6 ms·

> An engine running at 3000 RPM is only doing 50 rotations per second, so you have a 20 ms budget to calculate whatever you want, hit whatever spark plug timing

> An engine running at 3000 RPM is only doing 50 rotations per second, so you have a 20 ms budget to calculate whatever you want, hit whatever spark plug timing you need and then GC. The engine should still work at redline, so lets go for a conservative 6000 RPM, or 10ms budget. The spark plugs don't fire at the same time either, but (as far as I know) every second rotation in a staggered manner. So with a 4 piston engine you'd have 5ms (one firing every 180 deg) to do calculations, check for failure conditions and run the gc, with the latter one needing to finish in time. It might be possible to do a proof of concept, but I don't think its that easy.

nabilhat 6y ago
It's even worse considering all of the conditions being controlled for and the precision expected. Spark timing needs to fall within a degree of rotation. Modern cars get direct injection of fuel into the cylinders, which needs to be provided at a precise volume at somewhat less precise timing. Continuously variable valve timing and lift control cylinder conditions for improved burn efficiency while preventing an environment that encourages preignition, at the same time providing as much volumetric flow as possible. All of this needs to account for airflow, altitude, intake air temperature, variations in fuel quality, hiccups in fuel supply, engine temperature, over the entire range of possible engine load and speeds, and transitions throughout all of these states. It's a seriously hard optimization problem, one that's not yet up to the task of providing reliable engine management quickly enough to also provide throttle-by-wire response in general production cars that isn't as spongy as an old Mercedes diesel sedan. I mean, if Mazda could provide throttle response for the new throttle-by-wire Miata that was remotely similar to a 30 year old model, I think they would.

nabilhat 6y ago

It's even worse considering all of the conditions being controlled for and the precision expected. Spark timing needs to fall within a degree of rotation. Modern cars get direct injection of fuel into the cylinders, which needs to be provided at a precise volume at somewhat less precise timing. Continuously variable valve timing and lift control cylinder conditions for improved burn efficiency while preventing an environment that encourages preignition, at the same time providing as much volumetric flow as possible. All of this needs to account for airflow, altitude, intake air temperature, variations in fuel quality, hiccups in fuel supply, engine temperature, over the entire range of possible engine load and speeds, and transitions throughout all of these states. It's a seriously hard optimization problem, one that's not yet up to the task of providing reliable engine management quickly enough to also provide throttle-by-wire response in general production cars that isn't as spongy as an old Mercedes diesel sedan. I mean, if Mazda could provide throttle response for the new throttle-by-wire Miata that was remotely similar to a 30 year old model, I think they would.