This overview is not a comprehensive list of all aspects of the Two-Mode Hybrid vehicle. Refer to Automatic Transmission 2ML70 Electronic Component Description for information regarding transmission operation. More detailed and comprehensive information is also available through the dealer training program.

This vehicle does not use a 12 V starter motor to crank the internal combustion engine (ICE). A much more powerful 300 V motor/generator located within the transmission is utilized to crank the engine. The 300 V drive motor generator can rotate the engine to operating speed (800 RPM) within just a few hundred milliseconds. The 300 V drive motor generator allows near-instant starting of the engine. Once started, engine operation may cycle between Autostop (engine off) and Autostart (engine running) for the duration of the drive trip.

After a successful engine start, the hybrid powertrain control module (HPCM) may turn off the engine and operate in the Autostop mode. Some of the vehicle conditions that allow the engine to stop running and enter the Autostop mode include:

A chime will sound if the drivers door is opened while in Autostop as a reminder that the engine is not in the OFF mode.

Engine OFF and AUTOSTOP modes are indicated on the tachometer display.

The Two-Mode Hybrid vehicle does not require internal combustion engine (ICE) operation at all times. After a successful engine start, the hybrid powertrain control module (HPCM) may turn off the engine (Autostop) when not required for the current vehicle conditions. The engine will remain off while in Autostop mode, until such time that vehicle conditions require the engine to run. The near-instant starting of the engine from Autostop mode is called Autostart. Some of the vehicle conditions that may cause the HPCM to exit the Autostop mode and Autostart the engine include:

The transmission assembly contains two 300 V drive motor generator assemblies. These powerful 60 kW drive motor generators are capable of propelling the vehicle while the engine is in the Autostop mode or they may assist an already running engine. Depending upon accelerator pedal position, the vehicle may be propelled solely with the electric drive motor generators at speeds exceeding 41 km/H (26 mph) before assistance from the engine is required. The engine will Autostart when driving conditions require engine assistance. During engine running conditions, the torque provided by the drive motor generators is supplemented with the engine torque output.

When the vehicle is coasting or braking the HPCM may operate the drive motor generators in an electrical generation mode. Operating as electrical generators, the drive motor generators exert a driveline load that helps to slow the vehicle. The electrical energy that the drive motor generators create is transferred by the drive motor generator power inverter module (PIM) to the drive motor generator battery assembly (hybrid batteries). Constant communication between the HPCM and the electronic brake control module (EBCM) allows the blending of regenerative braking force with hydraulic braking force.

While not unique to the Two-Mode hybrid vehicle, the following modes of operation benefit from expanded operational ranges. Expanded operational range is possible because the drive motor generators can be utilized to smooth driveline disturbances that would be objectionable without the intervention of the drive motor generator.

Deceleration Mode

When the driver releases the accelerator pedal, air flow into the engine is reduced. The ECM monitors the corresponding changes in the TP, the MAP, and the MAF. The ECM shuts OFF fuel completely if the deceleration is very rapid, or for long periods, such as long, closed-throttle coast-down. The fuel shuts OFF in order to prevent damage to the catalytic converters. This mode is activated more quickly and for a longer duration in the Two-Mode hybrid vehicle.

Cylinder Deactivation (Active Fuel Management)

To provide maximum fuel economy under light load driving conditions, the engine control module (ECM) will command the cylinder deactivation system ON to deactivate engine cylinders 1 and 7 on the left bank, and cylinders 4 and 6 on the right bank, switching to a V4 mode. The engine will operate on 8 cylinders, or V8 mode, during engine starting, engine idling, and medium to heavy throttle applications. This mode is activated more quickly and for a longer duration in the Two-Mode hybrid vehicle.