Shock absorber project

1. SHOCK ABSORBER
ABDINASIR AHMED ABDIRAHMAN ID: 21
AYAN ABDI FARAH ID: 05
LIBAN XUSSEIN JIMCALE ID: 59
An assignment submitted in full filament of the
Requirements for the machine tool course
Faculty of Engineering
Department of electromechanical
SOMALI NATIONAL UNIVERSIT
DEC 2019 |

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DESIGN AND ANALYSIS OF A SHOCK ABSORBER

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ACKNOWLEDGEMENT
We would like to express our special thanks of gratitude to our teacher ENG. AHMED ALI ABDI who
gave us the golden opportunity to do this wonderful project on the topic SHOCK ABSORBER, which
also helped us in doing a lot of research and we came to know about so many new things.
We are really thankful to him.
Secondly we would also like to thank everyone who helped us a lot in finishing this project within the
limited time.
We are making this project not only for marks but to also increase our knowledge.
THANKS AGAIN TO ALL WHO HELPED US.

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ABSTRACT
A suspension system or shock absorber is a mechanical device designed to smooth out or damp shock
impulse, and dissipate kinetic energy. The shock absorbers duty is to absorb or dissipate energy. In a
vehicle, it reduces the effect of traveling over rough ground, leading to improved ride quality, and
increase in comfort due to substantially reduced amplitude of disturbances. When a vehicle is traveling
on a level road and the wheels strike a bump, the spring is compressed quickly. The compressed spring
will attempt to return to its normal loaded length and, in so doing, will rebound past its normal height,
causing the body to be lifted. The weight of the vehicle will then push the spring down below its normal
loaded height. This, in turn, causes the spring to rebound again. This bouncing process is repeated over
and over, a little less each time, until the up-and-down movement finally stops. If bouncing is allowed to
go uncontrolled, it will not only cause an uncomfortable ride but will make handling of the vehicle very
difficult. The design of spring in suspension system is very important. In this project a shock absorber is
designed and a 3D model is created using Auto Cad. The model is also changed by changing the
thickness of the spring. Structural analysis and modal analysis are done on the shock absorber by
varying material for spring, Spring Steel and Beryllium Copper. The analysis is done by considering
loads, bike weight, single person and 2 persons. Structural analysis is done to validate the strength and
modal analysis is done to determine the displacements for different frequencies for number of modes.
Comparison is done for two materials to verify best material for spring in Shock absorber. Modeling is
done in Auto Cad and Auto Cad is commercial computer-Aided design (CAD) and drafting software
application. Developed and marketed Autodesk.
Index Terms: damp shock, kinetic energy, Auto Cad, and 3D shock absorber

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List of figures page
Figure 1.1 “The horseless age”, March 1905, Truffault-Hartford advertisement...................................... 6
Figure 1.2 Drawing for the original shock absorber patent granted on March 18, 1902. ......................... 7
Figure 1.3All above from “The Horseless Age” November 7, 190 6 issue. ............................................. 7
Figure 1.4 “the horseless Age” October 26, 1906 issue, the”vestal shock absorber”................................ 8
Figure 1.5 Rear shock absorber and spring of a BMW R75/5 motorcycle. .............................................. 9
Figure 1.6 Twin tube shock absorber.................................................................................................... 10
Figure 1.7 Mono tube shock absorber................................................................................................... 11
Figure 1.8 Characteristic of the damping force ..................................................................................... 11
Figure 1.9 Parts of shock absorber........................................................................................................ 12
Figure 2.1 Picture showing the design of a twin-tube shock absorber, which is the type used in this
project.................................................................................................................................................. 13
Figure 2.2 Illustration of a shim stack valve ......................................................................................... 14
Figure 2.3 Shock absorber curve .......................................................................................................... 15
Figure 2.4 3. 1the detailed damper model from the Automotive Demos library..................................... 17
Figure 3.1 step one............................................................................................................................... 18
Figure 3.2 step two............................................................................................................................... 18
Figure 3.3 upper mount ........................................................................................................................ 19
Figure 3.4 inner parts ........................................................................................................................... 19
Figure 3.5 spring .................................................................................................................................. 20
Figure 3.6 Assembly ............................................................................................................................ 20

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Contents
ACKNOWLEDGEMENT ................................................................................................................................... 2
ABSTRACT........................................................................................................................................................ 3
List of figures...................................................................................................................................................... 4
1. INRODUCTION ............................................................................................................................................. 6
1.1 History of shock absorber........................................................................................................................ 6
1.2 Description............................................................................................................................................... 8
1.3 Explanation.............................................................................................................................................. 8
1.4 Applications ............................................................................................................................................. 9
1.5 Vehicle suspension ................................................................................................................................... 9
1.6 Structures and types shock absorber .....................................................................................................10
1.6.1 Twin tube type ...................................................................................................................................10
1.6.2 Mono tube type ..................................................................................................................................10
1.6.3 What are damping forces? ..................................................................................................................11
The same shape as the genuine shock absorber............................................................................................12
1.7 Design Calculations for Helical springs for Shock absorbers................................................................12
2 THEORIES AND LITERATURE STUDY......................................................................................................13
2.1 Shock absorber theory............................................................................................................................13
2.2 Overview .................................................................................................................................................16
3 DRAWING SHOCK ABSORBER IN AUTOCAD..........................................................................................18
3.1 Introduction to AutoCAD.......................................................................................................................18
3.2 Drawing in AutoCAD .............................................................................................................................18
3.3 Commands we use ....................................................................................................................................20
4 CONCLUSIONS.............................................................................................................................................21
5 REFERENCES................................................................................................................................................22

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1. INRODUCTION
A shock absorber or damper is a mechanical device designed to smooth out or damp shock impulse, and
dissipate kinetic energy.
1.1 History of shock absorber
Figure 1.1 “The horseless age”, March 1905, Truffault-Hartford advertisement.
In 1898, French cyclist J.M.M Truffault invented what appears to be the very first shock absorber to be used on
a vehicle, after installing it on a bicycle. It consisted of a front fork with a suspension that used coil springs and
a friction device that minimized vibration.
The next year Edward V.Hartford, an American, witnessed a motor-tricycle race in France that was won by a
Darracq ridden by Marcellin and powered by 12HP Buchet twin-cylinder engine.
It was equipped with a La fourche Truffautl, a sprung- fork built by the Frenchman with his new invention.

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Figure 1.2 Drawing for the original shock absorber patent granted on March 18, 1902.
The two soon became friends after Hartford had Truffault install a unit on his 21/4 HP de Dion tricycle with
what he described as most gratifying results. In the fall of 1900 he purchased one of the new 1901 curved-
dashed Oldsmobile’s and shipped it to France to have his friend experiment with and install a set of the device
on the little car. After the cars return to the states, the pair who was working together was unable to interest any
American manufactures in using the shock, other than one offer from one to buy the patent.
Negotiations back in France with Peugeot resulted in the automaker installing them on his own car and also
selling a few sets.
The first real marketing success of the friction dampers came when Leon Thery was able to see the merit of
using them and equipped his Richard-Brasier racing car with a set. The units in turn helped him as he went on to
win the 1904 Gordon Bennett Cup race.
Figure 1.3All above from “The Horseless Age” November 7, 190 6 issue.
Above is the earliest article we have been able to find covering the shock absorber and its development here is
this century. Shock absorber, written by E.S.Foljambe and found in The horseless Age October 26, 1906 issue,
covers the full range of friction, pneumatic, hydraulic and spring action devices that were available and being
applied at the time. It makes for an interesting read all about the use, testing and application of the subject at the
dawn of early motoring here in this country.

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Figure 1.4 “the horseless Age” October 26, 1906 issue, the”vestal shock absorber”
1.2 Description
Pneumatic and hydraulic shock absorbers commonly take the form of a cylinder with a sliding piston inside.
The cylinder is filled with a fluid (such as hydraulic fluid) or air. This fluid-filled piston/cylinder combination is
a dashpot.
1.3 Explanation
The shock absorbers duty is to absorb or dissipate energy. One design consideration, when designing or
choosing a shock absorber, is where that energy will go. In most dashpots, energy is converted to heat inside the
viscous fluid. In hydraulic cylinders, the hydraulic fluid will heat up, while in air cylinders, the hot air is usually

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exhausted to the atmosphere. In other types of dashpots, such as electromagnetic ones, the dissipated energy can
be stored and used later. In general terms, shock absorbers help cushion cars on uneven roads.
1.4 Applications
Shock absorbers are an important part of automobile and motorcycle suspensions, aircraft landing gear, and the
supports for many industrial machines. Large shock absorbers have also been used in structural engineering to
reduce the susceptibility of structures to earthquake damage and resonance. A transverse mounted shock
absorber, called a yaw damper, helps keep railcars from swaying excessively from side to side and are
important in passenger railroads, commuter rail and rapid transit systems because they prevent railcars from
damaging station platforms. The success of passive damping technologies in suppressing vibration amplitudes
could be ascertained with the fact that it has a market size of around $ 4.5 billion.
Figure 1.5 Rear shock absorber and spring of a BMW R75/5 motorcycle.
1.5 Vehicle suspension
In a vehicle, it reduces the effect of traveling over rough ground, leading to improved ride quality, and
increase in comfort due to substantially reduced amplitude of disturbances. Without shock absorbers, the
vehicle would have a bouncing ride, as energy is stored in the spring and then released to the vehicle,
possibly exceeding the allowed range of suspension movement. Control of excessive suspension movement
without shock absorption requires stiffer (higher rate) springs, which would in turn give a harsh ride. Shock
absorbers allow the use of soft (lower rate) springs while controlling the rate of suspension movement in
response to bumps. They also, along with hysteresis in the tire itself, damp the motion of the unspring
weight up and down on the springiness of the tire. Since the tire is not as soft as the springs, effective wheel
bounce damping may require stiffer shocks than would be ideal for the vehicle motion alone. Spring-based
shock absorbers commonly use coil springs or leaf springs, though torsion bars can be used in tensional
shocks as well. Ideal springs alone, however, are not shock absorbers as springs only store and do not
dissipate or absorb energy. Vehicles typically employ springs and torsion bars as well as hydraulic shock
absorbers. In this combination, "shock absorber" is reserved specifically for the hydraulic piston that
absorbs and dissipates vibration.

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1.6 Structures and types shock absorber
Today's automotive suspension systems incorporate cylinder-type shock absorbers, most of which are of the
double-acting type that generate damping forces in both the extending and contracting strokes.
These shock absorbers can be either the twin tube type or mono tube type, depending on the type of car and the
car's suspension.
1.6.1 Twin tube type
The twin tube type features a dual tube configuration. The piston valve generates damping forces in the
extending stroke, while the base valve generates damping forces in the contracting stroke.
This type offers a wide adjustment range for length and readily withstands minor chips from flying rock
particles. For this reason, it's widely used in automotive suspensions.
Figure 1.6 Twin tube shock absorber
1.6.2 Mono tube type
The mono tube type has an inline arrangement featuring an oil chamber and a gas chamber. The piston valve
generates damping forces in both the extending and contracting strokes.
Due to these characteristics, damping forces have a linear relationship to piston movement. In addition, this type
is easy to tune and offers good heat dissipation. They're often used in sport suspensions.

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Figure 1.7 Mono tube shock absorber
1.6.3 What are damping forces?
While the shock absorber's specific role is to limit spring motion and stabilize the car body, the damping forces
mentioned here refer to the force that damps the movement of the relatively massive frame of the car as quickly
as possible.
How are damping forces generated? As shown in the figure below and to the right, the piston moves inside a
barrel filled with oil.
The piston features a hole that passes through its length. As the car body pitches or bounces, moving the piston,
oil is forced through this hole against resistance. This resistance is the damping force.
That is a characteristic of the damping force. (See the figure below to the left.)
Figure 1.8 Characteristic of the damping force
The structure and types of shock absorber

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The same shape as the genuine shock absorber
The main body of the shock absorber has the same shape as the genuine part to enable use with the genuine
springs and other parts currently installed on your car. The genuine form type of shock absorber is ideal for
customers who want to replace worn main bodies or customers who want to use a combination of a genuine
form main body and a genuine form sport-type spring.
Another benefit is that maintenance procedures for the genuine form shock absorber are the same as for the
genuine part.
Figure 1.9 Parts of shock absorber
.
1.7 Design Calculations for Helical springs for Shock absorbers
Material: Steel (modulus of rigidity) G = 41000 Mean diameter of a coil D=62mm Diameter of
wire d = 8mm
Total no of coils n1= 18
Height h = 220mm
Outer diameter of spring coil D0 = D +d =70mm
No of active turns n= 14
Weight of bike = 125kgs
Let weight of 1 person = 75Kgs Weight of 2 persons = 75×2=150Kgs

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2 THEORIES AND LITERATURE STUDY
To be able to understand the problem and how others have approached it, a literature study was carried out
during the first weeks of the project. The basics of shock absorbers, earlier models of shock absorbers, modeling
in Auto Cad and validation and testing of earlier models were researched.
2.1 Shock absorber theory
The dampers that will be modeled in this project are twin-tube dampers. Twin-tube means that the shock
absorber consists of two chambers as can be seen in figure 2.1. The outer chamber contains, in addition to the
oil, pressurized gas on top. This gas is pressurized to keep the pressure of the oil from dropping too much,
which would result in cavitation. (Dixon, 2007)
The layout of the different parts of a twin-tube shock absorber can be seen in figure 2.1. The valves that control
the oil flow are located in the piston and in the base.
The damping during low speeds in the shock absorber is dominated by oil flow through channels in
the piston and base valves that are always open. These valves are commonly known as bleed valves
or low speed valves. When the speed increases a pressure difference occurs. Upon the pressure
difference the secondary valves start to open and the effective coefficient of damping decreases,
these valves commonly consists of shim stacks.
Figure 2.1 Picture showing the design of a twin-tube shock absorber, which is the type used in this project

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The piston and base valve consists of valves to control the oil flow. The configuration of the valves differ
between different shock absorbers, the shock absorbers modeled in this project use compression valves on both
the piston and base, a rebound valve on the piston and a check valve on the rebound side of the base. The most
common type of valve is the shim stack. A shim stack valve is a pile of thin discs on top of a channel, when a
pressure difference occurs on the top and bottom of the shim stack the discs deflect resulting in an increased
opening area. A schematic view of a shim stack can be seen in figure 2.2. To get satisfactory damping during
slow movements the shim stacks are often fitted with an orifice disc in the bottom, which acts as the low speed
valve. The orifice disc has cut-outs along the edge, providing a small area that is always open independent on
the pressure difference. Shim stacks may be set up in a number of different ways, with or without an orifice disc
and pyramidal or cylindrical are the most common differences. Some shim stacks use a spacer and a stop disc;
these are fitted on top of the stack and control the maximum deflection. The shock absorbers modeled in this
projects use a pre-tensioned spring on top of the shim stack that delay the opening of the valve, this is however
not very common. In Figure 2.2 the compression valve on the base of one of the shock absorbers used in this
project can be seen. The parts are, from the left hand side, the stop disc and spacer disc controlling the
maximum deflection, the four shims, the orifice disc and the base. Note the channels on the base leading up to
the shims.
Figure 2.2 Illustration of a shim stack valve

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The hysteresis phenomena that becomes obvious in the phase plot showing the force versus velocity curve
during higher frequencies, seen in figure 2.3 below, is one important reason that a simple damper model may
not adequately predict certain dynamic behavior. Hysteresis is the separation of the compression and expansion
lines in the force-velocity graph. The rebound part of the stroke displays as positive force and the compression
part as negative force in the diagram. During a stroke the curve is followed counter clockwise.
Figure 2.3 Shock absorber curve
The main causes for hysteresis are gas compression, oil compressibility, oil inertia and the expansion of the
cylinders. (Cossalter, Doria, Pegoraro, & Trombetta, 2010) Claesson contradicts this and states that the
expansion of the cylinders doesn’t have a significant effect. (Claesson, 2012)

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2.2 Overview
One very early model is described in H.H. Lang's doctoral dissertation. (Lang, 1977) Lang developed a model
of a twin-tube damper, and validated it over the frequency range of 1-10 Hz. The simulations were made on an
analogue computer with custom-made circuits representing each component.
In 2002 Talbott and Starkey developed a model of an Öhlins WCJ 22/6 mono-tube damper, designed for stock
car racing. One very interesting finding of their work is the shim stack modelling, they modelled the shim stack
as a pile of circular thin plates and found that it was a very accurate model. Areas of improvement that where
pointed out in this paper were to include fluid compressibility and temperature difference effects. However their
model is validated to be quite accurate when compared to the real damper. (Talbott & Starkey, 2002)
Chahine developed a model of the Ohlin’s TPX damper in his master's thesis using Simulink. (Chahine, 2011)
The model was very detailed but didn't match the performance of the real damper very well. Even though
Chahine's model turned out to not be valid his modeling procedure seemed to be good and will probably be
useful when creating the model. It is suggested to include temperature and pressure dependence in the bulk
modulus for the oil, which has not been done on Chahine's model.
An Öhlins damper with variable damping using a CES (Continuously controlled Electronic Suspension) system
was modelled in (Gällsjö & Johansson, 2012). Öhlins CES system uses an electrically controlled valve to adjust
the damper's stiffness dependent on the need. Even if the CES system differs from the damper modelled in this
thesis there are several similar components. The CES model was validated to be good. Areas identified to have
room for improvement are the check valves and the model for mechanical friction. It was also concluded that
the viscous friction might need to be different for compression and expansion.
In (Hou, Li, He, Zhang, & Chen, 2011) the authors develop a modular model that can be used for both mono-
and twin-tube dampers. They get good results when comparing to their test bench results of runs from several
shock absorbers. The most useful result from this report is probably the tests done to find the influence of
different parameters of the shock absorber. The influence is plotted for variations of, amongst others, fluid
compressibility.
Hou et al. developed a model of a shock absorber using the modelling language Modelica, which is the base for
Dymola. The shock absorber modelled was a twin-tube damper. Even if their model is probably over simplified
and is not validated against a real shock absorber it might be useful to look at, especially since the modelling
was done in Modelica. (Hou, Li, He, Zhang, & Chen, 2011)
In his master’s thesis Claesson developed a physical model of the Öhlins TTR damper, which is an adjustable
shock absorber used in motor cycle racing applications. The shock absorber has large number of adjustments
that can be done, both externally and internally by disassembling the damper. The model was created in Dymola
using components from Modelon’s hydraulics library. The model is one of the most complete models found
using a bulk modulus varying with pressure, temperature differences and heating of the damper. (Claesson,
2012)

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A detailed damper model can be found in the Dymola library AutomotiveDemos. The model is created using
the hydraulics and pneumatics libraries provided by Modelon. It is a mono-tube damper with check valves. The
layout of the damper model can be seen in figure 2.4.
Figure 2.4 the detailed damper model from the Automotive Demos library

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3 DRAWING SHOCK ABSORBER IN AUTOCAD
3.1 Introduction to AutoCAD
AutoCAD is a computer-aided drafting software program used to create blueprints for building, bridges, and
computer chips, among other things
To draw shock absorber we use 3D AutoCAD.
3.2 Drawing in AutoCAD
 Step one: draw two circles as shown below.
Figure
Figure 3.1 step one
 Step two: Add two perpendicular lines quadrants.
Figure 3.2 step two

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 Step three: Make it revolve to complete upper mount.
Figure 3.3 upper mount
 Step four: After some processes we get inner part of the shock absorber.
Figure 3.4 inner parts
 Step five: Draw helix.

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Figure 3.5 spring
 Step six: Assembly.
Figure 3.6 Assembly
3.3 Commands we use
 Commands of top part
Circles, line, trim, extrude, revolve and etc.
 Commands of inner part
Circle and extrusion only
.
 Commands of spring
Helix circles and sweep.
 Commands of bottom part
Circles and extrude.

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4 CONCLUSIONS
 In this project we have designed a shock absorber used in AutoCAD 3D software.
 To validate the strength of our design, we have done structural analysis and model analysis on the shock
absorber. We have done analysis by varying spring material spring steel and Beryllium copper.
 By observing the analysis result, the analysed stress values are less than their respective yield stress values.
So our design is safe.
 By comparing the result for both materials, the stress value is less for spring steel than beryllium.
 Also the shock absorber design id modified by reducing the diameter of spring by 2mm and structural,
model analysis is done on the shock absorber. By reducing the diameter the weight of the spring reduces.
By comparing the result for both materials, the stress value is less for spring steel than beryllium.
 By comparing the result for present design and modified design, the stress and displacement values are less
for modified design.
 We can conclude that as per our analysis using material spring steel for spring is best and also our modified
is safe.

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5 REFERENCES
 Machine design by R.S.Kurmi.
 PSG, 2008 “DESING DATA” kalaikathir achachgram publishers, COIMBATORE, INDIA.
 Automobile engineering by R.B Gupta.
 Automobile engineering by G.B.S.Narang.
 Automobile servicing and maintenance by K.Ashrif Ali.
 Automotive Maintenance and Troupe shooting by Emest Venk,&Edward D.Specer.