Finite Element Analysis of a Rocker Arm

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Finite Element Analysis of a Rocker Arm

 

  1. Component Description

 

1.1.            Component Function

The rocker arm is an oscillating,  two-arm lever that provides a means of actuating the valves in the combustion chamber of an internal combustion engine. It translates the radial motion of the profile of the cam lobe through a fulcrum into linear motion for opening and closing the intake and exhaust valves.  It also provides a means of multiplying the lift ratio.

During operation, the rocker arm experience stresses and undergo deflection. Severe rocker arm deflection causes inefficient engine performance, and often results in metal fatigue leading to increased wear and friction in the valve train and eventually engine failure.


Figure 1: Diesel engine valve train showing rocker arm (1)

1.2.            Component Geometry

The rocker arm is a two-arm lever that pivots about a fulcrum. One end is connected to the push rod which rests over cams on the camshaft, while the other acts on the spring-loaded valve stem and pivoted on the rocker shaft.

Figure 2:(From left) 3-D model of the rocker arm and the 2-D geometry

 

1.3.            Service Loading

The rocker arm is subjected to compressive load at the fulcrum on the rocker shaft during the opening and closing of the valves.  The forces acting at the valve end (FE) include; the gas back pressure on the valve, the spring force and the force due to valve acceleration. There is also the load at the cam end, (FC) which is transmitted to the rocker arm through the push rod.

Figure 3: Free Body Diagram of Rocker arm depicting the location of the acting forces: FE and FC

  1. Methodology (154)

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