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Toyota Previews Generation III 2010 Prius Hybrid

by Mike Millikin and Jack Rosebro

The 2010 Prius. Click to enlarge.

In preparation for the global launch of the much-anticipated 2010 Prius hybrid, informally referred to as “Generation III” or “Gen III”, Toyota has been staging a series of media briefings, bringing in key engineers from Japan as well as its North American technical center in Southern California, to discuss technical improvements of the new hybrid over its immediate predecessor, the 2004-2009 Generation II Prius. Toyota also previewed the vehicle this weekend in Los Angeles via its “Prius Connection” program for select early adopters and enthusiast forum participants, attracting potential buyers from across the US and Canada.

The Gen III Prius offers an EPA-rated combined cycle fuel economy of 50 mpg (now revealed to comprise 50 mpg city and 49 mpg highway). This is about a 10% improvement in EPA-rated combined cycle fuel economy over the older generation. Of that 10% improvement, about 6% can be attributed to the new hybrid system (including the larger combustion engine) and about 4% to efficiency improvements in other aspects of the vehicle, such as better aerodynamics, said Chief Engineer Akihiko Otsuka.

Hybrid Synergy Drive

The newest version of Toyota’s Hybrid Synergy Drive as applied in the 2010 Prius is more than 90% newly developed, and has produced more patents than previous Prius generations combined. Maximum system output, including the engine, is controlled to about 100 kW (134 hp).

The 2010 Prius 1.8L Atkinson cycle engine. Click to enlarge.

2ZR-FXE 1.8L DOHC 16-valve VVT-i engine. The 2010 Prius features a new 1.8-liter engine (up from 1.5 liters in the older Prius) that provides greater torque at lower RPM for improved fuel economy, especially on the highway. The 1.8L Atkinson cycle engine delivers 98 hp (73 kW) @ 5,200 rpm, and 142 Nm (105 lb-ft) of torque @ 4,000 rpm.

With the replacement of the engine’s belt-driven water pump, all engine coolant pumps are now electrically operated, reducing mechanical losses and providing engine coolant flow rate control independent of engine RPM at all times. As Prius power steering and air conditioning systems remain electrically driven, the 2ZR-FXE powerplant is Toyota’s first beltless engine.

As with the Generation II, cabin heating and air conditioning can continue operating with the engine stopped; the latter is a capability further leveraged by the use of Toyota’s optional Solar Roof system (below).

The complex engine coolant heat storage system utilized by the Gen II Prius has been replaced by an exhaust heat recirculation system that shuttles catalyst heat to a heat exchanger which interfaces with the engine cooling system, reducing engine-on time and improving cabin heater system performance. An exhaust gas recirculation (EGR) system has also been added. The 2ZR-FXE engine is SULEV-rated (with AT-PZEV) in California, and has a Federal Tier 2 Bin 3 rating.

Major components, including motor-generators, from the 2nd generation Prius transaxle (left) and the new 2010 Prius transaxle (right). Click to enlarge.

Transaxle. The all-new hybrid transaxle adopts improvements first used in previous post-2004 Toyota/Lexus hybrids such as the Camry hybrid, Highlander hybrid, and Lexus RX 400h, as well as refinements not previously employed. The result is 20% lighter in weight compared to the previous model.

The transaxle’s reduction chain assembly has been deleted in favor of a reduction gear. Power output of the more compact transaxle traction motor (motor-generator 2, or MG2) has been increased to 60 kW (80 hp), and torque has been reduced by about half to 207 Nm (153 lb-ft). (The revised gearing compensates for the new motor-generator’s torque reduction.) Maximum speed on MG2 has been increased to 13,500 rpm, according to Toyota, up from 6,400 rpm, and its maximum operating voltage has increased from 500V to 650V.

(Waste material from the construction of the 2010 Prius generator—most likely center cuttings from production of the generator’s stamped steel stator plates—is reused in the construction of the electric motor that drives the vehicle’s air conditioning compressor.)

The multifunction gearset incorporates two sets of planetary gears: a power-split planetary gearset and a speed reduction planetary gearset. Both gearsets share the same ring gear, which drives the transaxle’s counter gear. The sun gear of the power-split gearset is connected to the 42 kW motor generator 1 (MG1); the planet carrier is connected to the engine. In the speed reduction planetary gear set, the sun gear is connected to MG2, the carrier is fixed, and the ring gear connects to the counter gear. A parking pawl is also part of the assembly, which is connected to a differential with a final drive ration of 3.267:1.

Battery pack. Nominal pack voltage of the nickel-metal hydride (NiMH) battery remains at 201.6 VDC. The more compact battery pack and system main relay assembly were repositioned, resulting in increased cargo volume and cabin comfort. Cooling air velocity and volume have been increased for increased cooling efficiency, resulting in overall improved battery efficiency and fuel economy. The pack is warranted for 10 years/150,000 miles.

At end of life, every part of the battery is recycled or processed for disposal at a dedicated facility in Japan.

The 2nd generation inverter (left) vs. the 2010 Prius inverter (right). Click to enlarge.

Inverter. System operating voltage is now boosted from battery voltage to as high as 650 VDC by the vehicle’s boost converter before being converted into three-phase alternating current by the inverter, which Toyota refers to as a Power Control Unit (PCU). This represents a 30% increase over the boost employed by the Gen II Prius. All Hybrid Synergy Drive vehicles released subsequent to that vehicle have employed a boost converter capable of up to 650 VDC output to the inverter.

Similar in size and shape to current Toyota/Lexus hybrid inverters, the new unit features direct liquid cooling of the IGBT power transistors (developed in-house by Toyota), reducing energy losses. Company engineers will present a technical paper on the new inverter at SAE World Congress in April.

Fuel tank. A new resin 11.9-gallon fuel tank does away with the bladder used in previous North American iterations of the Prius, and utilizes an enhanced evaporative emissions system that complies with AT-PZEV zero fuel evaporation regulations.

Driving Modes

The new Prius offers four driving modes: the default (normal) mode and three others (EV, Eco and Power) selectable by buttons on the center console. EV mode helps keep the vehicle in electric-only operation for up to about 1 mile at speeds less than 25 mph. Among other parameters, the state-of-charge (SOC) level of the vehicle’s high-voltage battery pack, as shown on the energy monitor display, must be four bars or more for the Prius to operate in EV mode.

Eco mode reduces throttle opening angle to a maximum of 11.6%. Eco mode also modifies air conditioning operation, and improves performance in low-traction conditions such as ice and snow, as the reduced output helps to minimize wheel slippage.

Power mode essentially does the reverse of Eco mode, increasing mid-range throttle response to optimize acceleration performance.

Option Packages

Toyota will offer the 2010 Prius with four option packages, including a Advanced Technology Package and a Solar Roof Package. The Advanced Technology Package includes safety options that recently debuted in the North American market with the Lexus LS series: a pre-collision system that utilizes seatbelt pre-tensioners and brake assist, a millimeter-wave radar system that regulates the vehicle’s distance from cars ahead of it when cruise control is engaged, a Lane Keep Assist (LKA) system that reduces driver effort during straight-line driving and warns the driver if the vehicle begins to drift out of its lane, and a semi-automatic parallel parking system called Intelligent Parking Assist.

A solar roof is available on the 2010 Prius as part of a Solar Roof Package. 36 polysilicon solar cells in the roof generate up to 59 W of electricity, powering an interior ventilation system. One minute after the vehicle’s Solar Ventilation Switch is activated, the interior air intake is switched to outside ventilation, and blower mode is switched to the face vents. Cooling begins ten minutes after the vehicle is shut off so that air that was already cooled is not expelled, and continues until the system is manually switched off or the vehicle is started.

The solar-powered ventilation system is paired with a remote air conditioning system that allows the driver to remotely command the vehicle’s electric air conditioning system on for up to three minutes when the vehicle is parked. The air conditioning system is powered by the vehicle’s hybrid battery pack during this time.

“The body size and overall weight were optimized to achieve excellent environmental performance, fuel efficiency and cabin comfort. To achieve this, our thoughts were ‘Outside Minimum, Inside Maximum’.”
—Chief Engineer Akihito Otsuka

Although the vehicle is roughly the same size as its predecessor, its interior is slightly larger. Select interior parts in the new Prius are made of Toyota’s new “ecological plastic” which the company estimates to have around 20% less CO2 associated with its production. Coefficient of drag is Cd 0.25, aided in part by modifications to the body such as clean bumper edges accentuated by flat wheel flare surfaces to improve airflow and a large grille opening. Extensive aerodynamic undertrays reduce turbulence underneath the vehicle.

The 2010 Prius is 110 lbs (50 kg) heavier than the second generation. The decrease in the weight of the hybrid components is offset by the addition of new safety equipment and improvements to the body structure.


Bob Carter, Toyota Motor Sales USA Group Vice President and General Manager, Toyota Division, said that Toyota is projecting sales of about 100,000 units for the 2010 Prius in 2008, and of 180,000 for the car’s first full calendar year on the market.

We think it will appeal to current Prius owners,” he said. “More than 90% of Prius owners tell us they intend to buy another Prius. We also are confident that it will attract more buyers We have two main challenges: the economy, and the [Honda] Insight.

Carter said that Toyota believes there is ample room in the market for both the mid-sized Prius and the compact Insight, and that the Prius could achieve about a 7% share in the mid-sized segment and that the Insight could garner about 5% share in the compact segment. The 2010 Prius is scheduled to go on sale this May. Toyota has yet to announce the manufacturers’s suggested retail price (MSRP).



Personally, I would probably buy the Fusion Hybrid since it is a mid-size. Having said that, this car seems to make huge gains in overall technology over the Gen. 2 Prius. If they could only reduce the amount of smug emissions, I might considering buying one.


Ahhh, a truly appropriate South Park allusion!
The Gen III looks to be an excellent car, but the Fusion is a better car in my book. But, and this is a huge but, I have driven the Prius Gen II and the '09 Fusion SE and the Fusion was just a much more enjoyable drive, but I haven't driven the hybrid Ford yet.
Anyway, way to go Toyota, bring on the high mileage cars. Until the Volt, Fisker and the IMiev get here, high mileage is a very good thing to have.


I am disappointed that they do not offer a plugin option.


We all have a lot to thank Toyota for. While GM and the CARB folks bungled the American EV movement - Toyota took a large risk to develop hybrid technology. And typical of Japanese vision - they stuck with it until it found its niche and started gaining acceptance.

It may seem trivial but, the support of the nerdy little Prius by certain media and Hollywood entities gave it a strong boost. Plus, by early-2000 people got to understand it was the best high mileage vehicle in the world. Once Prius became a wait-list back order item, it really took off and now exceeds 1M sales.

We've got a lot to thank Toyota for. And we should.


The new Prius is an improvement on its earlier techno9logy. It doesn't duplicate the Ford Fusion technology but goes about its improvements in its own way.

It is easy to see that pure fossil fuel HEVs still have some technological improvements to be made. Making future generations of these vehicles combining the improvements, easily possible to average mid 50 mpg.

It also indicates that the PHEVs using some portion of electrical substitution can easily achieve 125 MPGE. And EREVS should be able to achieve mid 300 mpge in so called mid size or "family cars".

When we have newly installed idiots in charge of our fossil fuel policy, hell bent on wrecking the economy, in search of their pet ideas to prevent a theoretical doomsday existing only in their imaginations, it is nice to see the actual technology improving like this.

Now if the eco-idiots would just get out of the way, take a pause in their regulation-issuing urge, and let the automakers survive, to build these better products, we would all be better off.


Frankly I'm very dissapointed. It looks like Toyota has made little progress in the past five years. By now they could have cut 500 lbs from their Prius and improved Fuel economy to 100 mpg. This model is about where my 2006 Honda is.

It's one thing to talk. Another to do.



Stop dreaming and worshiping your Honda. If anyone has done nothing, the new Honda mild hybrid subcompact with its mild and not improved at all IMA on the Insight, is the disappointment.

We all like to laugh and poke fun at the Malibu's BAS mild hybrid. The Honda IMA is nothing but an analogue of the BAS. If it weren't for you Hondaphiles, we would be laughing at the Insight too. It deserves only hearty laughter.


It seems Toyota is working to mainstream the Prius Gen III, so more power in the ICE engine, minor incremental improvements, and a very similar battery to Gen II are what they offer. OK.

That opens the door for Honda with a lower cost hybrid vehicle.

That opens the door for any PHEV, EV (Aptera maybe?), or radical ICE to come in and expand the eco camp. I think Toyota is aware that more mileage for more money is a hard sell, but the same mileage for less money, or more mileage for the same money could get traction.


A good refinement. Why be disappointed or indignant that Toyota's engineers cannot ignore physics and economics?

Lighter weight structural materials are very costly.

They will raise prices or lose money on this model. Perhaps that can be offset with higher volumes and lower prices from their suppliers. It is likely that suppliers are lowering prices temporarily due to world economic conditions.

IMO US inflation will soon soar and that will be a far bigger problem than Prius cost inching upward.


"I am disappointed that they do not offer a plugin option."

That is because they are still using the NiMH battery, of which Chevron bought the patent. Chevron won't let anyone use it on a plugin hybrid because that would signal the end of the oil industry -- people would actually be presented with evidence that they can indeed power their car from a wall socket, a light bulb would go on in their heads --- "hey, we don't need gasoline anymore!!!" -- and then they would start demanding better and better performance every year.

To make a plugin Prius, Toyota would have to use Li ion batteries, and they are behind the mark on this.


Nice to see the details on the new Prius. Its a tough market to be dropping into (low fuel prices and the economy falling through the basement). I think this car will appeal to a slightly different market than the Fusion hybrid - the Fusion hybrid will be a bigger car and appeal to people who like that (and that like something not so Prius looking) and Ford is only making 25,000 of them (much less than demand will be, even in this economy). The Prius will get around 20% better fuel economy and lower CO2 emissions and appeal to folks that value that most. Plenty of room for both. Once oil turns around (year or two) nobody will be able to build these fast enough.

I don't think I could go for the whole letting my car's Hal drive itself thing on that radar option package (can't imagine how expensive that will be), but the solar roof for cooling sounds cool in several ways...


There are plenty of minor improvements here. That is the name of the game: incremental. We're not going to have an overnight solution. It's going to happen with continual improvments, like this.
Toyota deservers raves just for sticking with it doggedly. America, take note. Don't expect immediate payoff. The only way to get off gasoline is to keep refining the alternatives.

Nick Lyons


What's with the comments being repeated and out of order? I have been noticing this for some time now.

Love your blog, BTW--read it every day.


Willy Bio

Parallel = Passe

Non-PHEV = dopey short-sightedness

11/2010 = Volt = the new hotness


Making a really good car better.
Gotta love it.


is that 0w-20 oil cap i see on there! bout ****ing time!

but up from the epa numbers by a few points is dissapointing however, they have used the same battery in gen 2 and gave it a higher warrenty! So that should cut costs by a lot! Smart move Toyota.

richard schumacher

The comments weirdness is apparently browser related. They look fine under Safari 1.3.2 but messed up under Firefox


@Willy Bio

First of all it's power-split.
Second, there's another Prius coming as a PHEV (one year later?). Let's see how profitable that's going to be (or how high the price tag is going to be). The old Prius wasn't, afaik.
Third, Volt won't be economic, at least not for the customer. They aim to sell them for 39.000€ in Europe from what I've read. You could buy a Mercedes C-Class plus several thousand liters of gasoline or diesel for that money. Well, if you have too much money...


Bought the 2010 Prius about 6 weeks ago and am thoroughly enjoying it. This is probby the last new car the wife and I will get.
Our criteria were:
2)Gas mileage
3)Comfort and interior space
4)Performance (acceleration)
5) Initial cost & lifetime cost.
6) Hatchback (We go garage sailing a lot)
Buying "American" would be a top priority--except that GM Ford and Chrysler make parts and whole cars overseas, and we have had many years of really bad made in the USA "Lemons"
Our long-time mechanic recommended the Toyota Corolla as his first choice--for reliabilty. Consumer reports rates the Prius extremely high on reliability after ten years on the road. Prius owners we have talked to have few or no complaints after several years of ownership.
All these things convinced us to buy the new Prius.
We get an honest 45 to 48 MPG combined (computed the old-fashioned way, at the pump) and we do not drive it differently to maximize gas mileage. With stop-and-go, low speed around town driving, gas mileage actually goes UP, instead of down. There is no other car on the market that approaches this mileage, and the Prius is a Mid-sized car with 106" wheelbase, and rides like one. It is not an econobox, and has lots of room for our junque.
If it lasts, and is reliable, it may be the best car we've ever bought.

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