Motor Car

I

Introduction

Motor Car, any self-propelled vehicle with more than two wheels and a passenger compartment, capable of being steered by the operator for use on roads. The term is used more specifically to denote any such vehicle designed to carry a maximum of seven people.

The primary components of a car are the power plant, the power transmission, the running gear, and the control system. These constitute the chassis, on which the body is mounted. The power plant includes the engine and its fuel, the carburettor, ignition, lubrication, and cooling systems, and the starter motor.

II

How Car Engines Work

A

Four-Stroke Cycle

The overwhelming majority of car engines still employ the four-stroke cycle (four piston strokes per cycle), invented by Nicholas Otto in 1876.

The first downstroke of the piston that is attached to a connecting rod at its top end and to the crankshaft at the bottom, draws a petrol-air mixture into the cylinder. This is then compressed, which is the second stage of the process. The volatile cocktail is then ignited by a sparking plug and the resulting explosion forces down the piston, so turning the crankshaft. The final phase of the operation is the stroke that expels the exhaust gases from the cylinder.

B

Cylinder Head

The engine’s cylinder block is invariably made of cast iron on to which is bolted an aluminium cylinder head. This contains the valves that permit the petrol-air mixture to enter the combustion chamber and the exhaust gases to leave it. These can be actuated by pushrods from a block-located crankshaft-driven camshaft, although the head more usually incorporates single or twin “overhead” camshafts driven by a ribbed rubber belt.

C

Fuel Injection

A carburettor had been used from the earliest days of motoring as a component in which the petrol-air mixture was created. The limitation of such an arrangement was that the mixture was unevenly distributed which resulted in incomplete combustion and an undesirable amount of unburnt fuel reaching the atmosphere.

As a result, the carburettor has now been replaced by fuel injection. This first appeared on high-performance cars in the 1950s. Not only is a precise amount of metered petrol delivered by pump to each cylinder, but the air supply can also be carefully controlled by the use of an individual inlet manifold.