Suspension system for any vehicle

The simulation of a vehicles suspension system represents an important part of how the driver experiences ride quality. Without a suspension system, a vehicle acts in a stiff and uncomfortable way. The characteristics of a vehicles performance are dependent on the properties of the suspension. A model of this system would enable a manufacturer to test how certain changes to the properties change the behavior of the vehicle. This way they are able to see how the stiffness of the spring and damper in the suspension system affects the ride experience before building an actual car. This can also reduce the cost of development. The most basic suspension system consists of a spring and shock absorber and also includes the stiffness of the tire being used. More complex suspension systems consist of sensors that take into account and compensate for traction control, engine torque, steering, and braking systems.

1. SUSPENSION SYSTEM FROM
DAMPER

2. ABSTRACT

The simulation of a vehicles suspension system represents an important
part of how the driver experiences ride quality. Without a suspension system, a
vehicle acts in a stiff and uncomfortable way. The characteristics of a vehicles
performance are dependent on the properties of the suspension. A model of this
system would enable a manufacturer to test how certain changes to the properties
change the behavior of the vehicle. This way they are able to see how the
stiffness of the spring and damper in the suspension system affects the ride
experience before building an actual car. This can also reduce the cost of
development. The most basic suspension system consists of a spring and shock
absorber and also includes the stiffness of the tire being used. More complex
suspension systems consist of sensors that take into account and compensate for
traction control, engine torque, steering, and braking systems.

3. 1

TABLE OF CONTENTS:

LIST OF FIGURES
NOMENCLATURE
CHAPTER-1 INTRODUCTION
1.1 Suspension systems
1.1.1 Types of Suspension systems according to location
1.1.2 Front Suspension
1.1.3 Rear Suspension
1.1.4 Types of springs used in suspension system
1.1.5 Types of dampers used in suspension system
1.1.6 Types of suspension system according to no of shocks
1.1.7 Objectives of suspension system

CHAPTER-2 LITERATURE REVIEW

2.1 Study of FZ Suspension system
2.2 Study of Coil Springs
2.3 Study of damper
2.3.1 Advantages of Mono tube damper over twin tube damper
2.4 Working inside damper
2.5 Conventional spring damper assembly

CHAPTER-3 DESIGN PROCESS OF SUSPENSION SYSTEM

3.1 Step 1: Decide the thickness of damper cylinder
3.2 Step 2: Diameter of piston
3.3 Step 3: Piston rod diameter
3.4 Step 4: Estimation of Damping Force according to loading
3.5 Step 5: Estimation of force acting on spring and finding out stiffness of spring
3.6 Step 6: Design of spring
3.7 Step 7: Selection of fluid for damper

4. 2

CHAPTER-4 MODELLING IN CREO

4.1 Damper Cylinder
4.2 Piston with piston rod
4.3 Floating plate
4.4 Spring:
4.5 Assembly of spring and damper

CHAPTER-5 STRESS ANALYSIS IN ANSYS

5.1 Meshing of assembly [Finite Element Analysis]
5.2 Fixed Support
5.3 Damping Force [1260 N]
5.4 External load [2000 N]
5.5 Equivalent stress
5.6 Maximum shear stress

CHAPTER-6 CONCLUSION

REFERENCES

5. 3

LIST OF FIGURES:

 Figure 1: Dependent suspension
 Figure 2: Twin I-Beam independent suspension
 Figure 3: Type 1 coil spring
 Figure 4: Type 2 coil spring
 Figure 5: Torsion bar
 Figure 6: Double Wishbone Suspension
 Figure 7: Independent rear suspension
 Figure 8: Coil Spring
 Figure 9: Coil Spring in a bike
 Figure 10: Leaf Spring
 Figure 11: Leaf spring in truck
 Figure 12: Twin tube damper
 Figure 13: Mono tube damper
 Figure 14: Mono tube damper
 Figure 15: Conventional Spring Damper assembly
 Figure 16: Damper Cylinder Creo model
 Figure 17: Piston with piston rod Creo model
 Figure 18: Floating plate
 Figure 19: Coil Spring Creo model
 Figure 20: Assembly of spring damper in creo
 Figure 21: Meshing of assembly Ansys
 Figure 22: Fixed Support Ansys
 Figure 23: Damping force Ansys
 Figure 24: External load Ansys
 Figure 25: Equivalent stress Ansys
 Figure 26: Maximum shear stress Ansys

6. 4

NOMENCLATURE:



Do : outer diameter of cylinder
Di : inner diameter of cylinder
T : thickness of cylinder
σ : maximum allowable stress
Pmax : maximum pressure in cylinder
E : energy per stroke
m : sprung weight
g : acceleration due to gravity
h : damping distance
s : damping height
DCF : damping correction factor
ς : Damping ratio
Fgas : force due to gas ressure
Pgas : pressure of gas
Arod : area of piston rod
K : stiffness of spring
P : load on spring
δ : deflection of spring
G : shear modulas
Nt : no of turns of spring
?????? : permissible shear stress

7. 5

Sut : ultimate stress of spring material
Kw : wahl factor
C : spring index
d : wire diameter
Dmean : mean diameter of spring
p : pitch of the spring
μ : viscosity of damping fluid
D : equivalent diameter of flow
Vavg : average velocity of piston
P1 : pressure above the piston
P2 : pressure below the piston

8. 6










CHAPTER 1
INTRODUCTION

9. 7

1.1 Suspension systems

For many years vehicle dynamics engineers have struggled to achieve a
compromise between vehicle handling, ride comfort and stability. Every
automotive suspension has two goals: passenger comfort and vehicle control.
Comfort is provided by isolating the vehicle’s passengers from road
disturbances like bumps or potholes. Control is achieved by keeping the car
body from rolling and pitching excessively, and maintaining good contact
between the tire and the road

Today’s vehicle suspensions use hydraulic dampers (”shock absorbers”) and
springs
that are charged with the tasks of absorbing bumps, minimizing the
automobiles body motions while accelerating, braking and turning and
keeping the tires in contact with the road surface. Typically, these goals are
somewhat at odds with each other.

A typical vehicle suspension is made up of two components: a spring and a
damper. The spring is chosen based solely on the weight of the vehicle, while
the damper is the component that defines the suspensions placement on the
compromise curve. Depending on the type of vehicle, a damper is chosen to
make the vehicle perform best in its application. Ideally, the damper should
isolate passengers from low-frequency road disturbances and absorb
highfrequency road disturbances. Passengers are best isolated from
low-frequency disturbances when the damping is high.

However, high damping provides poor high frequency absorption. Conversely,
when the damping is low, the damper offers sufficient high-frequency
absorption, at the expense of low-frequency isolation. The need to reduce the

10. 8

effects of this compromise has given rise to several new advancements in
automotive suspensions.

1.1.1 Types of Suspension systems according to location
1. Front Suspension
2. Rear Suspension

1.1.2 Front Suspension
Types of front suspension
1. Dependent Suspension
2. Independent Suspension

1. Dependent Suspension

 Dependent front suspension uses a solid axle.
 It uses one steel or aluminum beam extending the width of the vehicle.
The beam is held in place by leaf springs.
 Solid axle is used in truck and off-road vehicles.


[figure 1]

11. 9

2. Independent Front Suspension

 It was developed in the 1930's to improve vehicle ride control and riding
comfort.
 Sprung weight is reduced, creating a smoother ride.
 Twin I-Beam, Type 1 Coil Spring, Type 2 Coil Spring, Torsion Bar,
Double Wishbone.

A. Twin I-Beam

 Similar to the solid axle.
 Improves ride and handling.
 Improves load carrying ability.
 Used on pickups, vans and four-wheel drive vehicles.



[figure 2]

12. 10

2. Type 1 Coil Spring


 upper control arms
 lower control arms
 2 steering knuckles
 2 spindles
 2 upper ball joints
 2 lower ball joints
 Bushings
 Coil springs
 Shock Absorbers
 Short-arm/long-arm, or the parallel arm design




figure 3]


3. Type 2 Coil Spring


 Coil spring is mounted on the upper control arm.
 Top of the spring is attached to the frame.
 Upper ball joint receives the weight of the vehicle and the force of the
coil spring.
 Makes it the load carrier.

13. 11




[figure 4]


3. Torsion Bar

 No coil or leaf springs.
 Supports the vehicle weight and absorbs the road shock.
 Performs the same function as a coil spring.
 Supports the vehicle's weight.



[figure 5]

4. Double Wishbone

 Type of strut suspension.
 More aerodynamic hood line.
 Portion of the strut forms a wishbone shape.

14. 12

 Does not rotate when the wheels turn.


[figure 6]

1.1.3 Rear Suspension:

1. Independent rear suspension



[figure 7]
Some other types of rear suspension are :

 Semi-independent rear suspension
 Live axle suspension

1.1.4 Types of springs used in suspension systems:

15. 13


1. Coil spring




[figure 8]






[figure 9]

16. 14

2.Leaf Spring




[figure 10]






[figure 11]

17. 15

1.1.5 Types of dampers used in suspension

1.Twin tube damper


[figure 12]


Twin tube damper use an inner and outer tube which separate the oil and
gas inside the damper. The smaller inner tube houses the piston shaft
assembly, base valve, and oil. The outer tube contains both nitrogen gas
and the damper oil. Twin tube dampers are the most commonly used type of
dampers by OEM and aftermarket manufacture as they are the cheapest
damper to make. However, twin tube dampers do not perform as well as
mono tube dampers as the oil heats up and destabilises under extreme
usage.

1. Mono tube damper

Mono tube dampers use a single outer tube. The oil and nitrogen gas inside are
separated by a free piston. Mono tube dampers use much higher gas pressure
than twin tube dampers to better stabilise the oil inside under extreme usage.

18. 16



[figure 13]

The advantages of the mono tube design are larger internal parts, which
mean greater damping force, increased oil capacity, improved heat
dissipation, and the ability to function when inverted. Mono tube dampers
are found in some OEM vehicle applications, mainly higher end
performance vehicles such as EVO MR, WRX STi, Porsche, etc.


1.1.6 Types of suspension according to number of shocks

1. Dual shock suspension
2. Mono shock suspension



1. Dual shock Suspension

The first motorcycle rear suspension was called dual shock suspension. It was
created in around 1913. It consisted of two pairs of spring and damper. All the
loads acting at the rear of the motorcycle are divided on the two spring damper
mechanism.

19. 17

2. Mono shock Suspension

Mono-Shock motorcycle rear suspension was created in the late 80′s and in
many applications has more advanced performance than that of the
twin-shocks. Single shock rear suspension requires less maintenance and
adjustments. In this type all the loads are damped by a single spring damper
mechanism.

On a motorcycle with a mono-shock rear suspension, a single shock absorber
connects the rear swing arm to the motorcycle's frame. Typically this lone
shock absorber is in front of the rear wheel, and uses a linkage to connect to
the swing arm. Such linkages are frequently designed to give a rising rate of
damping for the rear. Mono-shocks are said to eliminate torque to the swing
arm and provide more consistent handling and braking. Having only one shock
absorber, they tend to be easier to adjust than twin-shock systems.

1.1.7 Objectives of Suspension system
1. Comfort
Provide vertical compliance so the wheels can follow the uneven road,
isolating the chassis from the roughness of the road.
2. Safety
React to the control forces produced by the tires longitudinal, lateral forces,
braking and driving torques, in purpose to protect the passengers, the luggage
and the suspension system itself.
3. Handling
Keep the tires in contact with the road with minimal load variations and resist
roll of the chassis.

20. 18






















CHAPTER 2
LITERATURE REVIEW

21. 19

A detailed literature review was carried for studying the spring-damper system
in bikes. Also finding out the specifications required for designing of spring
and damper. Mono-suspension system used in various bikes were analysed
and studied.

2.1 Study of FZ suspension system:

Online data available about suspension system of FZ is as follows:
Front suspension: Telescopic fork, Coil spring/Oil damper, 130 mm
Rear suspension: Mono cross, Swing arm Coil spring/Oil damper, 120 mm
Bore/Stroke: 58 mm * 57.9 mm
Weight: 137 kg
Rake/Caster angle: 26 degree


[Reference: Wikipedia, Yamaha-motor-india.com]

2.2 Study of coil springs:

For design of coil springs, standard reference used is V.B. Bhandari.
Other references referred for design of helical coil springs are:

1. Design of coil springs-nptel [nptel.ac.in]
2. Design of springs-elearning [elearning.vtu.ac.in]
3. Wikipedia
4. Coil Springs- Design and Specifications [acewire.spring.com]
5. Design of Helical Coil Compression Spring A review – IJERA

From the literature review, we understood the procedure to design a helical

22. 20

coil spring. The standard procedure used in design of spring is shown in
chapter 3 in details.

2.3 Study of Dampers:

Selecting a right damper is crucial part of designing a suspension system.
There are two types of dampers used in mono suspension system, i.e. twin tube
damper and mono tube damper.

In FZ mono suspension system, twin tube damper is used. But in our project we
designed the suspension system using mono tube damper.

Both the dampers were studied in detail which included its construction and
working. Also its advantages and disadvantages were studied.

2.3.1 Advantages of mono tube damper over twin tube damper:

 Very wide damping rates can be achieved through bigger diameter
pistons and shims designs.
 Plush feel and full control over all piston speeds through higher gas and
damping rates.
 Cools faster and more reliable thought50 the single precision tube shock
body.
 Bigger diameter piston rods can be used because of bigger internal
chambers with sufficient oil.
 Can withstand higher pressures and temperatures without aeration or
foaming.

23. 21


References referred for studying damper are:

1. Damper basic equations- KAZ technologies
2. Selecting the right damper- Dictator Technik
3. Damping correction factors by Wanda I. Cameron and Russell A. Green
4. Simple procedure for preliminary design of structural dampers by Wei Liu,
Mai Tong and George C. Lee

2.4 Working inside a damper:



[figure 14]

Dampers also known shock absorbers work on the principle of fluid
displacement on both the compression and expansion cycle. The compression
cycle controls the motion of a vehicle's unsprung weight, while extension
controls the heavier sprung weight. There are two cycles in which shock

24. 22

absorber works:

a. Compression
In the compression cycle the piston moves downward and compresses the
hydraulic fluid in the chamber which is situated below the piston. In this cycle
or downward movement, the fluid flows to upper chamber from down chamber
through piston. Some of the fluid also flows into reserve tube through the
compression valve. Flow is controlled by valves in the piston and in the
compression valve.

b. Extension
In the extension cycle the piston moves upwards toward the top of the pressure
tube. The upward movement results in the compressing of the fluid in the
chamber lying above the piston. The extension cycle generally provides more
resistance than compression cycle.

2.5 Conventional Spring Damper Assembly:





[figure 15]

25. 23
















CHAPTER 3
DESIGN PROCESS OF SUSPENSION SYSTEMS

26. 24

Step 1: Decide the thickness of damper cylinder:

Basic Assumptions:
1. Material: Structural Steel [ductile]
2. Maximum pressure inside cylinder: 53 MPa
3. Outside Cylinder diameter: 53 mm
4. Tensile stress of structural steel: 215 MPa
5. Poisson ratio: 0.29
For finding out inner diameter of cylinder, considering it as pressure vessel,
Max pressure > Cavitation pressure


??????0
????????????
=√
6+????????????(1−2µ)
6+????????????(1−2µ)


Putting Do = 53 mm,
6 = 215 MPa
Pi = 53 MPa
μ = 0.29
we get, Di = 44 mm

Now, Thickness of the cylinder,

T =
??????0−????????????
2


Putting Do = 53 mm
Di = 44 mm
We get, T = 4.5 mm

27. 25

Step 2: Diameter of piston:

Piston diameter = Inner cylinder diameter - 2
= 44 -2
= 42 mm
Therefore, Diameter of Piston = 42 mm

Step 3: Piston rod diameter:

From literature survey about piston rod diameter, the usual piston rod
diameter for mono tube dampers is 25 mm.

Step 4: Estimation of Damping Force according to loading:

The reference used for estimating damping force was Dictator Technik –
Selecting the right damper.

The equation used for finding the damping force was,

Damping force =
����???????????? ��� ������ [??????.�.] ∗ �������??????�� �??????����∗����
������[��]

[equ 1]

1. For finding out damping force, first you need to find Energy per stroke in
N.m
Considering equation for inclined loading, energy per stroke is given by;

Energy per stroke, E = m*g*h + m*g*s [equ 2]

28. 26

m = impact mass [kg]
g = acceleration due to gravity [m/s2] = 9.81
s = acceleration height [m]
h = damping distance [m]
In our case, impact mass, m = 200 kg [designing suspension for 200 kg load]
Acceleration height = 0 m
Damping distance = 0.04 sin 26º = 0.017 m
Putting the above values in equation, we get,

Energy per stroke = 34.40 N.m

2. Damper Correction Factor
For finding out the damper correction factor, the equation used was the one
proposed by Priestley in 2003.
The equation is,

DCF = [
10
5+Ɛ
]
0.25


For underdamped system, ?????? = 0.4
Putting it in above equation, we get DCF = 1.17

3. Stroke
From the literature survey about FZ suspension system, we found out the free
length, i.e 180 mm.
We took the length of outer cylinder as 70 mm.
From this we calculated stroke = 40 mm
Putting all the values of 1,2 and 3 in equation of damping force, we get

29. 27

Damping force =
��.��∗�.��∗����
��

= 1006.2 N

Considering 1010 N damping force.

Now, finding out the force due to gas pressure, which is given by the equation,

Fgas = Pgas * Arod

[Reference used is Damper basic calculations by KAZ technologies]

In mono tube damper, the gas filled in a gas chamber is nitrogen. The pressure
ranges between 50 – 70 psi.

Considering 70 psi, i.e. 4.823 bar

Arod =
??????
4
(�????????????����� �� �??????���� ���)
2


Arod = 0.000491 m2

Putting this in equation of Gas pressure force,

Fgas = 236. 62 N
Considering 240 N.

Therefore, total damping force considered for analysis in ANSYS is,
= 1010 + 240
= 1250 N

30. 28


Step 5: Estimation of force acting on spring and finding out
stiffness of spring:

Assuming 2000 N load acting on the suspension system and damping force =
1010 N and force of gas = 240 N,

Load acting on spring = 2000 – [
1010
2
+ 240]
= 1260 N

Stiffness of the spring , K =
??????
??????

Considering displacement of spring = 20 mm,

Stiffness of spring =
1260
20

= 63 N/mm


Step 6: Design of spring:

1. Free length = 180 mm

2. Compressed length = free length – ??????
= 180 – 20
= 160 mm

3. Material: Cold drawn steel wire
4. Permissible Shear stress induced inside spring,
?????? = 0.5 S��

31. 29

For cold drawn steel wire, Sut = 1050 N/ mm2
Therefore, = 525 N/mm2

5. Spring Index, C = 6 [Assumption]

6. Wahl Factor,

Kw =
4�−1
4�−4
+
0.615
�


Therefore, Kw = 1.2525

7. Mean coil diameter,

Permissible shear stress induced is also given by,
?????? =
????????????∗ 8 ∗ ?????? ∗ �
?????? �
2


Putting values of Kw, P, C and ??????, we get mean coil diameter,
d = 10 mm

8. Mean diameter of spring

Spring Index is given by,
C =
??????
�

Putting the values of C and d, we get D = 60 mm

9. No. of active coils
Deflection,

32. 30

?????? = (8*P*Nt*�
3
)/(G �
4
)

Putting the values of ??????, P, D, d and G = 81370 N/mm2 for cold drawn wire, we
get number of active coils,

Nt = 8 (approx)
Assuming plane end spring,

No. of active coils = Total no of coils
Therefore, Inactive coils = 0

10. Solid length

Solid length = Nt * d = 80 mm
11. Gap

Total gap = compressed length – solid length
= 160 – 80 = 80 mm

Gap between 2 coils =
���??????� ????????????�
??????�−�


=
��
�−�


= 11.42 mm

33. 31

12. Pitch

Pitch =
????????????�� ??????�??????????????????ℎ
????????????−1


=
180
7

= 25.71 mm

Step 7: Selection of fluid for damper:

We are going to select the fluid inside damper based on the viscosity of fluid
that is obtained from equation of laminar flow of fluid.

[Reference: fluid mechanics]

Damping force inside damper is given by,

F = (P1 – P2) * A
Therefore, (P1 – P2) =
??????
??????


Equation of pressure difference for laminar flow is given by,

P1 – P2 = (32∗ µ∗????????????��∗1)/??????
2
[eqn
3]

D = Equivalent diameter of flow
μ = Dynamic viscosity
l = length of the flow

34. 32

Vavg = velocity of piston

Equivalent diameter,

4 [
??????
�
�
�
] =
??????
�
�
�


D = 2d
Replacing value of D in equation 3, we get

P1 – P2 = (32∗ µ∗????????????��∗1)/4�
2


Putting F = 1250 N, A = 0.00145 m2, Vavg = 2 m/s, l = 0.04 m , d = 0.01 m in
above equation we get viscosity,

μ = 0.45 Ns/m2

From this amount of viscosity Sasol oil damper 37 can be selected. [ reference
used- Datasheet of sasol oil damper]

35. 33











CHAPTER 4
MODELLING IN CREO

36. 34

1. Damper Cylinder:

[figure 16]

Thickness = 6 mm, Outer cylinder diameter = 53 mm
Height = 70 mm, Inner cylinder diameter = 44.1 mm
Diameter of piston rod = 25 mm,
Diameter of base plate = 75 mm

2. Piston with piston rod:


[figure 17]

37. 35

Length of the piston rod = 110 mm
Diameter of piston rod = 25 mm
Diameter of piston = 44 mm
Diameter of orifice = 10 mm
Length of the orifice = thickness of piston = 5 mm
Diameter of base = 75 mm


3. Floating plate:


[figure 18]

Diameter of plate = 39 mm
Spline size = 3*5*5

38. 36

4. Spring:


[figure 19]

Free length of spring = 180 mm
Stiffness of spring = 60 N/mm
Pitch of the spring = 25.7 mm
Diameter of coil = 10 mm
Mean diameter of spring = 60 mm
No of active turns = 8
Plane end spring
5. Assembly of spring and damper


[figure 20]

39. 37

















CHAPTER 5
STRESS ANALYSIS IN ANSYS

40. 38


1. Meshing of assembly [Finite Element Analysis]


[figure 21]


2. Fixed Support


[figure 22]

41. 39

3. Damping Force [1260 N]



[figure 23]



4. External load [2000 N]



[figure 24]

42. 40

5. Equivalent stress


[figure 25]
Maximum equivalent stress: 14.078 MPa
Minimum equivalent stress: 0.0021239 MPa
3. Maximum shear stress


[figure 26]


Maximum shear stress: 8.1214 MPa
Minimum shear stress: 0.0012021 MPa

43. 41














CHAPTER 6
CONCLUSION

44. 42

Conclusion:

 Successfully designed spring damper system for 2000 N load acting on
spring damper assembly.
 Successfully modelled Spring damper assembly in creo as per the
specifications obtained during design process.
 Obtained maximum and minimum shear stress and equivalent stress
values in permissible limits.

45. 43

REFERENCES :

 [Wikipedia and www.yamaha-motor-india.com]
 Machine Element Design by V.B Bhandari
 Selecting the right Damper – Dictator Technik
 Understanding your dampers by Jim Kasprzak
 Suspension in Bikes Considering Preload, Damping Parameters and
Employment of Mono Suspension in Recent Bikes by Prof. D. K.
Chavan, Sachin V. Margaje, and Priyanka A. Chinchorkar
 Suspension System by Dr. Paul J. Aisopoulos
 Datasheet Sasol Damper Oil 37 DAMPER OIL, SYNTHETIC,
ANTI-WEAR, VHVI, GRADE 37