Principles of Operation

High-Voltage Traction Battery

Principles of Operation

The High Voltage Traction Battery (HVTB) consists of D-cell type batteries packaged into modules which deliver approximately 330 volts DC to the high-voltage system. The HVTB provides power to the high-voltage generator motor inside the Electronically Controlled Continuously Variable Transmission (eCVT). The HVTB also supplies electrical energy to the traction motor (also internal to the eCVT) to propel the vehicle when it is operating in electric mode only or to assist the gasoline engine (heavy acceleration). When the engine is operating or the vehicle is moving, the high-voltage generator motor generates high-voltage AC electricity. High-voltage AC generated by the generator motor can be used by the traction motor or to re-charge the HVTB.

When the HVTB is being charged, high-voltage is converted from high-voltage AC to high-voltage DC electrical power inside the eCVT and transmitted through the high-voltage cables to the HVTB.

The high-voltage DC electrical power is converted to low-voltage DC electrical power through the DC/DC converter. This low-voltage high-current DC electrical power is then supplied to the 12-volt battery through the low-voltage battery cables.

The high-voltage system has a floating ground. The floating ground is designed to completely isolate the high-voltage system from the vehicle chassis. The high-voltage cables are fully insulated (isolated) from all vehicle components and circuits. There are no common connections (such as body grounds) used to conduct the high-voltage power. The Battery Control Module - High Voltage Traction Battery (BCM-HVTB) monitors this system for any leakage of current to the normal electrical system (similar to a household ground fault interrupter).

12-Volt Battery

The 12-volt battery is a standard automotive battery. It is a DC source connected in a negative ground system. The battery case is sealed, with 2 vent holes to release gases. The battery has 3 major functions:

- Storage of electricity for later use
- Voltage stabilizer for the low-voltage electrical system
- Temporary power source when electrical loads exceed the DC/DC converter output current

High Voltage Traction Battery (HVTB)

The HVTB is a 330 volt (operating range of 216-397 volts) DC energy source that receives high-voltage electrical power when required from the eCVT. The battery supplies high-voltage electrical power to the eCVT, the DC/DC converter and/or the Air Conditioning Compressor Module (ACCM). The HVTB system is connected to a floating ground system that keeps it isolated from the vehicle's 12-volt system. Inside of the HVTB case is the Battery Control Module - High Voltage Traction Battery (BCM-HVTB), which controls the higher functions of the battery. The BCM-HVTB also estimates the state of charge, estimates the power available and controls the battery temperature. The BCM-HVTB controls the battery temperature by activating or deactivating the fans contained within the HVTB.

HVTB Service Disconnect Plug

The HVTB uses a service disconnect plug which connects directly to the HVTB. The service disconnect plug has an internal circuit which includes a fuse. When the service disconnect plug is removed from the lock position on the HVTB case and placed in the servicing shipping position, high voltage is no longer supplied to the HVTB controls, and the vehicle is safe for service. For information on disconnecting the HVTB service disconnect plug for service, refer to the High-Voltage Traction Battery Systems Depowering general procedure.

High-Voltage Cable Assemblies

There are 2 separate cable assemblies which carry high voltage. One cable assembly runs from the HVTB to the eCVT and ACCM. The second high-voltage cable is connected between the eCVT and the DC/DC converter. Within each cable are 2 basic circuits:

- The high-voltage wiring carries high-voltage current between components of the high-voltage system
- The interlock circuit consists of small-gauge wiring wrapped around the high-voltage cables. The interlock connectors are built in with the high-voltage cable connectors, and are either disconnected simultaneously with the high-voltage cable or must be disconnected before disconnecting the high-voltage cable, depending upon the type of connector being serviced.

Battery Control Module - High Voltage Traction Battery (BCM-HVTB)

The BCM-HVTB manages the condition of the HVTB to control its charging and discharging. The BCM-HVTB also manages the cooling of the HVTB by controlling a fan attached to the HVTB cooling outlet duct. The BCM-HVTB communicates with other vehicle modules on the High Speed Controller Area Network (HS-CAN) bus.

Electronically Controlled Continuously Variable Transmission (eCVT)

The eCVT includes an internal generator motor and an internal traction motor. For information on the eCVT and its operation, refer to Automatic Transaxle/Transmission - Electronically Controlled Continuously Variable Transmission (eCVT) Testing and Inspection and Computers and Control Systems Information. The eCVT generator motor generates high-voltage electricity for charging of the HVTB and/or providing power to the traction motor. The generator motor is also used to start the gas engine. The generator motor is an internal part of the eCVT and it cannot be repaired, only installed new as an assembly. The eCVT traction motor is used to accelerate the vehicle from a stop when driving under electric power. The traction motor is also used to recover energy during regenerative braking. The traction motor receives power from the HVTB and/or from the eCVT generator motor. The traction motor is an internal part of the eCVT and it cannot be repaired, only installed new as an assembly. The regenerative braking system is designed to recapture some of the energy from braking and deceleration events. It accomplishes this through the use of the traction motor and generator motor. This recaptured energy is used to charge the HVTB. If the HVTB is adequately charged, the recaptured energy is used for gas engine braking to slow the vehicle. The regenerative brake system is a series system. A series system is one in which powertrain braking is used first, up to the limits of the powertrain torque capacity and battery capacity. After optimum regeneration is used, the friction brakes are applied to supplement braking demands. For information on regenerative braking, refer to Vehicle Dynamic Systems Testing and Inspection.

DC/DC Converter

The DC/DC converter is a liquid-cooled component that converts high-voltage (216-397 volt) DC power to low-voltage (12 volt) DC power. The converter provides power to the vehicle 12-volt battery and low-voltage electrical systems. The PCM controls the operation of the DC/DC converter through an enable message from the PCM to the DC/DC. For information on the DC/DC, refer to High Voltage Converter/Inverter Testing and Inspection.

R-Mode Rebalance

Individual cells can deviate over the life of the HVTB. The purpose of the R-Mode Rebalance is to equalize the individual cell charges. By rebalancing the cells, the HVTB will maintain top efficiency. The rebalance process charges the battery pack to near a full state of charge and keeps each individual cell charge within a prescribed range of each other. The R-Mode Rebalance is sometimes run during vehicle operation as needed and is controlled by the BCM-HVTB. In some situations, the BCM-HVTB may not be able to properly adjust the cell levels on its own and a DTC may be set. The DTC would direct the technician to perform a service R-Mode Rebalance. This is done with the use of a scan tool by following the directions within the service function.

Vehicle Shut Down

A vehicle shut down signal is sent when the battery is about to open the contactors due to an internal fault or has just opened the contactors due to an external input (external module commanding contactors to be opened such as a crash event or interlock circuit failure). When vehicle shut down occurs, the Stop Safely warning indicator will be illuminated, warning that the vehicle will be shut down within a matter of seconds and that the operator should pull off the road as soon as possible. Depending on the fault condition that lead to the shut down, the vehicle may or may not re-start if the condition has corrected itself. If the fault condition is severe enough, the fault will have to be repaired and DTCs cleared before the vehicle will re-start.