Vibration Analysis of 2 Wheeler Handle-Bar Assembly

Transcription

1 Vibration Analysis of 2 Wheeler Handle-Bar Assembly Harale Shivraj. N CAE Analyst Mahindra 2 Wheelers Ltd. D1 Block, Plot No. 18/2 (part) Chinchwad MIDC Gyanendra Roy Head - CAE Mahindra 2 Wheelers Ltd. D1 Block, Plot No. 18/2 (part) Chinchwad MIDC Abbreviations: expansion of any abbreviations used. Keywords: Handlebar Assembly, Modal Frequency Response Abstract To sustain in competitive market, 2 wheelers are becoming more complex in functionality and style aspect. At the same time weight constraint to enhance the performance is playing main role in design and development life cycle. The biggest challenge in design phase is to predict the potential failures as early as possible. Handlebar assembly is more susceptible to the failure because of various types of loading such as bump, braking, road excitations etc. Modal Frequency Response analysis enables to analyze the strength of structural mountings within the excitation frequency range on the vehicle. Frequency response analysis on handle bar assembly is carried out using Altair solver code Radioss Bulk data. In this analysis the handle bar assembly is excited with acceleration derived from road load data over an operational frequency range to evaluate the strength of mountings on handle-bar in vibration. Model is prepared using HyperMesh and Post processing is done using HyperView and HyperGraph. The simulation results are also well correlated by the experimental results in which failure location and pattern is exactly matched. Further modifications have been incorporated in design to meet the strength requirement. Introduction Two wheeler handle-bar assembly is user's first touch point to the vehicle, also it is very complex in construction and important in functionality and safety point of view. As handle-bar assembly consists of head lamp, mirrors, clutch and brake levers, speedometer with plastic coverings which are meant to be for aesthetic appeal as shown in figure 1. Whole handle bar assembly is more susceptible to the failures as it experience numerous forces such as bumps, braking, engine vibrations, rider force, road excitations etc. To simulate vehicle operating condition, modal frequency response analysis enables to analyze the strength of structural mountings within assembly for the excitation frequency range on the vehicle. Growing competition in automotive market makes it more and more necessary to reduce the development time and cost of the product development process. One of the most costly phases in the vehicle development process is the field durability test. High expenses for this phase can be attributed to the number of prototypes used and time/efforts needed for its execution. Also, multiple iterations during designing, building and prototype testing are no longer affordable against the time and cost constraints for developing a competitive product. Today, analytical tools in the form of computer simulation have been developed to such a level that they reliably predict performance. 1

2 Fig 1: Handle-Bar Assembly of Scooterate Objective and Methodology Sub-systems like fuel tank mounting, air-filter mounting, muffler mountings are prone to failures because of heavy dynamic loads during vehicle operation. To evaluate the structural performance of these subsystems of vehicle it is necessary to determine "g levels of acceleration at these systems. Also, once the test data is available, it can be used for correlating it with the FEA results and then load history can be used for reliable analysis to develop the product. The methodology helps in moving towards virtual testing and to avoid/reduce physical testing of the sub-systems to adhere to the constraints on time and cost. Objectives of the simulation are, 1. To carryout strength analysis for the mountings of assemblies. 2. To correlate the test results with FEA results using road load data. Methodology: The steps involved in the work are as follows: 1. Constrained Modal Analysis using Radioss Bulk Format to find out the System Level Natural Frequencies. 2. Stress Formulation using Modal Frequency Response Analysis method 3. FEA and test result correlation. 4. Design modifications for strength requirement. 2

3 Structural Modal analysis Handle-Bar Assembly modes are critical for vehicle functionality. A normal modes analysis should be performed to make sure that the frequencies of system does not line up with the frequencies of operating range. The modal analysis is helpful to determine the mode shape of assembly by which further improvement in structures can be done. The important modes are extracted between 0 to 200 Hz which is the operating range. The natural frequency and mode shapes are determined and compared with engine excitation frequency for resonance. Vibration Analysis The assembly receives vibration from engine and road which then transfers to the internal mounting locations. It is important to understand dynamic characteristics and the components sensitive to vibration. The dynamic equation for the system can be expressed as follows Where m, c, k are mass matrix, damping matrix and stiffness matrix respectively. X and F are displacement and force vectors respectively. The purpose of vibration analysis is to determine the strength of mountings. FE Model development The handlebar assembly components such as handle-bar, mirror mountings, steering column and brackets are made of stainless steel of various grades. FE model has been developed by using preprocessing software HyperMesh. Metal parts are modelled with shell elements CQUAD, CTRIA by extracting mid surfaces and plastic parts are modelled with CTETRA elements. The connections between plastic parts and bracket bolt holes are modelled with CBEAM elements. The weld between each component is modelled with shell elements of average of thickness. Contacts have been defined between guiding surface of headlamp casing and head lamp lug, to simulate exact behaviour. Loads and Boundary Conditions: Here acceleration derived from road load data is used to excite the assembly over an operational frequency range as dynamic load. Stress and displacement peaks are determined for the considered frequency range. This method can be used to simulate and predict the actual response. Frequencies below 20 Hz are not usually considered. The reason is that, lowest idling rpm is usually above 1400 rpm. 3

4 Fig 2: FE Model and Boundary Conditions of Handle-Bar Assembly Experimental Test Set-up: The Handle-bar assembly is tested on shaker table test rig by mounting on fixture at the steering column, with acceleration value generated from road load data, over the operational frequency range. Fig 3: Experimental Test Setup of Handle Bar Assembly on Shaker Table Results & Discussions: Modal Results: Base Design Table 1: Natural Frequencies and Mode Shapes of Assembly Mode No. Frequency (Hz) Mode Shape Local Mode Mirrors Local Mode Mirrors LH Mirror Bending 4

5 RH Mirror Bending Lateral Bending Vertical Bending Stress Plots: Base Design Fig 4: Stress Plot and Graph of Stress Vs Frequency of Assembly Fig 5: Stress Plot and Graph of Stress Vs Frequency of Head Lamp Experimental Test Results: 5

6 Fig 6: Failure Location in Test at Mirror Mounting Bracket and Head Lamp Casing Mounting Stress Plots: Modified Design Fig 7: Stress Plot of Modified Design Fig 8: Design Modification on Head Lamp Casing Mounting Benefits summary: Since, the FE and experimental tests are in good correlation, for new product development, FEM approach can be used to reduce design cycle time, number of prototypes and more importantly, testing time and its associated costs. 6

7 Conclusion: In this paper, RADIOSS has been used to model and simulate the behaviour of the Handle-Bar Assembly for Vibrations. The results are matching closely with the experimental test and required design modifications have been done from analysis and iterations. The work presented in this paper is in the early phases of ongoing work and it is important to note these promising results will strongly demand more detailed analysis for future projects. ACKOWLEDEGMENTS The authors would like to acknowledge our Design, Prototype and testing teams for extending their kind support. The authors would also like to thank the R&D Chief, Mahindra 2 Wheelers Management for providing this opportunity for publishing the work. 7