connectingroddesign.ppt

* * Design of IC Engine Connecting Rod * Dr.M.Senthil kumar Introduction: Intermediate member between the piston and the crankshaft. Transmits the push and pull from the piston pin to the crankpin Converts the reciprocating motion of the piston into the rotary motion of the crank. Combustion forces try to compress it and when the piston stops at the top of the cylinder, inertia forces try to pull it apart. * Connecting Rod Parts: It consists of long shank, a small end and a big end. Small end : Made in the form of an eye, provided with a Phosphor bronze bush Big end: Usually made spilt One half is fixed with CR and the other (cap) is fastened with two cap bolts. Bearing shells of big end are made of steel, brass or bronze with a thin lining of white metal or babbit metal. * * The cross-section of the shank: Rectangular, Circular, Tubular, I-section or H section Circular section – Low speed engines; I-section : High speed engines * * CR – Manufactured by Drop forging It should have adequate strength, stiffness and minimum weight Materials: Mild carbon steels (0.35 – 0.45 % C) to alloy steels ( Cr-Ni, Cr-Mb) Industrial Engines: Carbon steel (0.35 %) –750 MPa (when heat treated) Aeroengines and Automobiles: Alloy steels – 1050 MPa Lubrication: Splash and Pressure Lubricating Systems Length (l) of CR depends upon l/r Smaller l will decrease l/r. This increases the angularity of CR which increases the side thrust, hence more wear of liner. Larger l will increase l/r. This decreases the side thrust and leads to less wear. But, increases overall height of the engine. Therefore, a compromise has to be made. Generally, l/r = 4-5. Forces acting on the Connecting Rod: Force on the piston due to gas pressure and inertia of the reciprocating parts. Force due to inertia of the connecting rod or inertia bending forces. Force due to friction of the piston rings and or the piston. Force due to friction of the piston pin bearing and the crankpin b