Application of Optimization Techniques in Reducing the Weight of Engine.pdf

8/10/2019 Application of Optimization Techniques in Reducing the Weight of Engine.pdf

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Application of Optimization Techniques in Reducing the Weight of Engine

Mounting Bracket

Varun AhujaAssistant Manager-CAEMaruti Suzuki India LtdPalam Gurgaon Road

Gurgaon-122015

Sandip HazraManager-Engine DesignMaruti Suzuki India LtdPalam Gurgaon Road

Gurgaon-122015

Keywords: Topology, Weight-reduction, Morphing, OptiStruct

Abstract

Need for a compact and lighter vehicle has become need of the hour. Over the years designers have been continuously finding ways toreduce the overall engine weight, for it can help in improving engine performance, power to weight ratio and eventually fuel efficiency.With the growing emphasis on reducing the engine design cycle time, there has been a paradigm shift in the approach of designers.Optimization has become an integral part of product development cycle. With the time constraint being the prime concern, optimization toolgive us the best solution satisfying all possible constraints. This paper explicates an example of optimization techniques in reducing theweight of engine mounting bracket without compromising the strength, NVH and Vibration performance. In this case study enginemounting bracket of a current model is taken and optimized using Topology Optimization in OptiStruct. Final optimized model weighs 15%less as compared to the current model. The paper also briefly elucidates the application of morphing tools for fine-tuning of optimized

results. This case study is limited to application of Topology optimization of Engine components using OptiStruct.

Introduction

Gone are the days when it used to take innumerable iterations to design a product. Getting the best possibledesign with minimum iterations has become the prime target for the designers. With the advent of optimizationsoftwares the possibility of getting first time-best design seems quite achievable. With the government normson fuel efficiency and emissions getting stringent with each passing day the focus on Optimization of enginecomponent has gone sky-high.Design of engine components plays a very vital role in improving engine performance. Engine mount forms anindispensable part of the powerhouse of an automobile. They are not only responsible for taking distributed

engine load but also for minimizing the vibrations being transferred to body frame. A lighter engine mount canhelp in achieving better fuel economy and lesser emission levels, thereby improving overall engineperformance. Now, people may wonder if this is such a plain sailing process to improve engine performancethen why is this not frequently adopted? The main problem is that while reducing weight of the enginecomponents, the design criteria for which these components are designed has to be satisfied. For instance, incase of engine mounts their functional requirements have to go in line with their design considerations such asvibration isolation, strength and noise control. Thus, the optimization process becomes more tedious as anumber of design criterias have to be met while reducing the weight.

The case study deals with Topology Optimization of rear engine mounting bracket of a current running model.As mentioned above regarding the criticality of such an optimization, this study takes into consideration

strength, frequency and FRF targets


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Process Methodology

Optimization is a process of finding an optimal solution satisfying a given number of constraints. Anoptimization problem mainly consists of three components:

a) Design Variables

b) Design Objective

c) Design Constraints

Topology Optimization deals with the removal of redundant material based on a set of objectives andconstraints. Design variable for topology optimization is density of each element. In case of Topologyoptimization run in OptiStruct, the software calculates the density of each element on a scale of 0-1 . Elementswith density 0 represents state of void , whereas elements with density 1 represents state of solid. Intermediatedensities represent fictitious material.

In case of any Topology optimization problem complete FE model is divided into design and non design space.Choice of design and non design space is solely dependent on the user. In this study a part of rear mountingbracket is kept into non design space so as to not alter the bolt locations and to give optimization software adirection to remove the redundant material.

In this case study, optimization of rear engine mounting bracket,a sub-section of complete Power-train model (Refer to Figure 1) is taken into consideration, for it is computationally less expensive, although the finalvalidation of design parameters is done on complete Power-Train model after fine-tuning of Optimizationresults. Understanding the criticality of the component design and its functional aspects both in strength andvibration, optimization parameters are decided covering all the functional aspects of engine mount. FRFacceleration is also used as design response because only controlling the natural frequency might not help inachieving the desired vibration performance. Optimization parameters for the problem are as following:

a) DESIGN VARIABLES:Density of each element

b) DESIGN CONSTRAINTS:Mass, 1st natural frequency, FRF acceleration

c) DESIGN OBJECTIVE :Minimum weighted compliance

Design Responses

DESIGN RESPONSES


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Single type draw direction constraint is also used in the optimization setup. This is mainly employed for

obtaining results that are viable for casting, for the results obtained from topology may contain cavities that arenot in line with sliding direction of the die, and hence not feasible to cast.

Optimization Results

Density plot for the model is obtained after a topology optimization run (Refer to Figure 2). These densityvalues help in finding the redundant locations so as to remove the unnecessary material. In order to achieveviable results (mainly for manufacturing), elements having density values less than 0.3 are removed.

Figure 1: Sub-Section of an Engine

Non Design space

Design space

Cylinder Block - Cast Iron

T/M Casing - ADC 12

Rear Engine Mount- ADC 12

Figure 2.a Figure 2.b

Figure 2: Optimization results

13th iteration results

Iso-surface= 0.3


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In the above results element having density less than 0.3 are represented through transparent region. Basedon these density values, material can be removed from the FE model to get final optimized product. On postprocessing of these results, it can be interpreted that the results needs some fine-tuning to make thecomponent feasible for manufacturing. Some of the optimization results are incorporated in the FE modelthrough manual re-meshing whereas for some changes (for changing the dimensions of groves) morphingtechniques are adopted .

Morphing is a tool to alter FE model dimensions while keeping the distortions to minimum. In this case study,free hand morphing and morph volume applications are used to alter the mesh parameters. To increase thedepth of some groves free-hand morphing is used. Free hand morphing helps in mesh modification by selectingfixed nodes, moving nodes, affected elements and a moving direction (Refer to Figure 3.a ). For changing theradial dimensions, morph volume tool is used (Refer to Figure 3.b ).Final design modifications are elucidated inFigure 4. After implementing these modifications in the FE model, final optimized component is obtained, whichweighs 15 % less as compared to the original component.

Figure 3: Morphing

Fixed nodes

Affected elementsMoving nodes Morph volumeenclosing the displayed elements

Figure 3.a : Free Hand Morphing Figure 3.b : Morphing using morph volume


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Component Validation

As optimization was carried on a sub-section model, the final optimized model was re-validated for completePower-Train model. Comparison was made between the original and Optimized component and it was foundthat the optimized model is meeting the strength and vibration criteria (both in terms of natural frequency and

FRF). Vibration comparison was done in NASTRAN whereas for strength validation ABAQUS software wasused to incorporate the bolt-pre tension effects. For Vibration results Refer Figure 5 and Figure6.

Boss Arearemoved

Material removedas per optimization

results

Groves deepenedand widened

As boss area incylinder block isalso removed,

hence removal ofboss area in mountwill not result in any

crash issues

Figure 4 :Design Modifications


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Original Model Optimized Model

Freq.(Hz) Freq.(Hz)

1st Mode 246.7 246.6

2nd Mode 273 272

3rd Mode 284 283

Natural Fre uenc Result

RR Mount Bracket

Vibration Comparison

12 dB, 246.6 Hz

0.5 dB increase in amplitude in X-direction,No significant change in Y and Z direction

Figure 5 :Elemental strainenergy at 246.6 Hz

Figure 6 :FRF Comparison between Original and Optimized component


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It is noticeable (Referto Table 1 ) that the stress values in the optimized component has increased but still the

values are within the desired limits. From vibration point of view there is not much change in the performance ofthe component. On the basis of these results, it can be concluded that the optimized component is meeting thefunctional and design aspects of the original component and with an additional benefit of weight saving of .33kg(330 grams).

Conclusion

Optimized component is meeting the strength and vibration performance of the original component. There is0.33 kg/ 15 % weight saving.

Optimization has resulted in material cost saving of Rs 38 per component. (**ADC= Rs 116/kg).

Load Case

Original Optimized Limit

(ADC)Stress MPa

(Max)

Stress MPa (Max)

UP (WL+) 97 99.07 186

DOWN (WL-) 102 100 186

LEFT (BL+) 102 110 186

RIGHT (BL-) 101.57 99 186

FRONT (TL+) 101.49 99.23 186

REAR (TL-) 101 102 186

Strength Comparison

2.230 kg 1.9 kg

Original Component Optimized Component

Table 1: Stress Results


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Optimization is a scientific method for achieving the best possible design with minimum iterations. Thismethodology can be adopted for other engine components as well where weight reduction is to be achievedwithout affecting their functional and design criteria.

Drawbacks

Fine-Tuning of optimization results has to be done manually in HyperMesh which takes large amount of time. Inorder to expedite the optimization process special softwares must be developed which can directly refine theOptiStruct results to give a realistic model . This will help in saving considerable amount of time which is beingspent in manual refinement of Topology results.

Future PlansOptimized results have been validated only in CAE. There are no testing results to understand the correlationbetween CAE model and actual testing model. Although the changes in design are done in consultation withdesigners but still physical testing is required before incorporating optimized model in the running vehicle. Alsophysical proto-model will give an insight to the minute manufacturing details of the component.

ACKNOWLEDGEMENTS

The authors would like to acknowledge the continual help and support of Altair support team for this case study.Authors would also like to acknowledge the support and guidance of Research and Design team of MarutiSuzuki India Ltd. without whom the project wouldn't have achieved the present outcome.

REFERENCES

1. Performance -Base Optimization of structuresbyQing Quang Liang2. Altair OptiStruct Reference Manual.3.Topology Optimization for minimum stress design byG Allaire, F Jouve4. Bendse, M.P. and Sigmund, O. (1999) Material interpolation schemes in topology optimization, Arch.Appl. Mech., Vol. 69, pp.635654.

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Application of Optimization Techniques in Reducing the Weight of Engine.pdf