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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
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Replying to: robertsmx (Apr 21, 2004 6:53 am) We quoted numbers from EPA and Consumer Report standard testing. Your data is from 12 hard-core hybrid drivers. According to that database it shows that even the classic Prius gets higher mpg than HCH. You tell me if that is accurate. "If a set up is producing excess energy (out), it must use excess energy (in). VCM is designed around the premise of minimizing the excess AND reduce frictional and pumping losses." I totally agree with you about the VCM premise of reducing frictional and pumping losses by half. The excess energy out is in question here. Are you saying Honda's V6 engine is incapable of making only 25 hp(in our example)? The lowest it can achieve by throttling is 50 hp? What I am saying is, there is no excess energy out to begin with, just inefficiency from excessive throttling. "In the Japanese mode of estimating mileage, Honda 3.0/V6 with VCM has shown 27% improvement." Hmmm interesting. Current Accord LX V6 EPA city gets 21 mpg and I4 gets 24 mpg. That V6 VCM 27% improvement(26.7mpg) could probably be achieved by driving purely on 3 cylinders(performance sacrifice). Clearly it is not real city driving. "Nothing is perfect, every design is full of compromises." Sure but better design has less compromises. In term of weight by HSD design, Prius sits nicely between traditional Corolla and Camry. The performance that HSD gained from the extra 50KW motor over IMA, using the same space, is enormous. The efficiency, room and lower emission gained are obvious too. Full hybrid is more efficient than a mild one. About Atkinson/Miller cycle...  Note: Classic Prius test data from an Independent source. Prius engine can produce 12KW (16hp) with 35% efficiency. Perfect for cruising on highway.  Classic Prius ICE torque below 1,500 RPM is very weak but electric motor complements the design. Atkinson cycle does not make sense for ICE only car because Atkinson cycle engine make very low torque at low RPM(0-1,500 RPM). Atkinson cycle engine can maintain 35% to 37% efficiency from 1,500 to max RPM while Otto cycle peak efficiency is about 32%. Unless you supercharge Atkinson cycle to make up for low end torque, it isn't applicable for any ICE only car. The reason Atkinson cycle makes sense for a hybrid is because of high torque electric motor. AC brushless 50KW motor used in Prius can output 295 lbs-ft torque from 0-1,200 RPM.  . 04 Prius 50KW motor performance. Blue is the torque curve and red is horsepower curve. Dennis |
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Replying to: andy71 (Apr 20, 2004 4:42 pm)  Dennis |
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EPA estimates and CR "standard testing" do not reflect anything close to reality that the sampling on the website provides. If things were that simple, everything would be so predictable. Are you saying Honda's V6 engine is incapable of making only 25 hp(in our example)? No. You bring up several technical details, yet ask questions such as these. I quoted gearing limitations a while ago. Recap that, there is the answer. better design has less compromises Very true. But who determines compromises? Is developing a new engine around a very specific transmission choice, extensive "weight fixing" considered compromise? 27% improvement(26.7mpg) could probably be achieved by driving purely on 3 cylinders(performance sacrifice) You're not sacrificing performance nothing when the vehicle is cruising. In fact, without it, you would be consuming more energy for nothing. Open up the throttle and the cylinders get back to work!
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Atkinson-Miller cycle engines may have reduced pumping loss (primarily due to reduced compression), but that also affects their output. So, and as you said earlier, it is more effective with supercharger or electric assist. There goes a major compromise. Supercharger comes with its own set of issues, including pumping losses and cost. In the end, it might be better to adapt to something that is proven and widely used. I believe the last car we saw with Atkinson-Miller cycle engine was Mazda Millenia (2.3 liter V6). With supercharger, it produced 210 HP (?) and was often compared to its 3.0 liter V6 counterpart. Why did Mazda not continue with the engine? Instead, Mazda is now using Ford Duratec to address its V6 needs. Accord Hybrid does not need a “special” engine. It is going to use an engine that is used by non-hybrid cars, one that is already among the most powerful, cleanest, most compact, lightest and arguably the most fuel miser V6 of its class around, and widely used. That’s no compromise, that’s just the beginning. Add VCM to it, to improve fuel economy by way of cutting down on losses probably most noticeable on highways, and add electric assist to it to help in city driving economy. Choice between mild and full hybrid is based on compromises as well. Honda engineers must have considered the Honda 80 kW AC motor that has been around since the early 90s, and currently being used in FCX. But then, they also ventured into a lighter and more compact package and developed the DC motor for Insight, and later, improved it for Civic Hybrid. And FCX is heavy at about 3500 lb (Honda refrains from calling it a hybrid though, since its prime mover is only the electric motor, with ultra capacitor used to store the charge acquired from the fuel cell stack). And much of the weight might be from the necessary reinforcements not just the AC motor. Civic Hybrid is about 63 lb. heavier than Civic EX (2675 lb. compared to 2612 lb., both with manual transmission). There are subtle differences and the hybrid probably saves a few pounds by using a more compact/lighter gasoline engine but may give up the same with addition of sound deadening and aero pieces. OTOH, as Auto World reported, Toyota had to go lengths to shave off 400 lb. from the curb weight of Prius to the current 2890 lb. To get something, you have to give up something. That’s compromise.
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Replying to: robertsmx (Apr 21, 2004 8:07 pm) True, YMMV depending on your driving style. MPG difference between two cars shown by two different standard testing should be relative to the mpg difference in the real word. Therefore, Prius(HSD) should get higher mpg than HCH(IMA). "I quoted gearing limitations a while ago. Recap that, there is the answer." So, the answer to my question is YES. Accord V6 is incapable of making only 25 hp(in our example). This is not because the engine is technically incapable but rather, due to it's 5-speed transmission limitation. I did address that issue by suggesting the use of a better transmission rather than VCM. Use 6-speed, 7-speed, or mechanical CVT to address this design flaw. "Is developing a new engine(Atkinson) around a very specific transmission(ECVT) choice" You know what is ironic? Toyota did not develop a new engine for HSD. They used the same Otto cycle engine and turn it into Atkinson cycle engine just by changing the VVT-i timing. VVT-i in Prius vary the inlet camshaft timing over 43 degrees of crank angle, instead of 3 degrees. Fundamental change in timing of intake changes everything. Expansion ratio is greater than compression. Pumping loss is virtually eliminated. Emission is lower. Torque output is almost flat. Engine efficiency gained by about 15%. I expect to see a new engine designed with Atkinson cycle in mind from the ground up in the 3rd generation of HSD. You can read more about their implementation of Atkinson cycle. http://perso.wanadoo.fr/mc-engine/atkin/corps.htm  OPERATION: (at 50% load) • Steps 1 to 6: intake at atmospheric pressure; • 7 and 8: load control by using Late Intake Valve Closing (in this case, 50%), the excess gases taken in are forced back into the intake manifold (back flow); • 9: the intake valve closes, imprisoning the required charge in the cylinder; • 10 and 11: compression at 10:1; • 12: ignition, followed by an expansion at a 20:1 ratio. May I remind you to think about the need for a transmission in the first place. What is the ultimate purpose of a manual, automatic, or mechanical CVT transmission? Technically, HSD does not have a transmission! HSD achieves CVT functionality by the use of combining RPMs from ICE and a electric motor; thus a hybrid. A full hybrid(HSD) does not inherit the need for a transmission from the traditional ICE only cars. The design is mechanically more simple than a traditional cars! In contrast, a mild hybrid(IMA) still require the need for a transmission plus electric powertrain components, making it even more complex than a ICE only car. A huge difference! Your argument reminds me of that UPS ground TV ad. The guy who was in charge of shipping was complaining because they started to use UPS. His problem was sitting there and do nothing because there were no problem to deal with. You are basically saying, HSD transmission choices are limited because HSD does not need a transmission. Your other argument of IMA being simpler because IMA's electric powertrain is smaller(10KW) is a weak one. "You're not sacrificing performance nothing when the vehicle is cruising" The "japanese mode" of testing is to cruise and never stop? The first impression I got was the city driving conditions of Tokyo. I dont' think cruising is possible over there. It is clear that they were driving in the city and avoiding all six cylinders from activating to achieve 26.7mpg; therefore sacrificing performance. I understand that VCM can give V6 power at an instant. Dennis |
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Replying to: robertsmx (Apr 22, 2004 8:55 am) I agree with you regarding Mazda's failure with Atkinson/Miller engine. How is it a compromise for a hybrid? Electric torque is "free" or available by design in the first place. Note: Atkinson ICE and electric motors are like ying and yang achieving balance. "Add VCM to it, to improve fuel economy by way of cutting down on losses probably most noticeable on highways, and add electric assist to it to help in city driving economy." Again, VCM is necessary to fix design flaws of a transmission and a Otto cycle engine. V6 240hp engine was required to make up for delays of mechanical power build-up and low-end torque. If electric power provide low-end torque at an instant response, why do you need 240 hp in the first place? HSD has proven to have power efficiency of 1.91%. I estimated that Camry hybrid will only need 127 hp engine to out perform a 240 hp ICE only car. "they also ventured into a lighter and more compact package and developed the DC motor for Insight, and later, improved it for Civic Hybrid." HSD uses an AC synchronous-type motor, which is a high-efficiency DC brushless motor with AC current. Furthermore, by arranging the permanent magnets in an optimum V-shape, the drive torque is improved and the output is increased, producing the highest output per unit of weight and volume in the world. "Toyota had to go lengths to shave off 400 lb. from the curb weight of Prius to the current 2890 lb." 04 Prius is still using steel body frame. Majority of the parts are non-extoic unlike the Insight. With Toyota track record, they will be returning a profit from the 04 Prius soon like the classic Prius. Looking at the results, HSD is more powerful, fuel efficient, simpler, reliable, and cheaper to produce. Camry hybrid(HSD) will further the gap comparing to Accord hybrid(IMA). Dennis |
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The "japanese mode" of testing is to cruise and never stop? It is clear that they were driving in the city and avoiding all six cylinders from activating to achieve 26.7mpg; therefore sacrificing performance. Japanese testing mode or any other “standard” tests (EPA and CR methods included) have flaws, and should not be used as reality which can change based on a variety of factors. I don’t understand your concern on “sacrificing performance”. Why do you assume that? VCM is designed to shut down cylinders when performance is NOT needed. It turns them on instantly when performance IS needed. I’m assuming that THS and IMA work similarly when the vehicle is at a stop with the accessories on (air conditioning). So, the gasoline motor will have to be running/idling overriding the idle-stop feature. I’m sure Accord Hybrid will also have idle-stop feature, but with accessories on, only half of the cylinders (hence only half of the displacement) will be at work. The fuel economy and emissions would match that of a 1.5-liter engine in those situations. Engines are most efficient when operating at max load. This is easier to obtain with smaller displacement. During cruising, which would you rather have, a 1.5-liter engine operating near max load, or a 3.0-liter engine nowhere close to operating near max load? If you choose the latter, you would hear no argument from me. If you pick the former, you would have seen the point of using VCM. I did address that issue by suggesting the use of a better transmission rather than VCM. Use 6-speed, 7-speed, or mechanical CVT to address this design flaw. And the flaw is? The amusing thing here is that Honda IMA could offer, CVT, a conventional automatic (any number of ratios), a manual, or even a clutch less manual. That’s flexibility, not a flaw. You are basically saying, HSD transmission choices are limited because HSD does not need a transmission HSD HAS a transmission, just a different kind of CVT. It still uses gear ratios (a continuous range of, as is true with any CVT). BTW, I stand corrected. The DC motor in Insight adds 36 lb.-ft (10 lb.-ft less than the version in Civic Hybrid), but the peak torque jump is 25 lb.-ft, however at different rpm. The 1.0-liter gasoline motor, by itself, develops 66 lb.-ft at 4800 rpm, but the combined peak torque occurs at 2000 rpm with 91 lb.-ft.
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VCM is necessary to fix design flaws of a transmission and a Otto cycle engine. Multiple ways to look at it: You take an existing engine, add VCM to improve its operating load characteristics. You take an existing engine, modify it to work on Atkinson-Miller cycle to improve its operating load characteristics. I’m not sure I would call either of them “perfect” because they are ways to reduce mechanical imperfections. If electric power provide low-end torque at an instant response, why do you need 240 hp in the first place? Car driving is more than getting to 15 mph. Horsepower is needed for performance. Just having low end torque and little horsepower isn’t going to cut it. If it could, Toyota would had been wiser setting the red line in Prius in 1500-2000 rpm range. I will be tossing around numbers based on assumptions, but it would make for a decent argument here. Lets us assume Honda has developed a 30 HP electric motor (develops peak power at 5500 rpm) and about 80 lb.-ft off-idle (800 rpm) to 2500 rpm (we do know that Honda has showcased several prototypes with 30-50 HP electric motors, may be one of those will be part of the Accord Hybrid). The Honda 3.0-V6 with VCM (in Japan) is rated at 247 HP  6000 rpm. Let us assume that the power output from the electric motor drops to about 23 HP 6000 rpm. Maximum peak power in this case would be 270 HP 6000 rpm, about the power output of a good 3.5 liter V6 (at the same engine speed). Now, let us focus at the low-end torque. The 3.0-V6 develops 185 lb.-ft at 2000 rpm. With electric assist, the net torque output at 2000 rpm would be about 265 lb.-ft (comparable to a good 4.0 liter V8 at this engine speed). With a 100 lb. IMA system (estimate), using existing conventional power train, 270 HP 6000 rpm, 265 lb.-ft 2000 rpm in a 3500 lb. family sedan delivering 30-40 mpg (city or highway) with potentially PZEV emissions rating will earn more than bragging rights. And if Honda mates this hybrid motor to its slick 6 speed manual, 0-60 run of 5.5-6.0 seconds would change a lot of perception that people have regarding hybrids. It would be interesting if Camry Hybrid with 127 HP can do that. 04 Prius is still using steel body frame. Majority of the parts are non-extoic unlike the Insight. Primary goal with Insight was to minimize weight (its gasoline engine weighs only 124 lb.), hence use of lighter materials and the most basic platform that Honda uses (Struts up front, with semi-independent rear, I bet Prius uses similar), and without compromising safety ratings requirements. You cannot deny the issue of weight with HSD. Yes, Prius uses much of the same material as a conventional car does, but unless Auto World was dreaming about 1500 kg without weight savings, Toyota had to change things to put it under 2890 lb. The only way we can argue for or against this is by replacing powertrain in Corolla with that of Prius and see how weight grows. HCH has shown it using Civic chassis, as is. Looking at the results, HSD is more powerful, fuel efficient, simpler, reliable, and cheaper to produce. We can argue all day on power, fuel efficiency, reliability and simplicity (to me, IMA is a much simpler application). But, how do you conclude HSD being cheaper?
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Replying to: robertsmx (Apr 23, 2004 7:46 am) VCM is designed to save fuel without sacrificing performance. My concern is how they achieved 26.7mpg and how misleading it is. We both can agree that EPA numbers are higher than in reality right? We drive in more aggressive, faster, and worse conditions than EPA test "routes". And yet Accord 4 cylinder only get 24mpg. So, to achieve 26.7mpg with V6 VCM, it must be purely driving with 3 cylinders at all/most of the time. "Japanese mode" must mean driving with 3 cylinders to get the most MPG, regardless of traffic conditions. Unrealistic. That's all. 04 Prius uses electric A/C powered from 1.5KW HV battery. It can actually shut down ICE if not needed. So, Prius could make 750cc Atkinson engine emission or no emission at idle when A/C is on. " If you pick the former(I assume you meant 3.0L), you would have seen the point of using VCM." In ICE only cars, VCM will reduce half of PP and PL problems in certain situations. Atkinson cycle engine will virtually eliminate PP and PL in all cylinders in every situations. You are thinking only in term of ICE only cars. In hybrid, you would not need 3.0L to begin with because you have to count the electric half also. Because electric boost is instant, hybrid can afford to have smaller ICE. VCM will make less sense for hybrids. "And the flaw is?" The flaw that I was talking about is in 04 Accord where 240hp engine was equipped with a 5 speed transmission. The result is inability to throttle down to minor load situations, such as highway cruising. Sure it offers with 6 speed. It can even offer with CVT but with the extra cost. In HSD, there is no inefficiency due to transmission because HSD does not have a transmission. HSD is always in the top gear and lowest gear at the same time! You might be wondering how can it be? HSD can achieve this because there is only one gear ratio that is permanently engaged. A continuous range of ratio is achieved by rotating an electric motor forward or backward depending on the ICE RPM and the speed of the car! There is no reverse gear either, the main 50KW motor just spin backward. That is why HSD can save about $1,000 without producing a transmission. C&D Test Results: Prius Top-gear acceleration 30–50 mph 5.5 50–70 mph 7.9 BMW 530I Top-gear acceleration 30-50 mph: 13.3 50-70 mph: 12.3 Dennis |
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Replying to: robertsmx (Apr 23, 2004 8:20 am) Honda solves half of the problems by putting a higher speed/price transmission and add cost/complexity to the engine with VCM. Toyota virtually eliminate all the problems by removing the need for a transmission and changing engine cycle to Atkinson without any compromise. Simple! Many credits were given to this design with awards. "It would be interesting if Camry Hybrid with 127 HP can do that." Camry hybrid with 4 cylinder ICE(127 hp) estimate was to beat 04 Accord V6 with 240hp in performance. It might even be a competitive with Accord V6 hybrid in performance and will lead in fuel economy and low emission. "IMA system (estimate).... family sedan(Accord V6 hybrid) delivering 30-40 mpg (city or highway) with potentially PZEV emissions rating will earn more than bragging rights." Hybrid fuel consumption will be directly related to ICE displacement and the power of electric powertrain. The more a hybrid can stay in electric mode, the less fuel it will consume. IMA design is going to loose to HSD in fuel economy department. It will be very interesting. The hard part will be to wait until those cars become available. Dennis |
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