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Home >> Mercury >> 2009 >> Mariner 2WD L4-2.5L Hybrid >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Description and Operation >> Hybrid Electric Control Software

Hybrid Electric Control Software




Hybrid Electric Control Software

Creep 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 slightly vary if ambient temperature, altitude, relative humidity, engine temperature, or weight of the vehicle changes.

Driving Modes

There are 5 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.





Electric Mode

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.





Positive Split Mode

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:

- The engine is running.
- The vehicle speed is high.
- The high voltage traction battery is charged.
- Reducing engine throttle is not desired.





Negative Split Mode

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 2 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, and provide A/C. 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 1,000 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.





Engine Cranking Mode

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, 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 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
- P1A0F Hybrid Powertrain Control Module - Vehicle 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 key 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 traction battery control module (TBCM) 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 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 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, the TCM and the TBCM storing DTCs.

Power Up Sequence

The PCM conducts 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 communications 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.

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.





Regenerative Braking

Torque Monitor

The torque monitor resides within the PCM as both software and as a redundant safety processor. The torque monitor detects certain computer concern 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 3 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 key 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 (APPS). 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.





Torque Determination and Energy Management

Vehicle System Controller (VSC)

The PCM, TCM and traction battery control module TBCM 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 an on-demand and continuous memory self-test must be carried out.
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