CHAPTER 1 - PART 1 - THE ENGINE AND ITS COMPONENTS

THE ENGINE

The engine is the assembly that converts the thermal energy released by fuel combustion into mechanical energy used to propel the motor vehicle. In the construction of automobiles, reciprocating internal combustion engines are primarily used.

The main characteristics of internal combustion engines are:

• high power output;
• relatively compact dimensions and low mass;
• efficient fuel consumption;
• durability and reliability;
• good performance under various operating conditions.

Engine classification

Depending on how the air-fuel mixture is ignited, engines are classified as:

• spark-ignition (SI) engines - use petrol, with ignition provided by a spark plug;
• compression-ignition (CI) engines - use diesel fuel, with ignition resulting from air compression and fuel injection.

ENGINE COMPONENTS

The engine consists of two main categories of components:

• A. crank mechanism (slider-crank mechanism);
• B. auxiliary systems, which enable the engine to operate (lubrication, cooling, fuel supply, exhaust, etc.).

A. CRANK MECHANISM

The crank mechanism converts the reciprocating linear motion of the piston into the rotational motion of the crankshaft.

It consists of:

• Stationary components: the engine block, cylinder head, oil sump and cylinders. These support and guide the moving components;
• Moving components: the piston, piston rings, piston pin, connecting rod, crankshaft and flywheel. These components are directly involved in converting motion and in the mechanical operation of the engine.

Engine block (cylinder block)

The engine block is the main structural component of the engine, housing its principal components (crankshaft, cylinders, pistons, etc.).

The cylinder head is mounted on top of the engine block, sealing the combustion chambers, while the oil sump is mounted underneath.

The engine block is secured to the motor vehicle structure and connected to the gearbox.

Cylinder head

The cylinder head closes off the top of the cylinders and, together with the piston and cylinder, forms the combustion chamber.

The cylinder head contains:

• intake and exhaust ports;
• mounting holes for spark plugs (in SI engines) or fuel injectors (in CI engines);
• valve train components.

Oil sump

The oil sump is a reservoir mounted beneath the engine block that collects and stores the engine oil.

The oil returns to the sump by gravity and is circulated through the engine by the oil pump.

Crankshaft

The crankshaft, acting through the connecting rod, converts the reciprocating linear motion of the piston into rotational motion.

This rotational motion is transmitted to the motor vehicle's drivetrain to propel the motor vehicle, and also to the engine's auxiliary systems.

The crankshaft is supported at its main journals, which are aligned along a common axis.

Cylinders

The cylinders provide the working space in which the engine cycle takes place. Inside them, the piston performs a reciprocating linear motion.

Cylinders can be:

• integral with the engine block;
• removable, in the form of cylinder liners.

Cylinder liners can be wet or dry, depending on whether they are in direct contact with the coolant.

The flywheel is a metal disc mounted on the crankshaft that performs several functions:

• reduces shock loads transmitted to the engine components, engine mounts and drivetrain;
• helps maintain more uniform crankshaft rotation by reducing the effects of variations in angular velocity;
• has an important role in balancing the engine's operation;
• provides the friction surface for the clutch disc.

Connecting rod

The connecting rod links the piston to the crankshaft.

Its function is to transmit force from the piston to the crankshaft and, together with the crankshaft, convert reciprocating linear motion into rotational motion.

Piston

The piston is a cylindrical metal component that moves back and forth in a straight line inside the cylinder.

Its upper part helps enclose the working volume, while its lower part allows it to be attached to the connecting rod.

The piston encloses a space of variable volume in which pressurised fluid acts on it, with the resulting force transmitted to the connecting rod.

Piston rings

Piston rings are fitted to the piston and perform the following functions:

• seal the combustion chamber;
• prevent gases from entering the crankcase;
• help control and distribute oil on the cylinder walls.