Design of a suspension system for a formula student race car

Design of a suspension system for a formula student race car
اسم المؤلف
Ingi Níels Karlsson
التاريخ
14 نوفمبر 2020
المشاهدات
التقييم
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رسالة ماجستير بعنوان
Design of a suspension system for a formula student race car
by
Ingi Níels Karlsson
Thesis of 60 ECTS credits submitted to the School of Science and Engineering
at Reykjavík University in partial fulfillment
of the requirements for the degree of
Master of Science (M.Sc.) in Mechanical Engineering
June 2018
Supervisor:
Indriði Sævar Ríkharðsson, Supervisor
Assistant Professor, Reykjavík University, Iceland
Examiner:
Dr. Rúnar Unnþórsson, Examiner
Professor, University of Iceland, Iceland
Contents
Acknowledgements xi
Contents xii
List of Figures xiv
List of Tables xvi
List of Abbreviations xvii
List of Symbols xix
1 Introduction 1
1.1 Background 1
1.2 Design Constraints 2
1.3 FS rules 3
1.4 Objective . 3
1.5 Thesis structure 4
2 Research 5
2.1 Types of suspension systems . 5
2.2 Suspension properties . 5
2.2.1 Kingpin inclination 5
2.2.2 Caster . 5
2.2.3 Camber 6
2.2.4 Scrub radius . 7
2.2.5 Wheel rate 7
2.2.6 Roll rate 9
3 Design process 11
3.1 Identification of relevant rules 12
3.2 Identification of team constraints . 12
3.3 Preliminary design 12
3.3.1 A-arms 12
3.3.2 Push rods . 13
3.3.3 Bell cranks 15
3.3.4 Spring and damper 15
3.3.5 Anti roll bar 15
3.4 Adams . 18
3.4.1 Introduction 18
xii3.4.2 Adams Car model 19
3.4.3 Adams Car simulations 20
3.4.4 Results from Adams Car . 22
3.5 3D modeling . 25
3.5.1 A-arms 25
3.5.2 Pushrods . 27
3.5.3 Bell cranks 28
3.5.4 Anti-roll bar . 29
4 Manufacturing 31
5 Conclusion 39
6 Future work 41
Bibliography 43
A Datasheets 45
A.1 Aluminum 6061 T6 45
A.2 Aluminum 7075 T6 49
A.3 303 Stainless Steel 55
A.4 Structural steel S235 . 58
A.5 Structural steel S355 . 61
A.6 Öhlins TTX25 Mk II spring dimensions . 64
A.7 Öhlins TTX25 Mk II internal schematic . 66
A.8 Öhlins TTX25 Mk II external dimensions 70
A.9 Öhlins TTX25 Mk II dyno plot 72
A.10 Fluro spherical bearing 76
A.11 Fluro spherical bearing rod end 78
A.12 SKF 608-2RSH 80
B Drawings 83
C Tables and calculations 127
C.1 Hard point table 127
C.2 Results from Adams Car . 131
C.2.1 Summary of forces 131
C.2.2 Pothole simulation 133
C.2.3 Plank simulation . 147
C.2.4 Constant radius cornering simulation 161
C.2.5 Tilt simulation 175
C.2.6 Front parallel wheel travel simulation 189
C.2.7 Rear parallel wheel travel simulation 199List of Figures
1.1 The 2017 car at Silverstone after the competition 2
2.1 Kingpin inclination and caster angles . 6
2.2 Camber angle . 6
2.3 Sprung mass and unsprung mass definition 8
2.4 The roll center is found by drawing lines between the center of the tire patch to
instantaneous centers 9
3.1 Design flow chart . 11
3.2 Proposed A-arm design 13
3.3 Push and pull rod suspension [8] . 13
3.4 Force on the pushrod with 600 N force on the wheel . 14
3.5 Free body diagram of the forces acting on the pushrod 14
3.6 Cutaway model of the Öhlins TTX25 MkII FS damper [9] . 16
3.7 Öhlins TTX 25 MkII internal schematic [11] . 16
3.8 Adams Car[4] design flowchart 18
3.9 Two body position mechanism [12] . 19
3.10 Adams Car [4] 3D model of the formula student car . 20
3.11 Adams Car [4] suspension points table 20
3.12 Adams Car [4] part modification window. The preliminary Inventor model was
used to define the mass and properties of each part in the Adams model . 21
3.13 Adams Car [4] part modification window 21
3.14 Adams Car [4] parallel wheel travel simulation setup window 22
3.15 Adams Car [4] postprocessing window parallel wheel travel simulation camber
change results . 22
3.16 Adams Car [4] constant cornering simulation with wheel forces in red on the
picture . 23
3.17 Adams Car [4] parallel wheel travel simulation of the front suspension system
with wheel forces in red on the picture 23
3.18 Adams Car [4] parallel wheel travel simulation motion ratio of the spring and
damper versus the wheel . 24
3.19 Inventor [14] hard point 3D model 25
3.20 Front upper control arm 3D model from Inventor [14] 26
3.21 Front upper control arm FEA results and a free body diagram showing location
of whee the force of 3748.9 N is applied . 26
3.22 Front push rod assembly 3D model from Inventor [14] . 27
3.23 Buckling end conditions constants [17] 27
3.24 Front bell crank 3D model from Inventor [14] 28
xiv3.25 Front bell crank FEA results and a free body diagram showing location of where
the force of 3748.9 N is applied 29
3.26 Front suspension assembly 3D model from Inventor [14] 29
4.1 Sleipnir’s workspace at the university workshop . 31
4.2 The university workshop . 32
4.3 Laser cut brackets for the suspension, first from left is the insert for the rear arm
of the A-arms, second from left is the push rod mount bracket for the A-arms,
third and fourth from left are mounting brackets for the A-arms to the chassis 33
4.4 Spherical bearing seat for the control arms 33
4.5 Spherical bearing seat toolpath from Inventor HSM [18] 34
4.6 Inserts for spherical rod ends . 35
4.7 Spacer for spherical rod ends to increase the travel angle of the rod end 35
4.8 Spacer for spherical rod ends toolpath from Inventor HSM [18] . 36
4.9 Inserts welded to A-arm 36
4.10 Front A-arms mounted on the chassis 37
4.11 Bell crank machined front side 38
4.12 Bell crank machined back side 38
5.1 Final 3D model of the suspension assembly in Inventor [14] 39
C.1 Adams car [4] pothole simulation setup window . 133
C.2 Adams car [4] plank simulation setup window 147
C.3 Adams car [4] constant corner simulation setup window . 161
C.4 Adams car [4] tilt table simulation setup window 175
C.5 Adams car [4] parallel wheel travel simulation setup window 189
C.6 Adams car [4] parallel wheel travel simulation setup window 199List of Tables
3.1 Static setup of the suspension . 24
3.2 Forces from Adams Car [4] simulations 24
5.1 Comparison of weight of left side suspension components between 2017 and
2018 car 40
xviList of Abbreviations
RU Reykjavík University
FS Formula Student
SAE Society of Automotice Engineers
US United States
UK United Kingdom
FSAE Formula SAE
FSG Formula Student Germany
IMechE Institution of Mechanical Engineers
MIRA Motor Industry Research Association
CNC Computer numerical control
MDS Multibody Dynamics Simulation
CoG Center of Gravity
RC Roll Center
SF Safety Factor
CAD Computer Aided Design
FEA Finite element analysis
List of Symbols
Symbol Description Value/Units
Ks
Spring rate N m−1
KT Tire spring rate N m−1
Kw
Wheel rate N m−1
M Mass kg
MR Motion ratio
F Force N
f Frequency Hz
Ms
Sprung mass kg
M
us Unsprung mass kg
l Length m
Φ
r/Ay Roll gradient deg/g
g Acceleration 9.81m s−2
H Distance from roll center to CoG m
KΦF Front roll rate Nm/deg
KΦR Rear roll rate Nm/deg
tf Front track width m
tr Rear track width m
KLF Left front wheel rate N/m
KLR Right front wheel rate N/m
KLR Left rear wheel rate N/m
KRR Right rear wheel rate N/m
KΦA Total anti roll bar rate needed Nm/deg
tA Average track m
KΦdes Desired total roll stiffness Nm/deg
MA−arm Moment around the A-arm mount to the chassis Nm
Fwheel Normal forces on the wheel center N
L Length m
FN Normal force N
θ Angle deg
Fpushrod Force acting on the push rod N
MARB Torque on the anti roll bar Nm
FARB Force on anti roll bar arm N
x Length m
θ Rotation of the anti roll bar deg
G Modulus of rigidity GPa
J0 Polar moment of inertia mm4
FARB/θ Anti-roll bar torsional stiffness N/degC Buckling end condition
E Young’s modulus GPa
D outer diameter m
d inner diameter m
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