Our view: 2004 Toyota Prius

Photo of Joe Wiesenfelder
Executive Editor Joe Wiesenfelder, a launch veteran, leads the car evaluation effort. He owns a 1984 Mercedes 300D and a 2002 Mazda Miata SE. Email Joe Wiesenfelder

Toyota’s status as a manufacturer of gasoline/electric hybrid vehicles contradicts competing automakers, hydrogen fuel-cell zealots and even Kermit the Frog. Apparently it is easy being green. So easy that the Japanese company has sold more than 52,000 first-generation Priuses in the United States and more than 125,000 worldwide since 1997, plans to introduce hybrid versions of the Lexus RX 330 and Toyota Highlander roughly a year from now, and is licensing its drivetrain technology to Ford, Nissan and any other manufacturer that cares to join in. Being green is also profitable — if you can swallow Toyota’s claims that the vehicles not only turn a modest profit on a unit-for-unit basis but that the research and development costs have already been offset. A first drive in an all-new, larger, quicker and still more fuel-efficient 2004 Prius proves it’s getting easier for buyers to be green as well.

The first of the roughly 36,000 Priuses that Toyota expects to sell in the United States this year are now hitting dealerships, where response has been “overwhelming,” said Ernest Bastien, corporate vehicle marketing manager of Toyota Motor Sales, U.S.A., Inc. Of 18,000 current Prius owners contacted, 80 percent expressed interest in buying the 2004 model, Bastien said, and 1,200 took advantage of a pre-order offer extended to these “Prius Pioneers,” who will be the first customers to take delivery. “More than 3,000 additional orders had already been accepted by Toyota dealers through late September,” Bastien said. “When you add early orders from private and public fleets and Toyota Rent a Car, it adds up to nearly 10,000 orders.”

Though I typically weave technical information throughout Vehicle Profiles, some readers are sure to think they’ve landed in a physics lecture and will start manufacturing spitballs. So I’ll just give the brief hybrid overview for you students who’ve been sleeping for the past few years, and anyone who wants extra credit can stick around after class — after the review, actually — for more information on the engineering feats that result in a Prius that’s better in many ways than the original and seemingly worse in none.

Gasoline/electric hybrids employ both a gasoline engine and an electric motor or motors to propel a vehicle. The efficiency comes mainly from harnessing energy that is lost in conventional vehicles every time you use the brakes. Acceleration requires the most energy, in the form of gasoline. Cruising at a steady speed requires far less. So your momentum represents energy, which is wasted when you come to a stop. You have to expend more gas to get moving again. Through a system called regenerative braking, the same motor that propels the car serves as a generator during coasting and braking. Rotated by the wheels, the motor charges the high-voltage battery pack. That captured energy is then used to help propel the vehicle back up to cruising speed. For this reason, no current hybrid ever needs to be plugged in and charged up.

Further efficiency comes from the fact that the added power and torque of the electric motor allows the gasoline engine to be smaller and otherwise more efficient than it would have to be if it did all the work. As stated before, cruising doesn’t take nearly as much power as acceleration does. In practice, it’s the gas engine that keeps a hybrid vehicle moving at highway speeds, and the electric motor aids acceleration and is most useful in stop-and-go city-style driving where it most effectively captures and reuses energy, sometimes propelling the vehicle by itself. (The gas engine shuts off and restarts automatically.)

This is why the Prius’ fuel economy is lopsided — 60 mpg city/51 mpg highway, an improvement over the first model’s EPA-estimated 52/45. In California and other restrictive states that follow the California standard, it qualifies as a Super Ultra Low Emissions Vehicle (SULEV) and is certified in the Advanced Technology Partial Zero Emissions Vehicle (AT-PZEV) category — which means its overall emissions, tailpipe and evaporative, are within strict limits. In other states, the Prius is slightly less clean, but it’s difficult to express the difference. The EPA hasn’t published its simple Green Vehicle Ratings for 2004 yet, and the phase-in of new emissions requirements seems to have obliterated any hopes of comparing one to another. The Prius is certified Tier 2, Bin 3 in the less restrictive states. (See what I mean?)

You may have noticed that Honda’s Insight and Civic Hybrid don’t have the lopsided fuel-economy figures. This is because they are mild hybrids in which the electric motor can’t propel the car by itself. The engine shuts off only when the car comes to a complete stop. The Hondas are parallel hybrids where the Prius, now as in the first generation, is a series/parallel hybrid, which means the engine, motor or both can propel the car. Initially, I saw Honda’s approach as a distinct advantage. The simpler system, I reasoned, wasn’t as much of a departure from the conventional drivetrain and would probably prove more reliable. Though the Prius had one steering-related recall shortly after its introduction here, history has proven Toyota’s full-hybrid drivetrain to be plenty reliable and Honda’s parallel system to be something of a limitation in terms of efficiency. Honda is unlikely to match Toyota’s fuel economy with this design.

Meanwhile, Toyota has upgraded and renamed the Prius’ drivetrain. The upgrade was to boost fuel economy. The name change, from Toyota Hybrid System to Hybrid Synergy Drive (HSD), came in anticipation of using the tech in a Lexus and licensing the technology to other automakers that aren’t likely to put the word “Toyota” anywhere on their vehicles. If Toyota gets its way, some Hybrid Synergy Drive branding will appear on licensee vehicles. Considering the company’s substantial head start with the technology and a market that has shown surprising hybrid acceptance and demand, Toyota is very likely to get its way.

For now, if you want Hybrid Synergy Drive, the Prius is the only place to get it. The 2004 model is a four-door hatchback, which is 5.3 inches longer and 1.2 inches wider than the first-generation sedan, with 5.9 inches more wheelbase, at 106.3 inches. The interior is 2.4 inches wider, and headroom is up 0.3 inch in front. Legroom increases 0.7 inch in front and 3.2 inches in the backseat. Hip room and shoulder room have increased in all cases except backseat hip room, which has lost 0.3 inch. Overall, the passenger volume is up 7.2 cubic feet over the original Prius to 96.2 cubic feet, and cargo volume has increased from 12 cubic feet in the earlier model’s trunk to 16.1 cubic feet for the new one’s cargo hatch. Even better, the backseat now folds forward for still greater cargo volume. The previous model’s seats did not because of the location of the high-voltage battery pack.

With all the changes above, the new Prius is a midsize car, not a compact like the earlier Prius and the current Civic Hybrid. The larger interior, especially the roomier backseat, is a welcome change. The low dashboard and arched roof give the cabin an open, airy feel. Visibility is quite good all around. Some people are sure to object to the bar that spans the rear window. This is actually the rear spoiler, as shown in the photos. Below this cross-member is a separate window on the rear wall of the liftgate that gives the driver a lower field of vision than many sedans do. The Honda Insight has a similar design.

The Prius’ gear selector is now a small lever. In the previous model, it was larger, similar to a column shifter, but there’s no need for the lever to have so much, well, leverage because it’s not a mechanical control. All drivetrain duties are controlled by a Power Control Unit (PCU), so the gear selector lever and the Park button above it serve to tell the computer what you want done. The lever’s positions are R, N, D and B, which stand for Reverse, Neutral, Drive and, for want of a better term, engine Braking. The last position simply emulates a conventional transmission’s lower gear settings, providing the equivalent of engine braking for going down steep hills. In this case, regenerative braking is used.

Out on the road, the new Prius improves on the old in many ways. Despite the increase in fuel economy, acceleration is improved. The old model took more than 12 seconds to accelerate from zero to 60 mph, and the new one does it in about 10 seconds. It’s not going to win any races, but it’s quick enough and it seems to handle additional weight better. I drove both with four occupants and with two, and though the gas engine kicked in more frequently with four of us in the car, the Prius never felt as if it was straining. With just one passenger, I was able to accelerate gradually to about 30 mph without the engine starting up. The engine starts and stops almost imperceptibly — nothing like when you turn the ignition in a conventional car. A display on the standard 7-inch LCD touchscreen shows when the motor alone is propelling the car, when the engine joins in and when the engine alone is doing the work. It also shows by means of arrows which way the power is flowing — from the battery to propel the car or back to the battery when cruising or regenerative braking.

Under heavy acceleration, one knows when the engine has started because it’s a bit noisy. Toyota has a reputation for quiet interiors, and overall this car is probably better than the previous version in terms of refinement and road isolation. It’s only the high revving that penetrates the cabin. A possible explanation is that noise control in a car typically translates to weight, and weight is one of fuel efficiency’s greatest enemies. When you consider the increase in the new model’s size, its curb weight of 2,890 pounds — up only 125 pounds from the 2003 — is laudable.

The earlier Prius had a few quirks. There was some lag when accelerating, especially when attempting to pass when already in motion, and the brakes weren’t completely linear. The problem with the brakes was the transition between regenerative braking — when the drive motor is slowing the car by generating electricity — and the conventional brakes. In my experience, this was worst at low speeds or while coming to a complete stop.

Toyota has improved the braking performance markedly in the 2004 model by going to brake-by-wire. This is an electronic system in which the pedal tells a computer that you want to brake, and the computer in turn sends the hydraulic fluid to the front disc and rear drum brakes. I’ve questioned the need for this system in the Mercedes-Benz SL-Class and E-Class, but in the Prius it serves a tangible purpose. It both improves the braking linearity and increases regenerative braking by giving the computer full control over the regeneration, the regular brakes and the transition between the two — at all speeds. (For those of you who don’t trust computers, know that there is a hydraulic backup for the brakes, as in the Mercedes system.)

I wouldn’t say the braking is perfect — the pedal feel could be better, and a couple of times I think the system grabbed harder than warranted when I first stepped on the pedal, but it is much improved, and I suspect the average driver would never think twice about it. Paul Williamsen, curriculum development manager of Toyota Motor Sales, said the regenerative braking is the greatest contributor to the HSD’s fuel-efficiency gains. Williamsen, who manages technical training for Toyota dealers and technicians, said the new system exploits the regenerative braking so much better that the conventional brake pads and shoes may never come in contact with their discs and drums under normal driving conditions. This allowed the engineers to decrease the size and weight of the brake components for added fuel savings.

The acceleration is also more refined. The drivetrain still has the stepless feel of a continuously variable transmission (CVT), by which I mean it pulls steadily without the feel of revving/shifting/revving/shifting. Though HSD doesn’t technically have a CVT, the feeling is similar, a sensation some drivers need to adjust to and others don’t even notice. Accelerator response is pretty good from a dead stop. When you floor it to pass when already in motion, there’s still some lag, but it’s better than in the previous Prius and superior to a couple vehicles I’ve driven that have true CVTs.

Notable standard features include air conditioning, power locks with remote keyless entry, power windows, heated side mirrors, audio and ventilation controls on the steering wheel, cruise control and a CD stereo.

Options include a rear window wiper that probably ought to be standard, given the window’s shallow angle. Smart Entry and Smart Start are options that allow you to open the vehicle and start it without a key so long as the remote transmitter is on your person or in a purse or the like. Even if you don’t buy this option, the Prius lacks a conventional key. The keyless-entry transmitter docks in a slot in the dash, and one turns the car on (not necessarily starting the engine) by pushing a Power button. Similar features appeared first on luxury vehicles from BMW, Cadillac and Mercedes-Benz. Other high-tech options that were once the province of luxury brands include a DVD-based navigation system with voice activation, high-intensity-discharge headlights, Bluetooth wireless hands-free cellular phone compatibility and Vehicle Skid Control, an electronic stability system. All standard and optional features and their prices are available in the Buying Guide.

Safety has been a big concern since hybrids hit the market because of their high-voltage battery packs. I’ve heard no tales of voltage-related injury to date. It’s more relevant that in the National Highway Traffic Safety Administration’s (NHTSA) crash tests, the first-generation Prius earned a disappointing three stars for the driver and four stars for the front passenger in the frontal crash, out of a possible five stars. In the side-impact test, it earned three stars for both the front and rear occupants. Because the testing agencies purchase vehicles after they officially go on sale, their results always take several months. You can check for updates and compare the midsize competition on NHTSA’s Medium Passenger Cars page and the Insurance Institute for Highway Safety’s Midsize Inexpensive Cars page.

Williamsen said the “target” is a quadruple-five-star crash-test rating for the 2004 model equipped with side-impact airbags. Where the earlier Prius offered only conventional front-seat side-impact airbags, the 2004 adds side curtain-type airbags to the option. The front airbags are dual-stage designs that deploy at one of two intensities depending on crash severity.

Another concern about hybrids has been the availability of qualified mechanics and the cost of repairs. Though not all Toyota dealerships in this country were certified to sell and service the original Prius, they all are now. As on the previous model, the 2004 Prius starts out with Toyota’s basic 3-year/36,000-mile comprehensive warranty, 5-year/60,000-mile powertrain coverage and 5-year/60,000-mile corrosion warranty, and adds 8-year/100,000-mile coverage for the hybrid-related components, including the high-voltage battery pack. Replacing the battery out of warranty would definitely be expensive — well over $1,000 and possibly as high as $3,000. Williamsen said, “The good news is that we’ve never replaced a high-voltage battery pack because of wear,” regardless of mileage. One or two battery packs have been replaced because of manufacturing defects, but so far, he said, the nickel-metal-hydride (NiMH) batteries show none of the ill effects of age or repeated charging and discharging that eventually spell the end of other battery types, especially lead-acid.

Toyota has addressed at least one part that caused trouble for owners of the earlier Prius — the tires. The earlier model used Bridgestone Potenza RE92 tires chosen for their low rolling resistance. They also had a treadwear rating of 160 out of a possible 500 (with higher numbers representing longer wear). The combination of these tires and the high off-the-line torque output of the electric motor caused the tires to wear out after 10,000 to 15,000 miles. Owners complained of uneven wear and tread separation as well. When they sought replacement tires, there were few other options in this size, and supply was often limited. (John Fagnant, a Minnesota-based Prius pioneer and fanatic who’s active in Prius newsgroups, said the Prius community theorized that the recommended inflation pressure was too low. “Owners figured out that simply increasing the psi alone extended life and also increased the mpg,” he said.)

New Prius buyers won’t have to worry about that because the new model uses the same Goodyear Integrity tires as the Toyota Corolla CE. Aside from having a treadwear rating of 460, the new size (185/65R15) is one that numerous manufacturers supply (tire codes). A quick check of showed about 40 tire models, including performance, winter and all-season tires. Williamsen said Toyota also improved the traction control in the new model so it’s more subtle in its action and easier on the tires.

If you’re considering a Prius, you probably have some questions, so I’ll attempt to address the obvious ones. If you think a hybrid sport utility vehicle would meet your needs better, you’ll have to wait about a year. The Ford Escape Hybrid, which will feature a version of the original Prius drivetrain, not HSD, is likely to be the first to market. The Lexus RX 330 should be next, followed by the Toyota Highlander. Honda is likely to update or expand its hybrid offering, but the company has offered no hints. Nissan’s first Toyota-powered hybrids are expected in 2006.

If you’ve heard a lot about hydrogen fuel-cell cars and think you should wait for them, you’re going to be waiting a long time. Many manufacturers, including Toyota, are testing fuel-cell vehicles, and a few of them have small fleets in pilot programs as a part of their research and development — and their public relations initiatives. I support the hydrogen fuel-cell movement because no amount of hybrid technology will reverse the growing thirst for petroleum in developed and developing countries. We need a whole new way of doing things. But all aspects of the hydrogen infrastructure and vehicles themselves raise far more questions than answers. The notion of viable mass-market fuel-cell vehicles within 10 years is optimistic. Twenty years is more like it. For now, I think we should take advantage of the good work Toyota and Honda have done.

When the first Prius came out, I calculated some fuel-cost projections and found that it would take something on the order of 11 years for the fuel savings to pay off the difference in price between the Prius and a comparably equipped non-hybrid Honda Civic. At that point, environmental consciousness was the best reason to buy one. Two milestones have passed since then. One was the federal Clean-Burning Fuel Deduction of up to $2,000 for hybrids such as the Prius — a significant break. Unfortunately, that incentive is scheduled to begin phasing out at the turn of the year. On Jan. 1, the amount decreases to $1,500. Because the vehicle must be “placed in service” on or before Dec. 31, according to the IRS, having ordered a Prius won’t get you in under the $2,000 wire. You must take possession before the new year.

Martha Voss, Toyota’s Washington public affairs manager, said the full $2,000 deduction could remain available if an extension is filed. I’ll be keeping an eye on the Hill for this, and for the Bush Administration’s Energy Bill, currently in Conference Committee, which includes proposed hybrid tax credits. Some states also offer hybrid incentives, so be sure to check. Toyota dealers are likely to alert you to such incentives, but you’d best scrutinize the details on your own. Some locales are also considering the allowance of hybrids without passengers in high-occupancy vehicle lanes.

The second milestone was the Prius’ jump to the midsize category. Not only does this make it more versatile, but it also raises the starting price and decreases the fuel economy of cars against which the Prius is compared. Despite the many improvements, the 2004 Prius’ sticker price remains $19,995 plus a $515 destination charge. Without busting out my calculator, I can tell that the change in category, the tax rebate and the higher fuel economy result in a car that could actually save you money in the medium or even short term. I hate to contradict the venerable Muppet frog, but the 2004 Prius proves it’s easy being green.

Tech Talk: How They Did It
Thank you for staying after class. I’m fresh out of brownie points, but your interest will be rewarded in deeper understanding of the new Prius. I’ll address the changes that enable a larger, heavier Prius to be quicker and more fuel efficient, which is an accomplishment indeed. As in most parts of industry and, some would say, life, computerization has driven the most significant improvements in the design and engineering of cars, and it’s increasingly boosting their safety, efficiency and performance out on the road as well. The most compelling innovations I’ve seen in cars come not from any one component but from many components working together as they can only under the governance of the mighty microchip. The Prius is a prime example in the interest of efficiency.

As explained above, regenerative braking is the greatest contributor to the Prius’ efficiency gains. Now that the computer controls both regeneration and the hydraulic brakes, regeneration is happening more frequently. As I also mentioned, this allows the conventional brake components to be smaller and lighter for added efficiency gains.

Williamsen said the second biggest contributor to the efficiency gains is in control, including the hardware and software. All the processors are now 32-bit, where some were 8- and 16-bit in the previous Prius. Further research and many miles of experience with the Prius and Toyota’s other hybrids — the Estima minivan and the Crown light-hybrid sedan (the latter two in Japan) — has led to better and better software. Simply put, the Power Control Unit is getting smarter and better at controlling all aspects of the vehicle’s operation.

Many other changes and upgrades contribute. The switch to an electric-motor-driven air conditioning compressor is one of the important ones. In the previous Prius, a demand for cooled cabin air would turn the gas engine on to operate the belt-driven compressor. Now it runs on electricity, so a nice downhill cruise can provide plenty of cool air — compliments of regenerative-braking power. This change basically lets the engine stay off any time it otherwise would in the absence of air conditioning. The only circumstance in which the compressor would cause the engine to turn on is if it runs the high-voltage battery pack too low. There’s more to its efficiency, though, in the fact that it can run at different speeds depending on demand. Conventional air conditioning compressors, on the other hand, are either 100 percent on or 100 percent off. If the climate control is set to blow cool rather than cold air, it mixes in a little warm air, a waste of energy.

A car in which the engine shuts off while in motion required many revisions. The steering has used electric power assist since the first Prius because conventional power steering relies on a pump driven by the engine. Same story for the brakes. Vacuum-powered boost requires a running engine, so the earlier Prius used electric boost in the power brakes. The new by-wire system, naturally, is also electric. What’s interesting about these subsystems is that some of them are finding their way into conventional gas-powered vehicles as well, simply because they’re more efficient than anything that puts a load on the engine. Why use a steering pump that represents a parasitic load all the time when you only need the pressure it provides when turning the steering wheel?

Emissions are another challenge because catalytic converters are dramatically less effective when they’re cold. Modern cars emit more pollution in the period between engine startup and catalytic converter warmup, or “light-off,” than they do for innumerable miles hence. Because the Prius’ engine regularly turns off, emissions could become a problem at any time. The previous Prius used a hydrocarbon adsorber upstream of its catalytic converter that trapped unburned hydrocarbons. Once hot, the catalytic converter would convert them to benign compounds. In the new Prius, Toyota has traded in this miracle of organic chemistry for a large Thermos.

OK, that’s an oversimplification, but not by much. A 3-liter stainless-steel vacuum bottle in the engine-coolant path holds the hot coolant at close to boiling temperatures. When you turn the Prius on, the first thing it does — before starting the engine, if necessary — is pump this hot coolant to the cylinder head. Voila. When the engine does start, it’s already close to operating temperature. This solution does the trick while driving and also improves cold starts after the Prius has been sitting. Williamsen said the storage bottle can keep the coolant near boiling overnight and 176 degrees Fahrenheit after three days and nights. The use of an electric pump ensures engine cooling — and cabin heating — even if the engine shuts down.

The 1.5-liter four-cylinder engine is the same as in the earlier Prius, though it now has a maximum speed of 5,000 rpm, up from 4,500 rpm. Though the same block is used in the Echo and Toyota’s new Scion cars, in this application it runs an Atkinson cycle rather than the traditional Otto cycle. In the Atkinson cycle, the pistons have already begun their compression stroke by the time the intake valves close, which lets some of the air/fuel mixture back up into the intake manifold. The exhaust valves, on the other hand, stay closed until the end of the power stroke. What this gives you is a four-stroke engine with a long expansion ratio and a short compression ratio. The result is thermal efficiency. So why don’t all cars use this cycle? Because it results in poor low-end torque and limits maximum rpm. In the Prius, the electric motor — which has maximum torque at 0 rpm — takes care of the low-end grunt, and the transmission, with properties similar to a CVT, functions without the high revs.

Understanding the relationship between the engine and the motor is the key to grasping why, at some times, the computer will use some of the engine’s power to drive the generator to in turn power the drive motor instead of just sending all the engine power to the wheels. Don’t be confused by my mention of a generator. The nifty power-flow diagram on the Prius’ LCD doesn’t show it, but there is indeed a motor/generator in the system separate from the drive motor/generator, as there was in the earlier Prius.

Understanding how all these components are connected is one of the keys to understanding how the Prius operates. In lieu of a transmission, HSD has a power-split device — a planetary gearset to which the engine, both motor/generators and the front drive axle are attached. (If you don’t know what a planetary gearset is, the best I can do is say it involves several small planet gears that rotate on their own and also revolve around a sun gear in a solar-system kind of way — all within a surrounding ring gear that meshes with the planets. All of the other gears are also connected to each other, either directly or through an adjacent gear.) Now, if you’re like me, you could hold a planetary gearset in your hand and still envision only chaos. So imagine the confusion when Toyota stated in conjunction with the first Prius launch that the drivetrain has no actual CVT or transmission and no clutches, bands or other friction devices.

It is only now that I understand it, thanks to Paul Williamsen, a man whose knowledge is only exceeded by his capacity to boil it down for dolts like me and my autowriter peers. It is by controlling the motor/generators that the Power Control Unit directs torque and allows the engine, or the motor, or a little of both to propel the car. Likewise for the regenerative braking. Obviously it gets plenty complicated, but if you dwell on it awhile, it’s simple enough to understand that any torque in the system — be it from the engine or the turning wheels — is given somewhere to go, and typically somewhere useful. It is the relative speed, torque and direction of the generator, primarily, that controls power distribution.

Aside from the way it deftly handles distribution, the power-split device is valuable for what it’s not, namely a transmission. Transmissions are significant sources of energy loss in the form of friction. Any time there’s friction, there’s heat, and heat represents wasted energy. Though CVTs are touted as being more efficient overall than conventional automatic transmissions, they generate a great deal of heat in normal operation from the friction of the belt on the pulleys. The HSD’s planetary gearset is just that — a bunch of gears whizzing around in about 5 ounces of oil. When there’s resistance, it’s from a motor/generator capturing energy — and not from a clutch wasting it in the form of heat.

Though it’s not technically a continuously variable transmission, Hybrid Synergy Drive has the properties of a CVT — namely, that it allows the engine to operate over a smaller range of engine speeds and, through electronic control, endeavors to keep the engine in its most efficient rpm range even as vehicle speed varies. One could argue that HSD has the advantages of a CVT without the drawbacks.

Improvements in the permanent-magnet motors play a part in the new Prius’ power and efficiency gains. The drive motor generates a peak 67 horsepower from 1,200 -1,540 rpm (up 50 percent from 44 hp) and 295 pounds-feet of torque from 0 – 1,200 rpm (up 15 percent from 258 pounds-feet). The maximum rpm is up to 6,700 rpm. The engine’s power also increased, mainly from the higher redline, to 76 hp from 70 hp. The torque remains 82 pounds-feet. The Society of Automotive Engineers is still working on a way to present net horsepower ratings for hybrids, which may explain why Williamsen’s figure of 110 hp for the engine and motor combined is 4 hp shy of the net rating given for the less powerful earlier Prius when it came out.

The higher output power comes in part from higher input power, but don’t look to the battery for an increase: The new Prius’ battery pack is smaller and lighter, with 28 modules rather than 38, but its specific power is 35 percent higher, so its nominal rating remains a relatively high 201.6 volts. Though this is lower than the earlier Prius’ 274-volt battery, the new Hybrid Synergy Drive ramps the system voltage up to 500 volts. The extra 500 rpm of engine speed translates not only to higher engine power but also to greater electricity generation. The motor/generator, which is geared to run at twice the engine’s crankshaft speed, added 1,000 rpm for a top speed of 10,000 rpm — a feat that required some serious engineering and earned a patent. The higher output that results contributes to the Prius’ improved midrange acceleration.

When you dig a little deeper into the engineering behind Hybrid Synergy Drive, you start to see how lots of little efficiencies add up to twice the fuel economy of the average midsize car. Not all of the new Prius’ advances are as complex as those above. For instance, the new car’s aerodynamics improved simply by becoming a longer vehicle. The switch to a sloping hatchback in lieu of a trunk helped some more. The new Prius’ coefficient of drag is 0.26, down from 0.29 in the first generation.

The Prius is a fascinating study. I’m not typically one for testimonials, but I admire the engineering Toyota has presented here and the deftness with which the company has eased hybrid technology into the world market. For this, the whole industry owes them thanks. For when pioneers get it wrong, it can sour consumers on the technology for generations. Think of the diesel engines General Motors fielded in passenger cars two decades ago.

Thanks for sticking around, teacher’s pets. If you have any questions, see me after class — or send me a Yo, Joe! e-mail.

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