Int. J. Mech. Eng. & Rob. Res. 2013 Syed Mujahid Husain and Siraj Sheikh, 2013
ISSN 2278 – 0149 www.ijmerr.com Vol. 2, No. 3, July 2013 © 2013 IJMERR. All Rights Reserved Research Paper
DESIGN AND ANALYSIS OF ROCKER ARM
Syed Mujahid Husain1* and Siraj Sheikh1
*Corresponding Author: Syed Mujahid Husain, [email protected]
In this paper we discussed about 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.
Keywords: Design and analysis, Rocker arm, CAD models, ANSYS
INTRODUCTION lobe into linear movement at the poppet valve A rocker arm is a valve train component in to open it. One end is raised and lowered by a internal combustion engines. As a rocker arm rotating lobe of the camshaft (either directly or is acted on by a camshaft lobe, it pushes open via a tappet (lifter) and pushrod) while the other either an intake or exhaust valve (Yu and Xu, end acts on the valve stem. When the camshaft 2006; and Chin-Sung and Ho-Kyung, 2010). lobe raises the outside of the arm, the inside This allows fuel and air to be drawn into the presses down on the valve stem, opening the combustion chamber during the intake stroke valve. When the outside of the arm is permitted or exhaust gases to be expelled during the to return due to the camshafts rotation, the exhaust stroke. Rocker arms were first invented inside rises, allowing the valve spring to close in the 19th century and have changed little in the valve (Chin-Sung and Ho-Kyung, 2010). function since then. Improvements have been made, however, in both efficiencies of operation The drive cam is driven by the camshaft. and construction materials (Yu and Xu, 2006; This pushes the rocker arm up and down and Dong-Woo et al., 2005 and 2008). about the pin or rocker shaft. Friction may be reduced at the point of contact with the valve WORKING stem by a roller cam follower. A similar The rocker arm (Figure 1) is an oscillating lever arrangement transfers the motion via another that conveys radial movement from the cam roller cam follower to a second rocker arm.
1 Department of Mechanical Engineering, G H Raisoni Academy of Engineering & Technology, Maharashtra, India.
191 Int. J. Mech. Eng. & Rob. Res. 2013 Syed Mujahid Husain and Siraj Sheikh, 2013
Figure 1: Rocker Arm SPECIFICATION The rocker use for our experimentation is of Tata sumo victa which fails during it services. Cracked rocker arms are occasionally reported during routine inspections. The type, power and other engine specification are given in following Table 1. The material of rocker arm is forged steel. Design specification or design sheet of Rocker arm This rotates about the rocker shaft, and is shown in Figure 3. transfers the motion via a tappet to the poppet Table 1: Engine Specification valve. In this case this opens the intake valve of Sumo Victa to the cylinder head. The following figure Engine Specification (Figure 2) shows the rocker arm in valve train Type Turbo-Charged, Water Cooled, mechanism with cam at one end and valve Direct Injection Diesel Engine stem at the other end of rocker arm. No. of Cylinders 4-inline Bore/Stroke 97 mm x 100 mm Figure 2: Rocker Arm Capacity 2956 cc Max. Engine Output 51.5 kw at 3000 rpm Max. Torque 223 N-m at 1600-2200 rpm
Figure 3: Rocker Arm Design Specification
METHODOLOGY Let,
mv = Mass of the valve,
dv = Diameter of the valve head,
192 Int. J. Mech. Eng. & Rob. Res. 2013 Syed Mujahid Husain and Siraj Sheikh, 2013
h = Lift of the valve, w = 0.882 N a = Acceleration of the valve, Total load on the valve, P = P + w Pc = Cylinder pressure or back pressure, 1 = 502.4 + 0.882 Ps = Maximum suction pressure, P = 503.282 N d1 = is diameter of fulcrum pin, • Initial spring force considering weight of the D1 = is diameter of boss, valve, l = Length of arm, F = /4 (d )2 P – w = angle between two arms. s v s = /4 x (40)2 x 0.02 – 0.882 We have, F = 24.238 N m =.09 kg s v • The force due to valve acceleration (F ) may d = 40 mm a v be obtained as discussed below: h =13 mm We know that speed of engine 3000 RPM r = 13/2 The speed of camshaft = N/2 = 6.5 mm = 3000/2 =.0065 m = 1500 r.p.m
2 Pc = 0.4 N/mm and angle turned by the camshaft per 2 second Ps = 0.02 N/mm = (1500/60) X 360 d1 = 8 mm = 9000 deg/s D1 = 18 mm Speed of engine = 3000 RPM Time taken for the valve to open and close, Angle of action of cam = 110° t = Angle of action of cam Calculating Forces Acting Angle turned by camshaft • We know that gas load on the valve, = 110/9000 P = /4(d )2 P 1 v c t = 0.012 s = /4 x (40)2 x 0.4 We know that maximum acceleration of the 2 P1 = 502.4 valve a = · r Weight of associated parts with the valve, = (2/t)2 · r w = m · g = (2/0.012)2 X 0.0065 = 0.09 x 9.8 a = 1780.2 m/s2
193 Int. J. Mech. Eng. & Rob. Res. 2013 Syed Mujahid Husain and Siraj Sheikh, 2013
Force due to valve acceleration, R 2 d considering the weight of the valve, f 4 1 F = m · a + w a where, = 0.09 × 1780.2 + 0.882 d1 is diameter of fulcrum pin (d1 = 8 mm) F = 161.1 N a 1272 4. 2 8 Now the maximum load on the rocker arm 4 for exhaust valve, = 13.69 N/mm2 Fe = P + Fs + Fa This shear stress is critical. = 503.282 + 24.238 + 161.1 • Calculating bending stress of cross section. Fe = 688.62 N Since the length of the two arms of the The Rocker arm may be treated as a simple rocker are equal, therefore, the load at the supported beam and loaded at the fulcrum point. Therefore, due to the load on the valve two ends of the arm are equal, i.e., Fe = Fc = 688.62 N. the rocker arm is subjected to bending moment. • We know that reaction at the fulcrum pin We know that maximum bending moment 2 2 (M) of cross section, Rf Fe Fc 2Fe Fc cos
2 2 D R 688 2. 688 2. 2 688 2. 688 2. cos176 1 f M Fe l 2
Rf = 1376.43 N 18 Figure 4: Forces Acting on Rocker Arm 688.6227 2
M =12387.96 N-mm The rocker arm is of I-section Section module Z,
/1 12 5.2 t 6t 3 5.1 t 4t3 Z 6t / 2 Where t is thickness Z = 332.91 mm3
Calculating Stresses Bending stress,
• Calculating shear stress at the pin M b We have, load on the fulcrum pin Rf Z
194 Int. J. Mech. Eng. & Rob. Res. 2013 Syed Mujahid Husain and Siraj Sheikh, 2013
M12387.96 Figure 7: Equivalent Stress 332.91
2 b = 37.2 N/mm This bending stress is near to critical limit (i.e., 40/mm2).
ANALYTICAL RESULTS With the given design specification in Figure 3 following CAD model of Rocker is prepared on ProE. Figure 5 shows the CAD model of Rocker arm of sumo victa. Figure 8: Maximum Shear Stress Figure 5: CAD Model of Rocker Arm
Force Acting at the Exhaust Valve Reaction Force Acting at the Pin End of Rocker Arm First we will find the analytical results when Now when maximum load (Fe = 688.62 N) is Reaction force (Rf =1376.43 N) is acting at acting on the rocker arm for exhaust valve arm the fulcrum pin. end.
Figure 6: Reaction Force Acting at the Pin Figure 9: Force Acting at the Exhaust Valve End of Rocker Arm
195 Int. J. Mech. Eng. & Rob. Res. 2013 Syed Mujahid Husain and Siraj Sheikh, 2013
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