By accessing this website, you acknowledge that Edmunds and its third party business partners may use cookies, pixels, and similar technologies to collect information about you and your interactions with the website as described in our
Privacy Statement, and you agree that your use of the website is subject to our
Visitor Agreement.
Comments
First, the hydrid works by reusing the engery to stop the car. While alot of energy is wasted stoping the car you can't even recover enough of that energy to get the car back up to the speed that you were traveling. This would mean that you have a perfect system 100% efficent which is thermodynamically impossible.
So lets just say i am crusing at 100mph and i come to a stop (in my prius, hylander, escape, ect) and my car recovers 80% of the engery it took to stop me. My prius does after all still have break pads so they are respocible for some of that stoping that can't be recovered. lets say the electric motor, batteries, and the rest of the system was perfect I could get back to 80mph without using any gas. This is not how it works, but stick with me. The point of my story is at some point in my trip back to 100mph or shorty there after I am going to use all the stored engery in the batteries and they are not helping me. I fact they can do nothing but hurt me because that electric motor and and those batteris wiegh alot.
The only way to get power out of that system is to use the gas powered motor to produce electricity to charge the batteries which would then run the electric motor.
For those of you who are still reading, If at highway speed the prius is able to use the gas powered motor to charge the batteries and then use that charge to run on electric and get better gas milage than it would by just running on the gas motor. I will hand over my engineering degree and quit my job. If the electric motor part of that hybrid car is that effecient why does it run on gas engine at all. why not just use the gas engine running at optimum condition to turn the generator charge the the batteries and run off a seperate electric motor. That is what trains do.
At highway speeds on long trips the hybrid part of the car is not going to help you. The way they are setup it is thermodynamically impossible. You are not going to get more power out than you put in and in this case the power still comes from the gas engine and stoping.
Do I think that Diesel is better than hybrid, No. Do I think that hybrid is better than Diesel, No.
To each his own. If you drive 50 miles to work everday at 55mph a hydrid probably isn't the best thing for you. IF you drive 6 miles in traffic to work the Diesel probably isn't the best option for you.
Its a gas-electric-human powered hydrid. There is a mini digerster in the back so when on a long trip you can take a crap right into this tank. :surprise:. The digester turns the crap into methane using the exasut heat. The methan is injected into the engine intake air and give a little boost to the system. You could even crap in it at home to build up a methane charge for the next days commute.
It would be perfect for guys like myself and others on this forum who are full of it. I know some politicans that would get about 400mpg.
Diesel, gas, hybrid, alternative fuels there is not one answer. everyone should look at what is best for the enviroment and there situation.
And that was my 2 cents not since
i'm going to ask one of my fellow elec-eng alums who owns a prius to explain how HSD can provide better fuel economy at 80 mph steady-state than an 'equivalent' non-hybrid at that speed in same chassis, perhaps even with the same gasser engine in both cars.
Here is the synopsis of the HSD. It's actually very simple. The HSD computer, and more importantly the driver, can turn off the ICE when it's not needed then turn it back on instantly when conditions change. It's seemless and requires no special effort other than to press the 'GO' pedal.
At highway cruising speeds whether 55 or 65 or 75 all ICE's are relatively efficient. In fact in most cases only about 65-75 hp are needed to maintain cruising speed. If an ICE has 155hp or 270hp or even 115 hp much is being wasted while cruising. This is the basis for the GM DoD and the Honda Odyssey and HAH engines turning off half of the cylinders when cruising in 'ECO' mode. In the HSD the computer uses this otherwise wasted energy to recharge the battery while cruising at 65 mph for example.
Now aerodynamics will cause a loss of FE for all vehicles above especially in the 70+ mph speeds. The loss is in the order of 20-30% as you noted.
There is an additional 'penalty' for the hybrids at these speeds because to maintain a speed of 80 mph one has to ride the ICE nearly all the time and it can't recharge the battery as often since it's nearly in full use driving the wheels. It still does 'charge on the fly' just not as efficiently. When cruising at 75+ mph what you have is a 1.5L 4c engine driving a 3000# auto. At this speed you will still get great fuel economy but it's reduced significantly as with all vehicles. Likely one would use 2.5 GPC ( 38-40 mpg ).
Example: The Yaris with the same engine and 500# lighter uses 2.5 gpc ( 38-40 mpg ) at about 55 mph. But at 80 mph the Yaris will likely fall from 38 mpg into the high 20's range since more fuel will be needed as well as the increased drag effect. The heavier Prius at is still about 30% more efficient even at 80 mph.
There is nothing secret or mysterious about the HSD. It really does use only 2 GPC ( 50 mpg ) on the Hwy at 55 mph in moderate weather on flat terrain.
if your logic/facts/understanding is correct, then it would it not be a slamdunk that HSD-hybrids would hold all the long-distance-fuel-economy records. but they don't, do they?
Huh? wind+solar power is much better. How is this comment relevent?
google search shows that this dude craig vetter has built a 470 mpg vehicle. surely the 470 number is questionable but your premise seems to be that shoehorning HSD into such a vehicle would improve its fuel economy, right? (if you could actually engineer it into such a small space?)
HUH????
Nope I never said anything like this. All that I stated was that the HSD does actually improve fuel economy on the highway for ICE's.
While I appreciate the fact that HSD may be too complex to explain in a few sentences, here are certain laws that cannot be broken. If HSD has overcome any of them, please let us know.
1. On the highway (no brakes), all thrust comes from the 1.5l engine with CVT. If the PSD somehow generates electricity from it to charge the battery and provide the other source of power, it does so at less that 100% efficiency.
2. Hence, an efficient 76HP engine with ECU optimized for fuel mileage WILL provide better MPG than the Prius on the highway, at much less complexity and cost.
The fundamental limit of all (non-plug-in) hybrid systems is that the gasoline engine has to provide 100% of the energy. As you say, it is impossible to capture all the energy lost to braking and then re-apply it (indeed, this energy goes from mechanical to electrical, and then back to mechanical... that is not a recipe for efficiency).
However, the fuel efficiency of gasoline engines varies dramatically at different RPMs / loads.
The real genius of a hybrid system is using the hybrid drive to help the gas engine when it is most beneficial (when the gas engine is the least efficient). The benefits even increase because you can use a smaller engine (less displacement, less internal friction, etc.) without sacrificing HP. Regenerative braking also helps reclaim some lost energy (although I often wonder how much, as it strikes me as more of a gimmick than anything else).
In general, your statements are correct (and well understood, I thought) that hybrid systems are least beneficial when cruising at a single speed for extended periods of time. Whereas Diesels are least beneficial in stop-and-go traffic.
Hmm, I don't know that I'm really adding anything to this discussion.
I did have a thought about the whole issue after i wrote my statement. If you are driving in an area with alot of hills and slight grades then when you are costing you could generate electricity and then use the electricity to propel you up the next hill. Thus the hybrid would help on long trips more so then the tripowered methane car.
And to all member before posting your message just remember what my dad told me.
"Son, its better to be thought an idiot than to open your mouth and remove all doubt."
1. On the highway (no brakes), all thrust comes from the 1.5l engine with CVT. If the PSD somehow generates electricity from it to charge the battery and provide the other source of power, it does so at less that 100% efficiency.
2. Hence, an efficient 76HP engine with ECU optimized for fuel mileage WILL provide better MPG than the Prius on the highway, at much less complexity and cost.
Again two common misconceptions.
1. Not exactly correct. You will need to drive it to see the slight difference. But the huge misconception is that the ICE is driving the vehicle all the time. It is not.
Basically yes the power to move the vehicle at highway speeds is primarily based on the ICE. Part of the energy of the ICE is used to drive the wheels and part is often redirected through the PSD to charge the battery. Call it 'excess' energy being put in reserve.
The HSD computer stores the excess energy generated by the ICE in the battery until such a point ( determined by the HSD computer ) that the ICE no longer has to run. The ICE is then switched off for a time - thereby burning no fuel. How long? That depends on individual driving conditions, terrain, speed, etc. It could be off for as much as 1/4 mile or half a mile or in my case 1.5 miles as I finish my commute home.
There is one other source of energy that also charges the batteries, the kinetic energy of the vehicle itself. When one lets off the pedal, beginning to coast, the HSD computer senses a change in 'need' and that the vehicle is slowing. It switches the electric motor to a generator to charge the battery even at highway speeds. Some of the kinetic energy of the vehicle as it slows becomes stored in the batteries. It's small but it's there. Yes this energy orignally came from the ICE but in other vehicles it's just dissapated not recaptured in any manner.
When the ICE is not burning fuel the car is still moving at 45 or 55 or 65. This is the essence of the efficiency. The computer or the driver can turn the ICE off yet still cruise at the current speed.
2. Not necessarily correct. A 76 HP engine theoretically could be optimized for maximum fuel efficiency in highway cruising situations but still it would have to run all the time.
However even in your theoretical case if such a 76 HP engine was tuned to max fuel efficiency it could be further enhanced by inducing it to turn off for periods of time thus not burning any fuel - as noted above.
However such a vehicle would be intended for too narrow a use and would not be marketable.
The reason the TCH is so well balanced is that it uses the 4c engine with a powerful motor. If you do drive a lot of interstate milage the hybrid does not help much, if any during those drives. But by having a 4c instead of a V8 you'll use less gas and still have all the power needed to maintain cruising speed. However you do have to eventually stop or slow down (with the V8, mostly to get gas). There the hybrid takes over and helps you maintain the high FE that you were enjoying while cruising on gas.
Diesel vrs Hybrid. Doesn't matter to me. No smugs here. I just decided to get frugal with my $'s. I just want good mpg's and a powertrain that doesn't get me ran over in traffic.
I considered the TDI but after owning one Audi lately, (also owned several BMW's and a VW in the past) I've come to the conclusion that German cars of late are not dependable. High quality, but not high reliability. I checked out several forums on VW's and finally marked it off the list as a risky purchase. If Toyota or Honda made a diesel I probably would have considered it. However with deisel selling above premium gas prices I don't think it presently competes with the hybrid on overall driving economics.
The problem Ford and GM will have is when the world finally says they need Deisels and Hybrid for large mass market production vehicles, Ford and Chevy will experience massive losses and layoffs in the wait to get these to the market. Then the market won't thank them for giving them what they wanted all those years. They will abandon GM and Ford and complain that they are behind the times. The worst of it is when they do bring it to the market you'll want to wait two years for them to get the bugs out of the systems. What better way to be prepared for the future than to run a small scale operation (like Toyota) that can then crank it up when the time is right?
I agree, that VW lacks the high quality that you get say from the [non-permissible content removed] cars. Unfortunately, basicly only VW and mercedes are the only diesel cars in the USA. From what I read, Toyota said that they will starting in 2008 selling diesel cars in the USA. I surely hope so, as I would surely believe the quality would still be very high.
Another thing is the 2007 diesel standards will tighing up and VW might not make the higher standards for their diesels. But there is rummers that they will produce an excess amount of diesels cars so they can continue selling into the next yr.
Hummm, what's your point with this comment? Do you think the working class knows something that the liberal/snooty/rich towns don't? I guess with that analysis we'd all be better off rubbing snuff, drinking beer at the bar after work and not wearing seatbelts? I've heard working-class people have a tendency to do those things.
I think this is one of those debates that cannot be proven one way or the other. Toyota would have to use the Prius body with its .26 CD with an ICE only to find the answer.
The one thing for sure is owners of new Jetta TDI are getting better than the EPA ratings. It is getting close to the Prius based on folks that post their mileage on the EPA site. Average driver is getting 41.3 MPG combined.
The bottom line is they are both getting better than the average car on the road, and that is a big PLUS.
At highway speeds on long trips the hybrid part of the car is not going to help you. The way they are setup it is thermodynamically impossible. You are not going to get more power out than you put in and in this case the power still comes from the gas engine and stoping.
Great discussion, btw. The key point missing in your analysis is that presently even the best engines on the road are way over spec'd due to the many ways they are used. As zodiac2004 pointed out an engine could be designed theoreticially for max fuel efficiency while cruising at highway speeds but it would have little torque and be an absolute slug in normal driving. ( 1980's small vehicles ). This wouldn't be marketable today. But that's marketing intruding on engineering.
The key point that you don't state is that there is a significant amount of wasted energy while cruising in today's IC engines. Toyota has developed a system to recapture some of this wasted energy ( burning fuel ) by allowing the ICE not to burn all the time. This is similar but different from GM and Honda's approaches. Even their 3-cylinder cruisers could likely be made more efficient if some of that excess were able to be recaptured.
To each his own. If you drive 50 miles to work everday at 55mph a hydrid probably isn't the best thing for you. IF you drive 6 miles in traffic to work the Diesel probably isn't the best option for you.
This is just incorrect. What drive system on today's market uses less than 2.0 GPC ( 50 mpg ) at 55 mph in highway driving. ( 75 mi commute daily. 85% hwy/15% city at averages of 63 mph/40 mph in moderate weather on flat terrain. ). The HSD/IMA is significantly better than every other gasser-ICE-only on the market with regards to fuel efficiency. Diesel is also nearly as efficent for highway usage.
Each system saves about 30-40% of fuel vs a traditional system. This is just incontravertible fact.
Now if there are developments upcoming where a traditional gasser can offer significantly greater efficiency than 2.0 GPC - and still be marketable - I am sure that everyone is interested.
I'm not sure that could physically be possible or why you'd want it. If you let off the gas in a hybrid the engine shuts down. I can't imagine what shifting would do to the system. The setup in the Toyota uses planetary gears around the main cog (my non-technically correct description). It's a CVT set up without shifting. The motor assists as needed by driving the planetary gears. It only has "1 gear"
I'm sure someone will come up with a more technical explaination than this. I've seen the literature to see how it works and I don't see how a manual would work or even if it did what help it would be.
It drives the wheels, charges the battery or does both at the same time.
And you know this from what data source. :P
As you know from our many exchanges there is no more upkeep on a 5 y.o. Prius than a 5 y.o. Camry.
I do understand your personal pov though.
The Diesel is going to give you the best benifit on the open road. I would suggest doing some homework before you buy either and consider the amount of driving you are going to do and where.
I have a feeling that I am going to rub some people the wrong way but the hybrid is not going to last more than 5 years or so on the current battery technology. The batteries will die and you will have to replace them. I would ask the dealer about how much it will cost to have them replaced and if there will be a recycling fee. You will probably get much better return on your investment if you do alot of driving over the road with diesel. To each his own.
On the other hand the more the battery is cycled the faster it will die, the person doing alot of stop and go will kill there batteries faster than a person who does alot of long distance driving. Either way the diesel will probably last longer. So if you decide that the hybrid is the way to go, I would lease.
As for a manual, good luck. Manuals are a dieing breed because noone in this country learns to drive them anymore. In some cars the manual cost more than the auto. I just bought a Liberty CRD (averaging 25mpg) and it wasn't offered in this country with a manual. If its a manual you want you might have to go with mercedes.
Restating the same thing over and over again doesn't make it suddenly become the truth. The Prius still is more efficient.
I have a feeling that I am going to rub some people the wrong way but the hybrid is not going to last more than 5 years or so on the current battery technology. The batteries will die and you will have to replace them. I would ask the dealer about how much it will cost to have them replaced and if there will be a recycling fee. You will probably get much better return on your investment if you do alot of driving over the road with diesel. To each his own.
You just violated your father's dictum. Crushed it. Destroyed it.
This battery question had a whole forum dedicated to it. While there are still some 'flatworlders' that consider the batteries to have a dedicated lifespan ( where you got 5 yrs from is beyond me, the minimum warranty is 8 yrs/100,000 miles ) Toyota's own testing and 10 yrs of production lead them to state that the batteries will last the life of the vehicle.
On the other hand the more the battery is cycled the faster it will die, the person doing alot of stop and go will kill there batteries faster than a person who does alot of long distance driving. Either way the diesel will probably last longer. So if you decide that the hybrid is the way to go, I would lease.
I think you might have to talk with your Dad again. Were you the poster earlier betting your engineering degree and job. Don't
I know you follow this site with hawk like eyes. What is your take on the center console going out on these 2 year old Prii? With replacement cost of $4200. This is not isolated as several posters had this problem. Some were lucky enough to be under 36k miles. That is the kind of long term problems I don't want with a car.
kallen2223, "Toyota Prius Software Problems" #695, 30 Apr 2006 4:53 am
grannyfranny, "Toyota Prius Software Problems" #694, 22 Apr 2006 11:27 am
Good heads up tho.
:)I believe that you're making the same mistake that you attempted to avoid in your original message.
Adding hills doesn't (or shouldn't ... if I remember my physics correctly) change the situation. All you're doing is changing where that energy is being used (more going up, and less going down).
But i did do some research on the Escape and decided that the technology and the risk were not worth it for me. 34 mpg city is great, But i don't do any city driving. There are probably 4 total stop lights between my home and work. Maybe you know something about a prius that I don't, which you probably do. I should have probably started my discussion with a disclaimer that said that SUV hybrids. I also am a Jeep CRD faithful getting more than 30mpg (the same as the Escape) on my commute and will bet anything that my CRD will outlast any hybrid on the road. The price tag was much less too. I paid just over 23K.
I still stand by my statement that the diesel will outlast and be a better investment than a hybrid. Those batteries may last 10 years like you say but in ten years how effective are they going to be. My lap top batterys still work but they only last about half an hour now compared to the 2 hours 3 years ago. No i don't think that they are the same. Who is going to buy an 8 year old prius off of you. There is too much unproven technology on those cars that we don't know about.
You are obviously a prius driven hybrid enthusiast. I am a home improving, off roading, camping, diesel enthusiast. We both have our blinders on to a certain extent. I would like to drive my car well past the day that its paid off. We will not agree on this issue no more than the Clintons and the Bushs would agree on how the military should be run.
Like I said before to each his own.
Here is the link.
http://www.newsroom.ucla.edu/page.asp?id=4420
He claims that he can improve city milage by 64%. That is a real improvement. As I am said before I don't do alot of city driving so the 12% highway will help me.
No battery, no electric motor, no super complicated computer interface. Just electronic valves, while relativly new it has been proven. The Diesels high compressions ratios will make the compressed air design possible. This one sounds like a real low tech winner.
I believe that I failed.
Giving your opinion should not be thought of as failure, as long as you are not slamming someone personally. So welcome to the forum and keep us posted on how you like that CRD. I would like to have that engine in a Wrangler.
LOL.... Actually from what I have seen on c-span, now that these hybrids have been around a while they are showing some short falls. One is when the car is out of warranty, those batteries need replacing and they cost big time so people are traking them in rather then incure the cost.
Yes Diesel is proven technology. Even Adof Diesel(the inventer of the diesel) used peanut oil to run his first diesel engine.
Yes since diesels get better mileage and have high torque at low end for towing, they are a better soulution for many people.
However, diesel must change along with the rest of the fossil fuel hungry countries, of which the USA sucks up 25% of the world's energy production and strive to go with B100, which will work extremely well for. Well except for the oil refineries that is. they surely don't want any changes to the status que, just as the head of exxonmobil said the other day...... "we made record profits and we haven't invested in anything and we will not build any new refernies."
So without gov't demanding and pushing towards, all types of alt/fuels development and production, nothing will happen.
One is when the car is out of warranty, those batteries need replacing and they cost big time so people are traking them in rather then incure the cost.
Just as with the previous poster you have picked up the fears of the 'flatworlder press'. In fact there is no proof, or even any examples, of any hybrid battery failing with normal usage - ever. None have unless they have been abused. That's 10 years now with no failures and no deterioration in performance.
The writers who are normally unfamiliar with the technology compare it to what they know best, flashlights and laptops, and figure 'well these batteries fail so all batteries must fail'. That's faulty logic.
Toyota categorically states that the batteries should '.. last the life of the vehicle' with proper care and no abuse. It's a non-issue for the several hundred thousand drivers now on the road. Only the fearful worry about it.
I would like to see how the prius's hybrid tech is helping on long highway trips. Can anyone give me a link.
Some like the gizmos.
Some like the image. (am sure you don't care about the image your vehicle projects)
Some like the fact that it has less of a pollution footprint than other vehicles. (a factor you give little weight to in your own vehicle decision - which is fine)
YOUR car choice was likely not a matter of black and white - it was not "simple" - it's not fair to assume that every hybrid buyer's analysis is that simple.
Mean
Median
middle 50%
http://www.greenhybrid.com/compare/mileage/
If you have a statistical interest this the the best place to investigate.
Correct! In another forum I just stated I didn't buy the TCH to save money I bought it to save gas. Granted I believe with the tax breaks (close to $5500 Fed and State) and the FE (38 so far vrs 16 with my Infiniti) I am saving money. However the cars I considered other than the TCH were all in the $37,00 to $45,000 range. There is no way to justify those cars economically, nor would I try had I decided on a Lexus. I would not have considered a Camry V6 as an alternative but in addition to the Tax Credits and the FE I saved an additional $10,000 on a car that "interests" me and that I enjoy owning. If I do have what appears to be a smug face, it's actually a grin This car makes me feel happy, not morally superior.
It's not always about the money.
I'm not even an environmentalist (I work in the oil and gas production inductry).
While I do like technology, what I really hate is for the US to be dependant upon foreign oil. I can't save the whole US, but if I don't do my part I can't complain about those that refuse to see the problem.
2013 LX 570 2016 LS 460
PSI*CFM*.004=hp
It would take alot of math to figure out the CFM for the power stroke from the air cylinder.
Just give it some time, those Gen 2s won't be in this situation for a couple of years.
Did you see the forum entry by the guy who bought a 2001, only to have the dealer give an estimate of thousands to replace parts of the transmission? Or parts of the HSD, if you prefer. I recall it as MG1, but I'm not sure.
After three DC vehicles and two GM vehicles each of which cost several thousand each to repair or had major failures before 60,000 miles, I know that there is no guarantees in buying these products.
Now having never spent a dime to repair a Toyota after 15+ years of ownership of 7 vehicles and 500,000+ miles, they have earned my confidence. Your experiences may be different. At nearly 40,000 miles annually I will max out a vehicle in 6 years in any event. Hey they are just machines.
Can you explan how the electronic help on over the road driving. Besides just saying that i don't know anything how the computer works, and saying its more effecient. Forget comparing it to deisels or other IC. Bottom line how does the electronics help the prius or any other hybrid get better milage on long over the road driving.
http://www.toyotageorgetown.com/hybrid/index.asp
Specifically as concerns highway driving if I understand your question ( paraphrasing ):
'How do the electronics/mechanical design of the HSD system allow a 1.5L ICE/HSD system move a 3000# auto at 2.0 gpc ( 50 mpg ) in highway driving whereas the same 1.5L ICE-only engine only moves a 2500# auto at 2.5 gpc ( 40 mpg )?'
IOW what's so special in the HSD that it gets 25% better fuel economy in highway driving over the ICE-only version?
Correct?
OK there are three ways the electronics aid fuel economy in highway driving.
1) The extra power of the ICE while cruising is redirected to recharge the batteries on the fly, even at 65 mph. This extra power in IC and diesels is just lost forever in other vehicles. The electronics in the HSD system recaptures some of it. The big benefit of this recapture is that for periods of time the ICE can be shutdown and burn no fuel even while driving at 65 mph. A traditional system cannot do this.
2) Everytime you lift your foot off the accelerator you turn off the ICE yourself. While slowing down, even a little, the electronics switch the electric motor to a generator which allows some of the kinetic energy of vehicle - which normally is just lost into thin air - into stored energy in the battery. This too then allows the ICE to turn itself off more often even when cruising at 65 mph.
3) The regenerative braking system captures more kinetic energy as well. This is not so important for Highway driving but you do brake from time to time.
The summary of all these three is that in the end the lost energy in a traditional system is recaptured via the HSD system into the battery and then driven through the electic motor to shut down the ICE about 30% of the time on a long trip. Drive from NY to LA for 3000 miles and your ICE will be shut down for about 900 miles during the trip. You can't do this with a traditional ICE vehicle. Thus a 1.5L traditional gasser will use about 2.5 gpc in that 3000 mi trip or about 75 gal of fuel. An HSD 1.5L system will use 2.0 gpc or about 60 gal of fuel. Take the trip in these two vehicles you'll save 15 gal of fuel while driving the entire trip on the Highway.
Alternate option - also very good - use a diesel engine and instead of shutting it down 30% of the time just use 30% less fuel ( diesel vs gasser ). Similar results are obtained.
Next steps into the future: Do both.
Clear?
regarding the hybrid-on-highway discussion, i think everyone is adding just fine to the discussion, although i'm not caught up all the way yet! clearly many or all readers with engineering/science background agree with me regarding the solid thermodynamic analysis that shows us that a hybrid on the highway cannot be a "win" in long-term/steady-state highway driving. again, MBenz has a research report in whcih they have done all the math for some cases - supposedly proving that a pure diesel will always be more efficient for highway driving than gasoline-hybrid. i think many hills & regenerative-coasting change the equation somewhat, but not enough to change the bottom line. i bet MBenz engineers/scientists agree.
some readers might want to read up on "road-horsepower" with regard to the presumed "wasted energy/horsepower" from the engine.
my reading of the reliability data for hybrids so far is that so far they are MORE RELIABLE than equivalent/similar non-hybrids. also i believe Edmunds' "TCO" data are solid and clearly show that prius/HCH are *in fact* some of the lowest-total-cost-of-ownership vehicles available - *very* cost effective. so credit where due to the hybrids, even while i pass by priuses/HCH daily and put down a special diesel-sooty-cloud or monaro-tire-chirp for each one!
i grant that the regenerative braking can help on the highway too. but i've got a problem with this alleged "extra power" of the ICE. i believe that part of the explanation is not entirely accurate.
again, the concept of "road horsepower" for vehicles is relevant here - it is the number of horsepower necesary to keep the vehicle moving on flat surface at a certain speed. for 60 mph, usually it is a number much lower than 100hp. if the engine has 200 peak-rpm hp and road-horsepower is 100 hp that does NOT mean there is an extra 100 hp being "wasted" at any rpm. is there any recoverable-by-HSD energy being 1hp being "wasted" when a 400 hp engine is using only 70 hp to keep the car rolling? i don't see how.
if the HSD is going to somehow capture "wasted" energy in a steady-state highway situation, someone is going to have to identify where that energy comes from. bottom line is that it's going to come from gasoline in the end. but there is indeed waste energy produced by engines: heat and noise for example. does HSD capture wasted heat or noise? of course not. so, what "wasted" energy is the HSD capturing in the steady-state highway situation? i believe the answer is "none", because there's no free lunch thermodynamically here or anywhere else!
if toyota has empirical evidence about this "pure highway cruising" situation, i'd be very interested to read about it!
To add to your investigative information, one can also look up (VW TDI type)diesel.
Also a tad off topic but still germane or having nexus to this thread: in a plain jane work commute, our 2004 Honda Civic just yielded a tank full at 42 mpg!! So this pushes our range between 37-42 mpg. (EPA 29/38) As a comparison the VW Jetta TDI's range is between 47-53 mpg (EPA 42/49)
I would swag the hybrid/s at the same mileage to be flawless, as the Honda Civic AND VW Jetta TDI have been. I also suspect that at the VW Jetta diesel's mileage of 73,000 for a 2003 the Civic will also be flawless (26,000 currently) as would say a hybrid (HCH/Prius) would probably also be. However the hybrid/s would be a bit long in the tooth given the cinderella/cinderfella thing going on with the batteries. However I am looking forward to hearing from folks with 250,000 miles.