Body Types

There are five common body styles for light weight passenger vehicles, the main purpose of these is to provide comfort and safety for those inside as well as being a load bearing structure. Most cars are made by 'Unitary Construction' (chassis-less) with all the components assembled within.
This means cars can be mass produced, often with pressed steel bodies although this is heavier than the increasingly popular aluminium body. Hand made cars, F1 cars and more expensive sports cars are occasionally moulded from GRP (fibreglass) which is primarily a glass reinforced plastic, which is very light and strong, although very expensive.
Steel bodies have the advantage of being painted and treated and are therefore rust resistant and is generally more appealing to the eye as well as being relatively cheap.

The most common five styles of LPV are Estate, saloon, coupe, convertible and hatchback.

Saloon:


BMW M3

A very common style which typically carries 4 - 5 passengers, with either 2 or 4 passenger doors, the design is based on three 'boxes' the front box being the engine section, the middle for the passengers and the rear box for the boot (storage). Theses 'boxes' are blended together and the passenger shell strengthened with the front and rear sections providing 'crumple zones' which cushion damage and shock on impact to keep the passenger section in tact.

Estate:


Classic Estate - Volvo 240

(aka station wagon) has a larger interior than than most cars as the roof is extended to the rear creating a large boot area which can take large loads or extra seats very easily as well as having stronger suspension added to the rear to contain these loads.


Coupe:


A Modern Day Coupe - 2 door Mercedes Benz CL600

a coupe often has a rigid roof section and two doors although some have two very small seats in the back, these are often only suitable for children, this design is primarily for carrying two passengers including the driver, and as such is smaller and more sporty looking.

Convertible:


The king of the convertible: E-Type Jaguar

(aka cabriolet or drop-head coupe) this design has a mechanical or fabric roof which can be removed to form an open car, often used in hot countries. Although the increased drag caused by removing the roof can often cause minor handling problems, making the car under or over steer in corners as the aerodynamics are different.

Hatchback:


Peugeot 307

Very similar to the saloon, however the trunk (boot) is moulded into the centre section of the car, very popular due to its versatility, again containing 4 passengers and often with 4 doors and a fairly sizable storage area, larger than the saloon but smaller than an estate.

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Alternator Diode

The alternator is a form of generator. When the engine runs, this generator provides electrically energy to charge the cars battery. This provides electrical energy for the electrical systems within the vehicle as well as keeping the battery fully charged. (a Dynamo generator is used occasionally but an alternator is fitted in most common vehicles.) The generator must change the mechanical (kinetic) energy into electrical energy.
In very simple terms an alternator works by electromagnetic induction (try researching faraday's laws) the mechanical energy in this system is used to rotate a magnet within a 'stator' (often soft iron) usually with a multi phase output, meaning more electrical energy is created more frequently.

The energy this alternator provides must be limited roughly to the voltage of the battery (around 14.2 Volts) however as the engine rotates faster, as will the magnet within the stator and so more energy will be produced which must be controlled to prevent damage to electrical components or overcharging.
An alternator diode is a solid device which allows current in the circuit to flow in only one direction and are highly sensitive to both heat and voltage therefore they are used to prevent surges which can damage the battery and regulator. This diode provides a similar protection to these kind of conditions as a conventional fuse protects against current surges within a common home plug.

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Four Stroke Engine

Animation of a four stroke cycle

A four stroke engine is the most common internal combustion engine of modern times. It uses a spark ignition system which is very similar to the compression ignition in a diesel engine. The 'four - stroke' is so called as it applies driving power and supplies force through four 'strokes' which, amongst other things, applies fuel, compresses it, lights it, provides a driving force as well as pushing out the exhaust gases. (To under stand the following you will have to understand the basic layout and terminology of a reciprocating engine if you don't know do a Google image search or try Wikipedia for a good diagram of a cylinder.)

THE FIRST STROKE: Fuel Induction


Image of the first: intake stroke

In the first stroke the piston moves downwards within the cylinder, this downward movement creates pressure which opens the inlet port and closes the exhaust port (at the top of the cylinder) The sucking effect of the piston moving down pulls a mixture of air and fuel into the cylinder, this is inducing the fuel. As the piston reaches its BDC (bottom dead centre) this is the end of the first stroke, the inlet and exhaust ports are closed and the mixture of fuel and air is sealed within the cylinder.

THE SECOND STROKE: Fuel Compression


Image of the second: Compression stroke

In the second stroke, the piston is moving upwards from its BDC to its TDC (Top dead centre) this is an upward motion providing an upward force which compresses the fuel, both ports stay closed at the top of the cylinder throughout the stroke, maintaining the pressure to compress the fuel.

THE THIRD STROKE: Ignition and Power


An image of the third (power) stroke

The third stroke or 'the power stroke' is what provides the kinetic energy which powers the engine. In this stroke the piston moves in the same way as it does in the induction stroke (stroke one), from the TDC to the BDC, This time however both ports remain closed. Due to the compression in the previous stroke, the fuel is very hot, compressed at the top of the cylinder. At this point, in a petrol engine, a spark is applied to the fuel which then burns very rapidly into a high pressure gas forcing the pison down the cylinder and providing the force which powers the engine and is what moves the piston throughout the other strokes in the cycle, the stroke ends with the piston at its BDC and both ports closed.

THE FORTH STROKE: Exhaust release


Image of the forth stroke of the cycle: Exhaust

In this stroke the piston moves from its BDC to TDC providing an upwards force and the exhaust port opens. With the piston moving up and the port open, the burnt gas mixture is forced out of the cylinder through the port. When the piston reaches its TDC and all the fuel has been released the exhaust port closes and the inlet opens ready for the fuel induction which follows straight away.

This system is for a four stroke petrol engine, in a diesel however it works slightly differently. During the first stroke in a diesel, the engine draws in a charge of air only which is then compressed and reaches high temperature, then during the third stroke high pressure diesel is injected into the air creating a combustible mixture which is ignited by the temperature of the air which burns. Other than those two differences, the diesel four stroke works exactly as a petrol four stroke engine.

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