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 275 volts DC to the high-voltage system. The HVTB provides cranking 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 to DC Converter Control Module (DC/DC). 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 Energy Control Module (BECM) monitors this system for any leakage of current to the normal electrical system (similar to a household ground fault interrupter).

Battery Energy Control Module (BECM)

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

The BECM receives the following hard-wired inputs:

- HVTB interlock status
- Battery Pack Sensor Module (BPSM) information and status, via a dedicated (not accessible by a scan tool) CAN between the BECM and BPSM
- Immediate shutdown request from the Transmission Control Module (TCM)
- Event notification status from the Restraints Control Module (RCM)
- Vehicle HS-CAN
- BPSM power, ground and control circuits
- HVTB inlet air temperature sensor
- HVTB cooling fan feedback

The BECM provides the following outputs:

- HVTB cooling fan Pulse Width Modulated (PWM) supply voltage
- Vehicle HS-CAN information

The BECM receives HS-CAN messages from the following modules:

- PCM
- TCM
- Instrument Panel Cluster (IPC)
- RCM
- DC/DC

The PCM HS-CAN messages received by the BECM include:

- Gas engine status (running or off)
- Contactor control request status
- Current vehicle mode (power up, engine wait, shutdown, etc.)
- Ready light request
- Battery estimated current
- Transaxle gear position
- R-Mode Rebalance enable request
- Engine speed
- Throttle plate position
- Engine coolant temperature
- Ambient air inlet temperature

The TCM HS-CAN messages received by the BECM include:

- Vehicle speed, via the TCM
- TCM high-voltage input, via the TCM

The DC/DC HS-CAN messages received by the BECM include:

- DC/DC high-voltage input
- DC/DC high-voltage current
- DC/DC low-voltage input
- DC/DC over-temperature status
- DC/DC operation status

Battery Pack Sensor Module (BPSM)

The BPSM communicates with the BECM over a dedicated (not accessible by a scan tool) CAN bus. The BPSM provides the current, voltage and temperature status of the HVTB to the BECM. This information is needed by the BECM to control the HVTB and to determine the HVTB ability to receive and provide power to the vehicle.

DC to DC Converter Control Module (DC/DC)

The DC/DC converter is a liquid-cooled component that converts high-voltage (179-343 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 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.

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) Description and Operation 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.

High-Voltage Bussed Electrical Center (BEC)

The high-voltage Bussed Electrical Center (BEC) acts as an interface between the high-voltage cables and the HVTB. The high-voltage BEC houses the 3 contactors (precharge, positive and negative) which, when commanded closed by the BECM, connect the HVTB to various components for high-voltage consumption and/or charging of the HVTB. The high-voltage BEC design enables distribution of high-voltage to the high-current side (eCVT) and low-current side (DC/DC and Air Conditioning Compressor Module (ACCM)). The low-current side is protected by a high-voltage/low-current 40A fuse. Any fault resulting in excessive current on the low-current side will open the fuse, but will not affect operation of the high-current side. The high-voltage BEC contains the contactors, the current sensor and the high-voltage/low-current 40 amp fuse.

The high-voltage BEC also interfaces with the BECM for monitoring of the high-voltage cable interlock circuit and control of the contactors. The high-voltage BEC also houses the current sensor which is monitored by the BPSM. The current sensor is used to help determine the load or rate of charge of the HVTB by sensing current flow into or out of the HVTB.

High-Voltage Cable Assembly

All cables that carry high voltage are integrated into one high-voltage cable assembly that runs between the DC/DC, the eCVT, the ACCM and the HVTB (via the high-voltage BEC). Within the high-voltage cable assembly are 4 basic circuits:

- The high-voltage/high-current cables between the HVTB and the eCVT.
- The high-voltage/low-current cables from the HVTB to the DC/DC and the ACCM.
- The interlock circuit consists of small-gauge wiring wrapped around the high-voltage cables. The interlock circuit 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.
- The LED and high-voltage AC wiring between the DC/AC inverter and AC power point. For information on the DC/AC inverter system, refer to High Voltage Converter/Inverter Testing and Inspection.

High Voltage Traction Battery (HVTB)

The HVTB is a nominal 275 volts (actual operating range of 179-343 volts) DC energy source that receives high-voltage electrical power when required from the eCVT. The HVTB also supplies high-voltage electrical power when required to the eCVT, DC/DC and/or the ACCM.

The HVTB system is connected to a floating ground system that keeps it isolated from the vehicle's 12-volt system. All charging and maintenance of the HVTB is managed by the BECM. Sensing of the HVTB (battery state-of-charge, internal temperature, battery load) is done by the BPSM.

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 HVTB, high voltage is no longer supplied to the high-voltage BEC, although there is still high voltage available on 2 circuits monitored by the BPSM.

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 BECM. In some situations the BECM 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, interlock circuit failure, etc.). 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.