Honda Accord Hybrid teardown (Part 2)

Sport Hybrid i-MMD Battery components and electric servo brake system

2014/02/21

Summary

Lithium-ion battery pack being torn down
Lithium-ion battery pack removed at the teardown
* Click on the photo for a larger image.

 The teardown of the Honda Accord Hybrid was conducted  in January 2014 by the Automotive Technology Innovation Center of the Hiroshima Industrial Promotion Organization. The disassembled Power Control Unit (PCU) and chassis components were reported in the following first report:


Previous report:
Honda Accord Hybrid teardown (Part 1) (Feb. 2014)


This second report highlights the lithium-ion battery pack and the Intelligent Power Unit (IPU: a collective term of Honda's battery pack components), located in the trunk behind the rear seats. The report also presents the electric servo brake system that increases the efficiency of recovering regenerative energy. The teardown of the drive unit will be reported shortly in the coming third report.


Related Reports:
Honda Fit Hybrid teardown: Part 1, Part 2 (Dec. 2013)
Toyota Aqua (Prius c) teardown: Part 1, Part 2 (Nov. 2012)
Nissan Leaf teardown: Part 1 (Mar. 2012), Part 2 (Sep. 2012), Part 3 (Nov. 2012)



Before disassembly

 

Rear seats
Rear seats Rear seats
The right-side photo shows the rear of the vehicle with the rear seats removed. The Intelligent Power Unit (IPU), a collective term of Honda's battery pack components, is concealed behind the rear seats. Air for cooling the IPU is drawn in from the grid-like opening beside the seatbelt. The service plug is concealed behind the square metal cover at the center of the right-side photo (pointed by the white arrow).

 

Trunk
Trunk Trunk
The trunk has a two-tier structure to conceal the IPU behind the trunk lining at the center. The maximum permissible load above the IPU is 7kg. The trunk is shown without the trunk lining on the right-side photo. The red arrow points to the outlet duct where air is discharged after cooling the IPU. The blue arrow points to the IPU cooling fan.

 

 



IPU removal

 

Trunk
Trunk Trunk
The IPU is shown with the 1.29kg-front-cover removed. The IPU is mounted in the trunk behind the rear seats. The IPU is located at the center of the photo. The black duct by the seatbelt is the inlet duct (pointed by the white arrow) for drawing in the IPU cooling air. The red arrow points to the service plug (with the black tape attached). It is located between the junction board (pointed by the blue arrow) and the contactor board (pointed by the yellow arrow), An inner view of the right-side of the trunk. The red arrow points to the outlet duct where air is discharged after cooling the IPU. The blue arrow points to the IPU cooling fan. The white arrow points to the TV tuner supplied by Mitsubishi Electric, the yellow arrow to Clarion's radio tuner, the green arrow to the distributor of the radio antenna supplied by Yokowo. The TV tuner weighs 0.72kg and the radio tuner weighs 0.58kg.

 

Trunk with the IPU removed IPU Cooling fan
Trunk with the IPU removed IPU Cooling fan
The trunk view without the IPU from the rear seat side. The IPU cooling fan, outlet duct and TV and radio tuners are left intact in the trunk.The orange-colored high-voltage cable in the foreground connects the IPU to the PCU and the electric compressor located in the engine room. The IPU cooling fan is removed from the right side of the trunk. The fan body is manufactured by Valeo and the motor by Shinano Kenshi. The fan is 170mm in diameter.

 

 



IPU components

 

Intelligent Power Unit (IPU)
IPU IPU
The IPU is shown with the cover removed and viewed from behind the vehicle (left-side photo) and from the rear seats (right-side photo). The IPU measures 700mm in length, 400mm in width and 330mm in height. The IPU cooling air inlet duct and an insulator made of Styrofoam are at both sides of the IPU.
The white arrow points to the outlet duct that connects to the IPU cooling fan, the red arrow to the DC-DC converter supplied by Shindengen Electric Manufacturing. The blue arrow points to the battery ECU supplied by Keihin, the yellow arrow to the leak sensor supplied by Yazaki Corporation. The three green arrows in the foreground of the left-side photo point to the battery monitoring units supplied by Yazaki Corporation. The purple arrow on the right-side photo points to the contactor board, the light blue arrow to the junction board.
The junction board weighs 1.24kg and measures 130mm in length and 240mm in width. The contactor board weighs 1.05kg and measures 120mm in length and 225mm in width. The air drawn in from the inlet duct flows to the lithium-ion battery pack, DC-DC converter and the cooling fan before it is ejected from the outlet duct.

 

Battery monitoring units
Battery monitoring units Battery monitoring units
Battery modules are monitored by the battery monitoring units supplied by Yazaki Corporation.
Each unit weighs 180g and monitors two battery modules. The Honda Accord Hybrid has six battery modules that are monitored by three battery monitoring units. For comparison sake, the Honda Fit Hybrid has four battery modules that are monitored by two battery monitoring units.
An inner view of the battery monitoring unit. The portions in a white circle monitor the voltage of the battery module and the portion in a red circle monitors the temperature of the battery module.
Each battery module temperature sensor monitors two battery modules. Each battery monitoring unit is paired with a temperature monitoring board.

 

DC-DC converter
DC-DC converter DC-DC converter
An inner view of the DC-DC converter A rear view of the DC-DC converter showing the radiator fins. Fins are 2mm thick at the root, 1.4mm at the tip, and 20mm in height. There are 38 metal fins, 5mm apart from each other, in the converter. The DC-DC converter is cooled as the IPU cooling air is exposed to the radiator fins.

 

Battery ECU Battery pack
Battery ECU Battery pack
An inner view of the battery ECU supplied by Keihin. It measures 130mm in length, 160mm in width and 30mm in height. The battery pack is shown with the DC-DC converter, battery ECU and leak sensor removed. The top cover of the battery pack weighs 3.75kg including the ECU, DC-DC converter, etc. The grooves that indicate dimensions contained the radiator fins of the DC-DC converter. After cooling the battery pack, the air flows into the slit pointed by the white arrow and cools the DC-DC converter.

 

 



Lithium-ion battery

 

Lithium-ion battery pack
Lithium-ion battery pack Lithium-ion battery pack
The gray metal component on the left side of the photo is the IPU's lower frame. The black plastic part over the lower frame is the inlet duct. The IPU-cooling air taken from the side of the rear seat flows through the holes (pointed by the white arrow) to the cell pack. On the right side of the photo is the removed Blue Energy's lithium-ion cell pack. A rear view of the inlet duct that faces the IPU lower frame. The inlet duct in the photo weighs 0.67kg. The lower frame weighs 4.4kg and measures 810mm in length and 455mm in width. The inlet duct is upholstered with trim pad to absorb vibrations, sounds and frictions.

 

Battery module
Battery module Battery module
The lithium-ion battery pack is shown with one of the modules removed from the battery pack lower frame. The lower frame weighs 2.9kg. A battery module measures 260mm in length, 130mm in width ad 190mm in height. The battery module uses Sumitomo Electric Industries' battery wiring modules. The orange-colored parts are plastic cases. The battery cells are laid in series with the positive end of a cell connected to the negative end of the next cell.
Battery module Battery module
A rear view of the battery module in the upper right photo. It was mounted in this direction in the battery pack in the upper left photo.
The white arrow points to the temperature sensor that measures the temperature of the battery cells at ends or at the center. The temperature sensor is installed in three of the six modules.
The battery module components. A battery pack consists of six modules, and each module consists of 12 cells, namely with 72 cells per battery pack. Each module has a rated voltage of 43.2V, rated capacity of 5.0Ah along with 216Wh electric energy.

 

Battery cell
Battery cell Battery cell
The battery cell supplied by Blue Energy (sold under the trade name of EH5) weighs about 280g. A black plastic partition (pointed by the white arrow) is removed from a battery module. The black plastic partition is inserted to create a cooling air passage between cells.

 

 



<Reference> Lithium-ion battery pack of the Honda Accord Plug-in Hybrid

 

Lithium-ion battery pack from the Honda Accord Plug-in Hybrid
Lithium-ion battery pack Lithium-ion battery pack
The lithium-ion battery pack on the Accord Plug-in Hybrid (PHV) exhibited at the JSAE Automotive Engineering Exposition 2013 held in May 2013. The PHV battery pack was not used at the tear down, but shown for reference purpose. The battery pack has a 6.7kWh/ 20.8Ah capacity (The hybrid version has a 1.3kWh/5.0Ah capacity) and provides 320V total voltage. It consists of a hundred cells supplied by Blue Energy (The hybrid version has 72 cells). Each cell, sold under the trade name of E19, provides 3.2V and measures about four times as large as the EH5 of the hybrid model.
The right-side photo shows a side view of the same battery pack with a battery monitoring unit supplied by Keihin.

 

 



Electric servo brake system

 

Tandem motor cylinder (brake action)
Tandem motor cylinder Tandem motor cylinder
The left-side photo shows the teardown work of the drivetrain. The tandem motor cylinder in the center circle is located in the engine room by the dashpanel near the front passenger's seat. The right-side photo shows an enlarged view of the tandem motor cylinder. The silver-colored part at the leftmost end (pointed by the red arrow) contains a reduction gear and ball screw supplied by NTN. The black part above (pointed by the blue arrow) is the servo (brushless) motor supplied by Mitsuba Corporation. The silver-colored part to the right (pointed by the yellow arrow) contains the piston supplied by Nissin Kogyo. The piston generates hydraulic pressure and sends it to four wheels. The tandem motor cylinder measures about 150mm in length and 300mm in width.

 

Pedal feel simulator (pedal action) Electric servo brake ECU
Pedal feel simulator Electric servo brake ECU
The photo shows the brake pedal and the pedal feel simulator supplied by Nissin Kogyo. The brake pedal is normally blocked off from the tandem motor cylinder. The driver's brake input is sent by signal to the electric servo brake ECU (shown on the right-side photo). Since this does not help the driver feel a reactive force corresponding to the applied force, the pedal feel simulator is used to provide appropriate pedal feel to the brake pedal based on the braking force. The electric servo brake ECU, supplied by Honda Elesys, is located in the passenger compartment under the front pillar (A-pillar) by the front passenger's seat. The ECU weight 1.1kg.
The electric servo brake system consists of the pedal feel simulator (pedal action) and the tandem motor cylinder, stroke sensor, and electric servo brake ECU (brake action). The brake pedal movement is detected by the stroke sensor and the ECU sends corresponding signal to the motor of the tandem motor cylinder. This causes the ball screw and the piston to apply regulated hydraulic pressure to the brakes. The addition of the servo motor contributes to precise control of hydraulic pressure and faster response. This, in turn, enables recovering the otherwise wasted regenerative braking torque at the onset and at the end of braking. In an event of emergency braking or malfunction of the pedal stroke sensor, the hydraulic pressure in the pedal feel simulator bypasses to the tandem motor cylinder to activate the brakes directly. The electric servo brake is used in the Fit EV which was released for lease sale in the summer of 2012 for the first time. It is also used in the Accord Hybrid and the Fit Hybrid.

 

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