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Hybrid Vehicles Honda Accord Hybrid Honda Accord Hybrid vs. Toyota Camry Hybrid
337 messages, Last post on May 07, 2008 at 5:57 PM
You are in the Honda Accord Hybrid Forum. Your Host is pf_flyer
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Replying to: midnightcowboy (Sep 06, 2005 11:23 am) LOL Yes I understand, ICEs are about 60% efficient, diesels about 80%, and electric motors/generators are actually closer to 95% effciency. The highest efficiency gas ICE is from prius and it is only 35%. Diesel holds the title at 38-40%. All cars get lower efficiency in the City. The only reason the Hybrid HSD ( Toyota/Lexus) gets better mileage is because the electric motors use previously stored chemical energy ( batteries, i.e. potential energy) and convert it to motion (kinectic) through electric mtoors. The Honda IMA system is similar whereby the electric motor augments the ICE at low speeds; The reason hybrid gets good gas mileage at city is due to 2 things. One is regenerative braking. The other is the ability to produce low horsepower efficiently (either ICE or electric) 2-10 hp, needed for low speed cruising. Your regular engine is not efficient at that low hp running, city mileage/low speed mileage gets hurt. HSD and IMA has there own advantages and disadvantages. Toyota has better mileage but honda is catching up with the 06 HCH. And yes at 75 you get poorer mileage than you do at 55 mph. But this is true of any car and has absolutely nothing to do with Hybrids. True, Theoritically, the nonhybrid should even have better mileage at the highway since there is no added weight from the battery. But this is reality Roads have intersection, curves, stop signs, traffic jam. Even on regular travel to work most people only get city rating while on the highway. You have to keep up with the traffic and mileage becomes secondary to safety. Now for the twist, hybrid are geared for economy and has to the ability to glide, just like shifting neutral on a stick shift. This helps a lot on highway mileage. |
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Replying to: midnightcowboy (Sep 06, 2005 11:23 am) You can use a conservation of energy analysis to determine the mileage that you'll get. You can assume that the ICE produces energy at a particular efficiency. If there were no losses from friction, you would be able to travel at a particular elevation forever. Unfortunately, we lose energy in lots of places. The major ones that I can think of are: --Wind --Tire Rolling Resistance --Transmission Losses --Engine Losses (proportional to RPM^2) --Alternator (your 10 kW stereo, AC) --Water Pump --Braking Losses Now, to get higher efficiency, we need to eliminate or reduce some or all of the above. The hybrid reduces the Braking losses. It also reduces the engine losses, mainly through the use of a smaller engine, which will have fewer friction losses than a larger engine. Note that on the highway no car experiences the braking losses. The energy recycled by the battery/motor combination was originally produced by the ICE so the fact that it is recycled simply reduces the braking losses that occur during the EPA's city driving test. If they just drove around in the top gear at 40 mph or whatever speed would make sense with the top gear's ratio, then they would achieve better mileage than on their highway tests, which do not have stops, but are done at a higher speed. Now, this concept is the important one and requires some understanding of math. The friction in the fluids grows at the square of the velocity. That is why the wind makes a big difference at high speeds and almost none at low speeds. You get the same effect in the engine oil, transmission oil, and bearing grease. Remember, we were talking about why the hybrid gets better mileage in the city as compared to the highway so there is no need to compare the hybrid to the non-hybrid. If we look at the losses that I listed above, the engine losses, transmission losses, and tire losses all get smaller on a per-mile basis at lower speeds. The fact that the braking losses are reduced (lets say eliminated, even though that isn't true, even if we use your 95% number) would simply make the city mpg the same as the highway mpg if all of the other losses stayed the same. They don't. They get worse at high speeds so that is why the city mpg is higher. Your post is full of quite a few made up numbers. Lots of enthusiasm though. |
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Replying to: tradscott (Sep 06, 2005 7:10 pm) "The energy recycled by the battery/motor combination was originally produced by the ICE so the fact that it is recycled simply reduces the braking losses that occur during the EPA's city driving test" This is what I said all along, you sure have a funny way of admitting you were wrong and agreeing with me.  Yes, I threw out some numbers on the efficiency; it wasn't worth it to look it up. Gas engines are very inefficient, diesel are better and electric, at least brushless, are very efficient. However, no energy conversion is 100% efficient. Anyway thanks for finally agreeing with me that the stored energy in batteries ,derived from regenerative braking, makes hybrids more efficient in the CITY cycle, which is why the EPA of the Prius is 60/51 YMMV, MidCow
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Replying to: midnightcowboy (Sep 07, 2005 4:28 am) |
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Replying to: midnightcowboy (Sep 07, 2005 4:28 am) Eliminating the braking losses would only make city efficiency equal to highway efficiency, which also does not have braking losses because you don't use your brakes while cruising at a constant highway speed. The hybrid system makes the vehicle more efficient in the city than it would otherwise be, but does not make it more efficient in the city than the same vehicle is on the highway. That difference comes from other factors, as I already attempted to explain.
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Replying to: tradscott (Sep 07, 2005 5:37 am) 1) Kinetic energy to AC current done by the motor (~90% efficient) 2) AC to DC conversion through full wave rectifier ( ~ 82 % efficient) 3) DC to AC conversion by PWM (~90% efficient) 4) AC to kinetic by motor (~90%) To get the overall efficiency we multiply .9*.82*.9*.9=0.597. So the regenerative braking is only about 60% efficient. This is a best case estimate. Toyta only claims that 30% of the energy of braking is actually recycled. A large part of this is that the mechanical brakes do some of the braking in quick stops. The regenerative braking is not as effective as most people realize. It is a concept which has been highly advertised and can be readily understood, at least in concept, by the general public. The problem is than many people think that this energy comes for free, which it doesn't. It was originally produced by the ICE. That is, unless you plug your modified Prius in at night. Then the energy comes from a power plant, which is far more efficient than the ICE. |
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The original statement was about mileage ( miles per gallon) in the City on Hybrids being better than City mileage of Internal Combustion Engines (UCEs). Nothing was ever said about city versus highway effciency. That beng said with a 4 cylinder HSD type hybrid in the upcoming Camry is should get 45 city and 40 highway . 45 is 5 miles per gallon higher than 40 miles per gallon highway. The normal 4 cylinder automatic Camry currently is EPA rated at 24/34 the city mileage is 10 less than the highway mileage because it is not augmented by electric motors. Taking the ICE 4cylinder Camry as a base then the hybdrid Camry would be (45-24)/24= 87.5% more efficient in the city and (40-34/34) = 17.6% more efficient on the highway. The Hybrid Camry will be more efficient in the City than an equivalent ICE Camry. Also, comparing Toyota's HCS to Honda's IMA technoogy , Toyota as a full hybrid can run elctric only whereas the IMA (except for the new Civic hybrid) cannot. However, an interesting observation: Honda sems to do two things that Toyota doesn't: (1) It tends to meet EPA estimates and (2) tends to be more efficnet on the highway ( why spin MG1 when the traction battery is already fully charged ??). Cheers, MidCow P.S.- It is hard to judge the knowledge and experience of forum particpants. I believe you may have misjudged me
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Replying to: midnightcowboy (Sep 07, 2005 6:34 am) |
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Replying to: midnightcowboy (Sep 07, 2005 6:34 am) midcow- It has nothing to do with HSD; the HCH also gets better city mileage, as I recall, and it has a CVT. The higher mileage is achieved by the electric motors and turning off the engine while stopped. The original statement--made by you-- was that the prius and other Toyota hybrids get better city than highway mileage. A statement followed that this was due to the electric motors and turning off the engine while stopped. I stated that the regenerative braking and turning off the engine while stopped can only explain parity between the city and highway mileage; not an increase. The increase comes from other factors. |
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Replying to: bamacar (Apr 17, 2004 4:08 pm) If they use the same technology as the Hy-Highlander you can expect ~ 270 HP in the new V6 Camry. V8 power with Corolla/Civic gas mileage and emissions... and the styling of a Lexus. Interesting thought. With the Hybrid Camrys being built in KY in 4c or 6c configurations ... Is the Prius long for this world? People buy Camrys like they do any staple - with little or no hesitation. Imagine a long time Camry owner deciding between a Prius and a Hybrid 4c Camry with avg mpg in the 40's. It would seem to be a nobrainer. The Prius attracted the 'early adopters' and the techno-philes and won all the awards. I'd venture that the Hy-Camry will bring the technology into the mainstream and possibly make it commonplace. FWIW kdhspyder
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