What are Tie Rods and its Function?
For better understanding the use of tie rods and tie bolts let us first understand what is happening inside the cylinder of an IC Engine. The processes that take place inside an IC engine are Suction, Compression, Expansion, Exhaust. Do refer to this article for further information if needed.
When the piston is just after the top dead centre the pressure generated inside the cylinder above the piston head can rise up to 140 bar (14000kN/m2). This pressure exerts a force downwards through the piston rod and con-rod and pushes the crankshaft down into the bearing pockets. Parallelly, the pressure exerts force upwards as well, trying to lift open the cylinder cover. Since the presence of the cylinder head studs screwed into the entablature tends to prevent this from happening hence the upward acting force tries to separate the entablature from the frames and the frames from the bedplate, therefore, putting the fitted location bolts into tension.
When the piston moves downwards the pressure inside the cylinder falls then rises again when the piston changes direction and moves upwards during the compression stroke. This puts the fitted bolts under cyclic stresses which they are not designed for hence they fail.
Therefore tie rods, a long rod with bolts at both the ends are fitted through the bedplate, frames and entablature then tightened hydraulically in order to hold them firmly together in compression, and to transmit the firing forces back to the bedplate. The tie rods are positioned close to the centre of the crankshaft to prevent excessive bending moments in the transverse girders.
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Authored By:- Cdt. Subham Samantaray, TMI