Part 2
CONTROL SYSTEMLIMITED OPERATING STRATEGY (LOS) MODES
For some hybrid electric system concerns the PCM may initiate one or more of the LOS modes. The objective of the LOS modes is to manage vehicle operation after one or more of the following systems are disabled due to a concern: engine, electronically controlled CVT, traction battery, or regenerative brake system. Some LOS modes limit the vehicle capability to a limp home condition. Other LOS modes fully disable the vehicle. The PCM initiates the appropriate LOS mode depending on the severity of the concern that was detected.
When the PCM detects system faults for which the LOS mode is initiated, it stores a corresponding diagnostic trouble code (DTC). The root cause of the concern that initiated the LOS mode may be in a different subsystem or component than indicated by the DTC. Therefore, these DTCs should be considered LOS or failure mode effects management (FMEM) only and are always assisted by the other, more detailed, circuit DTCs. The circuit DTCs should always be used to diagnose the problem before LOS or FMEM DTCs. LOS or FMEM DTCs do not mean that the subsystem or component they describe actually failed, but indicate the subsystem or component that is effected by the LOS mode.
P1A0C-P1A14:
POWER UP SEQUENCE
The PCM must conduct a power-up sequence every time the key is turned from the OFF to the START position. The power-up sequence is carried out only with the electronically controlled CVT gear selector in the PARK position. During the power-up sequence the PCM:
- initializes and begins CAN communication with the TCM and the TBCM.
- checks for TCM error status.
- requests the TBCM to close the high voltage contactors.
- enables the DC/DC converter.
- starts the internal combustion engine.
If a concern is detected during the power up sequence, the PCM may initiate LOS mode and store a DTC.
NORMAL POWER DOWN SEQUENCE
The PCM must conduct a normal power-down sequence. Whenever the key is turned to the OFF or ACC position, modules that are powered up by the RUN circuit immediately shut down. However the PCM, transaxle control module (TCM), and the traction battery control module (TBCM) stay on, until the power-down sequence is complete. The PCM keeps the TCM alive by controlling the power sustain relay (PSR) which provides power to the TCM. The TBCM is powered directly from the low voltage battery which permits wake-up function when the vehicle is off. During the power-down sequence the PCM:
- cuts the power to injectors and ignition coils (engine shut down).
- requests the TCM to disable high voltage inverters.
- disables the DC/DC converter.
- requests the TBCM to open the high voltage contactors.
- requests the TCM to discharge the high voltage invertor capacitors.
- opens the power sustain relay.
If the power down sequence does not execute correctly, it is considered an abnormal shut-down, which may result in the PCM, the TCM and the TBCM storing DTCs.
REGENERATIVE BRAKING
The regenerative braking is a software strategy and is controlled by the PCM, the TCM, and the TBCM. Regenerative braking is the ability to capture and store a portion of the energy that would be lost as heat during a braking event. When the driver applies the brakes, the PCM determines how much negative torque (braking force) the traction motor should provide in addition to the friction brakes. Depending on the high voltage traction battery state of charge, the amount of negative torque provided by traction motor can vary between 0 and 100 percent. The traction motor then becomes a generator, which causes the energy to flow into the high voltage traction battery. The PCM strategy smoothly blends regenerative and friction brake effort to make the dual brake operation transparent to the driver.
ELECTRONICALLY CONTROLLED CONTINUOUSLY VARIABLE TRANSAXLE
The primary objective of the Electronically Controlled Continuously Variable Transaxle (eCVT) is to deliver torque to the drive axles of the vehicle. The eCVT transmits input torque from the internal combustion engine, or uses electrical power from the high voltage traction battery. The electrical power is converted into mechanical power by the traction motor and the generator motor. The eCVT operates in several different modes, and under certain conditions can transmit power from the traction motor and engine simultaneously or independently.
The key eCVT components are:
- Planetary gear set
- Generator motor
- Traction motor
- Transaxle control module
PLANETARY GEAR SET
The planetary gear set, the generator motor, and the traction motor are internal to the electronically controlled CVT. The planetary gear set mechanically links the internal combustion engine, the electric traction motor, and the electric generator together. It distributes power between the 3 elements that it connects. The engine is connected to the carrier, the generator motor is connected to the sun gear, and the traction motor is connected to the ring gear of the planetary gear set.
GENERATOR MOTOR
- The generator motor is a 3-phase permanent magnet AC motor connected to the sun gear of the planetary gear set.
- The generator power inverter (internal to the transaxle) receives a DC current from the high voltage traction battery. The DC current is inverted to an AC current, which is controlled by the TCM and the generator control unit (GCU).
- Depending on the mode of operation, the generator motor can rotate in the same (clockwise) or reverse (counter clockwise) direction as the internal combustion engine.
- The TCM also monitors generator position, speed, phase current, power inverter temperature, coil temperature, and voltage. It processes a variety of PCM and traction battery control module (TBCM) inputs to determine generator function.
- The inputs are divided into 2 categories: the hardwired signals and the network messages. The inputs are used to determine generator function include the total torque desired, the engine speed desired, the generator mode, the generator shutdown, and the vehicle mode.
- The generator operates in one of the following generator modes: torque, speed, engine cold start, engine normal start, engine high speed start, and engine enhanced speed control stop.
- The generator is used as a starter for the internal combustion engine, charges high voltage traction battery, and controls engine speed.
- The TCM reports the generator error status to the PCM. The PCM initiates an appropriate limited operating strategy (LOS) mode and sets the diagnostic trouble code (DTC) P1A0D (Hybrid powertrain control module - generator disabled) based on the error status it received. The TCM also sets a DTC which indicates why the generator motor failed.
TRACTION MOTOR
- The traction motor is a 3-phase permanent magnet AC motor connected to the ring gear of the planetary gear set.
- The traction motor is connected to the drive wheels through a series of gears and rotates whenever the drive wheels rotate.
- The traction motor power inverter (internal to the transaxle) receives a DC current from the high voltage traction battery. The DC current is inverted to an AC current, which is controlled by the TCM and the motor control unit (MCU).
- The traction motor can deliver positive torque by propelling the vehicle in the forward or reverse direction. It can also provide negative torque by functioning as a generator during the regenerative braking.
- The TCM receives input from the position sensor as well as the motor coil temperature sensor.
- The TCM monitors the motor coil temperature and sets a DTC if the temperature exceeds a maximum threshold value. The TCM also monitors motor position, speed, phase current, power inverter temperature, and voltage.
- The TCM processes a variety of the inputs from the PCM and the traction battery control module (TBCM) to determine motor function. The inputs are divided into 2 categories: the hardwired signals and the network messages.
- The inputs used to determine motor function include the total torque desired, the motor inverter shutdown, and the vehicle mode.
- The traction motor is used to provide torque to the axle shafts and recharge the high voltage traction battery during the regenerative braking.
- The TCM reports the motor error status to the PCM. The PCM initiates an appropriate LOS mode and sets the DTC P1A0E (Hybrid powertrain control module - traction motor disabled) based on the error status received. The TCM also sets a DTC which indicates why the traction motor failed.
HIGH VOLTAGE TRACTION BATTERY
- The high voltage traction battery stores energy for later use by the traction motor and the generator motor. It is connected to both the traction motor and the generator motor by the high voltage cables.
- The traction motor uses the traction battery power when it propels the vehicle.
- The generator motor uses the traction battery power when it starts the internal combustion engine.
- The traction battery also provides energy to the DC/DC converter, which steps down the high voltage to maintain the low voltage system charge.