This is probably already revealing how old some of us are, but we remember that we had to start our cars by turning the key and waiting to hear the engine “catch”. At that point you knew the engine was ok to proceed, and if you stopped turning the key it wouldn’t die.
How does the starter today (push button) know all this, and it never seems to get it wrong? I have never heard a push button starter fail to get it right unless some other issue like dead battery, etc. (and btw, today’s engines seem to have so far fewer issues like we used to have)
In: Engineering
It’s simpler than all this ECU stuff. The starter motor output shaft is threaded, (inertia system or “bendix gear”) then a small gear is threaded onto that, then that small gear interfaces with the flywheel on the engine. When the starter motor is engaged and the engine is off, the starter motor shaft is spinning faster than the little gear, so it winds its way down the shaft, until it engages with the flywheel. Since the starter shaft is pushing on the small gear, it stays out at the end of the threaded shaft. As soon as the engine turns over and starts running, the flywheel speeds up. Now the flywheel and the little gear are spinning faster than the starter motor shaft, and the little gear winds itself the other direction back up the shaft until it disengages itself from the flywheel.
No computers or sensors or anything, the starter motor little gear just disengages itself from the flywheel any time the engine is running.
More research shows there are several ways to accomplish this. Above is one, another is using active means to move the small gear in and out, also there can be a free wheel clutch on the starter.
https://www.howacarworks.com/basics/how-the-starting-system-works#:~:text=Also%2C%20if%20the%20engine%20starts,starter%20is%20turning%20the%20engine.
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