Quote:
Originally Posted by Old Mechanic
Imagine how well they could design an engine if it only had to run at one RPM and load regardless of power train demands. Much easier than trying to make an engine run efficiently at all loads.
One size fits all loads will always be a huge stumbling block for engine design. It should be one RPM, one specific load, then you could redesign every component for that load and RPM. Lighter pistons, rods, crankshaft (if it had one), valves (if it had them), bore to stroke ratio could be 1 to 2 or 3 or even more. No throttle restriction, only a fixed amount of fuel delivery.
It will happen when they realize that there are alternatives to connecting the engine-motor directly to the wheels.
regards
Mech
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Is engine speed really that much of an issue? Basically all normal driving happens under 4000rpm, between 2000 and 4000 what you lose in friction you gain in reduced cooling loss, unavoidable with these engine sizes. Without a very powerful hybrid assist there's no way to avoid the wide range of loads either. A mechanical gearbox and clutch is simple, cheap, lightweight, transmits power efficiently, and with the correct gear ratios allows the engine to run reasonably close to its maximum efficiency.
Considering cost restraints and fueling infrastructure, I think the way things are advancing mostly makes sense. Try to improve low load efficiency as much as possible (by sacrificing high load efficiency if necessary, which is what we're seeing with higher compression ratios + running extra rich and lots of spark retard at high load), more sensible gear ratios for fuel economy, downsizing and forced induction to make up for the power deficit, and slowly adding brake (and exhaust heat) regeneration capability and improving accessory efficiency. Compared to vehicles running near maximum possible tank to wheel efficiency via some sort of complex hybrid system, these steps can probably get us most of the way there at a much lower upfront cost (which is important as cars get replaced quite frequently).