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Sam Memmolo

Allison Electric Drive

Allison Electric Drive Bus

It’s no secret that the name  “Allison” is synonymous with world-class design and manufacturing of heavy-duty automotive systems worldwide.  Their name is associated with the world-renowned heavy-duty automatic transmissions, which reliably power trucks and buses of all descriptions.


Now Allison Electric Drives has released it’s newest product for the transit bus market.  The “EP-50 System” was designed specifically for articulated and suburban coaches. This system is referred to as “Split Parallel Hybrid Technology”, and is a design patented by Allison. It uses power from Allison’s advanced energy storage system that contains or uses no “Lead Acid Batteries”.

Allison EP50 Hybrid


The “EP-50 system combines the Allison automatic transmission with an integrated electric drive unit. This hybrid system uses “Concentric AC Induction Motors” with an electrically infinitely variable gear ratio and torque amplification transmission controlled by Allison’s “1000 / 2000” system controllers.  Combined with General Motors Corporation’s advanced inverter technology, the dual power inverter module (DPIM) provides 430 - 900 VDC 160KW 3-phase AC power.

 The EP-50 system also uses full regenerative braking to recover energy from 50 mph.  The unit is cooled by a “common oil cooling and lubrication” system that takes care of the motors, drive unit, and DPIM.  No water / Ethylene Glycol support pumps are required.

 The Allison bus’s EP system engine generates the power that keeps its propulsion batteries charged.  The engine also couples to a drive unit through an infinitely variable transmission to power the wheels.  The drive unit has electric motors that run off its batteries. When the vehicle accelerates from a stop, it use the superior torque of electric motors, eliminating the excessive exhaust cloud that usually results when a diesel powered bus accelerates.  The bus then maintains its speed with its diesel engine- the same one that charges the batteries.  The buses regenerative brakes capture energy normally spun off as heat and return it to the batteries for reuse. 

 What does all of this mean?  Glad you asked!   Take a typical transit bus, weighing in the neighborhood of 55,000 pounds.  They are normally powered by a large diesel engine with displacements of 10 to 14 liters.  These engines can be run on diesel or even on compressed natural gas.  But as you probably know already, these large diesel engines produce a large amount of emissions as they swallow large amounts of fuel.

 The EP-50 Allison Electric drive used in the same size coach is coupled to a much smaller displacement diesel.  Most use under 6 liters, combined with the hybrid electric drive, and deliver terrific power to operate the bus.  Here’s the good news!

This hybrid system REDUCES exhaust emissions up to 90 %.  That’s correct!  90 %!   The emission reductions break down this way: 

Particulates (PM) up to 90 %
Hydrocarbons (HC) up to 90 %
Oxides of Nitrogen  (NOx) up to 50 %

Remarkably, all of this is achieved while IMPROVING FUEL ECONOMY up to 60 %.    Sixty percent is a whopping number! 

Consider that there are approximately 13,000 transit buses in service in the nine largest U.S. cities.   If they were replaced with buses featuring hybrid technology, the nation’s diesel fuel consumption would decrease by nearly 40 million gallons a year- for an equivalent fuel savings of 584,000 small hybrid cars. 

That’s right, it would only take these nine cities to save 40 million gallons of diesel annually.  How about the top fifty cities?   

Hybrid bus systems developed by GM and its Allison Transmission Division are already in service by the Orange County Transit Authority in Anaheim, California and in Portland, Oregon.  About a dozen systems are scheduled for delivery this year (2002) and will be deployed in key sites in North America. 

The typical EP-50 system performance with energy storage is 298 KW or 400 horsepower.  This is pretty incredible technology.

 I had the privilege of riding on one of these buses around Georgia’s Stone Mountain Park, and also on the road.  It performed very well, and they are already in use in major cities throughout the United States.  We here at Sam’s Garage feel that GM and Allison have a sure winner with the EP-50 Hybrid System. 


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