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07 May 04.On a number of occasions over the past issues both myself and Scott Gourley have written about a variety of hybrid drive systems from the US and Europe. But yesterday , at the Millbrook Testing facility, BATTLESPACE Editor, Julian Nettlefold, drove a hybrid drive vehicle (and a bus!) for the first time, and what an experience!

Allison Transmission has become the first company in the world to begin high volume production of a parallel hybrid electric drive system for buses. This system dramatically reduces emissions and improves fuel economy while delivering striking improvements in performance and noise reduction. Production of the system has begun at Allison’s manufacturing facility in Castleton, Indiana and Allison has the capacity to build as many as 1,000 systems annually.

Allison’s EP System uses parallel hybrid technology combining direct power from a smaller engine with power from an energy storage system. The system’s controller selects the appropriate power source or draws on a blend of both. At the heart of the system is the EV drive unit, which furnishes infinitely variable torque to the wheels. This allows an engine in a hybrid system to run more efficiently, quietly and cleanly. Acceleration is also faster than in equivalent diesel-powered vehicles.

The Seattle local transport authority has begun taking delivery of 235 buses equipped with the Allison EP System. This is the largest order for hybrid buses ever placed in the United States and this single fleet has estimated they will reduce fuel consumption by up to three million litres annually.

Driving the bus was a new experience in driver control, less-fatigue and more positive handling. The constant variable transmission took the bus from a stand-still through a range of speeds at a seamless pace. There was none of the usual knocking associated with a heavy engine going through its gears to get to optimum operating efficiency. The most remarkable aspect of the whole system was that the driver hardly needs to touch the brakes. As I took my foot off the accelerator the bus slowed down as the power was put back into the batteries. The bus held on a hill when a computer controlled system stops any descent as an ABS system cuts in on any greasy or icy surfaces. The system is so easy to drive that any driver fatigue associated with changing gears frequently, heavy braking or stopping is hugely reduced, thus saving brake shoe wear. The weight of the system only adds approximately 500kgs and the bus has a range of approximately 450kms.

The EP System can improve fuel economy by as much as 50%, depending upon duty cycle, and dramatically reduces diesel engine emissions of Nitrogen Oxide, particulate matter, Carbon Monoxide, hydrocarbons and Carbon Dioxide.

The system can be easily adapted to fit into existing vehicle platforms and delivers about 60 percent better fuel economy than a conventional diesel system in urban transit bus applications. Buses equipped with the EP System™ produce much lower hydrocarbon and carbon monoxide emissions than conventional diesel buses, lowering particulate emissions (tiny pieces of soot and dust) by 90 percent and NOX emissions (nitrogen oxide) by 50 percent. Buses equipped with the Allison Electric Drives™ system also deliver 50 percent better acceleration than a bus equipped with a conventional diesel

Lawrence Dewey, President of Alison Transmissions told BATTLESPACE Editor Julian Nettlefold, that the U.S. Military had shown considerable interest in the system. Not only can hybrid systems provide back-up power on the battlefield, the stealth provided by the silent sunning, one noticeable feature on the drive, is extremely important on the battlefield. In addition the huge savings in fuel achieved by the system reduces the huge logistical tail of fuel supplies at an estimated cost to the US Army of some $700 a gallon once it gets to the front line.”

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