Internal combustion engine is a device converting the energy of a fuel-air mixture burning within a combustion chamber into mechanical energy.
Reciprocating internal combustion engine is an engine, in which burning process occurs within a cylinder equipped with a piston driven by the pressure of the combustion gases. The gas pressure force is transmitted to the crankshaft linked to the piston by means of a connecting rod. Such mechanical device called crank mechanism transforms the alternating linear motion of the piston into the rotation of the shaft.
Reciprocating engines are the most common type of internal combustion engines.
The figure below presents a scheme of a typical four-stroke reciprocating combustion engine.
The engine consists of four cylinders in different phases of the engine cycle (intake, compression, expansion and exhaust). Each cylinder has an inlet and exhaust valves, opening and closing of which is controlled by the cam mechanism.
Each piston is joined to the crank pin of the crankshaft though the connecting rod.
The four-stroke cycle:
Bearing is a device supporting a mechanical element and providing its movement relatively to another element with minimum power loss.
The rotating components of internal combustion engines are equipped with sleeve type sliding bearings.
The reciprocating engines are characterized by cycling loading of their parts including bearings. Such character of the loads is a result of alternating pressure of combustion gases in the cylinders.
Rolling bearings, in which a load is transmitted by rolls (balls) to a relatively small area of the ring surface, can not withstand under the loading conditions of internal combustion engines.
Only sliding bearings providing a distribution of the applied load over a relatively wide area may work in internal combustion engines.
The sliding bearings used in internal combustion engines:
Purposes of lubrication of engine bearings are as follows:
Engine bearings generally work in hydrodynamic regimes of friction.
Hydrodynamic friction implies the presence of a continuous lubricant film between the bearing and journal surfaces (Hydrodynamic journal bearing).
Constant supply of a lubricant (oil) in sufficient amounts is necessary for normal work of engine bearings.
Bearings lubrication is provided by the lubrication system.