An Optimization Study of Dynamic Stiffness for Transmission Support Brackets

Optimization of Dynamic Stiffness

for Transmission Support Bracket

Session 6: Lightweight Design

June 25th, 2014

Siwoo, Lee

Hyundai·Kia Motors R&D Center

Contents

Introduction

- Structure-borne Noise and Support Bracket

- Bracket Dynamic Stiffness

- Engineering Method for Bracket Stiffness Analysis

Topology Optimization of T/M Bracket (FF type)

- Steel Press Bracket / AL Die casting Bracket

- Analysis Procedure

- Optimization Results and Review

Topology Optimization of T/M Bracket (FR type)



Conclusion

- Summary and Conclusions

Introduction Background of Structure-borne Noise (1)

Downsizing is the major trend of powertrain in automotive industry

- Pros : Lightweight and consequently improving fuel economy

- Cons : Mounting distance increase → Bracket length needs to be increased

→ Reducing Dynamic Stiffness and Increasing Structure-borne Noise

An optimization of Bracket is required for robust design

Transmission path of Structure-borne Noise

Sources of Excitation

Path

Receiver

Oil pump

(Pulsating

Pressure)

Planetary

gear

(Whine)

FF type

T/M

FR type

T/M

Mount system

T/M

Human

Oil pump / Planetary gear

Harmonic Noise

Background of Structure-borne Noise (2) Introduction

Sources of Excitation

FR type T/M

Excitation force

Resonance Problems

Planetary gear Whine Noise (1)

Planetary gear Whine Noise (2)

Oil pump Pulsating pressure Noise

Bracket Vibration Cabin Noise

Bracket Vibration Cabin Noise CASE Vibration

Bracket Vibration Cell Noise

FF type T/M

Excitation force

Noise due to Resonance of Bracket and Planetary gear/Oil pump

Bracket Dynamic Stiffness Introduction

Vehicle Impact Test (FRF)

FRF Result (Acceleration) Bracket Inertance and Dynamic Stiffness

Inertance(m/s2/N)

: Bracket FRF Result

Dynamic Stiffness(kgf/mm)

: Bracket Evaluation Index

By FFT Analyzer

Graphing

Inertance

Conversion

Method for Bracket Stiffness Analysis Introduction

Bracket

T/M + Bracket

T/M + Bracket + Chassis item

Correlation of Test and Analysis

- Natural Frequency - Natural Frequency - Natural Frequency

- FRF Curve - FRF Curve

Test Analysis Test Analysis

Setting of Modeling method and Boundary condition

- Analysis Model Boundary (including Chassis item) - Generalized Modal damping

- Verification of Material property and Mass - Points of Excitation and Response

→ Freq. Error rate <1% @ 1st mode

→ Freq. Error rate < 1% @ 1st mode

Amp. Difference < 5dB @ 1st mode

→ Freq. Error rate < 3% @ 1st mode

Amp. Difference < 3dB @ 1st mode

(Ex. FF type Bracket)

Contents

Introduction

- Background of Structure-borne Noise

- Dynamic Stiffness

- Method for Bracket Stiffness Analysis








Conclusion


Analysis Procedure Optimization

Analysis Background

FE model construction

Current model evaluation

Optimization Setting/Running

Postprocessing

Optimized model evaluation

- Bracket mounting point upward

- Bracket stiffness apprehension

- Bracket stiffness should be

satisfied with target

☞ As a result, thickness increases

-Topology optimization is needed

for Bracket weight reduction Hz

dB

Stiffness target

satisfied

- Objective : Weight reduction

- Restraint : Equivalent stiffness

level comparing with

the current model

Non-design

Design

Stiffness

Contribution

Analysis

Hz d

B

Current

Optimized

Optimization Results Optimization

Objective Bracket Weight 20%

Response

Function

-1st mode Frequency : 2%

- Acceleration level : 0.5dB

- Dynamic stiffness : Equivalent

☞ Criteria Satisfied

Optimization Result

Hz

dB

Current

Optimized

Satisfied

Remaining Area Reflected CAD

55 Iterations

Considering

Press Forming

Finally

not applied

Results Review Optimization

Topology Optimization

Setting

Additional Weight

Reduction and Limit

Static Strength

@ Reference load

Non-design

Design_A (X Axis Draw)

Design_B (Y Axis Draw)

Design_C (Z Axis Draw)

- Considering 3-Axis Draw

→ More realistic shape

- Weight : Up to 50%

(Ideally)

→ But, practically 20%

Under consideration

Impossible in Press forming

Current

Optimized

- 1st Principal stress : 14%

→ But, Criterion satisfied

Contents

Introduction


- Dynamic Stiffness









Conclusion



Analysis Background




Postprocessing





the current model

Non-design

Design Stiffness Contribution Analysis

- Interference in Tool/Engine item

- Bracket type change (→ Casting)


for Bracket Stiffness improvement Hz

dB

Frequency target

Unsatisfied

Hz d

B

Current

Optimized


Objective Bracket Weight Equivalent

Response

Function

-1st mode Frequency : 4%

- Acceleration level : 5dB

- Dynamic stiffness : 16%

☞ Criteria Satisfied Hz

dB

Current

Optimized

Satisfied

Optimization Result Remaining Area Reflected CAD

12 Iterations

Considering

Die casting

Forming



Setting

Additional Weight

Reduction and Limit

Static Strength

@ Reference load

- Considering Y-Axis Draw


- Considering P/Grouping

→ Weight 15%

Rib pattern

Symmetry

- With optimized shape,

additional weight reduction

is possible (about 3%)

- Limit : Heavy thickness

→ Gas porosity happens

in the Die casting process

Current

Optimized


→ But, Criterion satisfied

Contents

Introduction


- Dynamic Stiffness









Conclusion



Analysis Background




Postprocessing


- Bracket material change

(Iron Steel → AL)

- Deficient bracket stiffness

→ Noise of Oil pump/Planetary

gear is inferior to Steel Bracket


for Bracket Stiffness improvement




the current model

Non-design

Design Stiffness Contribution Analysis

dB

Hz

Iron Steel

Current(AL)

dB

Hz

Current

Optimized


Objective Bracket Weight 11%

Response

Function

- Local 1st mode Frequency : 1%

- Acceleration level : 2dB

- Dynamic stiffness : 30%

☞ Criteria Satisfied

Optimization Result Remaining Area Reflected CAD

21 Iterations

Hz

dB

Iron Steel

Current

Optimized

Equivalent

Dynamic stiffness

54%

① ②

※ In comparison with ① AL Current, ② Iron Steel



Setting

Stiffness improvement

using Shape change

Static Strength

@ Reference load

- Draw direction

- Pattern grouping

- Volfraction

- Minmax FRF response


Volfraction = a

→ Lack of Stiffness

Volfraction = 2a

→ Stiffness satisfied

Current model

Span extension model

Hz

dB

Current

Optimized

Span extension d

B

Dynamic stiffness

= Curent x 2

Current

Optimized


→ Criterion satisfied

→ More effective method but,

Interference problem happened

Contents

Introduction


- Dynamic Stiffness






Topology Optimization of FR type T/M Bracket (FR type)



Conclusion


Summary and Conclusions Conclusions

Using the topology optimization technique with Optistruct,

1) FF type Steel press bracket :

a mass reduction of 20% has been achieved.

2) FF type AL Die casting bracket :

there was not a mass reduction but, additional mass reduction is

in progress.

3) FR type AL Die casting bracket :

there was a mass increase of 11% but, the optimized model is

54% lighter than previous Iron steel model.

satisfying our criterions and manufacturing restrictions

In case of excessive stiffness target, topology optimization

often falls into a result of mass increase.

It is necessary to optimize a relation of lightweighting and

robust design.

On-going study Study

Free shape Optimization : Overcoming the limits of Topology Optimization

FF type Bracket

FR type Bracket

Need to keep

the gap with

engine room

components

Need to keep

the gap with

propellar shaft

/cross member

Propellar shaft

Cross member

: Barrier mesh(Design boundary)

: Spaces of assembly tools(Non-design area)

Produce more effective

stiffness improvement

Thank you for your attention !!