Enhanced design and manufacturing of highperformance leaf springs with respect to vehicle kinematics, suspension and durability

Transcription

1 ARISTOTLE UNIVERSITY OF THESSALONIKI LABORATORY OF MACHINE ELEMENTS & MACHINE DESIGN G. Savaidis, S. Karditsas Enhanced design and manufacturing of highperformance leaf springs with respect to vehicle kinematics, suspension and durability 7 th international congress for SPRINGMAKERS, SUPPLIERS, CUSTOMERS OF SRPING INDUSTRY (ESF 7) September 20, 2013 Berlin

2 Outline 1. Basics Problem definition 2. Scope 3. Leaf spring design -Design requirements - Design parameters 4. FE analysis - Kinematic results - Stress results 5. Manufacturing -Requirements - Fatigue life analysis 6. Conclusions ESF 7 Berlin, 20/9/2013 Slide 2

3 Introduction Leaf spring suspension system determines the performance of the vehicle in terms of suspension and guidance Driving direction Steering gear Drop arm Drag link FRAME Shock Absorber Steering lever Track rod ESF 7 Berlin, 20/9/2013 Slide 3 S-buffer Middle Leaf spring buffer (stretched) Clamped area Wheel joint Shackle

4 Introduction Front axle kinematics interaction between steering and suspension systems ESF 7 Berlin, 20/9/2013 Slide 4

5 Introduction Design requirements Schematic representation of the wheel joint s orbits Drop arm Drag link UNLOADED BRAKING MAXIMUM VERTICAL CONDITION LOAD o Requirement: Compatibility of the two orbits ESF 7 Berlin, 20/9/2013 Slide 5

6 Design requirements o Specific dimensions introduced by the vehicle setting and the manufacturing process o Spring rate R within a specific range (comfort) o Compatibility between joint s orbit due to leaf-spring and joint s orbit due to steering rod o Durability: Acting stresses < permissible stresses ESF 7 Berlin, 20/9/2013 Slide 6

7 Scope 1. Optimum leaf-spring suspension design 1. Compatibility with steering kinematics 2. Developed stresses below the permissible stresses 3. Uniform stress distribution along the two arms 4. Lightweight structure 2. Reduction of development costs and time Parabolic mono leaf spring for the front axle of new generation heavy duty vehicles Parametrical FE investigation of the axle kinematics and the developed stresses ESF 7 Berlin, 20/9/2013 Slide 7

8 Case study Parabolic mono leaf spring for the 7.5to front axle of heavy duty vehicles Design: Parametrical FE investigation of the axle kinematics and the developed stresses Manufacturing: Influence of raw material, heat treatment and after-treatment on fatigue performance ESF 7 Berlin, 20/9/2013 Slide 8

9 Design parameters 1. Overall Spring Rate R vehicle configuration UNLOADED PAYLOAD MAX. VERTICAL Middle buffer S buffer Vertical Load Fv F V F V F V,MAX S buffer contact Middle buffer contact F F R = S S F 2 Payload F 1 S 1 S 2 Vertical Displacement of the middle of the clamped area ESF 7 Berlin, 20/9/2013 Slide 9

10 Design parameters 1. Overall Spring Rate R on the vehicle 2. Rate difference ΔR between the two arms load F Two cantilevers Cantilever 1 Cantilever 2 Front arm Fixed supports Rear arm load F Δs 1 Δs 2 R 1 F = R2 s1 R = R1 R2 F = s 2 ESF 7 Berlin, 20/9/2013 Slide 10

11 Design parameters 1. Overall Spring Rate R on the vehicle 2. Rate difference ΔR between the two arms 3. Type of eyes Stepped eye Berliner eye Normal eye Parabolic length Parabolic length Parabolic length Stepped eye Berliner eye Normal eye ESF 7 Berlin, 20/9/2013 Slide 11

12 Design parameters 1. Overall Spring Rate R on the vehicle 2. Rate difference ΔR between the two arms 3. Type of eyes 4. Lever e: distance between the eye-eye line and the middle line of the spring at stretched position e e Stepped eyes Berliner eyes eye-eye line middle line e Normal eyes ESF 7 Berlin, 20/9/2013 Slide 12

13 Vehicle configuration Modeled components Driving direction Front eye S-buffer Middle buffer Clamped area Leaf spring (stretched) Shackle Rear eye ESF 7 Berlin, 20/9/2013 Slide 13

14 FE Modeling Asymmetrical mono-leaf spring FE Model Bushing Middle Buffer S-Buffer One equivalent Shackle Buffer Bushing Front eye Clamped area Rear eye Solid hexaedra elements 1 st order elements 6 elements over thickness 5mm element length ESF 7 Berlin, 20/9/2013 Slide 14

15 Influence of lever e on kinematics Kinematic behavior for Berliner eyes, three values of e (R, ΔR : constant) Vertical loading Braking Berliner eye Origin (0,0): Front eye Origin (0,0): Front eye ESF 7 Berlin, 20/9/2013 Slide 15

16 Influence of lever e on kinematics Kinematic behavior for Stepped eyes, three values of e (R, ΔR : constant) Vertical loading Braking Stepped eye Origin (0,0): Front eye ESF 7 Berlin, 20/9/2013 Slide 16

17 Influence of lever e on kinematics Comparable kinematics with Berliner and Stepped eyes by modifying e (R, ΔR : constant) Origin (0,0): Front eye ESF 7 Berlin, 20/9/2013 Slide 17

18 Influence of eye type and lever e on stresses Stress distribution for Berliner eyes and Stepped eyes three values of e (R, ΔR : constant) Stepped eye Berliner eye ESF 7 Berlin, 20/9/2013 Slide 18

19 Influence of R on kinematics and stresses Berliner eyes, e=16, ΔR=26 N/mm e=16mm Braking Origin (0,0) : Front eye Vertical loading (a) Kinematic Behavior ESF 7 Berlin, 20/9/2013 Slide 19 (b) Stress distribution

20 Influence of ΔR on kinematics and stresses Berliner eyes, e=16, R=334 N/mm e=16mm Braking Origin (0,0) : Front eye Vertical loading (a) Kinematic Results ESF 7 Berlin, 20/9/2013 Slide 20 (b) Stress results

21 Manufacturing requirements Raw material - Homogenous microstructure - Sufficient degree of purity free of defects (inclusions, vacancies etc.) Significant defects in raw material Inclusion Inclusion ESF 7 Berlin, 20/9/2013 Slide 21

22 Manufacturing requirements Heat treatment - ARISTOTLE UNIVERSITY Homogenous martensitic martensitic microstructure microstructure(enhanced (enhancedstrength) strength) Slight surface surface decarburization decarburization(enhanced (enhancedductility) ductility) Homogeneous Homogeneous distribution distributionof ofwell-shaped well-shapedcarbides carbides(enhanced (enhancedstrength) strength) Absence of imperfections imperfectionssuch suchas asinclusions, inclusions,vacancies vacanciesetc. etc. Not acceptable structures Acceptable Inclusion Not acceptable Decarburized areas Typical martensitic microstructure ESF 7 Berlin, 20/9/2013 Slide 22 Inclusions Carbide concentration Martensitic microstructure with ferrite

23 Manufacturing requirements Surface treatment stress/shot peening ARISTOTLE UNIVERSITY - High degree of surface surface coverage coverage - High compressive compressive residual residualstresses stresses(positive (positiveinfluence influenceon onfatigue) fatigue) - Low roughness roughness (negative (negativeinfluence influenceon onfatigue) fatigue) acc. to DIN 743 acc. to DIN 743 K R,σ σ Ε,rough = σ Ε, polish acc. to DIN 743 acc. to DIN 743 ESF 7 Berlin, 20/9/2013 Slide 23

24 Conclusions 1. Parametrical studies regarding optimized design of leaf springs were performed aiming at - better understanding the leaf spring performance in the vehicle configuration and - developing optimized springs in a more efficient and economic way 2. The eye typeaffects the kinematic behavior but does not influence the stress performance 3. The most significant parameter regarding the kinematics is the lever e 4. The spring rate R and the rate difference ΔR do not affect on the kinematic behavior but have strong influence on the stress distribution 5. All parameters must be taken into account in a proper way to achieve optimal leaf spring design and performance of the vehicle 6. Raw material purity, optimal heat treatment and, especially the stress peening are necessary to achieve optimized fatigue performance ESF 7 Berlin, 20/9/2013 Slide 24

25 Acknowledgements The Company MAN Truck & Bus SA and the General Secretariat for Research and Technology of Greece are gratefully acknowledged for the financial support of the investigations ESF 7 Berlin, 20/9/2013 Slide 25

26 End THANK YOU FOR YOUR KIND ATTENTION ESF 7 Berlin, 20/9/2013 Slide 26