IRJET- Shock Absorber Testing using FFT Analyzer with Dewesoft

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 07 Issue: 01 | Jan 2020 www.irjet.net p-ISSN: 2395-0072
© 2020, IRJET | Impact Factor value: 7.34 | ISO 9001:2008 Certified Journal | Page 114
Shock Absorber Testing using FFT Analyzer with DEWESoft
1Student, M. Tech. Energy Technology, School of Energy Studies, SPPU Pune, Maharashtra, India
2Assistant Professor, Department of Mechanical Engineering, JSCOE, SPPU Pune, Maharashtra, India
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Abstract -This paper is based on Shock absorber testingon
different road texture by varying spring stiffness using FFT
Analyzer. Shock absorber is an important part of automotive
suspension system which reduce shock impulse and used for
driving safety. The road disturbance is generated in the model
by giving speed brakes fixed on drum which is rotatedby using
motor. In this paper study and analysis of single DOF spring-
mass-damper system (Hero Splendor and Honda Shine i.e.
Shock Absorber) and plotted its dynamic characteristicscurve
for different values of spring stiffness and different oils for
optimum motion transmissibility.
Key Words: FFT Analyzer, Shock Absorber, Motion
Transmissibility, Equation ofabsolutemotion, Dewesoft
software, Design and calculation etc.
1. INTRODUCTION
Now-a-days Modern vehicles come along with strong shock
absorbers to tolerate any type of bouncy conditions.Modern
motorcycle allows the driver to fine tune themachinetogive
him/her better control over it when driving. The vehicle is
subjected to bump at the bottom end of the rear wheel.
The primary function of the suspension system is to isolate
the vehicle structure from shocks and vibration due to
irregularities of the road surface. The Suspension system is
used to support weight, absorb and dampen road shock,and
help maintain tire contact as well as proper wheel to chassis
relationship. A vehicle in motion is more than wheels
turning. As the wheel revolves, the suspension system turns
in dynamic state of balance, continuously compensatingand
adjusting for changing driving conditions according to road
profile. Suspension of vehicle need to analyse before the
manufacturing. This is because to make sure components in
shock absorber system remain in good conditions.
The mechanism or setup should be able to create a vehicular
situation in which one end of the suspension test rig is
subjected to jerks and bounce producing unsteady
vibrations. While on the other side it should face loading
conditions representing the weight of passengerandvehicle
itself. So this encompasses the design and development of
shock absorber test rig in which the above mentioned
conditions are simulated and performance is evaluated.
2. PROBLEM STATEMENT
The aim of the project is to study andanalyze singledegreeof
freedom spring-mass-damper system and plot its dynamic
characteristics curve for different values of spring stiffness
for various speed conditions using FFT Analyzer
Fig -1: Problem Specification
3. OBJECTIVES
1) To determine dynamic characteristic of shock absorber.
2) To test suspension on different types of oils and stiffness
to find out optimum motion transmissibility.
3) Suspension will be test for multiple stiffness by varying
loads, speed and different oils.
4. SPEED BRAKER PROFILE
Fig -2: Speed Breaker Profile
Speed breaker profile is 250mm X 54mm selected.
Standard available size of rumbler is taken according to
Indian government standard. Suspension will be tested on
this speed breaker profile. It’s made by Lake Traffic
Solutions.
5. THEORETICAL BACKGROUND
In case of locomotives or vehicles the wheels act as base or
support for the system. The wheels can move vertically up
Snehal M. Walake1, Amol P. Kokare2

and down on the road surface during the motion of the
vehicle.
At the same time is relative motion between the wheels and
the chassis is having motion relative to the wheels and the
wheels are having motion relative to the road surface. The
amplitude of vibration in case of support motiondependson
the speed of vehicle and nature of road surface. The
vibration measuring instruments are designed on the
support motion approach. Such systems are supposed to
have single degree of freedom for the simplicity of
mathematical expression. In a vibratory system where the
support is put to excitation absolute and relative motion
become important from subject point of view.
5.1 Terminology Used
1) Natural frequency (ωn)
When no external force acts on the system after giving it an
initial displacement, the body vibrates. These vibrations are
called free vibrations and their frequency as natural
frequency. It is expressed in rad/sec or Hertz.
2) Damping
The external force which is provided to reduce the
vibrations.
3) Critically damping co-efficient
The critical damping co-efficient Cc is that value of damping
coefficient c at which the frequencyoffreedampedvibration
is zero and the motion is a periodic.
4) Damping co-efficient (ξ)
It is defined as the ratio of damping coefficient to critical
damping coefficient. Mathematically, ξ = C/Cc
5) Amplitude
The maximum displacement of vibrating body from the
equilibrium position.
6) Time period (tp)
The time required to complete one cycle.
7) Absolute Motion
Absolute motion of a mass means its motion with respect to
the coordinate system attached to the earth. As shown in
figure, the absolute displacement ifsupportisy=Bsinωt and
the absolute displacement of the mass m from its
equilibrium position is x. The displacement of mass m
relative to the support is z. The net elongation of the spring
is (x‟-y‟) and the relative motion between the two ends of
the damper is (x-y). Then z= x-y and z‟= x‟-y‟.
Fig-3: Absolute Motion
The equation of motion can be written as,
mx c ((x-) y ) k(x-y) =0
Or mx cx kx=cy ky.
Solve the equation, we get, Steady state amplitude can be
written as:
=
The ratio of X/Y is called the displacement
transmissibility which is the ratio of amplitude of the body
to amplitude of the support.
6. DESIGN AND ANALYTICAL CALCULATIONS
6.1 Spring Stiffness Calculation
Fig-4: Spring Stiffness Measurement of Splendor
Suspension and Honda Shine Suspension
As initially we don’t have spring stiffness value for two
suspensions those are usedforexperimentation.Forthisone
small experiment is done to calculate the stiffness. Initial
length of the spring is measured with scale. Then 60 Kg load
is applied on spring of one of the shock absorber. Thus
spring gets compressed and now again spring length is
measured. Now by using the formula for calculating spring
stiffness,
K= (F/X) ×9.81 N/mm
Where,
K-Spring stiffness in N/mm F-Load applied in Kg

X-Displacement due to loading=
(Free length -Compressed length)inmm.SampleCalculation
For Splendor,
K= (60 ×9.81)/ (230-205)
K= 23.54 N/mm
Table -1: Spring Stiffness of Splendor and Honda Shine
Shock Absorber
Sr.
No
Shock
Absorber
Load
on
Spring
(Kg)
Free
Length
(mm)
Comp.
Length
(mm)
Spring
Stiffness
(K)
(N/mm)
1 Splendor 60 230 205 23.540
2 Honda
Shine
60 240 206 17.31
Natural frequency:
ωn = = ωn= = ωn = 8.28 rad/sec.
Critical damping coefficient:
Cc= 2*
Cc = 2* = Cc =5685.93 Ns/m.
Damping coefficient:
ξ = C/Cc
0.25= = C = 1421.48 Ns/m
Time period:
t = t = 0.5/1.39 = t = 0.3597sec
Excitation frequency:
ω = = ω = = ω = 17.4678 rad/sec
Motion Transmissibility:
=
=
X = 0.1714 m
6.2 Shaft material and Calculation
EN 19 Alloy Steel used for shaft. It is a high quality, high
tensile steel usually supplied readily machineable in any
temperature condition, giving good ductility and shock
resisting properties combined with resistance to wear.
6.2.1 Applications:
EN19T was originally introduced for the use in the machine
tool and motor industries for gears, pinions, shafts, spindles
and the like. Later its applications became much more
extended and it is now widely used in areas such as the oil
and gas industries. EN19T is suitableforapplicationssuchas
gears, bolts, studs and a wide variety of applicationswherea
good quality high tensile steel grade is suited.
6.2.2 Calculation:
Perimeter of Drum
P=2πr ; P=2π ×0.305 ; P=1.91637 m
Volume of Drum
V=2πr^2 h ; V=2×3.14×0.305×0.305×0.005
V=0.00292246 m3
Mass of Drum
M=V×ρ ; M=0.00292246×7860 ; M=22.98 kg
Weight of Drum
W=m×g ; W=22.98×9.81; W=225.48 N
Fig- 5: Force Diagram
By maximum shear stress theory
Support reaction (RA, RB)
∑MA=0
[(-RB×0.6096) + (740×0.305×0.15252)]=0 RB=112.74N
RA= -RB+ (740×0.305) RA=112.74 N
Bending Moment (M)
M=RA×x- w × (0.15252)/2

M=112.74×0.305-740× (0.1525) 2/2 M=25.78 N-m
Torque
T=F×r ; T= (149×9.81) ×0.405 ; T= 592 N-m
Equivalent Torque
Te = √ (M2 T2) ; Te = √ (25.782 5922); Te = 593 N-m
Diameter of Shaft
d= ∛ (16×Te/ π τ) ; d = ∛ [(16×593×1000)/ (π×45)]
d=40.69 mm~50 mm
By maximum principal stress theory
Equivalent Moment Me= [M √ (M2 T2)] /2
Me= [25.78 √ (25.782 5922)] /2
Me=309.17 N-m
Diameter of Shaft
d= ∛ (32×Me/πς); d=∛((32×309.17)/(π×75)) ;d=41 mm
Selecting maximum diameter&afterselecttheroller bearing
Find Te < T
T= (60×1000×P/2πN)
T= (60×1000×2.238/2 π×240) T=89.047 N-m
Velocity
V= πDN/60 V=π×0.05×240/60 V= 628.31 m/s
V=2.2611 Kmph
6.3 Bearing
Bearing is mechanical element which locates two machine
parts relative to each other and permits a relative motion
between them. It has two or more contacting surfaces
through which a load is transmitted. UCP210 bearing used
for shaft. According to required torque of 89 Nm & internal
diameter of 50mm bearing selected is Plummer block.
Fig-6: Bearing UCP210
6.4 Key
Key is a mechanical element used on shafts to secure
rotating elements likegears,pulleys,orsprocketandprevent
relative motion between two. The keytransmitstorquefrom
the shafts to shaft supported element or vice versa. It is
always inserted parallel to the axis of shaft.
Carbon steels have carbon as the key alloying element in
their composition. They also contain up to 0.4% silicon and
1.2% manganese. In addition, the residual elements such as
copper, molybdenum, aluminium, chromium and nickel are
present in these steels.
TMax=1.25×593 TMax=741.25N-m 741.25×103= (π/16)
×d3×45
d=50mm w=h=50/4≈13mm l=75mm
Shear Stress
TMax= w×l× (d/2) × (τ per) Key
741.25×103= 13×l× (50/2) ×45
l= 50.68 mm
Crushing Stress
TMax= (h/2) ×l× (d/2) × (ς per) Key
741.25×103= (13/2) ×l× (50/2) ×80
l=57mm
Thus key dimensions should be taken as 13mm,
13mm, and 75mm in breadth, width and length
respectively.
7. EXPERIMENTAL SETUP
Fig-7: Experimental Setup (CAD Model)
It consist following parts
1) Frame - It is Base structure of setup. It is made of MS bars
in C-Section. Total material used is about 35 Feet. Frame
gives the support to all the assembly components.
2) Drum - It is made of MS sheet having thickness 4mm. It is
manufactured by rolling of sheet metal. Standard speed
breaker profiles are also made by sheet metal by giving
radius and welded to drum. Drum is supported by 3 spokes.
3) Wheel Assembly - It is wheel assembly of Hero Splendor
Bike. Wheel is fitted in swing arm. Shock absorbers lower
point is mounted on swing arm. Swing arms are assembled
to Frame.
4) Motor - 1440 RPM 3 HP single phase motor is coupled to
shaft. It rotates drum and ultimately drum

5) Dimmerstat - Dimmerstat is auto transformer having
continuously variable voltage. 20amperedimmerstatisused
to control the motor speed.
6) FFT Analyzer - FFT-Fast Fourier Transform. It is a noise
& vibration measurement instrument. Time domain data is
converted into frequency domain. We will take reading by
using accelerometer. DEWEsoftisusedtodisplaythe results.
SPECIFICATION
•Small USB- based system
•8 analogue input channels (strain, voltage; with MSI
adapters any input)
•200 kS/s aliasing-free 24bit-ADC
•8 precise real time counters
•2 CAN bus ports isolated
7) Accelerometer -The accelerometers consist of a
piezoelectric crystal which has a mass attached to one of its
surfaces. When the mass is subjected to a vibration signal,
the mass converts the vibration (acceleration)toa force,this
then being converted to an electrical signal. Accelerometer
output may then processed to provide the instantaneous
velocity and displacement signals.
8) The DEWE soft Software - The analysis is carried out in
DEWESoft Software. Various methods of dynamic signal
analysis are present in the software such as Sound level,
Torsional vibration, Human Vibration and Order Tracking.
9) Tachometer - A tachometer is a sensor device for
measuring the rotation speed of an object such as theengine
shaft in a car. This device indicates the revolutions per
minute (RPM) performed by the object. The device
comprises of a dial, a needle to indicate the current reading,
and markings to indicate safe and dangerous levels.
8. WORKING
Fig-8: Experimental Actual Setup
1. Shaft is mounted in bearing on which drum is mounted.
2. Speed breaker profiles is welded on drum.
3. On drum wheel assembly is mounted.
4. Shaft is coupled to motor. Motor shaft rotates the Drum
shaft which simultaneously rotates the wheel which in on
drum.
5. Motor speed is controlled by using Dimmer stat.
6. As wheel and drum rotates wheel reaches to speedbeaker
profile it create bump on shock absorber.
7. Shock absorber will get compress.
8. FFT analyzers sensors will attached to Upper and lower
point of shock absorbers and readings displayed on
computers screen.
9. OBSERVATION TABLE
Table -2: Splendor Suspension (Oil 1)
Sr.
No.
Spring
Stiffness
(K)
(N/mm)
Load
(Kg)
Peak(RMS) Transmissib
ility
TR=A/BTop
(A)
Bottom
(B)
1 23.54 5 11.085 23.347 0.4748
2 23.54 10 14.420 24.230 0.5951
3 23.54 15 14.224 22.955 0.6196
4 23.54 20 12.066 23.544 0.5125
Table -3: Honda Shine Suspension (Oil 1)
Sr.
No.
Spring
Stiffness
(K)
(N/mm)
Load
(Kg)
ility
TR=A/BTop
(A)
Bottom
(B)
1 17.31 5 13.34 24.32 0.5485
2 17.31 10 16.57 27.66 0.5993
3 17.31 15 24.52 26.19 0.9364
4 17.31 20 10.30 25.70 0.4019
Table -4: Splendor Suspension (Oil 2)
Sr.
No.
Spring
Stiffness
(K)
(N/mm)
Load
(Kg)
ility
TR=A/BTop
(A)
Bottom
(B)
1 23.54 5 12.1644 25.407 0.4787
2 23.54 10 12.1644 24.525 0.4960
3 23.54 15 14.8131 21.876 0.6771
4 23.54 20 9.81 21.876 0.4484
Table -5: Honda Shine Suspension (Oil 2)
Sr.
No.
Spring
Stiffness
(K)
(N/mm)
Load
(Kg)
Peak(RMS) Transmiss
ibility
TR=A/BTop
(A)
Bottom
(B)
1 17.31 5 11.085 25.8984 0.4280
2 17.31 10 16.3827 27.664 0.5922
3 17.31 15 9.4176 24.721 0.3809
4 17.31 20 7.651 23.093 0.33134

10. RESULTS
10.1 Result of oil 1 (MOTUL) and oil 2 (YAMALUBE)
Chart -1: Transmissibility Vs Load for oil 1 and oil 2
From above graph for oil 1 we conclude that at 15 Kg load
motion TR of Shine suspension(K=17.321N/mm)ishighand
it is low at 20kg,which is not continuous. Splendor
suspension (K=23.54N/mm) have less difference in motion
TR at different loads. So, splendor suspension have good
motion TR at different loads. And for oil 2 we conclude that
at initially for low load motion TR of Shine suspension
(K=17.31N/mm) is intermediate and it is decreasing with
respect to increase in loads. Splendor suspension
(K=23.54N/mm) have high motion TR for this oil than Shine
suspension
10.2 Result for Splendor and Honda shine using
both oils
Chart -2: Transmissibility Vs Load for both oils (Splendor
and Honda Shine)
From above graph, for oil 1 motion TR of Splendor
suspension (K=23.54N/mm) have less difference for
different loads. And for oil 2 motion TR of Honda Shine
suspension (K=17.31N/mm) have less fluctuations for
different loads.
10.3 FFT Result
Fig-9: Splendor Bottom for weight 10Kg for Oil 1
Fig-10: Splendor Top for weight 10Kg for Oil 1
Fig-11: Splendor Bottom for weight 10Kg for Oil 2
Fig-12: Splendor Top for weight 10Kg for Oil 2

11. CONCLUSIONS
From this Suspension testing setup we can test
multiple number of suspensions at different loads, different
angles and different speeds. Also we can use suspensions of
different height.
By changing different suspensions and oils we can
find out optimum motion transmissibility. With ultimate
objective of studying and plotting dynamic characteristics
for Hero Splendor suspension and Honda Shine suspension
using single wheel model of suspensionanalysistoproduced
large number of results. However it concludes the project
work with following points:
1. Input and output graph shows transmissibility which is in
limit.
2. The suspension system gives best performance when
designed to be slightly under-damped.
3. From experimental results and graphs we can conclude
that for good ride, transmissibility should be as low as
possible and this can be attained by using low damping
constant and high spring stiffness and Honda Shine
suspension gives the better results as compared toSplendor
suspension
12. REFERENCES
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