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GM has selected a 1.4L engine for its Volt
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Written on: 28 July 2008 [13:29]
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ecoadmin
Administrator
Topic creator
registered since: 20.07.2007
Posts: 583
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Apparently GM has decided what type of ICE is utilized for its range extended Volt. More info here: http://www.greencarcongress.com/2008/07/volt-to-use-14l.html#more I would have expected a somewhat smaller engine. If google is to be believed, the Volt ICE outputs 66kW power. Why and what for is all that power needed? Can the batteries restore the energy quickly enough to keep the charge at around 30%? Twike 890
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Written on: 01 August 2008 [16:17]
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Lensman
 registered since: 31.05.2008
Posts: 75
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The Tesla Roadster's electric motor is rated at slightly over 200 KW, according to the Tesla Motors website. That's only a two-seater car, altho of course as a high-performance sports car it's pretty high-powered for its weight. I'm not sure why 66 KW would be considered over-powered for a 4-passenger, highway-capable car. How does this compare to other such cars? ecoadmin wrote: Can the batteries restore the energy quickly enough to keep the charge at around 30%? I'm not sure what you mean. Did you actually mean "Can the ICE keep the batteries charged at around 30%?" Yes. The Volt is intended to have unlimited range, which means the ICE alone must have the power to push the car down the road at highway speed. But if I understand it correctly, it will be a serial hybrid, so the ICE will only indirectly power the car by charging the batteries, and all motive power will come from the electric motor. [This article was edited 1 times, at last 01.08.2008 at 16:28.] |
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Written on: 03 August 2008 [19:42]
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ecoadmin
Administrator
Topic creator
registered since: 20.07.2007
Posts: 583
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Hello, Sorry for my poor writing skills...Yes. I did mean 'How can the ICE keep the batteries charged at 30%'. Would't this mean that the batteries need to be able to be fast-charged? Normally batteries are drained quicker than recharged. In order to keep the charge at the same level while driving, the lost juice would have to be replaced 'on-the-fly', while you drive. To do so, is it necessary to have a 66kW ICE onboard? Couldn't this job be accomplished with a smaller engine? Are fast charges reducing battery life in general? From wikipedia: The initial design as envisioned in the Volt combines an electric motor and 16 kWh (58 MJ) lithium-ion battery plug-in system[17] with a small engine (1 liter) powered by gasoline linked to a 53 kW (71 hp) generator. The vehicle is propelled by an electric motor with a peak output of 120 kW (160 hp). Guess the 66kW are necessary to feed the 120kW (peak) electric motor...am I correct? Shouldn't have had a window seat in school when attending Electrical Engineering class...  Twike 890
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Written on: 04 August 2008 [04:23]
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Lensman
registered since: 31.05.2008
Posts: 75
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Hey, I didn't mean to come across as a know-it-all... sorry if I did. I haven't had any classes in electrical engineering. Most of what I know comes from reading everything I can find on the Tesla Roadster, and a smattering on other electric cars. Doing a bit of research via Google: A Honda Civic, a fairly common relatively small 4-door sedan here in the USA, develops 140 HP from its 1.8 liter, 4-cylinder engine. 140 HP = 104 KW Looked at that way, 66 KW certainly is *not* excessive for a motor designed to provide the power to push a car down the road at highway speed. But keep in mind, for a serial hybrid the ICE doesn't have to supply *peak* power, but only *average* power to keep the battery pack from being drained too far. The electric motor, which actually propels the car, is rated at 160 KW, so that sounds like it will have good acceleration. But how much energy does it really take to maintain a car's speed when rolling down a flat highway? According to this website: http://mb-soft.com/public/headlite.html It takes about 41 KW to push a Corvette (a large, fairly aerodynamic, 2-seater sports car) down a level highway at 70 MPH. Another website says for mountain driving-- that is, continuous uphill driving-- about double the normal power is required. So based on those two numbers, if the Volt can do 70 MPH driving up a mountain with only a 66 KW engine powering it, then it's doing pretty darn well. I would guess that it could not-- that you'd have to drive at a lower speed when driving uphill for long distances. So based solely on those numbers, 66 KW doesn't seem to be excessive. Ecoadmin, if you have some other numbers I'd like to see them. The numbers I found may not represent the average car. [This article was edited 1 times, at last 04.08.2008 at 04:33.] |
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Written on: 04 August 2008 [15:58]
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Franko30
Administrator
registered since: 08.09.2007
Posts: 88
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Hi Lensman, This is going to be difficult, as my technical English isn't quite that good... I'm wondering why the Volt developers incorporate a 160 kW electrical motor into a car like his. 160 kW electric make this car a rocket: A 160 kW electrical motor is much more powerful than a 160 kW internal combustion engine! Why? Because (as I read on German Wikipedia and other sources) an internal combustion engine has a theoretical maximum efficiency of about 37% (gasoline) to 45% (diesel). But in a car, the motor never runs at its optimum, which gives us an efficiency of about 15-20% in real life! Deduct from that about 5% losses from the gear train, catalytic converter for the exhaust etc. An electric motor has a theoretical maximum efficiency of 99,5%. Asynchronous motors (used in the Twike) reach about 87% efficiency, whereas synchronous motors (not used yet in cars) could reach up to 95%. Again: deduct about 5% for gear train etc. So let's say, a combustion engine in a car gives us 15% overall efficiency as explained above and the asynchronous electric motor gives us 87% overall efficiency, then: A 160 kW electric motor will bring 160/100*82 = 131 kW on the street. A combustion engine that is to bring 131 kW on the street wouzld have to have 870 kW (870/100*15 = 130,5 kW)!!! So, the question is: Any errors in reasoning on my side, or is this Volt supposed to be a rocket car? Cheers Franko30 [This article was edited 2 times, at last 04.08.2008 at 16:26.] Mitsubishi i-MiEV + Citysax 002, davor/formerly Twike 808 and 891
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Written on: 04 August 2008 [18:41]
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ecoadmin
Administrator
Topic creator
registered since: 20.07.2007
Posts: 583
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Franko30 wrote: A 160 kW electrical motor is much more powerful than a 160 kW internal combustion engine! Hello Lensman and Franko30 and all those reading this  I'm not sure if the above statement is correct. When an engine is rated at 160kW (electric or ICE), then this means IMHO the output power is 160kW. Please correct me if I am wrong... In order to deliver the 160kW, the electric motor is doing a much better job requiring far less energy because of its higher efficiency. Wikipedia: The Volt is expected to get 50 mpg (US) (4.7 L/100 km) if the battery is discharged... 4.7 L/100km or 50 mpg is equivalent to about 47kWh. Interesting to know would be how much kWh's are used to drive the Volt 100km. A Th!nk City for example uses about 15kWh/100km and a Tesla Roadster has a plug-to-wheel efficiency of 199 W·h/km or about 20kWh/100km. So the Volt should not use much more than 20kWh/100km. Lets assume we do the 60 miles / 100km in 1 hour. If we drive down the highway for an hour at constant speed, we could theoretically get 66kWh from the ICE of the Volt. But since this is a maximum power output with a much reduced mpg value, the ICE outputs probably less kWh if run at an economical level. Account for losses when recharging and you will get closer and closer to the 20kWh used in one hour when driving a distance of 60miles/100km. 20kWh are equivalent to about 2L/100km or 117mpg. So when the Volt is using its ICE its efficiency is greatly reduced. The unanswered question is how much power does this ICE deliver when running at its most efficient level and how much is lost when recharging. If the 20kWh plus the loss are below the average output of the ICE, then the ICE is a number too big. But I might be wrong here and the 66kW peak-output is needed to recharge and deliver the 20kWh to the batteries... One thing is for sure though: I would expect more mpg of an engine running always at its optimum performance just to recharge a battery. Even a Toyota Prius or other a small city car uses not more than that. The benchmark should be rather at around 3L/100km or 80mpg. Stephen Twike 890
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Written on: 04 August 2008 [19:17]
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Lensman
registered since: 31.05.2008
Posts: 75
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I don't know if a 160 KW electric motor means 160 KW input, or that amount of energy output. At any rate, it doesn't make much difference, because as has been said the electric motors used to power cars are extremely efficient. OTOH I'm fairly sure that if a gasoline engine is rated at XXX horsepower, it actually means the engine outputs that much HP (horsepower), and a rating in KW would just be converting HP to KW. So the difference in power between an ICE and an electric motor developing 160 KW wouldn't be that great, if any. I think that's the point Ecoadmin was making. But 160 KW *does* seem very powerful for a mid-sized car that's not marketed as a sports car... compare to 104 KW for the Honda Civic. I don't know why they would put in an electric motor that powerful. With only a 40-mile electric range I wouldn't expect the battery pack to be all that heavy, so the car shouldn't be excessively heavy, and I can't think of any other reason it would need such a powerful motor. [This article was edited 1 times, at last 04.08.2008 at 19:18.] |
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Written on: 04 August 2008 [19:41]
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Lensman
registered since: 31.05.2008
Posts: 75
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ecoadmin wrote: A Th!nk City for example uses about 15kWh/100km and a Tesla Roadster has a plug-to-wheel efficiency of 199 W·h/km or about 20kWh/100km. So the Volt should not use much more than 20kWh/100km. I'm not so sure. The Tesla Roadster is highly optimized for low rolling resistance and light weight. That's part of why it's so expensive, using carbon-fiber body panels and an all-aluminum frame. Unlike most cars, it has no toe-in on the front wheels, again to reduce rolling resistance. Chevrolet can't afford to spend that much on building an approx. $35,000 car, and I don't know if they'll be willing to eliminate toe-in for a car aimed at the general public. Plus, the Volt will be a 4-seater whereas the Roadster is a small 2-seater. I expect the Volt to use somewhat more than 20kWh/100km. I don't know enough to guess how much. |
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