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Prius c hybrid goes on sale in US with entry MSRP of $18,950; new transaxle, motor technology

Priusc1
The new transaxle in the Prius c features a new cooling system; overall this new hybrid unit with its 2 motor system is now approaching the same weight as single motor competitive systems and is maintaining a competitive size profile, according to Toyota. Click to enlarge.

Toyota Motor Sales, USA is putting the new Prius c, the fourth member of the expanded Prius family (earlier post), on sale in the US in mid-March with a starting MSRP of $18,950—a lower MSRP than the first-generation Prius carried 12 years ago, noted Bob Carter, Toyota Division Group VP & GM, at the media preview in January for the new hybrid.

With the Prius c (sold as the Aqua in Japan, earlier post), Toyota is striving to strike a balance between fuel efficiency, styling, intelligent connectivity and affordability to attract younger, eco-conscious buyers who may have desired, but couldn’t afford, a hybrid. To help meet that design target, Toyota engineers focused on making the hybrid system more compact and lighter in weight—the Prius c hybrid system is 14% lighter than that of the current Prius Liftback.

Priuscexterior
Prius c. Click to enlarge.

The Prius c (“c” for city) is targeted at young singles and couples, and is the gateway vehicle for the Prius Family, Carter said. The Prius c will offer a single grade with four equipment levels:

  • Prius c One (MSRP $18,950) features: power windows and door locks, automatic climate control, Multi-Information Display (MID), Hill Start Assist Control (HAC), Remote Keyless Entry, projector-beam halogen headlamps, steering wheel-mounted audio controls, 4-speaker audio, Bluetooth hands-free telephone controls, Bluetooth and USB auxiliary outlets, rear window wiper.

  • Prius c Two (MSRP $19,900) adds cruise control, tonneau cover, 6-way adjustable driver seat with vertical height adjustment, 60/40 split fold-down rear seat, engine immobilizer, tilt/telescopic steering wheel and 6-speaker audio system.

  • Prius c Three (MSRP $21,635) adds Display Audio with Navigation and Entune, Touch Tracer Display, Smart Key System on front doors and liftgate with Push Button Start and more.

  • Prius c Four (MSRP $23,230) adds SofTex-trimmed seats, heated front seats, alloy wheels, fog lamps.

The Prius Family will have a big hand in defining Toyota’s future. I can see combined Prius sales in the US leading Toyota by the end of the decade.

The Prius v is one of our quickest-turning vehicles at dealerships. We sold 8,399 in the first 10 weeks it was on the market; nearly two-thirds of Prius v buyers are first-time hybrid buyers. Now that we have two Prius Family members in showrooms [v and Liftback], it hasn’t dampened the strong popularity of the third-generation Prius Liftback. The early interest in the Prius v has drawn strong traffic to dealers, with some of those new Prius buyers liking the v but actually deciding that the Liftback fit their needs best.

The Prius c, like the v and the Plug-in, will add substantial incremental sales to Prius this year, with total family sales of about 220,000. Both the Prius c and the v will be about 15-20 percent of the mix, with the Plug-in around 5%.

—Bob Carter

The hybrid system in the Prius c comprises a SULEV (Tier 2 Bin 3)-rated 1.5-liter in-line, four-cylinder gasoline engine (INZ-FXE) that utilizes an Atkinson cycle to increase efficiency, a new hybrid transaxle (P510), an air-cooled, high-output 144V, 6.5 Ah NiMH battery and a variable-voltage system in which a boost converter boosts the operating voltage of the system to a maximum of 520 V DC. Maximum hybrid system output is 73.6 kW (98.7 hp)

Estimated EPA fuel economy ratings are 53/46/50 mpg US city/highway/combined (4.4/5.1/4.7 L/100 km).

Engine. The 1NZ-FXE is an in-line 4-cylinder, 1.5-liter, 16-valve DOHC engine. Although the engine number is the same as in earlier generations of the Prius, the engine for the Prius c is about 70% new, said Chief Engineer Satoshi Ogiso.

It features a high-expansion ratio Atkinson cycle, Variable Valve Timing-intelligent (VVT-i) system, Electric Throttle Control System-intelligent (ETCS-i) and Exhaust Gas Recirculation (EGR) system employing a newly designed, highly efficient EGR cooler from Denso (earlier post). The engine also uses Sequential Multiport Fuel Injection (SFI) and Electronic Spark Advance (ESA).

The adoption of a cooled-EGR system reduces cooling loss and pumping loss; with lower exhaust heat, heat efficiency was enhanced and, consequently, fuel efficiency was enhanced as well.

The VVT-i system controls the intake camshaft within a range of 47° of Crankshaft Angle to provide valve timing suited to the engine operating condition. This improves torque in all engine speed ranges as well as increasing fuel economy, and reducing exhaust emissions.

Toyota engineers eliminated the accessory drive belts, thereby reducing losses from friction. Too, the electrically driven water pump allows coolant flow rate to be controlled with greater precision based on vehicle conditions for better fuel efficiency.

Exhaust Heat Recirculation heats engine coolant using a newly designed heat exchanger. The more efficient fin-type heat exchanger provides improved cold-weather performance and reduces time for coolant to reach operating temperature. This shortens the time until the gasoline engine can stop and also improves heater performance, reducing time to warm air by 1 minute.

Maximum power is 54 kW (72 hp) @ 4800 rpm; maximum torque is 111 N·m (82 lb-ft) @ 3600 - 4400 rpm.

p510
The new P510 transaxle in the Prius c is 21.0 mm shorter and 19.5 mm narrower than current Prius 3G transaxle (P410). Click to enlarge.

P510 Transaxle. Toyota has introduced several innovations with the Prius c’s transaxle, two of which represent a departure from the company’s previous hybrid transaxle architectures. The transaxle assembly contains Motor Generator No. 1 (MG1) which functions as the starter and a generator, and Motor Generator No. 2 (MG2) which also functions as a generator as well as the vehicle’s traction motor, along with a final drive and differential. As with all Toyota hybrid transaxles introduced from 2006 forward, it utilizes a planetary reduction gear for the traction motor in addition to the planetary gearset that is employed as a power-split device. The P510’s MG1 offers maximum output of 42.4 kW (56 hp); MG2 offers maximum output of 45 kW (60.3 hp) and 169 N·m (124.6 lb-ft) of torque.

Prior to designing the P510 transaxle, Toyota had employed random-wound distributed windings, with the sole exception being the resin-encased, solenoidal MG1 winding used in the P410 transaxle (Gen 3 Prius Liftback, Prius v, and Lexus CT200h). While distributed windings often deliver excellent performance, they can be bulky as well as costly to build. For the P510 transaxle, however, Toyota designed compact, high-output solenoidal windings for both MG1 and MG2. The P510’s windings use much thicker wire than usual—some ten times thicker than that in the P410 generator winding—with a trapezoidal cross-section. The new winding design has made the P510 transaxle easier to mass produce, according to Chief Engineer Ogiso. In addition, solenoidal windings are typically less susceptible than distributed windings to turn-to-turn winding faults, which are themselves exacerbated by the fast rise times of pulse width modulated inverters.

The transaxle’s cooling system has also been simplified. Previous Toyota hybrid transaxles have supplemented a splash lubrication system with an engine-driven transaxle fluid pump for high-speed and/or sustained high torque operation. The transaxle fluid circuits have, in turn, been augmented by heat sinks which are cooled by a water-based coolant loop shared with the powertrain’s inverter. The P510 transaxle does away with the shared coolant loop, which is now exclusive to the inverter, and instead diverts some of the transaxle’s oil pump output, via an external pipe, to an internal manifold pipe mounted above the transaxle windings. Transaxle fluid then drips down onto the end turns of the windings, bypassing the transaxle’s rotors and keeping windage losses to a minimum.

The new transaxle is some 16% lighter than the P410 transaxle, and features a redesigned a new torsional vibration damper to help suppress engine noise as well as the transfer of vibration between the engine and transaxle. According to Chief Engineer Ogiso, Toyota will roll out the design changes to other hybrid platforms over time. A paper on the P510 transaxle, entitled “Development of New Hybrid Transaxle for Sub-Compact-Class Vehicles”, will be presented at SAE 2012 World Congress in April.

Priusc-battery
The battery pack in the Prius c is more compact than in the Liftback. Click to enlarge.

Battery pack. The 144V NiMH air-cooled battery pack in the Prius c has been made more compact and lightweight and is installed under the rear seat. (The NiMH pack in the Liftback is 201V.) The battery module includes the battery pack, battery ECU, system main relays and service plug. The 144V output from the battery is boosted to 520V DC maximum before conversion to alternating current.

The pack comprises 20 NiMH modules (120 cells), with each module 7.2V DC (1.2 volts x 6 cells). Pack peak output is 19.3 kW (25.9 hp). The smaller pack in the Prius c weighs about 68 lb (31 kg), compared to about 92 lb (42 kg) in the Liftback, with 168 cells.

Priusc-battery2
The battery pack is installed beneath the rear seat. Click to enlarge.

The cool air intake is positioned beneath rear seat; cooling air velocity and volume are optimized for cooling efficiency. The battery is warranted for 10 years/150,000 miles. At end of life, every part of the battery, from the precious metals to the plastic, plates, steel case and the wiring, will be recycled or processed for disposal.

Power electronics. The inverter on the Prius c is smaller and lighter than that in the Prius 3G. Weight is reduced 10% (3 lb, 1.4 kg) and volume is reduced 12 percent (1.6 liters).

Newly designed thinner IGBT (Insulated Gate Bipolar Transistor) chips reduce energy loss, contributing to enhanced fuel efficiency.

Aerodynamic features. Toyota applied a number of aerodynamic features to the Prius c to achieve a good coefficient of drag of 0.28. (As vehicles get shorter, it makes it more challenging to deliver a good Cd; the Liftback, by comparison, has a Cd of 0.25.)

Among the features are aero stabilizing fins installed on the side face of the rear combination lamp and at the base of the outer mirror; underbody covers to improve airflow; and lightweight aluminum wheels and wheel covers designed with aerodynamic performance in mind.

Driving modes. In addition to its base hybrid driving mode, the Prius c offers an ECO mode and an EV mode which can be activated via buttons next to the parking brake handle.

  • ECO mode maximizes fuel savings across all driving conditions. It modifies or smoothes out the electronic throttle control program to reduce throttle response, reducing throttle opening by up to a maximum of 11.6%. It also modifies air conditioning operation. It also can improve acceleration performance in low-traction conditions such as ice and snow as the reduced output helps to minimize wheel slippage.

    EPA label calculations do not include ECO Mode.

  • EV mode helps keep the vehicle in electric-only mode longer at low speeds. In EV Mode, the ECU operates the vehicle using only MG2 if required conditions are satisfied.

    Under certain operating conditions, the vehicle can go approximately 25 mph (40 km/h) for up to approximately one-half mile (possibly longer depending on vehicle and battery conditions). The SOC (state of charge) level display on the Energy Monitor must be four bars or more to operate in EV mode.

Driving first impressions. GCC had the opportunity briefly to drive the Prius c under a variety of city and highway conditions during the preview. The little hybrid is quite likeable—it handles well and is comfortable; Toyota’s focus on the comfort of the seats (at least the front seats, we didn’t climb into the back) paid off, as did its focus on reducing NVH.

The most noticeable downside in delivered performance is on a steep incline, or when attempting to overtake on the highway. Under those conditions, the power is not there, and the car labors. However, as Toyota pointed out, that wasn’t part of the core design target. They opted for keeping overall cost down and delivering a very fuel-efficient vehicle optimized for less strenuous conditions. (Again, “c” is for city.)

That said, once the Prius c was at speed on the highway, it kept securely to the pavement.

The ongoing tension between cost and content also shows at points. As an example, the entry grades do not offer the push-button start familiar to Prius Liftback drivers—however the rather substantial opening (sealed) remains in the dash as a visual reminder.

Resources

  • Development of New Hybrid Transaxle for Sub-Compact-Class Vehicles (SAE 2012-01-0623)

Comments

Davemart

Many thanks for the comprehensive cover of this car.

A plug in version may be difficult with this reduced battery space and weight, but cost in this class of car is probably the main reason why it is not offered, at least for the present time, and I would guess for the next several years.

Davemart

This, like the original Prius, is not a plug in car, and so doesn't run on electric only at all, or hardly at all.

The Prius plug in has an electric range of 15 miles.

kelly

50 mpg under $19,000US - priceless.

An extra grand for fold-down seats is kinda cheesy, but wonder how much 'ECO' mode improves mpg.

HarveyD

This will be a very good seller in Japan, most EU countries and where gas price is close to or above $6/gal. and where people are more environment and fuel economy minded. Another very good decision by Toyota.

Account Deleted

Great that Toyota is pushing the limit for how fuel efficient a small gasoline car can be without sacrificing usability.

Note that despite significant less weight than the Prius Liftback they both get 50 mpg average. The Liftback’s drivetrain is more efficient because it has a much more powerful electric motor. 60kw in the Liftback versus 19.5kW in the Prius c. So less regenerative braking and lees ability of the electric motor to maintain the combustion engine running only at its peak efficiency. Cleary the second generation Prius c could benefit from a more powerful battery and electric motor. That should be possible using lithium batteries and improved EV motor with say better cooling and or more powerful magnets etc.

Eschewo

It's nice to read an automotive article that covers a lot of technical details. Good job CCG! The efficiency combined with affordable MSRP makes the Prius c amazingly attractive. The Prius c will probably be my next new car purchase.

SJC

Requirements scale, you make a lighter car you don't need a bigger engine and motor and you can downsize the transmission and battery requirements..less is more.

usbseawolf2000

@Henrik:

MG2 power is 60kW/45kW for Liftback/Prius c.

Battery power is 27kW/19.3kW for Liftback/Prius c.

Account Deleted

@Usbseawolf

You are right. I got the numbers wrong. I did not realize the large power gab between the battery and the motor (I wonder why the EV motor is more than twice as powerful as the battery that powers it?). But I think my argument is still valid that the more powerful hybrid drive train in the Liftback can explain why the Prius c cannot get better MPG despite weighting significantly less.

Now that one of the world’s largest industries (the 1000B+ USD global auto industry) is getting seriously into batteries, electric motors and power electronics I think there is great hope for fairly dramatic improvement in both the power and cost of producing such items.

SJC

That has always been a good question, why would you have a 60kW motor and less than a 30 kW battery? If you have 1 kWh of the right battery chemistry, you could get 30 kW out of it for a short period of time, but the motor is capable of twice that.

Nick Lyons

53 city mpg is v. good.
46 hwy mpg is somewhat disappointing, but won't matter much to commuters using this car to navigate the congested freeways and streets of urban areas.

Great commuter car.

kelly

usbseawolf2000,

"144V, 6.5 Ah" NiMH battery = 936 watt hours(.936Kw hours) of battery energy storage.

"Pack peak output is 19.3 kW (25.9 hp)" is a max discharge rate of this battery, good for about 3 minutes - if it's a near linear discharge rate and:

"Under certain operating conditions, the vehicle can go approximately 25 mph (40 km/h) for up to approximately one-half mile (possibly longer depending on vehicle and battery conditions).

They note the Prius C battery having 120 cells:.936 kwatt hours. The 15 year-old Toyota EV RAV4 NiMH battery has 240 cells:25.6 kwatt hours http://www.evnut.com/rav_data.htm

In other words, how many hundred/thousand dollars cheaper would a/any Prius/C be with a 100 fewer, but bigger battery cells?

Thank a US firm for shelving EV scale NiMH batteries through selling the patent to an oil company and jacking hybrid battery costs for decades for the whole world.

Kinda makes one wonder how Europe/China etc. have high speed rail and the US has a firm convicted of destroying urban rail by the Supreme Court.. http://en.wikipedia.org/wiki/General_Motors_streetcar_conspiracy

3PeaceSweet

You could add a more powerful battery (plugin?) to the 520v inverter and skip the DC - DC converter.

I wonder if we will see a 4WD plug in Prius with a rear axle motor

HarveyD

It should be relatively easy to make all (most) PHEVs AWD with or without mechanical link between front and rear wheels. Same could be said for BEVs equipped with two e-motors (front and rear) or in-wheel on all four wheels. Electric drive trains will evolve to take better advantage of high efficiency e-motors, to improve driving conditions and capture more braking/deceleration energy.

mahonj

In Europe, this will have to compete with loads of small gasoline and diesel cars.
People are used to driving small cars and they are much easier to live with in the cities than larger cars.
Gasoline is already $8-$9 / US Gallon (and has been expensive for decades) [ but not at this level ].

It will have to compete with gasoline cars on price and diesel cars on economy and price.

The problem is price in two ways:
a: You can't charge as much for a small car as a large one, and a hybrid is inherently expensive due to its drivetrain.

b: The money saved in going from 40 mpg to 50 mpg is much less than that saved going from 30 - 50 mpg, so the motivation to buy an expensive hybrid is reduced.

Nonetheless, I wish them every success.

kelly

mahonj, it seems that Prius gives an honest 50 mpg(w/o hyper-milling) average, but the 40 mpg highway cars actually average in the low 30's.

SJC

There are several factors that go into a car purchase and mileage may be one of them. Is it fun to drive? Does it do everything I want a car to do? How is the resale, is there any status attached to owning one?

A car purchase is much more than a logical list of needs it can have more to do with wants. Look at all the makes and models to chose from and you can see that many different buyers have many different reasons for making the purchase.

Dave R

@SJC "That has always been a good question, why would you have a 60kW motor and less than a 30 kW battery?"

The Power Split Device transmission used in the Prius can generate electricity directly from the engine - so it needs to be able to handle more power than what the battery can push.

usbseawolf2000

@Henrik: The length of Prius c hurts (less aerodynamic) the highway fuel economy. Prius c is more efficient than the Liftback in the city (53 vs. 51). Keep in mind that 1.8L ICE in the Liftback is more efficient (in term of BSFC and wide rpm range) than the 1.5L.

If you look at it from GenII Prius angle, the lighter Prius c gets about 10% MPG boost (53/46->50 vs. 48/45->46).

usbseawolf2000

@SJC: "why would you have a 60kW motor and less than a 30 kW battery?"

Prius has an electric transmission (eCVT). It generates electricity to multiply torque through the 60kW electric motor. In contrast, traditional mechanical transmission would change gear ratio to multiply torque.

Prius has one gear ratio. Reverse gear is achieved by spinning the 60kW motor backward.

SJC

The answers seem to imply that you need the torque from the motor, but you can not get the torque if you do not have the current. Another explanation might be using the motor as an alternator, but with a small battery there is no place to put the energy.

usbseawolf2000

@Kelly: Prius c has high power (for HV) NiMh cells. RAV4 EV cells are high energy (for EV). RAV4 EV cells wouldn't be suitable for Prius c. They would not fit under the rear seat together with the gas tank.

The purpose of the HV battery is to use electricity when the gas engine is not efficient -- when power demand is very low (less than 15hp). The battery is also used for peak power acceleration that usually last about 10 seconds. The battery would get recharged quickly (thanks to two motor system) so you don't need a big battery.

SJC

After looking at the Power Split Device acting as a differential of sorts I understand. It is not the battery power density that is the driving factor, the first motor and second motor are acting like a eCVT, clever but complex.

MG

I'd just add to usbseawolf2000's explanation that the price to be paid for avoiding multi-speed gearbox (or mechanical CVT) in Toyota HSD system is quite high power output (along with power electronics) required from MG1 (MG1 rated at 42.4 kW and MG2 at 45 kW).
IMO, for short acceleration bursts a much smaller MG1 could be used if paired with some high power source (say ultracaps with 30+ Wh/kg, once they become available, currently they are at ~ 5Wh/kg). Plug-in Prius system, with much larger battery will supposedly have higher power output, so it could use significantly smaller MG1, for short bursts of power for MG2 (for acceleration, 10-15 seconds).

For sustained high load at low speed (ie steep up-hills, to keep up with traffic), again, powerful MG1 generator is needed, that mode is close to series hybrid (Chevy Volt uses 54 kW generator, in series mode). Otherwise, even plug-in Prius with smaller MG1, won't be able to keep up with ICE's of similar power output, but equipped with multi-speed gearbox (or mechanical CVT).

SJC

BYD has an interesting design, both motor/generators could be used together when needed. That would allow the car to have the power of BOTH motors to be an EV when in that mode. THEN you need a battery pack that can deliver the power in a PHEV.

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