Honda Fit (Jazz) Hybrid Teardown: Electric Components

Disassembly work of the new Fit Hybrid system

  The 4th generation new Fit hybrid model released by Honda in February 2020 adopts a 2-motor hybrid system named “e:HEV”, which is driven by the motor for most daily usage scenarios.

  To mount a two-motor hybrid system on a compact car, the new Honda Fit features newly developed components such as a new power device, an RC-IGBT (reverse conducting-insulated-gate bipolar transistor) for the power control unit (PCU), flat magnet wires with void-imbued polyimide insulation coating for the motor windings, as well as a more compact cooling system and layout.

  This report covers the disassembly work (conducted September 16 and 17 at the Saitama Institute of Automotive Technology) and the teardown components exhibition (held on October 1 and 2 at the Saitama Industrial Technology Center) which were organized by the Next Generation Vehicle Support Center of the Saitama Industrial Promotion Corporation. This report explains the electric components of Honda’s “e:HEV” two-motor hybrid system.

  At the time of this event coverage, detailed areas of components such as the motor rotor, the PCU power module peripheral components, and the battery module had not been disassembled.

Related reports: 
MarkLines Online Exhibition 2020: Electrification-Related Technology (Sep. 2020)
Automotive World 2020: Fuel-efficient engine technologies (Mar. 2020)
Tokyo Motor Show 2019: Exhibits from Nissan, Honda and Mitsubishi (Nov. 2019)

  The third-generation Fit launched in 2013 had a single-motor system (i-DCD), but the fourth-generation Fit uses a hybrid system that is a smaller, more advanced version of the two-motor system (i-MMD) found in the Accord (2018), Insight and other models, with the system being renamed to “e:HEV”.

  The power unit is a 1.5L Atkinson-cycle DOHC i-VTEC engine combined with a two-motor hybrid system, with the air cleaner located on the intake manifold and the PCU directly mounted on the transmission. The size of the new Fit transmission, including auxiliary equipment, has been reduced by more than 20% in both the lateral and front-rear directions compared to the previous two-motor hybrid system.

  As for the motor specifications, compared to the i-MMD-equipped Accord Hybrid (2016), which is also a two-motor hybrid system, the maximum output is reduced from 135 kW to 80 kW and the maximum torque is reduced from 315 Nm to 253 Nm.

New Fit power unit	List of specifications related to the electric components (Source: Created based on materials from the Next Generation Vehicle Support Center of the Saitama Industrial Promotion Corporation)

  The hybrid transmission, which contains the drive motor and generator, has connectors above the hybrid transmission to connect the power control unit and wiring, and a structure to connect the two when the units are joined together.

Hybrid transmission (engine side)	Hybrid transmission (generator side)

Disassembly of the gear portion

  When the engine-side cover of the hybrid transmission is removed during disassembly work, the gears are revealed.

  The long generator shaft is used to transfer power from the engine to the generator, which is located on the opposite side of the transmission via the step-up gears.

Gear portion	Inside the gear cover

Power generation motor (generator) with the unit assembled Magnet wire: Sumitomo Electric Wintech Inc.

  There are 2 motors on opposite sides of the gear portion, and when the cover is removed, the power generation motor (generator) is revealed.

  For both the drive motor and generator motor, the coating material for the SC windings has been changed from the conventional PAI + PEEK to PI with voids. The flat rectangular magnet wires with the new void imbued polyimide insulation for the motor windings, characterized by the yellow color, is probably made by Sumitomo Electric Wintech Inc., are adopted, with the company claiming that the thin film of the insulating layer is used to increase the cross-sectional area of the conductor by reducing the dielectric constant of the insulating layer, thus increasing the space factor.

  The wiring of the generator motor (generator) is directly connected to the connector on the upper left.

Resolver fixation member

  When the generator motor (generator) is removed, a member for fixing the resolver, which is a sensor that detects the magnetic pole rotation position required for current control, is revealed. The resolver for the generator is fixed to the front, and the stator of the resolver for the drive motor is fixed to the back side.

  The drive motor is revealed when the resolver fixation member is removed. Unlike the generator motor (generator), the drive motor has the welded side of the segment coil on the front side, so the new magnet wire is not yellow but has gray colored insulation coating.

Removing the resolvers and fixation members	Drive motor with the unit assembled

Empty hybrid transmission housing

  When the drive motor is removed, the hybrid transmission is in a state where the cast aluminum housing is empty.

Drive motor (left) and generator motor (right) immediately after disassembly

  The drive motor and generator motor removed from the hybrid transmission are in a state where the rotor and stator are now combined.

  The Fit Hybrid's motor is an embedded-magnet synchronous motor with a strong neodymium magnet built into the rotor. Therefore, when the mechanism that holds the rotor in place is removed during disassembly, the rotor is in a state of being attached to one side of the stator. The thicknesses of the generator and motor differ, but the stator core has an outer diameter of about 268mm and an inner diameter of about 200mm, excluding the protruding parts used to fix the bolts, and the basic structure seems the same, with no caulking and six welding points around the periphery.

  The stator of the drive motor has a laminated core thickness of electromagnetic steel plates with a thickness of approximately 56mm, which is shorter than the 61.5mm of the i-MMD in models such as the Accord and Insight, with six layers of 120-degree blocks transposed. The welded coil end is about 28mm long, but the other side is about 21mm similar to the i-MMD, and it is thought that this is due to the method of pre-molding and inserting four coils simultaneously.

  The stator of generator motor also seems to use the same core as that of the drive motor, but the stacked core thickness is about 31mm, which is shorter than that of the drive motor, and the stator is transposed into three 120-degree blocks. The sizes of coil ends were about 28mm and 21mm, similar to the drive motor.

Drive motor stator	Generator motor (generator) stator

  The end plate of the drive motor rotor has a drill hole for balance correction, but what was conspicuous in the teardown unit was that there were 5 drill holes for balance correction of the drive motor and 1 drill hole for balance correction of the generator motor. The rotor at the time of disassembly was exhibited in a state where magnetic flux was emitted from a strong magnet without being degaussed.

  The rotor core of the resolver remains near the shaft of the rotor of the power generation motor as it was when it was mounted, and since there are 6 protrusions, it can be seen that it is for a 6-pole pair = 12-pole motor. In addition, the rotor has 12 holes that appear to be weight-reduction holes, and it is believed that 12 magnetic holes are provided in the space surrounded by the 2 holes and the outer peripheral surface of the rotor.

  Since the rotor has not been disassembled, the details of the magnetic circuit are unknown, but it is believed that the motor torque characteristics have improved by 54%, and that the rotor is similar to the i-MMD in that it uses three magnets per pole, and uses a new type of magnet with finer particles and increased grain boundary phase, and that its size has changed.

  A closer look at the outer surface of the rotor reveals slight indentations on the surface of the electromagnetic steel plates core, an attribute also found in the i-MMD and other manufacturers' motors, which seems to be used to reduce the torque ripple that can lead to deterioration of sound vibration performance.

Drive motor rotor	Generator motor (generator) rotor

Resolver stator

  The resolvers are identical for both the drive and power generation motors. The resolver is connected using a connector instead of having a harness. Also, the resolver is most likely supplied by MinebeaMitsumi Inc. (Information based on an interview with a representative of the Saitama Industrial Promotion Corporation)

  The power control unit (PCU) made by Keihin that is adopted in the new Fit Hybrid is mounted directly on the hybrid transmission, and all wiring is connected using connectors, making it easy to separate.

  The connectors to the motor are located on the underside, with one for the drive motor and one for the generator motor arranged side by side.

Power control unit (top surface) (PCU made by Keihin)	Power control unit (bottom surface)

  The controller board is revealed when the top cover of the power control unit is removed. The motor controller circuit, gate driver circuit, boost controller circuit, and current sensor circuit are integrated on a single board. After mounting the chip components on the board, they are combined with IGBTs and soldered together with a flow solder.

• The motor controller controls the drive current of the two motors in the hybrid system, and uses a CPU made by Renesas.
• The gate driver is a circuit that converts the digital signal output from the motor controller to a signal level suitable for controlling the IGBTs in the power module. A total of 7 sets of circuits are mounted on the board, 6 sets corresponding to the three-phase AC drive of the two motors and 1 set for voltage boost control.
• The voltage booster controller is used to boost the battery voltage (172V) to 570V to drive the motor, and is connected to the reactor and IGBTs mounted on the back side to form a booster circuit.

  The power modules use a new type of power device, an RC-IGBT (Reverse Conducting Insulated Gate Bipolar Transistor), which combines IGBTs and freewheel diodes into a single chip for downsizing. The power module equipped on the Fit Hybrid was supplied by Keihin, who purchased the RC-IGBT bare chips and mounted them in the power modules. The RC-IGBT is believed to be made by Fuji Electric. (Information based on an interview with a representative of the Saitama Industrial Promotion Corporation)

Inside the upper part of the power control unit	Controller board

  The controller board cannot be separated easily because the power module and the signal line are soldered together, so the controller board, the power module and the water jacket for water cooling were removed as a single unit during disassembly.

  The coolant channel in the PCU consists of a water jacket that integrates a cast aluminum housing and the power module. The coolant from the inlet goes through the coolant channel in the center of the housing and then enters the sheet metal water jacket at the flange with a double O-ring to cool the power module. Afterwards, it enters the sheet metal water jacket at a flange with a double O-ring to cool the power module, before being discharged from the outlet via the housing through a flange with a double O-ring on the opposite side.

  There is no part of the capacitor that is in direct contact with the coolant, but it is cooled by the surrounding coolant channel.

  The capacitor module, which is an integrated smoothing capacitor and filter capacitor, is a film capacitor with three terminals. According to the notation on the side of the module, the capacitances are 340μF, 566μF, and 0.001μF, and the breakdown voltages are 270V, 624V, and 270V.

Coolant channel configuration	Condenser and housing coolant channel opening

  By removing the lower cover where the connector for connecting to the motor on the opposite side of the PCU is located, the DC-DC converter circuit and boost reactor are revealed. In the DC-DC converter area, there is the board on which the Renesas CPU is mounted, as well as a transformer and capacitors. In addition, the layout of this area also contains components such as a strong electric (PN) connector to which the harness from the 172V battery is connected, a terminal to connect to the bus bar, and the 12V battery circuit.

Inside the lower part of the power control unit	DC-DC converter and boosting reactor

  The intelligent power unit (IPU) is a collection of lithium-ion batteries, commonly referred to as a battery pack, and the peripheral high-power components. The IPU consists of components such as a battery module, high-voltage power distribution components with a power interruption function, a battery ECU that monitors and controls battery voltage and capacity, and a cooling mechanism. The new 48 lithium-ion battery cells provide a 62% increase in maximum power output. And, by using a compact layout for the cooling mechanism and ECU, the power output density per weight is more than double that of the previous model.

IPU (battery pack)	IPU built-in components

  The battery is made by Blue Energy (jointly funded by GS Yuasa and Honda), and the new battery cells (EHW5/EHW5B) are 17% smaller and 7% lighter than the previous model, with a capacity of 5Ah, a voltage of 3.6V, and maximum operating current of 300A.

  Each battery module contains 12 battery cells that are connected in series. A gap through which air flows is secured between the cells so that the cooling air drawn from the passenger compartment flows from the top to the bottom of the battery module. The IPU contains four battery modules, for a total of 48 cells, for a total battery pack voltage of 172V.

Battery module (Battery made by Blue Energy)	Cell electrode connection portion of the battery module

  The junction board is a collection of high-power components such as power contactors, fuses, and current sensors that cut off power. The main and sub contactors are made by Panasonic. The junction board is also equipped with a pre-charge resistor and pre-charge contactor to limit the inrush current when the power is turned on.

  The battery ECU is a battery controller that monitors and controls the voltage and capacity of each cell of the battery and, like the PCU, is manufactured by Keihin. It manages the SOC (battery State of Charge) to prevent battery deterioration, and limits the amount of motor assist and charge for the hybrid system when they are out of the normal use range. In addition, the operation of the cooling fan is controlled by the detection state of the temperature sensor.

Junction board	Battery ECU (Keihin)

The plastic case that houses the IPU

  The IPU is housed in a plastic case and located under the rear seat.

Battery cooling air flow

  The figure shows the flow path of the battery cooling air being drawn in through the intake air ducts in the cabin and next to the rear seats (Ⓐ), then enters through the ducts in the upper lid of the IPU (Ⓑ), and is evenly distributed to the four batteries. It flows down the battery module from top to bottom through the upper branch duct, passes through the exhaust ducts at the bottom of the batteries, and is then drawn into the cooling fan and discharged from the vicinity of the rear bumper (Ⓒ).

  The radiator for electrical component-related cooling is separate from the engine's cooling system and is located at the left front of the vehicle.

  The PCU coolant is used to cool power devices and other powerful electric parts, and since the engine coolant, which can reach close to 100ºC, is too hot, a separate radiator is often installed to provide coolant with an upper limit of about 60ºC. In the Honda Fit, a PCU radiator is installed vertically in the space next to the radiator for the main engine. The PCU coolant radiator is made by T.RAD.

Radiator mounting position	PCU coolant radiator (T.RAD.)

Hybrid transmission oil cooler

  The ATF oil cooler in the hybrid transmission is made by Mahle and is installed for the purpose of cooling the drive and power generation motors built into the transmission.

  In the two-motor hybrid system (i-MMD) equipped in the Accord (2018) and Insight, the ATF was cooled by turning it inside the rotors of the motors, but this could not be confirmed during the teardown of the Fit-equipped e:HEV. It seems that the ATF cooler drips cooled ATF from the upper part of each motor to cool the coil ends and other parts.

  The thick, long, orange, high-voltage aluminum pipe harness connects the IPU’s 172V battery under the rear seat to the PCU in the engine compartment, and carries a high current to charge and discharge the battery.

  The harness is believed to be made by Sumitomo Electric Industries (Sumitomo Wiring Systems) and the aluminum pipe section is long because of the need to reduce electromagnetic noise, and it is formed according to the shape of the vehicle.

High-current power harness	PCU side connector of the high-current power harness

Electric compressor (Denso)

  The electric compressor for the auto electric air conditioner is made by Denso and is connected to a junction board.

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Keywords
Teardown, Honda, Fit, e: HEV, HV, Electric, Transmission, Traction Motor, Generator, PCU, Inverter, ECU, RC-IGBT, DC-DC Converter, Battery, Condenser, Radiator, Oil Cooler, Connector, Wire Harness, Compressor, Sumitomo Electric Industries, MinebeaMitsumi, Keihin, Fuji Electric, Renesas Electronics, Blue Energy, Panasonic, T.RAD, Mahle, Denso

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