DESIGN AND ANALYSIS OF ROCKER ARM

5/26/2018 DESIGN AND ANALYSIS OF ROCKER ARM

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CHAPTER 1

INTRODUCTION

1.1 INTRODUCTION TO ROCKER ARM

Therocker arm is used to actuate the inlet and exhaust valves motion as

directed by the cam and follower. It may be made of cast iron, cast steel, or

malleable iron. In order to reduce inertia of the rocker arm, an I-section is used

for the high speed engines and it may be rectangular section for low speed

engines.

In four stroke engines, the rocker arms for the exhaust valve are the most

heavily loaded. Though the force required to operate the inlet valve is relatively

small, yet it is usual practice to make the rocker arm for the inlet valve of the

same dimensions as that for exhaust valve.

Fig.1.1 Rocker Arm

A typical rocker arm for operating the exhaust valve is shown in Fig.1.1

The lever ratio a / b is generally decided by considering the space available for

rocker arm. For moderate and low speed engines, a / b is equal to one. For high

speed engines, the ratio a / b is taken as 1/ 1.3.


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The various forces acting on the rocker arm of exhaust valve are the gas

load, spring force and force due to valve acceleration.

1.2 APPLICATION OF ROCKER ARM

1.2.1 Valve Gear Mechanism

The valve gear mechanism of an I.C. engine consists of those parts which

actuate the inlet and exhaust valves at the required time with respect to the

position of piston and crankshaft. Fig. 1.2 (a) shows the valve gear arrangement

for vertical engines. The main components of the mechanism are valves, rocker

arm,valve springs, push rod, cam and camshaft.

Fig.1.2 Valve gear mechanism

The fuel is admitted to the engine by the inlet valve and the burnt gases

are escaped through the exhaust valve. In vertical engines, the cam moving on

the rotating camshaft pushes the cam follower and push rod upwards, thereby

transmitting the cam action to rocker arm. The camshaft is rotated by the

toothed belt from the crankshaft. The rocker arm is pivoted at its centre by a

fulcrum pin.


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When one end of the rocker arm is pushed up by the push rod, the other

end moves downward. This pushes down the valve stem causing the valve to

move down, thereby opening the port.

When the cam follower moves over the circular portion of cam, the

pushing action of the rocker arm on the valve is released and the valve returns to

its seat and closes it by the action of the valve spring.

In some of the modern engines, the camshaft is located at cylinder head

level. In such cases, the push rod is eliminated and the roller type cam follower

is made part of the rocker arm. Such an arrangement for the horizontal engines

is shown in Fig.1.2 (b)


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CHAPTER 2

LITERATURE SURVEY

N. Lenin Rakesh [1] has been done the project to find out the stress

analysis of rocker arm and the hand crank by using finite element analysis

software ANSYS. The structure of the hand crank and rocker arm model was

performed using pro-E 4.0 version. Then finite element analysis are performed

using ANSYS. The tensile stress of rocker arm and torsional stress of hand

crank is calculated manually and is being compared with the experimentally

obtained results.

Siraj Sheikh [2] has been Rocker arm of Tata Sumo victa that was

designed and analyzed to find the critical regions. CAD models of Rocker Arm

was created using Pro/E and ANSYS V11software was used for analysis of

rocker arm. The CAD model was inputted in ANSYS Workbench and

Equivalent Stress and Maximum Shear Stress was found. The obtained results

provided by ANSYS Workbench are compared to the results obtained by

manual calculation.

Syed Mujahid Husain [3] has been optimized in rocker arm design and

material for better performance. This project present what rocker arm is, where

it is used and why it is used, History related to rocker arm and it working is

described. Various types of rocker arm used in vehicles and different materials

used for making rocker arm are studied in this project. Reasons for Failure of

rocker arm are also discussed in this project.

Mohd Hafiz Bin Ghazalli [4] has beenproject used the cam, rocker

arms, valve lifter, exhaust valve and accessories used in 4G13 engine in type.

Solidworks, Cosmosmotion and Algor software are used for determination of

stress concentration on the components.


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CHAPTER 3

ANALYTICAL DESIGN OF ROCKER ARM

3.1SPECIFICATIONS OF VALVE

We are going to design a rocker arm using analytical method of

calculation for that taking some standard specification are given on following

Table 3.1

Table 3.1 Specification of valve

Parameters Value

Diameter of the valve head 80 mm

Lift of the valve 25 mm

Mass of associated parts 0.4 kg

Angle of action of camshaft 110

Speed of the crankshaft 1500

Pressure on exhaust valves 0.4 N/mm2

Suction pressure 0.02 N/mm2

Angle between the two arms 135

3.2 DESIGN CALCULATION

First of all, the various forces acting on the rocker arm of the exhaust valve

shown in Fig. 3.2

Gas load on the valve,

P1 = (/4) dv2 pc

= (/4) 802 0.4

= 2011 N


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Weight of associated parts with the valve,

w = m g

= 0.4 9.8

= 3.92 N

Fig. 3.1 Layout of Rocker Arm

Total load on the valve,

P = P1+ w

= 2011 + 3.92

= 2014.92 N


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Initial spring force considering weight of the valve,

Fs = (/4) dv2 psw

= (/4) 802 0.23.92

= 96.6 N

The force due to valve acceleration (Fa) may be obtained as follows

Speed of camshaft

= N/2

= 1500/2

= 750 rpm

Angle turned by the camshaft per second

= (750/60) 360

= 4500 deg/s

Time taken for the valve to open and close,

t = (Angle of action of cam/Angle turned by camshaft)

= 110/4500

= 0.024 s

Maximum acceleration of the valve

a = 2 r = (2/t) 2 r

= (2/0.021)2 0.0125

= 857 m/s2


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Force due to valve acceleration, considering the weight of the valve,

Fa = m a + w

= 0.4 857 + 3.92

= 346.72 N

Maximum load on the rocker arm for exhaust valve,

Fe = P + Fs+ Fa

= 2014.92 + 96.6 + 346.72

= 2458.24 2460 N

Since the length of the two arms of the rocker are equal, therefore, the load at

the two ends of the arm are equal, i.e. Fe = Fc = 2460 N.

We know that reaction at the fulcrum pin F,

RF=

=

= 4545 N

3.2.1 Design of fulcrum pin

Let d1= Diameter of the fulcrum pin, and

l1= Length of the fulcrum pin

= 1.25 d1

Consider the bearing of fulcrum pin. Load on the fulcrum pin (RF),

4545 = d1 l1 pb


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= d1 1.25 d1 5 (pb= 5 N/mm2)

= 6.25 (d1)2

(d1)2 = 4545 / 6.25

= 727

d1= 26.97 30 mm

l1 = 1.25 d1

= 1.25 30

= 37.5 mm

Check the average shear stress induced in the pin. Since the pin is in double

shear, therefore, load on the fulcrum pin (RF)

4545 = 2 (/4) d12

= 2 (/4) 302

= 1414

= 4545/1414 = 3.2 N/mm2

This induced shear stress is quite safe,

External diameter of the boss,

D1= 2d1

= 2 30

= 60 mm


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Assuming a phosphor bronze bush of 3 mm thick, the internal diameter of the

hole in the lever,

dh = d1+ 2 3

= 30 + 6

= 36 mm

Check the induced bending stress for the section of the boss at the fulcrum

which is shown in Fig. 3.2

Fig. 3.2 Sectional view of Boss at fulcrum

Bending moment at this section,

M = Fe l

= 2460 180

= 443 103N-mm

Section modulus,

Z = [(1/12) 37.5 (603363)] (60/2)

= 17640 mm3


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Induced bending stress,

b = M/Z

= 443 103/17640

= 25.1 N/mm2

The induced bending stress is quite safe.

3.1.2 Design for fork end

Let d2= Diameter of the roller pin, and

l2= Length of the roller pin

= 1.25 d2

Consider bearing of the roller pin. Load on the roller pin (Fc),

2460 = d2 l2 pb

= d2 1.25 d2 7 (pb= 7 N / mm2)

= 8.75 (d2)2

(d2)2 = 2460 / 8.75

= 281

d2 = 16.76

18 mm

l2 = 1.25 d2

= 1.25 18

= 22.5 24 mm


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Check the roller pin for induced shearing stress. Since the pin is in double shear,

therefore, load on the roller pin (Fc),

2460 = 2 (/4) d22

= 2 (/4) 182

= 509

= 2460/509

= 4.83 N/mm2

This induced shear stress is quite safe.

The roller pin is fixed in the eye and thickness of each eye is taken as one-half

the length of the roller pin.

Thickness of each eye,

t2 = l2/2

=24/2

= 12 mm

Check the induced bending stress in the roller pin. The pin is neither simply

supported in fork nor rigidly fixed at the end. Therefore, the common practice is

to assume the load distribution as shown in Fig. 3.3.

The maximum bending moment will occur at YY. Neglecting the effect of

clearance, we have

Maximum bending moment at YY,

M = (Fc/2) [(lc/2) + (t2/3)][(Fc/2) (lc/4)]

= (2460/2) [(24/2) + (12/3)][(2460/2) (24/4)]


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= 12300 N-mm

Fig. 3.3 Sectional view of Roller End

Section modulus of the pin,

Z = (/32) d23

= (/32) 183

= 573 mm3

Bending stress induced in the pin

= M/Z

= 12300/573

= 21.5 N/mm2

This bending stress induced in the pin is within permissible limits.


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Since the radial thickness of eye (t3) is taken as d2 / 2, therefore, overall

diameter of the eye,

D2 = 2d2

= 2 18

= 36 mm

The outer diameter of the roller is taken slightly larger (atleast 3 mm more) than

the outer diameter of the eye.

In the present case, 42 mm outer diameter of the roller will be sufficient.

Providing a clearance of 1.5 mm between the roller and the fork on either side

of the roller, we have

l3 = l2+ 2 (t2/2) + 2 1.5

= 24+ 2 (12/2) + 3

= 39 mm

3.1.3 Design for tappet screwThe adjustable tappet screw carries a compressive load of Fe = 2460 N.

Assuming the screw is made of mild steel for which the compressive stress (c)

may be taken as 50 MPa.

Let d2= Core diameter of the taper screw

The load on the tappet screw (Fe)

2460 = (/4) dc2 c

= (/4) dc2 50

= 39.3 dc2


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dc2 = 2460 / 39.3

= 62.6 or

dc = 7.9

8 mm

Outer or nominal diameter of the screw,

d = dc/0.84

= 8/0.84

= 9.52 10 mm

We shall use 10 mm stud and it is provided with a lock nut. The diameter of the

circular end of the arm (D3) and its depth (t4) is taken as twice the diameter of

stud.

D3= 2 10 = 20 mm

t4 = 2 10 = 20 mm


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CHAPTER 4

FEM ANALYSIS OF ROCKER ARM

The data from the analytical calculation is used for modeling the rocker

arm, the CAD modeling is done on CREO Parametric 2.0 as shown in Fig. 4.1

Fig. 4.1 Rocker Arm modeled using Creo parametric

Then the model is imported to FEM Software, the FEM package used for

is ANSYS 14.0

4.1 ANALYSIS OF ROCKER ARM

There are four analysis are carried out in a Rocker arm

1. Total deformation2. Equivalent strain3. Equivalent stress4. Shear stress


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4.2 MATERIAL PROPERTIES

The material used for selected rocker arm is structural steel and the

properties of the material are presented in the Table 4.1

Table 4.1 Material Properties of Structural steel

Parameters Value

Density 7850 kg m-3

Youngs modulus 2E+5 MPa

Poissons Ratio 0.3

Bulk Modulus 1.6667E+5 MPa

Shear Modulus 7.6923E+4 MPa

Tensile yield strength 2.5E+02 MPa

Compressive yield strength 2.5E+02 MPa

Tensile ultimate strength 4.6E+02 MPa

4.3 DIMENSION OF ROCKER ARM

The Dimensions are obtained from the Analytical calculations done in

Chapter3 and arranged in Table 4.2

Table 4.2 Dimensions of Rocker Arm

Parameters Value

Diameter of the fulcrum pin 30 mm

Length of the fulcrum pin 37.5 mm

External diameter of the boss 60 mm

Diameter of the roller pin 18 mm


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Length of the roller pin 24 mm

Thickness of each eye 12 mm

Overall diameter of the eye 36 mm

Core diameter of the tappet screw 8 mm

Diameter of circular end of arm 20 mm

Depth circular end of arm 20 mm

4.4 MESHING

The mesh is done by default mesh element of ANSYS 14.0 using fine

mesh settings. The meshing must be very fine for obtain the highly accurate

analysis answer as shown in Fig. 4.2.

Fig. 4.2 Meshed model

4.5 LOADS AND BOUNDARY CONDITIONS

As shown in the Fig. 4.3 the loads and boundary conditions are assigned,

the analysis are carried out in without gravity settings.


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Fig. 4.3 Boundary condition applied model

4.6 RESULTS

Following four results are produced using ANSYS

1. Total deformation2. Equivalent strain3. Equivalent stress4. Shear stress

4.6.1 TOTAL DEFORMATION

The total deformation is obtained as shown in Fig. 4.4

Fig. 4.4 Total deformation


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4.6.2 EQUIVALENT STRAIN

The Equivalent Strain is obtained as shown in Fig. 4.5

Fig. 4.5 Equivalent strain

4.6.3 EQUIVALENT STRESS

The Equivalent Stress is obtained as shown in Fig. 4.6

Fig. 4.6 Equivalent stress


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4.6.4 SHEAR STRESS

The Shear Stress is obtained as shown in Fig. 4.7

Fig. 4.7 Shear stress


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CHAPTER 5

CONCLUSION

The analytical design calculation has been calculated and then 3D

modeling of the Rocker arm is done by using Creo parametric 2.0 software. The

modeling was done using Creo by the help of the calculated parameters and the

values. The stress analysis of the Rocker arm was found out manually by using

formula and data taken from the Design data book, and then the specified stress

concentration was analyzed by using ANSYS. The result found was compared

with the values found out manually. The compared result was found

satisfactory.

From this project, it was found that the analytical calculations of new

section are more effective than that of older section.


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REFERENCES

1.N. Lenin Rakesh, A. Thirugnanam and Jitesh Mishra Stress Analysis ofHand Crank and Rocker ARM Middle-East Journal of Scientific Research

12 (12): 1687-1689, 2012, ISSN 1990-9233

2. Syed Mujahid Husain, Prof.Siraj Sheikh Rocker Arm: - A ReviewInternational Journal of Innovative Research in Science, Engineering and

Technology Vol. 2, Issue 4, April 2013, ISSN: 2319-8753

3. Syed Mujahid Husain, Siraj Sheikh Design and Analysis of Rocker ArmInternational Journal of Mechanical Engineering and Robotics Research.

Vol. 2, No. 3, July 2013, ISSN 22780149.

4.Mohd Hafiz Bin Ghazalli Finite Element Analysis Of Cam And ItsFollower Contact Stress Mechanism.

5.Khurmi R S and Gupta J K (2011), I.C Engine Parts, Machine Design, pp.584-589 and 1192-1195.

6.Dong-Woo Lee, Soo-Jin Lee, Seok-Swoo Cho and Won-Sik Joo (2005),Failure of Rocker Arm Shaft for 4-Cylinder SOHC Engine, Engineering

Failure Analysis,Vol. 12, No. 3, pp. 405-412.

DESIGN AND ANALYSIS OF ROCKER ARM

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