Isn't that strongly dependent on aerodynamic properties of a car? Cars modelled for high downforce will have higher levels of friction at high speeds than at low speeds.
Chevy Volt - Electric Car
- Thread starter nintenho
- Start date
Isn't that strongly dependent on aerodynamic properties of a car? Cars modelled for high downforce will have higher levels of friction at high speeds than at low speeds.
DuckThor Evil
Legend
Rolling resistance has little meaning at high speeds. High downforce cars produces that downforce from air resistance, so with those cars the rolling resistance is even less important. Tires are quite important on fuel consumption though. I remember that everytime when I put winter tires on my previous car my fuel consumption went down almost one liter per 100km. My winter tires were 205/16" and my summer tires were 225/17", but the difference was mostly at normal driving speeds. If you drive 100 kmh and go to neutral, the car maintains it's speed quite well, but if you do the same with 250 kmh the speed loss is really rapid.
I remember hearing that a Formula 1 car loses it's speed from high velocity just by lifting off the gas pedal as well as a normal car with full braking, because the formula 1 car had 3.5 times the aerodynamic drag, I don't remember at what speed that was calculated from though.
Last edited by a moderator:
Arwin, about 5-6l/100km sound realistic if you drive those 120 pretty much constantly without much braking and very little uphill/downhill driving.
Which about equals my 2l diesel with 3x the power and like 6x the torque. So I'd call that a rape, yes. A diesel with similar power to your combustion engine will need much less than 4l and still have double the torque. And the one matching your car combined will need about 5l at best.
Sxotty, you'll find no AC in a car except in the generator and some very rare fuel pumps. About the losses in brushless DC motors - you'll find lots of info in any datasheet being worth described as such. Or Google for "losses in brushless DC motors", for example (page 6): http://www.integratedsoft.com/papers/techdocs/tech_6mx.pdf
I was talking about energy efficiency between what's released during combustion (or the battery charge drawn in case of electrics) and what reaches the wheels. There the electrics are way, way better than a combustion engine - there are next to no losses on the line and the DC-motor as such is 90+% efficient in converting electric into mechanic energy.
Which about equals my 2l diesel with 3x the power and like 6x the torque. So I'd call that a rape, yes. A diesel with similar power to your combustion engine will need much less than 4l and still have double the torque. And the one matching your car combined will need about 5l at best.
Sxotty, you'll find no AC in a car except in the generator and some very rare fuel pumps. About the losses in brushless DC motors - you'll find lots of info in any datasheet being worth described as such. Or Google for "losses in brushless DC motors", for example (page 6): http://www.integratedsoft.com/papers/techdocs/tech_6mx.pdf
I was talking about energy efficiency between what's released during combustion (or the battery charge drawn in case of electrics) and what reaches the wheels. There the electrics are way, way better than a combustion engine - there are next to no losses on the line and the DC-motor as such is 90+% efficient in converting electric into mechanic energy.
Last edited by a moderator:
Mintmaster
Veteran
Diesel is a dead end solution. There is a balance between diesel and gasoline consumption because you get both from refining crude oil. If more people drive diesel, the price will go up until we get back to the consumption ratio that matches production.
Hybrids get us a nice boost in city driving mileage, but the real promise is in PHEV to drastically reduce gasoline and eventually even diesel consumption long term. You get reduced urban air pollution that not even biofuels can match, and less dependency on limited natural/foreign resources.
Mass shouldn't matter because rolling resistance is a tiny factor at constant high speeds. Air resistance is the big one, and it depends on shape and frontal area.
Power density is a minor issue for the battery sizes you're talking about, as even the 1.3 kWh Prius battery can output 21 kW. Not only that, but 10-20kg of supercapacitors should hold enough energy for periods of high power acceleration (a smaller amount is already there for regenerative breaking).
I don't think it will take long for someone to make a fast, affordable PHEV. Electric motors should have far less cost than ICE's of the same power, given that a 300hp motor needs 100 lbs of material or less. Someone will eventually produce them very cheaply for a high volume customer.
In the meantime, though, I can ogle the Fisker Karma
xxx Electric cars do use ac motors often. The EV1 did:
http://en.wikipedia.org/wiki/General_Motors_EV1
http://www.teslamotors.com/performance/perf_specs.php
http://en.wikipedia.org/wiki/Wrightspeed_X1
I believe that the AC motors have advantages over DC motors though they are more expensive.
Mint power density is an issue. What you may not be aware of is there are limits to power from batteries both to prevent degradation and for safety reason due to ohmic heating in the cells which can lead to catastrophe. It is an issue, one that is acknowledged by those in the industry. The super cap thing is true and is one of the reasons that they were making capacitor packs for vehicles, if you could pull an arbitrary amount from battery you would not need it.
The wrightspeed X1 uses AC motors, the tesla roadster uses and AC motor, and so on and so forth.
http://en.wikipedia.org/wiki/General_Motors_EV1
http://www.teslamotors.com/performance/perf_specs.php
http://en.wikipedia.org/wiki/Wrightspeed_X1
I believe that the AC motors have advantages over DC motors though they are more expensive.
Mint power density is an issue. What you may not be aware of is there are limits to power from batteries both to prevent degradation and for safety reason due to ohmic heating in the cells which can lead to catastrophe. It is an issue, one that is acknowledged by those in the industry. The super cap thing is true and is one of the reasons that they were making capacitor packs for vehicles, if you could pull an arbitrary amount from battery you would not need it.
Silent_Buddha
Legend
Bah, too busy to keep up with this thread it seems.
But no, that wasn't the source, it was a more recent source that test drove a later build of the car that included the gasoline engine.Wish I could remember the source I got that from but I'm so busy right now I can't even find my arse when I go to the toilet half the time.
Also, it was noted that Chevy engineers were still working on the system. But there were two things pulling against each other.
[1], they wanted to increase the performance when the battery reached 30% charge.
[2], they want to find ways to decrease the cost of the car.
Unfortunately, with what they had been able to accomplish up to that point, [1] is increasing the cost of the car, sometimes dramatically depending on what they try...and [2] well, that's ending up in most cases reducing both overall performance of the car and performance when 30% charge is reached.
There's still plenty of time for them to achieve some sort of breakthrough, however, as it's still about a year away from official launch I believe.
Regards,
SB
Mass doesn't matter? LMAO
Why do you think every race car is being stripped down all the way? Ever heard of something called acceleration?Now if you mean that for constant speed while already rolling, theoretically you'd be right if the road was always perfectly straight and horizontal.
Sxotty: ok, didn't know the usage increased that rapidly. AC motors are usually more powerful but you need lots of additional electronics for them, so it's also a question of cost.
Though I'm totally puzzled why Tesla use only 1-phase AC motor, that kinda defies the purpose. A three-phase would be way better, this way they could have as well stayed with an AC motor.
Last edited by a moderator:
Yeah. It's one of the reasons for instance why the Prius isn't allowed to pull a caravan, and when you drive off, it's also very clearly set so that you drive off smoothly because if I remember correctly in theory the engine could start from standstill with the same amount of torque as most supercars.
FWIW last night I saw a repeat episode of "Fifth Gear" from 2005 featuring the electric Venturer Fetish which does seem to deliver considerable torque from rest. No idea what type of batteries (or additional parallel capacitors) it uses, but it looks like a lot of fun.
Simon I wonder if the fetish has the same motor setup as the tesla since they mentioned the 14000 rpm redline. Or maybe there is some other reason that is common.
Its too bad the tesla did not get a gear box in the end. It would be nice to extend the top speed a bit, might even be easier on the motor when cruising at 80-90mph.
Its too bad the tesla did not get a gear box in the end. It would be nice to extend the top speed a bit, might even be easier on the motor when cruising at 80-90mph.
Mintmaster
Veteran
Mass doesn't matter? LMAO
Would you enlighten me, what's so funny? Never heard of basic physics and that you need more force to accelerate a higher mass than a lower mass?
In my next sentence I also said that your assumption would only be valid under theoretical perfect circumstances which, to put it simple, do not exist in reality.
But another cheers to selective quoting, where would we end up if noone pulled stuff out of context
In my next sentence I also said that your assumption would only be valid under theoretical perfect circumstances which, to put it simple, do not exist in reality.
But another cheers to selective quoting, where would we end up if noone pulled stuff out of context
Don't get all upset. What mint meant is on the highway on cruises control through kansas it won't matter much. Throw in some hills and it will matter a bit. throw in some traffic so you need to adjust speed and it will matter more. Throw in a city and it will matter even more.
It does depend on regen braking though., The more efficient that gets the less important mass will be (as there is more energy created in braking as well).
It does depend on regen braking though., The more efficient that gets the less important mass will be (as there is more energy created in braking as well).
Mintmaster
Veteran
You still don't get it after I bolded the contradicting parts?
WTF does acceleration have to do with CONSTANT speed? If highway MPG was measured in LA rush hour then mass would matter, but otherwise mass is almost irrelevent to highway driving. Bigger cars get poorer highway mileage because they have larger frontal area.
Sxotty, you've got the right idea, though even hills don't matter because you use more gas on the way up and less on the way down, and no brakes are needed there because wind resistance will prevent acceleration except for the worst hills. You only lose the energy put into additional mass when you brake, so the purpose of regenerative braking is almost entirely for city driving.
That's the key to efficient driving - brake as little as possible by keeping enough buffer space in front of you and not reaching an unnecessarily high speed between lights/stops (and, of course, don't drive too fast on freeways). Unless your engine is very inefficient at high output, acceleration doesn't make much of a difference.
What is out of context? Do I need to remind you of your own statement?
It will be almost equal (which is why I agree with your general premise that regular hybrids are sort of useless), but it won't be higher due to mass._xxx_ said:
What's out of context? You left out the next sentence which would have made your post obsolete:
...which it isn't 99,9% of the time.
That's why there are certain profiles defined to measure the consumption, in Europe the NEFZ and in US the FTP75 or whatever's currently valid over there. Those resemble more realistic driving.
Edit: here you can see the cycles, it's in german but the pics speak for themselves:
http://www.hybrid-autos.info/Fahrzyklen.html
Or Wiki: http://en.wikipedia.org/wiki/Driving_cycle
...which it isn't 99,9% of the time.
That's why there are certain profiles defined to measure the consumption, in Europe the NEFZ and in US the FTP75 or whatever's currently valid over there. Those resemble more realistic driving.
Edit: here you can see the cycles, it's in german but the pics speak for themselves:
http://www.hybrid-autos.info/Fahrzyklen.html
Or Wiki: http://en.wikipedia.org/wiki/Driving_cycle
Last edited by a moderator:
When I googled the FTP75 says it is derived from US06 cycle, but it looks similar to the UDDS instead. Strange, maybe my eyes are playing tricks on me. (edit it is my reading comprehension that played tricks on me actually...)
http://www.epa.gov/nvfel/methods/quickdds.htm
Anyway I left the test cycles link if people are interested.
http://www.epa.gov/nvfel/methods/quickdds.htm
Anyway I left the test cycles link if people are interested.
Silent_Buddha
Legend
Mass does have an effect on constant velocity and ancilliary to that efficiency of any drive system. Unless, of course, you have steel tires that are perfectly non-deformable and relatively low friction (a train for instance), and even then mass will still influence it, although to a much lesser extent.
The whole purpose of downforce in any form of racing is to increase the "mass" of a vehicle to increase friction and resistence where the tires contact the road.
You can't have increased resistance to forces perpendicular to the direction of the car without it also affect the rolling resistence of the car. IE - any additional benefit you get for corner is also going to increase rolling resistence and act as a breaking agent.
Just take the Bugatti or any of the supercars designed purely for high speed. The will retract or ditch having any sort of spoiler to reduce downforce (thus reduce the perceived mass of a vehicle) in order to reduce rolling resistence to increase top speed.
BTW - if you uncomfortable with the use of mass, just exchange it for weight which would be more accurate.
Regards,
SB
The whole purpose of downforce in any form of racing is to increase the "mass" of a vehicle to increase friction and resistence where the tires contact the road.
You can't have increased resistance to forces perpendicular to the direction of the car without it also affect the rolling resistence of the car. IE - any additional benefit you get for corner is also going to increase rolling resistence and act as a breaking agent.
Just take the Bugatti or any of the supercars designed purely for high speed. The will retract or ditch having any sort of spoiler to reduce downforce (thus reduce the perceived mass of a vehicle) in order to reduce rolling resistence to increase top speed.
BTW - if you uncomfortable with the use of mass, just exchange it for weight which would be more accurate.
Regards,
SB
DuckThor Evil
Legend
Downforce is just a by-product from air resistance. lowering air resistance is the real key to high speeds, not reducing downforce. Downforce also doesn't increase the mass or weight of the car, but is just a down pushing external force. Real increase in mass hurts cornering whereas increase in downforce improves cornering. Now I'm not saying that downforce doesn't hurt at all, but the air resistance is the more important factor as far as reaching top speed goes.
Mintmaster
Veteran
First of all, it doesn't change the fact that you responded with "LMAO ever heard of acceleration". I replied to your remark about constant speed travel, and that was not out of context.
Secondly, it does not make my post obsolete. If you bothered to read (I'm getting real tired of this laziness), you would have seen that I already explained why it does NOT have to be perfectly straight and horizontal. The only time mass matters is when the additional mass is enough to reduce the engine BSFC during passing/climbing or when its enough to require braking during hill descent. It takes a very long, steep hill for the latter to happen at highway speeds.
You are the one lacking in basic physics knowledge, and if I may be a cocky prick for a moment, trust me when I say you don't want to challenge me there.