Nissan Leaf teardown (Part 2): main components disassembled

Lithium-ion battery pack, inverter and DC-DC junction box

2012/09/21

Summary

 The Nissan Leaf EV was torn down in a benchmarking session organized by the Next-generation Automobile Support Center of the Saitama Industrial Development Corporation in December 2011 and the event was reported by MarkLines in February 2012.


The earlier report: Nissan Leaf teardown (Part 1) (posted in February 2012)


 A new teardown event was recently conducted with the main units and components of the Nissan Leaf by the members of the automotive parts industries group of the Saitama Industrial Development Corporation. The result was exhibited for the public from July 17 to August 24 at the Saitama Industrial Technology Center located in the city of Kawaguchi. Among the components, the drive unit was disassembled into the motor stator, rotor, and power transmission device (reducer). Lithium-ion battery pack, inverter, DC-DC junction box, and the onboard charger were exhibited uncovered.

 This report "Nissan Leaf teardown (part 2)" contains the main components that were disassembled and exhibited for public, with the addition of the brake system and the systems for cooling high-voltage parts and for air conditioning.


* Click the photo for a larger view.



Electric powertrain from the motor and power transmission device (reducer) to the driveshaft

 

IPM motor Stator
IPM motor Stator
 EM61 type interior neodymium permanent magnet 3-phase AC synchronous motor. IPM is an acronym of interior permanent magnet. Drive voltage 345V, maximum output 80kW, maximum torque 280Nm, maximum revolution 10,390 rpm, weight 58kg. Front cover, stator, rotor, and rear cover shown from background to foreground. Manufactured at Nissan's Yokohama plant.  Controls power with control current. Distributed winding is used as preferred in terms of magnetic circuit.

 

Stator's housing Rotor
Stator's housing Rotor
 The cast aluminum housing contains core-formed water jackets for cooling the motor.  The shaft, right, goes through the rotor center. Three-phase AC current applied to the stator core coil generates a rotating magnetic field which pulls on the permanent magnet inside the rotor core and rotating torque is generated. The rotating torque is nearly proportional to the current.

 

Rear cover Front cover
Rear cover Front cover
 The blackish component, center, is the resolver (sensor for measuring degrees of rotation). The optimal rotor rotation is determined by the rotor timing (angle of rotation) and the amount of current. These are regulated by signals from the resolver and the current sensor.

 

Power transmission device (reducer) Actuator for electric parking brake
Power transmission device Electric parking brake and actuator
 The shaft running through the rotor of the motor connects to the shaft connector shown to the right. The driveshaft connects to the shaft connector shown to the left. The power transmission device (reducer), inner view not shown, consists of the input gear shaft, main gear shaft that changes the direction of rotation as well, and the final gear. Final reduction ratio is 7.9377. The final gear that serves as the output shaft contains the differential. Supplied by Aichi Machine Industry.  The parking lock mechanism, located inside the reducer, is activated by the shift actuator (supplied by Denso) fitted to the top of the reducer. Its ECU (supplied by Advics) is located in the rear cargo room.

 

Driveshaft (in the motor room) Larger view of the driveshaft
Driveshaft (in the motor room) Larger view of the driveshaft
 The driveshaft, center, connects to the drive shaft connector of the reducer to drive the vehicle. The motor is located in a position anterior to the driveshaft.  Larger view of the driveshaft. The electric power steering is seen in the background with the steering shaft coming down.

 

 



Inverter and DC-DC junction box

 The inverter changes direct current (DC) from the lithium-ion battery to alternating current (AC). The inverter, used in combination with the AC synchronous motor, is capable of detailed motor speed control and is a key component that supports the EV.

 The DC-DC junction box that contains the DC-DC converter is located between the lithium-ion battery and the inverter. It distributes high-voltage source from the lithium-ion battery to electric devices as needed. It also converts it to 12V which is used to charge the 12V battery.

 

Inverter
Inverter
 The inverter increases the motor efficiency based on the signals received from the resolver and the current sensor. It has DC voltage range 240~403V, measures 304×256.5×144.5mm (11.3 liter), and weighs 16.8kg. The bottom of the inverter forms a cast aluminum "water jacket" for the coolant. The power module that contains the IGBT (Insulated Gate Bipolar Transistor, the key part of the motor control) is placed above the bottom of the inverter (not shown).
 The circuit board at the center is the motor controller, located above the flat condensers identifiable by four square terminals (actually there are six terminals for three pairs of flat condensers). The inverter is manufactured by Nissan at the Zama Works and also by Calsonic Kansei at the Kodama plant (Saitama Prefecture).

 

DC-DC junction box Larger view of the DC-DC junction box
DC-DC junction box Larger view of the DC-DC junction box
 The DC-DC junction box is located between the lithium-ion battery pack under the cabin floor and the inverter. Shown sideways in the photo but is actually fitted with the left side pointing upward. The DC-DC junction box serves three functions: (1) distribute high-voltage source from the lithium-ion battery, (2) supply source to the 12V electric systems, and (3) charge the 12V battery.
 The box, shown to the left, is the DC-DC converter (supplied by Denso) and the relays are seen to the right. The boxes labeled "Panasonic" are the general-purpose EV relay "AEV 14012 M03" supplied by Panasonic Industrial Device Obihiro. The maximum permissible contact rating of the relay that supplies source to 12V systems is 120A with the coil voltage rating of 12V DC. The junction box also contains slow charging relay and quick charging relay.
 The charging circuits are switched over according to the charge mode.

 

Drive unit mounting frame
Drive unit mounting frame
 The vehicle's front is to the right of the photo. The DC-DC junction box is fitted to the left of the frame (vehicle's cabin side) with the inverter at the top center and the motor and the reducer underneath. The frame is of a sturdy structure for safety consideration in the event of crash against high-voltage current.

 

 



Lithium-ion battery

 

Lithium-ion battery pack Battery controller
Lithium-ion battery pack Battery controller
 The vehicle's front is to the left of the photo. Shown with nearly half of the battery modules removed. The black item at the back left is the battery junction box which is normally located at the center left in the photo. The "lithium-ion battery controller" (removed in the photo) is located at the front right.
 The Leaf uses modules each consisting of four laminated cells. A total of 48 modules are used with 24 front modules stowed horizontally and 24 rear modules stowed upright. Supplied by Automotive Energy Supply.
 The central device of battery control. It detects the battery voltage and current, pack temperature, and cell voltages to determine SOC (stage of charge), etc. The controller calculates the possible input and output values, chargeable values, meter displays, etc., and controls them accordingly.
 The voltage deviation between lithium-ion battery cells tends to remain small compared with nickel metal hydrate battery, but it does grow after extended use. The battery controller detects the cell voltage according to the signal from the bus bar (see below) and the bypass switch is turned on to discharge the cell of higher capacity. This helps to keep the deviation within a permissible range while using the cell capacities to the full. Supplied by Calsonic Kansei.

 

Battery junction box Bus bar (coupler)
Battery junction box Bus bar (coupler)
 The box contains (1) system relay (supplies DC current from the battery), (2) pre-charge relay (protects the high-voltage circuits from the large current directly after power on, and (3) current sensor (measures the battery current). In an event of system malfunction, the system main relay is turned off immediately by the VCM (vehicle control module) to cut off the battery and ensure safety.  The strip-like metal (copper) at the center is the coupler (called a bus bar) that connects 48 modules in series. The voltage in each cell is monitored by the sensor seen at the center of the bus bar.
Service disconnect switch
Service disconnect switch
 Located at the center of the battery pack. In an emergency, the switch may be pulled out by hand to disconnect power. The switch can also be operated from inside the cabin.

 

 



Charging connectors and onboard charger

 

Charging connectors
Charging ports
 The household AC source from the slow charging connector (shown at the center) is converted to DC by the onboard charger and supplied to the DC-DC converter in the DC-DC junction box. The quick charging connector (shown in foreground) receives DC which is supplied to the DC-DC converter directly without the intervention of the onboard charger. Supplied by Yazaki Corporation.

 

Onboard charger Larger view of the onboard charger
Onboard charger Larger view of the onboard charger
 The onboard charger (supplied by Nichicon) converts external AC source to DC (260~410V) and charges the lithium-ion battery. Located in the rear cargo room.  The aluminum electrolytic condenser (supplied by Nichicon) is shown in the foreground.

 

Cover of the onboard charger
Cover of the onboard charger
 Nichicon's product identification is shown with a warning label.

 

 



Electrically-controlled brake system and power backup unit

 

Electrically-controlled brake unit ECU for electrically-controlled brake unit
Electrically-controlled brake unit ECU for electrically-controlled brake unit
 The system uses the regenerative brake in coordination with the friction brake to create a natural braking feel. More than 80% of braking operation on city roads can be performed by the regenerative brake alone (without the help of the friction brake).
 The unit is located in the motor room and directly in front of the driver's seat. The white box at the top contains the control ECU. The round case contains the motor, and the master cylinder is seen in front of the motor (mechanical and electrical components integrated in a single unit). In designing the Leaf, the negative pressure booster in the internal combustion engine vehicle was replaced by a mechanism that converts the motor's rotation into direct action. Otherwise, the brake system from the gasoline-powered vehicle is used in the Leaf without major changes to maintain original reliability. The VDC (Vehicle dynamics control) is also taken from the gasoline-powered vehicle. Supplied by Hitachi Automotive Systems.

 

Pump to generate brake pressure
Pump to generate brake pressure
 Located in the engine room at the right (in front of the front passenger's seat) as viewed from the vehicle front. The pump is connected to the electrically-controlled brake unit.

 

Backup unit to supply
auxiliary power for brake
Backup unit for brake and
Electric parking brake control unit
Backup unit to supply auxiliary power for brake Backup unit for brake and Electric parking brake control unit
 In the event of the 12V battery voltage drop, the backup unit supplies auxiliary power to the electric brake. The backup unit and the associated capacitor are supplied by Panasonic. The cover is shown to the left and the unit is shown uncovered to the right. The unit is located in the rear cargo room.  Larger view of the backup unit. The case at the upper right contains the electric parking brake control unit supplied by Advics. It is located next to the backup unit in the rear cargo room.

 

Front wheel and main brake system Rear wheel and main brake system
Front wheel and main brake system Rear wheel and main brake system
 The brake is of the ventilated disc type and the suspension is of the independent strut type.  The brake is of the ventilated disc type and the suspension is of the torsion beam type.

 

Motor room

Motor room with main components removed Larger view of the motor room with main components removed
Motor room with main components removed Larger view of the motor room with main components removed
 The motor room is shown with the motor, reducer, inverter, DC-DC junction box, etc., separated or removed. The electric power steering is seen at the center (with the steering shaft lowered), the driveshaft in the foreground, and the brake systems at top right and left corners.

 

 



Systems for cooling high-voltage parts and for air conditioning

 The Nissan Leaf EV uses high-voltage current. It has separate systems for air conditioning (cooling and heating) and for cooling the high-voltage parts.

 

Radiator (for cooling high-voltage parts) and condenser (for air conditioning) Electric water pump for cooling high-voltage parts
Radiator (for cooling high-voltage parts) and condenser (for air conditioning) Electric water pump for cooling high-voltage parts
 The radiator and the air conditioner condenser are placed next to each other (as in gasoline-fueled cars). The radiator, together with the electric water pumps positioned near the driver's seat and the front passenger's seat, cools the high-voltage parts (drive motor, inverter, DC-DC junction box, and onboard charger).  One of the two water pumps (placed near the driver's seat) associated with the system for cooling high-voltage parts.

 

Electric compressor for cooling PTC heater
Electric compressor for cooling PTC heater
 A scroll type electric compressor. It integrates the inverter, the compressor and the motor to allow the compressor operation at any speed. Supplied by Panasonic.  The PTC element generates heat when current is applied and the Leaf uses PTC heater for heating the cabin. It uses a device similar to an electric water heater and uses the hot water for heating. Supplied by Eberspaecher in Germany.

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