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An engine has a number of systems that help it do its job of converting fuel into motion. Most of these subsystems can be implemented using different technologies, and better technologies can improve the performance of the engine. Here's a look at the different subsystems used in modern engines :
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| Valve Train |
The valve train consists of the valves and a mechanism that opens and closes them. The opening and closing system is called a cam shaft. The cam shaft has lobes on it that move the valves up and down.
Most modern engines have what are called overhead cams. This means that the cam shaft is located above the valves. The cams on the shaft activate the valves directly or through a very short linkage.
Older engines used a cam shaft located in the sump near the crankshaft. Rods linked the cam below to valve lifters above the valves. This meant more moving parts and also caused more lag between activation and motion.
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A - Intake Valve
B - Valve Cover
C - Intake Port
D - Head
E - Coolant
F - Engine Block
G - Oil Pan
H - Oil Sump
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I - Camshaft
J - Exhaust Valve
K - Spark Plug
L - Exhaust Port
M - Piston
N - Connecting Rod
O - Road Bearing
P - Crank Shaft
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A timing belt or timing chain links the crankshaft to the cam shaft so that the valves are in sync with the pistons.
The cam shaft is geared to turn at one-half the rate of the crankshaft. Many high-performance engines have four valves per cylinder (two for intake, two for exhaust), and this arrangement requires two cam shafts per bank of cylinders, hence the phrase dual overhead cams.
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| Ignition System |
A - Spark Plug Wire
B - Distributor Cap
C - Rotor
D - High Voltage Leads
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E - Distributor Body
F - Distributor Cam
G - Ignition Signal Sensor
H - Ignition Module
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I - Ignition Coil
J - Spark Plugs
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The ignition system produces a high-voltage electrical charge and transmits it to the spark plugs via ignition wires.
The charge first flows to a distributor, which you can easily find under the hood of most cars. The distributor has one wire going in the center and four, six, or eight wires (depending on the number of cylinders) coming out of it.
These ignition wires send the charge to each spark plug. The engine is timed so that only one cylinder receives a spark from the distributor at a time. This approach provides maximum smoothness.
Click here for a detailed explanation of the ignition system.
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| Cooling System |
The cooling system in most cars consists of the radiator and water pump. Water circulates through passages around the cylinders and then travels through the radiator to cool it off.
In a few cars, as well as most bikes, the engine is air-cooled instead. You can tell an air-cooled engine by the fins adorning the outside of each cylinder to help dissipate the heat. Air-cooling makes the engine lighter but hotter, generally decreasing engine life and overall performance.
Click here for a detailed explanation of the cooling system.
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| Air Intake System |
Most cars are normally aspirated, which means that air flows through an air filter and directly into the cylinders.
High-performance engines are either turbo charged or super charged, which means that air coming into the engine is first pressurized (so that more air / fuel mixture can be squeezed into each cylinder) to increase performance. The amount of pressurization is called boost.
A turbo charger uses a small turbine attached to the exhaust pipe to spin a compressing turbine in the incoming air stream. A super charger is attached directly to the engine to spin the compressor.
Click here for a detailed explanation of turbocharged engines.
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| Starting System |
The starting system consists of an electric starter motor and a starter solenoid. When you turn the ignition key, the starter motor spins the engine a few revolutions so that the combustion process can start.
It takes a powerful motor to spin a cold engine. The starter motor must overcome :
- All of the internal friction caused by the piston rings.
- The compression pressure of any cylinder(s) that happens to be in the compression stroke.
- The energy needed to open and close valves with the cam shaft.
- All of the "other" things directly attached to the engine, like the water pump, oil pump, alternator, etc.
Because so much energy is needed and because a car uses a 12-volt electrical system, hundreds of amps of electricity must flow into the starter motor. The start solenoid is essentially a large electronic switch that can handle that much current. When you turn the ignition key, it activates the solenoid to power the motor.
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| Lubrication System |
The lubrication system makes sure that every moving part in the engine gets oil so that it can move easily. The two main parts needing oil are the pistons (so they can slide easily in their cylinders) and any bearings that allow things like the crankshaft and cam shafts to rotate freely.
In most cars oil is sucked out of the oil pan by the oil pump, run through the oil filter to remove any grit, and then squirted under high pressure onto bearings and the cylinder walls. The oil then trickles down into the sump, where it is collected again and the cycle repeats.
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| Fuel System |
The fuel system pumps fuel from the fuel tank and mixes it with air so that the proper air / fuel mixture can flow into the cylinders. Fuel is delivered in three common ways : carburetion, port fuel injection and direct fuel injection.
In carburetion a device called a carburetor mixes fuel into air as the air flows into the engine.
In a fuel injected engine the right amount of fuel is injected individually into each cylinder either right above the intake valve (port fuel injection) or directly into the cylinder (direct fuel injection).
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| Exhaust System |
The exhaust system includes the exhaust pipe and the muffler. Without a muffler what you would hear is the sound of thousands of small explosions coming out your tailpipe. A muffler dampens the sound. The exhaust system also includes a catalytic converter.
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| Emission Control System |
The emission control system in modern cars consists of a catalytic converter, a collection of sensors and actuators, and a computer to monitor and adjust everything.
For example, the catalytic converter uses a catalyst and oxygen to burn off any unused fuel and certain other chemicals in the exhaust. An oxygen sensor in the exhaust stream makes sure there is enough oxygen available for the catalyst to work and adjusts things if necessary.
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| Electrical System |
The electrical system consists of a battery and an alternator. The alternator is connected to the engine by a belt and generates electricity to recharge the battery.
The battery makes 12-volt power available to everything in the car needing electricity (the ignition system, radio, headlights, windshield wipers, power windows and seats, computers, etc.) through the vehicle's wiring.
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