Design and stress analysis of mono suspension system

Project team:Nisarg Shah (100010119007)Krunal Rathod (100010119067)

Project guide:Prof. Krunal Shah

AbstractSuspension system is used in all

the automobiles for withstanding the load of the vehicle and absorbing shocks.

Suspension system located at the rear of the vehicle could be mono suspension type or dual suspension type.

Our project was inteded at designing a mono suspension system of a bike for the loading of 2000 N.

ObjectiveTo design a suspension system

consisting of helical coil spring and mono tube damper that can withstand 2000 N static load.

Modelling the spring, damper and its assembly in creo.

Performing Stress analysis in Ansys for static loading.

IntroductionMono suspension system: In this

type of suspension, a single spring damper unit is used to absorb all the shocks.

Spring used is a helical coil spring.

Damper used are of two types:1. Mono tube damper2. Twin tube damper

Mono-suspension sytem

Design of suspension systemSuspension system of FZ bike

was studied and some of the parameters were taken for our design process.

In FZ bike, coil spring and twin tube oil damper is used.

Our project aimed at designing a coil spring and a mono tube damper sustaining a load of 2000 N.

Parameters of FZ bike assumed in design process:

Outer diameter of cylinder = 53 mm

Free length = 180 mmLength of outer cylinder = 70 mmGas Chamber = 20 mm[assumed

i.e no data available]

Step 1 : Determining thickness of cylinder Basic Assumptions: 1. Material: Structural Steel [ductile] 2. Maximum pressure inside cylinder: 53

MPa 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

Putting all the values mentioned in above equation, we get, Di = 44 mm

Now, Thickness of the cylinder, Putting Do = 53 mm Di = 44 mmWe get, T = 4.5 mm

Step 2 : Diameter of pistonPiston diameter = Inner cylinder diameter - 2

= 44 -2 = 42 mmTherefore, Diameter of Piston = 42 mmDiameter of Piston rod:From literature survey about piston rod

diameter, the usual piston rod diameter for mono tube dampers is 25 mm.

[dictator technik data]

Step 4 : Estimation of damping forceThere is no standard reference

procedure for designing a damper.

Every damper making organizations designs their damper according to their own methods.

We used the Dictator Technik and Kaz Technologies methods and equations to design our mono tube damper.

Damping force is found by the equation,

Damping force = Energy per stroke, E = m*g*h

+ m*g*s [for inclined loading]m = 200 kg, g = 9.8 m/, s = 0 , h

= 0.017 m• Putting all these values, we get E

= 34.40 N.m

Damper correction factor was found out using priestley equation which was proposed in 2003 and is given by,

DCF = 0.25

• For an underdamped system, So we get DCF = 1.17

Stroke = length of the cylinder – length of the gas chamber - thickness of piston-thickness of floating plate

= 70-20-5-5= 40 mm Putting all these values in damping force equations, we get damping force = 1006.2 N

Force due to gas pressure = Pgas * ArodIn mono tube damper, the gas filled in

a gas chamber is nitrogen. The pressure ranges between 50 – 70 psi. [mx-tech.com]

Considering 70 psi, i.e. 4.823 barArod = Arod = = 0.000491 m2

Putting this in equation of Gas pressure force,

Fgas = 236. 62 N

Considering 1010 N damping force and 240 N force due to gas pressure, total damping force inside the damper

= 1010 + 240 = 1250 N

Step 5: Estimation of force acting on spring and finding out stiffness of springLoad acting on spring = 2000 -[] = 1255 N i.e 1260 N[approx]Stiffness of the spring , K = Considering displacement of spring

= 20 mm,Stiffness of spring = = 63 N/mm

Step 6: Design of spring 1. Free length = 180 mm

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

3. Material: Cold drawn steel wire

4. Permissible Shear stress induced inside spring, 𝜁 = 0.5 Sut For cold drawn steel wire, Sut = 1050 N/ mm2

Therefore, = 525 N/mm𝜁 2

5. Spring Index, C = 6 [Assumption]

6. Wahl Factor, Kw = Therefore, Kw = 1.2525

7. Mean coil diameter, Permissible shear stress induced is also given

by, 𝜁 = Putting values of Kw , P , C and , we get 𝜁

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, 𝝳 = Putting the values of , P, D, d and G = 81370 𝝳

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 coilsTherefore, Inactive coils = 0

10. Solid lengthSolid length = Nt * d = 80 mm

11. GapTotal gap = compressed length – solid length = 160 – 80 = 80 mm

Gap between 2 coils = = = 11.42 mm12. Pitch Pitch = = = 25.71 mm

Step 7: Selection of fluid for damperEquation of pressure difference

for laminar flow is given by, P1 – P2 = Damping force inside damper is

given by, F = (P1 – P2) * ATherefore, (P1 – P2) =

D = Equivalent diameter of flowµ = Dynamic viscosity l = length of the flow Vavg = velocity of piston Equivalent diameter, 4 [] = D = 2dReplacing value of D in equation of pressure

difference, we get P1 – P2 =

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

For this amount of viscosity Sasol oil damper 37 can be selected.

[ reference used- Datasheet of sasol oil damper]

 Chapter 4: Modelling In Creo

1. Damper Cylinder

Thickness = 6 mm, Outer

cylinder diameter = 53 mmHeight = 70 mm, Inner cylinder

diameter = 44.1 mmDiameter of piston rod = 25 mm,Diameter of base plate = 75 mm

2. Piston with piston rod

Length of the piston rod = 110 mm

Diameter of piston rod = 25 mmDiameter of piston = 44 mmDiameter of orifice = 10 mmLength of the orifice = thickness

of piston = 5 mmDiameter of base = 75 mm

3. Floating plateDiameter of plate = 39 mmSpline size = 3*5*5 mm

4. Spring

Free length of spring = 180 mmStiffness of spring = 60 N/mmPitch of the spring = 25.7 mmDiameter of coil = 10 mmMean diameter of spring = 60

mmNo of active turns = 8Plane end spring

5. Assembly of spring and damper

Chapter 5 : Stress Analysis in Ansys1. Meshing of assembly

[Finite Element Analysis]

2. Fixed Support

3. Damping force

4 . External load [2000 N]

5. Equivalent stressMaximum equivalent stress: 14.078 MPaMinimum equivalent stress: 0.0021239 MPa

6. Maximum shear stressMaximum shear stress: 8.1214 MPaMinimum shear stress: 0.0012021 MPa

Chapter 6: 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.

References

1. Yamaha FZ data sheet [Wikipedia and www.yamaha-motor-india.com]

2. Machine Element Design by V.B Bhandari 3. Damper Basic Equations – KAZ technologies 4. Selecting the right Damper – Dictator Technik 5. Understanding your dampers by Jim Kasprzak 6. Modelling and analysis of twin tube damper by Urszula

Ferdek and Jan Łuczko 7. 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

8. Suspension System by Dr. Paul J. Aisopoulos 9. Datasheet Sasol Damper Oil 37 DAMPER OIL, SYNTHETIC, ANTI-WEAR, VHVI, GRADE 37 10. Design and analysis of a shock absorber by Mr.

Sudarshan Martande, Mr. Y.N. Jangale, Mr. N.S. Motgi

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