests for battery fixing bracket in electrically driven vehicles, Procedia Engineering 10 (2011) Loh a, W.M. China, Waleed F. Faris, Fatigue analysis of Package Terminal Air Conditioner motor bracket under dynamic loading, Materials and Design 30 (2009) S. Irving *, F.Ferguson-Smith, X.Z. Hu, Y. Liu, Comparative fatigue assessment of soft toe and nested bracket welded aluminum structures, Engineering Failure Analysis 12 (2005) Mehmet, OsmanH.Mete, UmitKocabicak, MuratOzso y, Stamping process design using FEA in conjunction with orthogonal regression, Finite Elements in Analysis and Design 46 (2010) 992 All Rights Reserved 31