Once I put my key in the ignition and turn the car on what are the sequence of events that take place?
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How do the car electronics (or even before there really were electronics) know when the engine has turned over and it’s time to disengage the starter?
Was it that the starter could only ever plausibly get up to a certain limited speed, and if the engine was going faster than that, it knows the engine must be running on its own?
You extend key towards the ignition, bouncing off the plastic shroud a few times before getting it in. You have to wiggle the key to get it all the way in as you’ve bent it on countless beer bottle caps. When they key won’t turn you remember you accidentally engaged the steering-lock trying to squeeze out of the car with all of your bags. After jiggling the wheel and getting the key to turn you hear the ‘tick tick tick’ noise but no life comes from the engine. You call your dad who tells you it’s a battery or alternator issue and you need to try and jump-start it. Your friend finally comes and helps get the car started and tells you to get the battery tested and that your tires are bald.
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Your key is directly connected to the starter. This is a pre motor that turns the engine’s crank over and starts the combustion process.
Have you ever seen the old movies of the model t where they had to get out and physically turn that handle to get the engine started? Or the old ww2 Era planes that required the propeller to be spun by hand to start the plane? Or something as simple as lawn tools like a lawn mower, wead Wacker, or chain saw that use a draw string to turn the motor over and get it started.
The starter primes the engine with gas, and uses the battery to jump the spark plugs and crank the pistons. When the pistons crank, they creat compression in the combustion chamber, squeezing the air and gas in there, at maximum compression the park plug kicks in creating the combustion needed to operated the engine. Once this happens, the process becomes self sustaining, as long as the battery remains strong enough to send power to the spark plugs, and there’s enough gas to fuel the process.
Our engines run a 4 cycle process that sounds like a porno, suck, squeeze, bang, blow.
The intake valve opens, and due to vacume suction, air goes into the combustion chamber the pistons compress the air and fuel, this is the squeeze stage. The bang is the spark plug igniting the process. The preasure from the explosion builds up pushing the pistons down, opening the exhaust valve, and expelling the now combustion exhaust out through the exhaust system and eventualling the tail pipe, blow.
The engine has 4, 6 or 8 cylinders running in opposition to eachother, while one chamber is suckibg in, another is blowing out, the momentum of on vhambers blow forces another chamber to suck and compress. This requires a timing belt to sync these processes together allowing the system to run smoothly. Mostly the timing belt works to open and close the intake and exhaust valves, but it is times to the crank shift, which runs the pistons below.
Look up clamp 15 and clamp 30 in automotive design if you want the technical answer. Due to left over terminology this even still applies for startup processing for electric cars via pure software starts.
Source: I manage a team that does software management for the next gen of electric cars from a certain big car company.
Thanks for the great info! I always knew turning the key in the ignition got the engine going but I never really knew why. This explanation is really helpful and I can now better understand how an engine works.
Everyone’s failing to mention the fuel pump starting up first when you first turn the key to the click before ignition which turns all your dash lights on. This fuel pump will pump fuel through the fuel lines until they are primed and ready to squirt when the engine is on and the fuel pump will wait in a neutral position until it needs to keep pumping again when the engine actually starts. The fuel doesn’t magically get sucked out of the fuel tank when you start the ignition sequence
It will vary by car (diesel v gas, fuel injection v carburetor, etc…). For a modern 4-cycle gas engine:
1. Immobility sensor detects chip in key.
2. Turn to first click. Basic electric circuits energized (windows, radio, etc…)
3. Turn to second click. Engine sensors activate, fuel pump pressurizes line, engine systems are ready to run (which is why this is the position the key is in when you’re driving).
4. Turn to third click. Starter motor engages, cycling the engine.
* A fuel/air mixture is injected into each cylinder as the piston is drawn down by the rotating crankshaft.
* The piston rises in the cylinder, compressing the fuel/air mixture.
* The ignition system fires the spark plug, igniting the fuel/air mixture.
* The expanding ignited gasses force the piston back down. (This is what you feel when you accelerate – the forces of that contained explosion channeled through the crankshaft, transmission, and on to the wheels.)
* Once this process begins, you return the switch to the second position (see 3.)
There are many other things going on while the engine begins to spin and then runs. A belt or chain attached to cam shafts open and close the intake and exhaust valves (that fuel/air mixture – and the burned gasses – have to get in and out of the cylinder/combustion chamber). A water pump turns to cycle coolant through the engine. An oil pump turns to supply lubrication to the moving parts. You can get down to all sorts of levels of specificity.
This is one of those ELI5 subjects that could be like twenty words or five thousand.
Fundamentally the key closes the starter circuit and turns the engine until the cylinders fire as normal.
But in the brief moments between turning the key to the on position and the start position the computer (if it’s a fuel injected car) is running through dozens of operations; cycling the injectors, starting the fuel pump, checking fuel rail pressure, checking crank position, cam position, getting readings from the O2 sensors ahead of and behind the catalytic converter, checking transmission position, brake position, and a BUNCH of other stuff, and that’s before the engine even fires up.
Too complicated. After you turn the car on, check radio presets for best song. Select. Adjust volume. Glance in rear view mirror. Adjust nether regions, if required. Mandatory sequence completed.
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