Toyota Aqua (Prius c) teardown: Part 2

Hybrid systems behind the 35.4km/liter (53 mpg city) car

2012/11/30

Summary

 Disassembly of Toyota's New Aqua Hybrid (dubbed "Prius c" in the U.S.) was organized for public viewing by the Saitama Automotive Industry Support Center. The key part suppliers and battery components of the Toyota Aqua were posted in the previous report.


Previous report:
"Toyota Aqua (Prius c) teardown: Part 1"


 Reported below (Part 2) are the drive unit consisting of the engine and hybrid transaxle, the power control unit (PCU) affixed with a boost converter*, and the associated system functions of the Toyota Aqua.


* The boost converter is designed to step up the 144VDC input voltage to up to 520VDC; the DC-DC converter is designed to reduce high DC voltage to low DC voltage (12V).

Cutaway model of the drive unit
Cutaway model of the drive unit that was exhibited
at the Tokyo Motor Show 2011
* Click on the photo for a larger image.


Related reports:
"Nissan Leaf teardown" 1 (posted in March 2012), 2 (posted in September 2012), 3 (posted in November 2012)



Toyota hybrid system configuration (THS II)

Toyota hybrid system configuration (THS II)

 

 



Engine room before disassembly

A top view of the engine room Engine room viewed from the vehicle's front left
A top view of the engine room with the PCU to the right and the engine to the left. The transaxle is fitted directly under the PCU. Engine room viewed from the vehicle's front left showing the bottom of the transaxle.

 

 



Power control unit (PCU) with a boost converter

Cutaway model of the PCU
Cutaway model of the PCU that was exhibited at the 2012
Automotive Engineering Exposition
(viewed from the right side of the passenger cabin)

 

PCU before disassembly Engine room without the PCU
PCU before disassembly Engine room without the PCU
The PCU, designed specifically for Aqua, integrates the inverter, DC-DC converter and boost converter. All high-voltage cables (colored orange) are removed and the electrodes are shown protected with white taping.
The cable pointed by the red-arrow connects to the nickel metal hydride battery, the blue-arrow cable connects to the generator, the yellow-arrow cable connects to the drive motor, and the white-arrow cable connects to the electric compressor.
The PCU is fixed to the metal bracket at the center. The transaxle is located behind the bracket.
The red arrow points to the high-voltage cable that connects to the generator. The white arrow points to the low-voltage connector used to charge the auxiliary battery.
The PCU is cooled by water that runs through the black hose shown at the top of the photo.

 

PCU removed
PCU removed PCU removed
A front view of the PCU after removal.
The PCU is reduced by 1.1kg in weight and 12% in volume from the current Prius as a result of downsizing and weight reduction of the inverter and the converter.
PCU as viewed from the vehicle rear. The openings are for routing high-voltage cables. The round opening at far-right connects to the nickel metal hydride battery, the elongated opening at the center connects to the generator, and the elongated opening at far-left connects to the drive motor, respectively.
Toyota Industries, whose logo is seen at lower right, supplies the DC-DC converter only. The PUC assembly is manufactured in-house by Toyota.

 

Inside the PCU
Inside the PCU Inside the PCU
The left-side photo shows the underside of the PCU cover. The boost converter is fitted inside the black resin filling.
The circuit board in the top tier of the right-side photo is the MG (motor/generator) control board. The board in the lower tier is the gate drive board (pre-driver).
The DC-DC converter, located under the lower-tier board, reduces the 144VDC input voltage from the nickel metal hydride battery to 12V, which is supplied to the ECU and lighting, etc., and used to charge the auxiliary battery.
An IGBT (switching element, concealed in the photo) that controls the inverter and the converter is located under the DC-DC converter. The IGBT features the recently-developed direct cooling system.

 

 



Drive unit

Drive unit removal Engine room without the drive unit
Drive unit removal Engine room without the drive unit
The vehicle is lifted and rested on tires while the drive unit is being removed. A bottom view of the engine room without the drive unit. An exhaust pipe was contained in the heat shield shown at center left. The orange-colored cable to the right is the high-voltage cable that connects the nickel metal hydride battery and the PCU.

 

Drive unit
Drive unit Drive unit
The drive unit as viewed from the vehicle front with the transaxle to the right and the engine to the left.
The HVAC electric compressor, connected to the high-voltage cable at lower left, receives electric current boosted to 202-288VDC by the boost converter.
The drive unit as viewed from the passenger cabin.
The silver-colored item pointed by an arrow is the cooled EGR (exhaust gas recirculation) system. The heat shield at center contains the exhaust manifold with an integral catalyst. The integration of the catalyst and the exhaust manifold has resulted in reducing the catalyst warming time by 67% from the current Prius.

 

Engine
Engine Engine
The engine section of the drive unit without the transaxle, as viewed from the front right side (left-side photo) and from the vehicle left side where the transaxle was connected (right-side photo).
The Aqua is driven by the 1NZ-FXE engine as are the first- and second-generation Prius models. However, only about 30% of the engine parts are carried over from the second-generation Prius and most other parts have been either newly designed or adopted.
The silver object in the foreground of the left-side photo with regularly pitched protrusions is Aisin Seiki's electric water pump that is also used in the current Prius. The electric control means the necessary amount of cooling water is supplied when and as needed without the help of the engine power. It eliminates the auxiliary belt which, in turn, reduces overall friction, all contributing to improving the vehicle's fuel efficiency. The compact design creates extra space at the side of the cylinder block which, in turn, has led to the engine downsizing.
The black section pointed by an arrow in the left-side photo is the intake manifold downsized by the integration of the EGR passage. Denso's electric compressor is located under the electric water pump.

 

Air filter Exhaust pipe
Air filter Exhaust pipe
The air cleaner with the case disassembled. "Toyoda Gosei" is written outside the case (right) and "Denso" on the filter element.
The black item in the front right of the case at the left of the photo is the plug-in type airflow meter of the intake air temperature sensor (built-in).
Sango's exhaust heat recovery system (not shown) may be fitted as a factory option to the pipe assembly. According to Toyota announcement, the system increases fuel efficiency in cold areas by 9% since it shortens the time needed for warming the engine.

 

 



Transaxle

 The transaxle consists of the motor and the generator, and the gear train assembled between them. The motor and the generator were removed first.


Cutaway model of the transaxle
Cutaway model of the transaxle that was exhibited at the 2012
Automotive Engineering Exposition
(viewed from front)

 

Transaxle
Transaxle Transaxle
Transaxle as viewed from the vehicle left (motor side). The high-voltage cable at the top of the transaxle connects to the generator, and the high-voltage cable at the right connects to the drive motor.
The section (center) identified by a red arrow contains the oil pump. The section identified by a white arrow contains the motor resolver.
The transaxle designed specifically for the Aqua is shorter in length by 21mm and weighs 8kg less than the current Prius due to the fewer parts count along with downsizing and weight reduction efforts.
The drive motor appears when the outer cover in the left-side photo is removed.
The whitish cable at diagonally upper right of the motor is the temperature sensor. The pale red cable extending from the cover center is the motor resolver (angle sensor).
The motor coil is made of rectangular wire co-developed by Furukawa Electric and Furukawa Magnet Wire. It consists of rectangular conductor, enamel layer and extruded resin layer. The use of the rectangular wire reduces the resistance of the coil winding and increases the electric current running in the coil. This, in turn, increases the motor power. Furthermore, it allows regularly pitched swirl-like winding that results in 15% shorter coil height (coil end) compared to the current Prius.

 

Drive motor stator removal Drive motor without the stator
Drive motor stator removal Drive motor without the stator
Because of the strong magnetic force of the permanent magnet, removing the stator from the drive motor was performed by three students using a flat-end screwdriver-like tool with a bent end. The drive motor is shown with the rotor and without the stator.
The opening at upper right, identified by an arrow, is for routing the high-voltage cable that connects the PCU and the drive motor.

 

Drive motor rotor
Drive motor rotor
Side view of the rotor removed from the drive motor.

 

Engine side of the transaxle
Engine side of the transaxle
The contact point between the engine and the transaxle. The generator is located behind it. The shaft projecting at the center is part of the power split mechanism that transmits driving force from the engine.

 

Generator in the transaxle After the generator removal
Generator in the transaxle After the generator removal
The generator appears when the outer cover on the engine side is removed.
The whitish cable at diagonally upper left of the generator is the temperature sensor.
Unlike the drive motor removal, the generator was removed easily by a student.
The pale red cable at the top is the generator resolver (angle sensor).

 

Generator
Generator Generator
An enlarged image of the generator (engine side).
The generator is similar to the drive motor in terms of structure and winding except for the lower stator height.
The winding height (coil end) is reduced by making the winding parallel to the peripheral rim and slanting.
An enlarged image of the generator as viewed from the opposite side (gear train side).
The welds (gray sections) are resin coated for insulation to prevent conductors from exposure due to peeling.

 

 



Gear train disassembly

 "Gear train" serves four functions of power transmission, power splitting, motor reduction and parking.

Gear train split up
Gear train split up Gear train split up
Gear train is split into two parts after the drive motor and the generator were removed. The drive motor is to the right, and the engine to the left. Gear train as viewed diagonally from left.
A student is holding the counter driven gear.

 

Inside the gear train
Inside the gear train Inside the gear train
An inner view of the motor side of the gear train. The parking brake device is seen at lower right of the power split mechanism (center). An inner view of the engine side of the gear train. The small gear at center left (pointed by a red arrow) is the counter driven gear.
The larger gear (pointed by a white arrow) is the final driven gear. It connects to the driveshaft and drives the front wheels. It also serves as a differential device.
The gear teeth are finished by polishing and internal shaving to reduce vibration and increase quietness.

 

Power split mechanism (doubling as a motor reduction mechanism)
Power split mechanism Power split mechanism
The power split mechanism (doubling as a motor reduction device) is the key component of the gear train. The ring gear that connects to the drive motor, the planetary carrier that connects to the engine via shaft, and the sun gear that connects to the generator are assembled inside the power split mechanism. The multi-functional mechanism also incorporates the motor reduction gear. The power split mechanism is shown disassembled with the drive motor to the left and the engine to the right. The gear at far-left reduces the motor speed and transmits the motor rotation to the ring gear inside the central gear. The planetary carrier, right, transmits the driving force from the engine. The sun gear that connects to the generator is assembled in the planetary carrier.

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