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Toyota Reveals Third-Generation Prius; 50 mpg

The 2010 Prius. Click to enlarge.

Toyota Motor Sales (TMS), USA, unveiled the third-generation Prius hybrid vehicle at the 2009 North American International Auto show. The new version of the world’s top-selling hybrid vehicle (more than one million sold in 44 countries) offers better mileage ratings and enhanced performance, as well as new design features.

The first-generation Prius, which was EPA rated at 41 mpg US combined city/highway, was replaced by the current model, which is EPA rated at 46 mpg US, combined. Using a combination of technologies, fuel efficiency was increased to an estimated 50 mpg US combined for the new Prius.

Hybrid components like the inverter, motor, and generator are now smaller and lighter. An exhaust heat recovery system, exhaust gas recirculation, and an electric water pump contribute to a more efficient hybrid system with a net horsepower rating of 134.

The battery module carries over from the tried-and-true technology from the current Prius. Engineers applied enhancements throughout the entire vehicle to achieve 50 miles-per-gallon, more consistent efficiency in real-world driving, and further reductions in CO2 emissions.

Electric power consumption has been reduced through the use of a more efficient air conditioning system and new, optional LED head lamps. Internal tests show that Prius’ zero-to-sixty acceleration time has dropped from the previous generation’s mid 10-second range to 9.8 seconds, making it comparable to that of an average mid-size sedan with a 2.4-liter engine. This is in response to customer expectations for better every-day performance. In short, the entire Prius package has been made more efficient from overall power consumption to output.

—Bob Carter, Toyota Division Group Vice President and General Manager

The new Prius also features what Toyota is calling a “Solar Moonroof”. A small array of photovoltaic cells automatically powers a ventilation system on hot days. The system allows fresh air to circulate into the vehicle, cooling down the cabin so that the air conditioning doesn’t have to work as hard, thereby conserving power.

Preliminary 2010 Prius Powertrain Specs
Engine 1.8L I-4 with VVT-i
Engine power [hp (kW)] 98 (73)
Torque [lb-ft (Nm)] 105 (142)
Motor power [hp (kW)] 80 (60)
Motor torque [lb-ft (Nm)] 153 (207)
Net power [hp (kW)] 134 (100)
Emission rating SULEV (w/ AT-PZEV)
Battery pack NiMH
Est. combined fuel economy 50 mpg US

A larger and more powerful 1.8-liter Atkinson-cycle, four-cylinder engine powers the new Prius. The larger engine helps improve highway mileage. By making more torque, the new engine can run at lower average rpm on the highway. When operating at lower rpm, the new engine uses less fuel. Mileage is especially improved in cold-start conditions and at higher speeds.

Use of an electric water pump and a new exhaust gas recirculation (EGR) system also contribute to the engine’s efficiency. The 1.8-liter Prius engine is the first Toyota power plant that requires no belts under the hood for better fuel economy and less potential maintenance.

The patented Hybrid Synergy Drive system in the 2010 Prius is 90% newly-developed with significant improvements over previous models:

  • The transaxle is lighter in weight and reduces torque losses by as much as 20% compared to the previous model.

  • The inverter, which converts direct current to alternating current, has a new direct cooling system to reduce size and weight.

  • Taken together, the inverter, motor and transaxle are smaller and 20% lighter.

  • A newly developed electronically controlled regenerative braking system has been adopted, with control logic optimized to enhance regeneration.

Under the hood of the 2010 Prius. Click to enlarge.

The new Prius will offer three alternative driving modes. EV-Drive Mode allows driving on battery power alone at low speeds for about a mile, if conditions permit. There is also a Power Mode, which increases sensitivity to throttle input for a sportier feel, and an Eco Mode, which helps the driver achieve the best mileage.

Dimensionally, the new Prius has the same wheelbase as the current generation. Overall length is slightly increased by 0.6 inches, in part by moving the front cowl forward. Designers preserved the triangle form of the current model, but made alterations to the overall profile, pillar position and angle. The overall height of the Prius is the same, but the roof profile is altered by moving the top of the roof 3.9 inches to the rear. This emphasizes the wedge shape, and also allows for enhanced rear headroom and improved aerodynamics.

The new Prius received more wind tunnel hours of testing than any other Toyota vehicle yet. By focusing on the shape of the body, underfloor, wheelhouse liner and shape of the wheels, the designers of the new Prius were able to reduce the coefficient of drag (Cd) value to 0.25, compared to 0.26 for the previous model. The airflow under the car was studied extensively. Engineers made changes to the shape of the fender liner, front surface of the underfloor, and added a fin at the rear floor cover to increase linear stability.

The next-generation Prius is built on a new platform, which enables improved handling stability, quieter operation, and collision safety. The suspension consists of front struts and a rear intermediate beam design, as before, but handling stability is advanced by improving the stabilizer layout, higher caster angle and tuning the bushing characteristics. Disc brakes are now used on all four corners, replacing the front disc/rear drum brakes in the current model.

Weight was saved through use of aluminum in the hood, rear hatch, front suspension axle and brake caliper and super high-tensile steel in the rocker inner, center pillar, and roof reinforcement. To meet customer expectations for everyday performance, zero-to-60 acceleration has been improved to 9.8 seconds, more than a second faster, in internal testing.

Better-performing sound insulation, working with improved vibration damping, has been installed in various locations to reduce road noise.

Toyota will use plant-derived, carbon-neutral plastics in the 2010 Prius. The newly-developed plastics, known as “ecological plastic,” will be used in the seat cushion foam, cowl side trim, inner and outer scuff plates, and deck trim cover. Ecological plastic emits less CO2 during a product lifecycle (from manufacturing to disposal) than plastic made solely from petroleum; it also helps reduce petroleum use.

Sales of the 2010 Prius will start simultaneously in both the US and Japan in late spring, followed shortly by Canada and other countries. Toyota forecasts first full calendar year sales in the US will be around 180,000 units.

We expect a large portion of this volume to come from current Prius owners. That’s because more than 90 percent say they will buy another Prius.

—Bob Carter




As long as traditional 4 stroke (albeit Atkinson cycle) engines are used, I agree with you that the serial-parallel hybrids like the Prius are the best value. With ultracapacitors, they may even give hydraulic hybrids a run for their money fuel economy wise.

However, here is where I think parallel hybrids fall off the tracks: linear generators. Linear generators have a cylinder and free floating piston arrangement. There are no connecting rods and no crankshaft. There are combustion chambers on either side of the piston. The piston is magnetic and the cylinder walls are magnetic. The piston essentially plays ping-pong between the two ends of the cylinder. This back and forth motion induces a current through wires which wrap the magnetic cylinder walls. I've read that such engines are 50% brake thermal efficiency using plain old gasoline.

With the 15% loss of a serial hybrid "transmission", you're looking at 43% thermal efficiency from this arrangement and a relatively simple design. Also I've even heard that there may be a way to have the piston ride in a magnetic field so lubrication is much less critical. Think 3d maglev train inside of a tube. By the way, I wouldn't even use a large battery with this setup. I'd make the linear generator produce most of the AC power directly and then use the DC battery (with inverter) only when additional acceleration is needed. This would also save on cost as you don't have to wait for an exotic battery chemistry to get cheaper.

Personally, I don't understand why this design is not heavily championed by the serial hybrid folks since it is exactly the kind of genset they are looking for and I would imagine its life would be VERY long even using traditional lubrication since there is no piston side load as would be found in piston-connecting rod-crankshaft arrangements.

It just seems the perfect blending of the internal combustion engine and electric drive.

To others who have studied the linear generator, do you see any problems with my arguments? Is the 50% BTE I've read on this engine too optimistic? Are there lots of hidden pitfalls?


Brian P

Ralph, the free-piston linear-generator engine would be a game changer IF the hellish control problems can be resolved. That type of engine doesn't like running at varying speed (you cannot have a tickover speed that is 10% of maximum rated speed, for example). That type of engine also lends itself to HCCI operation over (almost) its entire load range. Direct fuel injection is required due to the inherent two-stroke operation, but that's not an obstacle. It's foreseeable that the peak thermal efficiency could be 50%, but the need for it to run at a constant speed might cause part-load efficiency to drop off fast. The powertrain must be sized for the maximum continuous power demand (i.e. top steady-state speed). I know of no free-piston engine that has been developed well enough for this supposition to be tested, though.

The maglev theory works but for one big hiccup ... you still have to seal the high pressure combustion space in! Still needs piston rings. But, without side loads, frictional losses can be expected to be lower than with a standard engine ... but there's no foreseeable way around having piston rings (and lubrication). This type of engine design pretty much relies on piston-ports. Lubrication + piston ports = lube oil out the exhaust. But a Mazda RX8 rotary has the same issue and that meets all current emission standards, so this should be manageable.

The pitfall is the control system. I've always found the free-piston design to be interesting.


Incremental improvement? Some of you need to re-read the press release. Toyota said that fuel economy in cold conditions will be especially improved, thanks to the exhaust gas recirculation and exhaust gas heat recovery systems. The press release also mentioned that engineers worked to give the new Prius more consistent economy in real-world conditions.

Also don't forget that this 3rd gen Prius initially starts off with NiMH batteries, but will soon move to Li-on batteries. With Li-on batteries fuel economy and performance will further increase.

The Insight has a combined EPA of 40mpg, or 43 city and 41 highway. Test drives have shown fuel economy numbers above the EPA ratings. What makes some of you think that the Prius won't do the same?

The Prius is estimated to have combined EPA mpg of 50, a full 10 mpg more than the Insight. That would translate to roughly 52 city and 49 highway mpg. I'm sure in test drives the Prius will achieve fuel economy numbers in the mid-to-high 50s.

Also T2, sorry but this is not the same engine as the Corolla. Just because it has the same displacement does not automatically make it the same engine. First off, the Prius has an Atkinson cycle engine and the Corolla does not. Secondly, the Prius engine is completely beltless, the Corolla engine is not.

Having the engine completely beltless should provide big improvements in maintenance costs as well as fuel economy.

Lastly, the Insight is categorized as a compact, while the Prius is classified as a midsize vehicle in the US. They cannot be directly compared price-wise since the Prius is a larger vehicle. Not just larger, but more fuel efficient and faster too.

While the Insight is a low-cost and accessible hybrid for the public, it does nothing significant in terms of advancing automotive or hybrid technology. The Prius does a number of things that will very likely appear on other future Toyota models. The technologies developed for the new Prius will spread to other models and benefit them as well. The same cannot be said regarding the Insight.


toyo - Thanks for responding.

Yes I assumed Atkinson camming would be adopted as per my reference to the 1NZ-FE earlier which becomes the 1NZ-FXE in the Prius.
The electric water pump is a good idea. What's left ? Servo driven camshafts ?

You sound knowlegeable. Let me ask, given that the Toyota Camry design has shown competency in 105Kw servos and inverters, how would you now defend the HSD against the pure series hybrid model ?

Brian P

During straight motorway driving, HSD allows most of the power to go through mechanically with fewer losses - not possible by definition with a series hybrid.


ToppaTom - are you paid by GM? Nothing GM has has comes close to 50 mpg and should the Volt arrive - it could come with their traditional crush date.

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