INTRODUCTION:

Rattle noise from instrumentation panel can cause discomfort, distraction to the driver and caneven harm the brand image of the vehicle. There are many parts in instrumentation panel like dashboard, glove compartment plate, lower control panel and knee bolster which are attached to each other through connections like clips or snap fit. If these connections are not proper then when vehicle experience any loads from roads or from internal sources, vehicle can experience rattle phenomenon and unwanted noise will be heard from instrumentation panel. Sometimes this noise results in wear and tear of material and overall decrease the quality of vehicle. Many experimental procedures have found to predict rattle noise. Su-Hyun Shin and Cheolung Cheong [1] have proposed a system to predict buzz, squeak and rattle which has three main parts like excitation jig, visualization technique for detection of potential rattle source and subsequent analysis for ranking the source from maximum to minimum. Vikram T. Pawar et al. [2]. clearly explained prediction methods such as ‘testing on track’ and lab testing’s in which experiments were performed on BSR rig under controlled environment to predict the rattle noise. Marc Morroquin [3] explained about different techniques for noise source identification. From sound intensity to acoustic holograph, there are seven methodologies which will help NVH engineer to locate noises. Experiments have done to simulate rattle noise so that overall cost can be reduced by identifying rattle prone areas in designing phase or before manufacturing phase. Jens weber et al. [4] presented simulation of squeak and rattle method known as SARLINE, which was based on evaluation of relative displacement in time domain due to random load. Studies present the correlation between results of the SAR-LINE method simulation with audible rattle occurrence. Patrick Sabiniaz et al. [5] integrated the new E-LINE™ methodology into existing virtual design process to simulate real squeak and rattle phenomenon and also correlates the results of simulation with real testing’s and found both were parallel to each other as shown in Fig.1

Fig. 1: Time Vs simulation results

Jens Weber and Ismail Benhayoun [6] have presented a new squeak and rattle simulation approach for complete development process of interior parts. The output of the simulations can be matched to the available FE model quality to improve the modal correlation. Thanassis fokilidis et al. [7] developed simulation procedure based on numerical analysis of squeak and rattle known as E line methodology in LS-dyna. This methodology focused on evaluating relative displacement between two components. The simulation result were in correlation with test results as shown in Fig. 2.

Fig. 2: Correlation of Test and simulation result [7]

Amadu and Fenieres [8] gave insight about how rattle can be controlled which includes change of mechanical properties such as mass, stiffness etc in order to optimize resonant frequency ,fix or removal the loosened parts of components responsible for rattle issues. S.Hsieh et al [9] provided a finite-element-based procedure that was applied to study rattle of glove compartment latch and corner rubber bumpers. Final results indicated in reduction of rattle in structural components. Santosh S Gosavi [10] gave information about prevention of buzz squeak and rattle (BSR) in the development cycle with the help of basic causes, design guidelines and validation technique using laboratory simulation and digital data acquisition.

Based on thorough literature survey it has been found that there has been a strong need of reduction of rattle noise through design modification after recognizing rattle prone areas during simulation. The objective of present study is to simulate rattle noise phenomenon in instrumentation panel in “hyper works squeak and rattle director tool” for observing the rattle prone areas in a given instrumentation panel model and to study different design modifications which will reduce the rattle to a minimum or nominal level. Meshing of model, creation of E-Lines, preprocessing and post processing were the basic steps of proposed methodology

MESHING AND SIMULATION:

The instrument panel (IP) model of a car of left hand side drive has been taken from Altair Engineering model library for this project work as shown in Fig. 3. For Meshing of instrumentation panel, 2D meshing in Hypermesh 13.0 has been used. Auto meshing technique has been applied to IP with quadrilateral and triangular as element shape. Element type which has been used is P-SHELL element as IP have thin shell structure and not solid structure which can be solved indeed with shell element. After meshing Modal analysis was done for checking proper connections of model which includes free free and fixed free analysis. Transient response analysis in preprocessing side was performed in Squeak and Rattle Director Tool (SNRD) of hyper works 13.0. This process had major steps which included loading of FEM model, creation of geometric lines, defining of gap and tolerance, time varying loads applied in Z directions for 3 seconds. After preprocessing, Solver deck was prepared for transient analysis for frequency range of 0 to 300 with damping ratio of 0.04 time step of 250. Optistruct was the solver which was used and then post processing was done. Post processing gave the images of rattle prone areas with red dots outlined as shown in Fig. 4. Measurement of relative displacement for checking of rattle prone areas on post processing side was done. Modification analysis is done after applying three different design modifications on the component chosen for the rattle study and Observed the method by which rattle can be reduced to minimum. E-Line methodology [w355] was used to simulate rattle on instrumentation panel.

Fig.3: Meshed Instrumentation Model

DESIGN MODIFICATIONS:

In order to reduce rattle, glove compartment plate has been considered. Three modification was considered for the rattle study and observed the method by which rattle can be reduced to minimum.

1. Change in design variable :

Design modifications such as change in design variable (thickness) were applied. Original thickness of plate was 3.3 mm; however it was increased to 3.5mm then 3.6 mm to see its effects on relative displacement. Increasing weight more than 3.6 mm can affect overall weight of instrumentation panel.

2. Incorporating Ribbing pattern:

Second design modification was incorporation of ribbing pattern to stiffen the part vertically and horizontally.

3. Connections made with different stiffness at maximum deflection points:

Third option which was studied was proper connections of different stiffness (K), 20k, 40k, 60k and 80k were applied to one the rattle experiencing component of instrumentation panel and analysis was performed to check the effect of applied design attributes on relative displacement.

RESULTS AND DSCUSSION:

For original instrumentation panel, rattle was recognized in post processing side which is shown in the Fig. 4.Glove compartment plate (1), Knee bolster (2), Lower control Panel (3) and HVAC Lower and upper casing (4) are the components where one can observe rattle problems. Red dots in the Fig.4 show issues in particular location, where as green dots indicating no rattle conditions. However these locations also contain certain predefined lines which are helpful in realizing rattle issues.

Fig. 4: Red dots exhibiting rattle locations

In Fig. 4, Glove compartment plate which has been marked as 1, has red dots which is indicating rattle issues at that particular location. Couple of graphs was also generated as result of post processing. Glove compartment has been represented by line 116019 as shown in Fig. 5 along with points. As per rule if points along line (116019) lie within (GAP-tolerance) limit, then no rattle issue can be found and if points lie beyond (GAP-tolerance) limit and within GAP limit then user may or may not be able to experience the issue. However points beyond GAP definitely indicating rattling issues in the component.

Fig. 5: Glove compartment plate exhibiting rattle along line 116019

The relative displacement along line 116019 which represented glove compartment plate was shown in Fig. 6. It can be observed that points from 116004.5 to 116007 are lying beyond gap limit, so these points will certainly generate rattle issue. X axis shows the points along 116019, while Y axis relative displacement in mm.

Fig. 6: Relative displacements along Line 116019of glove compartment plate

(1) Change in design variable :

Thickness of original glove compartment plate is 3.3 mm as shown in Fig. 7.Thickness was changed From 3.3 mm to 3.4 mm and then to 3.5 mm however thickness can’t be increased beyond a point as it will affect the overall weight of instrumentation pane

Fig. 7: Glove compartment plate of original thickness 3.3 mm

Thickness of glove compartment plate with their corresponding relative displacement after analysis has been tabulated in Table 1. It can be observed that as thickness increases, displacement decreases however at very slow rate.

Table 1: Thickness and corresponding relative displacement

Thickness of Glove Compartment Plate	Values observed for Relative Displacement along line 116019
3.3mm (original thickness)	1.84242mm
3.4mm	1.815mm
3.5mm	1.7935mm
3.6mm	1.7794mm

(2) Incorporating Ribbing pattern:

When ribbing pattern was applied horizontally and vertically as shown in Fig. 8, relative displacement decreased from 1.84242 to 1.7669; however this decrement was very less and result was not accordingly.

Fig. 8: glove compartment with ribbing pattern

(3) Connections made with different stiffness at maximum deflection points:

Maximum deflection can be observed from Fig. 8, which are 1, 2 and 3. At points 1 and 2 connections of different stiffness of 20k, 30k 40k and 80k with CBUSH element which act as spring connection between two components were made. Results were obtained after analysis for different stiffness which has been tabulated in Table 2.

Table 2: Stiffness and observed relative displacement

Stiffness	Relative displacement
20K	1.62mm
40K	1.24mm
60K	0.68mm
80K	0.35mm

It has been observed from the table that as the stiffness increases, relative displacement decreases. For 20k relative displacement was 1.62mm and for 80k was 0.35mm. Graph was also observed for 80k stiffness. From the Fig. 9, it can be observed that all points are within the limit (GAP-tolerance). Hence we can say that location is rattle free Maximum displacement is observed at point 116001 of 0.5 mm and minimum at point 116011 along line 116019. This graph is obtained after making connection of stiffness 80k.

Fig. 9: Effect of connection (stiffness 80K) on relative displacement

CONCLUSION:

· Rattle prone areas were identified. Glove compartment plate, knee bolster, lower control panel, HVAC lower and upper casing were the parts of instrumentation panel where issues were recognized.

· Change in design variable (thickness) of glove compartment plate was taken into account. One can infer from table 7.1 that as the thickness increases, displacement tends to decreases but at a very slow rate. Displacement decreased by 3.4% with respect to original relative displacement, when thickness was increased to 3.6 from 3.3mm.

· Ribbing Pattern was implied to stiffen the plate and major change in relative displacement can be observed when ribbing pattern was oriented vertically as well as horizontally. Displacement tends to decrease by 4.09% when plate was stiffened longitudinally and latitudanally.

· Clips connections were used at the position where maximum deflection was observed and concluded that as the stiffness (K) increases, relative displacement decreases. When stiffness of connection increased from 20K to 80K, relative displacement decreased from 1.62 mm to 0.35 mm thereby making all points inside GAP-tolerance limit and giving better option to resolve rattle issues than ribbing pattern and change in design variable (thickness).This method solved 85% of problem.

After making connections of 80K at the required points, analysis were done to check whether any red dots on the glove compartment panel can be seen or not. If plate is showing only green dot then glove compartment plate is free from rattle issues. After analysis, glove compartment plate with all green dots was found in Fig. 10, hence solving rattling issue. It can be concluded that as stiffness increases, relative displacement decreases (Table no. 2). Making connections at right position is a better way to handle any problematic unwanted noise like rattle then increasing thickness and intricating ribbing pattern on component.

Fig.10: Rattle free glove compartment plate

ACKNOWLEDGEMENT:

Te authors are greatful to the authorities of R.V collage of engineering for the facilities

CONFLICT OF INTEREST:

The authors declare no conflict of interest.

REFRENCES:

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Received on 27.03.2018 Accepted on 24.04.2018

Research J. Engineering and Tech. 2018;9(2): 201-206.

DOI: 10.5958/2321-581X.2018.00028.4