Driving Test Success

How Cars Work The Workings Of A Car Explained

The process by which a car works is a lot simpler than you may think. When a driver turns a key in the ignition:

What happens in the cylinders is the magic that gives power and motion to the car wheels. Most car engines use a four-stroke combustion cycle. This cycle starts with piston at the top of the cylinder. Then:

Inside A Car Cylinder

Inside A Car Cylinder

Four Stroke Combustion Cycle

Four Stroke Combustion Cycle

Intake stroke: intake valve opens and the piston moves down allowing the fuel-air mix to enter the open space.

Compression stroke: the piston moves upwards. This compresses the fuel-air mix by forcing it into a smaller space. Compression makes the fuel-air mix explode with greater force.

Power cycle: spark from a spark plug ignites the fuel-air mix. The explosion forces the piston down the cylinder.

Exhaust cycle: the exhaust valve opens and the piston moves back to the top of the cylinder which forces the exhaust fumes out.

The bottom of each piston is attached to the crankshaft.

As the pistons are forced up and down they rotate the crankshaft, which after sending the power through the transmission, turns wheels.

Most cars have at least four cylinders. More powerful cars have more. For example a V6 has six cylinders and a V8 has eight.

The harder a driver presses on the accelerator pedal the more fuel-air mix is passed into the cylinders and the more power is produced.

What Are Revolutions Per Minute?
The four-stroke cycle repeats itself thousand of times a minute. These repetitions are more commonly known as Revs.

A rev counter tells you how many thousand times per minute the cycle is repeated.

Car Engine Uncovered

Car Gears - Transmission

The Transmission

Controls the power contained in the crankshaft before it goes to the wheels and allows a driver to control the speed/power of a car by providing different speed/power ratios known as gears.

So first gear gives plenty of power but little speed whereas fifth gear provides little power but plenty of speed.

The crankshaft only connects to the transmission when the car is in gear and the clutch is engaged. If you press down on the clutch the crankshaft disconnects from the transmission.

The transmission is connected to the output shaft, which is connected to the axles, which are connected to the wheels. When the transmission rotates the output shaft this turns the axles, which in turn rotate the wheels.

Other Key Car and Car Engine Components

Alternator: turns mechanical energy into electrical energy. This energy powers a car's electrics, from lights to wipers. It also recharges the car battery. A belt that rotates once the engine is on powers it.

Brakes: cars use either drum or disc brakes. Disc brakes use a calliper to press onto the disc of the wheel in order to slow the wheel down. Drum brakes work on the same principle however a drum brake presses against the inside of the drum.

Camshaft: controls the opening and closing of the intake and exhaust valves.

Cooling System: car engines produce a lot of heat. This heat needs to be controlled. To do this water is pumped through passages that surround the cylinders and then through the radiators to cool down.

Distributor: operates the ignition coil making it spark at exactly the right moment. It also distributes the spark to the right cylinder and at the right time. If the timing is off by a fraction then the engine won't run properly.

Exhaust System: once the fuel-air mix has been burnt the remaining gas enters the exhaust system and is expelled from the car. If a catalytic converter is present the exhaust gas passes through it and any unused fuel and other certain chemicals are removed.

Handbrake: this is a separate system from the foot brake. As a rule it is mounted on the floor of the car and is connected by a cable to the two rear wheels.

Head Gasket: the cylinder head (a block that seals all the tops of the cylinders) and the engine block (which contains the main bodies of the cylinders) are separate components that need to fit seamlessly together. The head gasket is a piece of metal that sits between them and connects them.

Oil: a car engine consists of many moving parts. Oil lubricates these parts and allows them to move smoothly. In most car engines oil is pumped out of the oil pan through a filter that removes any dirt and then is squirted under high pressure onto the bearings and cylinder walls. The oil then trickles down to the sump where the process starts over.

Regulator: regulates the amount of energy in the alternator.

Shock Absorbers: also known as dampers, are fitted between the car's body and axle in order to prevent excessive rolling and bouncing of the car body during motion.

Suspension System: counteracts the effects of hitting bumps in the road. Without such a system a car would veer of course every time the tyres hit a bump or pothole. The system comprises of springs and shock absorbers. The springs absorb any of the energy released when the tyres roll over a bump and the shock absorbers absorb the energy from the springs. This keeps the main body of the car steady and stable.

Timing Belt: a belt connected to both the camshaft and crankshaft ensuring that they work in time with each other.

What is the difference between a Petrol and Diesel Engine?

In petrol engines fuel is mixed with air and then forced into the cylinders where the fuel-air mix is compressed by the pistons and ignited by spark plugs. In a diesel engine the air is compressed before the fuel is added to it. When air is compressed it heats up. This means that when the fuel is added to the compressed air it is very hot and the fuel-air mix ignites automatically. So there are no spark plugs in a diesel engine as pressure is used to ignite the fuel-air mix.

Author Richard Jenkins

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