How Does A Car Engine Work? - A Mechanics Answer [2023]

Almost every day you get in your car to go somewhere, but do you actually know everything that is happening from the time you turn the key to start the engine, to the time you turn the engine off again? That's what your going to learn here.

Today we are going to take a semi-deep dive in to the systems of your cars engine, the systems that make it go, and the systems that keep it going. This article will be broken up into sections for each system, and there will be subsections to explain the integral parts of each system. Lets get right in to in.

The Starting and Charging System

Unless you own an early 1900's car, you have an electric starter system in your car to start your engine, if you don't and you are still using a hand crank to start your daily driver, it might be time for an upgrade.

The starting and charging system is comprised of four main components, the Battery, the Starter Motor and Solenoid, the Ignition Switch, and the Alternator.

These three key components not only help start your engine, but also keep your battery charged at all times, this is why, barring mechanical failure, or an issue with the battery, car batteries don't eventually just die, like they would in your TV remote.

The Battery

Car Battery

The battery is a part of the car that almost every driver knows about, and just the same, most drivers have ran into a dead battery at one time or another, but what does this battery do for the car, and why does a dead battery mean you can't start your engine?

Your cars battery supplies power to the starter solenoid and in turn, the starter motor, and power is supplied to your battery by the alternator, but only when the car is running.

Your car also supplies power to all accessories when the car is not running, but the key is in the ACCESSORY position, this is why you can listen to those sweet tunes without burning gas.

But the drawback is, your battery is discharging to power your radio and other accessories in you car, and since the car is not running, the alternator is not spinning, and therefore not keeping the batteries charge topped up.

The Starter Motor

Car Starter Motor

The starter motor, often shortened to just "starter", is a relatively small electric motor that can pack a big punch. The starter motor is bolted to your transmission or engine, and a gear on the starter motor engages with the flywheel in the transmission to crank the engine over when you turn the key, this cranking is what provides the initial rotational force of the engine.

Your engine is considered started once the engine can turn on its own power. At the point you let off the key and the engine is running the spark plugs are firing, fuel is being injected, and the engine is operating under its own power with no help from the starter. We will get more into all of that stuff as we dive deeper into those systems later on in the article.

The Solenoid

The solenoid is an electromagnet, this electromagnet gets actuated by the battery voltage when you turn the key. The solenoid completes the circuit between the vehicles battery and the starter motor, at that same time, there is an electrically activated lever inside the solenoid, which when flipped, engages a drive pinion (also known as a pinion gear), and clutch assembly in the starter motor.

With the motor activated and now spinning, and the solenoid lever engaging the drive pinion by pushing the pinion arm out to mesh with the flywheel, the starter then spins the flywheel unleashing large amounts of torque to get the motor going.

Once The motor is turning on its own, or you let off the key, the solenoid disengages, and switches off the starter motor, moving out of the way of the flywheel. If it didn't move, it could damage the starter motor, or the flywheel, this is why you hear a grinding sound if you try to start a running car, the starter and the flywheel don't mesh right and it can cause damage if it happens too often.

The Ignition Switch

The ignition switch is not as advanced as it may sound, in fact, you interact directly with this at least twice every time you drive your car, once when you start the car, and once when you turn it off. Yep, the ignition switch is actually what you insert your key into when going to start the car.

In the case of a push button start car, it still has an ignition switch, and its activated when the key is in range, and the start button is pushed.

The ignition switch is fairly simple, and no more advanced than your house lock really. When you put the correct key in, and turn it, it creates an electrical connection in the ignition switch that tells the car to send power to the starter and also to everything else to get ready to start the car, it also sends power to the fuel pump to pressurize your fuel lines so there is gas ready to be burned in the engine.

On cars with a chip in the key, there is an extra step between turning the key, and creating the electrical connection, and that extra step is the computer in the car reads the digital code on the key, to make sure that key is not only the right key in terms of shape (if its not, it won't turn in the lock), but also to make sure that key is programmed for that car specifically.

This means that even if a thief was to have a key that turned your ignition, unless it has a chip and its programmed to the cars computer, it won't start, and if it does, it will start for a few seconds then shut right back off.

The Alternator

Car Alternator

Lastly, in the starting and charging system we have the alternator. The alternator (formerly and sometimes still called The Generator), is what actually supplies your car with electrical power once the car is running.

Your batteries reserve energy starts the car, and can run the electrical when the key is in accessory, but when the cars running, the alternator takes over, not only supplying power to the battery to keep it charged, but also supplying the rest of the car with power to make sure everything in your car works as it should.

This includes the lights, horn, radio, electric trunk lock, you name it!The alternator uses electromagnets to create a magnetic field, which is then converted into DC (Direct Current) power that is supplied to the battery, and the rest of the vehicle.

The alternator is driven by the Serpentine Belt, on the front of the engine, and therefore is only turning, and only generating power, when the engine is already turning.

The Ignition System

Car Ignition System

Now we are digging in more with the engine itself, the ignition system is what starts the combustion part of the engines famed "Internal Combustion Engine" name sake.

The ignition system is responsible for burning the fuel and air mixture that your engine receives, burning that fuel and air mixture creates combustion in an enclosed space, which creates compression.

The main components of the ignition system are as follows. For the sake of this informational article we will not be going into Distributors, and will be focusing on distributor-less engines, which are the most common cars on the road now. In this section we will focus on the ignition coil(s)/coil on plug, the spark plugs, and the spark plug wires, for engines that are not coil on plug.

The battery is also technically a part of the ignition system, as the ignition system draws its power from the battery and/or the alternator, depending on the vehicle. The ignition system in a modern automobile is timed by the ECM (Engine Control Module), which uses information obtained from various sensors in the cars engine to determine the timing between each spark on each spark plug.

The Ignition Coil

The Ignition Coil

An ignition coil is at its core just an electrical transformer. It contains a primary circuit and a secondary circuit. The primary circuit wire winding has to be insulated entirely, otherwise voltage could jump from the winding loops, shorting it out. If this happened it could not create the primary magnetic field.

The primary wire goes into the coil through the positive terminal, loops around the primary windings, then exits through the negative terminals. The secondary circuit contains 15 to 30 thousand wraps of fine copper wire which is also insulated from each other.

The secondary circuit is wound inside of the primary winding. The ignition coil takes the 12-14 volts from the battery/alternator to 20,000-30,000 volts which gets transferred to the spark plug, that electricity then jumps the gap on the spark plug, detonating the fuel and air mixture in the combustion chamber of the engine.

Some cars have a single ignition coil, or multiple ignition coils, and spark plug wires running from the coil(s) to the spark plugs. Most modern cars are coil-on-plug systems, where each cylinder, and each spark plug has its very oil ignition coil.

The Spark Plug

A spark plugs purpose is to produce a spark at the required time to ignite the combustible mixture in the cylinder. The plug is connected to the high voltage generated by the ignition coil, which we talked about above.

The spark plug is threaded into what is know as the Cylinder Head, the electrode tip protrudes ever so slightly into the cylinders of the engine, where the pistons are.

A spark plug is really just an insulated conductor to guide the current, it also provides the gap between the contact point and the electrode, where the spark happens as electricity jumps the gap, that spark is what in turn ignites the fuel air mixture in the cylinder.

The Spark Plug Wires

Spark plug wires

The spark plug wires are rather self explanatory, however many modern cars no longer use them, in favor of coil on plugs, which is an ignition coil for each spark plug, attached directed to the spark plug.

The spark plug wires transfer the power from a central point (either a distributor, on older cars, or a coil pack, on newer cars prior to coil on plug ignition systems). They are rubber shielded wires and there will always be one wire per spark plug on an engine equip with them.

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