An Optimization Study of Dynamic Stiffness for Transmission Support Brackets

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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.

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An Optimization Study of Dynamic Stiffness for Transmission Support Brackets

  1. 1. Optimization of Dynamic Stiffness for Transmission Support Bracket Session 6: Lightweight Design June 25th, 2014 Siwoo, Lee Hyundai·Kia Motors R&D Center
  2. 2. 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
  3. 3. IntroductionBackground 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
  4. 4. 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 NoiseCASE Vibration Bracket Vibration Cell Noise  FF type T/M Excitation force  Noise due to Resonance of Bracket and Planetary gear/Oil pump
  5. 5. 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
  6. 6. 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)
  7. 7. 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
  8. 8. 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 dB Current Optimized
  9. 9. 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
  10. 10. 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
  11. 11. 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
  12. 12. 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 dB Current Optimized
  13. 13. 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
  14. 14. 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
  15. 15. 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
  16. 16. 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
  17. 17. 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
  18. 18. 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 extensiondB Dynamic stiffness = Curent x 2 Current Optimized - 1st Principal stress : 15% → Criterion satisfied → More effective method but, Interference problem happened
  19. 19. 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
  20. 20. 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.
  21. 21. 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
  22. 22. Thank you for your attention !!

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