Quote:
Originally Posted by CeeforCitroen
I did find a link you might find interesting based on the semi truck idea
www(dot)yankodesign.com/2017/12/13/hey-elon-heres-an-idea-for-your-semi-trucks
Interestingly I was looking up about the Tesla Semi, because electric power has often been a challenge for long range vehicles. I'm surprised it's still only a single speed transmission as well because while electric motors generally get away with less gear range, as vehicle weight increases, a choice of ratios generally come back into the picture which is why a semi generally has more gears than a motorcycle. (I've drafted a write up of the efficiency of electric motors at different loadings and come to the conclusion that motors with high DC resistance and low mechanical friction should be lightly loaded, and vice versa for low resistance but high mechanical friction). I would be interested to know how the motor performs towing 80,000 lb up a hill, compared to coming back to the dock empty, because I find it hard to believe you would get optimal range using the same gear ratio for each task.
As for McLaren F1 fuel economy, usually with supercars and hypercars the efficiency island for the "over sized" engine puts you well over most speed limits. At which case the air drag is more than optimal if you can't cruise at peak efficiency until over 100 mph. For most city driving it would be like using the engine to run an electric toothbrush. A McLaren F1 body with a Smart Fortwo engine would do rather well - if a little boring to drive on a track. The other factor is the speed range the two cars are generally used.
It would seem to me though as speeds head north (possibly beyond the top speed of the Smart) that the McLaren would drink less petrol. Also whether the low mpg figures of these cars are measured puttering to the shops of caning it round the Nurburg Ring. Perhaps one of these cars should have a tiny engine to putter along to the track day and then switch over to the large engine to have some fun!
I'm curious as to where the fuel goes in some of these cars because 15 mpg US (18 UK) is what my Citroen C2 would get if I put it in 3rd or 4th, pushed the pedal to the floor and also put my other foot partway on the brake (or drove up a hill) enough to stop the car from accelerating. I mean a McLaren isn't exactly a 4 ton 2 lane wide garden shed, so where does the fuel go? Is the engine fighting itself? If I was to tow one with my Citroen with the McLaren in gear would the engine braking of the large engine cause my car to consume the same fuel? I'm assuming the "waste fuel" in an uneconomical large engine just goes to moving itself round - just like a 7 litre V8 geared to move a scooter at 30 mph at 4000 rpm is mainly fighting its own resistance and a tiny bit is used to move the scooter.
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1) with 100% torque available, from zero-to- full-rated rpm, the single, 10:1 ( just for for example) planetary gear set, behind an electric motor, gives virtually infinite 'gearing' with a BEV.
2) if you'll re-visit the Tesla Semi website, they spell out the performance comparison of the electric tractor pulling an 80,000-pound load up a grade, versus a conventional diesel-powered rig.
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3) any mpg figures published for the McLaren would be determined by the official testing protocol used. For those units sold in the USA, the numbers would come from the EPA procedure.
4) As to 'where' the fuel goes in the McLaren, it's the same as for any heat engine:
* internal friction
* pumping losses
* engine accessory losses
* heat flux from the cooling system
* heat flux out the exhaust
* actual road load at any moment
* inefficiency of transient engine loading on BSFC
* mechanical efficiency of the transmission
* mechanical efficiency of any universal joints, CVC-joints
* mechanical efficiency of the differential
* brake pad friction
* tire rolling resistance
* wet roads, other precipitation
* curve drag
* climbing losses
* traffic
* idling
* velocity
* local air density
* aerodynamic drag ( including all wind, gust spectra )