In article <[email hidden]>, Roger
Merriman
[email hidden] says...
Quoted message said:plus the electric motor is most effient on a low load, and high revs in
my experance unlike the car which likes high gears, and low revs.
AIUI maximum efficiency occurs at maximum torque, which in the case of
some types of electric motor will be at very low revs, but in the case
of ICEs it's generally somewhere in the middle of the rev range[1].
Electric trains don't have gears, despite that fact that they need to
produce very high starting torque and also push out high power while
running efficiently at higher speeds.
[1] The flexibility of an engine is basically determined by the
difference in revs between maximum torque and maximum power. Some
engines don't need this - a diesel generator is designed to run in a
very narrow rev range without variable gearing[2]. Road vehicle engines
need flexibility to avoid changing gears all the time. Race-tuned
engines are designed to produce maximum torque at higher speeds, because
power is the product of torque and revs, and race engines generally need
high power at the cost of mid-range flexibility - this is why they need
close-ratio gears to keep the engine speed in the narrow power band.
[2] Different types of ICE also have different load characteristics -
generally diesels work well at high load in a narrower rev range, while
petrol engines work better at moderate load over a broader rev range.
Turbos or blowers can be used to modify these basic characteristics - a
turbocharged petrol engine is basically set up to give a broad torque
curve when conventionally aspirated, and when the turbo kicks in it
boosts the curve and pushes it up the rev range.
[3] It's a long time since I studied this stuff, so I might have
misremembered something.
