Hybrid Gas Mileage Good? Bad? As Expected?

519 messages, Last post on Jan 16, 2007 at 7:14 AM

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What is this discussion about? Hybrid Cars, Fuel Efficiency (MPG)

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#62 of 519 Re: WOW [misterme] by usbseawolf2000 Jul 08, 2004 (1:48 pm)
"If Honda's 10KW motor does the job it is required to do and deliver the great MPG, why put in a larger one?" It's simple, the more a hybrid can rely on electricity, the more gasoline a hybrid will save. "What is the 0-30 and 0-30 specifications for Prius- I haven't located any." Prius' 0-60 is about 10 seconds. According to Car And Driver magazine, Prius' 30-50 is 5.5 seconds. It will be safe to say that Prius' 0-30 is around 4 seconds. "We both know our cars aren't rockets." I was surprised that HCH didn't make it to Consumer Report family car comparison test due to the performance issues but Prius did. Dennis Replies to this message: eaa (Mar 22, 2006 8:46 pm)
#63 of 519 Re: Synergy Drive [misterme] by djasonw Jul 08, 2004 (1:58 pm)
Paid $500 under MSPR. The Prius has a nice long wheelbase which makes the ride quite nice. I also have all the goodies that make the Prius so desirable. What goodies does the HCH have? Ah yes.. it has the IMA... what else? A tiny trunk? Seats that don't fold down? No electric A/C.. hmm... idling in traffic.. not too good for the environment if you have the AC on. Way too many things I hate to mention again. SCORE for the Prius!! Funny.. four major pubs averaged nearly 10 MPG better than the HCH. Tsk tsk.....
#64 of 519 Re WOW #50 Misterme by toyolla2 Jul 08, 2004 (10:58 pm)
Hi Misterme, I apologise my use of jargon that may be unfamiliar to you. And I did sprinkle blank lines amongst my text for increased clarity but when I posted they got removed automatically. Anyway I intend to answer your post where you seem to take exception that I said the electric motor was slapped on the side of the HCH's engine. So I did the Michael Moore thing and actually visited the Honda website to see what they have to say on the subject. On the IMA information page I found the following in HONDA's own words: " the crankshaft of the engine connects directly to the electric motor" and " The electric motor and the engine turn in tandem since they are connected together " If you could take a minute and go over to the Hybrid Honda Accord 2005 forum and look at that impressive post #193 USBSEAWOLF2000 prepared, you will find a color image of the HCH engine/transaxle. See the 10kw motor ? Slapped on the side isn't it ? However I don't need your apology we are all here to learn. I see USBSEAWOLF2000 has put up the Prius transaxle. You can see that neither of its two motors is constrained to run at the speed of the engine so they can work together to force optimal torque from the engine. Is that a good thing ? Yes, its a very good thing. This is only my third post this year, let's hope my technical writing will get better. Time for some math. Honda says their motor produces 36 lbs-ft 1000RPM but this is only represents 5.1 KW By extrapolation we can probably expect the full 10kw 2000RPM. Considering that the engine is barely producing torque at 1000RPM shouldn't the motor be producing 10kw here. You would think so because by the time the engine gets to 2000RPM that 1.3 litre will be starting to bite. And any power at all from the electric motor will start to become increasingly insignificant and less relevant as the torque from the engine rapidly ramps towards 87 lbs-ft as the engine gathers speed. Beyond 2000 RPM the electric motor torque will drop inversely with speed (because at full voltage the electronic controller will sit in current limit and supply constant power). In my previous post I alerted you to the fact that the motor was incorrectly geared and should be turning at least twice as fast as the engine so that it could deliver power to the system lower down the torque curve. I suggested that the mismatch was akin to pairing Arnie and DiVito as tag team wrestlers. It was meant to be humurous; clearly I was being too obtuse. But you can appreciate that 10Kw from 1000 to 2000 rpm could be useful. It would appear as 72 lbs-ft initially fading to 36 LBS-ft at 2000rpm in the area where the engine is weakest. But that would require the insertion of a 2:1 step up gear of course. Finally going back to that Honda website, did any one notice from their figures that at 3000Rpm the IMA provided only 18lbs-ft of torque? Get your calculator and and see that that works out to be 7.67kw. Where did the 10KW go ? Well that's exactly the problem when you use fixed field machines at high speed, it gets harder to force current in against the back EMF of the motor. I suggested the use of variable excitation to overcome that. It's probably not worth it for an extra 4lbs-ft of torque. But you could get a lot more than 4lbs-ft if you really cared enough. I am not going to speculate how much that's for the after market tuners to decide. THNX to USBSEAWOLF2000 and Misterme, I'm done. Replies to this message: usbseawolf2000 (Jul 09, 2004 10:41 am)
#65 of 519 Wow by motownusa Jul 09, 2004 (9:22 am)
Looks like this board is filled with automotive engineers and physicists. A layman like me will be too intimidated to post here. Anyway, just test drove an 04 Prius. My old man has ordered an 05 which he should be getting in late September or early October. This car is awesome. From the smart entry to the xenon head lamps and DVD navigation system, I think the $24G price tag is a bargain. I loved the near silent ride when the car is running on battery alone. Acceleration actually felt better than a Corolla or 4 cylinder Camry. Both my dad and I test drove the car and needless to say, we were both impressed. We couldn't drive the car for too long since it was someone else's pre ordered car. The salesman, whom my dad knows for a longtime really did us a favor.
#66 of 519 Re: Re WOW #50 Misterme [toyolla2] by usbseawolf2000 Jul 09, 2004 (10:41 am)
Replying to: toyolla2 (Jul 08, 2004 10:58 pm) "And I did sprinkle blank lines amongst my text for increased clarity but when I posted they got removed automatically" Did you use "Enter" to skip a line? I notice the board deletes extra "Spaces" "If you could take a minute and go over to the Hybrid Honda Accord 2005 forum and look at that impressive post #193 USBSEAWOLF2000 prepared, you will find a color image of the HCH engine/transaxle." I just found out that Prius's MG1 is at least 30kW, possibly 35kW. "Beyond 2000 RPM the electric motor torque will drop inversely with speed " If you want to see it visually, take a look at the graph. "It would appear as (HCH's IMA) 72 lbs-ft initially fading to 36 LBS-ft at 2000rpm in the area where the engine is weakest. But that would require the insertion of a 2:1 step up gear of course." We know Honda's IMA to ICE is 1:1, meaning engine RPM turns exactly at the same rate as the 10kW electric motor. There is no transmission between ICE and 10kW electric motor. For Prius, PSD enables three way CVT. It means ICE RPM and electric motors RPM can continuously vary to combine maximum output from gas and electric drivetrains. ICE, 30kW MG1 and 50kW MG2 ratio can vary at any time to maximize efficiency and fuel economy. All of this is made possible by a Pepsi can size PSD! I've pointed this out many times but no one seems to understand. Dennis
#68 of 519 MPG Averages by djasonw Jul 09, 2004 (12:40 pm)
I don't go by what people post as there tends to be a great deal of exaggeration. I go by what the major car pubs get as well as Consumer Reports. Each mag has a disparity of ~10 between the Prius and the HCH (the Prius ALWAYS on top). Still can't figure out what the HCH offers over a standard Civic besides a smaller trunk. Replies to this message: larsb (Aug 18, 2004 1:44 pm)
#69 of 519 re usbseawolf by toyolla2 Jul 09, 2004 (2:11 pm)
Hi Dennis, I think we are on the same page. In a nutshell what I was suggesting was moving the electric motor base speed down from 2000rpm to 1000 rpm artificially with the aid of a 2:1 reduction. In case you may not be familiar with the term "base speed". Base Speed is the lowest speed at which the motor can deliver full rated power. I was assuming that Honda wanted to assist the engine where it was weakest i.e. at 1000 rpm. So to connect a motor of 2000 rpm base speed -no one disputes this value do they ? - directly to it means that you only get the benefit of 5kw of power. Not the 10kw that you might have expected from the hype surrounding this vehicle. I call that a mismatch -an error. A financial tradeoff against the cost of coupling it separately on to the engine crankshaft via a 2:1 reduction gearbox. Without a gearbox, the only way they could get get 10kw power at 1000rpm would be to stretch the motor from its current 65mm thickness to 130mm. This goes with the general theory of machines that low base speed machines are always of larger frame size. There is no free lunch if you want to directly connect an electric motor to the crankshaft. And that, as we know, is what they did. Analyzing the IMA system We get at 2000rpm the rated 10kw while still pumping out 36lbs-ft. But then at 3000rpm it has dropped to 18lbs-ft (Honda's figures) If it was having no problems shouldn't this figure be 24lbs-ft !!! I don't know, you tell me. Clearly the controller being presented with higher frequencies and higher motor back EMF has run out of "headroom on the bus voltage" and is no longer able to supply the current needed. The transistors can put out the right frequency ok but it seems they've lost control of the current which is now being determined by the physical attributes of the system viz inductance and back EMF. And if it is 6lbs-ft lower than expected at 3000 rpm ....... Any guesses what the Integrated Motor Assist might be assisting at when the engine reaches a full bore acceleration at 5700rpm ? 2lbs-ft perhaps ? I don't know about you but that to me is one lame system. I would be happy to hear a rebuttal from genuine Honda fans. No salesman tirades thankyou very much. Why doesn't the Prius '04 have this problem particularly now they are using the lower 201v HV battery pack. Well, they headed it off by incorporating a seamless 500 volt up converter which gets energised before the inverters run into a voltage headroom shortage. Knocking the volts up will keep the inverters in control. Dennis any other issue ? Finally I hope tech talk won't scare anyone away who wants to post fuel consumption etc. Can't beat hands on experience. I believe that driving style and temperature are the largest factors affecting fuel consumption but knowing about your vehicle's system can be of help. For instance with the Honda Civic the above tech talk reveals that the IMA is fairly ineffective if the engine goes above 3000 rpm while accelerating. In closing, I must mention that on insightman's site he's put out an interesting fluff piece on Fuelorexia nervosa, you might wanna see. Replies to this message: usbseawolf2000 (Jul 09, 2004 6:23 pm)