There are a couple of other points Ashley. The engine is little in hybrids and runs constantly and more efficiently. They don't need such a big engine because when it's time to accelerate, the battery and electric motors kick in too.
Big engines idling at traffic lights are wasting a lot of energy. Big engines run more efficiently for a given power output, but it's not enough difference in automotive applications to matter. Power stations putting out gigawatts run much more efficiently than little car engines. They have thermodynamics and large scale on their side.
Once there is enough power available in a car to do the job, having a bigger engine just wastes energy. Having a battery and electric motors cuts the size of engine needed.
As you know air resistance is not significant at 10 kph, not a big deal at 40 kph [typical urban speed], becoming annoying at 100 kph and at 400 kph requires serious horsepower to plough through [better to go at a higher altitude to cut the drag]. Hence freeway driving gobbles a LOT of energy compared with tootling around town.
But as you say, highway driving is normally more efficient than town driving. Highway driving = get up to 100 kph, set cruise control, hum along at 4000 rpm or less. Set it to 130 kph and the savings won't be so good. Town driving = start cold [and inefficient], rev the engine a bit, back out of the shed, wait for wife to get in the car [maybe 10 minutes, so turn the engine off after a while unless it's cold in which case heating is a good idea - or cooling if it's hot], idle down the driveway, wait for a few cars, then accelerate up to 50 kph hoping the traffic isn't too bad despite the delay in leaving. Stop at the traffic lights at the end of the road for a couple of minutes to burn some more fuel. Turn onto the arterial road. Drive 400 metres, not really accelerating because there is already quite a queue of cars, stop at the next set of lights [turn engine off if you are like me]. Well, you know the story. Get to work the best part of an hour later having gone 10 km. There's not a lot of braking involved [for sensible drivers].
I agree that if it's worth doing, it's not trivial. My patented [soon to be] fully electric vehicle will definitely have regenerative braking as the main braking [a disc brake emergency system might also be good but with automated driving it wouldn't be needed]. It has been in design for a couple of decades now and is shaping up well. The prototype in the shed isn't yet mobile, but I think looks good. At present it looks like a washing machine, but I'm thinking of adding windows.
Mqurice |
