Chapter II - The engine and the engine components

The engine

It represents the power machine by means of which the thermal energy released by burning a fuel is transformed into mechanical energy. In most cases, the engines used in automobiles are internal combustion piston engines.

The main performances of internal combustion engines are:

• high power;
• reduced size and weight;
• reduced fuel consumption;
• durability and reliability;
• operational safety.

​According to the way the fuel mixture is ignited, the internal combustion engines are classified as:

• spark-ignition engines (SI engines – these engines use petrol as fuel, which ignites due to the spark produced by the spark plug);
• compression-ignition engines (CI engines – these engines use diesel fuel, which ignites by compression).

The components of the engine

The engine components are:

• A. The engine mechanism: its role is to transform the rectilinear–reciprocating motion of the piston into a rotational motion of the crankshaft. The engine mechanism is also called the connecting rod–crank mechanism;
• B. Auxiliary systems and installations: their role is to ensure the functioning of the engine.

A. The engine mechanism

It consists of:

• fixed parts (the engine block, the cylinder head, the oil pan, the cylinders);
• moving parts (the crankshaft, the flywheel, the connecting rods, the pistons, the rings, the pins).

The engine block (or the cylinder block)

It represents the main element, in which all the other components of the propulsion system (crankshaft, spark plugs, pistons, etc.) are gathered together.

At the upper part of the engine block, the cylinder head is mounted, which tightly closes the combustion, cooling, lubrication compartments, etc.

In the lower part, the engine block is closed with the oil pan. The engine block is fixed to the body of the motor vehicle and also to the housing of the gearbox.

The cylinder head

It is a component of the propulsion system; together with the piston and the cylinder, it forms the closed space in which the engine fluid evolves.

In the cylinder head are placed, as the case may be, the combustion chamber, the gas distribution channels and the openings for spark plugs or injectors.

The cylinder head also represents the mounting place of some parts from the distribution mechanism.

The oil pan

It is a metallic element whose role is to collect and store the engine oil.

The oil pan is positioned under the engine block, the collecting of the oil being ensured by the pressure in the system, generated by the oil pump, but also by gravity.

The crankshaft

It is also called the engine shaft and its role is to transform, together with the connecting rod, the translational motion of the piston group into rotational motion.

It receives the motion from the piston through the connecting rod and transforms it into rotational motion, which it transmits outside for driving various subassemblies of the engine and to the vehicle transmission for self-propulsion.

The crankshaft has a number of main journals equal to the number of cylinders plus one. The main journals are placed on the same geometric axis, and their width is different.

The cylinders

They represent the working space in which the engine cycle takes place, the piston moving inside them in a rectilinear–reciprocating motion.

The cylinders can be removable or non-removable, and according to the cooling method they can be wet or dry; the non-removable ones are always wet. The mounting of the cylinders in the engine block is done by pressing.

The flywheel

It is a metal disc having multiple roles:

• it significantly reduces the shock-type stresses at the level of the engine parts, its supports and the transmission. These shock stresses appear precisely due to the variation of the angular speed of the crankshaft;
• it plays an important role in balancing the functioning of the engine;
• it provides the friction surface for the clutch disc.

The connecting rod

It transforms the rotational motion into linear motion and/or vice versa.

The connecting rod is part of the engine mechanism and its role is to take over the pressing force of the piston and transmit it to the crankshaft.

The piston

It is a cylindrical metal body, having the upper flat face as the closing surface of the volume it forms part of, and the lower flat face used for assembly with the connecting rod.

The motion of the piston is rectilinear–reciprocating in a cylinder and serves to close a variable-volume space filled with a fluid under pressure.

The pistons are used for taking over the energy resulting from the explosion of the fuel and transforming it into mechanical work.