The engine is coupled to a drive unit providing infinitely variable torque to the wheels allowing an engine in a hybrid to run more efficiently, quietly and cleanly. In a bus for example, the batteries can provide powerful acceleration eliminating excessive emissions during acceleration.

Once on the move the hybrid uses the diesel engine to maintain speed. In the Allison system and depending on driving conditions the controller decides between electric or diesel or a blend of both to deliver the best performance and fuel economy. In "diesel mode" the engine charges the power source and regenerative braking also delivering energy normally lost as heat to the energy storage system for reuse.

The System Components

The system compromises EV Drive Unit, Dual Power Inverter Module (DPIM), Energy Storage Unit and two controllers

EV Drive

Similar to a transmission the unit has planetary gears and clutches, electronic solenoids and two motor generators. All work together to create continuously variable operating ranges. The unit is a truly infinitely variable transmission with respect to torque and speed. The unit has a maximum input torque 1220Nm

Energy Storage Unit

This unit supplies the electrical energy to the EV Drive's electric motors. The Nickel Metal Hydride unit also stores energy created during regenerative braking. Energy Storage lessens the demands on the diesel, reducing emissions, consumption and noise.

System Controllers

The two controllers are the brain of the system. Processing information from the components they provide the system commands for propulsion and energy production. Diagnostics are also handled by these controllers.

DPIM

The dual power inverter module converts electrical energy into alternating current or direct current. The EV driver motors use and produce alternating current. The energy storage device can only store direct current. This unit, operating between 400-900Volts converts the energy for easy transfer, storage and use.

What are the benefits?

The Allison system is bringing the benefits of reduced emissions, improved fuel economy, less noise and better performance

• 50% less Nitrogen Oxide (NOx)
• 90% less Particulate Matter
• 90% less Carbon Monoxide
• 90% less Hydrocarbons

(Based on the use of a CIDI engine with state of the art exhaust filter, oxidation catalyst and low sulphur diesel fuel)

Acceleration - An Allison Hybrid Electric Drive System can significantly out accelerate a vehicle with a conventional drivetrain. Acceleration is also seamless.

The conventional engine can be of smaller size/lower horsepower for maximum fuel efficiency and lower emissions. The parallel hybrid system is compatible with emerging fuel cell technology.

Is It Ready?

Yes - the product went into mass production in October 2003. There are now over 400 buses running in the US and Canada equipped with the system.