You could design a rear drive system with two large diameter motors and still retain almost the same efficiency as in-wheel motors. Here's how.
Use a CV joint in each wheel to allow a flexible connection to a half axel drive shaft. On the other end of each shaft, mount one of the motors.. Secure the motors to the chassis with a pivot connection, so that the motor's angle can change as the wheel goes up and down. As I understand it, CV joints run better than 99% efficient. Without having gear reduction, then, this means your drive train efficiency is 99% * efficiency of tires. Probably the best you can get. The only problem I see with this design is making room for large diameter motors. I'm not sure of the diameter of experimental in-wheel motors, but I'll guess somewhere around 10-12". They might need to drop down and be shielded with something strong (and heavy), or they might need to protrude up a bit into a trunk space or bed area. Better yet, if the battery is sandwiched under the floor, that gives a bit of vertical space to better accommodate large diameter motors. One other possibility is to do this with front wheel drive instead. Can that still be done with one CV joint per side? If so, there is much more vertical space under the hood and it seems that two large diameter motors could easily be fit in. Note this could be done with one motor if you add another pair of CV joints. This is getting awfully close to a typical front wheel drive, I think. The only real difference is the gear reduction. But, hey, if eliminating gear reduction can save 10%, why not? Well, I'm not building this, but I think it would be fascinating to see if it's possible to make this work and boost the efficiency of the drive train. Peri -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Bill Dube Sent: 24 December, 2013 1:39 PM To: Electric Vehicle Discussion List Subject: Re: [EVDL] VW Bora will have Protean in-wheel motors The supposed space savings is very much in the mind of the executive that funds a hub wheel endeavor. It turns out not to really save much space, unfortunately. The gear losses are about 7%, give or take, when you use a gear reduction to centrally mount a small high-speed electric motor. When you use a gear box, the motor/gearbox combination becomes much smaller and cheaper than the direct drive hub motor. This is because the torque of the motor is directly proportional to the size and the cost. Speed (rpm) has little influence on the cost of a motor. A gearbox thus greatly reduces the cost and makes the motor/gearbox combination smaller, so there really, in the end, is not much space saving. The trouble is, one cannot completely solve all of the innate problems of an in-wheel motor in a highway capable vehicle. At least not economically for most of the problems and for the other problems perhaps not at all. This is what every major car manufacturer has independently confirmed. The very first attempt was by Porshe in the late 1800's. http://press.porsche.com/news/release.php?id=642 It was not really highway capable, however, as its top speed was 22 mph. I could go on and on. (I have done so before. Look it up in the archives.) Hub motor vehicle prototypes die the "death of a thousand cuts". It is not just one problem, but many subtile, very serious, issues. Each takes its toll to eventually kill the production vehicle. I should note that for low speed vehicles and for racing vehicles, hub motors and individual wheel motors can sometimes make a lot of sense. Often for these specific applications, the problems fade away and the advantages can win out. Bill D. At 09:55 AM 12/24/2013, you wrote: >Let's say one could solve the problems of an in-wheel motor. Then, how much >advantage would it have over using some sort of transxle and mounting the >motor the chassis a little inwards from the wheel area. > >The only advantages I can think of are: >- slightly less space used since the motor would be almost completely in the >wheel well area, >- ever so slightly less weight and resistive loss (no transaxle). > >Peri > >-----Original Message----- >From: [email protected] [mailto:[email protected]] On Behalf >Of Bill Dube >Sent: 24 December, 2013 7:44 AM >To: Electric Vehicle Discussion List >Subject: Re: [EVDL] VW Bora will have Protean in-wheel motors > >I agree. Every car manufacturer has boldly announced in-wheel motors, >built a prototype, and then made an embarrassing retraction. > >Sounds like a terrific idea, then they build one and learn for >themselves the insurmountable safety issues of highway driving >(uncommanded asymmetric torque, unacceptable unsprung weight, etc.), >then as quietly as possible they bury all the prototypes and pretend it >never happened. > >I wish they would publish a book or report on the bad experience, but I >guess it is just too embarrassing. > >Bill Dube' > >On 12/23/2013 9:28 PM, Al wrote: > > Sigh, in-wheel motors, again, when will they learn. > > > > ----- Original Message ----- From: "brucedp5" <[email protected]> > > To: <[email protected]> > > Sent: Monday, December 23, 2013 8:11 AM > > Subject: [EVDL] EVLN: VW Bora will have Protean in-wheel motors > > > > > > _______________________________________________ > > 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) > > > > > >_______________________________________________ >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) > > > >_______________________________________________ >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) _______________________________________________ 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) _______________________________________________ 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)
