What about the energy losses of (effectively) constantly having to change direction on a circuitous course (or any course - especially a twisty mountainous one - lots of hair-pin bends)? This would manifest itself as the tyres scrubbing on the road surface giving off heat, noise and wear on the rubber/road. Not big but still significant. The losses on the outward trip would be aded to those of the return. They would not cancel out like a change in elevation would... or am I missing something? MW
On 21 Nov 2013, at 01:09, Cor van de Water wrote: > Hi Michael, > Since this is a theoretical experiment, we might just as well focus on > that theory and indeed, at first blush is appears that the theory says > that if you have a closes course, your *potential* energy level is > identical at finish as when starting, so there is no net build-up or > release of energy other than the friction and kinetic energy, since any > height gain or loss must be made up by the end of the trip. > > However, an electric motor works different than an ICE. Where the ICE > motor has a weird efficiency change (weirder for petrol as for Diesel > engines and the Prius' Atkinson cycle is again slightly different than a > regular petrol ICE) the efficiency of the electric drivetrain is in > theory perfectly linear falling with the amount of power delivered, > since losses go up squared with the current (force) delivered. > > Result is that if half the drive causes you to use double the current > and half the drive you can maintain the speed downhill at zero current, > your total *loss* will have doubled. It is 4x as large during half the > drive, compared to the 100% level ride. > > So, in theory, diving over hills and mountains at the same speed should > consume more power than driving the same speed and distance on a level > road. > > In an electric drivetrain, loss may be at or above 30% at full throttle, > while at half throttle it is typically at or below 10% for the same > reason. > So, the total energy difference is not very big, you may go from the > energy consumed at level road to an increase of around 8% for the > example drive half uphill and half downhill. (level would be 92% energy > to the wheels, 8% loss, for the doubled loss in the hills you would have > 16% total loss so the energy consumption rises by 8%) > > Hope this clarifies, > > Cor van de Water > Chief Scientist > Proxim Wireless Corporation http://www.proxim.com > Email: [email protected] Private: http://www.cvandewater.info > Skype: cor_van_de_water Tel: +1 408 383 7626 > > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Michael Ross > Sent: Wednesday, November 20, 2013 4:36 PM > To: Electric Vehicle Discussion List > Subject: Re: [EVDL] EVLN: Kia Soul EV goes global and > aimsfor120-miledrivingrange > > Cor, this is really a theoretical topic. Why should a level ride be > easier > than a hilly ride if it is a circuit? > > I disagree about regen saving anything except when used for braking, > then > you are trading waste heat for some charging.. If you use regen to slow > down on hills you are causing an inefficiency. > > If you are on a hill that is too steep for safe coasting and brakes must > be > used, then regen is better than heating your brake rotors. > > If you take all this out of the thought experiment, then hilly and level > are equal. > > > On Wed, Nov 20, 2013 at 7:22 PM, Cor van de Water <[email protected]> > wrote: > >> Michael, >> How often do you encounter a steep road that is completely straight in >> the mountains? All the roads in the surrounding mountains that I know >> have sharp turns, for which you will *definitely* want to slow down. > So >> except if you are in roller-coaster country, having regen will save at >> least part of the energy from the downhill run when you need to slow >> down for the next turn... >> >> BTW, it may be that the information is skewed due to the redefinition > of >> electric vehicle by some manufacturers. I have noticed that my Prius > can >> get better mileage going over a large hill than when doing a steady >> speed in flat terrain. This is probably similar to the "Pulse and > glide" >> hypermiling technique. This has of course nothing to do with pure >> electrics, but since GM calls their plug-in hybrid an EV, that may be >> where the confusion comes from... >> >> Regards, >> >> Cor van de Water _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
