Hybrid Transmission Modes of Operation

Hybrid Transmission Modes of Operation
Electric Launch
- Upon the driver removing their foot from the brake pedal and depressing the accelerator, the vehicle will launch in electric-only mode. Variable 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 HPCM where it is inverted 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.

EVT Mode 1
- After the engine is started the system operates in EVT 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.

EVT Mode 2
- As vehicle speed increases, the system shifts to EVT mode 2. EVT mode 2 uses a compound split configuration to transfer power through the transmission during higher speed operating conditions such as highway cruising. Similar to EVT 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 EVT 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 EVT 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 inverted to high-voltage DC power in the HPCM 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 variable low 1-2 clutch remains locked and motor 2 simultaneously provides output power to the wheels. The dampener bypass clutch is also applied to smooth engine starts and stops. During the engine start event motor 1 also provides active damping to reduce torque disturbances from engine cylinder firing pulses, and 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 HPCM controls each motor's speed and power independently. The HPCM 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 variable 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 HPCM where it is inverted into 3-phase AC power to drive motor 2.