The Electric Car
in [Design]
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From: Eeyore on 2 Aug 2007 03:41 Nobody wrote: > Eeyore wrote: > > >> > In city driving it's regenerative braking that can make a huge difference. The > >> > complexity of shoving electrical and ICE motive power through some combined > >> > transmission seems plain daft though. The series hybrid (in which the ICE simply > >> > recharges a battery) seems far more sensible all round. > >> > >> No, I disagree. The dual electrical machine design beats the series > >> system hands down. Having the engine go straight to the wheels when > >> it makes sense to do so makes the demand on the electrical system way > >> less. > > > > Why's that an advantage ? It also means you can't have 'meaningful' true electric only > > operation of it, plus it requiresa gearbox which otherwise may not be needed at all. > > The disadvantage of an all-electric or series hybrid vehicle is that the > maximum total power is constrained by both the ICE and the electrical > system, while a parallel hybrid can potentially combine the two, or at > least provide a more powerful ICE for motorway cruising without having to > size the electrical components to match. At the cost of a vastly more complicated drive train. > A secondary consideration is that the generator losses subtract from any > efficiency advantages of the electrical drivetrain. With a plug-in hybrid you may not even need to use the ICE/generator on shorter journeys. Hence no additional losses at all. > But mostly it's a case of having to size the electrical system to the > power requirements for motorway cruising even though it has fewer > advantages over a mechanical drivetrain in that context (i.e. regenerative > braking is of no benefit). Motorway cruising does not require high power. It's acceleration that requires high power. You can cruise at motorway speeds with say 30kW. Graham
From: Eeyore on 2 Aug 2007 03:44 Nobody wrote: > Eeyore wrote: > > >> >Drag DOES depend on body shape. > >> > > >> > ...Jim Thompson > >> > >> For a given shape, at automotive speeds, I think there is a square law > >> relationship between air speed and drag. > > > > You are correct at higher speeds. The relationship isn't simple it seems. > > http://en.wikipedia.org/wiki/Drag_(physics) > > Note that Stokes's drag isn't meaningful for vehicles. Where it meantions > "small objects", "small" means particles whose size comparable to the > gap between the molecules. IOW, it's useful for modelling a cloud of dust > settling, but not for modelling "objects". > > > Drag coefficient can make collosal differences too. > > http://en.wikipedia.org/wiki/Drag_coefficient > > > > Unfortunately current US styling (the trend for truck like 'slab fronts' ) is producing > > cars with greater rather than lesser drag. > > It isn't just the coefficient. Drag is also proportional to (effective) > cross-sectional area; large vehicles have more drag than small ones. The > sheer size of an American SUV is You'll see I covered this point in more detail an another post. > > The current hybrids also use skinny tyres to reduce rolling resistance. I hate to think > > of the adverse effect on road holding. > > Tyre width only matters when you get close to the limits of traction. It > doesn't affect total friction until the tyres start to distort > significantly and the force/area ratio exceeds the strength of the rubber. Some of the tyres being sold for this application are also low friction AIUI. Graham
From: Spehro Pefhany on 2 Aug 2007 09:04 On Thu, 02 Aug 2007 02:07:36 +0000, the renowned Guy Macon <http://www.guymacon.com/> wrote: > > > >Spehro Pefhany wrote: > >>I wonder at what speed a 500HP 'vette is most efficient? ;-) > >You get 500HP out of your Chevette? With a JATO, but it's an Impala. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff(a)interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
From: Michael A. Terrell on 2 Aug 2007 09:05 JosephKK wrote: > > But my favorite gal likes wearing dresses. Oh wait, that wouldn't > be drag then. I guess i will have to tell her not to wear pants. DRAG was from the theater when all parts were performed by males. It meant: 'DRessed As Girl' The other parts were DRAB, or "DRessed As Boy' I worked the stage crew on plays in high school, and the drama teacher couldn't let a day go by without dumping a lot of theatrical history on us, while we were working on the play. BTW, I was the sound man. So, if you want to keep her in dresses you DO want her in drag. -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
From: MooseFET on 2 Aug 2007 09:10
On Aug 1, 7:53 pm, Eeyore <rabbitsfriendsandrelati...(a)hotmail.com> wrote: > MooseFET wrote: > > Eeyore wrote: > > > John Larkin wrote: > > > > Spehro Pefhany wrote: > > > > > >>People don't buy Prius' to save gas, they buy them to be hip and > > > > >>stylish. So instead of smog, we have clouds of smug. > > > > > >Yes. _South Park_ dubbed it the "Toyota Pius". My calculations > > > > >indicate the payback to be marginal on hybrids, even with a $4K > > > > >government subsidy, so long as gas remains around $3US/US gallon, and > > > > >the Prius yields significantly better mileage than, say, the hybrid > > > > >Camry. > > > > > Both hybrids would get far better mileage if the batteries, the > > > > electrics, and all the fancy controls were dumped. What's left would > > > > be a small, light, slippery, ugly car with a small engine. All you'd > > > > give up is acceleration and the questionable advantage of regenerative > > > > braking, a small price to pay for dumping the batteries. > > > > In city driving it's regenerative braking that can make a huge difference. The > > > complexity of shoving electrical and ICE motive power through some combined > > > transmission seems plain daft though. The series hybrid (in which the ICE simply > > > recharges a battery) seems far more sensible all round. > > > No, I disagree. The dual electrical machine design beats the series > > system hands down. Having the engine go straight to the wheels when > > it makes sense to do so makes the demand on the electrical system way > > less. > > Why's that an advantage ? It also means you can't have 'meaningful' true electric only > operation of it, plus it requiresa gearbox which otherwise may not be needed at all. > > Graham Here's a picture to look at while I explain: http://www.cleangreencar.co.nz/page/prius-technical-info At low speeds or when you are running only on the electrics the electric machine connected to the wheels does all of the work of moving the car. In this situation the gear box from the engine to the wheels is disengaged. When more electrical power is needed, the electrical machine connected to the engine is used to start the engine. Using this large of a motor as a starter means that the engine can be started very quickly. On the highway, the engine gets connected directly to the wheels. This takes the sosses of the electric machines out of the picture. It also allows the engine and both motors to be used for passing power. |