 In SHOP-REPAIR.COM we know that a good way to know what happens to your car when there is a malfunction is knowing how it normally works. In this section we will explain the mechanism of the car and we will describe its main components. With the information you will find here, you will be able to start understanding your car’s symptoms. However, this is basic information about cars and does not replace the experience and skills of a qualified professional.
Engine
The engine is one of the main components of cars, as it is the mechanism that makes them move. The engines people use the most nowadays are the internal combustion engines, either diesel or gasoline engines, even though there are hybrid engines that combine the internal combustion and an electric motor.
The gasoline engine works based on the combustion of air and fuel mixture. This mixture ignites inside the engine cylinders. Each cylinder contents a certain amount of air, and a smaller amount of fuel is added to it through the intake of gasoline. In older cars, the air-fuel mixture occurs in the carburetor and then goes to the cylinder. When combined with the ignition system, the energy that is produced is really powerful and makes the car wheels move.
The diesel engine is also an internal combustion engine, but it depends on the self-combustion of the air-fuel mixture. This means that there is no ignition system or spark that fires the mixture: combustion occurs thanks to the high temperatures that are the result of the air compression in the cylinders. Self-combustion is only possible with fuels that are heavier than gasoline, such as diesel oil; besides, it is more economical and consumes less.
Engines are also regarded as by the number of cylinders they have and their position. They may have between three and twelve cylinders, with different shaping: they can be arranged in a line in a single bank, in two parallel lines or they can shape a «V». Each cylinder has a piston inside, which is the piece that moves up and down allowing the air-fuel mixture to go in and out through special valves. Inside the cylinders, the fuel ignites and the energy that moves the car is produced.
Gasoline engines, which are the ones people use the most, operate with a four-stroke cycle, which occurs in the same way in each cylinder. This is what happens inside the cylinder:
 Intake
In this phase, the piston is down and the intake valve opens so that the air and gasoline enter the cylinder. The valve is closed and the mixture remains inside.
Compression
Now the piston moves up to compress the air-fuel mixture. When the piston is up, the mixture is compressed to a tenth of its original volume.
Power
Due to the ignition system, a spark is produced, which ignites the air-fuel mixture. This combustion generates a powerful charge that pushes the piston back down and it moves the crankshaft, which joins the cylinders and, thus, the car starts moving. The cylinders ignite the fuel at different times.
Exhaust
The exhaust valve opens to eliminate the exhausted gas through the exit system. The piston goes up again and takes the remaining exhausted gas out, then the exhaust valve is closed and the four-stroke cycle begins again.
Engines need two essential liquids to properly work, oil and coolant. Oil is distributed in all the mobile parts of the engine through a pump. There is a light in the dashboard that indicates the low level of oil. As regards the coolant, you will find the information you need in the section related to this issue. It is also important to consider the engine balance to run the car smoothly. The number of cylinders is essential in this aspect: the more cylinders in the engine, the faster the ignition takes place and, thus, the car’s vibration is lower and the run is smoother. However, in order to reduce the movement caused by ignition, cars have a flywheel which lowers the unwanted vibration. Usually balance shafts are added to prevent the engine from moving and producing vibrations when driving.
Cooling system
As a running car involves a huge number of explosions and ignitions and, thus, it reaches really high temperatures, the cooling system is essential. It keeps the engine from overheating as, if this happens, it may break down. There are two ways of cooling the engine: air-cooling and liquid cooling, being the latter the one people use the most.
In the case of liquid cooling, the coolant circulates through pipes and passageways inside the engine, impelled by a water pump. This liquid absorbs the heat and reaches the radiator, where it cools down due to the air that enters the car through the grill at its front. The radiator is a metallic device that is made up of pipes, located at the front of the car.
Once the coolant has cooled, it circulates again to pick more heat from the engine. This liquid must not boil and it must have coolant, to withstand low environmental temperatures. Coolant consists of water and antifreeze —a poisonous substance. It is important that the cooling system keeps a medium temperature —not too cold, not too hot— since, in the first case more fuel is consumed, and in the second one, the engine can be destroyed.
Ignition system
The ignition system’s goal is to produce the necessary spark to generate air and gas combustion contained in each cylinder of the engine. A car has a battery, i.e., a secondary electrical generator. It has been called so since it is a device that provides electrical energy, but first it needs to be charged. A car battery is a 12-volt-battery. The coil ignition converts those 12 volts into 20,000 or more, and that voltage taken to the spark plug of each cylinder produces the necessary spark for combustion. The ignition system is in charge of controlling that sparks are produced in the cylinders in the right order, at the right moment. If the spark is delayed, the engine will not work. Combustion is done in each cylinder many times per minute. Cars that have been manufactured since the 80’s have computer controlled ignition systems.
Charging system
Charging system is important since it keeps the battery charged, i.e., the car has the necessary electrical energy to start the engine. Furthermore, charging system generates the required electrical current to keep the engine running once it has been started.
The alternator is the generator that charges the battery and provides energy to the engine while it runs. It produces alternating current and then converts it into direct current, since current cars need a 12-volt electric system of this kind of current. The alternator functions with the engine’s movement, thanks to a belt. Its function is important, since without this device the battery becomes dead and cannot be recharged, therefore there is no current to produce the initial sparks for combustion —with a dead battery the engine will not start— nor reserve energy just in case the charging system fails or to face an extra need of energy —in a winter night, more lights and heat are needed, and the alternator may not be able to provide all this. If the alternator does not work, besides, there is no current to keep the engine running.
Transmission
Transmission is the mechanism that sends the power generated by the engine to wheels and regulates the different gears. Transmission system is necessary so that the engine does not turn more revolutions per minute than its maximum limit, since if it does, it will explode. Thanks to gearshifts, it is possible to drive a car at different speeds, without surpassing the maximum revolutions per minute. Transmission system not only has different gearshifts but also has a neutral position that disconnects the engine from wheels, a reverse and park position, which prevents wheels from bending and the car from moving when parked.
Cars can have manual or automatic transmission. Those with manual transmission have a gearbox and a clutch. This means gearshifts are changed manually, by moving the gearbox accordingly and pressing down the clutch. The clutch is a device composed of disks that transmits or not the power produced by the engine to the wheels. These disks turn and mate to the engine to transmit their power to the wheels —clutch in «clutched» or «mated» position, the pedal is loose— or unmated to interrupt the transfer —clutch in the «unclutched» or «unmated» position, the pedal is pressed down. When you press down the clutch, it is unmated, and, at that moment of interruption, you change gears —modify the speed. It is necessary to step on the clutch when changing gears to smoothly shift them.
Automatic transmission system is different from manual transmission since it does not have a gearbox or a clutch. Once you start a car with this type of transmission, gearshifts are changed automatically. It is a complex mechanism in which mechanical, hydraulic and electric components interact. Its main components are the planetary gear sets—mechanical speed system—, hydraulic system —flow of transmission fluid through shafts and gear belts— and torque converter. The latter is a device that replaces the clutch and functions as such, since it transmits the power from the engine to the wheels; besides it makes it possible to interrupt the transmission to change gears, without the engine coming to a halt. Another important component is the modulator or throttle cable, which controls speed and indicates when it is necessary to change gears.
In the latest cars, this type of transmission is computer-controlled. This computer has sensors that register the car and engine’s speed to determine when gearshifts must be changed. Thus, gearshifts are automatic, and the car itself regulates them to avoid excesses in the engine’s performance to prevent damages.
Brake system
The braking system is essential in a car, since driving security greatly depends on it. The system consists of a master cylinder from which hoses come out that join brakes with it. Brakes people use the most are disk brakes, since they last longer, they are water resistant and they have great power to stop a car. Sometimes, however, drum brakes are used for rear wheels. Disk brakes are formed by a caliper with a piston, two metallic disks covered with a material to withstand heat and an iron rotor.
This is how the braking system works —when the brake pedal is pressed down, the master cylinder’s piston pushes the brake fluid. In each wheel, this fluid pushes the caliper piston and thus this make the brake pads—located at the sides— press down the rotor. This, in turn, by being attached to the wheel and being pressed down by the disks, makes the car stop or diminish speed. In the case of the drum brakes, there are brake shoes which cause friction with the drum attached to the wheel to stop.
It is important to check the brake fluid. It must not have air bubbles, since if it does, brake’s capacity is reduced, making the pedal spongy. This type of oil supports low and high temperatures, therefore it does not thicken nor boil and, thus, it can appropriately fulfill its function. It is highly important to always check that there is no leak of brake fluid, to prevent accidents due to brakes’ malfunction. You must never use another substance in this system. On the other hand, disks’ friction with the rotor when braking —or shoes with the drum—generates a great amount of heat that wears out these pieces. Therefore, you must regularly check the disks and rotor’s state and make the necessary changes or repairs to have the braking system in great conditions.
Wheel alignment
Car’s alignment is the right position of wheels —these must be perpendicular to the floor and parallel among them. If a car has a good alignment, it will properly run and tires will last longer.
Starting system
This electrical system makes it possible for the car to start. Its main component is the battery. When the key is put to start the car, a multiple process begins. With the battery’s current the fuel pump is moved and this one gets in touch with the air. Thanks to the battery’s energy, the starter motor also begins to operate, which activate the engine making each cylinder’s piston let in the air-fuel mixture. Simultaneously, the ignition system’s coil converts 12 volts of the battery into 20000 or more and sends this voltage to the spark plug that produces sparks. Thus, the air-fuel mixture combustion is produced within the cylinders. Once the engine works, the transmission system’s job begins, which transfers the power generated by the engine to the wheels.
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