Hybrid Electric Control Software
HYBRID ELECTRIC CONTROL SOFTWARECreep Mode
The hybrid electric system delivers torque to the wheels to mimic the creep normally found on vehicles equipped with an automatic transmission. The powertrain control module (PCM) commands a predetermined amount of torque to be delivered to the output shafts of the electronically controlled continuously variable transaxle (CVT). This torque is delivered from a combination of sources: the internal combustion engine, the traction motor, or the generator motor. The maximum creep speed in forward or reverse direction is about 6 km/h (4 mph). The creep speed may vary slightly if ambient temperature, altitude, relative humidity, engine temperature, or weight of the vehicle changes.
Driving Modes
There are five fundamental operating modes in the hybrid electric system:
- electric mode
- positive split mode
- negative split mode
- neutral gear mode
- engine cranking mode
Electric Mode
The hybrid electric system operates in the electric mode when the vehicle is propelled by the electrical power stored in the high voltage traction battery. The torque is supplied to the output shafts by the traction motor, the generator motor, or a combination of both. This is a preferred mode whenever the desired torque is low and the electrical system, rather than the engine, can produce it more efficiently. The electric mode is also used in reverse because the engine can deliver torque only in a forward direction.
Positive Split Mode
In this mode the internal combustion engine is running and powering the generator motor which produces the electricity. The power from the engine is split between the path through the generator motor and the path to the output shafts of the vehicle. The electricity produced by the generator motor charges the high voltage traction battery or powers the traction motor. In this mode the traction motor can operate as a motor or as a generator to make up the difference between engine power and desired power at the wheels. This mode is preferred whenever the traction battery needs to be charged.
Negative Split Mode
In this mode the internal combustion engine is running but the generator motor is reducing the engine speed. This mode is never preferred but occurs when all of the following vehicle conditions are met:
- engine is running.
- vehicle speed is high.
- high voltage traction battery is charged.
- reducing engine throttle is not desired.
Neutral Gear Mode
The hybrid electric system operates in this mode when the driver selects NEUTRAL. In neutral gear the electronically controlled CVT does not deliver any positive or negative torque to the output shafts of the vehicle. The neutral gear actually consists of two neutral operating states: active neutral activated above 10 km/h (6 mph), and passive neutral activated below 10 km/h (6 mph). In active neutral, the generator motor is permitted to start and stop the internal combustion engine as needed to maintain the high voltage traction battery charge. In passive neutral, the engine must remain in the state it was (running or not running) when the mode was entered and is not permitted to change state (start or stop). If the engine is running when entering passive neutral, the speed control of the engine is transferred from the generator motor to the engine itself. The engine controlling its own speed in passive neutral is described as secondary idle. The vehicle cannot be started in passive neutral, but can be started in active neutral.
Engine Cranking Mode
The electronically controlled CVT provides the engine cranking function to start or restart the internal combustion engine. When the PCM requests the engine cranking mode, the generator motor rapidly accelerates the engine speed up to about 950 RPM in about 0.3 seconds. When the engine speed reaches a calibrated speed the PCM commands the delivery of fuel and spark at the appropriate times.
Limited 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
- high voltage traction battery
- 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 the subsystem or component they describe actually failed, but indicate the subsystem or component that is effected by the LOS mode.
- P1A0C Hybrid Powertrain Control Module - Engine Disabled
- P1A0D Hybrid Powertrain Control Module - Generator Disabled
- P1A0E Hybrid Powertrain Control Module - Motor Disabled
- P1A10 Hybrid Powertrain Control Module - Battery Disabled
- P1A13 Hybrid Powertrain Control Module - Regenerative Braking Disabled
- P1A14 Hybrid Powertrain Control Module - Transmission Disabled
Normal Power Down Sequence
The PCM must conduct a normal power down sequence. Whenever the ignition is turned to the OFF or ACC position, modules powered up by the RUN circuit immediately shut down. However the PCM, transaxle control module (TCM), and the battery energy control module (BECM) stay on, until the power down sequence is complete. The PCM keeps the TCM alive by controlling the PCM relay which provides power to the TCM. The BECM 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 BECM to open the high voltage contactors.
- requests the TCM to discharge the high voltage inverter capacitors.
- opens the PCM relay.
If the power down sequence does not execute correctly, it is considered an abnormal shut down, which may result in the PCM, TCM and BECM storing DTCs.
Power Up Sequence
The PCM conducts a power up sequence every time the ignition 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 controller area network (CAN) communications with the TCM and the BECM.
- checks for TCM error status.
- requests the BECM to close the high voltage contactors.
- enables the DC/DC converter.
- illuminates the green ready indicator indicating the vehicle is ready to drive in electric, gasoline, or a combination of electric and gasoline modes.
- if required, starts the internal combustion engine. The internal combustion engine starts if it is required for cabin heating, windshield defrost or the outside temperatures are low. The internal combustion engine also starts if the high voltage battery charge is low.
If a concern is detected during the power up sequence, the PCM may initiate LOS mode and store a DTC.
Generator Motor Shut Down (GMSDN)
The PCM keeps the generator motor and traction motor inverters enabled by continuously toggling the generator motor shut down (GMSDN) output. Typical output frequency varies between 49 and 75 Hz at 50% duty cycle. The PCM also broadcasts a redundant not shutdown message to the TCM over the communication link. When a concern condition is detected, the PCM stops generating this frequency signal and broadcasts a shutdown message to the TCM over the communication link. The TCM then disables the generator motor and traction motor inverters and sets an appropriate DTC. In the event of GMSDN circuit failure, the PCM still broadcasts a not shutdown message but the hardwire signal frequency is out of expected range. If the circuit becomes open, the vehicle shuts down and the TCM sets the appropriate DTC.
Immediate Shut Down (ISDN) 1 and 2
The TCM receives the redundant ISDN1 and ISDN2 signals from the high voltage traction battery. Under normal operating conditions the TCM monitors both ISDN circuits for low voltage battery voltage. If at any time during normal operation the TCM detects voltage drop on both ISDN circuits, the electronically controlled continuously variable transaxle (CVT) immediately stops delivering any torque, reduces operating voltage to under 50 volts, and discharges the high voltage capacitors. This action disables the vehicle until the ignition is cycled OFF and ON. The voltage drop on both ISDN circuits is usually a result of some other concern in the hybrid electric system, and DTCs indicating root cause may be stored in other modules. If the voltage drop is detected on only one of the ISDN circuits, the TCM continues its operation and stores the appropriate DTC. The voltage drop on only one of the ISDN circuits usually indicates an open ISDN circuit.
Torque Of Generator-AC (TGAC) Signal
The TCM calculates an AC generator torque from an AC current measured by the current sensor which is located inside the transaxle. The TGAC is a 50% duty cycle signal which the TCM sends to the PCM over the TGAC circuit. The TCM also broadcasts a redundant generator torque message to the PCM over the communication link. The typical TGAC signal ranges from 200 Hz to 400 Hz, where 300 Hz is equal to 0 Nm (0 lb ft) of torque, 200 Hz is equal to 250 Nm (185 lb ft) of negative torque, and 400 Hz is equal to 250 Nm (185 lb ft) of positive torque. The PCM uses the generator torque value as an input to the energy management control strategy, the torque monitor strategy, and the regenerative brake torque limits strategy. In the event of TGAC circuit failure the PCM initiates limited operating strategy (LOS) shutdown mode which disables the vehicle. The PCM also stores an appropriate DTC.
Torque Of Motor-AC (TMAC) Signal
The TCM calculates an AC traction motor torque from an AC current measured by the current sensor which is located inside the transaxle. The TMAC is a 50% duty cycle signal which the TCM sends to the PCM using the TMAC circuit. TCM also broadcasts a redundant traction motor torque message to the PCM over the communication link. The typical TMAC signal ranges from 200 Hz to 400 Hz, where 300 Hz is equal to 0 Nm (0 lb ft) of torque, 200 Hz is equal to 250 Nm (185 lb ft) of negative torque, and 400 Hz is equal to 250 Nm (185 lb ft) of positive torque. Positive torque is perceived as vehicle acceleration and negative torque is perceived as braking. The PCM uses the traction motor torque value as an input to the energy management control strategy, the torque monitor strategy, and the regenerative brake torque limits strategy. In the event of TMAC circuit failure the PCM initiates limited operating strategy (LOS) shutdown mode which disables the vehicle. The PCM also stores an appropriate DTC.
Regenerative Braking
The regenerative braking is a software strategy and is controlled by the PCM, TCM, and BECM. 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.
Torque Monitor
The torque monitor resides within the PCM as both software and as a redundant safety processor. The torque monitor detects certain computer concerns of the PCM. The torque monitor also detects if the overall powertrain torque delivered to the output shafts of the vehicle is excessive to what the driver is requesting. The torque monitor detects three gross errors that are present for some calibrated amount of time:
- unintended vehicle motion - the powertrain accelerates the vehicle when it should not (such as in NEUTRAL) or provides torque in the wrong direction.
- excess acceleration - vehicle accelerates at greater rate than the driver or the speed control requests.
- excess powertrain deceleration - vehicle powertrain braking exceeds driver demand.
When any of the gross errors are detected, the torque monitor communicates it to the PCM, which initiates appropriate action such as LOS mode. The torque monitor requested LOS mode can be cleared when the concern is no longer present, and the ignition is cycled to the OFF position for about 10 seconds.
Torque Determination and Energy Management
The PCM is responsible for torque determination and energy management functions. The PCM monitors gear selector position (PRNDL), brake pedal position (BPP) and accelerator pedal position (APP). The PCM then makes a torque command determination. Positive torque is perceived as vehicle acceleration and negative torque is perceived as braking. Based on the amount of torque requested by the driver, the PCM decides which power source has to deliver the torque to meet the driver demand while the powertrain system is running most efficiently.
Vehicle System Controller (VSC)
The PCM, TCM and BECM are connected to a high-speed CAN to exchange information messages. The VSC is a software function integrated inside the PCM, and is responsible for vehicle system operation, generating and sending commands to initiate appropriate actions such as LOS modes when serious concern is detected. The PCM also stores DTCs along with the freeze frame PID related to the LOS action that was initiated. To retrieve DTCs from the PCM, carry out an on-demand and continuous memory self-test.