Green Technology - Hybrid - How It Works

The Saf-T-Liner® C2^e is an electric parallel drive system. Simply put, a hybrid system is added alongside the conventional powertrain already in use today. The hybrid electric drive system generates electric power and stores it in the hybrid batteries when the bus' brakes are applied. The vehicle uses this stored energy to add power back into the motor/generator when the throttle is depressed.

The system consists of these components:

• Hybrid drive unit (HDU)
• Power electronics carrier (PEC)
• Motor inverter/controller
• Hybrid cooling system
• Cummins ISB engine

Eaton Hybrid Drive System

1. An electric motor/generator mounted between the engine and the transmission generates electric power.
2. Power is stored in the lithium-ion battery when the bus is coasting or brakes are applied.
3. The vehicle uses stored energy to add power back into the transmission when the throttle is depressed.
4. If the hybrid system goes offline for any reason, the bus automatically switches back to the conventional powertrain system.

Four Modes of Operation

• 1. Engine Starting
  

  Engine Starting Mode

  • The hybrid electric motor is the primary engine starter.
  • When the hybrid system is offline or the hybrid battery system is low, the bus automatically defaults to the 12-volt cranking system to start the engine.
• 2. Electric Launch
  

  Electric Launch Mode

  • Depending on the charge level of the hybrid battery, the electric motor could provide up to 100% power to the driveline at vehicle launch.
  • The diesel engine can stay at idle while using the electric motor.
• 3. Engine & Motor Drive
  

  Engine & Motor Drive Mode

  • The engine and electric motor provide power to the drivetrain.
  • The hybrid control unit determines the torque mix from electric motor and engine.
  • Under heavy acceleration, the electric motor/generator can add up to 60 hp and 310 lb-ft torque to a 200 hp Cummins engine.
• 4. Regenerative Braking
  

  Regenerative Braking Mode

  • Regenerative braking occurs when the throttle is at idle, while coasting, or while pressing the service brake. At this time, the motor/generator will switch to generator mode to charge the hybrid battery system.
  • Regenerative braking is available in addition to the standard service brakes.
  • When the hybrid battery system is fully charged, the hybrid control unit automatically shuts off the regenerative braking mode.
  • The regenerative braking mode automatically shuts off during an anti-lock brake event.