an optimization study of dynamic stiffness for transmission support brackets
DESCRIPTION
Transmission support bracket is an important component in aspect of vibration and noise of vehicle transfer system. But shape and length of bracket are often determined passively according to fixed powertrain layout and mounting point on the vehicle development process. In General, main excitation sources of transmission are planetary gear and oil pump. In case of FF type transmission, the 1st mode of bracket mostly exists in frequency range of 300Hz~800Hz. This frequency range is overlapped with the excitation range(under 600Hz) of plenatary gear and oil pump. Therefore, bracket 1st mode amplifies excitation order of plenatary gear and oil pump, and resonance occurs. As a result, bracket vibration is transferred to vehicle chassis system, where structure-borne cabin noise level is poor in severe cases. This study produces optimized bracket that is satisfied with dynamic stiffness standard and lightweight using Radioss and Optistruct. In the near future, vibration and noise test results of optimized bracket will be correlated with analysis results. This optimization process provides bracket design guide in the initial stage of transmission development, and reduction of cost and weight.TRANSCRIPT
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)
- Analysis Procedure
- Optimization Results and Review
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
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)
- Analysis Procedure
- Optimization Results and Review
Conclusion
- Summary and Conclusions
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
- Background of Structure-borne Noise
- Dynamic Stiffness
- 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)
- Analysis Procedure
- Optimization Results and Review
Conclusion
- Summary and Conclusions
Analysis Procedure Optimization
Analysis Background
FE model construction
Current model evaluation
Optimization Setting/Running
Postprocessing
Optimized model evaluation
- Objective : Weight reduction
- Restraint : Equivalent stiffness
level comparing with
the current model
Non-design
Design Stiffness Contribution Analysis
- Interference in Tool/Engine item
- Bracket type change (→ Casting)
-Topology optimization is needed
for Bracket Stiffness improvement Hz
dB
Frequency target
Unsatisfied
Hz d
B
Current
Optimized
Optimization Results Optimization
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
Results Review Optimization
Topology Optimization
Setting
Additional Weight
Reduction and Limit
Static Strength
@ Reference load
- Considering Y-Axis Draw
→ More realistic shape
- 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
- 1st Principal stress : 4%
→ But, Criterion satisfied
Contents
Introduction
- Background of Structure-borne Noise
- Dynamic Stiffness
- 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)
- Analysis Procedure
- Optimization Results and Review
Conclusion
- Summary and Conclusions
Analysis Procedure Optimization
Analysis Background
FE model construction
Current model evaluation
Optimization Setting/Running
Postprocessing
Optimized model evaluation
- Bracket material change
(Iron Steel → AL)
- Deficient bracket stiffness
→ Noise of Oil pump/Planetary
gear is inferior to Steel Bracket
-Topology optimization is needed
for Bracket Stiffness improvement
- Objective : Weight reduction
- Restraint : Equivalent stiffness
level comparing with
the current model
Non-design
Design Stiffness Contribution Analysis
dB
Hz
Iron Steel
Current(AL)
dB
Hz
Current
Optimized
Optimization Results Optimization
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
Results Review Optimization
Topology Optimization
Setting
Stiffness improvement
using Shape change
Static Strength
@ Reference load
- Draw direction
- Pattern grouping
- Volfraction
- Minmax FRF response
→ More realistic shape
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
- 1st Principal stress : 15%
→ Criterion satisfied
→ More effective method but,
Interference problem happened
Contents
Introduction
- Background of Structure-borne Noise
- Dynamic Stiffness
- 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 FR type T/M Bracket (FR type)
- Analysis Procedure
- Optimization Results and Review
Conclusion
- Summary and Conclusions
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 !!