• Dec 28, 2006
Hybrids definitely do work -- we're not refuting that -- how well they work is open to debate, however, especially in light of the revisions to EPA mileage numbers. So, let's examine the Prius. Amazingly engineered vehicle, that's for sure. The way they got all those different systems to work as a team and perform smooth handoffs between functions is pretty incredible. We're not going to bother with the electric powertrain portion of it for now. Have you ever poked around the gasoline engine in the Prius? Interesting stuff, lots of little tweaks to boost efficiency. We're wondering, having looked over the Prius, whether you could realize most of the gains without the batteries and motor.

More after the jump

The first thing Toyota did was fit the Prius with an Atkinson-cycle engine. The Atkinson cycle leaves the intake valve open for part of the compression stroke. While that seems counter to efficiency gains, it keeps cylinder pressures in check and allows longer burns, ensuring more complete combustion and extracts more work from the intake charge. The lower cylinder pressures reduce NOx emissions by keeping temperatures down. We'd be curious to see the 1NZ-FXE engine in the Prius fitted with Toyota's trick "dual-injection" system. The dual-injection system uses both direct gasoline injection, into the cylinder, and indirect injection, into the intake port. The reason for the seemingly redundant systems lies in optimizing swirl and atomization. Teaming the two methods together allows more optimal tuning across the RPM range, resulting in better efficiency and performance.

Sticking to the engine, there's an insulated canister fitted to the Prius that works like the vacuum flask we fill with fine coffee every morning (lest we have to stoop to store-bought swill). Warm engine coolant is held in the canister and then re-used to speed engine warmup. This is a really slick trick and would likely bump every engine's MPG rating a hair, as time spent warming up would be greatly reduced. Another thing to consider for colder climates would be gasoline-fired coolant heaters. These are pretty commonly fitted to vehicles in Scandinavian countries. They consume a fraction of the gasoline used by a running engine and are a far more efficient way to pre-warm your coolant. It'd also mean an end to our neighbor's seemingly endless idling at 4AM. WIth the coolant pre-warmed, the engine is able to get into it's most efficient mode of operation much faster.

An automatic transmission (or CVT like the Prius) is undoubtedly the way to go for emissions control. With fly-by-wire throttles, the conditions of shifts can be tightly controlled so that the engine management isn't chasing the driver's input like less integrated systems have to do. The throttle plate can be feathered, timing optimized, fuel delivery exactly metered, all to ensure a perfect shift as cleanly as possible. Team the transmission with a steep final-drive ratio, and program it to short-shift, keeping the throttle plate open wide, and pumping losses are brought down. We're not sure what the current state of throttle-less gasoline engines is, but the last time we checked, it was difficult to get them to meet emissions targets. While it would seem great to just run the thing as lean as possible, cleanliness suffers. With a lean mixture, there's not as much fuel to absorb heat in the cylinder, leading to excessive cylinder temperatures and very high combustion pressures. Those lead to increased NOx, which is one of the more difficult internal-combustion byproducts left to control; engineers have done a great job figuring out how to tame most of the others.

A low coefficient of drag can have a marked effect on MPG at elevated speeds. The Prius has a low .26 Cd. Lessening the wind resistance through body shape has to be the most maintenance free way of lowering consumption and thus emissions. Those savings last for the life of the car (provided it's repaired after any crack-ups). Tires that offer low rolling-resistance are also a proven way to reduce fuel consumption. The tradeoff is typically that ride and handling suffer, but we're not sure how true that is anymore. A lot of it comes down to tuning the car for its prospective audience, and efficiency-geeks don't typically feel the need to go whipping around corners (though you could do it, and be efficient at the same time!).

Lastly, weight reduction is a huge factor. Cars today are heavy. Using composites and aluminum where possible helps, and safety equipment isn't light, either. Not only that, vehicles are expected to come full-boat loaded. Power everything, nice stereos, HVAC that'll roast marshmallows in the winter and chill sodas in the summer, etc. The Prius really shines at delivering a remarkably normal driving experience for all its technogeekery. We're just curious how the Prius would do without the weight of the battery pack and electric motor, and a little more gumption from underhood (perhaps throw a supercharger on the engine, making it a Miller Cycle).

Let's make sure we're clear here - this is not Prius hating. We're just wondering out loud about possible solutions that would yield across-the-board efficiency gains for all the cars that are not blessed with Hybrid Synergy Drive. We can learn some new tricks from the hard work that the Prius team has undertaken, and we'd love to see Toyota lead the way applying bits and pieces across their entire line of vehicles.


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  • 45 Comments
      • 8 Years Ago
      Toyota definitely deserves the respect they get for building these cars. All the "hype" that surrounds this car is what will sell hybrids from all the automakers willing to sell them. No one likes to mention that since this segment has become mainstream it won't be long before battery technology has advanced and Toyota/Honda have built a good economy of scale that will actually make hybrids deliver on their promises. Everyone who bemoans hybrid cars does so for the exact reasons that many new technologies are undercut. The average Joe doesn't understand that innovation is a long, expensive, ego filled process. Imagine the first owners of the CD player? They overpaid for an undersupported technology to make themselves look good, but thanks to those people, the average person can now afford digital music. See a pattern?
      • 8 Years Ago
      Another viable tool for any car is Orbital Corporations Air-Assisted Gasoline Direct Injection. It seems to me that it would be more efficient than the Toyota "Dual-Injection" system.
      • 8 Years Ago
      aaron-Hybrid sales are up in 2006, not down. As for payback, it depends on what you are comparing it to. A comparably equipped (non-hybrid) Camry costs not much less than a Prius.
      • 8 Years Ago
      Gotta echo #36's comments on #3's ignorance. Google on "Honda Accord Diesel" to learn about the presumptive 45-state car sold in Europe since MY'04. Google on "Toyota diesel" and skip over the hits on diesel generators to learn about the Avensis (Euro-version of the Avalon?), with 2,216 patents granted on its emission control system alone. Go to world.honda.com and search on "diesel" to learn about the 50-state (Tier II BIN 5) car whose _completed_ development was announced 9-25-06.
      • 8 Years Ago
      Prius is an engineering marvel unmatched on this side of the Pacific. If far outshines any other car in its class available for sale in the U.S. for mileage and low emissions. It does so while being a very practical and affordable mid-sized sedan, with all luxuries and features common in that class and then some. Choosing a Prius over any another new sedan in its class is economically justifiable and environmentally rational.

      These are facts. The rest is just sour grapes.


      • 8 Years Ago
      45. In auto engineeering the 'piddling' things all add up to a big impact, especially over time. The Prius is really Toyota's fist crack at an urban market mid-size sedan for the post MY 2013 period (yes,they think way ahead). The underlying assumption was made in 1993 by senior management that many of the vehicles then selling well (and vehicle technologies) would be uncompetitive in 20 years (MY 2013), just as the entire MY 1973 product line would have been uncompetitive in MY 1993. They decided to figure out just one big & predictable market segment (mid side sedan) and to tackle it piecemeal. The result was the 1997 Prius. followed by the 2004 2nd gen model (much closer to the target.) In 2009 they will introduce a third generation product and be exactly on target. By doing this they got a lead on things and are positioned to move quickly - especally if macro trends like 'peak oil' start to play out. There are more elements to consider as well. By doing this early they have built up a base of hard to replicate knowledge in the company and retail network about servicing electric drive trains. Meanwhile, Detroit squandered the recent high profit years (based largely on big SUVs that REQUIRE low cost fuel -something Detroit can't control) and did not allocate much to the next decade's products. For Toyota the Prius was a small wager on the future. Remember they make more money then then any other auto company. If they are right - they win big, if they are wrong - they just keep punching out the current stuff - either way they still win. They could write off the whole hybrid investment and not be hurt.
      • 8 Years Ago
      What about those skinny tires? If you're willing to trade grip for economy, that's the first place to start.
      • 8 Years Ago
      Not just skinny tires, but properly inflated tires. How many extra gallons of gas are burned every year because people don't manage their tire pressures?
      • 8 Years Ago
      The Prius gets a lot of it's extra mileage from the engine shutting off at stoplights and ohter stops. Sometimes I sit in a long construction zone and wonder how many hundreds of gallons of gas are being burnt for nothing. But not the Prius. A 45 minute mile of stop and go waiting costs absolutely nothing in gas. And that is all about the electric motor. And regenerative braking which keeps the charge up and ready for this kind of situation.

      Reading through these posts, there is no constructive criticism of the Prius, but there's sure a lot of sour grapes that it even exists and does so well. Denial, denial.

      The bottom line is that it's a fabulous car that works extremely well, and nothing else in the world can match it for what it can do. Wishing it would go away won't do any good. Pretending it isn't what it is won't work either.

      The only thing left to do is be like Ford - buy the technology from those who know how to do it (it's ok to pretend you worked it out yourself, but paid Toyota licensing fees 'just in case'), and make your own. Humility isn't such a bad trait, is it?
      • 8 Years Ago
      UK fuel economy numbers will be slightly inflated (different gallon). So, that's about 40 combined. There are other companies with better diesels than Toyota.

      The fact is the Prius averages around 45 for most people (if you claim you always get 50s, then I smell a lie somewhere). How much of that is battery and how much is all the tweaks? For the performance, it would be difficult to get 45. If you strip out the battery, you could have a slow trip to 60 and probably average 45+ on the hwy, but your city mileage would take a beating (probably like 30-35). So the battery adds something.

      If you really want to see what the battery adds, then look at the Ford Escape or the Toyota Camry. Contrary to epilonious up there, Ford's hybrid system runs on battery only as well. (Yes, it is similar, but Ford developed theirs seperately. The Escape also has a similar CVT to the Prius because its from the same supplier).

      Well, the Escape on the highway with the hybrid system has usually gotten 26-27 mpg in road tests, versus about 25 for the regular 2.3L. Swinging around a city, it has gotten about 26-28 depending on magazine versus around 20 for my rental car the other week. Not bad. Where it really shines is in stop and go where someone averaged over 50 in the Escape. You see similar numbers for the Camry. About 34-36 on both city and hwy versus EPA of 25-34 for the standard 2.4.

      These cars differ in a couple areas: weight (they're 300+ pounds heavier), a CVT and an Atkinson cycle engine. The numbers you see on the highway are probably a little lower than you could get out of just the Atkinson cycle engine (because of the extra weight), but the city figures are much better, period. The Atkinson could never match that.

      If you are looking for more significant increases, you'll have to wait for batteries that hold more charge and electric motors that drive cars up to higher speeds. Plug-in hybrids will add an interesting dynamic as well as the cars will be able to rely on the battery longer (assuming they can build a good enough battery). Maybe in 2009-2010 when the next gen of hybrids are due.
      • 8 Years Ago
      Remember yyou can't compare a Prius to a standard Camry,etc. They are not the same car at all. One is advanced electronics (Prius) the other just the same old car but new cover. I got mine for under $21K which I feel isn't too steep these days for a car. I would never pay $25K ~ 32K for an auto. I get 47 - 50MPG combined driving. I travel approx 1600 miles per month and my gas bill is about $73.00. I track every fill up.
      Cheers,
      • 8 Years Ago
      composites? supercharger and turbo's to get a little more gas mileage? First the extra polution to produce those things and the extra you will pay. whats the point?? Just pay for the gas and you will have money left over and probally polute less.
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