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Summary: In this guide you will learn basically how a car works.
How a car works
Introduction
Even those of you with little or no knowledge of the workings of a car have a basic understanding of its principals.On a very basic level you fill the tank with petrol, get in, put your key in the ignition, start it up, put it in gear and drive off.
In order for this to happen, a great many parts, some large and others small and intricate all work together in harmony and so with this in mind it is easy to understand how just one small problem with any of these components can cause a car to stop functioning.
For someone with very little knowledge in mechanics to understand how all of these components work together, we will take it back to the beginning and start with what power sources are required.
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Where does a cars electrical supply come from?
An electrical charge is essential to any car, new or old as without it you would not be able to create the spark necessary to ignite the fuel and power the car, turn on the head lights, use the indicators or even turn on the stereo.In order to create this constantly available supply of electrical charge, a car uses a battery. In order to maintain that charge and in turn the electrical current that flows around the car and supplies every powered device and component, the battery is being constantly topped up by the alternator so that it does not run flat.
Now that we have established how an electrical charge is created I will now explain how it is used and how it enables a car to start and run. For this, we will start with the ignition system.
Ignition stages and key position
The first stage of the ignition (when you insert the key and turn it once) is the “Off” stage (the stages sometimes do vary between manufacturers). This is rather self explanatory as all of the cars electrical systems are off. However, there are still a number of systems that will work, mainly for safety reasons such as the lights, horn, interior light, door locks (if the car has central locking), hazard warning lights etc….The second stage (sometimes marked Acc for Accessories) generally activates the more non-essential functions such as the stereo, heating blowers, electric windows, powered aerial etc….
The third and final stage activates all of the cars electrical systems and if everything is functioning as it should, the car will start.
What happens when you turn the key?
When the key is turned all the way around to the final “engine start” position (clockwise) it completes an electrical circuit which in turn supplies an electrical charge to the spark plugs, supplies power to the fuel pump which pumps fuel to the combustion chamber and activates a solenoid (a switch mechanism made from a coil of wire and a metal core) on the starter motor.NOTE: all cars work on DC or Direct Current meaning that the current travels in only one direction from the Negative to the Positive battery terminal.
The starter motor itself is an electric motor which has a gear attached to the end of a protruding shaft. The solenoid causes the motor to spin and in turn, the gear on the end of the motor’s shaft which then meshes with the flywheel (the large gear situated on the front of the engine) and turns the engine over in order for it to fire (start).
NOTE: it’s also worth mentioning that the internal workings of the starter motor (primarily the shaft and gear) are based around the idea of centrifugal force as when the engine is actually running the starter motor should not be constantly engaged with the flywheel as this would decrease its life span considerably.
To remedy this problem the starter’s shaft and gear are several inches shorter than the geared edge of the flywheel. When the starter motor receives a current, the rotational action and the weight of the gear cause the shaft to extend the necessary several inches to mesh with the flywheel and thus spin the engine over.
When the engine fires and you let go of the ignition key, the spring action in the ignition barrel causes the key to jump back to the “On” ignition step and in turn tells the starter that it has done its job and cuts its electrical current and causes the shaft to detract back, disengaging it from the flywheel.
What else has to happen?
Ignition System
The activation of the starter motor is only part of a more global process. There are a number of other things that must also happen.For the car to start, the spark plugs must receive an electrical charge, in order to create a spark that will ignite the fuel/air mixture that is pumped to each of the engines cylinders (sometimes called a combustion chamber). All of this must happen at precisely the right time and in the correct order. If the timing of the spark or firing order of the cylinders is out by even a thousandth of a second this will cause the engine to miss and run inconsistently and in extreme cases, not at all.
NOTE: you may expect a four cylinder engine (generally, the most common type) to fire in the order of cylinders 1 – 4, but this is not the case. The firing pattern for this type of engine is mostly 1,3,4,2 (except for Ford engines that fire 1,2,4,3)
The ignition system sends a very high voltage (usually 20,000+ volts) charge to the spark plug for each cylinder just before the piston for that cylinder has reached top, dead centre (the highest point that the piston can reach before it begins another cycle). This way, it is ensured that the piston will receive the maximum amount of down force at the pinnacle time making the engine as efficient as possible.
The voltage supplied by the ignition system travels down through the spark plug (from top to bottom) to its base where there is a gap.
To create the spark, the charge must jump this gap in order for it to ground (earth) and thus ignites the fuel/air mixture in the cylinder.
NOTE: each spark plug is screwed into the cylinder head. The cylinder head itself is bolted to the top of the engine block and allows the base of each spark plug to protrude down into each of the engines cylinders enabling it to ignite the fuel/air mixture that has been supplied to that cylinder.
Fuel System
At the same time that a charge is supplied to each spark plug, fuel has to be pumped to each cylinder. The fuel has to travel from the tank to each cylinder in the engine so that it can be mixed with air and ignited. The method by which the fuel reaches the cylinders depends on the weather the car in question has fuel injection or a carburetor.If the car has fuel injection then the fuel will be pumped via an electronic pump usually situated inside the fuel tank.
If it has a carburetor then the pump will generally be attached to the engine block and driven off of the camshaft.
Which ever system is used the fuel is drawn through steel lines attached to the underside of the car up to the fuel filter. This pretty much does what it says on the tin. It filters the incoming fuel for debris and passes the clean fuel onto the carb or injectors.
From here, the fuel is mixed with air (the ideal mixture being a ratio of 14.7:1, 14.7 parts of air to 1 part of fuel) in the inlet manifold and then it is distributed to each cylinder and ignited.
NOTE: almost every engine has an inlet and an outlet manifold. The inlet manifold is where the fuel/air mixture is created before it is supplied to each cylinder. The outlet manifold is usually attached to the exhaust system. This is where the waste products from the ignition of the fuel/air mixture inside each cylinder are disposed of.
I have previously mentioned the cylinder head and the fact that it houses the spark plugs, but I have not mentioned another vital component that is contained in the cylinder head (or head, as it is sometimes known), the valves.
There are two types of valve, inlet and outlet. You might be thinking that, that sounds similar to the manifolds and you would be right! Generally, there is one valve for the inlet and one for the outlet.
The timing for each valve to open depends on the position of the piston. When the piston has reached top dead centre and starts a new cycle, the inlet valve will open and the fuel/air mixture is drawn into the cylinder. When the piston reaches the bottom of its travel the valve will close and create an air tight chamber. When the piston then travels back up to top dead centre, the mixture is ignited and the piston is forced down.
This time, on its return journey back up to top dead centre the outlet valve will open allowing the waste gases left over from the ignition process to be forced out, down the exhaust and out of the tail pipe.
To simplify this slightly, the process can be broken down into four stages:-
- Intake stroke
- Compression stroke
- Combustion stroke
- Exhaust stroke
If all is well and functioning as it should, with every cycle of the above stages the crank shaft is turned and the motion from this is passed through the clutch, onto the gear box (which includes the differential) and finally to the wheels, via the drive shafts, propelling the car down the road.
NOTE: all the components that feature between the engine and the wheels are some times known as the “Drive Train”. This includes the clutch, gearbox, differential, drive shafts etc….).
Other essentials that a car needs
Aside from fuel and electricity there are two other items that a car requires for it to keep running, water and oil.Oil is primarily required to lubricate the majority of an engines bottom end, internal moving parts and sits in the sump at the base of the engine.
As the crank shaft turns it splashes oil around keeping all of the essential moving parts lubricated and free-moving.
The water system also has a similar function, to keep the engine cool.
As you can imagine, with a great many “explosions” happening in each cylinder a lot of heat is generate and if an engine gets too hot the components inside will expand and the engine will seize up.
The water system itself features several components, a water pump, a radiator and plenty of piping. The water pump pumps water around the “water jacket” that encases the engine block and then onto the radiator at the front of the car where it is cooled back down and the whole process is repeated over and over again.
With this system it can be pretty much ensured that the water will not reach and exceed a hundred degrees and cause the engine to boil as it also features a thermostat and backup fan that cuts in if the thermostat reaches a certain temperature.
The above is obviously a very brief outline of the main principals and components involved in the running and operation of a car.
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