Battery Control
BATTERY CONTROLSystem Diagram
System Description
BATTERY SMART UNIT
- The battery smart unit detects and transmits the HV battery condition signals (voltages, currents, and temperatures), which are used to determine charging or discharging values, to the hybrid vehicle control ECU.
- The battery smart unit also detects and transmits the cooling fan voltage signals which are necessary to effect cooling fan control, to the hybrid vehicle control ECU.
- A leak detection circuit is provided in the battery smart unit in order to detect any excessive current draw from the HV battery.
HV BATTERY
General
- The ALTIMA Hybrid model uses sealed nickel metal hybrid (Ni-MH) HV batteries. The HV batteries have a high power density, are lightweight and offer longevity to match the characteristics of the Hybrid Vehicle Control System. Because the Hybrid Vehicle Control System effects charge/discharge control to maintain the HV batteries at a constant SOC (state of charge) level while the vehicle is operating normally, it does not need to be recharged externally.
- The HV batteries use nickel-plated, metal container type cells to realize enhanced cooling performance and a compact construction. As a result, high power density, lightweight construction, and longevity have been accomplished at high levels.
- The HV battery unit consists of 34 separate batteries. The batteries each comprise 6 cells and they are connected to each other in series through a bus bar module. The cells of the batteries are connected at two locations in order to reduce the internal resistance and improve efficiency. The HV battery unit, which has a total of 204 cells (6 cells �34 batteries) and a nominal voltage of 244.8 V (1.2 V �204 cells), is located in the luggage compartment behind the rear seat.
- A junction block, battery smart unit and DC/DC converter are used. Integrated into the junction block are an SMRG (System Main Relay Ground), SMRB (System Main Relay Battery) and a current sensor. The battery smart unit monitors the HV battery. The DC/DC converter supplies power to the auxiliary battery after decreasing the nominal voltage of DC 244.8 V supplied by the HV battery to DC 12 V. Power to the lights, audio system, air conditioning system (except the electric inverter compressor) and ECUs is supplied by the auxiliary battery.
The battery smart unit, junction block, and DC/DC converter are located in the battery front side carrier, which is in the same housing as the HV battery unit. This realizes a compact package.
- An air-cooling method, which uses a dedicated cooling fan to cool the HV battery with air from inside the cabin, is employed. A dedicated cooling fan is also provided for the DC/DC converter. Thus, highly efficient air-cooling has been achieved.
- A service plug that shuts off the circuit is provided in the middle of the HV battery modules (between No.15 and No.16 batteries). Before servicing any portion of the high-voltage circuit, be sure to remove the service plug.
DC/DC Converter
The power source for auxiliary equipment of the vehicle such as the lights, audio system, and the air conditioning system (except electric inverter compressor), as well as the ECUs, is based on a DC 12 V system.
Because the HV battery outputs the nominal voltage of DC 244.8 V, the converter is used to transform the voltage from DC 244.8 V to DC 12 V in order to recharge the auxiliary battery.
Junction Block
A junction block, in which an SMRG and SMRB are integrated, is used.
Service Plug
By removing the service plug before performing any inspection or service, the high-voltage circuit is shut off at the intermediate position of the HV battery, thus ensuring safety during service.
The service plug assembly contains a reed switch for interlock. Lifting the clip lock up turns OFF the lead switch, which shuts off the SMR. However, to ensure safety, make sure to turn OFF the ignition switch before removing the service plug.
The main fuse for the high-voltage circuit is provided inside of the service plug assembly.
NOTE: After the service, please do not start the system until the service plug is connected.
HV BATTERY AND DC/DC CONVERTER COOLING SYSTEM
HV Battery Cooling System
- A dedicated cooling system is used to ensure that the HV battery performs properly, despite it generating significant heat during the repetitive charge and discharge cycles.
This cooling system employs an air-cooling method, which uses the dedicated cooling fan to cool the HV battery with air from inside the cabin.
- The air from inside the cabin, which is introduced through the intake duct located on the rear package tray trim, flows downwards through the battery module, reducing the temperature of the battery module, and is emitted from the vehicle through the exhaust duct.
- The hybrid vehicle control ECU controls the operation of the cooling fan for the HV battery. The hybrid vehicle control ECU receives the signals from the battery temperature sensor, which is built into the HV battery, via the battery smart unit. Then, it controls the cooling fan in order to control the battery module temperature appropriately.
For details, refer to THS ECU Control on "System Description".
DC/DC Converter Cooling System
As with as the HV battery cooling system, the DC/DC converter cooling system uses a dedicated cooling fan to cool the converter. Air from inside the cabin is introduced through the intake duct located on the rear package tray trim. In addition, the converter itself is equipped with cooling fins. Thus, excellent air-cooling performance is achieved.
