Hybrid Transmission Modes of Operation

WARNING: This page is about a different car, the 2011 GMC Yukon, 2011 Chevrolet Tahoe, and 2011 Cadillac Escalade. However, it is still accessible from the selected car via links, so may be relevant.

Electric Launch

Upon the driver removing their foot from the brake pedal and depressing the accelerator, the vehicle will launch in electric-only mode. Hybrid Low 1-2 Clutch is locked and motor 2 provides output torque to the wheels. Under low speed driving conditions the vehicle operates in full-electric mode without starting the engine or using drive motor 1. DC power from the battery flows to the hybrid powertrain control module where it is converted into 3-phase AC power to drive motor 2. The auxiliary oil pump runs to provide oil to the transmission for lubrication and hydraulic control. The vehicle continues to operate in electric-only mode, until additional power is required to accelerate the vehicle. At that point the engine starts.

EV Mode 1

After the engine is started the system operates in EV Mode 1 which is used for low speed urban driving conditions. Utilizing an input split configuration, engine simultaneously drives motor 1 to both generate electricity to charge the hybrid battery and provide power through the mechanical gearing in the transmission to the wheels. The energy generated by drive motor 1 is stored in the battery while drive motor 2 draws battery energy to provide additional output torque. Depending on driving conditions the engine will operate in either 4 or 8-cylinder mode to optimize fuel consumption while maintaining output power requirements. Combining EV operation with Active Fuel Management allows the engine to operate in 4-cylinder mode over a wider range of operating conditions than a non-hybrid vehicle. EV and active fuel management are synergistic technologies that enable greater fuel economy when combined together than when either technology is used independently. Drive motor 2 provides output power to augment the engine in 4-cylinder mode and drive motor 1 can be used to provide torque smoothing.

EV Mode 2

As vehicle speed increases, the system shifts to EV Mode-2. EV Mode 2 uses a compound split configuration to transfer power through the transmission during higher speed operating conditions such as highway cruising. Similar to EV Mode 1, engine power is used to both generate electricity through the motors and provide output torque via the mechanical gearing in the transmission. A synchronous shift point allows the 2-Mode transmission to shift between EV Mode 1 and Mode 2 without changing speed.

Fixed Gear Operation

Fixed gear operation is achieved by selectively locking Clutches in the transmission to transmit engine power through a mechanical path without the use of the drive motors. Advantages of having fixed ratios include the ability to increase engine size without having to increase motor size and improved towing, climbing, and maximum acceleration performance which are particularly important. In fixed gear modes the drive motors can be used entirely for power assist, rather than partially to carry power through the transmission. Furthermore, the drive motors can be partially powered down during cruising conditions.

Regenerative Braking

Regenerative braking is enabled in both EV Mode 1 and Mode 2. As the driver lifts their foot from the accelerator pedal and depresses the brake pedal the electric motors are used to decelerate the vehicle by applying negative torque to the output shaft and generate electricity thereby charging the battery. The 3-phase AC power generated by the motor is converted to high-voltage DC power in the hybrid powertrain control module and stored in the battery. The Hybrid Operating System coordinates requests for negative torque requests from the electronic brake module with electric motor and engine control functions.

Engine Start-Stop

As the driver depresses the accelerator pedal further, demanding increased vehicle acceleration, drive motor 1 is used to start the engine while the Hybrid Low 1-2 Clutch remains locked and motor 2 simultaneously provides output power to the wheels. During the engine start event drive motor 1 also provides active damping to reduce torque disturbances from engine cylinder firing pulses, and drive motor 2 is used to damp driveline disturbances. During this event the inverter draws DC power from the battery and converts it to AC power for both motors. They hybrid powertrain control module controls each motor's speed and power independently. The hybrid powertrain control module determines when to stop the engine and when to restart based on vehicle operating conditions and optimal hybrid battery power and fuel consumption. The engine is stopped at idle and during deceleration maneuvers to improve fuel economy.

Reverse

When the vehicle is placed in reverse the Hybrid Low 1-2 Clutch is locked and Motor 2 spins backwards and provides output torque to the wheels. When needed the engine starts and Motor 1 is used to charge the hybrid battery and DC power from the battery flows to the hybrid powertrain control module where it is converted into 3-phase AC power to drive motor 2.