Enhanced design and manufacturing of high- … UNIVERSITY OF THESSALONIKI LABORATORY OF MACHINE ELEMENTS & MACHINE DESIGN Enhanced design and manufacturing of high-performance leaf

ARISTOTLE UNIVERSITY OF THESSALONIKILABORATORY OF MACHINE ELEMENTS & MACHINE DESIGN

Enhanced design and manufacturing of high-

performance leaf springs with respect to

vehicle kinematics, suspension and durability

7th international congress for SPRINGMAKERS, SUPPLIERS, CUSTOMERS OF SRPING INDUSTRY (ESF 7)September 20, 2013 Berlin

G. Savaidis, S. Karditsas

A R I S T O T L E U N I V E R S I T Y

ESF 7 – Berlin, 20/9/2013 │ Slide 2 [email protected]

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



Introduction

Driving direction

Middlebuffer

S-bufferLeaf spring(stretched)

Shackle

FRAME

Shock Absorber

Steering gear

Drop arm

Drag link

Steeringlever

Track rod

Wheel jointClamped area

determines the performance of the vehicle in terms of suspension and guidance

Leaf spring suspension system



Introduction

Front axle kinematics – interaction between steering and suspension systems



Design requirementsDesign requirements – Schematic representation of the wheel joint‘s orbits

BRAKINGMAXIMUM VERTICAL LOAD

Introduction

UNLOADED CONDITION

o Requirement: Compatibility of the two orbits

Drop arm

Drag link



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



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



Case study

Design:

Parametrical FE investigation of the axle kinematics and the developed stresses

Parabolic mono leaf spring for the 7.5to front axle of heavy duty vehicles

Manufacturing:

Influence of raw material, heat treatment and after-treatment on fatigue performance



UNLOADEDPAYLOADMAX. VERTICAL

Design parameters

1. Overall Spring Rate R – vehicle configuration

S1 S2

F1

F2

Middle buffer contact

S – buffer contact

Payload

FV,MAX

Vertical Displacement of the middle of the clamped area

Vertical Load Fv

2 1

2 1

F FR

S S

−=−

FVFV

FV

S – buffer Middle buffer



Design parameters

1. Overall Spring Rate R – on the vehicle

2. Rate difference ΔR between the two arms

Two cantilevers

Cantilever 1 Cantilever 2

Δs1 Δs2

load F load F

Fixed supports

11

FR

s=

∆ 22

FR

s=

∆1 2R R R∆ = −

Front arm Rear arm



Design parameters

Berliner eye

Stepped eye

Normal eye

Stepped eye

Berliner eye



3. Type of eyes

Parabolic length

Parabolic length

Parabolic length

Normal eye



Design parameters

e Stepped eyes

Berliner eyes

Normal eyes



3. Type of eyes

4. Lever e: distance between the eye-eye line and the

middle line of the spring at stretched position

middle line

eye-eye line

e

e



Vehicle configuration – Modeled components

Driving direction

Middlebuffer

S-buffer

Leaf spring(stretched)

Shackle

Clamped areaRear eye

Front eye



Clamped area

Shackle

Bushing

Rear eye

Bushing

Solid hexaedra elements

1st order elements

6 elements over thickness

5mm element length

FE Modeling – Asymmetrical mono-leaf spring

Front eye

Middle Buffer S- BufferOne equivalent

Buffer

FE Model



Influence of lever e on kinematics

Kinematic behavior for Berliner eyes, three values of e (R, ΔR : constant)

Origin (0,0): Front eye


Vertical loading

Braking

Berliner eye




Vertical loading

Braking

Stepped eye


Kinematic behavior for Stepped eyes, three values of e (R, ΔR : constant)



Comparable kinematics with Berliner and Stepped eyes by modifying e

(R, ΔR : constant)





Influence of eye type and lever e on

stresses

Stress distribution for Berliner eyes and Stepped eyes

three values of e (R, ΔR : constant)

Berliner eye

Stepped eye

Stress distribution for Berliner eyes

three values of e (R, ΔR : constant)



Influence of R on kinematicsInfluence of R on kinematics and stresses

(a) Kinematic Behavior (b) Stress distribution

e=16mm

Berliner eyes, e=16, ΔR=26 N/mm

Origin (0,0) : Front eye

Braking

Vertical loading



Influence of ΔR on kinematics

Origin (0,0) : Front eye

Vertical loading

Braking

e=16mm

(a) Kinematic Results (b) Stress results

Berliner eyes, e=16, R=334 N/mm

Influence of ΔR on kinematics and stresses



Manufacturing requirements

Raw material- Homogenous microstructure

- Sufficient degree of purity

free of defects (inclusions, vacancies etc.)

Inclusion

Significant defects

in raw material Inclusion




Heat treatment- Homogenous martensitic microstructure (enhanced strength)

- Slight surface decarburization (enhanced ductility)

- Homogeneous distribution of well-shaped carbides (enhanced strength)

- Absence of imperfections such as inclusions, vacancies etc.

Typical martensitic microstructure Martensitic microstructure with ferrite

- Homogenous martensitic microstructure (enhanced strength)












Decarburized

areas A

cce

pta

ble

No

t

acc

ep

tab

le

Inclusion Inclusions

Carbide

concentration

Not acceptable structures



- High degree of surface coverage

- High compressive residual stresses (positive influence on fatigue)

- Low roughness (negative influence on fatigue)

,,

,

roughR

polish

K σ

σσ

Ε

Ε

=


Surface treatment – stress/shot peening- High degree of surface coverage









acc. to DIN 743

acc. to DIN 743

acc. to DIN 743

acc. to DIN 743



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 type affects 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



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



End

THANK YOU FOR YOUR KIND ATTENTION

Documents

Enhanced design and manufacturing of high- … UNIVERSITY OF THESSALONIKI LABORATORY OF MACHINE ELEMENTS & MACHINE DESIGN Enhanced design and manufacturing of high-performance leaf